1. Introduction ................................................. 1
1.1. Transmission Electron Microscopy ........................ 1
1.1.1. Conventional Transmission Electron Microscopy .... 1
1.1.2. High-Resolution Electron Microscopy .............. 3
1.1.3. Analytical Electron Microscopy ................... 5
1.1.4. Energy-Filtering Electron Microscopy ............. 7
1.1.5. High-Voltage Electron Microscopy ................. 7
1.1.6. Dedicated Scanning Transmission Electron
Microscopy ....................................... 9
1.2. Alternative Types of Electron Microscopy ............... 10
1.2.1. Emission Electron Microscopy .................... 10
1.2.2. Reflection Electron Microscopy .................. 11
1.2.3. Mirror Electron Microscopy ...................... 11
1.2.4. Scanning Electron Microscopy .................... 12
1.2.5. X-ray and Auger-Electron Microanalysis .......... 14
1.2.6. Scanning-Probe Microscopy ....................... 14
2. Particle Optics of Electrons ................................ 17
2.1. Acceleration and Deflection of Electrons ............... 17
2.1.1. Relativistic Mechanics of Electron
Acceleration .................................... 17
2.1.2. Deflection by Magnetic and Electric Fields ...... 20
2.2. Electron Lenses ........................................ 22
2.2.1. Electron Trajectories in a Magnetic Lens
Field ........................................... 22
2.2.2. Optics of an Electron Lens with a Bell-Shaped
Field ........................................... 25
2.2.3. Special Electron Lenses ......................... 29
2.3. Lens Aberrations ....................................... 31
2.3.1. Classification of Lens Aberrations .............. 31
2.3.2. Spherical Aberration ............................ 32
2.3.3. Astigmatism and Field Curvature ................. 34
2.3.4. Distortion ...................................... 36
2.3.5. Coma ............................................ 37
2.3.6. Anisotropic Aberrations ......................... 38
2.3.7. Chromatic Aberration ............................ 38
2.4. Correction of Aberrations and Microscope Alignment ..... 40
2.4.1. Correction of Astigmatism ....................... 40
2.4.2. Correction of Spherical and Chromatic
Aberrations ..................................... 42
2.4.3. Microscope Alignment ............................ 43
3. Wave Optics of Electrons .................................... 45
3.1. Electron Waves and Phase Shifts ........................ 45
3.1.1. De Broglie Waves ................................ 45
3.1.2. Probability Density and Wave Packets ............ 49
3.1.3. Electron-Optical Refractive Index and the
Schrodinger Equation ............................ 51
3.1.4. Electron Interferometry and Coherence ........... 53
3.2. Fresnel and Fraunhofer Diffraction ..................... 55
3.2.1. Huygens' Principle and Fresnel Diffraction ...... 55
3.2.2. Fresnel Fringes ................................. 59
3.2.3. Fraunhofer Diffraction .......................... 61
3.2.4. Mathematics of Fourier Transforms ............... 63
3.3. Wave-Optical Formulation of Imaging .................... 70
3.3.1. Wave Aberration of an Electron Lens ............. 70
3.3.2. Wave-Optical Theory of Imaging .................. 73
4. Elements of a Transmission Electron Microscope .............. 77
4.1. Electron Guns .......................................... 78
4.1.1. Physics of Electron Emission .................... 78
4.1.2. Energy Spread ................................... 81
4.1.3. Gun Brightness .................................. 82
4.1.4. Thermionic Electron Guns ........................ 84
4.1.5. Schottky Emission Guns .......................... 88
4.1.6. Field-Emission Guns ............................. 89
4.2. The Illumination System of а ТЕМ ....................... 90
4.2.1. Condenser-Lens System ........................... 90
4.2.2. Electron-Probe Formation ........................ 93
4.2.3. Illumination with an Objective Prefield Lens .... 96
4.3. Specimens .............................................. 98
4.3.1. Useful Specimen Thickness ....................... 98
4.3.2. Specimen Mounting ............................... 99
4.3.3. Specimen Manipulation .......................... 100
4.4. The Imaging System of а ТЕМ ........................... 103
4.4.1. Objective Lens ................................. 103
4.4.2. Imaging Modes of а ТЕМ ......................... 104
4.4.3. Magnification and Calibration .................. 107
4.4.4. Depth of Image and Depth of Focus .............. 108
4.5. Scanning Transmission Electron Microscopy (STEM) ...... 109
4.5.1. Scanning Transmission Mode of ТЕМ .............. 109
4.5.2. Dedicated STEM ................................. 112
4.5.3. Theorem of Reciprocity ......................... 113
4.6. Electron Spectrometers and Imaging Energy Filters ..... 115
4.6.1. Postcolumn Prism Spectrometer .................. 116
4.6.2. Wien Filter .................................... 119
4.6.3. Imaging Energy Filter .......................... 119
4.6.4. Operating Modes with Energy Filtering .......... 124
4.7. Image Recording and Electron Detection ................ 126
4.7.1. Fluorescent Screens ............................ 126
4.7.2. Photographic Emulsions ......................... 127
4.7.3. Imaging Plate .................................. 131
4.7.4. Detector Noise and Detection Quantum
Efficiency ..................................... 132
4.7.5. Low-Light-Level and Charge-Coupled-Device
(CCD) Cameras .................................. 134
4.7.6. Semiconductor and Scintillation Detectors ...... 138
4.7.7. Faraday Cages .................................. 139
5. Electron-Specimen Interactions ............................. 141
5.1. Elastic Scattering .................................... 141
5.1.1. Cross Section and Mean Free Path ............... 141
5.1.2. Energy Transfer in an Electron-Nucleus
Collision ...................................... 143
5.1.3. Elastic Differential Cross Section for Small-
Angle Scattering ............................... 146
5.1.4. Total Elastic Cross Section .................... 152
5.2. Inelastic Scattering .................................. 153
5.2.1. Electron-Specimen Interactions with Energy
Loss ........................................... 153
5.2.2. Differential Cross Section for Single-
Electron Excitation ............................ 156
5.2.3. Bethe Surface and Compton Scattering ........... 158
5.2.4. Approximation for the Total Inelastic Cross
Section ........................................ 162
5.2.5. Dielectric Theory and Plasmon Losses in
Solids ......................................... 163
5.2.6. Surface-Plasmon Losses ......................... 171
5.3. Energy Losses by Inner-Shell Ionization ............... 174
5.3.1. Position and Shape of Ionization Edges ......... 174
5.3.2. Inner-Shell Ionization Cross Sections .......... 177
5.3.3. Energy-Loss Near-Edge Structure (ELNES) ........ 179
5.3.4. Extended Energy-Loss Fine Structure (EXELFS) ... 182
5.3.5. Linear and Circular Dichroism .................. 183
5.4. Multiple-Scattering Effects ........................... 184
5.4.1. Angular Distribution of Scattered Electrons .... 184
5.4.2. Energy Distribution of Transmitted Electrons ... 186
5.4.3. Electron-Probe Broadening by Multiple
Scattering ..................................... 188
5.4.4. Electron Diffusion, Backscattering, and
Secondary-Electron Emission .................... 192
6. Scattering and Phase Contrast for Amorphous Specimens ...... 195
6.1. Scattering Contrast ................................... 196
6.1.1. Transmission in the Bright-Field Mode .......... 196
6.1.2. Dark-Field Mode ................................ 201
6.1.3. Examples of Scattering Contrast ................ 202
6.1.4. Improvement of Scattering Contrast by Energy
Filtering ...................................... 205
6.1.5. Scattering Contrast in the STEM Mode ........... 208
6.1.6. Measurement of Mass Thickness and Total Mass ... 209
6.2. Phase Contrast ........................................ 211
6.2.1. The Origin of Phase Contrast ................... 211
6.2.2. Defocusing Phase Contrast of Supporting
Films .......................................... 212
6.2.3. Examples of Phase Contrast ..................... 215
6.2.4. Theoretical Methods for Calculating Phase
Contrast ....................................... 216
6.2.5. Imaging of a Scattering Point Object ........... 218
6.2.6. Relation between Phase and Scattering
Contrast ....................................... 220
6.3. Imaging of Single Atoms ............................... 221
6.3.1. Imaging of Single Atoms in ТЕМ ................. 221
6.3.2. Imaging of Single Atoms in the STEM Mode ....... 225
6.4. Contrast-Transfer Function (CTF) ...................... 228
6.4.1. The CTF for Amplitude and Phase Specimens ...... 228
6.4.2. Influence of Energy Spread and Illumination
Aperture ....................................... 230
6.4.3. The CTF for Tilted-Beam and Hollow-Cone
Illumination ................................... 233
6.4.4. Contrast Transfer in STEM ...................... 236
6.4.5. Phase Contrast by Inelastically Scattered
Electrons ...................................... 237
6.4.6. Improvement of the CTF Inside the Microscope ... 238
6.4.7. Control of the CTF by Optical or Digital
Fourier Transform .............................. 238
6.5. Electron Holography ................................... 241
6.5.1. Fresnel and Fraunhofer In-Line Holography ...... 241
6.5.2. Single-Sideband Holography ..................... 244
6.5.3. Off-Axis Holography ............................ 245
6.5.4. Reconstruction of Off-Axis Holograms ........... 246
6.6. Image Restoration and Specimen Reconstruction ......... 249
6.6.1. General Aspects ................................ 249
6.6.2. Methods of Optical Analog Filtering ............ 250
6.6.3. Digital Image Restoration ...................... 252
6.6.4. Alignment by Cross-Correlation ................. 254
6.6.5. Averaging of Periodic and Aperiodic
Structures ..................................... 255
6.7. Three-Dimensional Reconstruction ...................... 258
6.7.1. Stereometry .................................... 258
6.7.2. Electron Tomography ............................ 259
6.8. Lorentz Microscopy .................................... 262
6.8.1. Lorentz Microscopy and Fresnel Diffraction ..... 262
6.8.2. Imaging Modes of Lorentz Microscopy ............ 264
6.8.3. Imaging of Electrostatic Specimen Fields ....... 270
7. Theory of Electron Diffraction ............................. 273
7.1. Fundamentals of Crystallography ....................... 274
7.1.1. Bravais Lattice and Lattice Planes ............. 274
7.1.2. The Reciprocal Lattice ......................... 279
7.1.3. Construction of Laue Zones ..................... 282
7.2. Kinematical Theory of Electron Diffraction ............ 283
7.2.1. Bragg Condition and Ewald Sphere ............... 283
7.2.2. Structure Amplitude and Lattice Amplitude ...... 285
7.2.3. Column Approximation ........................... 289
7.3. Dynamical Theory of Electron Diffraction .............. 292
7.3.1. Limitations of the Kinematical Theory .......... 292
7.3.2. Formulation of the Dynamical Theory as
a System of Differential Equations ............. 293
7.3.3. Formulation of the Dynamical Theory as an
Eigenvalue Problem ............................. 294
7.3.4. Discussion of the Two-Beam Case ................ 298
7.4. Dynamical Theory Including Absorption ................. 302
7.4.1. Inelastic-Scattering Processes in Crystals ..... 302
7.4.2. Absorption of the Bloch-Wave Field ............. 306
7.4.3. Dynamical n-Beam Theory ........................ 311
7.4.4. The Bethe Dynamical Potential and the
Critical Voltage Effect ........................ 313
7.5. Intensity Distribution in Diffraction Patterns ........ 317
7.5.1. Diffraction at Amorphous Specimens ............. 317
7.5.2. Intensity of Debye-Scherrer Rings .............. 318
7.5.3. Influence of Thermal Diffuse Scattering ........ 321
7.5.4. Kikuchi Lines and Bands ........................ 323
7.5.5. Electron Spectroscopic Diffraction ............. 326
8. Electron-Diffraction Modes and Applications ................ 329
8.1. Electron-Diffraction Modes ............................ 329
8.1.1. Selected-Area Electron Diffraction (SAED) ...... 329
8.1.2. Electron Diffraction Using a Rocking Beam ...... 331
8.1.3. Electron Diffraction Using a Stationary
Electron Probe ................................. 332
8.1.4. Electron Diffraction Using a Rocking
Electron Probe ................................. 336
8.1.5. Further Diffraction Modes in ТЕМ ............... 338
8.2. Some Uses of Diffraction Patterns with Bragg
Reflections ........................................... 342
8.2.1. Lattice-Plane Spacings ......................... 342
8.2.2. Texture Diagrams ............................... 343
8.2.3. Crystal Structure .............................. 345
8.2.4. Crystal Orientation ............................ 347
8.2.5. Examples of Extra Spots and Streaks ............ 349
8.3. Convergent-Beam Electron Diffraction (CBED) ........... 352
8.3.1. Determination of Point and Space Groups ........ 352
8.3.2. Determination of Foil Thickness ................ 352
8.3.3. Charge-Density Distributions ................... 353
8.3.4. High-Order Laue Zone (HOLZ) Patterns ........... 354
8.3.5. HOLZ Lines ..................................... 355
8.3.6. Large-Angle CBED ............................... 357
9. Imaging of Crystalline Specimens and Their Defects ......... 359
9.1. Diffraction Contrast of Crystals Free of Defects ...... 360
9.1.1. Edge and Bend Contours ......................... 360
9.1.2. Dark-Field Imaging ............................. 362
9.1.3. Moire Fringes .................................. 365
9.1.4. The STEM Mode and Multibeam Imaging ............ 367
9.1.5. Energy Filtering of Diffraction Contrast ....... 369
9.1.6. Transmission of Crystalline Specimens .......... 370
9.2. Calculation of Diffraction Contrast of Lattice
Defects ............................................... 373
9.2.1. Kinematical Theory and the Howie-Whelan
Equations ...................................... 373
9.2.2. Matrix-Multiplication Method ................... 375
9.2.3. Bloch-Wave Method .............................. 376
9.3. Planar Lattice Faults ................................. 378
9.3.1. Kinematical Theory of Stacking-Fault
Contrast ....................................... 378
9.3.2. Dynamical Theory of Stacking-Fault Contrast .... 379
9.3.3. Antiphase and Other Boundaries ................. 383
9.4. Dislocations .......................................... 385
9.4.1. Kinematical Theory of Dislocation Contrast ..... 385
9.4.2. Dynamical Effects in Dislocation Images ........ 390
9.4.3. Weak-Beam Imaging .............................. 391
9.4.4. Determination of the Burgers Vector ............ 394
9.5. Lattice Defects of Small Dimensions ................... 396
9.5.1. Coherent and Incoherent Precipitates ........... 396
9.5.2. Defect Clusters ................................ 398
9.6. High-Resolution Electron Microscopy (HREM) of
Crystals .............................................. 400
9.6.1. Lattice-Plane Fringes .......................... 400
9.6.2. General Aspects of Crystal-Structure Imaging ... 402
9.6.3. Methods for Calculating Lattice-Image
Contrast ....................................... 405
9.6.4. Simulation, Matching, and Reconstruction
of Crystal Images .............................. 407
9.6.5. Measurement of Atomic Displacements in HREM .... 409
9.6.6. Crystal-Structure Imaging with a Scanning
Transmission Electron Microscope ............... 411
9.7. Imaging of Atomic Surface Steps and Structures ........ 412
9.7.1. Imaging of Surface Steps in Transmission ....... 412
9.7.2. Reflection Electron Microscopy ................. 416
9.7.3. Surface-Profile Imaging ........................ 418
10.Elemental Analysis by X-ray and Electron Energy-Loss
Spectroscopy ............................................... 419
10.1.X-ray and Auger-Electron Emission ..................... 419
10.1.1.X-ray Continuum ................................ 419
10.1.2.Characteristic X-ray and Auger-Electron
Emission ....................................... 421
10.2.X-ray Microanalysis in a Transmission Electron
Microscope ............................................ 425
10.2.1.Wavelength-Dispersive Spectrometry ............. 425
10.2.2.Energy-Dispersive Spectrometry (EDS) ........... 427
10.2.3.X-ray Emission from Bulk Specimens and ZAF
Correction ..................................... 431
10.2.4.X-ray Microanalysis of Thin Specimens .......... 434
10.2.5.X-ray Microanalysis of Organic Specimens ....... 436
10.3.Electron Energy-Loss Spectroscopy ..................... 437
10.3.1.Recording of Electron Energy-Loss Spectra ...... 437
10.3.2.Kramers-Kronig Relation ........................ 439
10.3.3.Background Fitting and Subtraction ............. 441
10.3.4.Deconvolution .................................. 442
10.3.5.Elemental Analysis by Inner-Shell
Ionizations .................................... 444
10.4.Element-Distribution Images ........................... 447
10.4.1.Elemental Mapping by X-Rays .................... 447
10.4.2.Element-Distribution Images Formed by
Electron Spectroscopic Imaging ................. 448
10.4.3.Three-Window Method ............................ 449
10.4.4.White-Line Method .............................. 450
10.4.5.Correction of Scattering Contrast .............. 450
10.5.Limitations of Elemental Analysis ................ 452
10.5.1.Specimen Thickness ............................. 452
10.5.2.Radiation Damage and Loss of Elements .......... 452
10.5.3.Counting Statistics and Sensitivity ............ 453
10.5.4.Resolution and Detection Limits for Electron
Spectroscopic Imaging .......................... 456
11.Specimen Damage by Electron Irradiation .................... 459
11.1.Specimen Heating ...................................... 459
11.1.1.Methods of Measuring Specimen Temperature ...... 459
11.1.2.Generation of Heat by Electron Irradiation ..... 461
11.1.3.Calculation of Specimen Temperature ............ 463
11.2.Radiation Damage of Organic Specimens ................. 466
11.2.1.Elementary Damage Processes in Organic
Specimens ...................................... 466
11.2.2.Quantitative Methods of Measuring Damage
Effects ........................................ 470
11.2.3.Methods of Reducing Radiation Damage ........... 477
11.2.4.Radiation Damage and High Resolution ........... 479
11.3.Radiation Damage of Inorganic Specimens ............... 480
11.3.1.Damage by Electron Excitation .................. 480
11.3.2.Radiation Damage by Knock-On Collisions ........ 482
11.4.Contamination ......................................... 484
11.4.1.Origin and Sources of Contamination ............ 484
11.4.2.Methods for Decreasing Contamination ........... 485
11.4.3.Dependence of Contamination on Irradiation
Conditions ..................................... 486
References .................................................... 491
Index ......................................................... 575
|
