Materials Science and - NIST · 2016. 4. 11. · efforts relevant to emerging nanomaterial systems,...

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Materials Science andEngineering Laboratory

FY 2005 Programs andAccomplishments

Ceramics, MaterialsReliability, Metallurgy,NIST Center forNeutron Research, andPolymers DivisionsRichard F. Kayser, Director

Stephen W. Freiman, Deputy Director

NISTIR 7248

December 2005

National Institute ofStandards and TechnologyWilliam JeffreyDirector

TechnologyAdministrationMichelle O’NeillActing Under Secretary ofCommerce for Technology

U.S. Departmentof CommerceCarlos M. GutierrezSecretary

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Certain commercial entities, equipment, or materials may be identified in this document in order todescribe an experimental procedure or concept adequately. Such identification is not intended to implyrecommendation or endorsement by the National Institute of Standards and Technology, nor is it intendedto imply that the entities, materials, or equipment are necessarily the best available for the purpose.

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Table of Contents

Table of Contents

Director’s Message ...................................................................................................................1

Materials Science and Engineering Laboratory Organization Chart .........................................2

Year in Review

Ceramics Division ...............................................................................................................3

Materials Reliability Division ...............................................................................................5

Metallurgy Division .............................................................................................................7

Polymers Division ...............................................................................................................9

NIST Center for Neutron Research ................................................................................. 11

Nanometrology ........................................................................................................................ 13

Mechanical Metrology for Small-Scale Structures ........................................................... 14

Nanomechanics: Atomistics in Modeling and Experiments ............................................. 15

Modulus Mapping at the Nanoscale .................................................................................. 16

Reference Specimens for SPM Nanometrology .............................................................. 17

Nanotribology and Surface Properties .............................................................................. 18

Chemistry and Structure of Nanomaterials ...................................................................... 19

Nanotube Processing and Characterization ...................................................................... 20

Carbon Nanotube Applications: The Role of Nanotube Alignment ................................. 21

Combinatorial Adhesion and Mechanical Properties ........................................................ 22

Soft Nanomanufacturing ................................................................................................... 23

Defects in Polymer Nanostructures .................................................................................. 24

Critical Dimension Small Angle X-Ray Scattering ........................................................... 25

Nanoimprint Lithography .................................................................................................. 26

Nanomagnetodynamics ..................................................................................................... 27

Materials for Ultra-Low-Field Magnetic Sensors ............................................................. 28

A New Type of Antisymmetric Magnetoresistancein Materials with Perpendicular Anisotropy ...................................................................... 29

Nanostructure Fabrication Processes:Surface & Growth Stress During Thin Film Electrodeposition ........................................ 30

Multiscale Modeling of Quantum Dots in Semiconductors ............................................... 31

Brillouin Light Scattering:Dynamic Elastic and Magnetic Properties of Nanostructures ......................................... 32

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Table of Contents

Materials for Electronics ......................................................................................................... 33

Multifunctional Electronic Ceramics ................................................................................. 34

Spectroscopy, Diffraction, and Imaging of Electronic Materials ...................................... 35

Theory and Modeling of Electronic Materials .................................................................. 36

Advanced Materials for Energy Applications ................................................................... 37

Polymer Photoresists for Nanolithography ....................................................................... 38

Organic Electronics ........................................................................................................... 39

Nanoporous Low-k Dielectric Constant Thin Films ......................................................... 40

Electrical Methods for Mechanical Testing ...................................................................... 41

Thermochemical Metrology of Interfacial Stabilities ........................................................ 42

Combinatorial Metal Selection for Catalytic Growthof ZnO Semiconductor Nanowires ................................................................................... 43

Advanced Processes and Materials for On-Chip Interconnects ...................................... 44

Pb-free Surface Finishes: Sn Whisker Growth................................................................ 45

Materials for Advanced Si CMOS .................................................................................... 46

Metrology and Standards for Electronic andOptoelectronic Materials ................................................................................................... 47

Nano-Structured Materials for Sensors andUltra-high Density Data Storage ...................................................................................... 48

Advanced Manufacturing Processes ...................................................................................... 49

Mechanisms for Delivery of Thermodynamic and Kinetic Data ..................................... 51

FiPy: An Adaptable Framework for Phase Fieldand Level Set Modeling .................................................................................................... 52

Metrology Tools to Accelerate Industrial Developmentof Solid State Hydrogen Storage Materials ...................................................................... 53

Fundamental Nature of Crack Tips in Glass ..................................................................... 54

Hardness Standardization: Rockwell, Vickers, Knoop ..................................................... 55

NIST Combinatorial Methods CenterPioneer and Partner in Accelerated Materials Research ........................................... 56

Polymer Formulations:Materials Processing and Characterization on a Chip ...................................................... 57

Quantitative Polymer Mass Spectrometry ........................................................................ 58

Standard Tests and Data for Sheet Metal Formability ..................................................... 59

Microstructural Origins of Surface Rougheningand Strain Localizations .................................................................................................... 60

Underlying Processes of Plastic Deformation in Metal Alloys ........................................ 61

Evaluation of Friction Behavior During Metal Forming .................................................... 62

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Biomaterials ............................................................................................................................. 63

Combinatorial Methods for Rapid Characterizationof Cell-Surface Interactions .............................................................................................. 64

Cellular Level Measurements ........................................................................................... 65

Cell Response to Tissue Scaffold Morphology ................................................................. 66

3-Dimensional In Situ Imaging for Tissue Engineering:Exploring Cell/Scaffold Interaction in Real Time ............................................................. 67

Broadband CARS Microscopy for Cellular/Tissue Imaging ............................................ 68

Response of Tissues and Tissue-Engineered Constructsto Mechanical Stimulation ................................................................................................. 69

Mechanical Behavior of Tissue ......................................................................................... 70

Materials Design for Biomechanical Structures ............................................................... 71

Molecular Design and Combinatorial Characterizationof Polymeric Dental Materials .......................................................................................... 72

Safety and Reliability ............................................................................................................... 73

Analysis of Structural Steel from the World Trade Center ............................................... 74

Infrastructure Reliability: Charpy Impact Machine Verification ...................................... 75

Standard Test Methods for Fire-Resistive Steel ............................................................... 76

Frangible Bullets and Soft Body Armor ............................................................................ 77

Pipeline Safety: Corrosion, Fracture, and Fatigue ........................................................... 78

Polymer Reliability and Threat Mitigation ......................................................................... 79

Facilities and Capabilities

Databases .......................................................................................................................... 91

Recommended Practice Guides .............................................................................................. 92

Table of Contents

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DIRECTOR’S MESSAGEMSEL works with industry, standards bodies,

universities, and other government laboratoriesto improve the nation’s measurements andstandards infrastructure for materials.

W elcome to the Materials Science andEngineering Laboratory (MSEL).MSEL provides technical leadership

for the nation’s materials measurement and standardsinfrastructure, using expertise in ceramics, polymers,metallurgy, neutron characterization, and materialsreliability to anticipate and respond to industry and nationalneeds in areas such as microelectronics, automotive, andhealth care. The Laboratory also houses the Nation’s onlyfully equipped cold neutron research facility, the NISTCenter for Neutron Research.

This document provides a summary of accomplishmentsthat we hope will communicate our commitment to theneeds of our customers. Our projects fall into five broadtechnology focus areas: Nanometrology; Materialsfor Electronics; Advanced Manufacturing Processes;Biomaterials; and Safety and Reliability. The sectionson each of these areas begins with a brief programsummary.

Richard F. KayserDirectorMaterials Science and Engineering Laboratory

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National Institute of Standards and Technology

Materials Science and Engineering Laboratory

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Year in Review

Ceramics Division

It has been an exciting year in the Ceramics Division for forging new partnerships with industry

and other national laboratories, initiating researchefforts relevant to emerging nanomaterial systems, andstrengthening our ongoing core metrology, data, andstandards activities closely aligned with the missionof NIST. Our accomplishments predominately relateto Nanometrology and Materials for Electronics, twoof the five program areas in the Materials Science andEngineering Laboratory (MSEL). To crown theseachievements, our excellent technical staff membershave been honored with a host of prestigious NISTand external awards.

A concerted effort to partner directly with Sematechhas led to research activities in advanced metrology toaddress pressing needs in next-generation semiconductorproducts. One project is aimed at developing metrologyfor accurate thin film characterization using x-rayreflectometry, while the other is focused on applyingnovel combinatorial and synchrotron methods tooptimize the interfaces in advanced high-k dielectricCMOS gate stacks critical to the semiconductorindustry’s 21st century technology roadmap.

A partnership with the National Cancer Institute(NCI) was initiated this year. NCI has awarded NISTa three-year research grant to collaborate with NCI’snew Nanotechnology Characterization Laboratory inthe development and application of nanoparticle-basedsystems for cancer prevention, detection, and therapeutics.The Ceramics Division is contributing its long-standingexpertise in nanoparticle metrology to this effort bydeveloping measurement methods and protocols forcharacterizing the size, size distribution, and dispersionof inorganic and organic nanoparticles in aqueoussolutions compatible with body fluids.

The Ceramics Division has maintained its strongcommitment to two outstanding long-term partnershipsaimed at providing the reliable, high-quality data that isfundamentally essential for advanced technology researchand development: the celebrated NIST–AmericanCeramic Society collaboration on phase equilibriadiagrams and the collaboration with FIZ Karlsruhe(Germany) on the renowned FIZ–NIST InorganicCrystal Structure Database.

Ongoing partnerships at DOE synchrotron userfacilities have continued to provide high-quality, uniquecapabilities for structural and chemical characterizationof advanced materials. In a joint effort with Sandia NationalLaboratory, considerable progress has been made toestablish a synchrotron-based variable kinetic energy XPSfacility at the National Synchrotron Light Source (NSLS),Brookhaven National Laboratory (BNL), the first of its

kind in the U.S. For the fifth consecutive year, thesoft x-ray beamline jointly developed by NIST andDow Chemical Co. was the most productive soft x-rayfacility at NSLS, yielding over 25 publications. Ourlong-term partnership in UNICAT, a collaborative accessteam at the Advanced Photon Source (APS), ArgonneNational Laboratory, has continued to support and improvenumerous scattering and diffraction techniques. Thispartnership will undergo a transition next year as operationand management of the beamline will be assumed bythe APS.

The Ceramics Division has continued to supportthe upgrade and expansion of its unique measurementcapabilities. Instruments in the high-resolution x-raymetrology and nanotribology facilities in the NISTAdvanced Measurements Laboratory (AML) became fullyoperational this year and have already yielded results withunprecedented resolution. With the recent modernizationof two beamlines at NSLS dedicated to extended x-rayabsorption fine structure (EXAFS) and x-ray photoelectronspectroscopy (XPS), the Ceramics Division and itspartners have established the capability to performx-ray absorption spectroscopy spanning all elements inthe periodic table. A three-year SBIR project has led tothe development of a state-of-the-art multi-element detectorat the NSLS soft x-ray beamline, providing an orderof magnitude increase in data collection rates.

We represent MSEL in the AML, the world’s premiere metrologylaboratory.

There have been numerous notable scientificachievements across the Division this year; followingare several representative research highlights. Teninternational leaders worked together to create theIUPAC–NIST Crystal Phase Identifier standard to uniquelyidentify any chemical compound appearing in an electronicdatabase. This landmark standard is a major step forwardtowards the worldwide interoperability of crystal structuredatabases. In collaboration with BNL scientists, our uniquenear-edge x-ray absorption fine structure metrology facilityat the NSLS has been employed to characterize the surfaceorder and structure of carbon and boron nitride nanotubes,

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resulting in four refereed journal publications. A featurearticle reviewing the state-of-the-art in characterizingceramic materials by x-ray and neutron small-anglescattering was published in the Journal of the AmericanCeramic Society (A. Allen, J. Am. Ceram. Soc., 88,1367, 2005). The first computational model to correlatenanoscale chemical ordering, defects and propertiesin relaxor ferroelectrics, materials of choice for sonarand medical imaging transducers, was constructed,coupling first principles calculations and moleculardynamics simulations. Devices for calibrating force incommercial nanoindentors, instruments for measuringmechanical properties at the nanoscale used by thousandsof researchers worldwide, have been developed jointlywith scientists in the NIST Manufacturing EngineeringLaboratory. These force calibration cells will be producedin collaboration with the major nanoindentor instrumentmanufacturers.

In a far-reaching effort to respond to the anticipatedmetrology and standards needs for next-generationadvanced materials, particularly for nanotechnologyapplications, several new research efforts were initiatedthis year. In the area of CMOS technology, measurementmethods are being developed and applied to evaluatethermal and electrical stability at interfaces in high-kdielectric gate stack structures and to characterize theelectronic structure and chemical bonding in thesestructures at nanometer depth sensitivity. Metrology basedon Raman spectroscopy and x-ray topography is underdevelopment to evaluate the stress state and defectstructures in strained silicon layers for high-performanceMOSFET devices.

Multifunctional oxide materials, wherein thefunctional response of one constituent phase/subsystemis generated by the response of another phase/subsystemto an external field, offer the potential for integratingelectronic, magnetic and optical devices on a single chip.A combined experimental/theoretical modeling effort isunderway to analyze the formation of self-assembledepitaxial nanostructures of multifunctional oxides,measure the functional properties at the nanoscale, andultimately correlate the responses to the nanostructuralarchitectures. Foundational pre-standards research ontheoretical structural models for extracting film propertiesfrom x-ray reflectometry measurements and on referencecantilevers for calibrating AFM force measurementshas begun. A multi-year project was initiated to developan in situ nanocalorimetry technique with adequatesensitivity to detect hydrogen desorption in hydrogenstorage materials and interfacial reactions in multilayerstructures in collaboration with world leaders innanocalorimetry from the University of Illinois.

It is a pleasure to acknowledge the numerousprestigious honors bestowed upon the staff this year.Dr. Daniel Fischer was one of only twelve individualsto receive the coveted Arthur S. Flemming Award

honoring outstanding Federal Government employees.Dr. Fischer was cited for his pioneering work indeveloping and utilizing a first-in-the-world facility forsoft x-ray absorption spectroscopy that has enabled keyscientific and technological advances in cutting-edgeand emerging technologies of paramount importanceto the Nation. For these exemplary achievements,Dr. Fischer was also awarded the Department ofCommerce Gold Medal, the highest honorary awardgranted by the Secretary of Commerce.

Dr. Daniel Fischerreceived the Arthur S.Flemming Award andthe Department ofCommerce GoldMedal award.

The Silver Medal, the second highest Departmentof Commerce honorary award, was given to a NIST team,including Dr. Douglas Smith, for their technical innovationthat revolutionized the realization of the unit of forceat the micro- and nanoscales. Dr. Vicky Karen andDr. Alec Belsky (Technology Services) received theBronze Award, the highest honorary recognition presentedby the NIST Director, for their development andapplication of scientific algorithms and functional softwareembodied in the Inorganic Crystal Structure Databaseused for phase identification in commercial SEMs.

The esteemed NIST Edward Uhler Condon Awardrecognizing distinguished achievement in scientific andtechnical writing was awarded to Dr. Ronald Munro forhis eloquent and systematic exposition of data evaluationas a scientific discipline. Nearly 1500 printed and 40,000electronic copies of NIST Recommended Practice Guide“Data Evaluation Theory and Practice for MaterialsProperties” have been requested across the world, attestingto the broad appeal and applicability of the work.

We remain committed to providing high-qualitymetrology tools, standards, and data to support thedevelopment and implementation of advanced ceramicmaterials, components, and devices in the electronics,photonics, energy, and healthcare technology sectors.

Debra L. KaiserChief, Ceramics Division

Year in Review

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Year in Review

Materials Reliability Division

on Measurement Issues in Single Wall Carbon Nanotubes(SWCNTs) in January 2005. Over 80 leading researchersattended from industry, academia, and other governmentagencies to discuss two significant measurementproblems: how to determine nanotube purity and howto ensure nanotubes are well dispersed for deviceprocessing. Based on information provided fromattendees, we are currently drafting a NIST RecommendedPractice Guide to help industry with these problems.The collected data will also serve as the basis for anupcoming IEEE nanotube measurement standard.

RecognitionDr. Vinod K. Tewary was presented the Eric Reissner

Medal at the annual International Conference onComputational and Experimental Engineering and Sciencesmeeting held July 2004 in Portugal. He received thisaward for sustained and significant contributionsto mechanics at small-length scales.

Dr. Donna C. Hurley was named a Fellow of theInstitute of Physics (U.K.) in recognition of her statusin the physics community and her contribution to theInstitute as a member of the Editorial Board of theJournal of Measurement Science & Technology.

Division Highlights by Focus AreaMaterials for Micro- and Optoelectronics

The International Technology Roadmap forSemiconductors recognizes the importance ofmetrology to the advancement of the industry andcalls specifically for solutions to the near-termchallenge (through 2009) of achieving necessaryreliability. Our project in this area focuses ondevelopment of test and detection methodologies formechanical reliability of dimensionally-constrainedmaterials, as well as on learning more of the sciencebehind the observed mechanical behavior.

HighlightThis year a key advance was made in the

first known demonstration of time- and spatially-resolved measurements of Joule heating in patternedmetal interconnects, using alternating currents. Themeasurement is made with an atomic force microscope(AFM) that uses the probe tip as both a point-source heaterand a resistive element in a Wheatstone bridge circuit.

The left figure shows a thermal AFM imagedepicting temperature differences measured at thesurface of a non-passivated Al interconnect carryingan rms AC current density of 7 MA/cm2. A rapiddecrease in temperature with distance away fromthe interconnect is apparent. The right figure shows

The Materials Reliability Division focuseson reliability issues in microelectronics,nanocharacterization, biomaterials metrology,and infrastructure reliability. Because we donot concentrate on a specific class of material,the division takes advantage of the specificexpertise and complementary skills in the otherMSEL Divisions by running many joint projects.

The Materials Reliability Division’s mission is todevelop and disseminate measurement methods

and standards enhancing the quality and reliability ofmaterials for industry. Our work spans a wide rangeof materials, with a dimension span that extends fromnanometer scale devices, carbon nanotubes, and singlecells — to tall buildings, gas pipelines, and bridges.

Recent WorkshopsPipeline Coatings

The proceedings ofthe 2004 workshopCoatings for CorrosionProtection: OffshoreOil and Gas OperationsFacilities, Marine Pipeline,and Ship Structures hasbeen mailed to the 150participants and to keylibraries around the country.

This report is an important component of our supportfor the pipeline industry under the Pipeline Safety andImprovement Act of 2002 (HR 3609). Cosponsorship ofthe workshop (along with the Office of Pipeline Safety inDoT, DoI, and various academic and industry groups)helps drive improvements in safety in the pipeline industry.

Acoustic PropagationWith NIST’s Center for Theoretical and Computational

Materials Science (CTCMS), we sponsored a workshopon Computational Tools for Modeling AcousticPropagation in Real-World Materials (CTAP) inAugust 2004. Researchers came together to discussmodeling requirements for non-destructive evaluation,medical ultrasound, underwater acoustics, geophysics,and atmospheric acoustics. Despite these very differentuses of acoustics, the attendees faced similar modelingchallenges and were interested in pursuing collaborativesolutions with NIST’s support.

Carbon NanotubesAlong with other researchers in MSEL and CSTL,

we co-organized the 2nd Joint NASA–NIST Workshop

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Year in Review

the temperature variation at one position of the AFMprobe, over 0.2 s, for a 10 Hz current; the oscillation isapproximately 15 °C. These temperature measurementsare used to quantify cyclic thermal strains applied tointerconnects for the purpose of conducting quantitativethermal fatigue tests.

Key PaperR.R. Keller, D.T. Read, and R. Mahajan, “Report of

the Workshop on Reliability Issues in Nanomaterials,”NIST Special Publication, in BERB (June 2005).This report establishes us as a leader in the field ofreliability issues in nanomaterials.

NanocharacterizationNew measurement techniques play a key role in the

development and commercialization of nanotechnology.Reliable manufacturing of nanoscale products demandsvast improvements in our ability to measure materialdimensions, characteristics, and structures. In particular,measurement of mechanical properties on the nanoscaleis critical for fabricating structures with high-aspect-ratio features and ultra-thin and/or multilayer films.

used BLS to detect low-frequency vibrational modesin nanoimprinted polymeric lines, demonstrating theability to measure elasticity of sub-100 nm features.Key papers on these subjects have been published inNanotechnology, Advanced Engineering Materials,and Applied Physics Letters.

Mechanical Behavior of Biological MaterialsThe medical research community recognizes a need

to understand the role that the mechanical behaviorof biological materials play in normal and diseasedtissues. We use a multi-scale approach to elucidatethe mechanical behavior of individual cells andconstructs of a single type of cell, and different cellsin concert. We define mechanical behavior as themechanical properties (e.g., stress, strain, modulus)and the measured response to mechanical stimulus(e.g., change in phenotype, proliferation, signalingproduction). At present, our focus is on measuringcell response by developing specialized bio-MEMSdevices or with an optical trap, designing anddeveloping specialized bioreactors for tissue-engineeredconstructs, and measuring mechanical properties ofmembrane-like tissue.

InfrastructureThe nation’s

infrastructurecontinues to ageand is becomingmore vulnerableto catastrophicfailures, bothintentional andunintentional.In response, wedevelop bettermeasurementtechnology fordetermining amaterial’scharacteristics orfor assessing thesensitivity to failure. In FY05 we expanded our effortson pipeline safety by developing fatigue data on newand field-damaged pipe, advancing the procedures forcrack-tip opening angle (CTOA — a measure of theresistance to crack extension) testing, and holdingworkshops. The Charpy SRM program had over850 customers in FY05, and we organized andcontributed to an international workshop on Charpytest procedures. We finished measuring properties ofsteels used in the World Trade Center as part of theNIST-led study (reports released Summer 2005),and are looking at the issues that impede the useof fire-resistant steel.

Thomas A. SiewertActing Chief, Materials Reliability Division

To investigate elasticity at the nanoscale, we arepursuing two techniques, atomic force acousticmicroscopy (AFAM) and Brillouin light scattering(BLS), to measure Young’s modulus and Poisson’sratio. This year, we successfully transitioned theAFAM technique from quantitative measurements at asingle point to elastic modulus maps for an entire film(see figure for contact stiffness images of a compositeand a microelectronic test structure). In addition, we

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Year in Review

Metallurgy Division

now taken an academic position at Purdue University.Frank Gayle has assumed the position of Acting Chief.

This year we reorganized into four technical groups,each consisting of about 10 staff members and a likenumber of guest researchers.

■ The Thin Film and Nanostructure FabricationGroup performs cutting edge research in fabricationtechniques that range from electrochemical processingto vapor–liquid–solid growth of nanowires.

■ The Thermodynamics and Kinetics Group developsnew theory, simulation methods, and data forpredicting and controlling phase transformationsduring materials fabrication processes.

■ The Magnetic Materials Group develops newmaterials and metrology that allow magnetic devicesand sensors to be created at smaller size scales andwith greater sensitivities.

■ The Materials Performance Group develops newtheory and measurements for characterizing themechanical behavior of materials, with applicationsas varied as sheet metal forming and criticalinfrastructure protection.

Division HighlightsBy virtue of the interdisciplinary nature of materials

problems, teams are formed across the Division,MSEL, and NIST, and, in most cases, with externalpartners in order to meet our project goals. A fewhighlights of the past year are presented here, groupedby focus areas.

Safety and ReliabilityThe nation’s infrastructure continues to age and

is ever more vulnerable to catastrophic failures,whether accidental, intentional, or due to forces ofnature. To address infrastructure vulnerability issues,we have started a number of projects, several inclose collaboration with the Materials ReliabilityDivision (MRD).

This year, NIST completed the three-yearInvestigation of the World Trade Center Disaster.A critical aspect of the investigation was themetallurgical analysis of the recovered structuralsteel performed by the Metallurgy Division with MRD.We issued six reports totaling 1500 pages, and wecontinue to work on issues impeding the use offire-resistant steel.

In FY05 we expanded our efforts on pipeline safetyin a project working with DoT’s Office of Pipeline

The Metallurgy Division mission is to provide criticalleadership in the development of measurementmethods, standards, and fundamental understandingof materials behavior needed by U.S. industry.In extensive collaborations with industry and otheragencies, this year we have focused on complexmetallurgical issues in microelectronics, magnetics,automotive, and civil infrastructure areas.

In this summary, we describe highlights of the past year, as well as demonstrate how the capabilities ofthe NIST Metallurgy Division are being used to solveproblems important to the national economy and thematerials metrology infrastructure.

Establishing PrioritiesWe examine a wide range of possible research

topics and make choices for our research portfoliobased on well-tested criteria: the match to the NIST andDivision missions, the magnitude and immediacy of theneed, whether our contribution is critical for success,the anticipated impact relative to our investment, ourability to respond in a timely fashion with high-qualityoutput, and the opportunity to advance mission science,particularly in areas we believe are important for the future.

We establish our research priorities through extensiveinteraction with U.S. industry and other federal agencies,using a variety of methods, including roadmappingactivities, workshops, technical meetings, standardscommittee participation, and consultation with scientificand technical leaders. A key aspect is translating ourfundamental science into a form useful to our partners,integrating measurements, standards, software tools,and evaluated data as needed to solve industry needs.

We prefer to work in rapidly evolving technologies,where advances in measurement science are neededto understand the limitations on system behavior and,therefore, where our contributions are likely to havean impact on the course of technology. For NIST asa whole and the Metallurgy Division in particular, weare committed to having an impact on nanotechnology,homeland security, health care, and the materialsinfrastructure required for advances in informationtechnology. Over the last two years, we have shiftedsubstantial resources into the areas of nanomagnetics,nanomechanics, nanostructure fabrication, and criticalinfrastructure protection.

Division OrganizationCarol Handwerker led the Division as Chief for the

past nine years. Unfortunately for the division, she has

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Year in Review

Safety and DoE, with MRD focusing on crack arrestbehavior, and Metallurgy addressing corrosion issues,including topics arising at a Metallurgy-organizedPipeline Coatings Workshop held at NIST.

Advanced Manufacturing MethodsA software tool, FiPy, for simulating phase

transformations was released to the public. FiPygives materials scientists, physicists, and chemiststhe ability to simulate phase transformations usingstate-of-the-art, sophisticated numerical techniquesfor partial differential equations that allow dramaticallyfaster solutions to be found over larger physicaldomains and for longer elapsed simulation times.

NUMISHEET, a triennial international conference onsimulation techniques for sheet metal forming, was heldin Detroit in August 2005. Division scientists served ontwo organizing committees, gave a plenary lecture, andseveral additional invited talks. An integral part of thisconference is a round-robin simulation exercise wheremodeling groups try to predict the final sample shapefrom a prototypical forming operation. MSEL playedthe key role in providing new benchmark data usingits unique capabilities for in situ and ex situ stressmeasurement. Through thickness residual stresseswere measured at the NCNR, and surface stresses in asheet under load in a die were measured using a newlydeveloped X-ray stress measurement system integratedinto our metal forming machine.

Nanometrology

A new magnetoresistance (MR) effect discoveredthis year by scientists in the Metallurgy Division isantisymmetric with respect to magnetic field. This newMR effect is due to the presence of circulating currentscreated around domain walls when the magnetizationvector, current direction, and domain wall are mutuallyperpendicular. This effect may provide devicedesigners with much more flexibility in designingmagnetic switches and memory.

A new strategy for selecting appropriate catalyticmetals for vapor–liquid–solid growth of ZnOnanowires with specific semiconducting properties wasdeveloped by combining thermodynamic informationfrom phase diagrams with a high-throughput(combinatorial) approach recently demonstrated bythe MSEL Metallurgy Division for metallizations towide-band-gap semiconductors.

Materials for Microelectronics

Spontaneous formation of tin whiskers on thin filmsof lead-free solder is an enormous reliability issue in theconversion of microelectronics to lead-free solders.

The mechanism responsible for the nucleation andgrowth of Sn whiskers is a matter of considerabledebate. Our research this year has eliminated severalof the possible mechanisms and points to criticalexperiments needed to distinguish among some ofthe remaining possible mechanisms. Knowing themechanism for whisker formation will be key to thecontrol and hopefully suppression of Sn whiskerformation.

Our past work provided tools to chip manufacturersfor on-chip copper interconnect development for nextgeneration chips. We have moved successfully intoseveral new and exciting areas: we have included theimpact of leveling additives in our Curvature EnhancedAccelerator Coverage (CEAC) model — these areused industrially to control overfill bump formation;we have demonstrated gold superfill; we havecompleted a thorough assessment of the issuesrelevant to successful wetting and superfill of copperon ruthenium barriers that is already being requested byindustry and will be key to successful implementationin industry, should it occur; we have achieved seedlesssuperfill on osmium barriers, potentially superior toruthenium as a diffusion barrier, a key issue for barriersfor seedless superfill; we have started new projectson seedless superfill and experimental studies ofleveling agents.

RecognitionBill Egelhoff became a NIST Fellow, the highest

scientific and technical position at NIST.

Lyle Levine and Richard Fields (retired) were partof a team of scientists that won the Allen V. AstinMeasurement Science Award for outstandingachievement in the advancement of measurementscience. This award recognized the development oftechniques to measure stress–strain relationships ofmaterials under high heating-rate, high strain-rateconditions.

The Metallurgy Division was recognized by ScienceNews “News of the Year” in December 2004 for twobreakthrough developments:

■ Bob Shull led a team which found that a small amountof iron added to Gd5Ge2Si2 resulted in a significantlyimproved refrigerant, pointing the way to potentialcommonplace magnetic refrigeration.

■ Jim Warren (Metallurgy) and Jack Douglas(Polymers) were recognized for showing a dualitybetween kinetic and static effects controllingmicrostructure during solidification.

Frank W. GayleActing Chief, Metallurgy Division

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Year in Review

Polymers Division

This report marks an excellent year for the PolymersDivision in terms of impacts not only in technical areas,

but also in professional impact for our staff. This year,Joseph Antonucci of our Biomaterials Group was awardedthe FLC Technology Transfer Award for his research,patenting, and technology transfer activities resultingin commercialization of restorative dental resins; MichaelFasolka of our Multivariant Measurement Methods Groupreceived the Presidential Early Career Award for Scientistsand Engineers (PECASE) for his work in nanostructuredpolymer films and scanned probe techniques; andWen-li Wu was named a NIST Fellow for his high-impactadvances in measurement methods to assist industry,developments in the fundamentals of scattering, andsignificant scientific insights in polymer physics.

This year, we are pleased to present highlights inareas ranging from nanomanufacturing and nanofabricationto organic electronics to combinatorial methods tostandards test methods. Further information on thesetechnical highlights is available on the PolymersDivision’s website at www.nist.gov/polymers.

Chaotic Mixing inMicrofluidic Channel Flows

Realization of nanomanufacturing requires theability to efficiently mix disparate liquids, which isdifficult to achieve in small-scale microfluidic devices.This requires the development and use of new mixingtechnologies. A promising candidate for enhancingmixing is chaotic flow, where the flow-streamlinesrepeatedly cross themselves resulting in mixing thatis orders of magnitude more efficient than diffusion.We determined precisely how to generate a chaotic flowand developed metrics to assess the degree of chaos.

The “crossing-streamline” principle was used tostudy the generation of chaotic mixing in intersectingchannels driven by oscillatory flow boundary conditions,which serve as the source of the necessary temporalvariations. Our advances represent new paradigmsin nanomanufacturing.

Metrology for Nanoimprint LithographyNanoimprint lithography (NIL) is an exciting

technology for cost-effective routine fabrication ofpolymers and other soft materials into 3D nanoscalestructures by physically molding them with a hardmaster. Nanoimprinted structures with dimensions< 10 nm have been achieved without the expensive,complex infrastructure required of next generationphotolithography. Future advancements in NIL,however, require new measurements of dimensionswith sub-nm precision, the characterization ofstructures with complex shapes, and investigationsof the properties of new and unique nanostructuredmaterials. The importance of these metrology needswere established through a panel discussion consistingof 7 experts and 300 audience participants, led byChristopher Soles from the Polymers Division, atthe 2005 SPIE Microlithography Conference inSanta Clara, CA. The panel featured representativesfrom leading nanoimprint vendors, universities,semiconductor companies, and nanotechnologyindustries.

Influence of Interfacial Structureof Organic Semiconductors onDevice Performance

Organic electronic devices are increasinglyincorporated into electronics packaging and are projectedto revolutionize integrated circuits through newapplications taking advantage of low-cost, high-volumemanufacturing, nontraditional substrates, and designedfunctionality. Adoption of these devices will be advancedby developing an integrated and interdisciplinary suite ofmeasurement methods correlating device performancewith structure, properties, and chemistry of criticalmaterials and interfaces.

Near-edge x-ray absorption fine structure(NEXAFS) spectroscopy was used for investigatingthe electronic structure, chemistry, and orientation ofseveral organic electronic molecules near a supportingsubstrate. In collaboration with the University ofCalifornia–Berkeley, NEXAFS spectroscopy was appliedto successfully quantify the simultaneous chemicalconversion, molecular ordering and defect formation

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Year in Review

of soluble oligothiophene precursor films for applicationin organic field effect transistors (OFETs). Variationsin field-effect hole mobility on thermal processingcorrelated directly with the orientation and distributionof molecules within (3 to 20) nm thick films.

Gradient Libraries ofSurface-Grafted Polymers

Layers of grafted polymers provide the means forthe physically robust, chemically versatile surfacefunctionalization required for advanced applications,such as friction management in MEMS, adhesionpromotion for coatings, protein adsorption control inbiomaterials, and environmentally responsive surfacesfor sensors. However, while recent advances in controlledpolymerization enable grafted polymers that exhibitmany types of architecture and composition, identifyingthe optimal grafted system for a given application canbe difficult, time consuming, and expensive.

In response, the NIST Combinatorial Methods Centerhas developed tools for probing the optimal molecular-to micro-scale properties of grafted polymer systems.These methods employ microfluidic technology to delivertailored mixtures and sequences of monomers to aninitiator-functionalized surface. The resulting graftedpolymer libraries exhibit gradual, systematic changes incomposition, chain length, and architecture. Gradientsof grafted block copolymers prepared via these techniquesreveal composition regimes that “switch” their surfaceproperties in response to solvent exposure. Fabricationof layers, e.g., of grafted tapered copolymers exhibiting agradual change in composition along the polymer chain,have also been demonstrated. Moreover, our unique abilityto prepare statistical copolymer composition gradientsprovides comprehensive maps of complex surfacechemistry, which were previously impossible.

Polymer Grafting Density, ProteinAdsorption, and Cellular Response

A combinatorial library consisting of a cell-adhesiveprotein-coated poly(2-hydroxyethyl methacrylate)(poly(HEMA)) gradient with variable grafting densitieswas developed to investigate cell adhesion. Fibronectin(FN), a well-characterized extracellular matrix protein,was selected as a model protein to study the effect ofpoly(HEMA) grafting density on cell adhesion, proteinadsorption, and cellular response. The 2D conformationalgradient varied from low- to high-graft density with thepolymer chain structure changing from mushroom- tobrush-like regimes, respectively, with the FN positionedbetween poly(HEMA) chains. By varying the chemistry,morphology, and functionality of this film, the numberof adherent cells and their corresponding shapes variedsignificantly. Cell adhesion and spreading were usedto evaluate the effect of poly(HEMA) grafting densityon cellular response. A maximized cell adhesionand spreading response was found at low graftingdensity/high FN density, and little cell adhesion andspreading was found at high grafting density/low FNdensity. The experimental results of protein adsorption,cell adhesion, and spreading were consistent betweengradient samples and uniform samples, strongly indicatingthat gradient preparation technology can be used forcombinatorial studies of surface-protein-cells interactions.

ASTM Test Method for MassSpectrometry of Polymers

Charles Guttman of the Polymers Division initiatedand led Technical Working Activity 28 of the VersaillesProject on Advanced Materials and Standards (VAMAS)to developed an ASTM Standard Test Method todetermine the molecular mass distribution of polystyreneusing matrix-assisted laser desorption/ionization massspectrometry (MALDI MS). The method uses data andprotocols developed in a NIST-sponsored interlaboratorycomparison organized with the help of the AmericanSociety for Mass Spectrometry, a complete descriptionof which has been published in Analytical Chemistry.This method covers the determination of molecularmass averages and the distribution of molecular massesfor linear atactic polystyrene of narrow molecular massdistribution ranging in molecular masses from (2,000to 35,000) g/mol, and it provides detailed proceduresfor instrument calibration and sample preparation,as well as details for measuring thesamples on a mass spectrometer.

Eric J. AmisChief, Polymers Division

10

Year in Review

NIST Center for Neutron Research

membranes. The centerpiece of CNBT, funded by theNational Institutes of Health, is the Advanced NeutronDiffractometer /Reflectometer (AND/R).

The ExxonMobil Research and EngineeringCompany continued its long-standing partnership withthe NCNR through their participation in the operation,maintenance, and research at the NG-7 30 m SANSinstrument. They use neutron scattering techniques todeepen their understanding of ExxonMobil’s productsand processes, so as to improve customer service andthe return on shareholders’ investment.

The Department of Energy (DOE) maintainsseveral programs at the NCNR. Brookhaven NationalLaboratory directly partners with NIST through theBNL–NIST Scientific Alliance. In the last year, theNCNR joined the Metal-Hydride and Carbon-BasedMaterials Centers of Excellence, sponsored byDOE’s Office of Energy Efficiency and RenewableEnergy, to develop materials for hydrogen storage.The Center for Food Safety and Applied Nutrition,U.S. Food and Drug Administration (FDA) maintains aneutron activation analysis (NAA) facility at the NCNRthat provides analytical support for FDA programs.The Smithsonian Institution’s Nuclear Laboratoryfor Archeological Research has had a productive28-year partnership with NCNR, during which timeit has analyzed over 30,000 archaeological artifactsby NAA.

The NCNR has continued to upgrade and expandits measurement capabilities. These instrumentdevelopments remain a priority since improvementsin capabilities lead directly to the long-term scientificsuccess of the facility. The NCNR is in the advancedstages of manufacturing and installation of twonew crystal spectrometers that will bring enormousimprovements in capability for inelastic neutronmeasurements to the NCNR and open up new researchopportunities. The new BT-7 thermal triple-axisspectrometer will be ready for users in the next year.The other new instrument, the Multi-Analyzer CrystalSpectrometer (MACS), is a partnership between NIST,the National Science Foundation, and The Johns HopkinsUniversity. It will also begin commissioning in the nextyear. Substantial progress has also been achieved onan additional thermal triple-axis spectrometer to beinstalled at BT-9 and on the new time-resolved SANScapability that will allow researchers to access kineticphenomena on time scales of 50 ms to 100 ms usingstroboscopic techniques.

The more than 300 publications resulting fromwork done at the NCNR during the past year include

The NIST Center for Neutron Research (NCNR)is the nation’s leading neutron facility. This year

more than 2000 research participants from all areas ofthe country, from industry, academia, and governmentused the facility for measurements. These researchersprimarily gain access through a peer-reviewed proposalsystem with beam time allocated by a ProgramAdvisory Committee twice a year. The NCNR alsosupports important NIST research programs innanotechnology, materials science, chemistry,physics, and biotechnology.

The NCNR source provides intense beams ofneutrons to nearly thirty experimental stations.In addition to a thermal neutron D2O moderator, theNCNR has a large area liquid hydrogen moderator,or cold source, that provides intense neutron beamsto the only cold neutron facility operating in the U.S.The operation of the facility over the past twelvemonths has been outstanding. This year, the NCNRran as scheduled, completing nearly 200 beam daysof operation and a major outage for maintenance andupgrade of the source and to install new instruments.The cold source and beam delivery systems alsocontinue to provide highly reliable service.

Partnerships are integral to the success of theNCNR. The Center for High Resolution NeutronScattering (CHRNS), a partnership with the NationalScience Foundation that funds the operation ofsix world-class neutron scattering instruments, wasrenewed for another five years. CHRNS serves morethan 500 users who produce nearly 100 publicationsannually.

The Cold Neutrons for Biology and Technology(CNBT) consortium is dedicated to studies of biological

11

Year in Review

numerous notable scientific achievements. Thefollowing are two representative research highlights.

Developing safe, cost-effective, and practicalmeans of storing hydrogen is crucial for theadvancement of fuel-cell technologies. The NCNR’sTaner Yildirim, in collaboration with Prof. Salim Ciraci,has used first-principles calculations to show thatcarbon nanotubes “decorated” with titanium orother transition metals can bond to up to fourhydrogen molecules per Ti. This corresponds tonearly 8 percent of the weight of “decorated” carbonnanotubes, one-third better than the 6 percent minimumstorage-capacity requirement set by the FreedomCar Research Partnership involving the DOE and thenation’s “Big 3” automakers. These bound hydrogenmolecules are readily relinquished when the system isgently heated. Such reversible desorption is anotherrequirement for practical hydrogen storage. Thus,these findings suggest a method of engineering newnanostructures for efficient, high-capacity hydrogenstorage. This work, which appeared in PhysicalReview Letters, has been featured in a wide variety offorums including Materials Today, Fuel Cell Review,and C&E News.

This year, severalprestigious honors werebestowed upon the usersand staff of the NCNR.Charles F. Majkrzak wasnamed the recipient ofthe 2006 Warren Awardfor Diffraction Physics.Dr. Majkrzak wascited “for his seminalcontributions to thedevelopment of neutronreflectivity and for hispioneering work in theexploration of many issuesin interface science using this technique.” An NCNRteam including Charles Majkrzak, Susan Krueger,Joseph Dura, and Donald Pierce was awarded aDepartment of Commerce Silver Medal for theirscientific and engineering leadership in establishingCNBT at the NCNR.

Taner Yildirim received a Bronze Award fortheoretical research which showed how the physicaland chemical properties of carbon nanotubes can betuned with pressure. Paul Brand and Henry Praskof the NCNR, along with Richard J. Fields of theMetallurgy Division, were awarded the NISTJacob Rabinow Applied Research Award for developingthe nation’s best capabilities for measuring residualstress depth profiles and texture in metals, ceramics,and composites. Brian Toby was elected Fellow ofthe International Centre for Diffraction Data (ICDD)for his contributions to the standardization of dataformats and the creation of tools to use these formatsefficiently. Vanessa Peterson received the 2005Brunauer Award from the Cements Division of theAmerican Ceramic Society for the best paper on thetopic of cements published by the American CeramicSociety during the previous year.

Two long-time NCNR users won awards for workin which neutron scattering results played a major part.Dr. Frank Bates, Distinguished McKnight UniversityProfessor and Head of Chemical Engineering andMaterials Science at the University of Minnesota, waspresented the Turnbull Lecturer Award “for pioneeringcontributions to the fundamental understanding ofstructure and properties of complex polymeric materials,particularly block copolymers and polymeric vesicles,coupled with outstanding lecturing, writing, teaching,and educational leadership.” Dr. Thomas Russell,Distinguished Professor of the Polymer Science& Engineering Department of the University ofMassachusetts Amherst was awarded the 2005Polymer Physics Prize “for his pioneering researchand fundamental elucidation of the surface andinterfacial behavior of polymers.”

Patrick D. GallagherDirector, NIST Center for Neutron Research

Wormlike micellar solutions formed by self-assembledsurfactants exhibit rheological properties such as shearthinning and suppression of turbulent flow that arerelated to the flow-induced changes in their structuralconformations or orientations. These flow propertiesare important in applications such as thickeners,drag reducers and flow improvers in the food andcosmetics industries. A collaboration between theUniversity of Delaware and the NCNR combined SANSwith a novel shear cell to measure the microstructureof a shear-induced phase separating wormlike micellarsolution. The results show that both concentrationfluctuations and gradients in segmental alignmentoccur, and they link shear banding in wormlike micellarsolutions to a shear-induced phase separation.

Dr. Charles F. Majkrzak

12

Program Overview

Nanometrology

Nanotechnology will revolutionize and possiblyrevitalize many industries, leading to new and improvedproducts based on materials having at least one dimensionless than 100 nm. The federal government’s role inrealizing the full potential of nanotechnology is coordinatedthrough the National Nanotechnology Initiative (NNI),a multi-agency, multi-disciplinary program that supportsresearch and development, invests in a balancedinfrastructure, and promotes education, knowledgediffusion, and commercialization in all aspects ofnanoscale science, engineering, and technology.NIST’s unique and critical contribution to the NNI isnanometrology, defined as the science of measurementand/or a system of measures for nanoscale structuresand systems. NIST nanometrology efforts focuson developing the measurement infrastructure —measurements, data, and standards — essential toadvancing nanotechnology commercialization.This work provides the requisite metrology toolsand techniques and transfers enabling measurementcapabilities to the appropriate communities.

MSEL plays a vital role in nanometrology work atNIST with efforts in four of the seven NNI ProgramComponent Areas — Instrumentation Research,Metrology and Standards for Nanotechnology;Nanomaterials; Nanomanufacturing; and FundamentalNanoscale Phenomena and Processes. Innovativeprojects across MSEL are defining and addressingthe forefront research issues in these areas.

Instrumentation Research, Metrologyand Standards for Nanotechnology

R&D pertaining to the tools needed to advancenanotechnology research and commercialization.The design, development, and fabrication of nanodeviceswill require nanomechanical measurements that are rapid,accurate, predictive, well-understood and representativeof a device or system’s environment in real time. MSELis addressing this need by developing instrumentation,methodology, reference specimens and multi-scalemodeling approaches to quantitatively measure mechanicalproperties such as modulus, strength, adhesion, andfriction at nanometer-length scales. This year, novelinstruments for measuring adhesion and friction forcesbetween surfaces and nanoparticles were developed jointlywith industrial partners. Quantitative maps of elasticmodulus were obtained by innovative methodologies basedon atomic force microscopy and strain-induced elasticbuckling instability. To address the need for quantifyingmeasurements made with widely-used commercialnanoindentors and scanned probe microscopyinstruments, MSEL is developing reference specimensand SI-traceable force calibration methodology.

NanomaterialsResearch aimed at discovery of novel nanoscale

and nanostructured materials and at a comprehensiveunderstanding of the properties of nanomaterials.Among the many classes of nanomaterials, nanotubeshave received great attention due to their remarkablephysical properties relevant to many applications.In response to needs expressed by industry and otherfederal agencies, MSEL has embarked on a new effortto develop a suite of metrologies and standards aimed atcharacterizing key structural features and processingvariables of carbon nanotubes. These include dispersion,fractionation, orientation, alignment, and manipulationof individual single-walled nanotubes, all critical toestablishing efficient bulk processing schemes to meetthe imminent high demand for carbon nanotubes.

NanomanufacturingR&D aimed at enabling scaled-up, reliable,

cost-effective manufacture of nanoscale materials,structures, devices, and systems. Nanoimprint lithography(NIL) is rapidly emerging as a viable high-throughputtechnique for producing robust structures with apatterning resolution better than 10 nm. MSEL isdeveloping metrologies that are crucial to advancingNIL as an industrial patterning technology for theelectronics, optics, and biotechnology industries.The current focus is on characterizing shape andthe fidelity of pattern transfer, two key factors inachieving widespread commercial application of NIL.

Fundamental NanoscalePhenomena and Processes

Discovery and development of fundamental knowledgepertaining to new phenomena in the physical, biological,and engineering sciences that occur at the nanoscale.The magnetic data storage industry needs the ability tomeasure and control magnetization on nanometer lengthscales and nanosecond time scales to meet increasingdemands for reduced size and increased speed of devices.MSEL is developing measurement techniques to elucidatethe fundamental mechanisms of spin dynamics anddamping in magnetic thin films. Work this year hasfocused on measurements of the effects of interfacesand interface roughness on magnetization dynamics andmagnetic characterization of edges in magnetic devices.

Through these and other research activities,MSEL is maintaining its committed leadership indeveloping the measurement infrastructure forcurrent and future nanotechnology-based applications.

Contact: Debra L. Kaiser (Ceramics Division)

13

Mechanical Metrology for Small-Scale Structures

Significant progress has been made in the designof a compressively loaded test configuration with awell-defined, tensile gage section. The inset of Figure 1shows one such specimen fabricated by James Beall usingdeep reactive ion etching (DRIE) of a silicon wafer. Whena load is applied to the top of this theta-like geometry, auniform uniaxial tensile stress develops in the middle gaugesection. Finite element analysis gives (horizontal) gaugesection stress and strain as functions of the applied loadand load-point displacement, respectively. Dimensionlesscalibration factors have been obtained for several specimenand fillet geometries, and as a function of the gauge width.

Industrial trends toward miniaturization requirequantitative mechanical property data fordesign, development, and fabrication of modernsmall-scale devices. Developments in disruptivetechnologies require engineering materials datafor structures and architectures at multiple (nanoto macro) length scales. Accordingly, we aredesigning and developing mechanical testingconfigurations from small-scale in-situ structuresfor localized measurements of fracture anddeformation behavior of materials and interfaces.

Edwin R. Fuller, Jr. and Douglas T. Smith

This project aims to: (i) measure mechanicalproperties of microstructures for myriad industrial

and biological systems that cannot be fabricated in bulksamples; (ii) study small-scale phenomena, which maybe controlled by surface effects (e.g., the influence ofsurface stresses on crack nucleation and extension);and (iii) obtain quantitative mechanical property data ofmaterials and interfaces for designing small-scale structuresand components and for assessing their mechanicalreliability. Well-characterized testing configurationsare being designed and developed for measurements ofstrength and crack extension of small-scale structures andinterfaces. We are pursuing four tasks: (i) configurationdesign, optimization, and characterization via finite-elementanalyses; (ii) specimen fabrication; (iii) mechanical testingand fracture analysis (fractography); and (iv) length andforce metrology. In addition to work in the CeramicsDivision (tasks i, iii, and iv), two collaborations wereestablished in the fabrication task (ii): one with James A.Beall of the Quantum Electrical Metrology Division in NISTBoulder, and one with Northwestern University.

Specimens are tested using a depth-sensing nanoindenteras a universal testing machine, thereby giving a continuousrecord of applied load and load-point displacement.Repeatability is illustrated in Figure 1. Strength datafor DRIE silicon, Figure 2, suggest that differencesfor round and hexagonal specimen configurations arenot significant.

To extend this technique to a wider variety ofmaterial systems, focused-ion-beam (FIB) milling isbeing explored in collaboration with NorthwesternUniversity. Hexagonal theta specimens fabricatedfrom a lamellar directionally solidified eutectic ofNi0.5Co0.5O and ZrO2 are approximately 1/15 thesize of the silicon specimens.

Contributors and Collaborators

D. Xiang, G.D. Quinn, D.L. Henann (CeramicsDivision, NIST); J.A. Beall (Quantum ElectricalMetrology Division, NIST); N. Alem, V.P. Dravid(Northwestern University)

Nanometrology

Figure 1: Repeatability for multiple loading of a single specimen.

Figure 2: Weibull plots for round and hexagonal configurations.

14

Nanomechanics: Atomistics in Modeling and Experiments

Nanoscale mechanical behavior (includingfailure) is inherently difficult to measureaccurately, and existing modeling tools are onlyqualitative at best. We are developing modelingtechniques that provide quantitative predictionsand validating these results experimentally.

Lyle E. Levine, Douglas T. Smith, andAnne M. Chaka (838)

Mechanics at the nanoscale is inherently difficultto model accurately. Finite element models

(FEM) can effectively capture the elastic behavior ofmacroscopic structures but include no accurate failurecriteria, since this depends upon atomic-scale behavior.Classical atomistic simulations can handle millions tobillions of atoms, enough to model such events, but thesepotentials become inaccurate for large strains and cannoteffectively handle chemistry. Quantum-mechanics-basedsimulations using density functional theory (DFT) areextremely accurate and handle the chemistry exactly,but such simulations are so CPU-intensive that they canhandle only a few hundred atoms. A combination of allthree modeling techniques is required to accuratelymodel device behavior at the nanoscale.

Over the past year, we have been developingquantitative multiscale modeling techniques forquasistatic applications. At the macroscale, FEM isused to simulate the elastic behavior of a nanomechanicalsystem. Figure 1 shows an example in which a <111>Al crystal is indented by a nanoindenter. The shape ofthe nanoindenter was obtained using an atomic forcemicroscope with closed-loop displacement control.The fine central mesh has nodes on fcc atom positions.The figure shows the resulting von Mises stressdistribution (in cross-section) after indenting 1.5 nm.

The use of classical potentials in a large simulationcell allows us to propagate long-range stresses to thecritical regions where bond distortions are large or wherechemistry effects need to be explored. In these criticalregions, we embed a DFT simulation. The critical regionis relaxed iteratively using DFT, and the classical cell isrelaxed using a molecular dynamics algorithm.

Figure 1: FEM model of a rigid nanoindenter indenting a <111>aluminum single crystal to a depth of 1.5 nm.

Figure 2 shows a classical atomistic simulationusing the embedded atom method (EAM). Initial atompositions and boundary conditions came from a FEMsimulation. The subsurface structure is composedof dislocations that nucleated from a single event.

After an initial dislocation nucleation event,nanoindentation progresses through the complex evolutionof dislocation structures. For example, the raised liparound an indent is produced by large numbers ofdislocations exiting the surface. We are modeling the earlystages of this process using 3D dislocation dynamics,assuming a random distribution of dislocation sources.

Finally, connection to experimental measurementsrequires careful force calibration of the indenter andcalibrated atomic force microscopy measurementsof the indenter tip. We are setting up to grow bulksingle-crystal copper samples, which will be cutand polished using non-contact chemical methodsto minimize the dislocation density. We are alsodeveloping SI-traceable calibration methodologyfor nanoindenters and atomic force microscopes.


S.M. Khan, L. Ma, F. Tavazza, F. Biancaniello(Metallurgy Division, NIST); H. Burdette, B. Hockey,R. Wagner (Ceramics Division, NIST)

Figure 2: EAM simulation showing dislocations produced bynanoindentation of <111> Al to a depth of 4.5 nm.

Nanometrology

15

Nanometrology

Modulus Mapping at the Nanoscale

We are developing metrology for rapid,quantitative assessment of elastic propertieswith nanoscale spatial resolution. Atomic forceacoustic microscopy (AFAM) methods enablemodulus measurements either at a single pointor as a map of local property variations.The information obtained furthers ourunderstanding of nanopatterned surfaces,thin films, and nanoscale structures.

Donna C. Hurley

As critical dimensions shrink well below 1 µm, new tools are required to investigate materials properties

on commensurate scales. Not only is higher spatialresolution needed, but it is also increasingly importantto assess not just the “average” properties from a singlesample position, but to visualize the spatial distributionin properties. To meet these needs, we are developingmethods to measure and image elastic properties basedon the atomic force microscope (AFM). Atomic forceacoustic microscopy (AFAM) involves the vibrationalmodes of an AFM cantilever when its tip is in contactwith a sample. With AFAM, the indentation modulus Mof the sample can be determined. The small tip radius(~5–50 nm) enables nanoscale spatial resolution.

In FY05, we combined single-point AFAM methodswith scanning to achieve quantitative nanomechanicalmapping. We developed a frequency-tracking circuit topinpoint the contact-resonance frequencies at each imagepixel. A digital signal processor architecture enablesrapid data acquisition (~20 min. per 256 x 256 image).Figure 1 shows an example of a modulus map calculatedfrom resonant-frequency images. The calculations usea Hertzian model for the tip-sample contact. The valuesof M agree with both single-point AFAM measurementson the same sample and literature values for theconstituent materials in bulk form. This mappingcapability greatly expands our ability to evaluate theproperties of multicomponent nanostructures.

Accurate AFAM measurements depend on a detailedknowledge of the contact mechanics between the tip andthe sample. In FY05, we continued tandem AFAM andhigh-resolution scanning electron microscope (SEM)experiments to better understand the contact mechanics.We found that the actual behavior varies from tip to tipand is best described by a mixture of Hertzian andflat-punch models. We are now working to integratethese results into our measurement and analysis proceduresin order to improve accuracy and precision.

Another aspect of measurement accuracy involvesthe static forces applied by a tip. The magnitude of the

force is determined by the stiffness of the cantilever, butthis quantity is often poorly known. We began work onthis issue in FY05 using NIST’s electronic force balance(EFB). The EFB provides SI-traceable force calibrationat the nano- to micronewton scale. With the EFB, weobtained the voltage-versus-force relationship for severalpiezoresistive cantilevers. These cantilevers will serve asforce transfer standards to calibrate the cantilevers ofunknown stiffness used in our experiments.

We also continued experiments on relative humidity(RH) effects using self-assembled monolayers (SAMs)of n-octyldimethylchlorosilane on silicon. The calculatedcontact stiffness did not depend on RH for a hydrophobicSAM, but increased strongly with RH for a hydrophilicSAM. Because the contact stiffness represents the elastictip-sample interaction, it should not depend on humidity.The data can be explained by capillary forces that causea viscoelastic interaction. To include capillary forces, ahumidity-dependent damping term was added to the dataanalysis model. The contact stiffness calculated with thismodel was constant with RH, and the damping behaviorwas similar to that observed for AFM pull-off forces.Such results enhance our measurement capabilities fora range of materials and environmental conditions.

FY05 project results were described in 6 contributedand 2 invited journal articles, 5 conference presentations(3 proceedings), and 2 invited workshop presentations.


M. Fasolka, R. Geiss, D. Julthongpiput,M. Kopycinska-Müller, P. Rice, D. Smith (MSEL,NIST); A. Kos (EEEL, NIST); J. Pratt (MEL, NIST);M. Prasad (Colorado School of Mines); J. Turner(University of Nebraska); W. Arnold, U. Rabe(Fraunhofer Institute, Germany)

Figure 1: AFM topography (L) and AFAM modulus map (R)images of a thin-film sample containing a niobium (Nb) stripe~200 nm thick on top of a silica (SiO2 ) blanket film ~350 nm thick.

16

Engineering of nanomaterials, biomaterials, andorganic electronic devices hinges on techniquesfor imaging complex nanoscale features. In thisrespect, new Scanned Probe Microscopy (SPM)methods promise mapping of chemical, mechanical,and electro-optical properties, but these techniquesgenerally offer only qualitative information.Our reference specimens, fabricated with acombinatorial design, calibrate image data fromemerging SPM methods, thereby advancing thesenanometrology tools.

Michael J. Fasolka

Anew generation of SPM techniques intend to measure chemical, mechanical, and electro/optical

properties on the nanoscale. However, contrast in newSPM images is difficult to quantify since probe fabricationcan be inconsistent, and probe/sample interactions are notunderstood. Our research at the NIST CombinatorialMethods Center (NCMC) provides reference specimensfor the quantification of next-generation SPM data.Using a gradient combinatorial design, our specimensgauge the quality of custom-made SPM probes andcalibrate SPM image contrast through “traditional” surfacemeasurements (e.g., spectroscopy and contact angle).

Nanometrology

Reference Specimens for SPM Nanometrology

Figure 2: Demonstration of ∇µp specimen. SPM frictioncontrast (κ) vs. surface energy (γ) differences obtained withprobes of different chemical quality. The red arrow marks theγ-difference sensitivity of a UV-ozone cleaned probe.

Figure 1: Schematic illustration of the ∇µp for calibration ofchemically sensitive SPM techniques. Blue “droplets” illustratewater contact angle measurement along the calibration strips.

of the matrix. Accordingly, traditional measurements,e.g., water contact angle, along these fields relatethe chemical contrast in the ∇µp to known quantities,e.g., surface energy differences.

Figure 2 demonstrates the utility of the ∇µp specimenfor SPM data calibration. This plot was generated from aseries of SPM friction images acquired along the gradedpattern. A frictional contrast parameter, κ, which reflectsmeasured friction force differences between the lines andmatrix, was extracted from each image. To create acontrast calibration curve, κ is plotted against surfaceenergy data derived from water contact measurementsalong calibration fields. As shown in Figure 2, thecombinatorial ∇µp provides, in a single specimen, a full-spectrum relationship between SPM friction force andsurface energy. As shown through the three curves, thespecimen also enables direct comparison between differentprobe functionalization strategies. Moreover, the curvesilluminate the minimum γ-difference detectable by a givenprobe (where κ → 0), i.e., its chemical sensitivity.

Our fabrication route for the ∇µp, and its use asa reference specimen for emerging SPM techniques,is the subject of an article published in Nanoletters(2005, ASAP).


K.L. Beers, D. Julthongpiput (Polymers Division,NIST); D. Hurley (Materials Reliability Division, NIST);T. Nguyen (Materials and Construction Research Division,NIST); S. Magonov (Veeco/Digital Instruments)

This year, we demonstrated the fabrication and use ofa reference substrate that combines patterning of aself-assembled monolayer (SAM) with a surface energygradient. Our gradient micropattern (∇µp) specimensincorporate a series of micron-scale lines that continuouslychange in their surface energy compared to a constantmatrix. Patterning is achieved via a new vapor-mediatedsoft lithography of a hydrophobic chlorosilane SAM onSiO2 (matrix). A subsequent graded UV-Ozone exposuregradually changes the chemistry of the patterned SAMalong the specimen from hydrophobic to hydrophilicspecies. As shown in Figure 1, the specimen designincludes two calibration fields, which reflect the changingchemistry of the SAM lines and the constant chemistry

17

Nanometrology

Nanotribology and Surface Properties

Accurate determination of adhesive and frictionalforces between surfaces and particles is criticalfor efficient and effective design and developmentof nanoscale devices and manufacturing processes.Working with diverse industrial partners (instrument,device, and magnetic storage industries), weare addressing this critical need by developingmetrology tools and methods for nanomechanicalproperty measurements.

Stephen M. Hsu and Richard S. Gates

One of the major conclusions from theNational Nanotechnology Initiative workshop

on instrumentation and metrology (held at NIST inJanuary 2004) was need for improved tools, methods,and calibration procedures for nanoscale measurements.Several advances in measuring friction and adhesionand controlling surface lubrication and texturingwere achieved this year.

Advances in InstrumentationExisting atomic force microscopy (AFM) and

multiscale friction testing instruments were upgraded toimprove measurement accuracy and extend applicabilityof the methods. The AFM was extensively modified toincrease the signal-to-noise ratio. A joint effort withHysitron resulted in a new 3-D force sensor to conductfriction and scratch tests with much higher accuracy.Sample stage modulation is being implemented acrossseveral platforms to increase sensitivity and expandmeasurement capability. In-house cantilever and tipfabrication capability and collaborations with numerousspecialty tip fabricators were established.

Figure 1: Surface features on colloidal probes.

In adhesion and friction measurements, surface forcesare critical parameters that depend upon the real area ofcontact. Figure 1 illustrates typical colloidal probes showingrandom surface features. A computational procedure wasdeveloped to estimate the bearing area for this type ofprobe enabling better determination of contact areas.

The first nanoscale probe using an ultra-thin sheet ofmica glued on a colloidal probe was successfully developedto measure surface forces on extremely small areas(Figure 2). To avoid snap-on of the probe tip duringapproach, the cantilever stiffness and signal-to-noise ratiowere increased.

Surface ControlAdvances were made in the organization of mixed

molecules on surfaces for hydrophobicity, anti-adhesion,and friction control properties. Ultra-durable hydrophobicfilms and friction control films were demonstrated lastyear. Collaboration with Dan Fischer at the NIST beamline at the National Synchrotron Light Source continuesto be vital in characterizing these complex molecularmixtures.

Surface textures are increasingly being used tocontrol surface energy, polarity, adhesion, and friction.In work supported by other agencies and industries, thesurface properties of materials were controlled by useof specific surface features such as dimples, triangles,and ellipses at micro- and nanoscale dimensions.

InteractionsOngoing interactions with domestic and international

partners included a cantilever force calibration studywith other National Measurement Institutes andJon Pratt (NIST, MEL), and surface texture researchwith seven other countries.


C. Ying, S. Yang, M. Reitsma, D.-I. Kim, Y. Liang,X. Wang, J. Grobelny, D. Fischer, Y.T. Hsia (Seagate);W. Gerberich (University of Minnesota); O. Warren(Hysitron); C. Su (Veeco); D. Mendel (NPL);E. Santner (BAM)

Figure 2: Surface force measurement down to 1 nm. The insetshows a schematic of a typical force curve from the AFM.

18

Nanometrology

Chemistry and Structure of Nanomaterials

Successful nanoscale materials fabrication isempowered by a detailed knowledge of thechemistry and structure of surface boundmolecules; e.g., the optimization of SAMs,molecular templates, MEMs lubricants, andfunctionallized nanotubes. We develop,demonstrate, and advance cutting-edgesynchrotron metrologies to bring nanoscalematerials phenomena to practical applications.

Daniel A. Fischer, Vincent A. Hackley,and Andrew J. Allen

In potential MEMs lubricants, we have found that the degree of surface ordering in self-assembled

monolayers (SAMs) governs the friction properties ofthe film. n-Alkyltricholorosilanes films with differentchain lengths (Cn films where n=5–30) werecharacterized by near-edge x-ray absorption finestructure (NEXAFS), Fourier transform infraredspectroscopy (FTIR), and atomic force microscopy(AFM). The chain lengths having 12, 16 and 18carbon atoms were found to be highly oriented with apreferential molecular orientation of the polymeric C-Cchains perpendicular to the surface. C5 and C30 SAMsdid not exhibit preferential orientation of the alkyl chainand C10 showed partial ordering. Complementary FTIRtudies were done to estimate order qualitatively bypeak positions of asymmetric CH2 and the symmetricCH2 stretches. The molecular order informationfrom FTIR followed similar trends as determined byNEXAFS. The frictional properties of the organicmonolayers were determined through the simultaneousmeasurement of normal (load) and lateral (friction)interfacial forces with AFM. Friction measurementson different chain lengths follow inverse trends withsurface order from NEXAFS as shown in Figure 1.

The flow-cell developed by NIST for in situultra-small-angle x-ray scattering (USAXS) studiesof solution-mediated nanoscale materials has beenapplied to the technologically important case of ahomogeneously precipitating solution of nanosizeceria (n-CeO2). n-CeO2 has multiple applications incatalysis, as a solid oxide fuel cell electrolyte material,and in a number of other areas.

Figure 1: SAM order and friction versus chain length.

Modeling of in situ USAXS data taken duringreaction at 25 ºC indicates a co-precipitation of solidprincipal particles (see Figure 2) and a populationof fine particles with a core-shell morphology.The principal population grows in size and volumefraction, V, but the fine secondary features grow onlyin volume fraction. It has been postulated that thefine features constitute a step in the formation of theprincipal particle population, a theory currently beingtested with additional experiments in conjunctionwith Columbia University collaborators.

A strong temperature affect is seen: at 35 °C,the volume fraction of principal particles increaseswith a growth rate roughly twice that at 25 °C.The activation energy for the n-CeO2 precipitation wasestimated from USAXS data to be about 46 kJ mol–1.Additional studies with the flow-cell focus ondispersion and flow-induced alignment of carbonnanotubes in various solvent/dispersant systems.


S. Sambasivan, S. Hsieh, S. Hsu (Ceramics Division,NIST); P.R. Jemian (University of Illinois); J. Ilavsky(APS XOR); S.-W. Chan (University of Columbia);J. Randall, M. Banesh (Zyvex Inc.); H. Wang(Michigan Tech.)

Figure 2: Homogeneous precipitation of n-CeO2.

19

Nanometrology

Nanotube Processing and Characterization

Single-wall carbon nanotubes (SWNTs) exhibitremarkable physical properties, and there isconsiderable interest in using them as nanoscalebuilding blocks for a new generation ofapplications. Despite this promise, fundamentalissues related to the dispersion, fractionation,orientation, and manipulation of individualsingle-walled carbon nanotubes remainunresolved, and efficient bulk processing schemesdo not exist. We are working at the scientific frontof this rapidly emerging field to establish researchprotocols that will help ensure that this newtechnology progresses as quickly and efficientlyas possible, but with uniformly high standards.

Barry J. Bauer, Kalman Migler, and Erik K. Hobbie

Upon their discovery in 1991, carbon nanotubeswere recognized as ideal materials for nanotechnology

applications. Properties of carbon nanotubes differvastly depending on their diameter and chirality, andinterest in these materials stems from their extraordinarycombination of properties: superior thermal conductivity,electrical conductivity, and mechanical strength.Nanotubes are thus attracting great attention foremerging technologies such as bio-chemical sensors,next generation displays, and nano-electronics.Regardless of the ultimate applications, nanotubesclearly represent the most important new class ofmaterials in the past 15 years.

However, application development is plagued byinconsistent sample quality, compounded by a lack ofconsensus on material characterization methods and by

poor measurement reproducibility. The qualityproblems plaguing the nanotube community weredescribed in a recent news article in Nature whichstated, “the situation will not improve until an externalbody introduces standards that suppliers can follow.”Few people were surprised by the conclusion of therecent workshop: NIST must take the lead in aquantitative nanotube metrology that will allowsuppliers and customers to develop standards forthe developing industry.

The Nanotube Processing and CharacterizationProject within the Polymers Division is actively engagedin this effort. As a starting point, we are currently usingsmall-angle neutron scattering (SANS) to quantify thedegree of SWNT dispersion using a variety of dispersionchemistries (Figure 1) and, in doing so, have identifiedDNA wrapping as desirable for the purpose of fractionatingSWNTs by length, diameter, chirality, and band structure.

Figure 2: Refractive index and viscosity as a function of elutiontime in a size-exclusion chromatograph from DNA wrappedSWNTs, showing clear separation by length.

Figure 1: Measured SANS profiles obtained for two differentSWNT dispersion chemistries, showing how DNA wrappingprovides superior dispersion to other methods, such as chemicalfunctionalization.

Taking this one step further, we have begun usingsize-exclusion and ion-exchange chromatography to sortSWNTs by length and chirality (Figure 2). Followingthe protocol pioneered by DuPont researchers, we areproducing ultra clean SWNT fractions that will becharacterized with a broad suite of NIST metrologies.These results will in turn be used to establish universalscientific standards for SWNT purity and dispersion.


W. Blair (Polymers Division, NIST); A. HightWalker (Optical Technology Division, NIST);T. Yildirim (NIST Center for Neutron Research);M. Pasquali (Rice University); M. Zheng (DuPont)

20

Carbon Nanotube Applications: The Role of Nanotube Alignment

Carbon nanotubes are currently being producedby over 50 companies worldwide, with scale-upprogressing at a rapid rate. Of particular importancefor many potential applications is nanotubealignment, which can affect thermal, mechanical,and electrical properties. We are developingmethods to deposit and grow aligned nanotubeson a variety of measurement platforms, as wellas to measure the degree of alignment achieved.

Stephanie A. Hooker

Carbon nanotubes are truly revolutionary materials,exhibiting properties vastly different than any

other bulk form of carbon. Their unique combinationproperties make them valuable for electronics, advancedstructures, biotechnology, and thermal management.However, reliable property measurement continues toprove difficult due to supplier variability, difficultiesmanipulating materials at this small scale, and physicaland chemical interactions (e.g., with substrates, contacts,other nanotubes, and the surrounding environment).Alignment of the individual nanotubes also plays asignificant role in dictating ultimate performance.

One potential application for which alignmentis particularly critical is absorptive coatings for infrareddetectors. Many such detectors are based on pyroelectriccrystals that become electrically polarized with temperaturechanges. To enhance response, coatings are appliedto improve heat transfer. Carbon nanotubes are anexcellent choice for such coatings due to their highthermal transport, which can be tailored by varyingdiameter and orientation (i.e., alignment). Alignmentin such coatings is often achieved using chemicalvapor deposition (CVD). Unfortunately, however,pyroelectric crystals present new challenges for CVDgrowth, as high temperatures, reducing atmospheres,and metal catalysts are required. When these are

combined, undesirable (and irreversible) changes in thepyroelectric crystal are observed. Recently, however, wedemonstrated a new combination of catalyst, barrier layer,growth temperature, and processing gas mixture thatpermits direct synthesis of vertically aligned nanotubearrays on lithium niobate (LiNbO3) and lithiumtantalate (LiTaO3) pyroelectric crystals (Figure 1).

Figure 1: SEM image of vertically aligned nanotubes grown onLiNbO3 at 725 °C. Critical to the process is a thin silicon nitride(Si3N4) barrier layer, preventing catalyst diffusion into the crystal.The graph shows the associated spectral response of the crystalafter application of the coating.

Nanotube alignment is also important for manyother applications, including those in electronics andadvanced structures. One measurement technique withpromising sensitivity to tube alignment is Brillouin LightScattering (BLS). In FY05, we used BLS to evaluate ahighly-aligned single-wall nanotube rope. The resultingspectra showed a distinct peak associated with therope, much different than the broader pattern previouslyreported for a more randomly aligned nanotubenetwork. BLS is also being explored in conjunctionwith nanotube separation techniques to provide anindication of size exclusion.

In FY05, we also helped organize a 2nd jointNASA–NIST workshop on Measurement Issues inSingle-Wall Carbon Nanotubes. This meeting, heldJanuary 26–28, 2005, addressed challenges in measuringpurity and dispersion quality. Over 75 technical andbusiness leaders participated, debating a wide portfolioof characterization tools including Raman spectroscopy,near-IR spectroscopy, thermogravimetric analysis, andelectron microscopy. These techniques are currentlybeing drafted into a Recommended Practice Guide,which will then be adapted by IEEE into a PurityStandard for Carbon Nanotubes.


W. Johnson, S. Kim, T. Oreskovic, P. Rice, V. Tewary,N. Varaksa (Materials Reliability Division, NIST); K. Migler(Polymers Division, NIST); S. Freiman (MSEL);S. Arepalli, L. Yowell (NASA-JSC); R. Mahajan(University of Colorado); R. Hauge (Rice University)

Figure 2: TEM image of a single-wall carbon nanotube rope(courtesy of Rice University). The high degree of alignment in therope was observed in the BLS spectrum to the right.

Nanometrology

21

Combinatorial Adhesion and Mechanical Properties

Traditional methods for evaluating the engineeringproperties of polymers are time-consuming andinherently single specimen tests. Current marketdrivers increasingly demand rapid measurementplatforms in order to keep pace with competitionin the global marketplace. In this project, we aredelivering innovative combinatorial and high-throughput (C&HT) tools for the physical testingof materials, built around measurement platforms inthe NIST Combinatorial Methods Center (NCMC).

Christopher M. Stafford

Our current C&HT efforts in this project areconcentrated in two main areas: buckling mechanics

for thin film mechanical measurements and adhesiontesting platforms for probing interfacial adhesion andfracture. Here, we highlight: (1) the inversion of ourbuckling-based metrology to study the mechanicalresponse of soft polymer gels, (2) application of finiteelement analysis to study buckling in multilayer geometries,and (3) the implementation of our combinatorial edgedelamination test to study the interfacial adhesionstrength of epoxy films.

of our buckling-based technique is that a “modulus map”can be constructed by measuring the buckling wavelengthas a function of spatial position.

Figure 1: Elastic modulus of model PDMS gels measured viabuckling (■ — gradient modulus specimen, ▲ — single specimens)and via tensile test (● ).

In addition to our experimental efforts, we are alsoutilizing finite element analysis (FEA) to help guideexperimental design in our buckling-based metrologyby verifying the validity of available analytical solutionswhen applied to more complex specimen geometries.For example, we examine a composite film consistingof a soft layer confined between two stiff layers. InFigure 2, FEA reveals a critical modulus ratio belowwhich shear deformation becomes significant, thus thestandard analytical solution can no longer be applied tomeasurements in this regime.

As part of the NCMC, we have launched a FocusProject aimed at developing a C&HT measurementplatform for testing interfacial adhesion and fracture inthermally cured epoxy materials. This method is basedon the modified edge-liftoff test.[2] In this Focus Project,we are building capabilities to evaluate the governingparameters for interfacial delamination and reliabilityby fabricating suitable gradient libraries in composition,thickness, temperature, and applied stress. Industrialsponsors for this Focus Project are ICI National Starchand Intel Corporation.

1. C.M. Stafford, et al. Nature Materials 3, 545 (2004).2. M.Y.M. Chiang, et al. Thin Solid Films 476, 379 (2005).


M.Y.M. Chiang, S. Guo, J.H. Kim, E.A. Wilder,W. Zhang (Polymers Division, NIST); Daisuke Kawaguchi(Nagoya University); Gareth Royston (University ofSheffield)

Figure 2: Normalized wavelength versus modulus ratio of atri-layer thin film. E2 and E1 are the moduli of the soft and stifflayer, respectively. The solid line is the analytical solution.

Nanometrology

This year, we applied our buckling-based metrology[1]

to measure the elastic modulus of soft-polymer gels. Elasticmodulus is an important design criterion in soft polymergels for biomedical applications since it impacts criticalproperties such as adhesion, swelling, and cell proliferationand growth. Leveraging our C&HT buckling-basedmetrology, we can rapidly assess the elastic modulus ofpolymer gels by inverting the experimental design: thebuckling of a sensor film of known modulus and thicknessreports the elastic modulus of the substrate, Es. Figure 1illustrates the accuracy of our approach as compared totraditional tensile tests on the same material. One advantage

22

Soft Nanomanufacturing

assembly applications, image analysis was replaced byembedded electronic sensors that detect the presence ofa particle and its size (Figure 1). This electronic signalactivates a valve to isolate a set of particles. Electronicdetection is further advantageous because it is readilyscalable to smaller particles. In comparison to previoussystems, the valves we have developed are alsoadvantageous, since they are not limited to shallowchannel profiles.

Figure 1: Inline particle characterization and counting. In theimage, a polystyrene particle is seen passing electrodes (dark).At right is shown a bimodal size distribution of liquid dropsproduced at a T-junction upstream.

Figure 2: Tubular structures (right) arise from the simulatedorganization of triangular arrangements of dipole particles,shown schematically at left.

High-throughput sensing and processing methodsrequire precision flow design and control, such as wedemonstrated and reported previously by a microfluidicanalog of the four-roll mill. Advancing beyond, wedeveloped a framework for generating chaotic flowin microchannels (described in a separate highlight).

Theoretical simulations probe the organization ofgeometrically and electrostatically asymmetric targetparticle arrangements (Figure 2). These demonstratethe relationship between particle symmetry andorganized structure. Depending on this symmetry,the assemblies exhibit filaments, sheets, tubes andicosahedra. Whereas ordinary phase separationis driven by attractive and repulsive interactions,self-assembly of more complex and finite-sizedstructures requires directional interactions.

Of consequence for sensor applications, organizationkinetics were also investigated. In particular, nucleatingagents were found to control the kinetics of assemblyand, in polymorphic systems, to specify uniquestructure.


F. Phelan, Jr., J. Douglas, K. Migler, H. Hu, P. Stone,J. Taboas, K. VanWorkum (Polymers Division, NIST);Y. Dar, S. Gibbon (ICI/National Starch); M. McDonald(Procter & Gamble); D. Discher, V. Percec (Universityof Pennsylvania); R. Tuan (NIH)

Nanomanufacturing is widely noted as a centralchallenge of nanotechnology. In the realm of softmaterials and suspended particles, it is necessaryto design particle interactions, manipulateself-assembly processes, and measure what isproduced. Guided by theoretical simulations,we are therefore developing high-throughputmicrofluidic methods for particle characterization,processing, assembly, and on-chip quality control.

Steven D. Hudson

The intricacy of biological systems inspires thedesign of artificial systems that also function

through dynamic self-assembly and in-situ monitoringand self-correction.

Our industrial partners identified measurement ofinterfacial tension as a first hurdle for high-throughputmicrofluidic fluids analysis. Particle processing andassembly methods represent the next hurdle. In thisproject, high-throughput tools are developed forthese purposes, and theoretical simulations identifyparticle arrangements whose dynamic assembly anddisassembly is promising for sensor applications.

High-throughput measurement of drop shapeby image analysis represents the cornerstone of aninstrument, developed in collaboration with industrialsponsors, that determines interfacial tension betweenfluids. The measurement principle is simple androbust — drops are stretched by known viscousforces as they traverse a constriction in the channel.The computer controlled system tracks drop positionand deformation more than one hundred times a second.

However, systems that count, isolate, and direct theassembly of particles must operate more efficiently toenable internal feedback mechanisms. Therefore, for

Nanometrology

23

Defects in Polymer Nanostructures

Nanostructured materials create new and uniquefunctionality through the accurate placement,precise shaping, and chemical modification ofnanometer scale patterns. Such materials are tobe the basis of a wide range of emerging nano-technologies that span optics, data storage, andbiomembranes. In each of these applications,defects in pattern placement, shape, and chemicalcomposition can compromise device functionality.The rapid development of these technologiesis currently offset by a lack of quantitativecharacterizations of critical defects. We haveinitiated this project to develop metrologies forcharacterizing critical defects, such as loss oflong-range order, in nanostructured materials.

Ronald L. Jones and Alamgir Karim

The optical, magnetic, and electronic properties of afilm or surface are dramatically changed by the

inclusion and placement of nanometer-scale patterns.The capability to adjust material properties in thismanner is central to the development of sub-wavelengthoptics, high selectivity biomembranes, nanoparticlesynthesis, and ultrahigh capacity data storage. In eachof these applications, variations in pattern shape andplacement can drastically alter functionality and deviceviability.

Fabrication of nanostructured surfaces is performedthrough a wide range of patterning platforms. Whilephotolithographic techniques are traditional routestoward precise patterning, the high cost and complexityof patterning at nanometer length scales has spawneda variety of alternative techniques such as nanoimprintlithography (NIL), self-assembly, and templatedself-assembly. Each fabrication technique strivesagainst a common set of critical defects such asvariation in pattern placement, chemical uniformityacross the pattern cross section, and precision inpattern shape.

To address the needs of this emerging technologicalarea, we have initiated a new program to developmetrologies for long-range order, a critical parameterin optical and data storage applications. Currently,long-range order is quantified from Fourier transformsof real-space microscopy images. However, thedisparity in the pattern length scale (~ 10 nm) and thelength scale of ordering (~ 100 µm) challenges themeasurement range of existing techniques based onscanning electron and scanning probe microscopies.Visible light probes are often complicated by complexinteractions with nanometer scale features.

Using small angle x-ray scattering (SAXS), we aredeveloping quantitative descriptions of long-range order,grain size, and pattern shape in hexagonally arrayedcylinders produced on silicon substrates using bothnanoimprint lithography (NIL) and self-assembledblock copolymers (BCP).

Figure 1: Scanning electronmicroscopy image showinga regular array of hexagonallypacked columns formed insilicon oxide.

Figure 2: SAXS data from arrays of hexagonally packed columnsformed by NIL (left) and self assembly (right).

For each method of pattern formation, long-rangeorder results in a characteristic diffraction pattern.However, the occurrence of a hexagonal diffraction patternfrom the NIL pattern indicates a single crystal spanningthe entire 150 x 150 µm beam spot, while the BCP filmconsists of multiple, randomly oriented crystals. In bothcases, systematic errors in the placement of the patternson the lattice create a characteristic decay in the intensityas a function of the distance from the beam center.

In addition to developing metrologies for long-rangeorder, we continue to develop a suite of metrologies thataddress critical needs in a wide range of nanostructuredmaterials applications. These include nanostructuredsurfaces for adhesion and wettability, as well asnanostructured materials designed for uniqueelectro-optical and magnetic properties.


J.F. Douglas (Polymers Division, NIST);S. Satija (NIST Center for Neutron Research);R. Briber (University of Maryland); H.-C. Kim (IBM)

Nanometrology

24

Critical Dimension Small Angle X-Ray Scattering

The feature size in microelectronic circuitry isever decreasing and now approaches the scaleof nanometers. This creates a need for newmetrologies capable of non-destructivemeasurements of small features with sub-nmprecision. NIST has led the effort in developingsmall angle x-ray scattering to address this need.This x-ray based metrology has been included inthe ITRS roadmap as a potential metrologicalsolution for future generation microelectronicsfabrication. Other applications of thistechnique in areas such as nano-rheologyand nanofabrication are being explored.

Wen-li Wu and Ronald L. Jones

The demand for increasing computer speed anddecreasing power consumption continues to shrink

the dimensions of individual circuitry componentstoward the scale of nanometers. When the smallest,or “critical”, dimensions are < 40 nm, the acceptabletolerance will be < 1 nm. This creates significantchallenges for measurements based on electronmicroscopy and light scatterometry. Device viabilityalso requires the measurement be non-destructive.In addition, the continuing development of new materialsfor extreme ultraviolet photoresists, nanoporous low-kdielectrics, and metallic interconnects all requirehigh-precision dimensional measurements for processdevelopment and optimization.

To address industrial needs, we are developing ahigh-precision x-ray based metrology termed CriticalDimension Small Angle X-ray Scattering (CD-SAXS).This technique is capable of non-destructivemeasurements of test patterns routinely used bymicroelectronic industries to monitor their fabricationprocess. A collimated monochromatic x-ray beamof sub-Å wavelength is used to measure the patterndimensions on a substrate in transmission mode.CD-SAXS has previously demonstrated a capabilityfor sub-nm precision for periodicity and line widthmeasurements.

This year, we have extended the capabilities toprovide more detailed quantifications of the patterncross section. This includes both basic dimensions,such as pattern height and sidewall angle, as well as thedepth profile of the sidewall damage of nano-patternedlow-k dielectrics. The capability to provide basicdimensions is complementary to existing analysesprovided by SEM, however CD-SAXS offers significantadvantages in its non-destructive capability. In contrastto visible light scatterometry, detailed information on

refractive indices and composition of the pattern are notrequired for data reduction. These capabilities and theability to measure patterns approaching dimensions of10 nm have led to the inclusion of CD-SAXS on theInternational Technology Roadmap for Semiconductors(ITRS) as a potential metrology for the 45 nmtechnology node and beyond.

So far, all CD-SAXS measurements have beencarried out at the Advanced Photon Source ofArgonne National Laboratory. As an important stepin demonstrating the potential of technology transfer,we are constructing the world’s first laboratorybased CD-SAXS instrument. When completed, thisinstrument will serve as a prototype for lab-based tooldevelopment as well as a world-class metrology toolfor nanotechnology research.

Future efforts will develop capabilities forquantifying defects and features with complex shapessuch as vias or contact holes. In addition, we willcontinue to expand efforts in supporting othernanofabrication technologies such as those basedon nanoimprint and self assembly.


C. Soles, H. Lee, H. Ro, E. Lin (Polymers Division,NIST); K. Choi (Intel); D. Casa, S. Weigand, D. Keane(Argonne National Laboratory); Q. Lin (IBM)

Figure 1: Diffraction patterns collected over a range of samplerotation angles. The distance between the pronounced horizontalridges provides the sidewall angles β, while the relative intensityand placement of the other diffraction spots provide periodicity,line width, and line height. [qx = 4 π sin(θ /2)/λ, where θ is theangle relative to the diffraction axis and λ is the wavelength ofthe radiation.]

Nanometrology

25

Nanoimprint Lithography

Nanoimprint lithography (NIL) is emerging as aviable next generation lithography with a highthroughput and a patterning resolution better than10 nm. However, wide-spread availability of suchsmall nanoscale patterns introduces new metrologychallenges as the ability to pattern now surpassesthe capability to measure, quantify, or evaluate thematerial properties in these nanoscale features.We develop high-resolution metrologies to augmentand advance NIL technology, with current focuson characterizing shape and the fidelity ofpattern transfer.

Christopher L. Soles and Ronald L. Jones

Nanoimprint Lithography (NIL) is a conceptuallysimple process whereby nanoscale patterns are

written once into a master, typically Si, quartz, or someother hard material, using a high resolution but slowpatterning technology such as e-beam lithography.This master can be rapidly and repeatedly replicatedby stamping it into a softer resist film. This imprintreplication technique is a cost-effective way to combinethe high-resolution patterning of e-beam lithographywith the high throughput of a stamping process.

cross-section (height, width, side-wall angle) withnm resolution. Likewise, specular x-ray reflectivity(SXR) was introduced to quantify the patterncross-section and the residual layer thickness with nmresolution. In turn, these accurate shape metrologiesenable quantitative studies of imprint resolution andthe stability of nanoscale imprinted patterns.

Using CD-SAXS, we demonstrated the fidelity ofpattern transfer concept. The pattern cross-sectionsin the master and the imprint were independentlycharacterized and then compared, to quantify how wellthe resist material fills and replicates the features ofthe master. Varying the imprint temperature, pressure,time, and the molecular mass of the imprint materialimpacts the fidelity of pattern transfer process. Wealso tracked the in-situ evolution of the cross-sectionwhile the patterns were annealed close to their glasstransition. Rather than a viscous decay, the patternsdecreased in height much faster than they broadened inwidth, owing to the residual stresses in the structuresinduced by the imprinting procedure. These residualstresses appear to increase with molecular mass,leading to faster rates of pattern decay in highermolecular mass resists.

NIL holds great promise in semiconductorfabrication. The high resolution and low cost ofownership make NIL attractive in comparison toexpensive next-generation optical lithography tools.However, over the past few years, the interest in NILhas dramatically expanded beyond the realm oftraditional CMOS applications. NIL-based solutionsare being implemented for optical communications,memory, displays, and biotechnology. Because of theseemerging niche applications, NIL is quickly becominga widely used and versatile nanofabrication tool.

Our objective is to develop metrologies that arecrucial to advancing NIL as an industrially viablepatterning technology. Initial efforts have focused ondeveloping and applying very accurate pattern-shapemeasurements. Critical dimension small angle x-rayscattering (CD-SAXS) is a transmission x-ray scatteringtechnique that can quantify the pattern pitch and

SXR was used to quantify the residual layerthickness, pattern height, and the relative line shapecross-section. The residual layer is the thin layer ofresist that the master is unable to fully displace as it ispressed into the resist film. Precise knowledge of theresidual thickness is critical for subsequent etchingprocesses. The key to this measurement is that thex-rays average density over length scales larger thanthe sub-µm dimensions of the patterns. This leads tothe bilayer equivalency model shown above where thepatterns can be modeled as a uniform layer of reduceddensity to extract pattern height and residual layerthickness with nm precision. Like CD-SAXS, SXRquantitatively compares the imprint and the mold toevaluate the fidelity of pattern transfer.


H.W. Ro, H.-J. Lee, A. Karim, E.K. Lin, J.F. Douglas(Polymers Division, NIST); W. Wu (MSEL Office,NIST); S.W. Pang (University of Michigan); D.R. Hines(University of Maryland); C.G. Willson (University ofTexas–Austin); L. Koecher (Nanonex); D. Resnick(Molecular Imprints)

Nanometrology

26

Nanomagnetodynamics

In order to pursue the rapid development pathset out for hard drives and magnetic memory,industry needs the ability to measure and controlmagnetization on nanometer length scales andnanosecond time scales. This project focuses onthe metrology of spin dynamics and damping inmagnetic thin films, especially on the properties oflithographically prepared edges of magnetic films.

Robert D. McMichael

We develop measurement techniques to determinethe static and dynamic properties of both

continuous and patterned thin films of technologicallyimportant ferromagnetic metals and their interfaceswith normal metals. The primary results this yearinclude measurements of the affects of interfaces andinterface roughness on magnetization dynamics andproof-of-concept experiments for measurements oflithographically prepared magnetic edges. These resultshave been communicated to the magnetic data storageindustry through conference presentations, journalarticles, and site visits.

Although the edge metrology aspect of theproject has just started, we have already performedproof-of-concept magnetometry of edge saturationfields and ferromagnetic resonance measurements oflocalized edge modes (see Figure 2). These measurementsare interpreted through corresponding micromagneticmodeling of the static and dynamic behavior of spinsnear edges. The stage is also set for magnetoresistivemeasurements that would be more suitable forwafer-level probing of the lithography process.


J. Rantschler, B. Maranville, J. Mallett, T. Moffatt,W. Egelhoff, Jr., A. Chen (Metallurgy Division, NIST);C. Ross, J. Cheng (MIT)

Figure 1: Damping as a function of roughness in Permalloyfilms on thick Cu substrates. The quadratic behavior is explainedby a model featuring eddy currents that are excited by theroughness-induced stray magnetic fields in the copper.

Figure 2: Image composed of 180 FMR spectra measured on anarray of Permalloy stripes. An AFM image of the stripes is shownin the inset. At 90 ° the applied field is perpendicular to thestripes, and the peak is the resonance of the edge modes.

It is well known that surface affects and interfacialaffects are important in nanostuctured materials.This is especially true for magnetic materials, wherelong-range interactions couple the surface magnetismto the bulk. Figure 1 shows a set of measurementresults that show how interfacial properties affectdamping in Ni80Fe20, (Permalloy) on a copper substrate.

The increased damping is due to the excitation ofeddy currents by magnetostatic fields associated withthe roughness. We have also measured an additionalcomponent of interfacial damping that exists forsmooth interfaces.

We have started a new effort within this project todevelop measurement techniques for characterizationof magnetic edges. The edge properties of a magneticdevice are critical because they affect the shapeanisotropy of a patterned device and the nucleationof vortices in the critical stage for switching.While accepted techniques exist for characterizingbulk materials and interfaces, there are no suchtechniques available for characterizing the edgesof thin film devices.

Nanometrology

27

Materials for Ultra-Low-Field Magnetic Sensors

Magnetic sensors play a central role in manyimportant technologies ranging from health care tohomeland security. A common need among thesetechnologies is greater sensitivity and smaller size.A NIST competence program initiated in 2004 isfocusing on developing the metrology that will enablenew generations of magnetic sensors to be produced.

William F. Egelhoff, Jr.

In the past decade, small inexpensive magnetic sensors have gained important footholds in a wide

variety of technologies. Sales of small inexpensivemagnetic sensors have been soaring. However, onerelatively neglected aspect of these magnetic sensorshas been their sensitivity to very small magnetic fields.

We are focusing on small inexpensive thin-filmmagnetic sensors to avoid the disadvantages of SQUIDs.Existing precedents suggest that such sensors could bemass produced at a cost of a few cents each, will havea size measured in microns, and will operate at roomtemperature. These characteristics make them idealfor the applications indicated in Figure 1.

To achieve our goal we will need magnetic thinfilms of great sensitivity. The best thin films previouslyknown had susceptibilities of a few thousand. In ourfirst year of work, we have already achieved valuesabove 100 thousand.

One of the prime applications that we may impactis magneto-cardiography, or imaging the beating heartin real time. In principle, magneto-cardiography couldgive very high quality 3-D images. However, at present,SQUID-based magneto-cardiography is hugely expensive,has poor resolution, and is practiced only at a few researchinstitutions. If small, inexpensive sensors could makehigh-resolution magneto-cardiography generally available,it would change the practice of cardiology. The followingquote arose in a discussion of our plans.

Figure 1 indicates, for particular applications, therange of fields that the sensor must be able to detectand the range of frequencies at which the fields appear.For comparison, the Earth’s magnetic field is about 104

times larger than the top value of Figure 1. The plotsof “Present technology” and “Our sensitivity goal” inFigure 1 indicate that deep inroads can potentially be madeinto important technologies if we can reach our goal.

It should be pointed out that the technique ofsuperconducting quantum interference devices (SQUIDs)can already reach sensitivities corresponding to thebottom values of Figure 1. Unfortunately, SQUIDs areexpensive, bulky, and require cryogenic cooling. Thesefactors rule out SQUIDs for all applications exceptthose for which size and cost are not a factor and forwhich cryogenic cooling is not prohibitively inconvenient.

Figure 1: A plot of the sensitivity to very small magnetic fieldsthat is required for various applications as a function of thefrequency of the signal to be detected. Also indicated are the limitsof present technology for small inexpensive solid-state sensorsand the goals of the Competence Program.

Nanometrology

“Real-time magneto-cardiography with 1 cm resolutionwould have revolutionary diagnostic impact.”

Bob Balaban, DirectorNational Heart, Lung, and Blood InstituteNational Institutes of Health

As Figure 1 would suggest, magneto-encephalographymay be too demanding an application for the magneticsensors we envision. However, it is always difficult toforecast the limits on new technologies. The one thingthat is very clear is that we have very little competitionin this field of research. The companies that currentlyproduce the small, inexpensive magnetic sensors do nothave active research and development programs in thearea of ultra-low fields. The narrow profit marginsfor existing products will not support such programs.This situation puts NIST in an ideal position to takethe lead and perform a high-risk/high-payoff researchprogram that would not otherwise be undertaken.


R. McMichael, C. Dennis, F. Johnson, B. Maranville,J. Rantschler, A. Shapiro (Metallurgy Division, NIST);J. Unguris (Physics Lab, NIST); D. Pappas, S. Russek(EEEL, NIST)

28

A New Type of Antisymmetric Magnetoresistancein Materials with Perpendicular Anisotropy

When the magnetization reverses direction in aferro-magnet upon the application of a reversedmagnetic field, it usually occurs by the nucleationof local domains with a reversed magnetizationvector which subsequently grows to envelop thewhole material. The ease (or difficulty) by whichsuch a process occurs is key to determininghow useful that material will be for its intendedapplication. The metrology for detecting, measuring,and imaging the process in various classes ofmaterials is being developed in this project. Thisknowledge is necessary for quick implementationof new magnetic materials for the recording,refrigeration, theft control, and power industries.

Robert D. Shull, Valerian I. Nikitenko,and Alexander J. Shapiro

The simplest way to detect the magnetic state of amaterial is to sense the magnetic field that surrounds

it. However, as magnetic devices are reduced in size,the magnitude and spatial extent of these fields are alsoreduced. Recently, very sensitive field sensors (e.g., giant(GMR), tunneling (TMR), and colossal (CMR) magneto-resistance detectors) have been developed which arebased upon measuring the resistance changes caused bythe presence of small magnetic fields. In all these devices,the resistance changes are all symmetric with respect tothe sign of the magnetic field. We report here the discoveryof a new magnetoresistance effect in a multilayer whichchanges sign with changes in the direction of the magneticfield. Furthermore, the phenomenon is found to be caused

by the presence of domain walls running perpendicularto the current direction.

Figure 1 shows the antisymmetric Hall resistance(RH) and in-line resistance (R) for a [Co(0.6 nm)/Pt(1 nm)]4 multilayer as the magnetic field (H) iscycled between positive and negative fields. Note that∆R(H) = –∆R(–H) in (b), indicating the magnetoresistance(MR) is negative when switching from negative fieldsto positive fields while it is positive when switchingfrom positive fields to negative fields, is similar to theHall effect but quite different from normal MR phenomena.

Figure 1: Arrows denote the sequence of measurements; insetshows the domain patterns correlated with magnetization reversalat the MR and RH peaks.

Figure 2: Wedge sample showing: (a) leads for measuringcurrent, I, and voltage, V; (b) domain positions as a function offield.

By the controlled creation of a single domain wallrunning perpendicular to the current direction (shownin Figure 2), the antisymmetric magnetoresistance hasbeen shown to be due to the presence of such a domainwall. This configuration was created by preparing atrilayer containing a wedge-shaped Co layer (varying inthickness from 0.3 nm–0.6 nm) sandwiched by 3 nmthick Pt layers. We had earlier found in such a trilayerthat one could create such a single domain wall runningperpendicular to the wedge at a position along thewedge determined by the magnitude of the reversedfield applied, as shown in Figure 2(b).

The unusual magnetoresistance effect is due tocirculating currents created at the domain wall due tothe opposite Hall voltages on either side of the wall.The results, which were published in Phys. Rev. Letters94, 17203 (2005), provide much more flexibility to thecircuit designers and may point the way to creatingdouble pole magnetic switches.


X. Cheng, S. Urazhdin, O. Tchernyshyov, C. Chien(Johns Hopkins University)

Nanometrology

29

Nanostructure Fabrication Processes:Surface & Growth Stress During Thin Film Electrodeposition

The adsorption of species onto a surface altersthe surface stress since the local interaction ofeach adsorbate alters the bond strength betweenneighboring atoms on the surface. Our immediatefocus is to use surface stress to examine substrate-adsorbate interactions of various molecules forself-assembled monolayers (SAM). A naturalextension of this work is to examine the surfacestress associated with adsorbate-adsorbate lateralinteractions. This could lead to a general in situmetrology for control of surfactants and adsorbate-based surface modification for a variety ofmolecular electronics and sensor applications.

Gery R. Stafford and Carlos Beauchamp

Surface stresses arise because the atomicconfiguration of atoms at a surface is different

from the bulk. Interior atoms exert a stress on thesurface atoms, i.e., the surface stress, which movesthem out of the positions they would occupy in a bulkcrystal configuration. The adsorption of species ontothe surface can be expected to alter the surface stresssince the local interaction of each adsorbate will alterthe bond strength between neighboring atoms onthe surface. An understanding of adsorbate-inducedsurface stress is critical to emerging technologies suchas molecular electronics, nanostructure fabrication,and chemical/biological sensors.

We have established a Class II (1 mW) HeNe opticalbench dedicated to in situ measurement of surface andgrowth stress during electrochemical processing usingthe wafer curvature method. Measurements are made ona borosilicate glass cantilever onto which 250 nm of Au isevaporated. The curvature of the substrate is monitoredwhile in solution and under potential control by reflectinga HeNe laser off the glass/metal interface, through a seriesof mirrors, and onto a position-sensitive detector. Therelationship between force exerted onto the cantilever bythe electrochemical processes occurring at the Au-solutioninterface and the radius of curvature of the cantileveris given by Stoney’s equation. Forces on the order of0.008 N/m (23 km radius of curvature) can be resolved.This is sufficient to study the adsorption of molecularmonolayers onto the electrode surface. As a demonstration,we have measured the surface stress associated withreversible monolayer adsorption of both sulfate and chlorideions onto the Au surface from aqueous solutions.

Figure 1 shows the linear sweep voltammetry (threeconsecutive transients taken 5 minutes apart) as wellas the associated surface stress of a (111)-textured Au

electrode in 1.0 mol/L H2SO4. As the electrode potentialis swept in the positive direction from 0.2 V, a positivecurrent is measured as the result of sulfate ion adsorptiononto the Au surface. As negative charge is removed fromthe electrode with potential increase, the surface stressmoves in the negative (compressive) direction, consistentwith charge redistribution models that appear in theliterature. The adsorption of electronegative species suchas sulfate ion increases the compressive trend in the surfacestress by removing additional charge from the Au surface.Figure 2 is a plot of the surface stress vs. charge densityfor the sulfate adsorption/desorption process. The datasuggest that the slope of the stress-charge curve providesa measure of adsorbate strength that can be used toquantify adsorbate-substrate interactions.


U. Bertocci (Metallurgy Division, NIST);C. Zangmeister (Process Measurements Division, NIST)

Figure 1: Linear sweep voltammetry and surface stress associatedwith sulfate adsorption on (111)-textured Au in 1.0 mol/L H2SO4.

Figure 2: Surface stress vs. charge density associated withsulfate adsorption on (111)-textured Au in 1.0 mol/L H2SO4.

Nanometrology

30

Multiscale Modeling of Quantum Dots in Semiconductors

A computationally efficient multiscale model has beendeveloped for a quantum dot in a semiconductor.The model links the subnano, nano, and macro lengthscales by integrating the powerful techniques ofmolecular dynamics, lattice-statics, and continuumGreen’s functions. The model is applied to Gequantum dots of realistic sizes up to 8 nm in Si.The topography of a free surface of Si, containinga buried quantum dot, is calculated. This surfacecan be measured and used to characterize the QD.The model can also predict the formation of arraysof quantum dots and can be a useful tool forstrain engineering of quantum dots.

Vinod K. Tewary and David T. Read

Technical Description

Currently there is a strong interest in modeling themechanical characteristics of quantum dots (QDs)

in semiconductors because of their potential applicationin powerful new devices like huge memory systems,ultra low threshold lasers, and quantum computers.A QD has to be modeled at the following scales:(i) the core region (sub-nanometer) where the nonlineareffects may be significant; (ii) the region of the hostsolid around the QD (nanometer); and (iii) free surfacesand interfaces in the host solid (macro). Modeling isneeded for interpreting measurements and design ofnew devices. A multiscale model is especially usefulfor strain engineering of QDs and their arrays.

A QD causes lattice distortion in the host solidwhich is manifested as strain and a displacement fieldthroughout the solid. Strains and a displacement field ata free surface can be measured and used to characterizethe QD. A strain field determines the elastic energy ofthe system and is mainly responsible for the formationof arrays of QDs. The strain and displacement field areessentially a continuum-model parameter whereas thelattice distortions are discrete variables that must becalculated by using a discrete lattice theory. Hence oneneeds a multiscale model that relates the discrete latticedistortions at the microscopic scale to a macroscopicparameter such as strain.

We have developed a computationally efficientmultiscale model that links the length scales fromsub-nano to macro and can be used on an ordinarydesktop computer. The model integrates classicalmolecular dynamics (MD) with Green’s functions(GF). We use MD at the core of the QD to account

for the nonlinear effects and the lattice-statics GF, G,near the quantum dots which reduces asymptotically tothe continuum GF near a free surface. The displacementfield in this model containing N atoms is given by:

u(l) = (1/N) ΣkG(k) F(k) exp(ik.l)

where l is a lattice site, k is a reciprocal space vector,and F(k) is the Kanzaki force which is calculated byusing MD. For large l, the above equation reducesasymptotically to the macroscopic continuum while thediscrete lattice effects are retained in F(k). Thus, ourmodel is truly multiscale as it seamlessly links the discreteatomistic effects in F(k) to macroscopic scales throughthe GF and directly relates microscopic lattice distortionat nanoscale to measurable macroscale parameters.

Accomplishments

Figure 1: Topography of a free surface in Si due to a buried1.1 nm Ge QD in Si.

We are now able to model quantum dots of realisticsizes, up to about 8 nanometers, on a desktop computer.To model such a large QD, it is necessary to include atleast a million atoms in the host lattice. An attempt tomodel such a large system using only MD would requirea huge computational effort and involve somewhatarbitrary assumptions for relating discrete latticedistortion to continuum parameters. We have calculatedsurface strains and surface topography (Figure 1)which can be measured and used to characterize theQDs. Note the local minimum at (0,0). A similarminimum occurs in the strain energy for certain QDs.The position of the minimum is a possible favorablelocation for the nucleation of a new QD.


R.R. Keller (Materials Reliability Division, NIST);B. Yang (Florida Tech); R. Pandey (Michigan TechUniversity)

Nanometrology

31

Brillouin Light Scattering:Dynamic Elastic and Magnetic Properties of Nanostructures

Brillouin light scattering can be used to provideinformation on acoustic waves and spin wavesat gigahertz frequencies in nanometric thin-filmmaterials and devices. During FY05, we focusedon developing the metrology and models forcharacterizing waves in several material systems,including nanoimprinted polymers and ferro-magnetic thin films with nanoscale edge effects.

Ward Johnson, Sudook Kim, andColm Flannery

Brillouin light scattering (BLS) is an experimentaltechnique that measures the intensity of spectral

components of light that is inelastically scattered byvibrational waves (acoustic phonons) or spin waves(magnons) in a material. Fabry–Perot interferometrictechniques are used to acquire accumulated spectrathrough repeated mechanical sweeping of the etalonspacing.

In the Materials Reliability Division, BLS is beingpursued as a technique for characterizing dynamicelastic and magnetic properties of a variety of materialsand devices with nanoscale dimensions. During FY05,research on elastic waves focused on nanoimprintedpolymeric lines (highlighted below), carbon nanotubes,and polymeric membranes. Research on spin wavesfocused on magnon–magnon interactions in Ni81Fe19,modes localized near edges of ferromagnetic thin-filmstructures, and modes excited in spin-momentum-transfer devices.

Research on nanoimprinted polymers was pursuedin collaboration with the NIST Polymers Division,Colorado State University, and the University of Akron.The goal of this work is to develop experimental andanalytical methods for characterizing elastic properties,which are expected to deviate from bulk propertieswhen one or more dimensions of a nanoline are lessthan a few tens of nanometers. Figure 1 shows atypical BLS spectrum from an array of imprintedpolymethyl-methacrylate (PMMA) nanolines and plotsof dispersion curves from a series of spectra obtainedat various scattering angles. The general characterof the observed modes, except for the lowest, isdetermined through Fresnel–Adler calculations (blacklines) for a uniform film with a thickness equal to theheight of the nanolines plus the thickness of a residualPMMA layer beneath the lines. The lowest-frequencyset of points arises from transverse flexural modesof the lines. The identification of these modes isbased partly on the correspondence of the datawith calculations of the lowest order flexural modes(antisymmetric Lamb waves) of a plate with thicknessequal to the width of the nanolines (blue curve inFigure 1). Finite-element calculations* have beenemployed to provide detailed information on thevibrational displacements, such as those of theflexural mode shown in Figure 2.


C. Soles, C. Stafford (Polymers Division, NIST);R. McMichael (Metallurgy Division, NIST); P. Kabos,W. Rippard, S. Russek (Electromagnetics Division,NIST); P. Heyliger, P. Krivosik (Colorado State University);R. Hartschuh, A. Sokolov (University of Akron)

Figure 1: (a) BLS spectrum for PMMA nanolines; (b) Measureddispersion curves (blue circles), calculations for a uniform film(black curves), and Lamb-wave calculations (blue curve).

Figure 2: Finite-element calculation of displacements of a flexuralmode of a PMMA nanoline.

Nanometrology

Cou

nts

(s)

Wave number (µm–1)

32

Program Overview

Materials for Electronics

The U.S. electronics industry faces stronginternational competition in the manufacture of smaller,faster, more functional, and more reliable products.Many critical challenges facing the industry requirethe continual development of advanced materialsand processes. The NIST Materials Science andEngineering Laboratory (MSEL) works closely withU.S. industry, covering a broad spectrum of sectorsincluding semiconductor manufacturing, devicecomponents, packaging, data storage, and assembly,as well as complementary and emerging areas such asoptoelectronics and organic electronics. MSEL has amultidivisional approach, committed to addressing themost critical materials measurement and standardsissues for electronic materials. Our vision is to bethe key resource within the Federal Government formaterials metrology development and will be realizedthrough the following objectives:■ Develop and deliver standard measurements and data

for thin film and nanoscale structures;■ Develop advanced measurement methods needed by

industry to address new problems that arise with thedevelopment of new materials;

■ Develop and apply in situ as well as real-time, factoryfloor measurements for materials and devices havingmicrometer to nanometer scale dimensions;

■ Develop combinatorial material methodologies forthe rapid optimization of industrially importantelectronic and photonic materials;

■ Provide fundamental understanding of the divergenceof thin film and nanoscale material properties fromtheir bulk values;

■ Provide fundamental understanding, including firstprinciples modeling, of materials needed for futurenanoelectronic devices.

The NIST/MSEL program consists of projects ledby the Metallurgy, Polymers, Materials Reliability, andCeramics Divisions. These projects are conducted incollaboration with partners from industrial consortia(e.g., SEMATECH), individual companies, academia,and other government agencies. The program isstrongly coupled with other microelectronics programswithin the government such as the National SemiconductorMetrology Program (NSMP). Materials metrologyneeds are also identified through the InternationalTechnology Roadmap for Semiconductors (ITRS), theInternational Packaging Consortium (IPC) Roadmap,the IPC Lead-free Solder Roadmap, the NationalElectronics Manufacturing Initiative (NEMI) Roadmap,the Optoelectronics Industry Development Association(OIDA) Roadmap, and the National Magnetic Data StorageIndustry Consortium (NSIC) Roadmap.

MSEL researchers from each division have madesubstantial contributions to the most pressing technicalchallenges facing industry, from new fabricationmethods and advanced materials in the semiconductorindustry, to low-cost organic electronics, and to novelclasses of electronic ceramics. Below are just a fewexamples of MSEL contributions over the past year.

Advanced Gate DielectricsTo enable further device scaling, the capacitive

equivalent thickness (CET) of the gate stack thicknessmust be 0.5 nm to 1.0 nm. This is not achievable withexisting SiO2/polcrystalline Si gate stacks. High dielectricconstant gate insulators are needed to replace SiO2, andmetal gate electrodes are needed to replace polycrystallineSi. Given the large number of possible materials choicesfor the gate dielectric/substrate and gate dielectric/metalgate electrode interfaces, the MSEL Ceramics Divisionis establishing a dedicated combinatorial film depositionfacility to study the complex interfacial interactions.This same methodology is applicable to a wide varietyof problems in the electronic materials field.

Advanced LithographyLithography is the key enabling technology for the

fabrication of advanced integrated circuits. As featuresizes decrease to sub-65 nm length scales, challenges arisebecause the image resolution and the thickness of theimaging layer approach the dimensions of the polymersused in the photoresist film. Unique high-spatialresolution measurements are developed to identify thelimits of materials and processes for the developmentof photoresists for next-generation lithography.

Advanced MetallizationAs the dimensions of copper metallization

interconnects on microelectronic chips decrease below100 nm, control of electrical resistivity becomes critical.The MSEL Metallurgy Division is developing seedlessdeposition methods that will simplify thin-film processingand result in film growth modes that increase trenchfilling, thus lowering interconnect resistivity.

Mechanical Reliability of MicrochipsOne of the important ITRS challenges is to achieve

effective control of the failure mechanisms affectingchip reliability. Detection and characterization methodsfor dimensionally constrained materials will be critical tothe attainment of this objective. Scientists in the MSELMaterials Reliability Division are addressing this issue byfocusing on electrical methods capable of determiningthe thermal fatigue lifetime and mechanical strength ofpatterned metal film interconnects essential to microchips.

Contact: Martin L. Green (Ceramics Division),Eric K. Lin (Polymers Division)

33


Multifunctional Electronic Ceramics

Materials which exhibit exploitable and coupledresponses to multiple external fields (electric,magnetic, etc.) present entirely new designopportunities for multifunctional, miniaturizeddevices such as sensors or actuators. The goal ofthis project is to establish transferable engineeringprinciples for multi- and single-phase electronicceramics which exhibit a functional response byone constituent phase/subsystem that is generatedby the response of another phase/subsystem to anexternal field.

Igor Levin, Julia Slutsker, and Terrell A. Vanderah

The development of next-generation multifunctionaldevices now includes a search for materials exhibiting

simultaneous magnetic, electronic, and/or photonicresponses (e.g., magnetic semiconductors, magneticsuperconductors, multiferroics, etc.). Multiferroicmaterials display a coexistence of ferroelectric andferromagnetic responses and have attracted particularinterest for several novel device applications includingmemories, sensors, and actuators. Self-assembled,epitaxial heterophase nanostructures consisting ofboth ferromagnetic and ferroelectric phases representone promising class of multiferroics. The strongmagnetoelectric coupling obtained in these materials isattributed to the nanoscale distribution of the phases, whichfacilitates highly efficient elastic interactions and a strongmagnetic response to an electric field (or vice versa) viamagnetostriction and the piezoelectric effect. The sameelastic interactions also control the self-assembly of thecomponent phases, so that the architecture and the scaleof the nanostructures can be predicted and controlledby manipulating the stress state of the film.

We analyzed the affect of stress conditions on themorphologies of epitaxial, self-assembled nanostructures

using PbTiO3-CoFe2O4 thin films. The two-phasenanostructures were grown on single-crystal SrTiO3;the strain conditions were varied by deposition ondifferently oriented substrates. Regardless of orientation,the nanostructures consisted of vertical columns offerromagnetic CoFe2O4 dispersed in a ferroelectricPbTiO3 matrix, or vice versa (Figure 1). However,the morphologies of these columns and their spatialarrangements exhibited a marked dependence on substrateorientation. Phase field modeling of these nanostructures,which assumed an equilibrium corresponding to theminimum of elastic and interfacial energies at a given phasefraction, succeeded in reproducing the morphologicaldifferences (Figure 2). The modeling confirmed that thesedifferences are related to elastic anisotropy in the film.Our results, which demonstrate that the architecture ofself-assembled multiferroic nanostructures can indeed becontrolled by a careful choice of the stress conditions,open a tantalizing opportunity for the rational designof self-assembled, multifunctional nanostructures.

Research on bulk single-phase materials includedphase equilibria studies of the Bi2O3-Fe2O3-Nb2O5and Bi2O3-Mn2O3-Nb2O5 systems. Surprisingly,both systems feature extensive pyrochlore-type phasefields at compositions requiring mixing of the magneticions with far larger Bi3+ ions on the A-sites, inapparent violation of traditional substitutional rules.The pyrochlore phases exhibited relative permittivities~150, and were readily deposited on Si as crystallinethin films using pulsed laser deposition. Although themultiferroic phase BiFeO3 was found to participate inambient-pressure phase assemblages, BiMnO3 did not,and was not stabilized by the presence of Nb5+.

Contributors and CollaboratorsP.K. Schenck (Ceramics Division, NIST);

V. Provenzano (Metallurgy Division, NIST);J. Li, A.L. Roytburd (University of Maryland)

Figure 1: Plane view and cross-sectional images of the0.33CoFe2O4-0.67PbTiO3 nanostructures grown epitaxially on(001) and (110) SrTiO3.

Figure 2: Plane view of CoFe2O4-PbTiO3 nanostructures grownepitaxially on (001), (110), and (111) SrTiO3. For each compositionand orientation, the experimentally observed structure is shown onthe left and the simulation is shown on the right.

34

Spectroscopy, Diffraction, and Imaging of Electronic Materials

We are working to develop, establish, andprovide synchrotron-based metrology, includinginstrumentation and technical expertise, forspectroscopy, diffraction, and imaging techniquesapplicable to the study of nanoscale and otherphenomena that are important in the design,application, and performance of electronicmaterials.

Joseph C. Woicik

The epitaxial growth of oxides on silicon opened thepossibility of incorporating many of their unique

electronic properties into silicon device technology.We have studied the epitaxy and lattice expansionof SrTiO3 thin films grown coherently on Si(001)by kinetically controlled sequential deposition.Coherent growth is achieved by repetition of thedeposition sequence that includes a low-temperatureand high-oxygen partial-pressure step followed by ahigh-temperature and low-oxygen partial-pressure step,thereby suppressing the detrimental oxidation of thesilicon substrate.

Unlike films grown by more traditionalmolecular-beam-epitaxy (MBE) methods, these filmsare found to have an in-plane lattice constant thatis indistinguishable from the silicon substrate, anout-of-plane lattice constant that is expanded by anamount twice that predicted by the bulk elastic

constants of SrTiO3, and a critical-thickness behaviorbeyond ~ 2 nm (5 unit cells or 5 monolayers (ML’s)).

The experimentally determined c/a-ratio as afunction of in-plane misfit strain is shown in Figure 1,for both 5 ML and 10 ML films. The experimentalresults are compared to the results of density functionaltheory for the c/a ratio of a 5 ML film in coherentregistry with the silicon substrate as shown in Figure 2.The difference between the two structures in Figure 2is the presence of OH adsorbates on the surface andoxygen vacancies at the interface, as revealed byhigh-resolution x-ray photoelectron spectroscopyfor films that have been exposed to air.


Figure 1: Measured c/a ratio for 5 ML and 10 ML films asa function of in-plane lattice mismatch. Also shown are thepredictions of elastic theory and density functional theory (DFT).

Figure 2: Structure of the ideal 5 ML SrTiO3 /Si(001) system (a)and the system with O vacancies and OH adsorbates (b).Note the ferroelectric polarization in (b) but not in (a).

This energetically favorable interfacial-defect/surface-charge structure compensates the ferroelectricdepolarization field and allows the ferroelectricpolarization in these ultra-thin films that is confirmed byTi K-edge x-ray absorption fine-structure measurements.


H. Li (Motorola Labs); P. Zschack, E. Karapetrova(UNICAT); P. Ryan (Ames Lab); C.R. Ashman,C.S. Hellberg (NRL); A. Allen, D. Black, M. Green,I. Levin (Ceramics Division, NIST)

35

Theory and Modeling of Electronic Materials

Optimizing the properties of electronic materialsrequires fundamental understanding of the originof their useful properties and computational toolsthat connect atomic-scale knowledge obtainedfrom first-principles calculations to propertiesthat emerge at larger length scales. We aredeveloping first-principles based modeling toolsfor calculating the physical properties of materialsas a function of chemical ordering on differentlength scales and how these properties respondto changes in the environment (temperature,pressure, electric field, etc.). Such techniqueshave applications in a variety of areas, includingdielectrics, dilute spin glass magnets, light-emittingdiodes, multiferroics, phase diagrams, piezoelectrics,semiconductors, and spectroscopy.

Eric J. Cockayne, Richard J. Wagner, andBenjamin P. Burton

Understanding and predicting the physicalproperties of solid solutions is a difficult problem

in general. Even in the simplest case of a harmoniccrystal, the vibrational energy as a function of atomicarrangement can have a strong affect on the phasediagram. The calculated maximum temperature for themiscibility gap in NaCl-KCl is reduced by about 50 %when vibrational entropy is included, and the agreementwith the experimental phase diagram is much improved.Many systems with useful electromechanical properties,such as PbMg1/3Nb2/3O3 (PMN), the relaxorferroelectric that is a constituent of the ultrahighpiezoelectric compound PMN-PbTiO3, are highlyanharmonic. Effective Hamiltonian (Heff) techniqueshave been developed to simplify the modeling ofthese systems, but the effect of chemical disorderon the lattice dynamics of solid solutions is not wellunderstood. We published a methodology, based onmaximum localization, for automatically determiningthe appropriate Heff basis for solid solutions andshowed that it correctly reproduces the phonon densityof states for low-frequency phonons. In PMN, thesephonons were determined to be of two types: thoseinvolving displacements of Pb, and those involvingrotations of oxygen octahedra.

Experiments suggest that the relaxor behavior inPbSc1/2Nb1/2O3 (PSN) is associated with nanoscalechemically ordered regions in a disordered matrix. Weperformed a molecular dynamics simulation of a PSNHeff on a 320000 atom cell. Polarization fluctuationsare much larger in the chemically ordered regions,

which thus dominate the dielectric behavior of PSNnear its dielectric peak. This work demonstrates theimportance of Heff methods that allow us to make adetailed investigation of the effects of nanoscalechemical ordering on dielectric properties.

The semiconductor industry is interested in HfO2as an alternate gate dielectric material. Experimentstypically show significant numbers of defects in HfO2.First principles calculations show that O vacancies aremost stable on the 4-fold coordinated O site and thatHfO2 remains insulating with both a neutral and a 2+charged vacancy. Work is underway to determine howeach kind of vacancy affects the dielectric properties.

Quantitative modeling of mechanical behavior at thenanoscale requires connecting the large-scale elasticdisplacement fields experienced by the whole device tothe small-scale atomistic regions where bond breakingcan mark the initiation of device failure through fractureor plastic deformation. We are working to developmultiscale models for connecting the microscopicapplied load in a nanoindentation experiment to theinitiation of the first broken bond. The sample is abulk Al single crystal with a <111> surface.


S. Tinte, I. Levin (Ceramics Division, NIST);L. Levine, F. Terrazza (Metallurgy Division, NIST);A. Chaka (CSTL, NIST); A. van de Walle, M. Astar(Northwestern University); D.J. Singh (ORNL);W. Kleeman (University of Duisberg); U.V. Waghmare(J. Nehru Center for Advanced Scientific Research)


Figure 1: Snapshot of local polarization in PSN model showinglarger polarization and polarization correlations in the chemicallyordered regions (blue) than in the disordered matrix (red).

36

Advanced Materials for Energy Applications

Fundamental understanding, uniquecharacterization facilities, and standardizedmaterials and data form the technological basisfor advances in materials for energy-relatedtechnologies. We are working to developthe metrology required to relate propertiesand performance of energy materials toprocessing/manufacturing routes viaunderstanding the roles of chemistry, phaserelations, and microstructure, to establish asound physical basis for material system design.

Winnie Wong-Ng, Andrew J. Allen,Daniel A. Fischer, and Lawrence P. Cook

Achallenge for the U.S. economy in the new millennium is for both emerging and mature

industries to provide environmentally friendly,inexpensive, efficient, compact, and cutting-edgesynergistic technologies for energy conversion,distribution, and storage applications. This projectaims to facilitate commercialization of energy-relatedtechnologies by addressing various near-term andlong-term materials issues.

The proliferation of portable telecommunicationdevices, computer equipment, and hybrid electricvehicles has created a substantial interest inmanufacturing rechargeable Li-ion batteries that areless expensive, non-toxic, durable, and small in sizeand weight. The electronic structure of the electrodematerials during the electrochemical cycling isparticularly important to the implementation of Li-ionbatteries. This year, we studied the electronic structureof the Li-ion deintercalated Li(1–x)Co1/3Ni1/3Mn1/3O2materials with soft X-ray absorption spectroscopy(XAS) at O K-edge and metal Lα, β-edges, in combinationwith metal K-edge XAS spectra in the hard x-ray regionto elucidate the charge compensation mechanism.We found that a large portion of the charge compensationduring Li-ion deintercalation is achieved in the oxygensite due to the presence of Co.

Characterization of the triple phase boundary insolid oxide fuel cells (SOFC), where the electron- andion-conducting phases and the gas transport (void)phases meet, is a priority in understanding SOFCperformance and durability. By combining studies of thelarge microstructure scale range, accessible using theNIST-built ultrasmall-angle x-ray scattering (USAXS)facility at the Advanced Photon Source, with anomaloussmall-angle x-ray scattering (ASAXS) measurements,it has been demonstrated that ASAXS can providethe differential contrast for distinguishing betweenthe ion- and electron-conducting phase morphologies.

Figure 1 shows the spatial variation of the void/solidsurface areas involving the ion-conducting yttria-stabilizedzirconia (YSZ) and lanthanum strontium manganate(LSM), and Ni that are the electron-conducting phasesin the cathode and anode layers.

Phase equilibria data are critical for the coatedconductor high Tc materials for cable, generator,fly-wheel, and transformer applications. As anintegral part of a DOE R&D program, phase diagramswere developed for the Ba-R-Cu-O (R = Tm and Yb)systems. The “BaF2” process is a promising methodfor producing long-length coated conductors.We have investigated the role of low-temperature meltand intermediate superlattice phases in the formationof Ba2YCu3O6+x (Y-213). A new Ba(OH)F phase(Figure 2) was discovered that may be related to thelow-temperature melting. The interaction of Y-213with SrTiO3 substrates was studied in terms ofphase equilibria of the Ba-Sr-Y-Cu-Ti-O system.

In collaboration with the University of South Florida,we have characterized the structure and providedx-ray reference patterns for two clathrate phases(Sr8Ga16Ge30 and Cs8Na16Ge136) that are promisingcandidates for thermoelectric power conversionapplications. The structure of Na1–xGe3, whichoften coexists with Cs8Na16Ge136, was also studied.Defining the industrial needs for thermoelectricmetrologies and the uses of combinatorial approachesfor materials optimization remain a high priority.


F. Biancaniello, M. Green, R. Radebaugh, G. Nolas(USF); Z. Yang, I. Levin, Q. Huang, R. Feenstra(ORNL); A. Goyal, V. Maroni (ANL); W.S. Yoon(BNL); K.Y. Chung, X.Q. Yang, J. McBreen,M. Balasubramanian, C.P. Grey, J. Ilavsky (APS XOR);P.R. Jemian (University of Illinois); J. Ruud (GE),W. Dawson (Nex Tech); A. Virkar (University of Utah)

Figure 2: Structure ofBa(OH)F.

Figure 1: Spatial variation incomponent phase surface areas.


37

Polymer Photoresists for Nanolithography

Photolithography, the process used to fabricateintegrated circuits, is the key enabler and driverfor the microelectronics industry. As lithographicfeature sizes decrease to the sub 65 nm lengthscale, challenges arise because both the imageresolution and the thickness of the imaginglayer approach the macromolecular dimensionscharacteristic of the polymers used in thephotoresist film. Unique high-spatial resolutionmeasurements are developed to reveal limitson materials and processes that challenge thedevelopment of photoresists for next-generationsub 65 nm lithography.

Vivek M. Prabhu

Photolithography is the driving technology used bythe microelectronics industry to fabricate integrated

circuits with ever decreasing sizes. In addition, thisfabrication technology is rapidly being adopted inemerging areas in optoelectronics and biotechnologyrequiring the rapid manufacture of nanoscale structures.In this process, a designed pattern is transferred to thesilicon substrate by altering the solubility of areas ofa polymer-based photoresist thin film through anacid-catalyzed deprotection reaction after exposureto radiation through a mask (Figure 1). To fabricatesmaller features, next-generation photolithographywill be processed with shorter wavelengths of lightrequiring photoresist films less than 100 nm thick anddimensional control to within 2 nm.

To advance this key fabrication technology,we work closely with industrial collaborators todevelop and apply high-spatial resolution andchemically specific measurements to understandchanges in material properties, interfacial behavior,and process kinetics that can significantly affect thepatterning process at nanometer scales.

This year, we initiated two new collaborations.With SEMATECH, we are determining the materialssources of line-edge roughness in model 193-nmphotoresists. With the Intel Corporation, we areinvestigating the effect of extreme ultraviolet (EUV)exposure on pattern resolution of model EUVphotoresist materials. With these partners, we continueto provide new insight and detail into the complexphysico–chemical processes used in advancedchemically amplified photoresists. These methodsinclude x-ray and neutron reflectivity (XR, NR), smallangle neutron scattering (SANS), near-edge x-rayabsorption fine structure (NEXAFS) spectroscopy,combinatorial methods, solid state nuclear magnetic

Photoresists are multi-component mixtures thatrequire dispersion of additives, controlled transportproperties during the interface formation, and controlleddissolution behavior. The fidelity of pattern formationrelies on the materials characteristics. We examine theinfluence of copolymer compositions, molecular weight,and photoacid generator additive size to determinethe root causes of image quality by highlightingthe fundamental polymer physics and chemistry.In addition, our collaborators test our hypothesesusing 193-nm and EUV lithographic production tools.

Accomplishments for this past year include:quantification of the developer profile in ultrathin films byNR and QCM; quantification of the deprotection reactionkinetics and photoacid-reaction diffusion deprotectionfront for resolution and roughness fundamentals bycombined NR and FTIR; photoacid generator miscibilityand dispersion in complex photoresist co- and ter-polymersby NMR; and aqueous immersion dependence onphotoresist component leeching by NEXAFS.


B. Vogt, A. Rao, S. Kang, D. VanderHart, W. Wu,E. Lin (Polymers Division, NIST); D. Fischer,S. Sambasivan (Ceramics Division, NIST); S. Satija (NISTCenter for Neutron Research); K. Turnquest (Sematech);K-W. Choi (Intel); D. Goldfarb (IBM T.J. WatsonResearch Ctr); H. Ito, R. Allen (IBM Almaden ResearchCtr); R. Dammel, F. Houlihan (AZ Electronics);J. Sounik, M. Sheehan (DuPont Elect. Polymers)

Figure 1: Key lithographic process steps; each step requires aninterdisciplinary array of experimental techniques to measure thepolymer chemistry and physics in thin films. A model 193-nmresist under investigation is shown with the acid-catalyzeddeprotection reaction.

resonance (NMR), quartz crystal microbalance (QCM),Fourier transform infrared spectroscopy (FTIR),fluorescence correlation spectroscopy (FCS), andatomic force microscopy (AFM).


38

Organic Electronics

Organic electronics has dramatically emerged inrecent years as an increasingly important technologyencompassing a wide array of devices andapplications including embedded passive devices,flexible displays, and sensors. Device performance,stability, and function critically depend upon chargetransport and material interaction at the interfacesof disparate materials. We develop and applynondestructive measurement methods to characterizethe electronic and interfacial structure of organicelectronics materials with respect to processingmethods, processing variables, and materialscharacteristics.

Eric K. Lin and Dean M. DeLongchamp

Organic electronic devices are projected torevolutionize new types of integrated circuits

through new applications that take advantage of low-cost,high-volume manufacturing, nontraditional substrates,and designed functionality. The current state of organicelectronics is slowed by the concurrent developmentof multiple material platforms and processes and a lackof measurement standardization between laboratories.A critical need exists for new diagnostic probes, tools,and methods to address these technological challenges.

Organic field effect transistor test structures werealso designed and fabricated onto silicon wafers withvariations in transistor channel length and width. Devicesconstructed using organic semiconductors such aspoly(3-hexyl thiophene) (P3HT) were tested for theirelectrical characteristics such as the field effect holemobility, on/off ratios, and threshold mobilities. Variationsin mobility, for example, are observed with changes inprocessing variables such as annealing temperature andcasting solvent. Correlations are found between deviceperformance and the microstructure of P3HT as quantifiedby NEXAFS, optical ellipsometry, and FTIR spectroscopy.


J. Obrzut, B. Vogel, C. Chiang, K. Kano, C. Brooks,N. Fisher, B. Vogt, H. Lee, Y. Jung, W. Wu (PolymersDivision, NIST); S. Sambasivan, D. Fischer (CeramicsDivision, NIST); M. Gurau, L. Richter (ChemicalScience and Technology Laboratory, NIST); C. Richter,O. Kirillov (Electronics and Electrical EngineeringLaboratory, NIST); R. Crosswell (Motorola);L. Moro, N. Rutherford (Vitex); A. Murphy,J.M.J. Frechet, P. Chang, V. Subramanian (Universityof California–Berkeley); M. Ling, Z. Bao (StanfordUniversity); M. Chabinyc, Y. Wu, B. Ong (Xerox)

Figure 1: Schematic of the geometry of near-edge x-ray absorptionfine structure (NEXAFS) spectroscopy for the determination ofthe orientation of an oligothiophene organic semiconductorsynthesized by the University of California–Berkeley.

Organic electronics presents different measurementchallenges from those identified for inorganic devices.We are developing an integrated suite of metrologies tocorrelate device performance with the structure, properties,and chemistry of materials and interfaces. We applynew measurement methods to provide the data andinsight needed for the rational and directed developmentof emerging materials and processes. Studies includeAC measurements of organic semiconductor thin films,

Figure 2: Schematic of an organic field effect transistor (OFET)and a photo of the NIST OFET test bed fabricated onto silicon.

the influence of surface modification layers on deviceperformance, and the evaluation of moisture barrierlayers for device encapsulation.

This year, near-edge x-ray absorption fine structure(NEXAFS) spectroscopy was applied to several classesof organic electronics materials to investigate theelectronic structure, chemistry, and orientation ofthese molecules near a supporting substrate. NEXAFSspectroscopy was used successfully to quantify thesimultaneous chemical conversion, molecular ordering,and defect formation of soluble oligothiopheneprecursor films for application in organic field effecttransistors. Variations in field-effect hole mobilitywith thermal processing were directly correlated tothe orientation and distribution of molecules within3 nm to 20 nm thick films.


39

Nanoporous Low-k Dielectric Constant Thin Films

NIST provides the semiconductor industry withunique on-wafer measurements of the physicaland structural properties of nanoporous thin films.Several complementary experimental techniques areused to measure the pore and matrix morphology ofcandidate materials. The data are used by industryto select candidate low-k materials. Measurementmethods such as x-ray porosimetry and smallangle x-ray scattering are developed that may betransferred to industrial laboratories. Methods arebeing developed to measure patterned low-k samplesand to assess the extent of structure modificationcaused by plasma etch.

Eric K. Lin and Wen-li Wu

Future generations of integrated circuits will requireporous low-k interlayer dielectric materials to

address issues with power consumption, signalpropagation delays, and crosstalk that decrease deviceperformance. The introduction of nanometer scalepores into a solid film lowers its effective dielectricconstant. However, increasing porosity adverselyaffects other important quantities such as the physicalstrength needed to survive chemical mechanicalpolishing steps and barrier properties to contaminantssuch as water. These effects pose severe challengesto the integration of porous dielectrics into thedevice structure.

There is a need for nondestructive, on-wafercharacterization of nanoporous thin films. Parameterssuch as the pore size distribution, wall density, porosity,film uniformity, elemental composition, coefficientof thermal expansion, and film density are needed toevaluate candidate low-k materials. NIST continuesto develop low-k characterization methods using acombination of complementary measurement methodsincluding small angle neutron and x-ray scattering(SANS, SAXS), high-resolution x-ray reflectivity (XR),x-ray porosimetry (XRP), SANS porosimetry, and ionscattering. To facilitate the transfer of measurementexpertise, a recommended practice guide for XRP isavailable for interested researchers.

In collaboration with industrial and universitypartners, we have applied existing methods to newlow-k materials and developed new methods to addressupcoming integration challenges. A materials databasedeveloped in collaboration with SEMATECH is usedextensively by SEMATECH and its member companiesto help select candidate materials and to optimizeintegration processing conditions. We address theeffects of the ashing/plasma etch process on the low-k

material during pattern transfer. Often surfacesexposed to ashing/plasma densify and lose terminalgroups (hydrogen or organic moiety) resulting in anincreased moisture adsorption and thus dielectricconstant. XR measurements enable quantificationof the surface densification or pore collapse inashing-treated and/or plasma-treated blanket films.

Figure 1: Four models of the damage layer profile plotted asscattering length density (SLD) as a function of position within aline. The matrix has a relative SLD of zero in the above plots.

This year, a new method using SAXS wasdeveloped to investigate the effect of plasma etch onpatterned low-k films. After the plasma etch process,samples are backfilled with the initial low-k material.Any densification of the sidewall may be observable byx-ray scattering from the cross-section of a patternednanostructure. This SAXS work was carried out atArgonne National Laboratory using line gratings oflow-k material. The resulting data can then becompared with several different scattering modelsfor the densification of the patterned low-k materialas shown in Figure 1. Distinctions between modelssuch as these will significantly help semiconductormanufacturers to accelerate the integration of low-kmaterials into next generation devices.


H. Lee, C. Soles, R. Jones, H. Ro, D. Liu, B. Vogt(Polymers Division, NIST); C. Glinka (NIST Centerfor Neutron Research); Y. Liu (SEMATECH); Q. Lin,A. Grill, H. Kim (IBM); J. Quintana, D. Casa (ArgonneNational Laboratory); K. Char, D. Yoon (Seoul NationalUniversity); J. Watkins (University of Massachusetts)


40

Electrical Methods for Mechanical Testing

The International Technology Roadmap forSemiconductors calls for solutions to thenear-term challenge (through 2009) of achievingnecessary reliability because “new materials,structures, and processes create new chip reliability(electrical, thermal, and mechanical) exposure.Detecting, testing, modeling and control of failuremechanisms will be key.” To this end, we developtest and detection methodologies for mechanicalreliability of dimensionally-constrained materials,and further materials science understanding ofthe observed mechanical behavior.

Robert R. Keller, Nicholas Barbosa III,Roy H. Geiss, David T. Read, andAndrew J. Slifka

This year we have consolidated three distinctprojects addressing different aspects of the reliability

of materials for microelectronics into one Divisionprogram. The present focus is on electrical methodsfor measuring thermal fatigue lifetime and mechanicalstrength of patterned metal films. These methodsare based on the principle of applying Joule heatingto specimens in a controlled manner, by use oflow-frequency, high-current density a.c. electricalsignals. Thermal expansion mismatch between filmand substrate then leads to thermal strains, which canbe used as the basis for mechanical testing.

A key aspect of developing time-varying electricalmethods for mechanical metrology is knowledge of thetemperature of the specimen, with sufficient spatial andtemporal resolutions. Details are provided in the MaterialsReliability Division Technical Highlights section.

model material. Figure 1 depicts an inverse pole figure(IPF) showing surface normal grain orientations beforeand after a.c. stressing. Blue dots represent orientationsprior to stressing, and red dots represent orientations ofseverely deformed regions after stressing. Black dotsalong IPF edges indicate 10 ° increments. Reorientationis consistent with a recent analysis of slip asymmetryin cyclic deformation of bulk fcc crystals, whichshowed that for the case of fully reversed loading,a single crystal reorients such that during the tensilehalf-cycle, the loading axis rotates toward the primaryslip direction, [011], and during the compressivehalf-cycle, it rotates toward the normal to the primaryslip plane, (1 –1 1). The net result of this ratchetingaction is an ultimate crystal orientation near (113).

Development of methods to electricallymeasure strengths of thin films is now underway,with microtensile testing as a reference throughout.Yield strength measurement is based on detection of theonset of plasticity using changes in residual resistanceafter accumulated cyclic damage. Ultimate strengthmeasurement is based on extrapolation of cyclic datato a single cycle, by use of the Coffin-Manson rule.

Results from our work appeared this year intwo archival journal articles, and we target threemore journal submissions by October 2005; thisseries of papers will establish us as the leaders inthis novel approach to mechanical testing of materialswith constrained dimensions. One paper writtenwith German colleagues (R. Mönig, R.R. Keller,C.A. Volkert, “Thermal Fatigue Testing of Thin MetalFilms,” Rev. Sci. Instrum. 75, 4997–5004 (2004))represents the first archival journal publication of thiswork and describes in detail the test methodology.We also completed the final report of our August 2004workshop on Reliability Issues in Nanomaterials(R.R. Keller, D.T. Read, and R. Mahajan, Report ofthe Workshop on Reliability Issues in Nanomaterials,NIST-SP, in BERB), which was reviewed by ninenon-NIST plenary speakers; this workshop establishedus as being among the recognized leaders in thebroad field of reliability of nanomaterials.

Seven presentations of this work were given at fiveconferences in FY05 (MRS, ASME, Characterizationand Metrology for ULSI Technology, GOMACTech,Mechanics and Materials); two more conferencepresentations are planned in October 2005.


Y. Cheng (Protiro, Inc.); R. Mönig (MIT); C. Volkert(Forschungszentrum, Karlsruhe, Germany); B. Sun (Intel)

Figure 1: Inverse pole figure showing surface normal orientationsbefore and after a. c. stressing of Al-1Si at 12.2 MA/cm2 for1.4 x 105 temperature cycles.

We have made additional progress in documentingthe damage processes leading to failure during thermalfatigue of patterned interconnects, using Al-1Si as a


41

Thermochemical Metrology of Interfacial Stabilities

Hetero-interfaces are present in the majority ofelectronic materials and affect the operatingcharacteristics of many devices. For successfulfabrication and optimal performance of advanceddesigns, data on the behavior of interfaces duringthermal processing is essential. Efficientmeasurement and prediction of the interfacialthermochemical stabilities of potentially usefulmaterials combinations require new technologyand new approaches, which are being developedin our laboratories.

Lawrence P. Cook, Mark Vaudin, andMartin L. Green

By using thin-film differential scanning calorimeters(DSCs), it is possible to study materials interactions

on a very fine scale — both in terms of the massof the samples involved, as well as the magnitude ofthe thermodynamic quantities measured. A furtheradvantage of the thin-film DSC approach tothermochemical metrology is that it lends itself tocombinatorial studies, in which compositionallygraded thin films can be deposited over a DSC array.In this way, interfacial stabilities of various materialscombinations can be rapidly evaluated. Our plan is tocorrelate thermochemical data from DSC arrays withcharacterization by x-ray microdiffraction, using an areadetector and an automated stage to sample each elementof the array. The products formed during interfacialreaction will be identified, and these experiments will formthe basis for more detailed examination of the kineticsof reaction for appropriate materials combinations.

To date, our efforts on thin-film DSC haveconcentrated on proof-of-concept using well-known

thermochemical events such as the melting ofSn (232 ºC), the ε/α transition in metallic Co (422 ºC),and the reaction between elemental Si and Ni thin films(kinetically determined). Studies of the latter two reactionsare still in progress, but our preliminary studies of Snmelting have been completed. Figure 1 shows a 200 nmthick layer of Sn deposited on the sample side of athin-film DSC sensor. The sample was deposited bypulsed laser deposition (PLD) through a 60 µm x 100 µmmask; a range of particle sizes is evident. Figure 2 is anuncalibrated average of multiple DSC scans from a samplelike that in Figure 1. The melting (endothermic) andcrystallization (exothermic) scans show multiple events,possibly related to differences in thermal behavior ofdifferent size fractions of the particles. A large thermalhysteresis between melting and crystallization is evident.This example suggests that the thin-film DSC is sensitiveto variations in materials properties, in this case probablyinfluenced by the interfacial tension between the metallicSn in the core of the particles and the thin SnO2 skin onthe surface of the particles.

Work has already begun on a second generationof thin-film DSCs that will be optimized to give truenanometric sensitivity. This work is being donein collaboration with the University of Illinois atUrbana–Champaign. Currently, instrumentation isbeing set up to utilize the enhanced sensitivity thatwill be achieved through a chip design minimizingthermal mass. With the newer devices, near-adiabaticmeasurements will be possible.


R. Cavicchi, C. Montgomery, S. Semancik,M. Carrier (Process Measurements Division, NIST);P. Schenck, W. Wong-Ng, J. Blendell (CeramicsDivision, NIST); L. Allen (University of Illinois, Urbana–Champaign); M. Efremov (University of Wisconsin)Figure 1: PLD-deposited Sn on DSC sensor.

Figure 2: Thin-film DSC of Sn in Figure 1.


42

Combinatorial Metal Selection for Catalytic Growthof ZnO Semiconductor Nanowires

Semiconductor nanowires (NWs) offer a uniquetype of nanoscale building block for creatingnext-generation lasers and chemical/biologicalsensors. Control of NW dimension and structuraland electronic properties is a major barrier todevice fabrication. To address these issues, weare developing a strategy for selecting metals forcatalytic growth of zinc-oxide (ZnO) nanowiresusing an approach based on phase diagrams andhigh-throughput fabrication and analysis.

Albert V. Davydov

Semiconductor NWs show significant promise for a wide variety of optoelectronic and electronic

devices including nano-lasers, detectors, and chemicaland biological sensors. To advance commercializationof such devices, it is necessary to control propertiesincluding size, orientation, and structural and electronicdefects of the fabricated nanostructures.

NWs are often produced using a vapor-liquid-solid(VLS) approach, in which nanometer size islands ofcatalytic metals act as nucleation and growth sites forsemiconductor NW growth. The choice of the metalcatalyst can significantly affect the NW properties. Weare developing a strategy for selecting appropriate catalyticmetals and applying this strategy to VLS growth of ZnOsemiconductor. The selection and screening of catalysts

has been achieved using thermodynamic informationfrom phase diagrams as well as a high-throughput(combinatorial) approach recently demonstrated formetallizations to wide-band-gap semiconductors.[1]

We have examined the role of elemental noble metalsand their alloys on ZnO NW growth and properties.An experimental library was designed using the ternarysilver-gold-copper phase diagram and included elemental,binary and ternary compositions as well as twogrowth temperatures (850 and 950 ºC). The metallibrary elements were deposited on a single galliumnitride/sapphire substrate, which was subsequentlyannealed to form isolated metal droplets upon whichthe ZnO NWs were grown. The resulting set ofmetal islands and ZnO NWs was characterized usingelectron microscopy, x-ray diffraction, and opticalspectroscopy. It was found that the ZnO NW growthwas significantly influenced by the nature of the catalyticmetal droplets formed on the substrate. For example,growth from the Au islands at 850 ºC yielded only a thinZnO nucleation layer with no NWs, while other metalcompositions, which melt at lower temperatures thanAu, produced a variety of NW shapes, sizes andorientations at this temperature (Figure 1).

A combinatorial approach also permits rapidcorrelation of the optical properties of the nanowireswith the composition of the metal islands fromwhich they were grown. For example, ZnO NWsfabricated from the silver islands at 850 ºC producedthe sharpest excitonic peak near 3.36 eV on thecathodoluminescence spectrum (comparable to thatfor bulk ZnO single crystal), indicating superiorcrystalline structure. In contrast, the spectra weresignificantly broader for the NWs grown from thegold and copper containing islands. A comprehensiveassessment of the correlation of structural andspectroscopic data for the ZnO NW library is stillunderway. These initial results demonstrate the powerof the combined phase diagram/combinatorial approachfor controlling semiconductor NW properties.

1. A.V. Davydov, A. Motayed, W.J. Boettinger,R.S. Gates, Q.Z. Xue, H.C. Lee, and Y.K. Yoo,Phys. Stat. Sol.(c), 2(7), 2551.


W. Boettinger, D. Josell, C. Handwerker, U. Kattner,M. Vaudin, I. Levin, L. Robins (MSEL); B. Nikoobakht(CSTL); N. Sanford (EEEL); A. Motayed (Universityof Maryland)

Figure 1: Scanning electron microscope images from thecombinatorial library: (a) ZnO wetting layer grown using goldcatalyst (note the absence of NWs); (b) ZnO NWs grown usinggold-copper alloy catalyst; (c) ZnO NWs grown using silvercatalyst. Growth temperature 850 ºC. The scale bar on the topimage is 1 µm.


43

Advanced Processes and Materials for On-Chip Interconnects

As dimensions of copper wiring in on-chip electricalconductors drop below 100 nm, control of electricalresistivity has become critical. We have demonstratednew barriers for seedless deposition processes thatwill simplify processing and replace high resistivitytantalum barriers. We have also demonstrated goldsuperfill as an alternative metallization.

Daniel Josell and Thomas P. Moffat

As dimensions of transistors in integrated circuits shrink, the dimensions of the metal wires

connecting them shrink as well. With industrypassing through the 90 nm node, electron transportis reduced and fabrication is increasingly difficult.

Figure 1: Copper superfill in trenches with ruthenium barriersand no copper seed. (A) Desired copper wetting and superfill.(B) Poor wetting in the presence of surface oxide. (C) Intriguinglocalized deposition in trenches, the origin of which is unknown.

Figure 2: Gold superfill in trenches of three different aspect ratiosafter indicated deposition times, showing bottom-up superfill.

Figure 3: The impact of leveling additives on trench superfilland overfill bump formation. Higher adsorption kinetics k+

leads to reduced overfill bump formation (top), consistent withexperimental observation. Corresponding coverage ofaccelerator is shown beneath.

Consistent with dimensional requirementsspecified in the International Technology Roadmap forSemiconductors, we have been exploring new barriermaterials that will permit copper electrodeposition withouta copper seed layer. We have explored platinum groupelements and have found several that permit seedlessdeposition. As part of this effort, we have exploredin depth the role of oxide removal and underpotentialdeposition of copper in determining the wettability ofruthenium barriers and associated reliability for seedlesscopper superfill. This work has demonstrated a processfor “repair” of seeds through removal of surface oxide.

We have also explored novel metallizations.With the successful demonstration of gold superfillthis year (Figure 2), we have now established processesfor superfill with three metals, our work being the firstto demonstrate superfill with either silver or gold.

Recognizing the significance of leveling additivesin industrial processing, we have now extended ourCurvature Enhanced Accelerator Coverage (CEAC)mechanism to account for their presence duringsuperfill. The resulting equations predict reductionof overfill bump through the use of levelers (Figure 3),consistent with observation. Experiments are underwayto assess kinetics to permit quantitative comparisonto experiment.


C. Witt (Cookson–Enthone); D. Wheeler (Universityof Maryland)


44

Pb-free Surface Finishes: Sn Whisker Growth

Soldered joints are increasingly tenuous links inthe assembly of microelectronics as a consequenceof ever shrinking chip and package dimensions,the broadening use of flip-chip technology, andthe movement toward environmentally friendlylead-free (Pb-free) solders. To support needs inthis area, the goal of this project is to providedata and materials measurements of criticalimportance to solder interconnect technologyfor microelectronics assembly.

Maureen E. Williams and Kil-Won Moon

It is well known that the use of pure tin protective deposits can lead to problems with whiskers —

filamentary whiskers typically 1 µm diameter andseveral mm long which grow from the platingand cause electrical shorts and failure. Historically,lead was added to tin plate to prevent whiskergrowth as well as lower costs. The present projectfocuses on Pb-free, Sn-rich deposits with alloyingadditions that could potentially retard whiskerformation. The Sn-Cu system was selected forcompatibility reasons, since Sn-Cu-Ag is likelyto be the Pb-free solder of choice for industrialapplications. The substitution of a different solutefor Pb in the Sn-rich deposit was proposed to alsoretard whisker growth. A detailed microstructuralcomparison of deposits with high- and low-whiskeringtendency has been conducted, leading to a correlationof Sn grain size, shape, and residual stress withwhisker growth.

A manuscript submitted to Acta Materialia,“Hillock and Whisker Formation in Sn, Sn-Cu andSn-Pb Electrodeposits,” presents measurements ofcompressive stress in the electrodeposits and howvarious microstructural features of the deposits affectwhisker growth. Relief of the compressive stressoccurs by uniform creep for Sn-Pb because it has anequiaxed grain structure. On the other hand, localizedcreep in the form of hillocks and whiskers occursfor Sn and Sn-Cu because both have columnar grainstructures. Compact hillocks form for Sn depositsbecause the columnar grain boundaries are mobile.Contorted hillocks and whiskers form for the Sn-Cudeposits because the columnar grain boundarymotion is pinned by intermetallic precipitates.

Some reports suggest that restraining and crackingof a tin oxide surface film are necessary steps in thenucleation of Sn whiskers. However, results at NIST,accepted for publication in the Journal of ElectronicMaterials showed little support for this mechanism.

For instance, whiskers were observed onbright Sn-Cu electrodeposits but not on pure brightSn electrodeposits on pyrophosphate Cu substrates.In order to understand the role of the depositsurface, the Sn oxide surface film and surfacestructures were analyzed by Auger and ElectronBackscatter Diffraction (EBSD). In Auger analysis,residuals of the Sn oxide surface film were observedafter Ar+ ion cleaning. This feature allowed us todiscriminate the Sn whisker growth with or withoutthe oxide surface film.


W. Boettinger, C. Johnson (Metallurgy Division,NIST)

Figure 1: Low and high magnification SEM micrographs of theelectrodeposited surface of a 16 µm thick pure Sn layer on acantilever beam showing bimodal size distribution of conicalhillocks. Such hillocks form to relieve compressive residualstress. Whiskers form when grain boundaries in the depositare pinned by precipitates.


45

Materials for Advanced Si CMOS

Further size reduction of complementary-metal-oxide-silicon (CMOS) devices in the Simicroelectronics industry, necessary for continuedadherence to Moore’s law, is currently materialslimited. The gate stack, composed of the SiO2gate dielectric and the doped polycrystallineSi gate electrode, is no longer sufficient andmust be replaced by new materials. Further, startingSi wafers must be strain engineered to increasecarrier mobility and subsequent device performance.NIST plays an active role in both activities.

Martin L. Green

NIST/MSEL is poised to play important rolesin the introduction of new materials to the Si

microelectronics industry, so that further scaling(size reduction) may be enabled. One example isthe advanced gate stack for Si CMOS. To enablefurther device scaling, the capacitive equivalentthickness (CET) of the gate stack must be 0.5 nmto 1.0 nm. This will not be achievable with existingSiO2/polycrystalline Si gate stacks. Since replacementsfor SiO2 have already been identified, it is now particularlyimportant to replace the doped polycrystalline Si gateelectrode with a true metal. Given the large number ofpossible choices of alloys for the metal gate electrode,the combinatorial approach is seen as the most effectiveway of identifying alloys possessing the proper workfunction and stability as metal gates on HfO2.

Figure 1 shows flatband voltage data, from whichwork functions may be derived, measured on hundredsof capacitors, where each small square represents adifferent metal gate composition in the Nb-W-Pt ternarysystem. Variations in flatband voltage, due to alloycomposition, are readily observed. As can be seen fromFigure 2, work functions determined through combinatorialexperiments are in excellent agreement with thosedetermined by other, less straightforward means.

Figure 1: Flatband voltage measurements obtained fromcapacitance — voltage data, for the Nb-Pt-W metal gate system.

Figure 2: Comparison of work function data determined throughcombinatorial experiments and other techniques.

Figure 3: Raman shift of strained Si with respect to relaxed Si.

Another example of NIST activity in advanced Simaterials is strained Si, which is increasingly beingused to enhance carrier mobilities in high performancedevices. Figure 3 shows the characteristic Raman shiftthat accompanies strain in the Si lattice. MSEL/NISTis working to calibrate the Raman shift to an absolutestrain measurement (via precision lattice parameterdetermination) to facilitate the introduction of thistechnology.


D. Black, K.-S. Chang, T. Chikyow (NIMS,Japan); M. Gardener (Sematech); D. Josell, R. Lei(Intel); P. Majhi (Sematech); A. Paul, P. Schenck,W. Wong-Ng, J. Suehle (EEEL/NIST); I. Takeuchi(University of Maryland)


46

Metrology and Standards for Electronic andOptoelectronic Materials

The electronics and optoelectronics industriesrequire accurate materials properties data toimprove their device fabrication, modeling, andevaluation processes. Our recent activities haveemphasized optical and structural metrologiesapplicable to wide bandgap semiconductornanowires, and UV Raman spectroscopyfor the evaluation of strain in strainedsilicon-on-insulator structures.

Lawrence H. Robins and Albert J. Paul

Nanowires, defined as semiconductor or metalstructures having a quasi-cylindrical geometry

with diameter in the range 1 to 100 nm, are expectedto have a major impact on future electronic andoptoelectronic technologies. A NIST program wasrecently started to develop growth and manipulationtechniques, metrologies, and test structures forsemiconductor nanowires, based on GaN growthby molecular beam epitaxy (MBE), and ZnO growth bythe catalyst-assisted vapor-liquid-solid (VLS) method.We are contributing to this program by developingmetrologies for structural and optical characterizationof the nanowire samples and test structures.

in the dark-field image (Figure 1(b)), and also give riseto streaking in electron diffraction (not shown here).In contrast, the nanowires appear free of extendeddefects in TEM.

Figure 1: Dark-field TEM images of GaN nanowire and matrixstructure grown on AlN/Si. (a) Lower magnification image showsnanowires and unwanted matrix layer both growing from AlNbuffer. (b) Higher magnification image shows basal-plane defectsin matrix layer.

Figure 2: Low-temperature CL of GaN nanowire sample. Redcurve: as-grown. Blue curve: nanowires only, removed frommatrix layer. Green curve: matrix layer + nanowire “roots,”with tops of nanowires polished off.

The nanowire structure from Figure 1 wascharacterized by low-temperature cathodoluminescence(CL), as shown in Figure 2. The CL of the nanowiresis dominated by excitons bound to shallow donorimpurities (3.4716 eV peak) while the matrix layer CLis dominated by excitons bound to structural defects(peaks “d1” through “d5”) that may be related to thedefects seen by TEM.

Similarly to the GaN samples, the ZnO samples werefound to contain a highly defective “matrix” layer togetherwith relatively defect-free vertical nanowires, but thematrix layer in the ZnO was found to consist of horizontallygrowing nanowires. The choice of metal catalyst(Ag, Au, or Cu-containing alloy) for VLS growth of theZnO samples was found to have a strong affect on theCL spectra, ascribed to catalyst doping of the ZnO andconcomitant formation of catalyst-related impurity levels.Our characterization results on GaN and ZnO nanowireswere reported at the 2005 Electronic Materials Conference(Santa Barbara, CA, June 22–24).


A. Davydov, A. Motayed (Metallurgy Division,NIST); J. Barker, K. Bertness, N. Sanford (OptoelectronicsDivision, NIST); B. Nikoobakht (Surface andMicroanalysis Science Division, NIST); R.Z. Lei(Intel Corporation); G. Celler, M. Kennard (SOITEC)

TEM structure of one of our first GaN nanowiresamples, grown by MBE on an AlN buffer layer onSi(111), is shown in Figure 1. The sample containsboth nanowires and a rough, faceted “matrix” layer(lower half of Figure 1(a)). Growth of most nanowiresappears to initiate at the AlN buffer, rather than withinthe matrix layer. The matrix layer contains a highdensity of basal-plane defects, which produce striations


47

Nano-Structured Materials for Sensors andUltra-High Density Data Storage

Magnetic sensors play a central role in manyimportant technologies ranging from health careto homeland security. A common need amongthese technologies is greater sensitivity throughnano-structured materials.

In ultra-high density data storage, one of the mostpressing needs is for nano-structured media thatstore data at ever-increasing densities. Improvedmethods for the magnetic isolation of grains inultra-thin films are a key need. We have initiatedresearch programs in both areas.

William F. Egelhoff, Jr.

Over the past decade, NIST’s Magnetic EngineeringResearch Facility (MIRF) has made important and

widely recognized contributions to the thin magnetic filmsused as read heads for hard disk drives. MIRF is one ofthe most versatile facilities in the world for the fabricationand analysis of novel magnetic thin films. This versatilityis illustrated by two new areas of research that haverecently been initiated. One is magnetic sensors and theother is magnetic media. The common link is that bothrequire nano-structured thin films.

thin-film form. Second, some of the bulk sensitivitycan be recovered by nano-layering the magnetic thinfilms with non-magnetic thin films. Third, conventionalthin-films sensor designs contain a design flaw thatallows magnetic irregularities to reduce the potentialsensitivity by over a factor of 100. Fourth, we havefound a way to use nano-structuring of the thin films toreduce these irregularities sharply and achieve a factorof 40 improvement in sensitivity. Fifth, an analysis ofthe physics of the nano-structuring immediately suggeststhat opportunities exist for significant further gains.

In the area of novel magnetic media we have beencollaborating very closely with Seagate. Seagate is theworld’s leading manufacturer of hard-disk drives, and forthe past two years, they have been sending a Ph.D. physicistfrom their research labs to work with us, first on ballisticmagnetoresistance, and then on novel magnetic media.

Figure 1: The Magnetic Engineering Research Facility.

We are now 1.5 years into the Magnetic SensorsCompetence Program. We have evaluated a series ofcomplex magnetic alloys that in bulk form are verysensitive to small magnetic fields but had not previouslybeen studied in thin-film form (e.g., Ni77Fe14Mn5Cu4).Our approach is to carry out the metrology needed tooptimize these materials in thin-film form.

We have made several surprising discoveries.First, these alloys are uniformly less sensitive in

In recent work, we have found a novel method formagnetically decoupling grains in CoPd media. CoPdmultilayers are one of the leading candidates for the nextgeneration of magnetic media. We have found that ifwe deposit an Au film on top of the CoPd and anneal thesample in air, two unexpected phenomena occur as aresult of rapid diffusion of atoms along grain boundaries.One is that Co atoms diffuse to the surface, react withoxygen, and remain at the surface. The other is that Auatoms diffuse into the grain boundaries replacing Co. Thenet effect is that the grain boundaries are demagnetized,and each grain can magnetically switch independently ofits neighbors. This method provides the best magneticisolation of grains yet found.

This work has been reported at several conferencesand industrial workshops.


E.B. Svedberg, D. Weller (Seagate); R.D. McMichael,T.P. Moffat, J. Mallett, A.J. Shapiro, J.E. Bonevich(Metallurgy Division, NIST); D.P. Pappas(Electromagnetics Division, NIST); M.D. Stiles(Physics Lab, NIST)

Figure 2: Grains isolated magnetically by Au diffusing into grainboundaries.


Annealed at 300 °C, 1 hour

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Program Overview

Advanced Manufacturing Processes

The competitiveness of U.S. manufacturers dependssubstantially on their ability to create new product conceptsand to quickly translate such concepts into manufacturedproducts that meet their customers’ increasing expectationsof performance, cost, and reliability. This is equally truefor well-established “commodity” industries, such asautomotive, aerospace, and electronics; for materialssuppliers of aluminum, steel, and polymers; and forrapidly growing industries based on nanotechnologyand biotechnology. In support of these industries,MSEL is developing robust measurement methods,standards, software, and process and materials dataneeded for design, monitoring, and control of newand existing materials and their manufacturing processes.The Advanced Manufacturing Processes Program focuseson the following high-impact areas:

■ Development of combinatorial and high-throughputmethods for developing and characterizing materialsranging from thin films and nanocomposites to microand macroscale materials structures;

■ Automotive industry-targeted R&D for improvedmeasurement methods for sheet metal formingof lightweight metals and for the developmentof hydrogen storage materials needed forhydrogen-powered vehicles;

■ Development of innovative, physics-based processmodeling tools for simulating phase transformationsand deformation during manufacturing and creationof the databases that support such simulations;

■ National traceable standards having a major impacton trade, such as hardness standards for metals andMALDI process standards for polymers; and

■ Development of innovative microfluidic testbedsfor process design and characterization of polymerformulations.

Our research is conducted in close collaborationwith industrial partners, including industrial consortia,and with national standards organizations. Thesecollaborations not only ensure the relevance of ourresearch, but also promote rapid transfer and utilizationof our research by our partners. Three projects fromthe Advanced Manufacturing Methods Program arehighlighted below.

NIST Combinatorial Methods Center (NCMC)

The NCMC develops innovative combinatorial andhigh-throughput (C&HT) measurement techniques andexperimental strategies for accelerating the discoveryand optimization of complex materials and products,such as polymer coatings and films, structural plastics,

fuels, personal care goods, and adhesives. TheseC&HT array and gradient methods enable the rapidacquisition and analysis of physical and chemicaldata from materials libraries, thereby acceleratingmaterials discovery, manufacturing design, andknowledge generation. In 2005, the NCMCConsortium consisted of 19 institutions from industry,government laboratories, and academic groups, whichrepresents a broad cross-section of the chemical andmaterials research sectors. A growing component ofthe NIST NCMC program is focused on acceleratingthe development and understanding of emergingtechnologies, including nanostructured materials,organic electronics, and biomaterials, and, in particular,on the nanometrology needed for C&HT-basedresearch for these technologies.

Forming of Lightweight Materials

Automotive manufacturing is a materials intensiveindustry that involves approximately 10 % of the U.S.workforce. In spite of the use of the most advanced,cost-effective technologies, this globally competitiveindustry has major productivity issues related tomaterials measurements, materials modeling, andprocess design. Chief among these is the difficultyof designing stamping dies for sheet metal forming.An ATP-sponsored workshop (“The Road Ahead,”June 20–22, 2000) identified problems in the productionof working die sets as the main obstacle to reducingthe time between accepting a new design and actualproduction of parts. This is also the largest singlecost (besides labor) in car production. Existing finiteelement models of deformation and the materialsmeasurements and data on which they are based areinadequate to the task of evaluating a die set design:they do not accurately predict the multi-axial hardening,springback, and friction of sheet metal during metalforming processes and, therefore, the stamping diesdesigned using finite element analyses must be modifiedthrough physical prototyping to produce the desiredshapes, particularly for high-strength steels andaluminum alloys. To realize the weight savings andincreased fuel economy enabled by high-strengthsteel and aluminum alloys, a whole new level offormability measurement methods, models, and datais needed for accurate die design, backed by a betterunderstanding of the physics behind metal deformation.The MSEL Metallurgy Division is working with theU.S. automakers and their suppliers to fill these needs.A key component of our program is the uniquemulti-axial deformation measurement facility withwhich local strains in deformed metal sheet can bemeasured in situ. This facility has enabled NISTto take a key role in developing new methods for

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assessing springback, residual stresses, frictionbetween the sheet metal and die during forming, andsurface roughening, and in providing benchmark datafor international round-robin experiments for finiteelement code. New techniques for detecting localdeformation events at surfaces are providing insightsinto the physics of deformation and are leading tophysics-based constitutive equations.

Hardness Standardization:Rockwell, Vickers, and Knoop

Hardness is the primary test measurement used todetermine and specify the mechanical properties ofmetal products and, as such, determines compliancewith customer specifications in the national andinternational marketplace. The MSEL MetallurgyDivision is engaged in developing and maintainingnational traceability for hardness measurements andin assisting U.S. industry in making measurementscompatible with other countries around the world,enabled through our chairing the ASTM InternationalCommittee on Indentation Hardness Testing and headingthe U.S. delegation to the ISO Committee on HardnessTesting of Metals, which oversees the developmentof the organizations’ respective hardness programs.Our specific R&D responsibilities include thestandardization of the national hardness scales,development of primary reference transfer standards,leadership in national and international standards writingorganizations, and interactions and comparisons withU.S. laboratories and the National Metrology Institutesof other countries.

Contact: Frank W. Gayle (Metallurgy Division)

Program Overview

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Mechanisms for Delivery of Thermodynamic and Kinetic Data

Many commercial processes are controlled by thethermodynamic and diffusion properties of thematerial. The ready availability of reliable datais a key component to successful design ofnew materials and manufacturing processes.Thermodynamic and diffusion mobility databasesprovide an efficient method of storing the wealthof these data, and software tools allow the userto efficiently retrieve the needed information.

Ursula R. Kattner and Carelyn E. Campbell

The complexity of thermodynamics and diffusionkinetics prevented their direct application in the

design of complex materials and processes in the past.Graphical representation of multicomponent systems istoo complex, and, because of the enormous number,storage of every single datum is impractical. However,mathematical functions representing thermodynamicand diffusion properties of the phases permit efficientstorage. Since these functions are based on physicalmodels, they further provide the power to extrapolatebinary and ternary systems to higher order systems.Software then allows calculation of the desiredquantities. This approach is called the CALPHADmethodology. Unfortunately, previous software wastailored for expert users and was difficult for theoccasional, less experienced user.

manipulation. Links to a downloadable Mathematicascript for DTA analysis simulation using these outputtables as well as tutorial pages on the interpretationof phase equilibria information are also found onthe Metallurgy Division Phase Diagram web site(www.metallurgy.nist.gov/phase/).


The databases and software developed in this projectare designed to provide users with simple tools toretrieve and disseminate information needed for efficientmaterials and process design. A web site is beingdeveloped for interactive solidification calculations usingthe NIST superalloy and solder thermodynamicdatabases (Figure 1). Results are provided in tabularform and can be used with other software packages,such as Mathematica or spreadsheets, for further

Multicomponent multiphase diffusion couples canbe simulated using NIST thermodynamic and diffusionmobility databases, and experimental and calculatedcomposition profiles can be compared. Figure 2shows the comparison of calculated and experimentalcomposition profiles for a γ + γ´/γ diffusion couple(IN100/René-88). The high fraction of γ´ in theIN100 alloy leads to the observed experimental scatteron the left-hand side. Efforts to incorporate thediffusion in ordered phases such as B2 (NiAl) andγ´ (Ni3Al) are being pursued. Future work will assessthe diffusion mobilities in the Ni-Al-Cr system for theB2 and γ´ phases.

Interactions developed through our “High ThroughputAnalysis of Multicomponent Multiphase Diffusion”workshop series are posted at (www.ctcms.nist.gov).The NIST Diffusion Data Center is being converted intoan electronic searchable form, and a preliminary versionis now available at <winweb.nist.gov/diffusion>.


W.J. Boettinger (Metallurgy Division, NIST);A.R. Roosen (CTCMS, NIST); J.-C. Zhao (GeneralElectric)

Figure 2: Experimental and calculated composition profiles forIN100/René-88 diffusion couple (1150 ºC, 1000 h).

Figure 1: Web site for interactive solidification calculations.

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FiPy: An Adaptable Framework for Phase Fieldand Level Set Modeling

Phase field and level set methods have enjoyedconsiderable success for phase transformationmodeling. However, any but the simplestimplementations of these methods are beyond thecapabilities of otherwise interested researchers.An adaptable software tool is being developed tosupport these scientists.

Jonathan E. Guyer and Daniel Wheeler

The equations that model the evolution of manyphysical, chemical, and biological systems have

a remarkably similar form. Despite the commonmathematical structure of these models and the commonapproaches to solving them, most research codes aredeveloped by individuals for one particular problemand then abandoned. They tend not to be documentedwell enough nor designed well enough to be adapted byother scientists. In fact, many scientists have difficultyadapting their own previous codes and opt, instead, tostart from scratch for each new problem.

Another problem with research codes is thatthey are often implemented with the solution schemesthat result in a functioning code in the shortestamount of time. As a result, little advantage is takenof sophisticated numerical techniques that could allowdramatically faster solutions, over larger physicaldomains, for longer elapsed simulation times.

method of solving PDEs, which is widely employed inthe demanding field of computational fluid dynamics.The goal of the project has been to encapsulate existinglibraries and tools for tasks such as sparse matrixsolutions and data visualization into a framework thatis approachable by materials scientists. At the sametime, every aspect of the tool is open, allowing anyuser to adapt, extend, or improve as they desire.

First released in November 2004, FiPy is already beingused for phase field work by researchers at NIST andelsewhere. Existing codes have been re-implemented inFiPy, making them easier to understand and opening themto a wider battery of solution methods. FiPy has alsoenabled prototyping new problems in a matter of hours,rather than the days or weeks that were previouslyrequired. In addition, FiPy is being applied to newmodels of both cell chemotaxis and drug delivery.

Figure 1: Phase field calculations of anisotropic grain growth.

Figure 2: Level set calculations of “superfill.”

Perhaps the greatest success of the tool has beento allow dissemination of NIST’s Curvature EnhancedAccelerator Coverage (CEAC) model to researchersoutside of NIST. This model of electrochemical “superfill”has successfully explained many aspects of themetallization of microchips, however the FORTRAN-basedlevel set code to implement the model was impracticalto use by anyone other than its author. Since beingre-implemented in FiPy, the code has already been putinto use by both industrial and academic researchers.The FiPy implementation of CEAC was highlighted byJohn Dukovic of Applied Materials in his ElectrochemicalResearch Award Address at the 2004 ElectrochemicalSociety meeting. FiPy can be obtained via the web athttp://www.ctcms.nist.gov/fipy.


J. Warren (Metallurgy Division and CTCMS, NIST);D. Saylor (FDA); W. Losert (University of Maryland);J. Dukovik (Applied Materials); Y. Shacham-Diamand(Tel-Aviv University and Waseda University); D. Lewis(General Electric)

A software framework called FiPy has been jointlydeveloped in the Metallurgy Division and the Centerfor Theoretical and Computational Materials Science(CTCMS) to address this constant reinvention of phasetransformation codes. FiPy is based on the finite volume


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Metrology Tools to Accelerate Industrial Developmentof Solid State Hydrogen Storage Materials

Realization of the “Hydrogen Economy” will requiretechnological advances in hydrogen production,storage, and fuel cell implementation. Hydrogenstorage poses the greatest technical challenge,and solid-state storage of hydrogen in metalhydrides will eventually be required to alleviatethe safety issues associated with on-boardvehicular storage of high pressure or liquefiedhydrogen. The current state of metal hydridestorage technology falls far short of targets forvehicular applications. A suite of versatilemeasurement tools is needed to accelerate thedevelopment of hydrogen storage materials.

Leonid A. Bendersky, Ursula R. Kattner,and Martin L. Green

The hydrogen economy has enormous potential tomake the United States less dependent on foreign

sources of energy, as well as create a healthier globalenvironment. In 2003, the hydrogen-powered“Freedom Car” was put forth as a grand challenge tothe American people, and funded at the level of $1.2 B.Of the three enabling technologies necessary for therealization of this vehicle, i.e., hydrogen production,storage, and fuel cell implementation, hydrogen storageis viewed as the biggest obstacle.

On-board storage of high-pressure or liquefiedhydrogen, the most direct approach, has insurmountablesafety issues. In addition, neither liquid hydrogen(8.4 MJ/L) nor high-pressure (133 MPa) hydrogen(4.4 MJ/L) meet the fuel energy density specificationof 10 MJ/L established for the Freedom Car. Solid-statestorage of hydrogen in metal hydrides is a safer alternativefor automobiles, as well as for ships, aircraft andspacecraft. However, the development of solid-statehydrogen storage materials poses many challenges, andcurrent materials fall far short of the Freedom Car goals.

Major limitations of metal hydride storage areas follows: energy density is presently limited toabout 4 MJ/L; desorption behavior (delivery) is notsufficiently rapid; excessive heat is evolved as a resultof hydrogen adsorption (“filling up”); the fundamentalthermochemistry of hydrides and hydrogen adsorptionand desorption kinetics are a poorly understoodfunction of composition and microstructure; finally,reliability of the hydrides, i.e., fatigue and degradationduring reversible hydrogen cycling, is not known.

The goal of this project is the development of newhigh-throughput measurement methods to study this

extremely important phase transformation in a widevariety of metal and intermetallic-based hydrides,thereby providing tools for industry to develop thesematerials at a greatly accelerated pace.

A multidisciplinary approach is used to addresssome of the major problems associated withsolid-state hydrogen storage: (i) development of IRemission spectroscopy and microcalorimetry-basedhigh-throughput metrologies for measuring hydrogenadsorption and desorption kinetics, as well asthermochemical parameters of metal hydrides; and(ii) development of thermodynamic and kinetic dataunderlying this behavior, to guide future development.

Figure 1: Synthesis of combinatorial continuous compositionalspreads.

During the initial phase of this project, combinatorialfilm libraries of a metal alloy system have been fabricatedin a form of thin film continuous compositional spreads.Initial systems include: Fe2Ti-FeTi2, Ni-Mg, andZr35Ni65–xVx. The synthesis of the compositional spreadis verified by EDS, x-ray diffraction, and cross-sectionalTEM. The construction of the reaction chamber for thehydrogenation and IR measurement experiments has beeninitiated. Special precautions were made in the design toaddress safety issues arising from working with hydrogengas at elevated temperatures and pressures.

For the construction of the thermodynamic database,the available Gibbs energy functions of the alloy systemsand the metal hydride are also being evaluated.


D. Josell (Metallurgy Division, NIST); L.P. Cook(Ceramics Division, NIST); E.J. Heilweil (Physics Lab,NIST); S. Semancik (CSTL, NIST)


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Fundamental Nature of Crack Tips in Glass

Lifetimes of glasses and structural ceramics aredetermined by the size and severity of mechanicalflaws and defects found in their surfaces.Understanding the nature of these flaws and howthey respond to the surrounding chemical andphysical environment is of particular importance forthe prediction of component lifetime. This projecthas as its objectives the quantification of crackgrowth parameters in glasses and ceramics in orderto provide design information to colleagues (NASA,SSG Inc.) wanting to improve the reliability of realcomponents. Thus the project provides crack growthparameters for glasses and ceramics, characterizescracks and crack tips in these materials usingadvanced detection techniques, and developsmethods of assuring structural reliability.

Sheldon M. Wiederhorn

The static fatigue limit in glasses is importantfor predicting the long-term reliability of glass.

The static fatigue limit is the applied stress intensityfactor (load times the square root of crack length)below which cracks will no longer grow. Someglasses (soda-lime-silica glass) have a static fatiguelimit; others (silica) do not. The methodology forassuring structural reliability can depend on which kindof glass is being considered for an application. Hence,it is important to characterize the factors that determinethe effectiveness of this limit in controlling fracture.

Using atomic force microscopy, we characterizedcrack shape and other features that develop at cracktips in glass near the static fatigue limit. Both ofthese characterizations require measurements at thenanometer scale. The techniques developed on thisproject are proving very promising to explore thehigh-stress region at crack tips.

During the past year, we concluded that the fatiguelimit is a consequence of the exchange of alkali ions inthe glass for hydroxyl ions in the external environment.The ion exchange results in a compressive stressaround the crack tip that retards crack motion whenthe load is increased above the fatigue limit. Althoughthe flanks of the crack are corroded, the corrosiondoes not reach the crack tip, which is held closedby the compressive stresses arising from the ionexchange process.

Finally, fracture areas taken from opposite sidesof the fracture surface have been shown to match toan accuracy of 0.3 nm normal to the surface and 5 nm

parallel to the surface. No evidence of cavitation isobserved, which means that the fracture of glass occursby a completely brittle process. This observation iscontrary to mechanisms reported for very brittle bulkmetallic glasses, for which cavity formation precedesthe fracture process in the glass.

Figure 1: A comparison of opposing fracture surfaces ofsoda-lime-silicate glass, AFM scan. The two surfaces arescanned separately. The sections of the surface are placed in thefigure in such a way that the highlights in the two figures match.Note the overlap of the polygons formed by connecting the samehighlight features in each figure. Within experimental scatter, thetwo images are identical.

The difference in behavior between silicate glassesand bulk metallic glasses is probably related to the typeof bond holding the material together. Bonds in silicateglasses are covalent in nature. These are directionaland resistant to shear. By contrast, bonding in metallicmaterials is non directional, which makes themsusceptible to displacements by shear stresses, hencethe ease of cavity formation at the tips of cracks inbulk metallic glasses.

PublicationsJean-Pierre Guin and Sheldon M. Wiederhorn,

“Fracture of Silicate Glasses: Ductile or Brittle?”Phys. Rev. Let. 92 [21] 215502 (2004).

Jean-Pierre Guin, Sheldon M. Wiederhorn, andTheo Fett, “Crack-Tip Structure in Soda-Lime-SilicateGlass: Experimental Observations,” J. Am. Ceram. Soc.88 [3] 652–659 (2005).


Prof. Tanguy Rouxel (University of Rennes, France);Prof. Theo Fett (Forschungszentrum, Karlsruhe,Germany)


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Hardness Standardization: Rockwell, Vickers, Knoop

Hardness is the primary test measurement used todetermine and specify the mechanical propertiesof metal products. The Metallurgy Division isengaged in all levels of standards activitiesto assist U.S. industry in making hardnessmeasurements compatible with other countriesaround the world. These activities include thestandardization of the national hardness scales,development of primary reference transferstandards, leadership in national and internationalstandards writing organizations, and interactionsand comparisons with U.S. laboratories and theNational Metrology Institutes of other countries.

Carlos Beauchamp and Sam Low

At the international level, the Metallurgy Division is leading the Working Group on Hardness (WGH)

under the International Committee for Weights andMeasures (CIPM), with a goal to standardize hardnessmeasurements worldwide. As Secretary of the WGH,we have led an effort this year to better define theRockwell hardness test procedure used by NationalMetrology Institutes (NMIs). The new definitionis awaiting approval by the CIPM. Other activitiesinclude chairing the ASTM-International Committeeon Indentation Hardness Testing and heading theU.S. delegation to the ISO Committee on HardnessTesting of Metals, which oversees the developmentof the organizations’ respective hardness programs.

In conjunction with ASTM International and IMEKO,the Metallurgy Division organized the HARDMEKO2004 Conference, an international conference forscientists and specialists involved in the measurementof hardness (see Figure 1). The conference was verysuccessful, bringing together an international audienceto hear over 25 technical presentations by expertsfrom 11 countries.

Our primary task at the national level is tostandardize the U.S. national hardness scales andto provide a means of transferring these scale valuesto industry. Currently, we are producing test blockStandard Reference Materials® (SRMs) for the Rockwell,Vickers, and Knoop hardness scales, as well as developingnew reference standards. A new microindentationstandardizing machine has been acquired and is currentlyundergoing testing and uncertainty analysis. Vickersand Knoop microindentation SRMs are available athardness levels of 125, 600, and 760 kgf/mm2. Additionalhardness levels are being investigated ranging from 900to 1,400 kgf/mm2. These blocks will significantly extendthe range of microindentation SRMs offered by NIST.

In addition to newly introduced Standard ReferenceMaterials® (SRMs) for the Rockwell B scale and threeSRM Rockwell C scale blocks currently available,we are in the process of producing new SRMs for theHR15 N and HR30 N Rockwell scales. The N scalesare used primarily for measuring thinner gage materialor case depth. Work is also continuing to producea new Rockwell hardness diamond indenter SRM.A joint project with Gilmore Diamond Tools hasrecently demonstrated that diamond indenters canbe repeatedly produced with the correct shape andadhere to the very tight calibration grade tolerances.

Other activities at the national level occurring thisyear included the assessment of commercial secondaryhardness calibration laboratories for the NIST NationalVoluntary Laboratory Accreditation Program (NVLAP)and the development of indentation Finite ElementAnalysis models used to analyze effects of differentindenter materials for all Rockwell hardness scalesin support of proposed revisions to internationaltest standards.


J. Fink, D. Kelley, L. Ma, H. Gates (MetallurgyDivision, NIST); J. Song (MEL, NIST); W. Liggett, Jr.,N. Zhang (ITL, NIST); S. Doty, B. Belzer, D. Faison(NVLAP, NIST); W. Stiefel (TS, NIST); M. Mihalec(Gilmore Diamond Tools, Providence, RI)


Figure 1:HARDMEKO2004 Conferenceorganized byNIST with ASTMand IMEKO.

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NIST Combinatorial Methods CenterPioneer and Partner in Accelerated Materials Research

Combinatorial and high-throughput (C&HT)methods hold great potential for making materialsresearch more productive, more thorough, and lesswasteful. However, significant barriers preventthe widespread adoption of these revolutionarytechniques. Through creative, cost-effectivemeasurement solutions, and with an eye towardsfruitful collaboration, the NIST CombinatorialMethods Center (NCMC) strives to ease theacquisition of C&HT techniques by the materialsresearch community.

Michael J. Fasolka

The NIST Combinatorial Methods Center is now inits fourth year of service to industry, government

laboratories, and academic groups interested in acquiringC&HT research capabilities for materials research.In 2005, the NCMC consortium included 19 memberinstitutions (see table), which represent a broad cross-section of the chemical and materials research sectors.

The NCMC fosters wide-spread adaptation ofC&HT technologies through two complementary efforts.The first is an extensive research program, centered inthe Multivariant Measurement Methods Group of the NISTPolymers Division. Our research provides innovativemeasurement solutions that serve to accelerate thediscovery and optimization of complex products suchas polymer coatings and films, structural plastics, fuels,personal care goods and adhesives. Moreover, a growingcomponent of our program aims to speed the developmentand understanding of emerging technologies includingnanostructured materials, nanometrology, organicelectronics, and biomaterials. Several of these researchdirections are highlighted elsewhere in this report,as identified by the NCMC symbol (see top right).

emerging industrial needs for C&HT measurements ofmaterials systems such as biomaterials and organicelectronics. Accordingly, NCMC-6 included plenarysymposia outlining engineering issues in these advancedsystems, sessions illustrating NIST capabilities in theseareas, and a panel discussion aimed at determining newmeasurements that should be pursued.

In addition, on May 2–3 2005, we hosted NCMC-7:Adhesion and Mechanical Properties II. Central tothis event was a symposium presenting new NCMCmethods for the development and optimization ofadhesives. Highlights included a new gradient peel-testfor the HT assessment of backed adhesives (e.g., tapes),and approaches for the rapid screening of epoxyformulations. A variation of our buckling technique tomeasure modulus, useful for evaluating soft systemssuch as polymer gels, was also described.


“As a member of NCMC, I believe that Procter & Gamble hasaccess to a high-performance work group with expertise in highthroughput and combinatorial techniques. The conferenceshave been particularly valuable for networking with NISTscientists as well as other industrial members of NCMC.”

— M. McDonald (Procter and Gamble)

“The coatings industry has been traditionally perceived to reactslowly to implementing newer and quantifiable measurementtechniques for characterizing structure–property relationshipsin paints and films. The [NCMC] has pioneered elegantapproaches that can significantly reduce experimental time[for] testing coating formulation performance.”

— D. Bhattacharya (Eastman Chemical)

In conjunction with its research program, theNCMC conducts an outreach effort to disseminateNIST-developed C&HT methods, assess industrymeasurement needs, and form a community to advancethe field. A key component of NCMC outreach is ourseries of member workshops. On November 8–9 2004,we hosted our 6th workshop, NCMC-6: AdvancedMaterials Forum. The goal of NCMC-6 was to gauge

“The combinatorial methods program at NIST makes the NCMCcritical to any company’s development of high-throughputworkflows. The import of this effort to industry is clearlyindicated by your center’s number of industrial members.”

— J. Dias (ExxonMobil)

Moreover, this year the NCMC continued communityforming activities by organizing several high-profilesessions dedicated to C&HT research at nationalconferences, including meetings of the American PhysicalSociety, the American Chemical Society, the MaterialsResearch Society, and the Adhesion Society.


C.M. Stafford, P.M. McGuiggan, K.L. Beers,A. Karim, E.J. Amis (Polymers Division, NIST)

NCMC Members (*New in FY2005):Hysitron International

IntelICI/National Starch & Chemicals

L’Oreal*PPG Industries

Procter & GambleRhodia

Univ. of Southern MississippiVeeco/Digital Instruments

Air Force Research LabAir Products & Chemicals Arkema Inc.BASFBayer PolymersBPDow Chemical CompanyEastman ChemicalExxonMobil ResearchHoneywell International

For more information on the NIST CombinatorialMethods Center, please visit http://www.nist.gov/combi.

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Polymer Formulations:Materials Processing and Characterization on a Chip

We develop high-throughput methods toadvance polymer formulations science throughthe fabrication of microscale instrumentationfor measuring physical properties of complexmixtures. Adaptation of microfluidic technologyto polymer fluid processing and measurementsprovides an inexpensive, versatile alternativeto the existing paradigm of combinatorialmethods. We have built a platform of polymerformulations-related functions based onmodified microfluidic device fabricationmethods established in our facilities.

Kathryn L. Beers

Microfluidic device fabrication methods previouslydeveloped in the Polymers Divison enable

combinatorial fabrication and characterization ofpolymer libraries. Recent accomplishments includethe integration of multiple functions on a chip for theformulation, mixing, processing, and characterizationof polymer particles for evaluation of dental compositematerials and the fabrication of gradient polymerbrush surfaces for measuring the behavior ofstimuli-responsive surfaces.

with shrinkage. The first publication on this work(Langmuir 21, 3629, 2005) was recently profiled inthe Research Highlights of Lab on a Chip.


Figure 1: (a) A thiolene microfluidic device used to create,mix, polymerize and characterize monomer droplets.(b) Optical images of monomer droplets and polymer particles.(c) Raman spectra of monomer (red) and polymer (black).

Figure 2: (a) Schematic of amphiphilic block copolymer brushgradients representing the proposed conformation shift in responseto good and poor solvents for the top block layer. (b) Water contactangle measurements as a function of top block thickness on threegradients of top block thickness on uniform bottom blocks of threedifferent lengths (blue – 4 nm, red – 10 nm, green – 14 nm) in good(open) and poor (filled) solvents for the top block.

Building on our ability to form organic-phasedroplets in thiolene-based microfluidic devices(Figure 1a), we can establish libraries of dropletswith systematic composition variations. The dropletsare subject to various processes such as mixing andphotopolymerization on the chip. Raman spectroscopyon the chip (Figure 1c) and optical imaging (Figure 1b)are used to measure and correlate properties such asmonomer composition and conversion to polymer

Microchannel confined surface initiated polymerizationwas used to prepare surfaces with gradients of molecularweight and block and statistical copolymer composition.The block copolymer surfaces were studied for their abilityto reorganize at the air/solution interface dependingon the nature of the polymer and solvent (Figure 2a).The ability of the surface layer to rearrange was shownto depend on the thickness of both the top and bottomblock layers (Figure 2b).

The capabilities for controlled radical polymerizationon a chip (CRP Chip) were also extended this year toinclude block copolymer synthesis and higher-ordercontrol of solution compositions. A three-input devicewas developed, enabling stoichiometric variations inreactions and faster measurement of kinetic behavior(Macromol. Rapid Commun. 26, 1037, 2005).


Z.T. Cygan, C. Xu, S. Barnes, T. Wu, A.J. Bur,J.T. Cabral, S.D. Hudson, A.I. Norman, J. Pathak,W. Zhang, M.J. Fasolka, E.J. Amis (Polymers Division,NIST)

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Matrix-assisted laser desorption ionizationtime-of-flight mass spectrometry (MALDI-TOF-MS)is being developed as a method for absolutemolecular mass distribution measurement ofsynthetic polymers. This means determining acomprehensive uncertainty budget for a complexmeasurement technique that must include bothType A (“random”) and Type B (“systematic”)uncertainties.

William E. Wallace

In mass spectrometry, methods exist to calibrate the mass axis with high precision and accuracy.

In contrast, the ion-intensity axis is extremely difficultto calibrate. This leads to large uncertainties inquantifying the content of mixtures. This is even truewhen the mixture is composed solely of different massoligomers of the same chemical species as in the caseof polymer polydispersity. The aim of this project isto calibrate the ion intensity axis. This task hasbeen divided into three parts: sample preparation/ionproduction, instrument optimization/ion separation,and data analysis/peak integration. Each part isnecessary but on its own is not sufficient toguarantee quantitation.

We study the MALDI ion-creation processphenomenologically using combinatorial libraries.The ratio of analyte to matrix is varied along a linearpath laid down by nebulizing a continuously varyingmixture of two solutions, one analyte+ matrix+ saltand the other matrix+ salt. In our case, the analyte isa mixture of two polymers having different end groupsand closely matched molecular mass distributions.The figure on this page shows such a librarywhere the blue arrows indicate a linearly changinganalyte:matrix ratio.

To this, we add stochastic-gradient numericaloptimization to adjust the instrument parameters ateach composition to give a mass spectrum that bestmatches the known polymerA:polymerB ratio in theanalyte. Instrument parameters optimized includelaser energy, ion extraction voltage, ion lensvoltage, extraction delay time, and detector voltage.Stochastic methods must be used because the datahas some measure of Type A random uncertainty(i.e., “noise”) to it; therefore, exact values of thefunction to be optimized are not available.

Finally, to this we add our MassSpectator softwarewhich ensures unbiased, logically-consistent integration

of the peaks in the (noisy) mass spectrum. A softwarescript has been written around MassSpectator thatautomatically identifies oligomeric series in the massspectrum and calculates the total amount and themolecular mass moments for each series identified.


Quantitative Polymer Mass Spectrometry

An early embodiment of our approach can befound in ASTM Standard Test Method D7134, thefirst MALDI-TOF-MS method endorsed by ASTM.Working through the Versailles Project on AdvancedMaterials and Standards (VAMAS), and in closecooperation with our industry and national metrologyinstitute (NMI) colleagues from around the world, aninterlaboratory comparison was initiated to understandthe nexus of critical measurement factors whenperforming quantitative polymer mass spectrometry.From the knowledge gained by the interlaboratorycomparison, D7134 was written with particularattention paid toward controlling the critical factors.

The MALDI project maintains a vigorous,worldwide outreach program including an onlinepolymer MALDI recipes catalog, annual polymer MSworkshops, and the availability of our MassSpectatorsoftware on the web. For more information onany of these topics please visit our web page at:www.nist.gov/maldi.


W.R. Blair, K.M. Flynn, C.M. Guttman (PolymersDivision, NIST); A.J. Kearsley (Mathematical &Computational Sciences Division, NIST)

58

Standard Tests and Data for Sheet Metal Formability

rolling directions of the sheet. These data will beused by industry to eliminate several assumptions thatextrapolate estimated biaxial flow behavior based ona series of uniaxial tensile tests. This should lead tomore accurate designs and cost savings.

This year, NIST was asked to generate materialsproperty data for simulations of prototype parts as partof the NUMISHEET 2005 conference. In addition,the NUMISHEET 2005 benchmark tests are addinga new level of complexity by requiring modelers topredict stresses at specific sample positions duringa benchmark forming process. NIST provided thecorresponding measurements using our uniquecapabilities described above. This work alsowill be the subject of a plenary presentation atNUMISHEET 2005.

In order to meet goals for fuel efficiency, theU.S. automotive industry is moving to lighter,high-strength materials for auto bodies. NIST hassurveyed the industry and found that accuratematerial properties and methods for die designersto incorporate them into finite element models ofsheet-metal forming dies, is a critical need for theU.S. auto industry. This project seeks to developnew standard tests and metrology to accuratelydetermine sheet metal mechanical response underforming conditions.

Timothy J. Foecke and Mark Iadicola

Successful introduction of new high-performance alloys into automotive production requires

comprehensive data on alloy behavior under realisticforming conditions. Existing tests are inadequate.This project is developing two sheet metal formabilitytests, along with associated metrology, that can bestandardized and used by industry.

Work on the first formability test, the springbackcup, was undertaken at the direct request of industrialrepresentatives in the United States Council forAutomotive Research (USCAR). Springback is theshape change that occurs during elastic relaxation ofthe residual stresses that develop during the stampingprocess. Accurate springback predictions wouldgreatly decrease the cost and number of iterationsrequired for producing stamping dies.

The proposed test for springback consists ofsplitting open a ring cut from the sidewall of a deepdrawn cup. The springback cup test was submittedto ASTM, and a subgroup has been formed to seek itsstandardization. In addition, an alternative springbackstandard based on stretch flanging over a cylindricalmandrel, developed by Kuwabara of Japan, has beensubmitted to ISO, with NIST staff developing theASTM commentary on shortcomings of the standardgeometry and procedures.

The second test method under development usesunique X-ray system that allows the direct, in situmeasurement of stress in a given direction while thesample is under multiaxial load. This year we havemade significant progress in mapping the multiaxialstress-strain surface for DQSK steel, an industryworkhorse alloy, as well as high-strength steels suchas HSLA and DP600. As with the aluminum alloysstudied last year, both the flow stress and the hardeningexponent were found to differ in the transverse and


Figure 1: NUMISHEET benchmark sample loaded for planestrain deformation.

Plans for the upcoming year involve completingmeasurement of the multiaxial stress–strain surfacesfor several alloys. This project will determine how theflow surface evolves with different types and amountsof multiaxial prestrain in a collaboration with modelersat GM. In addition, studies to date show that theinfluence of plastic strain on the elastic modulus ofthe material appears to be significant, and we intend toquantify the affect of plastic strain state and magnitudeon the effective x-ray elastic constants of aluminumand alloy steel sheet.


R.F. Fields; T. Gnaupel–Herold (NIST Center forNeutron Research); M. Shi (USS); E. Chu (ALCOA);C. Xia (Ford); T. Stoughton, M. Wenner, C.T. Wang(GM); J. Siekirk (DaimlerChrysler)

59

Existing data, measurements methods, and basicunderstanding of metallurgical factors thatinfluence friction, tearing, and surface finishduring sheet metal fabrication are insufficient tomeet the predictive modeling requirements of theautomotive industry. This project addresses themeasurement and data needs through evaluationof the microstructural origins of the distribution ofslip, surface roughening, and strain localizationduring plastic straining. These studies focus onthe relationships between initial materialcharacteristics and deformation behavior ofaluminum and iron base sheet. New protocolshave resulted that incorporate high-resolutionconfocal microscopy imaging to assess theroughening character over an entire field of view.

Mark R. Stoudt and Stephen W. Banovic

Lightweight materials, such as high-strength steels and aluminum alloys, are designed to reduce vehicle

weight and increase fuel economy. The widespread useof these new alloys in automotive components is limited,however, by insufficient property data and constitutivelaws required for accurate numeric predictions of themechanical behavior and friction during metal formingprocesses. One approach to meeting these critical dataneeds is a careful examination of the structure propertyrelationships that directly influence formability.

The inability to reliably predict the deformed surfacemorphology with numeric methods raises serious questionsas to how well the analytical tools employed to interpretroughness data actually represent the real surface.The underlying principles used to interpret surfaceroughness measurements were examined to ascertain themagnitude and source of any inconsistencies. The studyassessed the variability within the surface roughnessdata that occurs over a surface by acquiring multipleroughness profiles from regularly spaced locations onan image (Figure 1) and establishing the actual form ofthe data with a set of mathematically rigorous protocols.

Most roughness analyses tacitly assume that ameasured profile is completely described by idealGaussian statistics. However, the deviations observedin the skew and kurtosis data in this study revealedthat roughness profiles taken from plastically deformedsurfaces do not exhibit an ideal Gaussian form.The significance of this conclusion is twofold:first, non-Gaussian behavior means the roughness isproduced by a small number of active mechanisms.This agrees with the literature in that deformation-inducedsurface roughness is primarily crystallographic slip

Microstructural Origins of Surface Rougheningand Strain Localizations

and near grain boundary deformation. Second, thesedeviations from ideal Gaussian behavior provide directevidence that the roughening behavior of a polycrystallinematerial cannot be accurately characterized with anyparameter that presumes an ideal Gaussian form(i.e., mean(Ra) or rms(Rq)). These parameters alsocompress the complex surface information within a profileinto a singular expression that can be quite coarse withrespect to the length scale of the surface features.


Figure 1: Scanning laser confocal image of the surface producedby 12 % uniaxial strain in AA6022. The dashed lines indicate thegeneral locations where surface roughness data were acquired.

Since surface roughness evaluations are highlydependent upon the statistical methods used in theanalysis, small deviations from the ideal condition, suchas those produced by plastic deformation, are likely tohave pronounced influences on the accuracy of theanalytical methods used to interpret the roughness data.Hence, the current practice of extrapolating averaged,compressed values into representations of an entiresurface in a particular strain condition introducessubstantial measurement error into numeric predictionsof behavior. Expressions are being developed to moreaccurately represent the stochastic nature of variationsin surface roughness.


J.B. Hubbard, R.E. Ricker, L.E. Levine (MetallurgyDivision, NIST); S.A. Janet (ITL, NIST); R. Reno,E. Moore (UMBC); J.T. Liu (ALCOA)

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Underlying Processes of Plastic Deformation in Metal Alloys

A substantial increase in the use of aluminum alloysand high-strength steels in automobiles would greatlyincrease fuel efficiency. The primary reason whythis has not yet occurred is a lack of accuratedeformation models for use in designing the stampingdies. This project is developing a physics-basedmodel of plastic deformation using a combinationof statistical physics approaches, atomistic modeling,and advanced measurement techniques.

Lyle E. Levine

Plastic deformation of metals (as in cold rolling,stamping, drawing, and metal fatigue) is a topic

of great importance to industries worldwide, andimprovements in the basic technology would have asignificant impact on our economy. Unfortunately,existing constitutive equations cannot accurately predictthe material behavior, and many tryout and redesignsteps are required. Another related difficulty is inthe design of new alloys with improved formabilitycharacteristics. Currently, alloy design is doneempirically with little understanding of how thevarious constituents affect the mechanical properties.

In the current work, we have developed a theoreticalframework called the segment length distribution (SLD)model for fcc single crystals that describes howmacroscopic deformation arises from the statisticalbehavior of large numbers of dislocations. Although workon the SLD model is continuing, the primary emphasisover the past year has been on validation testing withWashington State University and new experimentalmeasurements of the distribution of stresses withindislocation cells (with the University of Southern Californiaand Oak Ridge National Laboratory). These stressescould affect the assumptions used in the SLD model.

Single crystal aluminum tensile specimens arebeing produced at NIST for the validation tests. Thesespecimens are then strained, in situ, in ultra-high vacuum.A pulsed ultra-violet laser produces photostimulatedelectron (PSE) emission from fresh (unoxidized) Al inthe slip lines/bands, and the electrons are collected byan electron multiplier. These time-resolved studies allowus to measure the time dependence of slip line/bandproduction and compare these results to SLD modelpredictions. The SLD model predicts intermittent slipevents under some conditions. Figure 1 shows preliminaryPSE results that are consistent with these predictions.

Figure 1: PSE data from Al single crystals.

Figure 2: 117 reflection from deformed Cu crystal.

Preliminary measurements of residual stresses inplastically deformed Cu single crystals were carriedout using X-ray micro-beams at the Advanced PhotonSource, Argonne National Laboratory. Spatial resolution(in all three dimensions) is approximately 0.5 µm.Large fluctuations in elastic strain (and thus stress)were observed over length scales consistent withdislocation cells. Figure 2 shows an integrated energyscan of a 117 reflection from a Cu single crystaldeformed 24 % in compression. The localized anddiffuse features originate primarily from dislocationcells and cell walls, respectively.

Finally, NIST researchers served on the executivecommittee of Dislocations 2004, and were co-organizersof Fall 2004 MRS and Plasticity 2005 symposia.


F. Tavazza (Metallurgy Division, NIST);A. Chaka (Physical and Chemical Properties Division);T. Dickinson, S. Langford, M. Cai (Washington StateUniversity); M. Delos-Reyes, Z. Gao, M. Kassner(University of Southern California); B. Larson,W. Yang (Oak Ridge National Laboratory)


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Evaluation of Friction Behavior During Metal Forming

Unpredictable friction resulting frominhomogeneous surface deformation is a significantobstacle to the widespread introduction of newhigh-strength alloys in the automotive industry.Metal-forming computer models still rely heavily onempirical friction data. Most existing approachesare unable to address the strong influences thatvariations in metallurgical condition have on thedynamic material properties and on the evolutionof surface roughness. This project addresses theneed for improved friction measurements, data, andmodels, which will allow the auto industry to improvedie design and processes for forming lightweight,high-strength sheet metal alloys.

Mark R. Stoudt

Many new alloys intended to decrease automobileweight are sensitive to variations in processing

conditions. This variability causes inconsistencies inpredicted friction behavior that exacerbate the formingdifficulties. Traditional measurements normally focus onfriction mechanics and do not account for the stronginfluences that dynamic loading and variations inmetallurgical conditions have on the material properties.Hence, the friction values selected for a finite elementanalysis (FEA) simulation may not fully reflect the actualmetal behavior under those particular conditions. Sinceone measurement cannot provide all essential data, newapproaches are needed that: (a) evaluate both static anddynamic properties, and (b) improve the understandingof the relationships between friction and microstructuralvariations that affect properties during metal forming.

A single-pull measurement protocol (shownschematically in Figure 1) that produces friction dataunder a wide range of carefully controlled loading andstrain conditions to help meet this critical need is underdevelopment. The principal advantage of this techniqueis that it enables direct assessment of the influencesof metallurgical variables (i.e., grain size, orientationeffects, strengthening mechanisms, slip homogeneity)as well as microstructural changes that are producedduring deformation. This new information is anticipatedto guide the development of improved numeric modelsthat predict the final shape of formed parts.

Figure 1: Schematic diagram of the prototype friction apparatus.

The suitability of this approach was establishedthrough a series of friction experiments conductedon hot-dipped draw quality semi-killed (DQSK) steel.The data in Figure 2 demonstrate that the prototypecan easily distinguish the transition from the static tothe sliding state and that the magnitude of the frictioncoefficient can be determined in real time at any pointduring the test. In addition, the measurement sensitivityof the apparatus is such that the quality of the resultingdata is amenable to detailed statistical analysis.

Results to date indicate that the measurementprotocol is appropriate for further development.A matrix of experiments is planned to further evaluatethe influences of initial surface roughness and asperitydistribution, strain rates and surface lubricants.


S.P. Mates, J.B. Hubbard, D.J. Pitchure, R.E. Ricker,L.E. Levine (Metallurgy Division, NIST); G.B. Dalton,(TribSys, Inc.); D.E. Green (University of Windsor)

Figure 2: Variation in friction coefficient as a function of time forlubricated DQSK steel under a 1250 N indentation force.


62

Biomaterials

Rapid development of medical technologiesdepends on the availability of adequate methods tocharacterize, standardize, control, and mass producethem. To realize this goal, a measurement infrastructureis needed to bridge the gap between the exponentiallyincreasing basic biomedical knowledge and clinicalapplications. The MSEL Biomaterials Program is acollaborative effort creating a new generation ofperformance standards and predictive tools targetingthe metrology chain for biomedical research.

Today, all areas of materials science confront realsystems and processes. In the biomaterials arena,we can no longer advance science by simply studyingideal model systems. We must comprehend complexrealistic systems in terms of their structure, function,and dynamics over the size range from nanometers tomillimeters. MSEL is uniquely positioned to make amajor contribution to the development of measurementinfrastructure through three focus areas: SystemsBiology, Bioimaging, and Nanobiosensing.

Systems BiologyMSEL research in systems biology focuses on

quantifying relationships of systems at the cell, tissue,and organ level. To meet this need, we are developinglibraries of reference materials, high-throughputtechniques for screening libraries, and informaticsapproaches for data analysis and interpretation.Physicochemical and biochemical components areorganized using patterning, phase separating, andself-assembling processes. Physicochemicalcomponents of interest include modulus and surfacetopography; biochemical components of interestinclude peptide moieties that interact specificallywith cell receptors.

Gradient libraries of tyrosine derivatizedpolycarbonate blends and fibronectin/poly(hydroethyl-methacrylate) gradients were developed as referencematerials for biomaterial research, such that cellresponses included changes in geometry, distribution,and proliferation, to assess intercellular communicationamong osteoblast and fibroblast cells. Complementingthese surface studies, we are developing metrologiesto establish the relationship between 3D scaffoldmorphology (i.e., porosity and permeability) andcell response. Studies focused on identifying therelationship between applied macroscopic stressesand local stresses at the cellular level is also underway,which will provide valuable input into developmentof finite-element models.

Experiments on the mechanical stimulationof tissues and tissue engineered constructs wereconducted to understand the role of metrologyin diagnostic testing of healthy or disease states.Stress–strain relationships were defined for vascularsmooth muscle cells and bovine cardiac tissues.Specialized bioreactors coupled to ultrasound andinfra-red spectroscopy were successful in differentiatingresponse among the systems. We have demonstratedthat the structure–property relations in healthy tissueof pulmonary arteries, and in tissue that has remodeledin response to the onset of disease, can be assessedusing mechanical testing, quantitative ultrasoniccharacterization, and histology.

BioimagingAdvances were made in developing and optimizing

physical methods and informatics tools to enhancebioimaging and visualization technologies at multiplelength scales. With the reduction of backgroundnoise, images were obtained using broadband coherentanti-stokes Raman scattering microscopy with a 10-foldincrease in signal, and proteins on the surface of polymerblends were differentiated. Optical techniques like OCMand CFM, with spatial resolutions of ≈1 µm, wereemployed to image dynamic cell culture experimentsin-situ in a bioreactor. Other advances in computationalmodeling of single cell forces and cell populations werecarried out to predict normal ossification patterns andcartilage formation. By combining information fromdifferent techniques on the same sample and visualizingstructure using interactive, immersive visualizationtechniques, scientists will gain new insights into thephysics and materials science of complex systems.

NanobiosensingResearch in this focus area concentrates on the

development of techniques to measure and manipulatebiological atoms, molecules, and macromolecules atthe nanoscale level (1–100 nm). Mechanical toolsincluding an optical trap and bioMEMS devices thatcan be integrated with currently used biologicaltechniques for evaluating and measuring cellularresponse (i.e., gene expression, cell morphology,area of adhesion) were developed. Additional studiesfocus on identifying mechanical forces that indicatethe onset of osteogenesis and angiogenesis.

Contact: Lori A. Henderson (Polymers Division)

Program Overview

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Combinatorial Methods for Rapid Characterizationof Cell-Surface Interactions

The increasingly complex nature of functionalbiomaterials demands a multidisciplinaryapproach to identify and develop strategiesto both characterize and control cell-materialinteractions. A robust framework outlining theinteractions governing biomaterial performancedoes not exist but is desperately needed. Thisproject provides the basis for this frameworkby focusing on fabrication of single andmulti-variable continuous combinatorial librariesto rapidly identify compositions and physicalproperties exhibiting favorable cell-materialinteractions.

Matthew L. Becker and Lori A. Henderson

Developmental biology and tissue engineering areavenues of research that must be fully integrated

to realize the opportunities in regenerative medicine.For example, while the interactions between cell andextracellular matrix have been studied extensively, muchless is understood regarding the influence of syntheticmaterials. There is little doubt that having good control ofsurface morphology as well as advanced high-throughput(HT) metrologies for analyzing cell-surface interactionsare needed for biological interpretations, and whilechemical and topographical manipulations of surfaceshave been established, HT methods to evaluatebiological responses to these manipulations have not.For these reasons, we are developing metrologies andHT platforms to rapidly analyze physicochemical,mechanical, and material properties of biomaterials.We provide examples of two of our sample fabricationmethods, distinct from traditional self-assembledmonolayer approaches, that are being used to design,manipulate, and quantify cell-surface interactions.

Two functional polymer surfaces, phase separatedtyrosine-derived polycarbonate blends (DTR-PC) andconformational-based poly(2-hydroxyethyl methacrylate)brushes [poly(HEMA)], were analyzed using combinatorialmethodologies. The DTR-PC films, consisting ofhomopolymer and discrete composition blends oftyrosine-derived polycarbonates, were shown to havecompositionally dependent gene expression profiles withthe blends differing significantly from the respectivehomopolymers. Figure 1 illustrates the effect that polymerblending has on cell spreading; the extension and distortionof the lamellapodia increase and the cells appear to spreadless in the blend samples with increasing DTO content.The surface properties from these discrete films will beused to establish correlations and limitations for comparingmeasurements from discrete samples and single andmulti-variable continuous gradient substrates.

Figure 1: AFM micrographs of the tyrosine-derived polycarbonatehomopolymers and discrete blends show compositionally dependentphase separation, which is reflected in the immuno-fluorescentstaining for actin (red, cell spreading) and vinculin (green, focaladhesion contacts) on MC3T3-E1 osteoblasts.

Figure 2: Schematic representation of the poly(HEMA)-FNgradient and Fibroblast cell distribution.

Poly(HEMA) gradients were prepared to studymolecular interactions and cell conformation onfibronectin (FN) coated poly(HEMA) by combining“controlled” free radical polymerization with gradientpreparation technology. This gradient covers“mushroom” to “brush” regimes in order to determinehow grafting density influences protein adsorption andcellular response as shown in Figure 2. The numberof cells, their shape, and size were thus correlated tothe density of fibronectin across the gradient.

In summary, the tools developed in this programwill enable the design of material libraries to be usedto probe the behaviors of cells.


N.D. Gallant, L.O. Bailey, C. Simon, Jr., T.W. Kee,Y. Mei, J.S. Stephens, E.J. Amis (Polymers Division,NIST); K. Langenbach, J.T. Elliot (BiotechnologyDivision, NIST); J. Kohn, A. Rege, J. Schutt (RutgersUniversity & The New Jersey Center for Biomaterials)

Biomaterials

64

Cellular Level Measurements

Another tool uses Bio-MEMS for cell pulling andadhesion. Both adhesion and the mechanical responseof a cell to varying mechanical environments arefundamental to understanding cell motility andnumerous disease mechanisms. A device has beendesigned and built that has a transparent platform onwhich a single cell can adhere. The focal adhesionsof the cell can be viewed using reflection interferencemicroscopy or appropriate staining. The platform issplit so that the cell can be strained from one side andforces measured on the other by way of thin cantileverbeams (see Figure 1). Image analysis can yield strainand also the cross-sectional size of the cell so thatstress can be determined using the force information.Therefore, force- or stress-strain response of a singlecell can be done in addition to force as a function ofadhesion area. The device and instrumentation canalso be operated in a cyclic mode, which can be usedto determine the change in mechanical response ofthe cell as a function of cyclic fatigue. The designof this device and results on vascular smooth musclecells will be presented at the Biomedical EngineeringSociety Annual Fall Meeting in Baltimore, Marylandin September.

Another tool under development is a Bio-MEMSdevice for quartz-crystal microbalance (QCM)-typemeasurements. The QCM is used extensively in themedical research field for characterizing antibodysystems. It is a macroscale device with high sensitivitydue to its oscillating nature. We believe that aBio-MEMS device that works similarly could yield athousand-fold increase in sensitivity and have as wideapplication as the QCM. We have made measurementson a model antibody system as a baseline and havedesigned and built a Bio-MEMS device that mimicsthe QCM. We have developed a model of the deviceresponse in order to optimize future designs forparticular applications. A manuscript on the devicedesign and model has been written for the Journal ofApplied Physics. We are pursuing simple methodsfor electrical measurement of the change in oscillatorresponse, which is the heart of the QCM measurementtechnique.


V.M. Aponte, E.S. Drexler, D.S. Finch, D. Lauria,C.N. McCowan, H. Panchawaugh, R.A.L. Rorrer,D.B. Serrell, R.P. Vinci (Materials Reliability Division,NIST)

Techniques and tools that facilitate the exposureof single cells (and arrays) to controlledmechanical environments and quantificationof mechanical forces, and at the same time allowfor the characterization of other biologicalphenomena, are needed for the study of tissuesand cells. The development and evaluation ofone of these tools, a Bio-MEMS cell puller,is the focus of this year’s effort.

Andrew J. Slifka

Research on the mechanical response of biological materials at the cellular and sub-cellular levels is

being done with the development of a number of tools.Optical trapping for cellular mechanics and small-forcematerials science is one. We use an optical trap witha scanned laser to trap multiple dielectric spheres.These spheres can be attached to a cell. We planto use four balls to perform a biaxial mechanicalmeasurement of a single cell. We are developing dataanalysis routines to allow measurement of transientmechanical response. The optical trap is also beingused to study attractive forces by measuring thoseforces required to pull apart two-dimensional islandsof self-assembling nanoparticles.

Figure 1: Detail of the cell platform of the Bio-MEMS deviceused for mechanical and adhesion measurements, showing a cellbeing stretched.

Biomaterials

65

Biomaterials

Cell Response to Tissue Scaffold Morphology

Industrial and regulatory sectors have expresseda need for standards and new metrologies relatingto properties of tissue scaffolds for regenerativemedicine. We seek to meet these needs in severalareas where the criteria are clear, and to helpclarify industrial and regulatory needs in otherareas where such clarification is required. We aredeveloping a reference scaffold for porosity andpermeability. Also, we are developing metrologiesfor establishing the relationship between scaffoldporosity/morphology and cell response, forassessing the ability of a tissue scaffold to safelyhost cytokine, and for quantifying mechanicalstimulation requirements for cells — at the cellularlevel — from macroscopic inputs.

Marcus T. Cicerone

In the field of regenerative medicine, one seeks to guide cell differentiation and proliferation, and

production of the extracellular matrix through functionalproperties of 3D tissue scaffolds. Developing the abilityto guide such cell behaviors requires first the ability tocharacterize and assess properties of tissue scaffoldsas they relate to cell response. This, in turn, requireswell-defined physical and biological systems for whichquantitative rules can be formulated and verified.

We are developing methods for quantitativelycharacterizing tissue scaffolds and the cellularresponses they elicit. There are three classes ofscaffold properties that we focus on relative to theirimpact on cell behavior; these are: (i) morphological/topological properties, (ii) mechanical properties, and(iii) ability of biodegradable scaffold materials to actas biopreservents in connection with hosting growthfactors and other cytokines.

We led a worldwide collaboration under ASTM with17 other laboratories to establish a series of referencescaffolds for porosity and permeability. Our primarycharacterization method for these scaffolds is based ontomographic image analysis of scaffold morphology.

We are developing metrologies for assessing osteoblastresponse to pore size distributions in tissue scaffolds basedon extracellular matrix (ECM) production. We are alsoinvestigating morphology effects on osteoblast responseto surface chemistry. The image analysis methodsdeveloped in the reference scaffold activity serve tosupport these efforts. The ability to uniformly andreproducibly seed 3D scaffolds with adherent cells isanother critical factor for quantifying links betweenscaffold morphology and cell response, and we havedeveloped methods to accomplish this.

We are using computational modeling coupled withhigh-resolution imaging, atomic force microscopy(AFM), and optical trapping to develop metrology inthe area of cell response to environmental mechanicalstresses. It is clear that mechanical stimulation isrequired for some cell types to differentiate properly.Thus, it is important to be able to measure preciselywhat stress conditions are necessary for properphenotypic expression for selected cell types. We arecollaborating with the Materials Reliability Divisionof MSEL to establish methods to quantify the stressconditions at the cellular level based on macroscopicforces placed on the scaffold construct. Our approachis to translate ranges of macroscopic stresses to localstresses experienced by cells using a finite elementmodel. These local stresses will be correlated withcell response in terms of ECM production.

Biopreservation of cytokines in tissue scaffolds is acomplex but important area of regenerative medicine thathas been historically underserved. We are collaboratingwith six academic and one national lab to create a holisticapproach to stabilizing proteins in solid hosts such as tissuescaffolds. We are leading the grant-writing efforts in thiscollaboration and are focusing on clarifying the relationshipbetween fast glassy dynamics and biopreserving abilityof a material, which we have already observed in neutronscattering experiments. In keeping with this goal, we areestablishing accessible time-resolved optical metrologiesfor measuring these dynamics.

NIST Contributors and Collaborators

J. Dunkers, F. Wang, J. Cooper, T. DuttaRoy,J. Stephens, F. Phelan, M.Y.M. Chiang, L. Henderson(Polymers Division, NIST); Tim Quinn (MaterialsReliability Division, NIST)

Figure 1: A reconstruction of a candidate reference scaffold,generated from a tomographic image. Each colored objectrepresents a separate unit cell within the pore structure of the scaffold.

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3-Dimensional In Situ Imaging for Tissue Engineering:Exploring Cell /Scaffold Interaction in Real Time

Real time investigations of cell/scaffoldinteractions provide valuable information aboutthe dynamic nature of cells and their spatialarrangements with respect to the three-dimensional(3D) architecture of tissue engineering scaffolds.In situ imaging capabilities will enable determinationof the structure/function relationship of tissueengineering scaffolds and definition of thenecessary properties to promote tissueregeneration. We demonstrate tools forin situ imaging of cells/scaffold interactions.

Jean S. Stephens and Joy P. Dunkers

The ability to image live cells and their correspondinginteractions with the surrounding environment

provides critical information about the ability to promotedesired cellular activity (proliferation, differentiation,etc.) for tissue regeneration. In order to developin situ optical imaging capabilities, we must be ableto nondestructively and noninvasively image theinteractions at the cell/scaffold interface whilemaintaining cell viability.

In our laboratory, collinear optical coherentmicroscopy/confocal fluorescence microscopy(OCM/CFM) has successfully been used to imagethe 3D interconnected porous structure of polymericscaffolds. This system combines high spatial resolution(~1 µm), high sensitivity (>100 dB), and exceptionaldepth-of-penetration associated with OCM with the

fluorescent capabilities of CFM. This, therefore, allowsus to not only investigate the 3D scaffold, but also theuse of conventional fluorescent staining techniques toevaluate cellular response.

In order to perform live cell imaging, a systemor bioreactor that can sustain cell viability outside ofan incubator and allow for imaging was constructed(Figure 1). The bioreactor is a perfusion flowbioreactor. This design forces the media to flowthrough the scaffold, therefore ensuring nutrientdelivery and oxygen perfusion, as well as wasteremoval, throughout the entire structure. Also, adynamic cell culture creates an environment that bettermimics physiological conditions. The temperatureof the bioreactor system is maintained by circulatingwater (37 °C) through a copper element.

Figure 1: Bioreactor in OCM/CFM, open and top view.

Figure 2: Time-lapse images of cell movement.

Initial in situ imaging studies indicate themaintenance of cell viability, and we have successfullyimaged cells for several hours. The series of imagesin Figure 2 illustrate cell movement over a 2 hour timeperiod. The ability to collect images in real time willgive a great insight and understanding of how cellsare responding to different materials, scaffoldarchitectures, and culture conditions. These datawill provide new metrics for the evaluation oftissue engineering scaffolds.


J.A. Cooper, C.R. Snyder (Polymers Division,NIST)

Biomaterials

67

Broadband CARS Microscopy for Cellular/Tissue Imaging

In many of the biological sciences, as well asmany areas of polymer science, there is a needfor high-resolution, noninvasive, and chemicallysensitive imaging. We have developed a broadbandcoherent anti-Stokes Raman scattering (CARS)microscopy that provides an unprecedentedcombination of imaging speed and spectral coverage(i.e., chemical sensitivity). Our current efforts arefocused on eliminating nonresonant backgroundeffects, which can limit sensitivity of the technique.

Marcus T. Cicerone

We have developed a broadband CARS microscopymethod which allows us to obtain vibrational

spectra in the range (500 to 3000) cm–1 in less than1/50th the time required to obtain similar spectra byspontaneous Raman. This development was reportedat the first meeting of National Institute for BiomedicalImaging and Bioengineering (NIBIB) grantees, inBethesda, Maryland, the 11th Annual Time ResolvedVibrational Spectroscopy Conference, and the2005 Biophysical Meeting.

One key to the method we have developed is thegeneration of a broadband continuum. Optical pumpingof a tapered silica fiber was used to generate broadbandcontinuum in the first prototype of this instrument.Accumulative photo-damage limits the lifetime of thetapered fiber, and seriously limits the power level ofthe light that can be generated, significantly restrictingthe taper fiber as a reliable light source for CARSmicroscopy. With the assistance of an outside vendor,we have designed and procured a photonic crystalfiber (PCF) that is sealed at the ends, and which avoidsthe above issues. The PCF did not show any sign ofdegradation after a month, under long-term irradiationof 40 kW peak power femtosecond laser pulses. Thisadvance provided ≈10-fold increase in signal levels,so that, in principle, we can gather broadband spectrain 1/500th the time required for spontaneous Ramanspectroscopy. In practice, this rate exceeds thecapabilities of the CCD camera, which therefore setsthe limits on data acquisition; a faster camera wouldallow higher data collection rates.

A blend of chemically similar biodegradablepolymers, abbreviated as DTE and DTO (see Figure1a), have induced remarkable low immune responseupon fibroblast cell adhesion. These two polymersphase-separate upon annealing, and since they havesimilar indices of refraction, optical microscopy cannotbe used to image the phase-separated domains. On theother hand, broadband CARS microscopy has thesensitivity to distinguish the two polymers. Figure 1shows the three-dimensional imaging of a 50/50

DTE/DTO blend sample. In this sample, the spatialresolution is approximately 0.4 µm. We are currentlyexploring the hypothesis that the low cellular immuneresponse to the blends has its origins in spatialpatterning of the adhesion proteins. We are workingto correlate the protein adsorption with spatialpatterning of DTO and DTE rich domains.

In Figure 2, bright circular features are triglyceridelipid droplets in adipocytes, and the more subduedquasi-circular objects are the cells. We were unableto image the presence of protein in the cytosol due tononresonant background. Detection of these proteinsis crucial to identifying cell type, and we are currentlyfocusing our efforts on substantially reducing theeffects of nonresonant background.


T.W. Kee, H. Zhao, J. Taboas (Polymers Division,NIST); W-J. Li, R. Tuan (NIH/NIAMS)

Figure 2: Micrograph of adipocyte. This image was obtained withoutthe use of contrast agents such as fluorescent stains; the 2845 cm–1

C-H stretch vibrational band was the only image contrast.

Figure 1: (a) Chemical structures of DTE and DTO. CARSimages of a 50/50 DTE/DTO blend at depth: (b) 0 µm, (c) 3 µm,(d) 6 µm. The white areas in these images are DTO; the blackregions are DTE.

Biomaterials

68

Biomaterials

Response of Tissues and Tissue-Engineered Constructsto Mechanical Stimulation

noted in the reactor at any time in the verification testing.Stress–strain testing was also accomplished during thetrials. An example of the utility of online monitoring wasevidence of damage to the scaffold in the form of fiberde-adhesion at a strain of 10 %.

Mechanisms for the Increased Bioavailabilityof Materials Using High-Intensity FocusedUltrasound

At low powers, the mechanical stimulation ofhigh-intensity focused ultrasound (HIFU) can be usedto increase the permeability of tissues and, therefore,could be used to increase the effectiveness of drugsdelivered to treated tissues. At these power levels,the tissue is not permanently damaged but can healand return to its original pre-HIFU state.

In order to optimize the HIFU treatment, we needto know the mechanism by which the tissue is mademore permeable. To understand this, a simple modelof the sound propagation is being developed togetherwith a parameterized model of the openings (“cracks”)between cells, and between cells and the extracellularmatrix. Concepts from the field of damage mechanics(usually reserved for materials like metals) are beingused to develop this model.

Supporting experiments using bovine cardiac tissueare being conducted to identify the unknown parametersto the models and to identify the mechanical mechanismthat leads to the increased permeability. This newlyimplemented system relies on confocal therapeuticand imaging ultrasonic elements, packaged togethercommercially. A gated function generator and poweramplifier is used to drive the outer, therapeutic HIFUelement in pulsed mode at 1 MHz. An ultrasonicpulser/receiver simultaneously drives the inner 10 MHzimaging element and collects data for processing.The system has a number of unique capabilities forbiological application. The imaging element is used tomonitor the radiation force, which has been proposedas the main mechanism behind the effect. Followingdesigns used in the literature, we have constructed adevice to measure the permeability of the tissue samples.

1. Martin, et al., Ann. Biomed. Eng., 27, 656, 1999.


A. Slifka, E. Drexler (Materials Reliability Division,NIST); F. Landis, L. Henderson (Polymers Division,NIST); V. Frenkel, K. Li (NIH)

Figure 1: The biodegradable scaffold with tissue ingrowth takenduring a stress–strain test. Image correlation is used to measurestrain.

Human coronary smooth muscle cells (passages 7–9)were obtained from a commercial source and used inthe experiments. The coronary smooth muscle cellspropagated on the scaffold and were seen without difficultyby day 7 (Figure 1). No evidence of contamination was

Mechanical stimulation of tissue as it is beinggrown in a bioreactor has been shown to maketissue engineered constructs more like healthy,natural tissue. However, little effort has gone intostudying exactly how the stimulation should bedone.[1] Mechanical stimulation can also be usedfor enhanced drug delivery. Researchers at theNational Institutes of Health have been developingan ultrasonic system to enhance drug delivery intumors that are not easily treated with chemotherapy.We are developing instrumentation and models tooptimize these methods.

Timothy P. Quinn, Tammy L. Oreskovic,and Brian E. O’Neill

Mechanical Stimulation ofTissue-Engineered Constructs

Abioreactor has been developed that can provide both mechanical stimulation to a tissue-engineered

(TE) construct and mechanical testing while the tissueis being grown in the bioreactor. The reactor wasdesigned to facilitate studies to determine the optimalvariables for growing TE constructs for vasculargrafts. In this bioreactor, we can stimulate a planarsheet of tissue/scaffold construct with an arbitrarywaveform. The reactor can be configured to apply agiven force or a given displacement. It is equipped withactuators, load cells, and viewports to conduct online,biaxial stress–strain tests without removing the samplefrom the reactor.

69

Biomaterials

Mechanical Behavior of Tissue

crotaline-treated, and hypoxia-treated genetically modifiedto disable a receptor responsible for activating vasodilators.Figure 1 shows the stress–strain behavior of the treatedpopulations compared with the controls. The differencebetween the two hypoxic populations and the controlsare readily obvious. However, the monocrotaline-treateddata indicate that the arteries have not remodeled similarlyto the hypoxic rats, and an entirely different mechanism,other that arterial wall remodeling, may be operating.

Complementary work is underway on the histologyand quantitative ultrasonic properties of the pulmonaryarteries. The reduction in elastic fiber, which accompaniesthe increase in thickness in the hypoxic samples isconsistent with the change in mechanical propertiestypically associated with hypertension, where the arteriesbecome less compliant. The increased thickness of themedial layer is mostly due to thicker muscular layersbetween elastic lamellae. At constant pressures, increasesin thickness and reductions in elastin content contributeto a stiffer response. We have used quantitative ultrasoniccharacterization to correlate mechanical properties due toremodeling to the ultrasonic properties of the unstressedremodeled tissue. Ultrasonics is also used to predictfracture risk in osteoporitic patients. Dispersion(or how the speed of sound changes with frequency)appears to be sensitive to changes in bone mineraldensity. We organized a topical meeting on ultrasoniccharacterization of trabecular and cortical bone thatwas sponsored by the Acoustical Society of America.

The results comparing the arteries from thehypoxia-treated rats to those of the controls, along withthis histology, were presented at the ASME SummerBioengineering Conference in Vail, Colorado, in June.The comparison between the monocrotaline and hypoxicto the controls will be presented at the BiomedicalEngineering Society Annual Fall Meeting in Baltimore,Maryland, in September. A manuscript on the technique,and the control results, was submitted to the Journalof Biomechanics. Three papers have been publishedon the topic of improving quantitative ultrasonics fortissue characterization, and a NIST IR is now availablesummarizing the Inaugural Workshop on ComputationalTools for Modeling Acoustic Propagation in Real-WorldMaterials. Additional presentations have been madeat the IEEE International Ultrasonics Symposium in2004 and the 148th Meeting of the Acoustical Societyof America.


C. McCowan, K. Waters, A. Slifka, T. Quinn(Materials Reliability Division, NIST); R. Shandas,D. Ivy, C. Cool, K. Colvin (University of ColoradoHealth Sciences Center)

Using a rat model as a first approximation to thebehavior of human arteries, we have measured thestress–strain properties of pulmonary arteries from fourdifferent populations: control, hypoxia-treated, mono-

Figure 1: Graph showing the stress–strain behavior of the control,hypoxic, and monocrotaline-treated rat pulmonary arteries.

Measurements of the structure and mechanicalproperties of biological materials elucidatemechanisms of disease, and permit qualityassessment of tissue-engineered constructs.Certain diseases may be identified by changesin the mechanical properties of the affectedtissue before loss of function is detected, thusenabling earlier diagnoses and intervention.Our objective is to provide support to cliniciansby developing measurement techniques and bymeasuring the properties of tissue.

Elizabeth S. Drexler

Research on the mechanical properties at the tissue level has focused on the properties of pulmonary

arteries with the onset of pulmonary hypertension(PHT). The onset of PHT is known to causeremodeling of the walls of the pulmonary arterialsystem, and, if left untreated, can lead to right-sideheart failure. We have tested the left and right mainarteries, and the trunk (the arteries most accessible forclinical diagnostics) in the direction of blood flow andin the circumferential orientations. Our goals are:(i) to determine the onset of pulmonary hypertensionby correlating our measured mechanical properties tothe output of tissue Doppler and ultrasound techniquescurrently being developed as diagnostic tools and(ii) to develop structure–property relations.

Monocrotaline vs. Hypoxic Treatments

70

Materials Design for Biomechanical Structures

Biomechanical prostheses such as dental crowns,total hip and knee replacements, heart valves,and spinal disk devices are becoming morecommonplace in an ever-aging population.The lifetimes of such prostheses are limited bymaterials properties. Accordingly, it is imperativethat we understand the modes of failure in thesesystems, in order that materials can be developedfor superior performance. This programwith extramural partners (New York University,University of Maryland) and internationalinstitutions seeks to determine fundamental groundrules for designing biomechanical systems forimproved lifetime performance by identifyingand analyzing clinically relevant damage modes.

Brian Lawn

Cracking and other damage modes in ceramic layerson soft substrates are of broad general interest

because of the potential for lifetime-limiting prematurefailures. This is especially true of biomechanicalprostheses — dental crowns, hip and knee replacements,heart valves, spinal disk replacements — where ceramiccomponents introduced to enhance wear resistance,strength, chemical durability and, in the case of dentalcrowns, aesthetics are exposed to cyclic concentratedloads under stringent in vivo environmental conditions.A proper understanding of the materials aspects ofany such ceramic-based prosthetic device becomesa quality-of-life issue. In many such applications theceramic is just one component in combination withpolymer and/or metal support sublayers, so a systemsapproach is essential.

In this program, we characterize contact-induceddamage modes in model layer systems — bilayers,trilayers, and even multilayers — that simulate thebasic loading features of biomechanical structures and,at the same time, allow direct in situ observations ofthe damage evolution during loading and unloading.The most revealing are model layer structures madefrom transparent components, e.g., ceramic coatinglayers on clear polymer substrates, or glass coatingson metal substrates. Critical conditions for damageinitiation can then be directly monitored and quantified.

Using this approach, we have been able to identifydamage modes believed to be responsible for thefailure of clinical prostheses, especially dental crowns.Analytical relations expressing the critical applied loads(e.g., biting force, body weight on hip replacements)

in terms of ceramic layer thicknesses and materialproperties (strength, toughness, modulus, hardness)have been determined. These relations can be usedto predict optimal interlayer dimensions and materialproperties for any given layer system. Design criteriafor this optimization are being laid down.

This work has been funded by the NationalInstitute of Dental and Craniofacial Research.Materials scientists, engineers and clinicians areinvolved. The first five-year stage of this programhas been completed. A second five-year stage is underway. Several dental materials companies participatein this program.

PublicationsBrian Lawn’s publications can be viewed and

downloaded at http://www.msel.nist.gov/lawn/index.html.


D. Rekow, V. Thompson, Y. Zhang (New YorkUniversity); I. Lloyd (University of Maryland); A. Pajares,F. Guiberteau, P. Miranda, E. Sanchez (University ofExtremadura); M. Bush, X. Hu (University of WesternAustralia); S. Bhowick, I. Hermann, J.-W. Kim (GuestScientists); Ivoclar-Vivadent (Norton-Desmarquest);V. Zahnfabrik (Ceramco, Therics)

Biomaterials

71

Biomaterials

Molecular Design and Combinatorial Characterizationof Polymeric Dental Materials

Polymeric dental materials are finding increasingapplications in dentistry and allied biomedicalfields. As part of a joint research effort supportedby the National Institute of Dental and CraniofacialResearch and also in collaboration with theAmerican Dental Association Health FoundationPaffenbarger Research Center, NIST is providingthe dental industry with a fundamental knowledgebase that will aid in the prediction of clinicalperformance of dental materials.

Joseph M. Antonucci and Sheng Lin-Gibson

In contrast to current methods that rely onone-specimen-at-a-time measurements, metrologies

based on combinatorial and high-throughput (C&HT)approaches can accelerate fundamental and appliedresearch in dental materials. For dental polymersand their derivatives (sealants, adhesives, restorativecomposites), many critical properties depend on thechemical, structural, and compositional nature of theinitial monomer (resin) system. For multiphase dentalmaterials, e.g., composites, similar factors govern thequality of the interphase between the silanized filler phaseand the resin matrix. The objective of this research wasto determine the feasibility of adapting C&HT techniquesto measure material properties and screen variousexperimental resin chemistries for molecular design ofnovel dental polymers and composites. The technologiesdeveloped to enable this research include nanoindentationand the fabrication of single component or multi-variablediscrete and continuous gradient films.

instability for mechanical measurements test. SIEBIMMon PMMA, a linear polymer, yielded a modulus comparableto that obtained by the 3-point bend test. Buckling patternsfrom cross-linked BisGMA/TEGDMA films (Figure 1)resulted in moduli with increased variability, i.e., thebuckling patterns were not straight, parallel lines.Reasons for this behavior are under study.

Figure 2: Elastic moduli of photopolymerized BisGMA-TEGDMAof different compositions as a function of irradiation time(represented as distance).

Figure 1: Buckling patterns of BisGMA-TEGDMA in mass ratiosof 30:70 (left) and 70:30 (right).

BisGMA-TEGDMA networks with 2D gradients,varying in monomer composition and conversion,were fabricated with a broad conversion range for allmonomer compositions. Conversions were measuredusing near-IR spectroscopy, and elastic modulus andhardness. As shown in Figure 2, the conversion andthe mechanical properties correlated well.

Additional techniques with the potential for C&HTapproaches are being evaluated for their ability to screenother properties of dental materials, including the interfacialsilane chemistry and cellular response. Studies on theinterfacial chemistry have shown that covalent bondingof nanoparticles with the polymerized matrix resulted inwell-dispersed composites. To screen the biologicalresponse to dental materials, methods to measure cellviability, apoptosis, and gene expression levels as a functionof vinyl conversion have been developed.


E.A. Wilder, K.S. Wilson, N.J. Lin, C.M. Stafford,L. Henderson (Polymers Division, NIST);P.L. Votruba–Drzal (Materials and ConstructionResearch Division, NIST)

Among the different resin chemistries underinvestigation, 2D compositional gradients using BisGMA-TEGDA were selected as the benchmark for developingmetrologies and rapid screening techniques for optimizinghardness, shrinkage, and biocompatibility. The elasticmodulus was determined by two methods, nanoindentationand SIEBIMM — a strain-induced elastic buckling

72

Safety and Reliability

includes the development and innovative use ofstate-of-the-art measurement systems; leadership inthe development of standardized test procedures andtraceability protocols; development of an understandingof materials in novel conditions; and development andcertification of Standard Reference Materials® (SRMs).Many of the tests involve extreme conditions, such ashigh rates of loading, high temperatures, or unusualenvironments (e.g., deep underwater). These extremeconditions often produce physical and mechanicalproperties that differ significantly from handbook valuesfor their bulk properties under traditional conditions.These objectives will be realized through innovativematerials property measurement and modeling.

We take for granted that the physical infrastructurearound us will perform day in and day out withconsistent reliability. Yet, failures occur when thesestructures degrade to where they no longer sustain theirdesign loads, or when they experience loads outsidetheir original design considerations. In addition, wehave become increasingly aware of our vulnerability tointentional attacks. The Safety and Reliability Programwithin MSEL was created to develop measurementtechnology to clarify the behavior of materials underextreme and unexpected loadings, to assess integrityand remaining life, and to disseminate guidance andtools to assess and reduce future vulnerabilities.

Project selection is guided by identification andassessment of the particular vulnerabilities withinour materials-based infrastructure, and focusing onthose issues that would benefit strongly by improvedmeasurements, standards, and materials data. This year,we have worked with the Department of HomelandSecurity and the Office of Science and TechnologyPolicy in developing the National Critical InfrastructureR&D Plan, which will provide guidance across muchof the national infrastructure. Ultimately, our goal isto moderate the effects of acts of terrorism, naturaldisasters, or other emergencies, all through improveduse of materials.

Our vision is to be the key resource within theFederal Government for materials metrologydevelopment as realized through the followingobjectives:■ Develop advanced measurement methods needed by

industry to address reliability problems that arise withthe development of new materials;

■ Develop and deliver standard measurements and data;■ Identify and address vulnerabilities and needed

improvements in U.S. infrastructure; and■ Support other agency needs for materials expertise.

This program responds both to customer requests(primarily other government agencies) and to theDepartment of Commerce 2005 Strategic Goal of“providing the information and framework to enablethe economy to operate efficiently and equitably.”For example, engineering design can produce safeand reliable structures only when the property datafor the materials are available and accurate. Equallyimportant, manufacturers and their suppliers need toagree on how material properties should be measured.

The Safety and Reliability Program works towardsolutions to measurement problems on scales rangingfrom the macro to the micro. The scope of activities

The MSEL Safety and Reliability Program isalso contributing to the development of test methodstandards through committee leadership roles instandards development organizations such as theASTM International and the International StandardsOrganization (ISO). In many cases, industry alsodepends on measurements that can be traced toNIST SRMs.

In addition to the activities above, MSEL providesassistance to various government agencies on homelandsecurity and infrastructural issues. Projects includeassessing the performance of structural steels as part ofthe NIST World Trade Center Investigation, collaboratingwith both the Department of Transportation and theDepartment of Energy on pipeline safety and bridgeintegrity issues, advising the Bureau of Reclamation onmetallurgical issues involving pipelines and dams, andadvising the Department of the Interior on the structuralintegrity of the U.S.S. Arizona Memorial.

Contact: Thomas A. Siewert (MaterialsReliability Division),Frank W. Gayle (Metallurgy Division)

Program Overview

73


Analysis of Structural Steel from the World Trade Center

In 2005 NIST completed the three-year FederalBuilding and Fire Safety Investigation of theWorld Trade Center Disaster. The investigationaddressed many aspects of the catastrophe, fromoccupant egress to factors affecting how long theWTC towers stood after being hit by the airplanes,with a goal of gaining valuable information forthe future. A critical aspect of the investigationwas the metallurgical analysis of the recoveredstructural steel. The analysis includedcharacterization of mechanical properties,failure modes, and structural responsedetermined from photographic evidence.

William E. Luecke, Stephen W. Banovic,Timothy J. Foecke, J. David McColskey,Christopher N. McCowan, Richard J. Fields,Thomas A. Siewert, and Frank W. Gayle

The collapse of the World Trade Center (WTC)towers was the worst building disaster in human

history. Engineers, emergency responders, and the nationwere largely unprepared for such a catastrophe. The taskof the NIST investigation was to determine the detailsof why and how the towers collapsed. As part of thisinvestigation, the Metallurgy and Materials ReliabilityDivisions characterized the recovered structural steel.

The project is comprised of five tasks:1. Collect and catalog physical evidence.2. Categorize failure mechanisms from visual evidence.3. Determine steel properties to support modeling.4. Correlate determined and specified steel properties.5. Analyze steel to estimate temperature extremes.

Analysis of fracture surfaces of recovered perimetercolumns struck by the aircraft showed that the steel

remained ductile even at high deformation rates. Datasuch as these were important in assuring the accuracyof the steel properties supplied to the modeling efforts.

Photographic analysis demonstrated that perimetercolumns of WTC 2 began to pull into the buildingalmost 30 minutes before collapse. Our staff developedpull-in maps based on pre-collapse photographs,Figure 1, which were instrumental in constrainingthe finite element models of the building deformation.

Figure 2: Measured yield strength of perimeter column specimens.

Figure 1: Pull-in map of perimeter columns (in inches) on theeast face of WTC 2, 9:03 a.m.

Tensile tests of the dozens of steel types and gradesrecovered showed that their yield and tensile strengthsare consistent with the expected values. In a few cases,the strengths of the NIST-tested specimens were slightlyless than called for, but the number of under-strengthsamples is consistent with the natural variability in steelstrength and the damaged state of the recovered steel.Figure 2 shows the ratio of measured to specified yieldstrength for recovered perimeter column steels.

Photographic evidence indicated that 16 of therecovered perimeter column panels from WTC 1 wereexposed to fire before the collapse. Our staff developeda forensic test based on paint cracking due to thermalexpansion of the steel. This test placed limits on the timeand temperature exposure of the recovered columns.Results indicate that only three locations on these 16recovered columns reached temperatures above 250 °C.

The final draft of the investigation report was issuedfor public comment in June 2005.


R. Santoyo (Materials Reliability Division, NIST);M. Iadicola (Metallurgy Division, NIST)

74

Infrastructure Reliability: Charpy Impact Machine Verification

We assist owners of Charpy impact machines inachieving conformance with the requirements ofASTM Standard E 23. We interact with the ASTMCommittee responsible for the Charpy impactstandard, to improve the service and to maintaina high-quality verification program. We alsoparticipate in the activity in ISO Committee TC164, so our specimens and procedures remaincompatible with the associated international andregional standards.

Thomas A. Siewert

Technical Description

The Charpy impact test uses a swinging hammer toassess the resistance of a material to brittle fracture.

The absorbed energy is measured from a calibratedscale, encoder, and/or an instrumented striker. The lowcost and simple configuration of the test have made ita common requirement in codes for critical structuressuch as pressure vessels and bridges. This project ishandled jointly by the Standard Reference MaterialsProgram (of the Office of Measurement Services),which oversees the administrative aspects of theprogram, and the Materials Reliability Division,which handles the technical and verification aspects.NIST provides highly characterized StandardReference Materials® (SRMs) to machine ownersand independent calibration services, then evaluatesthe results of tests of these specimens on theirimpact machines. Owners of machines that meet therequirements of ASTM Standard E 23 are given a letterof conformance, while owners of nonconformingmachines are given recommendations on correctiveactions. Our special facilities include three masterCharpy impact machines (all 300 J to 400 J capacity).These three machines are used to establish certifiedvalues for the NIST reference materials sold throughthe Standard Reference Materials Program Office.In addition, we have several more machines(3 J to 400 J capacities) that are used for researchpurposes.

AccomplishmentsRay Santoyo continues in his role as Charpy

Coordinator. We have served about 850 customersin the past year, a slight increase over the year before.The great majority of these machines were withintolerances required by ASTM Standard E 23.As usual, many customers took advantage of our

support services, as shown by over 674 emails,730 faxes, and 500 phone calls in the first 9 monthsof FY05. We immediately contact the machineowner if their machine fails to meet the verificationcriteria. In this contact (by phone, mail, email, or fax),we suggest corrective measures.

NIST’s support of ISO Standard 17025 meansthat we have been reformatting our quality manual forthe Charpy program to match the new NIST stylesand to fit with the overall NIST Quality Manual (QM-I).Thus, Chris McCowan has refined our Division qualitymanual (QM-II) and the Charpy program manual(QM-III) to match those of the other Laboratoriesand Divisions. We expect to perform an independentaudit by September 2005 and then formally adoptthese new quality manuals.

We helped to organize another internationalsymposium, the Second Symposium on PendulumImpact Machines: Procedures and Specimens, held inconjunction with the November 2004 meeting of ASTMCommittee E 28 in Washington, D.C. We also helpedto lead the symposium and contributed to three of thepapers. Previous symposia have provided valuableinsight into improvements in our program.

This year, we produced the first batch of Izodimpact verification specimens, which has been testedand is undergoing statistic evaluation. Soon, it isexpected to enter inventory as SRM 2115.

Chris McCowan serves as the Chairman of ISOTC164 SC4 P, on pendulum impact and also asthe Chairman of ASTM Subcommittee E28.07 onimpact testing.


R. Santoyo (Charpy Program Coordinator);C. McCowan, J. Clark, D. Cyr, C. Dewald, S. Vincent,N. Neumeyer, J. Percell (Materials Reliability Division,NIST); IRMM (Europe); NRLM (Japan); Members ofASTM Subcommittee E 28.07


75

Standard Test Methods for Fire-Resistive Steel

The fires and subsequent collapse of theWorld Trade Center focused attention on thevulnerability of structural steel to fire. Recentlysteels designated as “fire-resistive” have becomeavailable. This project is developing a standardtest method for quantitatively evaluating andcomparing the resistance of structural steels tohigh-temperature deformation.

William E. Luecke and J. David McColskey

All steels lose strength with increasing temperature. By 600 °C, most structural steels have lost more

than half their strength. At intermediate temperaturesthe strength is independent of time, but above 500 °C,creep, or time-dependent deformation, further reducesthe load-carrying capability. To combat this loss ofload-carrying capability, structural steel in buildings isinsulated to keep it cool in fire.

Fire resistive (FR) steels are intended to be drop-inreplacements for existing grades of structural steel.They can meet the same specifications, have similarweldability, cost only marginally more, but havesuperior elevated temperature strength. Their superiorhigh-temperature properties have the potential to provideextra time for building occupants to escape a fire.

In Japan and Europe, FR steels are qualified basedon high-temperature retained yield strength. Althoughthis definition employs a simple, familiar test, becauseit is a short-term test, it ignores the time dependenceof the deformation resistance. Domestic standards forstructural components use a critical temperature criterionfor failure of steel, so effectively all steels are identical,regardless of high-temperature deformation resistance.

We are studying three possible test methodsfor standardization. The first is the conventionalhigh-temperature retained yield strength. The secondis a slow-rate (several hours to failure) tension test,which should capture the time-dependent deformationeffects. The third method is a hybrid of a creep and aconventional tension test in which the test specimen isheld under constant load as the test temperature rampsupward linearly. Over a narrow temperature range,which can be approximated as a critical temperature,the deformation rate increases drastically, and thespecimen fails. This critical temperature can be usedas a measure of the fire-resistance.

One goal of this project is to build on recentworldwide research on similar tests, but to take theproof of concept to a draft standard. Each potentialmethod has advantages, but there has been noresearch to compare the results of each to the others.

Our research focuses on understanding the limitations,repeatability, and reproducibility of the methods bycharacterizing several different classes of constructionsteels. In the near term, after selecting a single method,we will organize an interlaboratory study (ILS) toprobe the limitations and establish precision and bias.

Figure 1 compares the behavior of two FR steelsevaluated using high-temperature, tensile yield strength,Fy , measured in a high-temperature tensile test and thecritical temperature evaluated using the temperature ramptest. Although the normalized yield strengths divergesignificantly above 600 °C, the critical temperaturesmeasured in the ramp tests are very similar.


R.J. Fields (Metallurgy Division, NIST)

Figure 1: Comparison of tensile and ramp tests.


76

Frangible Bullets and Soft Body Armor

The NIST Office of Law Enforcement Standards(OLES) is currently involved in modifying existingstandards for the ballistic resistance of personnelbody armor and providing new performancestandards for frangible bullets (designed tofully disintegrate on impact with hard surfaces).The deformation behavior of this frangiblematerial when impacting a soft surface suchas NIJ Level II or IIIA soft body armor is not aspredictable as conventional bullets and requiresa better understanding of the high-strain ratedeformation behavior of the fabrics used in softbody armor and the various frangible materials.

Stephen D. Ridder and Steven P. Mates

As part of this multi-year project, the Metallurgy Division is testing Pressed and Sintered Cu-Sn

(PS Cu-Sn) bullets, one of the frangible ammunitionmaterials selected for testing by OLES. PS Cu-Snfrangible material is made by blending a 9:1 mass ratioof Cu and Sn powder with nominal particle sizes of50 µm, pressing the powder mixture in molds andthen using transient liquid phase sintering to bind thecompacts and form a Cu-Sn reaction layer (≈30 min @260 °C). Sintering time and temperature are controlledto limit the reaction zone and avoid formation of theless frangible α-bronze phase.

Microstructural analysis of the as-received PSCu-Sn material has shown that the matrix consists of amixture of copper particles with varying morphologies— some with equiaxed grain structures and others withCu-P precipitates (possibly the result of copper powderfrom different suppliers). EDS analysis indicates thatthe binding region between the copper matrix particlesconsists of columnar grained Cu3Sn (ε) phase, a moreblocky shaped Cu6Sn5 (η´) phase, and unreacted Sn.SEM fractographs of Kolsky Bar specimens haveshown brittle fracture in the ε phase, brittle cleavagein the η´ phase, and ductile failure with micro-voidcoalescence in the copper matrix adjacent to theintermetallic layers.

The mechanical deformation of PS Cu-Sn frangiblebullets has been examined at conventional strain ratesand at high strain rates in compression in the NISTKolsky Bar facility. Kolsky bar tests have beenperformed to assess the compressive stress–strainbehavior at strain rates up to 103 s–1. Dynamic tensilestrength has also been measured using the Kolsky Barto perform diametral compression tests, or Brazil tests.In this test, a disk of the bullet material is exposed to


a rapidly rising stress pulse along its diameter, whichcreates a tensile stress perpendicular to the applied load.A crack eventually forms due to this tensile stress, fromwhich the tensile strength can be measured. TypicalBrazil tests involve purely brittle materials, and only theelastic deformation behavior of the sample is needed todetermine tensile strength. However, in the case offrangible bullet materials, significant plastic deformationwas observed before failure. Finite element modeling(Figure 1) was used to determine how plastic yieldingaffected the evolution of tensile stress in the sampleduring the test in order to obtain a more accurateestimate of the tensile strength. The high-strain rateplastic flow and tensile strength data can then be usedto model the deformation and breakup of a frangiblebullet as it impacts a soft armor-like surface.

Expected ImpactsThese data and associated bullet impact modeling

efforts will be used by the NIST Office of LawEnforcement Standards in a continuing effort to developa performance standard for frangible ammunition and inthe revision of the National Institute of Justice BallisticResistance of Personnel Body Armor Standard.


S. Banovic, R. Fields, L. Levine, L. Ma (MetallurgyDivision, NIST); M. Kennedy, R. Rhorer, E. Whitenton(Manufacturing Metrology Division, NIST); T. Burns(Mathematical and Computational Sciences Division,NIST)

Figure 1: 3-D simulation of diametral test of frangibleammunition cross-section.

77

Pipeline Safety: Corrosion, Fracture, and Fatigue

A critical element of the nation’s infrastructure isthe more than 3 million km of natural gas andhazardous liquid pipelines that deliver almost 2/3of the nation’s energy. Following the passage ofthe Pipeline Safety Improvement Act in 2002, NISTbegan working with the pipeline industry, DoE,DoI’s Minerals and Management Service, andDoT’s Office of Pipeline Safety to provide themeasurement methods, standards, and data neededto understand corrosion, fracture, and fatiguefailure mechanisms in this critical element of thenation’s infrastructure.

Richard E. Ricker and J. David McColskey

After Congress passed the Pipeline Safety Improvement Act in 2002, NIST, DoE, and DoT developed a

memorandum of understanding (MOU) detailinga coordinated program of research, development,demonstration, and standardization. The goals of theprogram are to continue improvements in the safety andoperation of pipelines and related facilities. NIST has along history of contributions to pipeline safety and, in thisproject, is responsible for materials research addressingconcerns with corrosion, fatigue, and fracture, especiallyas pipelines are pushed to higher performance using newmaterials and higher pressures.

in the original study to that determined by moderncomputer curve fitting routines. This figure shows:(i) strong evidence of non-linear kinetics and decreasingcorrosion rates, and (ii) that only minor differenceswere obtained with modern analysis. In both originaland new analyses, the scatter in the data limits theconclusions. The origin of this scatter needs to beunderstood before less conservative non-linear kineticscan be used for rate models.


At the urging of the Pipeline Research CouncilInternational (PRCI) and DoT’s Office of PipelineSafety (OPS), NIST reexamined data from the originalNBS underground corrosion studies conducted between1920 and 1957, involving over 36,000 samples buried at128 different sites across North America. The originalstudy was found to be thorough and ahead of its timewith respect to statistical analysis. Figure 1 comparesthe results of the power law exponent fit determined

Figure 1: Corrosion analysis (historical data), power law exponents.

Figure 2: Crack tip opening angle behavior — conventional steel.

Fracture and fatigue studies are underway onboth traditional and modern steels. By acquiring andpublishing data on these properties, NIST hopes toenable better modeling of performance. The focus ofthis study is to assess the ability of different pipelinesteels to arrest crack propagation. Crack tip openingangle (CTOA) measurements were made on samplescut from the pipeline samples. Figure 2 shows theCTOA measurements on two baseline steels and theregion of stable crack growth.

Working with OPS, MMS (DoI), DoE, PRCI,American Gas Association, the Gas Technology Institute,ASTM Intl. NACE Intl. CANMET, and the National EnergyBoard (Canada), NIST organized a workshop on AdvancedCoatings for Pipelines and Related Facilities held at NISTJune 9–10. Sixty representatives of the pipeline industry,suppliers, and government agencies from the U.S., Canada,and the UK attended this meeting. NIST also assistedOPS in organizing the Government/Industry Pipeline R&DForum in Houston, Texas, March 22–24, 2005.


F. Gayle, T. Foecke, S. Mates, R.J. Fields,C. Handwerker (Metallurgy Division, NIST); T. Siewert,C. McCowan (Materials Reliability Division, NIST);M. Smith (PRCI); C. Sames (AGA); J. Merritt, S. Gerard,R. Smith (DoT/OPS); C. Freitas, R. Anderson, D. Driscoll(DoE); M. Else (DoI/MMS)

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Polymer Reliability and Threat Mitigation

This project is developing metrologies andpredictive models to test and predict the long-termreliability of polymers used in ballistic resistantarmor and machine readable travel documents.Use of these methods and models will enable oneto monitor the performance of polymeric materialswhile in use, elucidate how environmental andmechanical factors influence performance, andprovide a basis for estimating durability andestablishing care procedures.

Chad R. Snyder, Gale A. Holmes, andWalter G. McDonough

Ballistic Resistant Armor

In response to an apparent failure of ballistic resistant armor during first responder use, NIST’s Office of Law

Enforcement Standards initiated a research programdesigned to strengthen the certification process of theseprotective devices. We are working to identify and developanalytical metrologies for quantifying the mechanicalproperties and degradation pathways of ballistic fibers thatcomprise this armor, with the ultimate goal being anestimate of vest durability and care procedures.

as quantified through the method of Cuniff and Auerbach.Ongoing research is examining the effects of fold radiusas well as the effects of repeated folding.[1]

Complementing our mechanical properties studies,our research into the degradation pathways of PBOand PBO-like materials has made significant headway.In addition to completion of our review article,[2]

we have synthesized the model compounds2-phenylbenzoxazole and bis-1,4-(2-benzoxazolyl)phenylene, and their hydroxy analogs, and we arecurrently analyzing, through matrix assisted laserdesorption/ionization (MALDI) mass spectrometry,the degradation products resulting from exposure toour newly acquired solar simulator.

Machine Readable Travel DocumentsAs indicated in an October 14, 2004 press release

from the U.S. Government Printing Office (GPO),NIST is testing the candidates for the new U.S.electronic passports for their ability to meet durability,security, and electronic requirements. This newtechnology will eventually be incorporated intoelectronic U.S. passports to enhance the securityof millions of Americans traveling around the world.At the request of the U.S. Department of State, weparticipated in the WG3 (Working Group 3 of ISO)meeting of the Document Durability Task Force forthe EPassport in Tsukuba, Japan. The purpose of thetask force meeting was to update the participants on thestatus of the Test Specification for Machine ReadableTravel Documents (MRTD). The main recommendationfrom the meeting was that any proposed test specificationby ISO would serve as the guideline to help nationswriting requests for proposals to develop their ownMRTDs. Also, the task force chairs have decided touse more complex testing sequences to better representreal-world applications; this was in line with therecommendations made by NIST.

References1. P.M. Cunnif and M.A. Averback, 23rd Army Science

Conference, Assistant Secretary of the Army (Acquisition,Logistics and Technology), Orlando, FL (Dec. 2002).

2. G.A. Holmes, K. Rice, and C.R. Snyder, Journal ofMaterials Science, in press.

Contributors and CollaboratorsJ. Dunkers, C.M. Guttman, K. Flynn, J. Kim,

F.A. Landis, D. Liu, W. Wallace (Polymers Division,NIST); D. Novotny, J. Guerrieri, G. Koepke, M. Francis,N. Canales, P. Wilson (Electromagnetics Division, EEEL);K. Rice (Office of Law Enforcement Standards, EEEL);T. Dang (Air Force Office of Scientific Research)

This year, we have made considerable progress onmultiple fronts towards these goals for poly(benzoxazole)(PBO) ballistic fibers. The modified single fiberfragmentation test, developed last year, was used toexamine the effect of fiber fatigue on ballistic resistance.Figure 1 shows the effect of folding on the morphologyand mechanical properties of a PBO fiber. Our analysissuggests that, for this case, folding resulted in anestimated >10 % reduction in overall ballistic performance,

Figure 1: Top and Left: Micrograph and yield strength dataobtained from modified single fiber test on an unfolded PBO fiber;Bottom and Right: Micrograph and figure for a folded PBO fiber.


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space, while single crystal methods can be adapted tohigh-resolution analysis of materials such as thin films.

However, results from both powder andhigh-resolution techniques are affected by a complexoptical aberration function that is specific to thediffraction optics and goniometer assembly used inthe experiment. NIST Standard Reference Materials(SRMs) are the recognized means by which theseaberrations may be characterized to achieve improvedmeasurement accuracy. To address these issues,Dr. James Cline of the Data and Standards TechnologyGroup conceived and designed the Ceramics DivisionParallel Beam Diffractometer (CDPBD).

Advanced Measurement CapabilitiesUHV STM/AFM

Figure 1: Ultrahigh vacuum STM/AFM apparatus.

Figure 2: The Ceramics Division Parallel Beam Diffractometerin the AML.

Enhanced by the superior vibration isolation andclean room environment in NIST’s new AdvancedMeasurement Laboratory (AML), our UHV STM/AFMsystem, Figure 1, provides atomic imaging and forcemeasurement with an unprecedented resolution andaccuracy. Combined with our conventional AFM,equipped with a “triboscope” attachment, we are ableto image and manipulate surface features and measurea wide range of material characteristics and propertiesimportant in nanodevice operation. As a result, wenow are leading fundamental metrological efforts,working with device and magnetic hard disk industries,as well as academic institutions, to establish reliablemeasurement methods, calibration artifacts, andinfrastructural support for current and future industries.

High Resolution X-ray MetrologyPowder and single crystal x-ray diffraction are

widely used in industry, research facilities, andacademia as one of the principal means of characterizingmaterials. Both techniques yield a wealth of informationon the crystallographic and microstructural character ofthe specimen. The powder diffraction method has thevirtue that it can probe a continuous sequence ofcrystallographic reflections with a single scan in angular

The CDPBD, Figure 2, was designed and builtspecifically to perform traceable measurements onpowder and thin film specimens. Installed in the newNIST Advanced Measurement Laboratory, this facilityprovides the environmental and temperature controlsrequisite for a new generation of NIST SRMs thatwill enable unprecedented measurement accuracy ina highly competitive, data conscious, materialsresearch community.


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X-ray Absorption SpectroscopyAdvances in our x-ray absorption spectroscopy

facilities have achieved an unrivaled capability enablingour Characterization Methods Group (CMG) to addressa remarkably broad range of challenging structure andchemistry issues at the forefront of materials scienceresearch today. Through the application of a trulyunique combination of beamline facilities, we are ableto examine characteristics of surfaces, interfaces, andbulk materials in a manner heretofore inaccessible.

Figure 3: The soft x-ray spectroscopy station on beamline U7A.


To achieve this capability, CMG, led by Dr. DanielFischer, brought together a suite of three uniquehigh-throughput x-ray spectroscopy beamlines(designated U7A, X24A, and X23A2). Housed in theNational Synchrotron Light Source located at BrookhavenNational Laboratory in New York, these beamlines,taken together, can easily examine nearly all of thenaturally occurring elements in the entire periodic table.This year, the capabilities of beamline U7A, used forsoft x-ray materials science applications, weresignificantly enhanced by the addition of a 14 element,state-of-the-art, Si (Li) fluorescence yield detector,providing best-in-the-world resolution. Furtherenhancement of U7A, Figure 3, was achieved throughthe installation of a 6-axis manipulator that enables theexciting prospect of molecular alignment studies.

Figure 4: Tammy Oreskovic adds cells to a tissue-engineeredscaffold.

Building on these capabilities, CMG has initiateda long-term plan, co-funded with Sandia NationalLaboratory, for establishing a variable energy XPS(x-ray photoelectron spectroscopy) and NEXAFS/EXAFS(near edge/extended x-ray absorption fine structure)scientific program utilizing beamline X24A. A new,fully automated materials science end-station is planned,modeled after the very successful high throughputattained on U7A. The emphasis for this work willbe on the use of variable energy XPS for chemicaldepth profiling, sub-surface chemistry, and interfacechemistry.

Combinatorial Thin Film LaboratoryA new laboratory for the synthesis of inorganic

combinatorial thin-film libraries is under construction.Combinatorial methodologies can greatly acceleratethe optimization of materials in complex systems and,thus, their introduction into commercial products.The Ceramics Division’s state-of-the-art combinatorialdeposition tool will have dual capability, featuringsputtering as well as pulsed laser deposition (PLD)chambers. The tool will be used to synthesizelibraries of multilayer structures, such as advancedcomplementary-metal-oxide-silicon (CMOS) gatestack structures, in situ, for metrology developmentand characterization studies.

Tissue Engineering (TE) BioreactorsThe Center for Mechanical Behavior of Biological

Materials (CMBBM) has developed unique bioreactorsthat allow for experiments to optimize the variables that

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Figure 5: BioMEMS devices fabricated at NIST allow themeasurement of single-cell mechanical properties.


control the mechanical properties of the engineeredtissue. The bioreactors that have been developedprovide mechanical stimulation to a TE construct andmeasure mechanical properties while the tissue is beinggrown in the bioreactor. Cyclic, mechanical stimulationof TE constructs is necessary to make the constructsmore like natural tissue. In these bioreactors, we canstimulate a planar sheet of tissue/scaffold construct withan arbitrary waveform. The reactor can be configuredto apply a given force or a given displacement.The bioreactor is equipped with actuators, load cells,and view ports to conduct biaxial stress–strain testswithout removing the sample from the reactor. We areequipped with the necessary equipment to culture tissueand assess its growth and viability.

Optical TrapWe have assembled an optical trap that uses a

scanned laser at 1064 nm as the trapping source.The long wavelength allows us to make measurementson biological samples with minimal damage to cellularproteins. The scanned laser system provides multipletime-shared traps and movement of trapped objects sothat transient mechanical measurements can be made.The laser operates from 100 mW to 500 mW, providinga range of trap stiffnesses. Trap stiffnesses on theorder of 10-6 N/m are typical, which allows mechanicalmeasurement of cells, subcellular fibers and structures,DNA strands, and assembled nanoparticles.

Crack-Tip Opening AngleMechanical Testing

Better measurements of the tendency to stop arunning crack in a structure come from a new testcalled crack-tip opening angle (CTOA). This testmeasures the angle at which a crack progresses at astable rate through a material with a fatigue precrack.It has substantial advantages over its predecessor,the crack-tip opening displacement test, by allowingmultiple measurements directly at the crack tip.We are using our system to measure the crack arresttendencies of a variety of pipeline steels. Improvementsthat we make in the procedures are being fed back tothe ASTM Committee (E08.08) responsible for itsdevelopment and promulgation.

MEMS Fabrication FacilityThe fabrication facility at NIST–Boulder is a

200 square meter multifunction class 100 clean roomcapable of 50 nm linewidths. It is currently used tofabricate micro- and nanoelectromechanical systems(MEMS/NEMS/BioMEMS) which are essential tomuch of the ultra-sensitive equipment designedand used across many divisions at NIST.

From start to finish, all aspects of small-scalefabrication are available within the NIST facility.The facility includes: computer-aided design (CAD),a pattern generator (PG), a 5x wafer stepper or a 1xcontact printer with backside alignment capability,an electron beam lithography system, various sputterand e-beam deposition tools, as well as an electroncyclotron resonance (ECR) system for low-temperatureplasma-enhanced chemical vapor deposition (PECVD),a multiuse chemical vapor deposition (CVD) furnacebank, various reactive ion etching (RIE) tools, a XeF2isotropic etcher, a chemical mechanical polisher (CMP)for planarization, and a deep reactive ion etcher (DRIE).The facility is professionally staffed by experienced andknowledgeable NIST researchers.

Biaxial Membrane Test CapabilitiesThe Materials Reliability Division in Boulder,

Colorado, has a program in measuring the mechanicalbehavior of biological materials. One facet of thatprogram is to measure the biaxial, load-displacementbehavior of membrane-like tissue. That is accomplishedwith a bubble test fixture and a computer-driven systemto pressurize the specimen and collect images from fourcameras. The multiple camera angles (3 side views +stage rotatability, and 1 top view) allow capture ofanisotropic displacement behavior. We have twodifferent sized fixtures, 2.38 and 20.0 mm in diameter,so we can test materials of different thicknesses whilemaintaining the 1:10 thickness-to-diameter ratio requiredfor a valid bubble test. All tests on natural tissue areconducted in a 37 °C, phosphate-buffered saline waterbath to sustain cell viability.

Laboratory Setup andEstablishment of Cell Lines

The biological laboratory in the Materials ReliabilityDivision has approximately 400 square feet available

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within two adjacent lab areas. A fully equipped tissueculture facility is available for culturing vascular smoothmuscle cells and future osteoblast-like and fibroblastcell lines. Also, a flow bioreactor for mechanicalevaluation of biological scaffold materials with aspecially modified incubator is available. Laboratoryequipment includes a biological laminar flow hood withultraviolet lights, two water-jacketed CO2 incubators,benchtop centrifuge, liquid nitrogen storage vessel,inverted microscope with fluorescent capabilities andintegrated firewire camera and analysis software,refrigerator (4 oC)/freezers (–20 oC & –50 oC), andan automated plate reader. Additionally, a probe stationfor conducting Bio-MEMS testing and single-cellexperiments occupies one of the lab areas.

Ultrasonic Imaging andMeasurement Facilities

Our ultrasound measurement equipment includes:■ Range of ultrasonic transducers (<1 MHz up to

150 MHz);■ Calibrated hydrophone (up to 20 MHz);■ 150 MHz square-wave pulser/receiver;■ 200 MHz negative-spike pulser/receiver;■ Arbitrary waveform generator (up to 15 MHz);■ Broadband amplifier (>50 dB up to 400 MHz);■ High-frequency digitizer (1 GHz — 8-bit);■ Three-axis automated motion control system;■ Automated acquisition system;■ Temperature-controlled immersion baths;■ Custom specimen fixtures.

The acoustic microscope has been used tomeasure properties of bone, cartilage, arterial tissue,and imaging-enhancing bubbles, to date.

Microfluidic and ParticleProcessing Facility

The Polymers Division’s new microfluidic facilityenables entirely new research programs in polymerchemistry, nanoparticle assembly, and complex fluidsmetrology. This capability stems from new fabricationmethods accommodating organic complex fluids,multilayer architecture integrating functions, and flowsimulations central to device design. A suite of in-situchemical and physical measurements are brought tobear, including Raman spectroscopy, fluorescence,high-speed image analysis, electronic sensing, andrheometry. On-chip processing and production

methods comprise controlled radical synthesis, dropletformation and handling, and particle manipulationand assembly.

Two technological problems currently underexamination by exploiting these high-throughputmetrologies are polymerization-induced shrinkage ofdental resins and interfacial tension between two liquids.These applications rely on our capability to measuretwo-component flow, droplet chemistry, and droplet-shapedynamics. In addition, high-frequency on-chip particlesize analysis, using embedded electrodes, is a feature ofa more complex device that integrates particle countingand analysis, encapsulation, and automatic valvetriggering. These capabilities will enable constructionof complex nanomanufacturing operations.

Small Angle X-ray Scattering FacilityAs pattern sizes in the semiconductor electronics

industry decrease to sub-50 nm dimensions, techniques

Figure 6: Phillip Stone using microfluidic interfacial tensiometer.

Figure 7: Modeled CD-SAXS data.

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such as critical dimension-scanning electronmicroscopy (CD-SEM) face significant technicalhurdles in quantifying parameters such as Line EdgeRoughness (LER). NIST is evaluating the potentialapplication of small-angle x-ray scattering (SAXS) asa metrology tool for both process development andthe production of nanoscale dimension standards.The Polymers Division is building a laboratoryscale SAXS system to measure with sub-nanometerresolution, quantitatively and non-destructively, criticaldimensions and feature shape of patterns on productionscale test samples. This system will use a highlyfocused molybdenum source with a wavelength wheresilicon is transmissive and a two-dimensional detectorfor the evaluation of critical dimension, sidewall angle,and statistical deviations across large areas for densehigh-aspect ratio patterns with sub-50 nm dimensions.In addition to these capabilities, this facility will includestate-of-the-art SAXS equipment including a coppersource and sample handling equipment for themeasurement of nanostructured materials, fibers,and polymer solutions.

Organic Electronics CompetenceIn 2005, the Polymers Division led a successful

5-year competence proposal, “Metrology to Enablethe Realization of Organic Electronics Devices,”in collaboration with the Ceramics Division, theElectronics and Electrical Engineering Laboratory(EEEL), and the Chemical Science and TechnologyLaboratory (CSTL). In this project, NIST plans todevelop an integrated and interdisciplinary suite ofmetrologies correlating device performance with thestructure, properties, and chemistry of critical materials

and interfaces. NIST will guide the development ofstandard test methods and provide the fundamentalmeasurements needed for the development of materialsand processes to realize the potential of organic electronics.Several new capabilities have been added at NIST toachieve these goals, including the design of a controlledatmosphere glove box train, a programmable, shieldedprobe station, and new optical spectroscopy equipment.These facilities, plus the clean room facility availablein the Advanced Measurement Laboratory, allowNIST to measure both the structure of materialsand device performance.

MSEL Electron Microscopy FacilityThe MSEL Electron Microscopy Facility consists of

two transmission electron microscopes, three scanningelectron microscopes, a specimen preparation laboratory,and an image analysis/computational laboratory.

Figure 9: Evolution of texture (EBSD maps) in DQSK steelsheets. Initial conditions (left) and after 10 % uniaxial tensilestrain (right).

Figure 8: Oleksiy Anopchenko (left) and Dean DeLongchamp (right) at Organic Electronic characterization and preparation facilities.

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The JEM3010 TEM resolves the atomic structureand employs an energy selecting imaging filter (IF) andX-ray detector (EDS) for analytical characterization ofthin foil specimens. The S-4700-II FE-SEM employselectron backscattered diffraction/phase identification(EBSD) and EDS systems to characterize the textureand composition of materials.

Highlights from the EM Facility for FY2005 include:■ A new stage compatible with EBSD acquisition will

allow analysis of texture evolution under dynamicloading (tensile/compressive) conditions (see Figure 9).

■ New forward scatter detectors for the FESEM-EBSDcamera allow simultaneous, multiple mode acquisitionof secondary and backscattered electrons.

Thin Film Deposition Facility

Figure 12: NUMISHEET benchmark sample in the FormabilityStation being loaded in plane strain.

Figure 11: The two sources in the combinatorial thin-filmdeposition system are each capable of depositing up to six differentmaterials in a single deposition run.

Figure 10: The combinatorial thin-film deposition system has abase vacuum in the low 10–8 Torr (10–6 Pa) range and isequipped with a load-lock for specimen transfer.

The Thin Film and Nanostructure Processinggroup of the Metallurgy Division has two high-vacuum,electron-beam evaporator systems for fabricationof thin-film and multilayer thin-film specimens.One system has three independent 15 cc sourcesand is used for deposition of thin films and multilayerthin films of materials from lower melting metalslike aluminum, silver, and copper up to refractorymetals like ruthenium, iridium, and tungsten.The other system (Figure 10) has two independentsources (Figure 11), each capable of depositing as manyas six different materials in a single deposition run. Withits two-axis, computer-controlled specimen shutter, it isused for fabrication of combinatorial-layered as well ascompositionally graded specimens.

Sheet Metal Formability StationThe Metallurgy Division Materials Performance

Group is using the Sheet Metal Formability Station todevelop two new formability tests. The closed-loopservo-hydraulic system has 500 kN capacity for boththe ram and blank hold-down, and it is capable ofdeformation rates up to 30 s–1. A unique and importantcapability is that the system is outfitted with an in situX-ray diffraction system that makes it possible tomeasure the stress in the test specimen at discretepoints during the test. From these data, it is thenpossible to produce true-stress-true strain curves forthe multiaxial stress states encountered in forming,rather than relying on curves derived from unixial tests.

Currently the Materials Performance Group membersare producing materials property data for simulationsof prototype parts in a benchmark forming processas part of the NUMISHEET 2005 Conference.

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Figure 13: The Kolsky Bar Facility is equipped with a specialpulse-heating capability (not shown) provided by conductivebearings at the bar supports nearest the sample.

Figure 14: The Magnetic Engineering Research Facility is theworld’s most elaborately instrumented system for magneticthin-film deposition and in situ characterization.

Kolsky Bar FacilityThe Materials Performance Group of the Metallurgy

Division has developed a Kolsky or Split-Hopkinson barfacility (Figure 13) to measure the high strain-rate, highheating-rate constitutive response of metals to providedata for developing predictive models of these materialsfor use in finite element codes or other numericalanalysis techniques. A key feature of the NIST KolskyBar is the ability to rapidly heat samples prior to testing.Sufficiently rapid heating can short-circuit normaldiffusion-related microstructural changes that wouldordinarily occur under quasi-equilibrium heating.

As a result, the flow stress of rapidly heated materialscan be much different than what is measured underquasi-equilibrium conditions. There is currently a lackof such high-temperature non-equilibrium constitutivedata for most metals and alloys of interest. An importantapplication of industrial interest is high-speed machining,where rapid temperature increases occur at thetool/workpiece interface.

Magnetic Engineering Research FacilityThe Magnetic Materials Group of the Metallurgy

Division has an elaborate facility specifically designed

for advancing key enabling technologies in the fieldof ultrahigh-density data storage. It has many uniquefeatures. Films can be deposited both by the methodpreferred in basic research (molecular beam epitaxy)and by the method of industrial manufacturing (magnetronsputtering). Numerous in situ characterization techniquesare available including scanning tunneling microscopy,x-ray photoelectron spectroscopy, Auger electronspectroscopy, ion scattering spectroscopy, low-energyelectron diffraction, reflection high-energy electrondiffraction, and mass spectrometry. For in situmagnetic measurements both a superconducting magnetand an electromagnet are available and are equipped formagnetoresistance and magneto-optical Kerr effectmeasurements.

In Situ Stress Measurement Facility

Figure 15: Optical bench showing components of in situ stressmeasurement system.

Figure 16: Close-up of electrochemical cell showing cantileverelectrode.

The Thin Film and Nanostructure Processing groupof the Metallurgy Division has established a Class II(1 mW) HeNe optical bench dedicated to the in situmeasurement of surface and growth stress duringelectrochemical processing using the wafer curvature

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method. Surface stresses on the order of 0.008 N/m(23 km radius of curvature for 0.1 mm thick borosilicateglass substrates) can be resolved while the beam is insolution, sufficient to study the adsorption of molecularmonolayers onto the electrode surface. The curvatureof the substrate is monitored during electrodepositionby reflecting the laser off of the glass/metal interface,through a series of mirrors, and onto a position-sensitivedetector, Figures 15 and 16. Surface and internalstresses for metal films electrodeposited onto thesubstrate can be calculated from the deflection of thebeam as a function of time.

Supporting an increasing number of users, thereare several notable developments at the NCNR in:Sample Preparation and CharacterizationLaboratories, Commissioning of a DoubleFocusing Triple-Axis Spectrometer, Beginninginstallation of the High Intensity Multi-Axis ColdNeutron Spectrometer (MACS), Data Analysis,Visualization, and Modeling Software — DAVE II,and Deployment of Electronics for LargeDetector Arrays.

Sample Preparation andCharacterization Laboratories

The NCNR completed in 2005 the renovation ofthree, 7.3 m x 4.9 m (24 ft x 16 ft), laboratories, nearlydoubling the space and equipment available for thepreparation and characterization of samples forneutron scattering experiments by users and staff.Users preparing to come to the NCNR for anexperiment can find detailed descriptions of availablelaboratory equipment and supplies on the NCNR’swebsite at http://www.ncnr.nist.gov/userlab/.

One of the new laboratories is the result of abioengineering research partnership between the NCNRand five universities, with partial funding from theNational Institutes of Health. This Cold Neutronsfor Biology and Biotechnology (CNBT) laboratoryis equipped with a high-volume laminar flow hooddesigned for working with acids (e.g., for cleaningsubstrates); a 1.44 m3 (51 ft3) chromatographyrefrigerator; a large –40 ºC freezer; a temperaturecontrolled, 13 200 rpm microtube centrifuge; as wellas standard wet chemistry equipment for preparingbiology-related samples for diffraction, reflectometry,and SANS experiments.

One laboratory is dedicated primarily to samplecharacterization and includes equipment for dynamiclight scattering, infrared spectroscopy, UV-VisibleSpectrophotometry, gas chromatography, and an opticalmicroscope with temperature-controlled sample stage,camera, and attachments for fluorescence measurements.

Figure 17: Yamali Hernandez keeps a watchful eye on theLangmuir–Blodgett trough in one of the NCNR’s recentlyrenovated user laboratories.

This laboratory also has a rotary evaporator for purifyingsolvents and a computer controlled Langmuir–Blodgett(LB) trough (see Figure 17) for depositing multi-molecularlayer LB films on solid substrates.

In addition to the above, there are laboratorieswith specialized equipment for x-ray diffraction,solid-state chemistry, surface and interface science,and general solution chemistry. Also implemented thisyear is a bar-coding system for maintaining an accuratechemical inventory for all the laboratories. Users cannow quickly obtain Materials Safety Data Sheets anddetermine the availability, location, and quantity ofchemicals kept in any laboratory.

Commissioning of a Double FocusingTriple-Axis Spectrometer

The first measurements to characterize theperformance of the new state-of-the-art thermalneutron triple-axis spectrometer at beam port BT-7 havebeen carried out and have met expectations. The newinstrument features the choice of either a Cu(220) orPG(002) doubly-focusing monochromator, providing acontinuous incident neutron energy range from 5 meVto 500 meV. The 400 cm2 reflecting area for eachmonochromator yields as much as an order-of-magnitude gain of neutrons onto the sample comparedwith other thermal triple-axis spectrometers at theNCNR. The reactor beam and post monochromaticbeam elements (collimators, slits, and filters) offer awide range of choices to optimize the resolution andintensity of the instrument, with available fluxes wellinto the 108 n/cm2/s range.

The sample stage of the instrument includes twocoaxial rotary tables, one for sample rotation and one

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for the independent rotation of magnetic field coils,and a computer-controlled sample goniometer andelevator. Polarized 3He cells are under construction forthe instrument to provide full polarization analysis witheither one of the monochromators and any of thestandard analyzer crystals.

Figure 18: Comparison of the beam intensities (monitor countrates) for the PG(002) monochromators for the new BT-7triple-axis spectrometer and the conventional triple-axisspectrometer at BT-2. The BT-7 monochromator featuresvertical focusing that varies with energy, whereas the BT-2monochromator has a fixed vertical focus optimized for 14.7 meV.The collimation was open-50’ before and after the monochromator,respectively, on both instruments. The much larger BT-7monochromator provides more neutrons that fully illuminate thesample over a wider range of incident energies. The new doublefocusing mode is seen to provide a dramatic gain in neutronintensity by relaxing the wave vector resolution of the instrument.

Figure 19: Peter Hundertmark and Timothy Pike examine theball screw mechanism that will rotate the sample and detectoraround the green monochromatic beam transport system, whichthey designed.

the instrument is now fully operational as a triple-axisspectrometer, although the full measurement capabilityand flexibility won’t be realized until the new analyzersystem is available.

Installation of the High IntensityMulti-Axis Cold Neutron Spectrometer(MACS) Begins

While inelastic neutron scattering in principle canelucidate atomic-scale dynamics in almost any material,experiments on the most exciting new materials areoften impractical because high-quality samples are toosmall. Arguably, this is not a fundamental limitation ofthe technique but due to the lack of flux and detectionefficiency of current instrumentation. The MACSproject aims to increase both factors by an order ofmagnitude to enable informative experiments on 1 mgsamples and comprehensive maps of inelastic scatteringwhen larger samples are available.

MACS is a third generation cold neutronspectrometer and, as such, presents many fascinatingengineering challenges. In the past year, most of thesehave been overcome, and MACS is now in the midst ofa busy manufacturing and installation phase. Led byDonald Pierce, George Baltic, and Nick Maliszewskyj,the NCNR facilities engineering group has designed,procured, painted, and filled more than 50 metric tons(50 tons) of beamline shielding and beam conditioningoptics for MACS.

The BT-7 spectrometer is designed to be used withinterchangeable customized analyzer/detection systemssupported on air pads. The first new analyzer systemwill have a multi-strip PG(002) analyzer array that canbe used in a horizontally focused mode, or in a flatconfiguration either with a linear position-sensitivedetector or with conventional Söller collimators. Alloptions will be under computer control and can beselected and interchanged by the experimenter withoutrequiring any mechanical changes or user intervention.A separate diffraction detector is provided in front ofthe analyzer for Bragg peak measurements, and a seriesof 13 detectors embedded in the shielding behind theanalyzer will continuously monitor the neutron fluxentering the analyzer system. These detectors can alsobe used for measurements of the instantaneouscorrelation function, for example, or with a radialcollimator to determine a diffraction pattern over alimited angular range. This analyzer system is at anadvanced stage of development and is scheduled to beinstalled early in 2006. In the interim, a conventionalanalyzer system has been installed on air pads so that

Figure 19 shows parts of the monochromatic beamtransport system for MACS along with Timothy Pikeand Peter Hundertmark who designed it. The shieldingpenetration consists of an adjustable channel lined bym = 3.5 super mirrors that will guide a convergingmonochromatic beam to the sample position whileminimizing the aperture for fast neutrons and gamma


PG Monochromator Performance

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radiation. The ball screw actuation mechanismvisible in Figure 19 will position the super mirrorchannel, the sample table, and the detector system toreceive a monochromatic beam with energies varyingfrom 2.5 meV to 20 meV. Anticipating high-fieldsuperconducting magnet systems, all materials within750 mm of the sample position are non-magnetic.

Figure 21: Data in DAVE II can be imported, manipulated, anddisplayed in easily customizable yet sophisticated plots.

Figure 20: Stephen Smee (left) and Gregg Scharffstein with theMACS monochromating system. (The monochromator is betweenand behind them on the bench.) Not shown are Joe Orndorff andRandy Hammond who complete the team from the InstrumentDevelopment Group at Johns Hopkins University that designedand assembled the system.

Apart from the intense NCNR cold neutron source,the key to enhancing flux on sample is the monochromatingsystem, which will focus the beam from 1400 cm2 to8 cm2. It consists of a variable beam aperture tominimize background and to control wave vectorresolution, a four-position radial collimation system tocontrol energy resolution, and a translating, doublyfocusing graphite monochromator. These will inhabit ahelium-filled cask to reduce air scattering and packshielding close to the complex beamline elements.Figure 20 shows these items during tests by theInstrument Development Group at Johns HopkinsUniversity where they were designed and assembled.The monochromating system now stands ready forneutrons at the NCNR.

All the equipment described above was installed inthe beamline in the late summer and early fall of 2005.Sample stage and detector system installation will startin the fall so MACS can be ready for commissioningexperiments and friendly users in the spring of 2006.While MACS will eventually become a Center forHigh Resolution Neutron Scattering (CHRNS) userfacility for a broad range of science spanningcondensed matter physics, chemistry, and biology,principal investigators Collin Broholm and Jeff Lynnare particularly excited about the new capabilities thatMACS will provide for research in quantum magnetismand superconductivity.

Data Analysis, Visualization, andModeling Software — DAVE II

Significant development activity in the DataAnalysis and Visualization Environment (DAVE) teamover the last year has resulted in a brand new look andfeel for DAVE. DAVE II brings a new paradigm todata visualization and analysis via a novel data-centricuser-interface. The infrastructure includes a projectmanager, data manager, visualization manager,user-interface, visualization modules, and mechanismsfor easy integration of additional applications as theybecome available. All of this has been designed tohelp the user get the most from his/her neutron data.

The project manager concept promises to greatlysimplify the user experience because it allows a userto save a complete session (plots, reduction steps, dataoperations, etc.) and restore it at a later time. Moreoverthere is much greater flexibility in DAVE II with theimplementation of a document/view architecture.


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Figure 22: Preamplifier-Amplifier-Discriminator 2 (PAD2)system components.

Multiple datasets can be loaded simultaneously andmultiple views (even of the same dataset) can becreated (line, contour, image, surface and volumerenderings using OpenGL, the industry standard forhigh performance graphics). The visualizations arefeature-rich allowing simple creation of sophisticatedplots resulting in publication-quality output. Undo/redofunctionality is implemented allowing scientists toperform what-if types of analyses with ease, thusenhancing the user experience. In the initial release,support for ASCII and the current DAVE format areprovided. Operations to perform specific data analysistasks are being implemented, and the initial datareduction functionality is identical to that of thecurrent version of DAVE.

Deployment of Electronics forLarge Detector Arrays

As the number of detectors on an instrumentincreases and the detectors themselves are buried inlocations that are not readily accessible, the task oftuning the discriminator thresholds and periodicallyinspecting the banks for quality control becomes amajor undertaking. The Preamplifier-Amplifier-Discriminator 2 (PAD2) system (Figure 22), developedby the NCNR’s Jeff Ziegler and Nick Maliszewskyj, isa state-of-the art solution to the needs of instrumentswith a large number of detectors. This systemconsists of compact front-end modules combining thefunctions of preamplifier, amplifier, and discriminator;concentrator boards that multiplex control anddata signals for eight front-end units; and a system

controller that can set the gain and signal threshholdsfor a collection of up to 2048 individual detectors.The differential signal levels employed allow for longercable runs and greatly improved noise rejection overthe existing TTL solutions. Live quality control isnow possible thanks to in situ pulse height analysis.A single point of control makes it possible to tune thediscriminator settings for detectors behind shieldingor in vacuo. Taken in combination, the capabilitiesof this new system are groundbreaking and surpassanything available commercially. The system wassuccessfully deployed on the 32-detector BT-1 powderdiffractometer and the HFBS backscatteringspectrometer in 2005.


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Databases

Databases

SRD 31: Phase Equilibria DataT.A. Vanderah

The Phase Equilibria Data project is a joint effortof NIST and the American Ceramic Society (ACerS).Working together, NIST and ACerS have publishedmore than 20,000 diagrams depicting graphicalrepresentations of the regions of distinct chemicaland structural behavior of materials in thermodynamicequilibrium. The diagrams are distributed by ACerS intraditional printed volumes and in a modern searchablePC database system. Phase Equilibria Diagrams,Volume XIV, Oxides, completed this year and unveiledat the annual ACerS meeting in April, contains figuresnumbered from 10841 to 11637 and covers oxidesystems originally published in the literature between1980 and 2004 and not previously included in the series.

SRD 83: NIST Structural DatabaseV.L. Karen

The NIST Structural Database (NSD) containsevaluated crystallographic data (lattice parameters,atomic positions, and symmetry classifications) formetallic crystalline substances, including alloys,intermetallics, and minerals. The data set is licensedfor use in both personal computers and instrumentation.This year’s updates doubled the accessible data to morethan 16,000 records.

SRD 84: FIZ–NIST Inorganic CrystalStructure DatabaseV.L. Karen

The Inorganic Crystal Structure Database (ICSD) isproduced cooperatively by the FachinformationszentrumKarlsruhe (FIZ) and the National Institute of Standardsand Technology (NIST). The ICSD is a comprehensivecollection of crystal structure data for inorganiccompounds. In addition to the full three-dimensionalcrystal structure data, chemical composition, reducedcell symmetry data, and bibliographic information, theICSD includes enhanced features for the characterizationof materials based on lattice and chemistry search modules,3-dimensional visualization, and powder pattern simulationof inorganic structures. Two updates this year addedapproximately 2000 entries and brought the totalnumber of entries to more than 70,000.

SRMsThe Ceramics Division is the world’s leading producerof x-ray Certified Reference Materials. Last year,determination of the amorphous content of NISTStandard Reference Material® (SRM) 676 (the primaryinternal standard for quantitative analysis by x-raydiffraction) launched a recertification effort for a suiteof additional SRMs also utilized in quantitative analysis.Recertification now has been completed for SRMs656 (two mixtures of α and β phases of silicon nitride),674b (oxide powders for internal intensity standards),and 1878a (respirable quartz) and 1879a (respirablecristobalite) for quantitative analysis in occupationalsafety and health applications.

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Recommended Practice Guides


SP960-1: Particle Size CharacterizationAjit Jillavenkatesa, Stanley J. Dapkunas,and Lin-Sien H. LumThe consequences of improper particle size analysesinclude poor product quality, high rejection rates, andeconomic losses. Hence, the ceramic manufacturingindustry and the broad range of applications utilizingpowders have a strong and active interest in themetrology required for accurately determining thedistribution of particle sizes in a powder. This Guidedescribes the techniques most commonly used formeasurement of particle size and size distribution,including sieving, gravitational sedimentation, laserlight diffraction, and microscopy-based methods.The capabilities and limitations of these techniquesare examined together with discussions of thegeneral principles on which the techniques are based.The Guide includes discussions of the fundamentalissues in representative sampling, the procedures andprecautions generally followed for sample preparationand analysis, and the assessment of sources of error, bias,and other potential variations in the measurement results.

SP960-2: The Fundamentals ofNeutron Powder DiffractionJohn R.D. CopleyThis Recommended Practice Guide introduces thereader to neutron powder diffraction, a powerfultechnique that complements x-ray diffraction as ameans to determine crystal structures. The principaldifferences between the x-ray and neutron techniquesare discussed, and several examples of applications tomaterials of industrial interest are described.

SP960-3: The Use of Nomenclature inDispersion Science and TechnologyVincent A. Hackley and Chiara F. FerrarisMeasurements and standards enhance reliability inmanufacturing by providing a common basis forquantifying and comparing material properties duringeach phase of the manufacturing process, from rawmaterials to the finished product. Underlying this ability,and essential to its success, is the use of a well-defined,widely accepted, and uniformly applied nomenclature.An established nomenclature significantly enhancesthe accuracy and efficiency of the descriptions ofexperimental methods and instrumentation, facilitatesthe sharing of technical ideas and concepts, andprovides a sound basis on which to standardizemeasurement methods and data reporting practices.This Guide was prepared as a resource for researchers,

engineers, and students working on dispersion-basedapplications. While emphasizing commonly encounteredterms, every effort was made to maintain a degree ofuniformity with existing standards and conventions toprovide a consistent framework for improved technicalcommunication. The result was a comprehensiveglossary of terms related to the central issues indispersion science and technology.

SP960-4: Installing, Maintaining, andVerifying Your Charpy Impact MachineDaniel P. Vigliotti, Thomas A. Siewert, andChris N. McCowanThe quality of the data developed by pendulum impactmachines depends on how well the machines areinstalled, maintained, and verified. This is the reasonthat ASTM Standard E 23 Standard Test Methods forNotched Bar Impact Testing of Metallic Materialsspecifies annual direct and indirect verification tests.Each year, NIST provides reference specimens forindirect verification of over 1000 machines around theworld. From evaluation of the absorbed energies andthe fractured specimens, we attempt to deduce theorigin of energies that are outside the ranges permittedby Standard E 23 and report these observations backto the machine owners. This Recommended PracticeGuide summarizes the bases for these observationsand, hopefully, will allow machines to be maintainedat higher levels of accuracy. In addition, we providedetails of the NIST verification program proceduresand the production of the specimens.

SP960-5: Rockwell HardnessMeasurement of Metallic MaterialsSamuel R. LowThe Rockwell hardness test continues to be applied asa tool for assessing the properties of a product whilethe tolerances on the acceptable material hardness havebecome tighter and tighter. Adhering to “good practice”procedures when performing Rockwell hardnessmeasurements and calibrations is a beneficial step toreducing measurement errors. The purpose of thisGuide is to explain the causes of variability in Rockwellhardness test results and to supplement the informationgiven in test method standards with good practicerecommendations. Although this Guide is directedmore towards the users of Rockwell hardnesshaving the greatest concern for accuracy in theirmeasurements, much of the information given is alsoapplicable for users that only require test results to bewithin wide tolerance bands, where high accuracy isnot as critical.

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SP 960-7: Capacitance CellMeasurement of the Out-of-PlaneExpansion of Thin FilmsChad Snyder and Frederick MopsikThis Guide describes the construction, use, and dataanalysis methods for a capacitance-based metrologyfor robust and highly accurate measurement of theout-of-plane expansion of films between 2 µm and1 cm in thickness. This metrology was developedbecause the coefficient of thermal expansion (CTE)continues to be a critical design parameter for thesemiconductor electronics industry and is increasinglyimportant to nanotechnology applications, as it isneeded to estimate the stresses generated by thermaldifferentials. In response to a lack of robust methodsfor measuring the out-of-plane expansion of thinpolymer films in the thickness range between thecapabilities of typical thermomechanical analyzers(TMA) and x-ray reflectometers, NIST developed thiscapacitance-based measurement technique. This guideclosely examines the sources of error associated withthe metrology, and the descriptions are sufficientlydetailed that the reader should be able to reproducethe metrology and achieve its typical measurementreproducibility upon thermal cycling of ±2 µm/m.

SP960-8: Test Procedures forDeveloping Solder DataThomas A. Siewert and Carol A. HandwerkerThis publication documents standardized testprocedures that can produce valid and reproduciblemechanical-property data for lead-free solders.Such data speeds the application of lead-free soldersin high-volume, automated production of electronicassemblies, especially when current productionexpectations combine high levels of quality with thelowest cost. Use of standardized procedures facilitatesthe comparison of data between laboratories andpermits the combination of data from differentsources into a single, comprehensive database.

Most dimensions and temperatures are listedwithout tolerances. Unless otherwise specified, use± 5 % on dimensions, times, and pressures, and ± 3 °Cfor temperatures.

Many of the procedures assume some skill inthe arts of specimen production and testing. Varioustextbooks and industry brochures (some listed in theBibliography) can provide background informationon these skills and any hazards associated withthese procedures.

SP960-9: Surface EngineeringMeasurement Standards forInorganic MaterialsStanley J. DapkunasApplications as diverse as medical implants and gasturbines have been the beneficiaries of the substantialaccomplishments in the surface engineering ofmaterials. Characterizations of surfaces andmeasurements of surface properties have becomevital to systems design, maintenance, and analysisand, hence, to the commerce that depends on thosesystems. This Guide identifies pertinent propertiesand characteristics of engineered surfaces andprovides descriptions of the most prevalent standardtest methods applied to the measurement or assessmentof those characteristics. The type of data producedusing each method is described as well as the specimenrequirements, the intended application, and the limitsof the method. An extensive cross index of keywords allows identification of standards by method,property, or type of material.

SP960-10: X-Ray TopographyDavid R. Black and Gabrielle G. LongThe study of the interrelationships among processing,structure, and properties is fundamental to the field ofmaterials science and engineering. The important roleof microstructure in these relations has driven thedevelopment of a wide variety of x-ray basedcharacterization techniques, including the techniqueof x-ray topography (XRT). This powerful toolprovides a nondestructive means of imaging the defectmicrostructure of crystals for defects in the sizerange of micrometers to centimeters. This technique,however, has been underutilized in the United States.Consequently, this guide was developed to make thetechnique more accessible to materials scientists whocan benefit from the rich variety of microstructuralinformation it offers. The basic principles and practicalaspects of topography are discussed, and numerousexamples are presented to illustrate the diversity ofapplications that can benefit from this technique.

SP960-11: Data Evaluation Theoryand Practice for Materials PropertiesRonald G. MunroTechnology thrives on data, and advances in scienceare propelled by advances in data. It follows that thequality of the available data is a concern of centralimportance to all of science and engineering. Theprocess by which collections of data are assessed withrespect to reliability, completeness, and consistency is

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known as data evaluation. This guide addresses dataevaluation for materials properties as a scientificdiscipline that evolves from the formal underpinningsof materials metrology. After carefully establishing atheoretical foundation, an extensive collection ofexamples is used to examine, in succession, the issuesof accessibility, reproducibility, consistency, andpredictability. Distinctions are made among definitiverelations, correlations, derived and semi-empiricalrelations, heuristic theories, and value estimates.Special subtopics include the use of properties asparameters in models, the interpretation of ad hocparameters, and the treatments of procedural properties,response dependent properties, and system dependentdata. The principles and practices set forth in thiswork serve as a guide to data evaluation across manydisciplines, wherever considerations of numericproperty data are crucial to the interpretation andapplication of quantitative observations.

SP 960-13: Pore Characterization inLow-k Dielectric Films Using X-rayReflectivity: X-ray PorosimetryChristopher L. Soles, Hae-Jeong Lee,Eric K. Lin, and Wen-li WuThis recommended practice guide describes theequipment and methodology for quantifying the averagepore size, pore size distribution, and wall density in thinfilms where the sample mass is prohibitively small fortraditional porosimetry measurements. This methodwas initially developed for nanoporous low-dielectric-constant thin films needed for the further advancementof semiconductor devices where in-house structuralcharacterization methods are needed to evaluatecandidate materials and processing methods, but canbe easily generalized to other nanoporous thin films.The developed porosimetry method uses X-rayreflectivity to measure the density of the film whilegradually increasing or decreasing of the partialpressure of condensate vapors such as toluene inthe presence of the film. The change in film densitycan be directly related to the amount of adsorbedcondensate, and thus porosity, if the density of thecondensed fluid is known. Monitoring the amountof adsorbed condensate as a function of the partialpressure defines a physisorption isotherm, thebasic starting point for any number of analyticalinterpretations. The X-ray Porosimetry RecommendedPractice Guide provides detailed information so thatthis knowledge and expertise may be transferred toindustrial research and university laboratories. It ishoped that X-ray porosimetry will be widely adoptedfor the evaluation and characterization of newlydeveloped nanoporous thin-film materials.

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Ceramics Division FY04 Annual Report Publication List

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