INTERPRETATION OF TRANSMISSION ELECTRON MICROGRAPHS

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1 3 INTERPRETATION OF TRANSMISSION ELECTRON MICROGRAPHS

2 Already published in this series 1. The Operation and Calibration of the Electron Microscope 2. Electron Diffraction in the Electron Microscope In preparation 4. Typical Electron Microscope Investigations

3 Philips Technical Library Monographs in Practical Electron Microscopy in Materials Science 3 INTERPRETATION OF TRANSMISSION ELECTRON MICROGRAPHS J. W. EDINGTON Department of Metallurgy and Materials Science, University of Cambridge, Cambridge, England M

4 N.Y. Philips' Gloeilampenfabrieken, Eindhoven, 1975 Reprint of the original edition All rights reserved. No part of this publication may be reproduced or transmitted, in any form or by any means, without permission. This book is sold subject to the standard conditions of the Net Book Agreement. SBN ISBN ISBN (ebook) DOI / First published 1975 by THE MACMILLAN PRESS LTD London and Basingstoke Associated companies in New York, Dublin, Melbourne, Johannesburg and Madras ~PHILIPS Trademarks of Philips' Gloeilampenfabrieken

5 PREFACE This is the third of a series of monographs on electron microscopy aimed at users of the equipment. They are written as both texts and sources of reference emphasising the applications of electron microscopy to the characterisation of materials. In some places the author has referred the reader to material appearing in other monographs of this series. The following titles have already been published: 1. The Operation and Calibration of the Electron Microscope 2. Electron Diffraction in the Electron Microscope and in preparation is: 4. Typical Eh:ctron Microscope Investigations BF DF CDF WB DP SADP SRO APB g s eg w b bp J1 FN B ANO Abbreviations and Symbols Frequently Used in this Monograph Bright field (image) Dark field (image) Centred dark field (image) Weak beam (image) Diffraction pattern Selected area diffraction pattern Short-range order Antiphase domain boundary A vector normal to the reflecting plane The deviation from the Bragg reflection position The extinction distance seg The Burgers vector of an undissociated dislocation The Burgers vector of a partial dislocation The line vector of a dislocation The upward drawn foil normal (normal to the specimen surface) The upward drawn incident beam direction in the specimen, that is opposite to the direction of the electron beam Anomalous absorption coefficient

6 CONTENTS 3. INTERPRETATION OF TRANSMISSION ELECTRON MICROGRAPHS 3.1 IMAGE CONTRAST I. DIFFRACTION CONTRAST 3.2 SUMMARY OF THEORY The Perfect Crystal Absorption Characteristic Images of Perfect Crystals Thickness fringes Bend extinction contours Bend contours Bend centres Crystal Containing a Defect with a Strain Field 3.3 RELEVANCE OF DIFFRACTION THEORY TO STUDIES OF CRYSTAL DEFECTS Experimental Conditions for Quantitative Analysis Recognition of Dynamical and Kinematical Diffracting Conditions Microscope II. QUANTITATIVE ANALYSIS OF CRYSTAL DEFECTS 3.4 DISLOCATIONS A Simple Treatment of Dislocation Images Images of Perfect Dislocations Elastically isotropic materials Elastically anisotropic materials Determination of the Burgers Vector of Perfect Dislocations Elastically isotropic materials Elastically anisotropic materials Images of Partial Dislocations (bp < Lattice Translation Vector) Fault invisible Fault visible A partial dislocation between extrinsic and intrinsic faults Determination of the Burgers Vector of Partial Dislocations Image Characteristics of Slightly Dissociated Partial Dislocations Overall Procedure for Determining the Burgers Vector of Dislocations Image Characteristics of the Special Case of End-on Dislocations Determination of the Sense of the Burgers Vector of End-on Dislocations Image Characteristics of Dislocation Pairs Image Characteristics of Dislocation Dipoles Faulted Dipoles 3.5 DISLOCATION LOOPS Large Loops (Diameter~ 500 A) Quantitative Information Image Characteristics of Medium-sized Loops (Diameter A) Quantitative Information Image Characteristics of Small Loops (Diameter ~ 100 A) g b #: g b = Quantitative Information Determination of the Burgers vector Determination ofthe vacancy/interstitial sense ofthe loop in the Electron

7 viii Contents 3.6 oc BOUNDARIES, STACKING FAULTS, PLANAR PRECIPITATES Image Characteristics of Stacking Faults Single stacking faults oc = 0, ±2n/3, ±4n/3, ±2n Overlapping stacking faults Quantitative Information on Stacking Faults Identification Determination of the direction of the displacement Rn Determination of the extrinsic/intrinsic nature Image Characteristics of Plate Precipitates Quantitative Information on Plate Precipitates 3.7 1t BOUNDARIES: ANTIPHASE DOMAIN BOUNDARIES Image Characteristics Single boundaries Overlapping boundaries Quantitative Information 3.8 ~ BOUNDARIES Image Characteristics Single boundaries Overlapping boundaries Quantitative Information 3.9 MIXED OC-~ BOUNDARIES Image Characteristics Quantitative Information 3.10 INTERFACES Image Characteristics of Interfaces Between Like Crystal Structures Low-angle boundaries High-angle boundaries Twin boundaries Quantitative Information on Interfaces Between Like Crystal Structures Low-angle boundaries High-angle boundaries Twin boundaries Image Characteristics of Precipitate-Matrix Interfaces Coherent interfaces Partially coherent interfaces Incoherent interfaces Quantitative Information on Precipitate-Matrix Interfaces Coherent interfaces Partially coherent interfaces Incoherent interfaces 3.11 STRAIN FIELD IMAGES FROM SMALL MISFITTING PRECIPITATES Image Characteristics P. ~ P. ~ Quantitative Information Determination of the sense ofthe strain field Estimation ofthe magnitude of the misfit e Image Characteristics of Misfitting Plate Precipitates Quantitative Information on Misfitting Plate Precipitates 3.12 CAVITIES Image Characteristics Quantitative Information

8 3.13 GAS BUBBLES Image Characteristics Quantitative Information Contents 3.14 VISIBILITY OF DEFECTS IN STRAIN FIELD DIFFRACTION CONTRAST IMAGES 3.15 DIFFERENTIATION BETWEEN SIMILAR TYPES OF IMAGES 3.16 MANY-BEAM EFFECTS Extinction Distance Images Perfect crystals Dislocations Misfitting precipitates Stacking faults 3.17 WEAK BEAM IMAGES Image Characteristics Dislocations Dislocation loops Applications ix SUMMARY OF THEORY III. PHASE CONTRAST IV. APPLICATIONS OF PHASE CONTRAST TO STUDIES OF CRYSTALS LATTICE PLANE RESOLUTION (TWO- OR THREE-BEAM IMAGES) The Perfect Crystal Crystal Imperfections MULTI-BEAM LATTICE IMAGES 3.21 MOIRE PATTERNS Parallel Rotational Mixed Magnification Summary Applications Detection 3.22 DARK FIELD IMAGES OF SHORT-RANGE ORDERED (SRO) OR AMORPHOUS MATERIALS 3.23 MAGNETIC DOMAIN BOUNDARIES (LORENTZ MICROSCOPY) Types of Domain Boundary Diffraction Pattern Effects Image Characteristics Fresnel images (out offocus) Foucault images (in focus) Diffraction contrast images Applications Determination of magnetisation direction Measurement of domain wall thickness Determination of magnetisation Determination of Curie temperature Determination of anisotropy constant K Observations of Magnetic Flux Lines 3: Recommended Reading 3 : References

9 X Contents APPENDIX 3. ELASTIC CONSTANTS 97 Appendix 3: References 101 APPENDIX 8. ATOMIC SCATTERING AMPLITUDES 103 Appendix 8: Reference 103 APPENDIX 10. EXTINCTION DISTANCES IN SOME COMMON MATERIALS 105 Appendix 10: References 105 APPENDIX 11. VALUES OF g b FOR PERFECT DISLOCATIONS IN f.c.c. 107 AND c.p.h. CRYSTAL STRUCTURES APPENDIX 12. PREPARATION OF HIGH-RESOLUTION TEST SPECIMENS 109 A12.1 SINGLE-CRYSTAL (100) GOLD FILMS 109 A12.2 PARTIALLY GRAPHITISED CARBON BLACK 109 A12.3 REPLICAS FOR POINT-TO-POINT RESOLUTION TESTS 109 Appendix 12: References Appendix 13: References APPENDIX 13. HOLEY CARBON REPLICAS

Imaging with Diffraction Contrast

$Imaging with Diffraction Contrast$ Imaging with Diffraction Contrast Duncan Alexander EPFL-CIME 1 Introduction When you study crystalline samples TEM image contrast is dominated by diffraction contrast. An objective aperture to select either