Lecture Notes Nanomaterials

7/29/2019 Lecture Notes Nanomaterials

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MM-407: NANOSTRUCTURED MATERIALS

NANOTECHNOLOGY

Nanotechnology deals with small structures or small-sized materials

Prefix of nanotechnology i.e. nanoscomes from the Greek word for dwarf

Nanometer (nm) is one billionth of a meter, or l0-9 m

One nanometer is approximately the lengthequivalent to 10 hydrogen or 5silicon atoms alignedin a line

Small features permit more functionality


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Physical Properties of Nanomaterials

Copper which is an opaque substance becometransparent.

Platinum which is an inert material become catalyst.

Aluminum which is a stable material turns

combustible.

Silicon insulators become conductors.

Gold which is solid, inert and yellow on roomtemperature at micro scale becomes liquid and red incolor at nano scale on room temperature. It also gets

unusual catalytic properties not seen at macro scale.


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Nanotechnology Definitions

The development and use of devices that have a size

of only a few nanometreswww.physics.about.com

Research and technology development at the atomic,molecular or macromolecular level in the length scaleof approximately 1 - 100 nm range, to provide afundamental understanding of phenomena andmaterials at the nanoscale and to create and usestructures, devices and systems that have novel

properties and functions because of their small and/orintermediate size.

www.nano.gov

Branch of engineering that deals with things smallerthan 100 nm (especially with the manipulation ofindividual molecules).

www.hyperdictionary.com

The art of manipulating materials on an atomic ormolecular scale especially to build microscopicdevices.

Miriam Webster Dictionary


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Nanotechnology, or, as it is sometimes called,molecular manufacturing, is a branch of engineeringthat deals with the design and manufacture of

extremely small electronic circuits and mechanicaldevices built at the molecular level of matter.

www.whatis.com


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OLD NANOTECHNOLOGY

Stained-glass windows

Silver-Halide Photography

AR-coated lenses(anti-reflecting)

Viruses are nanomachinesNEW NANOTECHNOLOGY

Vastly improved catalysts enhance surface areato volume ratios

Designer drugs

Cheap, sensitive medical diagnostics

Transparent Sunblock

Nanotube-strengthened cables

Difference:Designing and manipulating at the molecular level whereasbefore it was either evolution that did it for us or results


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happened which we never really understood and socouldnt optimize

HISTORY OF SCIENTIFIC REVOLUTIONS

Discovery type Name Age Start date

Industrial Tools Stone2,200,000

BC

Industrial Metallurgy Bronze 3500BC

Industrial Steam power Industrial 1764

Automation Mass production Consumer 1906

Automation Computing Information 1946

HealthGeneticEngineering

Genetic 1953

Industrial Nanotechnology Nano age 1991

AutomationMolecularassemblers

Assemblerage?

2020?

Health, industrial,automation

Life assemblers Life age 2050?

Wilson et al. 2002. Nanotechnology: basic science and emergingtechnologies. Chapman & Hall/CRC. New York.


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PERSPECTIVE OF SIZE

Water molecules 3 atoms

DNA molecules millions of atoms

Carbon nanotubes millions of atoms

Molecule of DNA

Carbon nanotubes


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Examples of zero-dimensional nanostructures or nanomaterialswith their typical ranges of dimension


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SURFACE VS. VOLUME

a

Diamond unit cell

Si has a diamond structure with a = 5.43 A Si nanocube 10 nm on a side is composed of:~6250 unit cells

~50,000 atoms

Each nanocube face is composed of:~340 unit cells per face~680 surface atoms per faceTotal surface area is:~4080 atoms (~10% surface atoms)

A bulk Si film 1 m thick on a 10 cm square:~6.3 X 1019 unit cells~5 X 1020 atoms~1.4 X 1017 surface atoms (~0.03% surface atoms)


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MORE THAN SIZE.

Interesting phenomena:

Chemical Take advantage of large surface to volume ratio,interfacial and surface chemistry important, systemstoo small for statistical analysis

Electronic Quantum confinement, bandgap engineering, changein density of states, electron tunneling

Magnetic Giant magneto-resistance by nanoscale multilayers,change in magnetic susceptibility

Mechanical

Improved strength hardness in light-weightnanocomposites and nanomaterials, altered bending,compression properties, nanomechanics of molecularstructures


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Optical Absorption and fluorescence of nanocrystals, single

photon phenomena, photonic band gap engineeringFluidic Enhanced flow properties with nanoparticles,nanoscale adsorbed films important

Thermal Increased thermoelectric performance of nanoscalematerials, interfacial thermal resistance important


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WHAT ARE NANOSTRUCTURES?

At least one dimension is between 1 - 100 nm

2-D structures (1-D confinement): Thin films

Planar quantum wells Superlattices

1-D structures (2-D confinement): Nanowires Quantum wires Nanorods

Nanotubes

0-D structures (3-D confinement): Nanoparticles Quantum dots

Dimensionality, confinement depends on structure: Bulk nanocrystalline films Nanocomposites


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THIN FILMS

Nanoscale Thin Film

Single two dimensional film, thickness < ~100nm

Electrons can be confined in one dimension;affects wavefunction, density of states

Phonons can confined in one dimension; affectsthermal transport

Boundaries, interfaces affect transport


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FABRICATION OF NANOSTRUCTURES AND

NANOMATERIALS

Group according to the growth media:

(1) Vapor phase growth, including laser reaction

pyrolysis for nanoparticle synthesis and atomiclayer deposition (ALD) for thin film deposition.

(2) Liquid phase growth, including colloidalprocessing for the formation of nanoparticles andself assembly of monolayers.

(3) Solid phase formation, including phasesegregation to make metallic particles in glassmatrix and two-photon induced polymerizationfor the fabrication of three-dimensional photoniccrystals

.

4) Hybrid growth, including vapor-liquid-solid(VLS) growth of nanowires.


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Group the techniques according to the form ofproducts:

(1) Nanoparticles by means of colloidal processing,flame combustion and phase segregation.

(2) Nanorods or nanowires by template-basedelectroplating, solution liquid solid growth(SLS),and spontaneous anisotropic growth.

(3) Thin films by molecular beam epitaxy (MBE)and atomic layer deposition (ALD).

(4) Nanostructured bulk materials, for example,photonic bandgap crystals


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CHALLENGES IN NANOTECHNOLOGY

Integration of nanostructures/nanomaterials intoor with macroscopic systems that can interfacewith people

Building & demonstration of novel tools tostudy at the nanometer level what is beingmanifested at the macro level

The small size and complexity of nanoscale

structures make the development of newmeasurement technologies

New measurement techniques need to bedeveloped at the nanometer scale and mayrequire new innovations in metrological

technology.

Measurements of physical properties ofnanomaterials require extremely sensitive


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instrumentation, while the noise level must be keptvery low.

FABRICATION AND PROCESSING OF

NANOMATERIALS THE FOLLOWING

CHALLENGES MUST BE MET:

(1) Overcome the huge surface energy, a result

of enormous surface area or large surface tovolume ratio.

(2) Nanomaterials with desired size, uniformsize distribution, morphology, crystallinity,chemical composition, and microstructure

(3) Prevent nanomaterials and nanostructuresfrom coarsening through either Ostwald ripeningor agglomeration as time evolutes.

For the fabrication of nanoparticles, a small sizeis not the only requirement.


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PRACTICAL APPLICATION

&

PROCESSING CONDITIONS FOR

NANOMATERIALS

(i) Identical size of all particles (also calledmonosized or with uniform sizedistribution)

(ii) Identical shape or morphology,

(iii) Identical chemical composition andcrystal structure that are desired amongdifferent particles and within individual

particles, such as core and surface

composition must be the same


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(iv) Individually dispersed or mono-dispersed, i.e. no agglomeration.

If agglomeration does occur,nanoparticles should be readily

redispersible.EXCITING APPLICATIONS OF

NANOTECHNOLOGY INCLUDE:

Nanopowdersthe unusual properties of particles less than 100 nmallow a range of new and improved materials with a

breadth of applications, such as plastics that behavelike ceramics or metals; new catalysts forenvironmental remediation; improved food shelf-lifeand packaging; and novel drug delivery devices.

Carbon nanotubes graphite can be rolled into acylinder with a diameter of about 1 nm. These strongbut light carbon nanotubes are being developed fora raft of uses, such as sensors, fuel cells, computersnd televisions.

Nanomembrane filtration systems these have

the potential to address one of the most pressingissues of the 21st Century safe, clean, affordablewater.


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Molecular electronic cross bar latchesHewlett-Packard believes that silicon computer chipswill probably reach a technical dead end in about a

decade, to be replaced by tiny nanodevices describedas cross bar latches.

Quantum dots these are small devices thatcontain a tiny droplet of free electrons essentiallyartificial atoms. The potential applications areenormous, such as counterfeit-resistant inks, new bio-sensors, quantum electronics, photonics and the

possibility of tamper-proof data transmission.

New technologies for clean and efficient energygeneration.


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Nanostructures

Definition:

A nanostructure is an object of intermediate sizebetween molecular and microscopic (micrometer-sized) structures.

Number of dimensions on the nanoscale

Nanotextured surfaces one dimension on nanoscale

i.e., only the thickness of the surface of an object isbetween 0.1 and 100 nm.

Nanotubes have two dimensions on the nanoscale,i.e., the diameter of the tube is between 0.1 and 100nm; its length could be much greater.

Spherical nanoparticles have three dimensions onthe nanoscale,
http://en.wikipedia.org/wiki/Molecularhttp://en.wikipedia.org/wiki/Microscopichttp://en.wikipedia.org/wiki/Micrometrehttp://en.wikipedia.org/wiki/Structurehttp://en.wikipedia.org/wiki/Nanoscalehttp://en.wikipedia.org/wiki/Nanotubeshttp://en.wikipedia.org/wiki/Nanoparticleshttp://en.wikipedia.org/wiki/Molecularhttp://en.wikipedia.org/wiki/Microscopichttp://en.wikipedia.org/wiki/Micrometrehttp://en.wikipedia.org/wiki/Structurehttp://en.wikipedia.org/wiki/Nanoscalehttp://en.wikipedia.org/wiki/Nanotubeshttp://en.wikipedia.org/wiki/Nanoparticles


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i.e., the particle is between 0.1 and 100 nm in eachspatial dimension.

The terms nanoparticles and ultrafine particles (UFP)

often are used synonymously although UFP can reachinto the micrometer range.

Two approaches to the synthesis of nanomaterials and the fabrication ofnanostructures:

1) Top-down2) Bottom-up

Attrition or milling is a typical top-down methodin making nanoparticles.

Colloidal dispersion is a good example of bottom-upapproach in the synthesis of nanoparticles.

Lithography may be considered as a hybrid approach,since the growth of thin films is bottom-up whereasetching is top-down, while nanolithography and
http://en.wikipedia.org/wiki/Ultrafine_particleshttp://en.wikipedia.org/wiki/Ultrafine_particles


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nanomanipulation are commonly a bottom-upapproach.

BOTTOM-UP APPROACH

Build-up of a material from the bottom:

atom-by-atom molecule-by-molecule

In organic chemistry and/or polymer science, weknow polymers are synthesized by connectingindividual monomers together.

In crystal growth, growth species, such as atoms, ionsand molecules, after impinging onto the growthsurface, assemble into crystal structure one afteranother.

AdvantagesLess defects,Homogeneous chemical composition,Better short and long range ordering


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ReasonDriven mainly by the reduction of Gibbs

free energy,, therefore closer to athermodynamic equilibrium state

Examples:

Production of salt and nitrate in chemical industry,

Growth of single crystals and deposition of films inelectronic industry.

For most materials, there is no difference in physicalproperties of materials regardless of the synthesisroutes, provided that chemical composition,

crystallinity, and microstructure of the material inquestion are identical.

Top-down Approach

DisadvantagesIntroduces internal stress,Surface defects (i.e. imperfections)Contaminations


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SOLID SURFACES PHYSICAL CHEMISTRY

Nanomaterials possess a large fraction of surfaceatoms per unit volume.

The ratio of surface atoms to interior atoms changeson dividing macroscopic object into smaller parts.

The total surface energy increases with the overall

surface area.

Large surface energy therefore thermodynamicallyunstable or metastable


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The percentage of surface atoms changes with the palladium clusterdiameter.


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SURFACE ENERGY REDUCTION

(i) Surface RelaxationThe surface atoms or ions shift inward

(ii) Surface RestructuringCombining surface dangling bonds into new bonds


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Original Restructured

(iii) Surface adsorptionChemical or physical adsorption of terminalchemical species onto the surface by forming

chemical bonds or weak attraction forces such aselectrostatic or van der Waals forces

(iv) Composition segregation or impurity enrichmentThrough solid-state diffusion.

AGGLOMERATION OF INDIVIDUAL

NANOSTRUCTURES

(1) SinteringIndividual structures merge togetherPolycrystalline material

(2) Ostwald ripeningLarge structures grow at the cost of

smaller onesAppreciable solubility in a solvent


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Single uniform structure

(a) Sintering (b) Ostwald ripening

Sintering

Solid-state diffusion(i) Surface diffusion

Requires the smallest activation energyStart at relatively low temperature

(ii) Volume diffusion

Require moderate temperatures,

Volume diffusion dominates

(iii) Cross grain-boundary diffusion

Requires highest activation energySignificant only at high temperatures


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Evaporation-condensation

Nanomaterials have an appreciable vapor pressure atthe processing temperature.

Dissolution-precipitation

Solid is dispersed in a liquid in which the solid ispartially soluble


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Vapor pressure of a number of liquids as a function of dropletradius


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Variation in solubility of silica with radius of curvature of surface


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OSTWALD RIPENING

Can have either positive or negative influence on theresulting materials, depends on process & application

Can either widen or narrow the size distribution,depending on the control of the process conditions

Abnormal grain growth, leading to inhomogeneousmicrostructure and inferior mechanical properties

Specifically, it has been used to narrow the sizedistribution of nanoparticles by eliminating small one

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Lecture Notes Nanomaterials

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