14
Introduction to Analytical Electron Microscopy
Introduction to Analytical Electron Microscopy
Introduction to Analytical Electron Microscopy
Edited by
JohnJ.Hren University of Florida Gainesville, Florida
Joseph I. Goldstein Lehigh University Bethlehem, Pennsylvania
and
David C. Joy Bell Laboratories Murray Hill, New Jersey
SPRINGER SCIENCE+BUSINESS MEDIA, LLC
SPONSORS:
Electron Microscopy Society of America
Microbeam Analysis Society
Library of Congress Cataloging in Publication Data
Main entry under title:
Introduction to analytical electron microscopy.
Inc1udes index. 1. Electron microscopy. I. Hren, John J. II. Goldstein, Joseph,1939-
III. Joy, David, 1943-TA417.23.I57 502'.8 79-17009 ISBN 978-1-4757-5583-1 ISBN 978-1-4757-5581-7 (eBook) DOI 10.1007/978-1-4757-5581-7
This volume contains the proceedings of a workshop on Analytical Electron Microscopy, held in San Antonio, Texas, August 13-14, 1979, as part of the joint meeting of the Electron Microscopy Society of America and the Microbeam Analysis Society.
© 1979 Springer Science+Business Media New York Originally published by Plenurn Press, New York in 1979 Softcover reprint ofthe hardcover lst edition 1979
All righ ts reserved
No part of this book may be reproduced, stored in a retrieval system, Of transmitted, in any form or by any means, electronic, mechanical, photocopying, microfilming, record ing, or otherwise, without written permission from the Publisher
PREFACE
The birth of analytical electron microscopy (AEM) is somewhat obscure. Was it the recognition of the power and the development of STEM that signaled its birth? Was AEM born with the attachment of a crystal spectrometer to an otherwise conventional TEM? Or was it born earlier with the first analysis of electron loss spectra? It's not likely that any of these developments alone would have been sufficient and there have been many others (microdiffraction, EDS, microbeam fabrication, etc.) that could equally lay claim to being critical to the establishment of true AEM. It is probably more accurate to simply ascribe the present rapid development to the obvious: a combination of ideas whose time has come.
Perhaps it is difficult to trace the birth of AEM simply because it remains a point of contention to even define its true scope. For example, the topics in this book, even though very broad, are still far from a complete description of what many call AEM. When electron beams interact with a solid it is well-known that a bewildering number of possible interactions follow. Analytical electron microscopy attempts to take full qualitative and quantitative advantage of as many of these interactions as possible while still preserving the capability of high resolution imaging.
Although we restrict ourselves here to electron transparent films, much of what is described applies to thick specimens as well. Not surprisingly, signals from all possible interactions cannot yet (and probably never will) be attained simultaneously under optimum conditions. As a'consequence there is a variety of analytical electron microscopes (home-built and commercial) with a wide array of possible accessories. Since most current AEM's are converted TEM's, this book allots considerable space to the special problems inherent to the transformation of a TEM into an AEM. It is likely that most of these problems will be absent from future generations of commercial instruments. User feedback (i.e., your complaints) has been an important feature of instrument development and will continue to remain so. This process will never end, of course, since we will never have the ideal microscope that does everything perfectly for everyone at all times!
A few words about the development of this book and its purposes are in order. The need for such a volume became apparent to the societies and to the editors through the widespread response of attendees to the annual meetings of EMSA and MAS at sessions organized under the var-
v
vi Preface
ious guises of AEM. In effect, the membership voted for greater coverage with their feet. Having established the need, it remained to define a suitable mechanism for satisfying it. It was clear that no single author, or even a reasonable number of co-authors, could write a suitable textbook within the forseeable future. A combined multi -authored and edited book accompanying a tutorial was selected as the most efficient means to achieve the proper level and scope of coverage. The selection of the subjects and their coverage is the responsibility of the editors. Like the instrument manufacturers, we look to the readers for comments (that is, "constructive criticism") so that future volumes of a similar nature may be improved.
Because of the press of publication deadlines for the annual meeting, there will undoubtedly remain minor errors, both technical and typographical in this volume. With 22 co-authors and the variety of material presented, the depth of coverage also varies somewhat. We judged these to be tolerable imperfections under the circumstances, since the alternatives were not satisfactory.
Analytical electron microscopy is ripe for application today. The proven methods described in this volume can and should be widely utilized by the research community as soon as possible. If this occurs, as seems likely, AEM promises to open up still more research doors down to the atomic level. We eagerly await this response.
A book like this (and the associated workshop) could not take place without the generous cooperation and assistance of many people. We first deeply thank our co-authors without whom nothing could have been done. Their efforts will be remembered and welcomed. Secondly, we are truly heartened by the fine cooperation of both societies who were willing to risk such a venture and then to back it wholeheartedly. We hope their confidence has been well-placed. Thirdly, we thank Ellis Rosenberg and Steve Dyer of Plenum Press for their flexible and understanding attitudes and for their cooperation throughout this enterprise. Finally, we thank the multitude of editorial assistance at the University of Florida. In particular, we are deeply indebted to Jerry Lehman, his mother, Irene Lehman, and JoAnne Upham, who labored heroically over mounds of paper with the word processer, aud to Pam Fugate, Linda King, and Vicki Turner for stellar secretarial assistance.
John Hren
David Joy
Joe Goldstein
TABLE OF CONTENTS
CHAPTER 1 PRlNCIPLES OF IMAGE FORMATION
1.1
1.2
1.3 1.4
1.5
1.6
1.7
1.8
Introduction Electron Scattering and Diffration The Physical Optics Analogy Diffraction Patterns Mathematical Formulation
The Abbe Theory of Imaging Incident Beam Convergence Chromatic Aberration Mathematical Formulation
Inelastic Scattering STEM and CTEM STEM Imaging Modes Mathematical Description
Thin, Weakly Scattering Specimens Beam Convergence and Chromatic Aberration Mathematical Formulation
Thin, Strongly Scattering Specimens Mathematical Formulation
Thin, Periodic Objects: Crystals Special Imaging Conditions Mathematical Formulation
Thicker Crystals Lattice Fringes Mathematical Considerations
1.9 Very Thick Specimens Mathematical Descriptions
1.10 Conclusions Classical and General References Other References
INTRODUCTORY ELECTRON OPTICS CHAPTER 2
2.1 Introduction Geometrical Optics Refraction
2.2
2.3
Cardinal Elements Real and Virtual Images Lens Equations Paraxial Rays
Electrostatic Lenses Refraction Action of Electrostatic Lenses Types of Electrostatic Lenses
J.M. COWLEY
1
7
12 13
18
23
25
30
34
36
R.H. GEISS
43 43
49
vii
viii
2.4
2.5
2.6
2.7 2.8
Magnetic Lenses Action of a Homogeneous Field Action of an Inhomogeneous Field Paraxial Ray Equations Bell Shaped Field Lens Excitation Parameters wand k2
Cardinal Elements of Magnetic Lenses Objective Lenses Lens Aberrations and Defects Special Magnetic Lenses
Prism Optics Magnetic Sectors Electrostatic Sectors Wein Filter
Optics of the Electron Microscope Introduction Electron Gun Condenser Lens System Coherence Magnification Lens Systems
Comparison of CTEM and STEM Optics Conclusion
References
CHAPTER 3 PRINCIPLES OF THIN FILM X-RA Y MICROANALYSIS
3.1 3.2
Introduction Quantitative X-ray Analysis Primary Emitted X-ray Intensities Quantitative X-ray Analysis Using the Ration Technique and Thin Film Criterion Limitations of the Thin Film Criterion Absorption Correction Fluorescence Correction
3.3 Spatial Resolution Analytical and Computer Models Measurements of Spatial Resolution
3-4 Sensitivity Limits 3.5 Summary Acknowledgments References
Contents
53
69
72
77
J.I. GOLDSTEIN
83 84
100
109 117
CHAPTER 4 QUANTITATIVE X-RA YMICROANALYSIS: INSTURMENTAL N.J. ZALUZEC
CONSIDERATIONS AND APPLICATIONS TO MATERIALS SCIENCE
4.1 4.2 4.3
4.4
4.5
Introduction Instrumental Limitations in AEM Based X-ray Microanalysis Instrumental Artifacts: Systems Background Fluorescence by Uncollimated Radiation: Remote Sources Fluorescence by Uncollimated Radiation: Local Sources Specimen Contamination Detector Artifacts
Optimum Experimental Conditions for X-ray Analysis Detector/Specimen Geometry Detector Collimation Selection of Incident Beam Energy and Electron Source Imaging and Diffraction Conditions During Analysis Specimen Preparation Artifacts
Data Reduction for Quantitative Analysis
121 121 122
130
137
Contents
4.6
4.7
4.8
4.9
Application of Quantitative X-ray Microanalysis: Parameters of Standardless Analysis Absorption Correction
Applications of Standardless Analysis Standardless Analysis Using the n.in·Film Approximation: Fe·13Cr-40Ni Standardless Analysis Using the Absorption Correction: NiA1
Standardless Analysis in Complex Systems Analysis of Totally Buried Peaks Quantitative Analysis of Precipitated Phases Procedures for Analysis of Radioactive Specimen.
Summary Acknowledgments References Tables
139
149
155
CHAPTERS EDS QUANTITATION AND APPLICATION TO BIOLOGY T.A. Hall and B.L. GUPTA
5.1 5.2
Introduction Measurements on Thin or Ultrathin Sections Mounted on Thin Films Elemental Ratios Millimoies of Element Per Unit Volume M.ilIimoles of Element Per kg of Dried Tissue (Continuum Method) Millimole. of Element Per kg Wet Weight (Continuum Method, Frozen.Hydrated Sections) Dry.Weight and Aqueous Fractions Conversion to mM of Element Per Litre of Water Absorption Corrections Standards
5.3 Effects of Contamination Within the Microscope Column 5.4 Effects of Beam Damage 5.5 Specimen Preparation 5.6 Specimens Other Than Sections Mounted on Thin Film Main literature References list of Symbols Used in this Article Subscripts References Appendix I
Derivation of Equation 5.12 for Dry-Weight Determination
Appendix II Sample Calculations Calculations
CHAPTER 6 MONTE CARW SIMULATION IN ANALYTICAL ELECTRON
169 170
180 181 182 183
MICROSCOPY DAVID F. KYSER
6.1 6.2
6.3
6.4
Introduction Basic Physical Concepts in Monte Carlo Simulation Electron Scattering Energy Loss Between Elastic Scattering Events Sequence of Calculations Spatial Distribution of Energy Loss and X-ray Production
Design, Implementation, and Output of a Monte Carlo Program Computer Generation and Utilization of Random Numbers Computational TIme and Its Control Condensation and Output of Results Obtained
Applications to X-ray Microanalysis Depth Distribution of X-ray Production Total X-ray Production in Foils Radial Distribution of X-ray Production Electron Trajectory Plotting
199 200
206
208
ix
x
6.5 Summary Acknowledgments References
CHAPTER 7 THE BASIC PRINCIPLES OF ELECTRON ENERGY LOSS SPECTROSCOPY
7.1 7.2 7.3 7.4
7.5 7.6 7.7 7.8
What is Electron Energy Loss Spectroscopy? What is Required? Describing the Energy Loss Spectrum The Micro-Analytical Information in the EEL Specimen Region 1 . Around Zero·Loss Region 2 . The Low·Loss Region Region 3 . Higher Energy Losses
Collecting the Energy Loss Spectrum Recording and Analyzing the Data The Effects of Specimen Thickness To Summarize
References
CHAPTER 8 ENERGY LOSS SPECTROMETRY FOR BIOLOGICAL RESEARCH
8.1 8.2 8.3
8.4
8.5
8.6
Introduction Characteristics of a Typical Spectrum Sensitivity of ELS Techniques Elemental Microanalysis Chemical and Molecular Microanalysis
Approaches to the Quantitative Use of ELS Elemental Microanalysis Ch emical Microanaly sis Molecular Microanalysis Dielectric Constant Determination
Examples of Typical Experimental Results Experimental Spectra Low Z Elemental Mapping Molecular Species Mapping Extended Fine Structure (EXAFS)
Practical Limitations Radiation Damage i Mass Loss ii Bond Scission Specimen Thickness i Effect on Background and Peak Heights ii Specimen Mass Thickness Effects in Mapping
8.7 Summary References Classic References
Contents
219
DA VID C. JOY
223 223 225 227
236 239 241 242
DALE E. JOHNSON
245 245 247
248
249
253
257
CHAPTER 9 ELEMENTAL ANALYSIS USING INNER-SHELL EXCITATIONS: A MICROANALYTICAL TECHNIQUE FOR MATERIALS
9.1 9.2
CHARACTERIZATION DENNIS M. MAHER
Introduction Basic Considerations Spectrum Dynamic Range Spectral Background Edge Shapes
259 260
Contents
9.3
9.4
9.5
Progress in Quantitation Analysis Methods Method 1: Efficiency Factors Method 2: Calculated Partial Cross Sections Method 3: Standards Tests of Analysis Methods Stability of Quantitation Methods Relative Accuracy of Atomic Ratios Absolute Accuracy of Quantitation Future Considerations
Elemental Identification Threshold Energy Shape Analysis Elemental Maps
Detection Limits Importance of f3 Minimum Detectable Limits
9.6 Summary References
265
281
285
287
CHAPTER 10 ANALYSIS OF THE ELECTRONIC STRUCTURE OF SOLIDS JOHN SILCOX
10.1 Introduction 10.2 Scattering Kinematics 10.3 Inner-Core Excitations 10.4 Valence Electron Excitations Final Comments Acknowledgments References
CHAPTER 11 STEM IMAGING OE CRYSTALS AND DEFECTS
11.1 Introduction 11.2 Principle of Reciprocity in STEM and CTEM
Reciprocity of Electron Microscopes Reciprocity and the Coherence of the Source and Detector The Inapplicability of Reciprocity for Thick Specimens Qualitative Reciprocity of the Top-Bottom Effect Procedure if Reciprocity is not Applicable
11.3 Image Recording and SignaljNoise Signal/Noise and Reciprocity Z-Contrast Applied to Materials
11.4 The Optimum Beam Divergences for Imaging Crystal Defects Typical Values of aand f3 in CTEM and STEM Effects of Varying f3s on STEM Images Two-Beam Dynamical Theory Interpretation Choice of Optimum f3s Value
11.5 The Identification of Crystal Defects Properties of Dislocation Images Properties of Stacking Fault Images
11.6 The Breakdown of the Column Approximation in STEM The Nature of the Column Approximation High Resolution STEM Image Calculations Without the Column Approximation
11.7 Penetration in Crystals Using CTEM and STEM Defmition of Penetration Factors Limiting the Penetration of CTEM (W Filament) Penetration in STEM The Penetration in STEM and CTEM The Top-Bottom Effect
295 296 300 302
c.j. HUMPHREYS
305 306
310
312
317
320
323
xi
xii
11.8 Current Developments in the STEM Imaging of Defects Post Specimen Lenses On-Line Optical Image Processing Lattice Imaging High Voltage STEM In-Situ Imaging and Analysis
Acknowledgments References Classical References
CHAPTER 12 BIOLOGICAL SCANNING TRANSMISSION ELECTRON MICROSCOPY
12.1 Introduction 12.2 Quantitative Measurement with the STEM
Length Mass Substrate Noise Heavy Atom Signal Resolution Specimen Modification During Imaging
12.3 Conclusion Acknowledgments References
CHAPTER 13 ELECTRON MICROSCOPY OF INDIVIDUAL
Contents
327
J. WALL
333 335
341
ATOMS M. ISAACSON, M.OHTSUKI and M. UTLAUT
13.1 Introduction 13.2a Basics - Electron Scattering 13.2b Basics - Operation 13.3a Practical Considerations - Electron Optics
Probe Formation Further Stability Requirements
13.3b Practical Considerations - Specimen Preparation Low Noise Support Films
13.3c Practical Considerations - Clean Support Films Heavy Atom Contamination
13.3d Practical Considerations - Organic Contaminants 13.4 How to Visualize an Atom 13.5 Some Examples of Single Atom Microscopy 13.6 Conclusion Acknowledgment References
CHAPTER 14 MICRODIFFRACTION
14.1 Introduction 14.2 Focused Probe Microdiffraction 14.3 Focused Aperture Microdiffraction 14.4 Rocking Beam Microdiffraction 14.5 Applications 14.6 Summary References
343 344 346 347
352
355
357 357 360 366
J.B. WARREN
369 371 373 375 377 383
Contents
CHAPTER 15 CONVERGENT BEAM ELECTRON DIFFRACTION l.W. STEEDS
15.1 Introduction Development of Convergent Beam Diffraction The Microscope TEMMode STEM Mode Intermediate Configurations Effects Connected with the Specimen Beam Broading Beam Heating Perfection of the Specimen Contamination Goniometry
15.2 The Dimensional Electron Diffraction Higher Order Laue Zones Diameters of Holz Rings Indexing and Origin of Holz Lines i Indexing ii Origin of Lines Lattice Parameter Determination Determination of the Reciprocal Lattice Space Group Determination Measurement of Chemical Variations and Strains
15.3 Crystal Point and Space Groups Use of High Symmetry Zone Axes Point Group Determination Determination of the Reciprocal Lattice Space Group Determination Handedness of ~ Cry stal
15.4 Atomic Arrangements Intensities of Holz Reflections Atomic String Approximation
15.5 Finger Printing Techniques 15.6 Crystal Potential and Thickness Determination Acknowledgments References
387
395
406
412
416 417
CHAPTER 16 RADIATION DAMAGE WITH BIOLOGICAL SPECIMENS AND ORGANIC MATERIALS ROBERT M. GLAESER
16.1 Introduction 423 16.2 Primary Events in Radiation Physics and Radiation Chemistry 425 16.3 Empirical Studies of Radiation Damage Effects Measured Under Conditions
Used in the Electron Microscope 428 16.4 Signal-to-Noise Considerations at Safe Electron Exposures 429 16.5 Additional Processes of Radiation Damage that Occur at Very High Electron
Exposures 432 Acknowledgments References
CHAPTER 17 RADIATION EFFECTS IN ANALYSIS OF INORGANIC SPECIMENS BY TEM L. W. HOBBS
17 .1 Introduction Radiation Damage in Compact Lattices Electron-Atom Inelastic Interaction Electron-Beam Heating Charge Acquisition by Insulating Specimens
437
xiii
xiv
17.2 Knock-On Displacement Displacement Energy Momentum Transfer
17.3 Radiolysis Electronic Excitations Energy-to-Momentum Conversion Influence of Temperature, Impurity and Radiation Flux
17.4 Degradation Kinetics 17.5 Radiation-Induced Structural Changes During Analysis
Frenkel Defect Condensation i Planar Aggregates ii Volume Inclusions Ordering and Disordering Segregation and Precipitation
17.6 Minimizing The Effects of Irradiation Reducing the Electron Dose Reducing the Temperature
17.7 Conclusions References
Contents
444
450
457 460
472
476
CHAPTER 18 BARRIERS TO AEM: CONTAMINATION AND ETCHING J.J. HREN
18.1 18.2 18.3 18.4 18.5 18.6 18.7 18.8 18.9
Introduction Some Defmitions Early Observations of Contamination The Nature of the Contaminant Relationship Between Contamination and Etching Surface Diffusion and Beam Size Effects Recent Studies of Contamination and Etching Summary of Phenomenological Observations The Mechanisms of Contamination Physiosorption of Hydrocarbon Molecules Surface Diffusion of Hydrocarbon Molecules Polymerization and Fragmentation of Hydrocarbon Molecules in the Electron Beam Beam Induced Thermal Gradients Electrical Gradients in the Surface
481 481 482 483 484 486 487 490 491
18.10 The Mechanisms of Etching 495 Physiosorption of a Potentially Reactive Gas Activation of the Reactive Gas by Electrons Specimen or Contaminant Molecules that Will React with the Excited Physiosorbed Gas The Reactant Molecules must be Volatile
18.11 Working Solutions: Proven and Potential 497 18.12 Some Effects of Contamination and Etching on AEM 500 References
CHAPTER 19 MICROANALYSIS BY LATTICE IMAGING
19.1 19.2
19.3 19.4 19.5 19.6 19.7
Introduction Theoretical Considerations Fringe Imaging Specimen-Related Parameters Microscope Parameters Multi-Beam Imaging
Experimental Procedures Analysis of Fringe Images Composition Determination Experimental Examples Future Directions
ROBERT SINCLAIR
507 508
515 520 521 524 527
Contents
19.8 Summary Acknowledgments References Note on Key References
530
CHAPTER 20 WEAK-BEAM MICROSCOPY JOHN B. VANDER SANDE
20.1 20.2
20.3
Introduction Theoretical Background Strong·Beam Images Weak-Beam Images
The Practice of Weak-Beam Microscopy Instrumental Needs Establishing a Weak-Beam Condition
i The Ewald Sphere Construction for Strong-Beam Microscopy ii The Ewald Sphere Construction for Weak-Beam Microscopy iii Determining the Deviation Parameter, s
20.4 Applications of Weak-Beam Microscopy Separation of Partial Dislocations Dense Defect Arrays: Dislocation Dipoles, Dislocation Tangles, and Dislocation Cell Walls Precipitation on Dislocation Lines: Second Phase Particle Interfaces Comments
Acknowledgments References
CHAPTER 21 THE ANALYSIS OF DEFECTS USING COMPUTER SIMULATED
535 536
539
543
IMAGES PETER HUMBLE
21.1 Introduction 21.2 Theory and Computational Considerations 21.3 Experimental Method and the Conection of Information 21.4 Examples of the Use of Simulated Images in the Analysis of Defects 21.5 The Context of this Technique in AEM References Major References
551 552 559 560 571
CHAPTER 22 THE STRATEGY OF ANALYSIS RON ANDERSON and J.N. RAMSEY
22.1 22.2 22.3 22.4 22.5
Introduction Where to Begin? Specimen Type Strategy Identification-Solving Unknown Phases and Structures with AEM Input AEM and Complimentary Technique Examples AI-Cu Thin Film Corrosion AI-Cr Films and AI-Hf Films Organic Residue on Fired Thick Film Conductors Premature Collector - Base Breakdown
Acknowledgments References
575 575 576 583 586
xv
