Scanning Electron Microscopy and X-Ray Microanalysis

Mục Lục

 

Electron Beam—Specimen Interactions: Interaction Volume ………………………………………………. 1
1.1 What Happens When the Beam Electrons Encounter Specimen Atoms? …………………………………………………. 2
1.2 Inelastic Scattering (Energy Loss) Limits Beam Electron
Travel in the Specimen ……………………………………………………………………………………………………………………………………… 2
1.3 Elastic Scattering: Beam Electrons Change Direction of Flight …………………………………………………………………. 4
1.3.1 How Frequently Does Elastic Scattering Occur? ……………………………………………………………………………………………… 4
1.4 Simulating the Effects of Elastic Scattering: Monte Carlo Calculations ……………………………………………………. 5
1.4.1 What Do Individual Monte Carlo Trajectories Look Like? ………………………………………………………………………………. 6
1.4.2 Monte Carlo Simulation To Visualize the Electron Interaction Volume ………………………………………………………… 6
1.4.3 Using the Monte Carlo Electron Trajectory Simulation to Study
the Interaction Volume ………………………………………………………………………………………………………………………………………. 8
1.5 A Range Equation To Estimate the Size of the Interaction Volume …………………………………………………………. 12
References ………………………………………………………………………………………………………………………………………………………….. 14
2 Backscattered Electrons ……………………………………………………………………………………………………………….. 15
2.1 Origin …………………………………………………………………………………………………………………………………………………………………… 16
2.1.1 The Numerical Measure of Backscattered Electrons ……………………………………………………………………………………….. 16
2.2 Critical Properties of Backscattered Electrons ……………………………………………………………………………………………… 16
2.2.1 BSE Response to Specimen Composition (η vs. Atomic Number, Z) …………………………………………………………….. 16
2.2.2 BSE Response to Specimen Inclination (η vs. Surface Tilt, θ) …………………………………………………………………………. 20
2.2.3 Angular Distribution of Backscattering ……………………………………………………………………………………………………………. 22
2.2.4 Spatial Distribution of Backscattering ………………………………………………………………………………………………………………. 23
2.2.5 Energy Distribution of Backscattered Electrons………………………………………………………………………………………………. 27
2.3 Summary ……………………………………………………………………………………………………………………………………………………………… 27
References ……………………………………………………………………………………………………………………………………………………………. 28
3 Secondary Electrons ……………………………………………………………………………………………………………………… 29
3.1 Origin …………………………………………………………………………………………………………………………………………………………………… 30
3.2 Energy Distribution …………………………………………………………………………………………………………………………………………… 30
3.3 Escape Depth of Secondary Electrons ……………………………………………………………………………………………………………. 30
3.4 Secondary Electron Yield Versus Atomic Number ……………………………………………………………………………………….. 30
3.5 Secondary Electron Yield Versus Specimen Tilt ……………………………………………………………………………………………. 34
3.6 Angular Distribution of Secondary Electrons ……………………………………………………………………………………………….. 34
3.7 Secondary Electron Yield Versus Beam Energy …………………………………………………………………………………………….. 35
3.8 Spatial Characteristics of Secondary Electrons …………………………………………………………………………………………….. 35
References ……………………………………………………………………………………………………………………………………………………………. 37
4 X-Rays ……………………………………………………………………………………………………………………………………………….. 39
4.1 Overview ……………………………………………………………………………………………………………………………………………………………… 40
4.2 Characteristic X-Rays …………………………………………………………………………………………………………………………………………. 40
4.2.1 Origin ……………………………………………………………………………………………………………………………………………………………………. 40
4.2.2 Fluorescence Yield ………………………………………………………………………………………………………………………………………………. 41
4.2.3 X-Ray Families ……………………………………………………………………………………………………………………………………………………… 42
4.2.4 X-Ray Nomenclature …………………………………………………………………………………………………………………………………………… 43
4.2.5 X-Ray Weights of Lines ……………………………………………………………………………………………………………………………………….. 44
4.2.6 Characteristic X-Ray Intensity ……………………………………………………………………………………………………………………………. 44
4.3 X-Ray Continuum (bremsstrahlung) ………………………………………………………………………………………………………………… 47
4.3.1 X-Ray Continuum Intensity ………………………………………………………………………………………………………………………………… 49
4.3.2 The Electron-Excited X-Ray Spectrum, As-Generated …………………………………………………………………………………….. 49
4.3.3 Range of X-ray Production …………………………………………………………………………………………………………………………………. 50
4.3.4 Monte Carlo Simulation of X-Ray Generation ………………………………………………………………………………………………….. 51
4.3.5 X-ray Depth Distribution Function, φ(ρz) …………………………………………………………………………………………………………. 53

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4.4 X-Ray Absorption ……………………………………………………………………………………………………………………………………………….. 54
4.5 X-Ray Fluorescence ……………………………………………………………………………………………………………………………………………. 59
References ……………………………………………………………………………………………………………………………………………………………. 63
5 Scanning Electron Microscope (SEM) Instrumentation …………………………………………………………. 65
5.1 Electron Beam Parameters ……………………………………………………………………………………………………………………………….. 66
5.2 Electron Optical Parameters …………………………………………………………………………………………………………………………….. 66
5.2.1 Beam Energy ……………………………………………………………………………………………………………………………………………………….. 66
5.2.2 Beam Diameter ……………………………………………………………………………………………………………………………………………………. 67
5.2.3 Beam Current ………………………………………………………………………………………………………………………………………………………. 67
5.2.4 Beam Current Density ………………………………………………………………………………………………………………………………………… 68
5.2.5 Beam Convergence Angle, α ……………………………………………………………………………………………………………………………… 68
5.2.6 Beam Solid Angle ………………………………………………………………………………………………………………………………………………… 69
5.2.7 Electron Optical Brightness, β ……………………………………………………………………………………………………………………………. 70
5.2.8 Focus …………………………………………………………………………………………………………………………………………………………………….. 71
5.3 SEM Imaging Modes ………………………………………………………………………………………………………………………………………….. 75
5.3.1 High Depth-of-Field Mode …………………………………………………………………………………………………………………………………. 75
5.3.2 High-Current Mode …………………………………………………………………………………………………………………………………………….. 78
5.3.3 Resolution Mode …………………………………………………………………………………………………………………………………………………. 80
5.3.4 Low-Voltage Mode ……………………………………………………………………………………………………………………………………………… 81
5.4 Electron Detectors …………………………………………………………………………………………………………………………………………….. 83
5.4.1 Important Properties of BSE and SE for Detector Design and Operation …………………………………………………….. 83
5.4.2 Detector Characteristics …………………………………………………………………………………………………………………………………….. 83
5.4.3 Common Types of Electron Detectors………………………………………………………………………………………………………………. 85
5.4.4 Secondary Electron Detectors …………………………………………………………………………………………………………………………… 86
5.4.5 Specimen Current: The Specimen as Its Own Detector ………………………………………………………………………………….. 88
5.4.6 A Useful, Practical Measure of a Detector: Detective
Quantum Efficiency …………………………………………………………………………………………………………………………………………….. 89
References ……………………………………………………………………………………………………………………………………………………………. 91
6 Image Formation …………………………………………………………………………………………………………………………….. 93
6.1 Image Construction by Scanning Action ……………………………………………………………………………………………………….. 94
6.2 Magnification ……………………………………………………………………………………………………………………………………………………… 95
6.2.1 Magnification, Image Dimensions, and Scale Bars ………………………………………………………………………………………….. 95
6.3 Making Dimensional Measurements With the SEM:
How Big Is That Feature? …………………………………………………………………………………………………………………………………… 95
6.3.1 Calibrating the Image …………………………………………………………………………………………………………………………………………. 95
6.4 Image Defects …………………………………………………………………………………………………………………………………………………….. 98
6.4.1 Projection Distortion (Foreshortening) ……………………………………………………………………………………………………………. 98
6.4.2 Image Defocusing (Blurring) ……………………………………………………………………………………………………………………………. 100
6.5 Making Measurements on Surfaces With Arbitrary Topography:
Stereomicroscopy …………………………………………………………………………………………………………………………………………….. 102
6.5.1 Qualitative Stereomicroscopy …………………………………………………………………………………………………………………………. 103
6.5.2 Quantitative Stereomicroscopy ………………………………………………………………………………………………………………………. 107
References ………………………………………………………………………………………………………………………………………………………….. 110
7 SEM Image Interpretation ………………………………………………………………………………………………………….. 111
7.1 Information in SEM Images…………………………………………………………………………………………………………………………….. 112
7.2 Interpretation of SEM Images of Compositional Microstructure …………………………………………………………….. 112
7.2.1 Atomic Number Contrast With Backscattered Electrons ………………………………………………………………………………. 112
7.2.2 Calculating Atomic Number Contrast …………………………………………………………………………………………………………….. 113
7.2.3 BSE Atomic Number Contrast With the Everhart–Thornley Detector …………………………………………………………. 113
7.3 Interpretation of SEM Images of Specimen Topography ………………………………………………………………………….. 114
7.3.1 Imaging Specimen Topography With the Everhart–Thornley Detector ……………………………………………………… 115
7.3.2 The Light-Optical Analogy to the SEM/E–T (Positive Bias) Image ……………………………………………………………….. 116
7.3.3 Imaging Specimen Topography With a Semiconductor BSE Detector ……………………………………………………….. 119
References ………………………………………………………………………………………………………………………………………………………….. 121
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8 The Visibility of Features in SEM Images ………………………………………………………………………………… 123
8.1 Signal Quality: Threshold Contrast and Threshold Current ……………………………………………………………………… 124
References ………………………………………………………………………………………………………………………………………………………….. 131
9 Image Defects ……………………………………………………………………………………………………………………………….. 133
9.1 Charging ……………………………………………………………………………………………………………………………………………………………. 134
9.1.1 What Is Specimen Charging? …………………………………………………………………………………………………………………………… 134
9.1.2 Recognizing Charging Phenomena in SEM Images ………………………………………………………………………………………. 135
9.1.3 Techniques to Control Charging Artifacts (High Vacuum Instruments) ……………………………………………………… 139
9.2 Radiation Damage……………………………………………………………………………………………………………………………………………. 142
9.3 Contamination ………………………………………………………………………………………………………………………………………………….. 143
9.4 Moiré Effects: Imaging What Isn’t Actually There ……………………………………………………………………………………….. 144
References ………………………………………………………………………………………………………………………………………………………….. 146
10 High Resolution Imaging ……………………………………………………………………………………………………………. 147
10.1 What Is “High Resolution SEM Imaging”? …………………………………………………………………………………………………….. 148
10.2 Instrumentation Considerations …………………………………………………………………………………………………………………… 148
10.3 Pixel Size, Beam Footprint, and Delocalized Signals …………………………………………………………………………………. 148
10.4 Secondary Electron Contrast at High Spatial Resolution ………………………………………………………………………….. 150
10.4.1 SE range Effects Produce Bright Edges (Isolated Edges) ………………………………………………………………………………. 151
10.4.2 Even More Localized Signal: Edges Which Are Thin Relative
to the Beam Range ……………………………………………………………………………………………………………………………………………. 152
10.4.3 Too Much of a Good Thing: The Bright Edge Effect Can Hinder
Distinguishing Shape ……………………………………………………………………………………………………………………………………….. 153
10.4.4 Too Much of a Good Thing: The Bright Edge Effect Hinders
Locating the True Position of an Edge for Critical Dimension Metrology …………………………………………………… 154
10.5 Achieving High Resolution with Secondary Electrons ………………………………………………………………………………. 156
10.5.1 Beam Energy Strategies ……………………………………………………………………………………………………………………………………. 156
10.5.2 Improving the SE1 Signal ………………………………………………………………………………………………………………………………….. 158
10.5.3 Eliminate the Use of SEs Altogether: “Low Loss BSEs“ …………………………………………………………………………………… 161
10.6 Factors That Hinder Achieving High Resolution …………………………………………………………………………………………. 163
10.6.1 Achieving Visibility: The Threshold Contrast ………………………………………………………………………………………………….. 163
10.6.2 Pathological Specimen Behavior …………………………………………………………………………………………………………………….. 163
10.6.3 Pathological Specimen and Instrumentation Behavior ………………………………………………………………………………… 164
References ………………………………………………………………………………………………………………………………………………………….. 164
11 Low Beam Energy SEM ………………………………………………………………………………………………………………… 165
11.1 What Constitutes “Low” Beam Energy SEM Imaging? ……………………………………………………………………………….. 166
11.2 Secondary Electron and Backscattered Electron Signal Characteristics
in the Low Beam Energy Range……………………………………………………………………………………………………………………… 166
11.3 Selecting the Beam Energy to Control the Spatial Sampling
of Imaging Signals……………………………………………………………………………………………………………………………………………. 169
11.3.1 Low Beam Energy for High Lateral Resolution SEM ………………………………………………………………………………………. 169
11.3.2 Low Beam Energy for High Depth Resolution SEM ……………………………………………………………………………………….. 169
11.3.3 Extremely Low Beam Energy Imaging ……………………………………………………………………………………………………………. 171
References ………………………………………………………………………………………………………………………………………………………….. 172
12 Variable Pressure Scanning Electron Microscopy (VPSEM) ………………………………………………… 173
12.1 Review: The Conventional SEM High Vacuum Environment …………………………………………………………………….. 174
12.1.1 Stable Electron Source Operation …………………………………………………………………………………………………………………… 174
12.1.2 Maintaining Beam Integrity ……………………………………………………………………………………………………………………………… 174
12.1.3 Stable Operation of the Everhart–Thornley Secondary Electron Detector ………………………………………………… 174
12.1.4 Minimizing Contamination ………………………………………………………………………………………………………………………………. 174
12.2 How Does VPSEM Differ From the Conventional SEM
Vacuum Environment? ……………………………………………………………………………………………………………………………………. 174
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12.3 Benefits of Scanning Electron Microscopy at Elevated Pressures ……………………………………………………………. 175
12.3.1 Control of Specimen Charging ………………………………………………………………………………………………………………………… 175
12.3.2 Controlling the Water Environment of a Specimen ………………………………………………………………………………………. 176
12.4 Gas Scattering Modification of the Focused Electron Beam …………………………………………………………………….. 177
12.5 VPSEM Image Resolution ……………………………………………………………………………………………………………………………….. 181
12.6 Detectors for Elevated Pressure Microscopy ………………………………………………………………………………………………. 182
12.6.1 Backscattered Electrons—Passive Scintillator Detector ……………………………………………………………………………….. 182
12.6.2 Secondary Electrons–Gas Amplification Detector ………………………………………………………………………………………… 182
12.7 Contrast in VPSEM ……………………………………………………………………………………………………………………………………………. 184
References ………………………………………………………………………………………………………………………………………………………….. 185
13 ImageJ and Fiji ……………………………………………………………………………………………………………………………… 187
13.1 The ImageJ Universe ……………………………………………………………………………………………………………………………………….. 188
13.2 Fiji ……………………………………………………………………………………………………………………………………………………………………….. 188
13.3 Plugins ……………………………………………………………………………………………………………………………………………………………….. 190
13.4 Where to Learn More ……………………………………………………………………………………………………………………………………….. 191
References ………………………………………………………………………………………………………………………………………………………….. 193
14 SEM Imaging Checklist ……………………………………………………………………………………………………………….. 195
14.1 Specimen Considerations (High Vacuum SEM; Specimen Chamber Pressure<10−3 Pa)……………………… 197
14.1.1 Conducting or Semiconducting Specimens ………………………………………………………………………………………………….. 197
14.1.2 Insulating Specimens ……………………………………………………………………………………………………………………………………….. 197
14.2 Electron Signals Available ………………………………………………………………………………………………………………………………. 197
14.2.1 Beam Electron Range ……………………………………………………………………………………………………………………………………….. 197
14.2.2 Backscattered Electrons …………………………………………………………………………………………………………………………………… 197
14.2.3 Secondary Electrons ………………………………………………………………………………………………………………………………………… 197
14.3 Selecting the Electron Detector …………………………………………………………………………………………………………………….. 198
14.3.1 Everhart–Thornley Detector (“Secondary Electron” Detector) …………………………………………………………………….. 198
14.3.2 Backscattered Electron Detectors …………………………………………………………………………………………………………………… 198
14.3.3 “Through-the-Lens” Detectors …………………………………………………………………………………………………………………………. 198
14.4 Selecting the Beam Energy for SEM Imaging ……………………………………………………………………………………………… 198
14.4.1 Compositional Contrast With Backscattered Electrons ………………………………………………………………………………… 198
14.4.2 Topographic Contrast With Backscattered Electrons ……………………………………………………………………………………. 198
14.4.3 Topographic Contrast With Secondary Electrons ………………………………………………………………………………………….. 198
14.4.4 High Resolution SEM Imaging …………………………………………………………………………………………………………………………. 198
14.5 Selecting the Beam Current……………………………………………………………………………………………………………………………. 199
14.5.1 High Resolution Imaging …………………………………………………………………………………………………………………………………. 199
14.5.2 Low Contrast Features Require High Beam Current and/or Long Frame Time to Establish Visibility ……… 199
14.6 Image Presentation………………………………………………………………………………………………………………………………………….. 199
14.6.1 “Live” Display Adjustments ………………………………………………………………………………………………………………………………. 199
14.6.2 Post-Collection Processing ………………………………………………………………………………………………………………………………. 199
14.7 Image Interpretation ……………………………………………………………………………………………………………………………………….. 199
14.7.1 Observer’s Point of View …………………………………………………………………………………………………………………………………… 199
14.7.2 Direction of Illumination ………………………………………………………………………………………………………………………………….. 199
14.7.3 Contrast Encoding …………………………………………………………………………………………………………………………………………….. 200
14.7.4 Imaging Topography With the Everhart–Thornley Detector………………………………………………………………………… 200
14.7.5 Annular BSE Detector (Semiconductor Sum Mode A+B and Passive Scintillator) ……………………………………. 200
14.7.6 Semiconductor BSE Detector Difference Mode, A−B ……………………………………………………………………………………. 200
14.7.7 Everhart–Thornley Detector, Negatively Biased to Reject SE ………………………………………………………………………. 200
14.8 Variable Pressure Scanning Electron Microscopy (VPSEM) ………………………………………………………………………. 200
14.8.1 VPSEM Advantages …………………………………………………………………………………………………………………………………………… 200
14.8.2 VPSEM Disadvantages ………………………………………………………………………………………………………………………………………. 200
15 SEM Case Studies………………………………………………………………………………………………………………………….. 201
15.1 Case Study: How High Is That Feature Relative to Another? …………………………………………………………………….. 202
15.2 Revealing Shallow Surface Relief ………………………………………………………………………………………………………………….. 204
15.3 Case Study: Detecting Ink-Jet Printer Deposits ………………………………………………………………………………………….. 206
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16 Energy Dispersive X-ray Spectrometry: Physical Principles and User-Selected
Parameters …………………………………………………………………………………………………………………………………….. 209
16.1 The Energy Dispersive Spectrometry (EDS) Process ………………………………………………………………………………….. 210
16.1.1 The Principal EDS Artifact: Peak Broadening (EDS Resolution Function)……………………………………………………. 210
16.1.2 Minor Artifacts: The Si-Escape Peak ………………………………………………………………………………………………………………… 213
16.1.3 Minor Artifacts: Coincidence Peaks …………………………………………………………………………………………………………………. 213
16.1.4 Minor Artifacts: Si Absorption Edge and Si Internal Fluorescence Peak …………………………………………………….. 215
16.2 “Best Practices” for Electron-Excited EDS Operation …………………………………………………………………………………. 216
16.2.1 Operation of the EDS System …………………………………………………………………………………………………………………………… 216
16.3 Practical Aspects of Ensuring EDS Performance for a Quality
Measurement Environment ……………………………………………………………………………………………………………………………. 219
16.3.1 Detector Geometry …………………………………………………………………………………………………………………………………………… 219
16.3.2 Process Time ………………………………………………………………………………………………………………………………………………………. 222
16.3.3 Optimal Working Distance ……………………………………………………………………………………………………………………………….. 222
16.3.4 Detector Orientation ………………………………………………………………………………………………………………………………………… 223
16.3.5 Count Rate Linearity …………………………………………………………………………………………………………………………………………. 225
16.3.6 Energy Calibration Linearity …………………………………………………………………………………………………………………………….. 226
16.3.7 Other Items ………………………………………………………………………………………………………………………………………………………… 227
16.3.8 Setting Up a Quality Control Program ……………………………………………………………………………………………………………. 228
16.3.9 Purchasing an SDD ……………………………………………………………………………………………………………………………………………. 230
References ………………………………………………………………………………………………………………………………………………………….. 234
17 DTSA-II EDS Software ………………………………………………………………………………………………………………….. 235
17.1 Getting Started With NIST DTSA-II ………………………………………………………………………………………………………………… 236
17.1.1 Motivation ………………………………………………………………………………………………………………………………………………………….. 236
17.1.2 Platform ……………………………………………………………………………………………………………………………………………………………… 236
17.1.3 Overview ……………………………………………………………………………………………………………………………………………………………. 236
17.1.4 Design…………………………………………………………………………………………………………………………………………………………………. 237
17.1.5 The Three -Leg Stool: Simulation, Quantification and Experiment Design ………………………………………………… 237
17.1.6 Introduction to Fundamental Concepts …………………………………………………………………………………………………………. 238
17.2 Simulation in DTSA-II ………………………………………………………………………………………………………………………………………. 245
17.2.1 Introduction ………………………………………………………………………………………………………………………………………………………. 245
17.2.2 Monte Carlo Simulation ……………………………………………………………………………………………………………………………………. 245
17.2.3 Using the GUI To Perform a Simulation ………………………………………………………………………………………………………….. 247
17.2.4 Optional Tables ………………………………………………………………………………………………………………………………………………….. 262
References ………………………………………………………………………………………………………………………………………………………….. 264
18 Qualitative Elemental Analysis by Energy Dispersive X-Ray Spectrometry……………………. 265
18.1 Quality Assurance Issues for Qualitative Analysis: EDS Calibration ………………………………………………………… 266
18.2 Principles of Qualitative EDS Analysis ………………………………………………………………………………………………………….. 266
18.2.1 Critical Concepts From the Physics of Characteristic X-ray Generation
and Propagation ……………………………………………………………………………………………………………………………………………….. 266
18.2.2 X-Ray Energy Database: Families of X-Rays ……………………………………………………………………………………………………. 269
18.2.3 Artifacts of the EDS Detection Process …………………………………………………………………………………………………………… 269
18.3 Performing Manual Qualitative Analysis ……………………………………………………………………………………………………… 275
18.3.1 Why are Skills in Manual Qualitative Analysis Important? ……………………………………………………………………………. 275
18.3.2 Performing Manual Qualitative Analysis: Choosing the Instrument
Operating Conditions ……………………………………………………………………………………………………………………………………….. 277
18.4 Identifying the Peaks ………………………………………………………………………………………………………………………………………. 278
18.4.1 Employ the Available Software Tools ……………………………………………………………………………………………………………… 278
18.4.2 Identifying the Peaks: Major Constituents ……………………………………………………………………………………………………… 280
18.4.3 Lower Photon Energy Region ………………………………………………………………………………………………………………………….. 281
18.4.4 Identifying the Peaks: Minor and Trace Constituents ……………………………………………………………………………………. 281
18.4.5 Checking Your Work ………………………………………………………………………………………………………………………………………….. 281
18.5 A Worked Example of Manual Peak Identification ……………………………………………………………………………………… 281
References ………………………………………………………………………………………………………………………………………………………….. 287
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19 Quantitative Analysis: From k-ratio to Composition ……………………………………………………………. 289
19.1 What Is a k-ratio? ……………………………………………………………………………………………………………………………………………… 290
19.2 Uncertainties in k-ratios ………………………………………………………………………………………………………………………………….. 291
19.3 Sets of k-ratios ………………………………………………………………………………………………………………………………………………….. 291
19.4 Converting Sets of k-ratios Into Composition …………………………………………………………………………………………….. 292
19.5 The Analytical Total ………………………………………………………………………………………………………………………………………….. 292
19.6 Normalization …………………………………………………………………………………………………………………………………………………… 292
19.7 Other Ways to Estimate CZ ………………………………………………………………………………………………………………………………. 293
19.7.1 Oxygen by Assumed Stoichiometry ……………………………………………………………………………………………………………….. 293
19.7.2 Waters of Crystallization …………………………………………………………………………………………………………………………………… 293
19.7.3 Element by Difference ………………………………………………………………………………………………………………………………………. 293
19.8 Ways of Reporting Composition ……………………………………………………………………………………………………………………. 294
19.8.1 Mass Fraction …………………………………………………………………………………………………………………………………………………….. 294
19.8.2 Atomic Fraction …………………………………………………………………………………………………………………………………………………. 294
19.8.3 Stoichiometry…………………………………………………………………………………………………………………………………………………….. 294
19.8.4 Oxide Fractions ………………………………………………………………………………………………………………………………………………….. 294
19.9 The Accuracy of Quantitative Electron-Excited X-ray Microanalysis ………………………………………………………. 295
19.9.1 Standards-Based k-ratio Protocol ……………………………………………………………………………………………………………………. 295
19.9.2 “Standardless Analysis” …………………………………………………………………………………………………………………………………….. 296
19.10 Appendix…………………………………………………………………………………………………………………………………………. 298
19.10.1 The Need for Matrix Corrections To Achieve Quantitative Analysis ……………………………………………………………. 298
19.10.2 The Physical Origin of Matrix Effects ………………………………………………………………………………………………………………. 299
19.10.3 ZAF Factors in Microanalysis ……………………………………………………………………………………………………………………………. 299
References ………………………………………………………………………………………………………………………………………………………….. 307
20 Quantitative Analysis: The SEM/EDS Elemental Microanalysis k-ratio
Procedure for Bulk Specimens, Step-by-Step ………………………………………………………………………… 309
20.1 Requirements Imposed on the Specimen and Standards ………………………………………………………………………… 311
20.2 Instrumentation Requirements …………………………………………………………………………………………………………………….. 311
20.2.1 Choosing the EDS Parameters …………………………………………………………………………………………………………………………. 311
20.2.2 Choosing the Beam Energy, E0 ………………………………………………………………………………………………………………………… 313
20.2.3 Measuring the Beam Current …………………………………………………………………………………………………………………………… 313
20.2.4 Choosing the Beam Current …………………………………………………………………………………………………………………………….. 314
20.3 Examples of the k-ratio/Matrix Correction Protocol with DTSA II ……………………………………………………………. 316
20.3.1 Analysis of Major Constituents (C>0.1 Mass Fraction)
with Well-Resolved Peaks …………………………………………………………………………………………………………………………………. 316
20.3.2 Analysis of Major Constituents (C>0.1 Mass Fraction)
with Severely Overlapping Peaks ……………………………………………………………………………………………………………………. 318
20.3.3 Analysis of a Minor Constituent with Peak Overlap From
a Major Constituent ………………………………………………………………………………………………………………………………………….. 319
20.3.4 Ba-Ti Interference in BaTiSi3O9 …………………………………………………………………………………………………………………………. 319
20.3.5 Ba-Ti Interference: Major/Minor Constituent Interference in K2496
Microanalysis Glass……………………………………………………………………………………………………………………………………………. 319
20.4 The Need for an Iterative Qualitative and Quantitative
Analysis Strategy ……………………………………………………………………………………………………………………………………………… 319
20.4.1 Analysis of a Complex Metal Alloy, IN100 ………………………………………………………………………………………………………. 320
20.4.2 Analysis of a Stainless Steel ……………………………………………………………………………………………………………………………… 323
20.4.3 Progressive Discovery: Repeated Qualitative–Quantitative Analysis
Sequences ………………………………………………………………………………………………………………………………………………………….. 324
20.5 Is the Specimen Homogeneous? …………………………………………………………………………………………………………………… 326
20.6 Beam-Sensitive Specimens …………………………………………………………………………………………………………………………….. 331
20.6.1 Alkali Element Migration ………………………………………………………………………………………………………………………………….. 331
20.6.2 Materials Subject to Mass Loss During Electron Bombardment—
the Marshall-Hall Method ………………………………………………………………………………………………………………………………… 334
References ………………………………………………………………………………………………………………………………………………………….. 339
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21 Trace Analysis by SEM/EDS ………………………………………………………………………………………………………… 341
21.1 Limits of Detection for SEM/EDS Microanalysis ………………………………………………………………………………………….. 342
21.2 Estimating the Concentration Limit of Detection, CDL ………………………………………………………………………………. 343
21.2.1 Estimating CDL from a Trace or Minor Constituent from Measuring
a Known Standard …………………………………………………………………………………………………………………………………………….. 343
21.2.2 Estimating CDL After Determination of a Minor or Trace Constituent
with Severe Peak Interference from a Major Constituent …………………………………………………………………………….. 343
21.2.3 Estimating CDL When a Reference Value for Trace or
Minor Element Is Not Available ……………………………………………………………………………………………………………………….. 343
21.3 Measurements of Trace Constituents by Electron-Excited Energy
Dispersive X-ray Spectrometry………………………………………………………………………………………………………………………. 345
21.3.1 Is a Given Trace Level Measurement Actually Valid? ……………………………………………………………………………………… 345
21.4 Pathological Electron Scattering Can Produce “Trace” Contributions
to EDS Spectra ………………………………………………………………………………………………………………………………………………….. 350
21.4.1 Instrumental Sources of Trace Analysis Artifacts …………………………………………………………………………………………… 350
21.4.2 Assessing Remote Excitation Sources in an SEM-EDS System ……………………………………………………………………… 353
21.5 Summary ……………………………………………………………………………………………………………………………………………………………. 357
References ………………………………………………………………………………………………………………………………………………………….. 357
22 Low Beam Energy X-Ray Microanalysis …………………………………………………………………………………… 359
22.1 What Constitutes “Low” Beam Energy X-Ray Microanalysis? ……………………………………………………………………. 360
22.1.1 Characteristic X-ray Peak Selection Strategy for Analysis …………………………………………………………………………….. 364
22.1.2 Low Beam Energy Analysis Range …………………………………………………………………………………………………………………… 364
22.2 Advantage of Low Beam Energy X-Ray Microanalysis ………………………………………………………………………………. 365
22.2.1 Improved Spatial Resolution ……………………………………………………………………………………………………………………………. 365
22.2.2 Reduced Matrix Absorption Correction ………………………………………………………………………………………………………….. 366
22.2.3 Accurate Analysis of Low Atomic Number Elements at Low Beam Energy ………………………………………………… 366
22.3 Challenges and Limitations of Low Beam Energy X-Ray Microanalysis …………………………………………………. 369
22.3.1 Reduced Access to Elements ……………………………………………………………………………………………………………………………. 369
22.3.2 Relative Depth of X-Ray Generation: Susceptibility to Vertical Heterogeneity ………………………………………….. 372
22.3.3 At Low Beam Energy, Almost Everything Is Found To Be Layered ………………………………………………………………. 373
References …………………………………………………………………………………………………………………………………………………………. 380
23 Analysis of Specimens with Special Geometry: Irregular Bulk
Objects and Particles …………………………………………………………………………………………………………………… 381
23.1 The Origins of “Geometric Effects”: Bulk Specimens ………………………………………………………………………………….. 382
23.2 What Degree of Surface Finish Is Required for Electron-Excited X-ray
Microanalysis To Minimize Geometric Effects? …………………………………………………………………………………………… 384
23.2.1 No Chemical Etching ………………………………………………………………………………………………………………………………………… 384
23.3 Consequences of Attempting Analysis of Bulk Materials
With Rough Surfaces ……………………………………………………………………………………………………………………………………….. 385
23.4 Useful Indicators of Geometric Factors Impact on Analysis ……………………………………………………………………… 386
23.4.1 The Raw Analytical Total …………………………………………………………………………………………………………………………………… 386
23.4.2 The Shape of the EDS Spectrum ……………………………………………………………………………………………………………………… 389
23.5 Best Practices for Analysis of Rough Bulk Samples ……………………………………………………………………………………. 391
23.6 Particle Analysis ……………………………………………………………………………………………………………………………………………….. 394
23.6.1 How Do X-ray Measurements of Particles Differ
From Bulk Measurements? ……………………………………………………………………………………………………………………………….. 394
23.6.2 Collecting Optimum Spectra From Particles ………………………………………………………………………………………………….. 395
23.6.3 X-ray Spectrum Imaging: Understanding Heterogeneous Materials ………………………………………………………….. 400
23.6.4 Particle Geometry Factors Influencing Quantitative Analysis of Particles ………………………………………………….. 403
23.6.5 Uncertainty in Quantitative Analysis of Particles ………………………………………………………………………………………….. 405
23.6.6 Peak-to-Background (P/B) Method …………………………………………………………………………………………………………………. 408
23.7 Summary ……………………………………………………………………………………………………………………………………………………………. 410
References ………………………………………………………………………………………………………………………………………………………….. 411
Contents

XXII
24 Compositional Mapping …………………………………………………………………………………………………………….. 413
24.1 Total Intensity Region-of-Interest Mapping ………………………………………………………………………………………………… 414
24.1.1 Limitations of Total Intensity Mapping …………………………………………………………………………………………………………… 415
24.2 X-Ray Spectrum Imaging ………………………………………………………………………………………………………………………………… 417
24.2.1 Utilizing XSI Datacubes …………………………………………………………………………………………………………………………………….. 419
24.2.2 Derived Spectra …………………………………………………………………………………………………………………………………………………. 419
24.3 Quantitative Compositional Mapping ………………………………………………………………………………………………………….. 424
24.4 Strategy for XSI Elemental Mapping Data Collection ………………………………………………………………………………… 430
24.4.1 Choosing the EDS Dead-Time ………………………………………………………………………………………………………………………….. 430
24.4.2 Choosing the Pixel Density ………………………………………………………………………………………………………………………………. 432
24.4.3 Choosing the Pixel Dwell Time ………………………………………………………………………………………………………………………… 434
References ………………………………………………………………………………………………………………………………………………………….. 439
25 Attempting Electron-Excited X-Ray Microanalysis in the Variable Pressure
Scanning Electron Microscope (VPSEM) …………………………………………………………………………………. 441
25.1 Gas Scattering Effects in the VPSEM ……………………………………………………………………………………………………………… 442
25.1.1 Why Doesn’t the EDS Collimator Exclude the Remote Skirt X-Rays? …………………………………………………………… 446
25.1.2 Other Artifacts Observed in VPSEM X-Ray Spectrometry …………………………………………………………………………….. 448
25.2 What Can Be Done To Minimize gas Scattering in VPSEM? ………………………………………………………………………. 450
25.2.1 Workarounds To Solve Practical Problems ……………………………………………………………………………………………………… 451
25.2.2 Favorable Sample Characteristics ……………………………………………………………………………………………………………………. 451
25.2.3 Unfavorable Sample Characteristics ……………………………………………………………………………………………………………….. 456
References ………………………………………………………………………………………………………………………………………………………….. 459
26 Energy Dispersive X-Ray Microanalysis Checklist ………………………………………………………………… 461
26.1 Instrumentation ……………………………………………………………………………………………………………………………………………….. 462
26.1.1 SEM ……………………………………………………………………………………………………………………………………………………………………… 462
26.1.2 EDS Detector ……………………………………………………………………………………………………………………………………………………… 462
26.1.3 Probe Current Measurement Device ………………………………………………………………………………………………………………. 462
26.1.4 Conductive Coating ………………………………………………………………………………………………………………………………………….. 463
26.2 Sample Preparation …………………………………………………………………………………………………………………………………………. 463
26.2.1 Standard Materials ……………………………………………………………………………………………………………………………………………. 464
26.2.2 Peak Reference Materials………………………………………………………………………………………………………………………………….. 464
26.3 Initial Set-Up ……………………………………………………………………………………………………………………………………………………… 464
26.3.1 Calibrating the EDS Detector …………………………………………………………………………………………………………………………… 464
26.4 Collecting Data …………………………………………………………………………………………………………………………………………………. 466
26.4.1 Exploratory Spectrum ………………………………………………………………………………………………………………………………………. 466
26.4.2 Experiment Optimization …………………………………………………………………………………………………………………………………. 467
26.4.3 Selecting Standards ………………………………………………………………………………………………………………………………………….. 467
26.4.4 Reference Spectra ……………………………………………………………………………………………………………………………………………… 467
26.4.5 Collecting Standards…………………………………………………………………………………………………………………………………………. 467
26.4.6 Collecting Peak-Fitting References …………………………………………………………………………………………………………………. 467
26.4.7 Collecting Spectra From the Unknown ………………………………………………………………………………………………………….. 467
26.5 Data Analysis …………………………………………………………………………………………………………………………………………………….. 468
26.5.1 Organizing the Data ………………………………………………………………………………………………………………………………………….. 468
26.5.2 Quantification ……………………………………………………………………………………………………………………………………………………. 468
26.6 Quality Check ……………………………………………………………………………………………………………………………………………………. 468
26.6.1 Check the Residual Spectrum After Peak Fitting …………………………………………………………………………………………… 468
26.6.2 Check the Analytic Total …………………………………………………………………………………………………………………………………… 469
26.6.3 Intercompare the Measurements ……………………………………………………………………………………………………………………. 469
Reference ……………………………………………………………………………………………………………………………………………………………. 470
27 X-Ray Microanalysis Case Studies …………………………………………………………………………………………….. 471
27.1 Case Study: Characterization of a Hard-Facing Alloy Bearing Surface …………………………………………………… 472
27.2 Case Study: Aluminum Wire Failures in Residential Wiring ………………………………………………………………………. 474
27.3 Case Study: Characterizing the Microstructure of a Manganese Nodule ………………………………………………. 476
References ………………………………………………………………………………………………………………………………………………………….. 479
Contents

XXIII

28 Cathodoluminescence ………………………………………………………………………………………………………………… 481
28.1 Origin …………………………………………………………………………………………………………………………………………………………………. 482
28.2 Measuring Cathodoluminescence ………………………………………………………………………………………………………………… 483
28.2.1 Collection of CL …………………………………………………………………………………………………………………………………………………. 483
28.2.2 Detection of CL ………………………………………………………………………………………………………………………………………………….. 483
28.3 Applications of CL ……………………………………………………………………………………………………………………………………………. 485
28.3.1 Geology ………………………………………………………………………………………………………………………………………………………………. 485
28.3.2 Materials Science ………………………………………………………………………………………………………………………………………………. 485
28.3.3 Organic Compounds …………………………………………………………………………………………………………………………………………. 489
References ………………………………………………………………………………………………………………………………………………………….. 489
29 Characterizing Crystalline Materials in the SEM …………………………………………………………………… 491
29.1 Imaging Crystalline Materials with Electron Channeling Contrast …………………………………………………………. 492
29.1.1 Single Crystals ……………………………………………………………………………………………………………………………………………………. 492
29.1.2 Polycrystalline Materials …………………………………………………………………………………………………………………………………… 494
29.1.3 Conditions for Detecting Electron Channeling Contrast ……………………………………………………………………………… 496
29.2 Electron Backscatter Diffraction in the Scanning Electron
Microscope ………………………………………………………………………………………………………………………………………………………… 496
29.2.1 Origin of EBSD Patterns ……………………………………………………………………………………………………………………………………. 498
29.2.2 Cameras for EBSD Pattern Detection ………………………………………………………………………………………………………………. 499
29.2.3 EBSD Spatial Resolution ……………………………………………………………………………………………………………………………………. 499
29.2.4 How Does a Modern EBSD System Index Patterns ………………………………………………………………………………………… 501
29.2.5 Steps in Typical EBSD Measurements ……………………………………………………………………………………………………………… 502
29.2.6 Display of the Acquired Data …………………………………………………………………………………………………………………………… 505
29.2.7 Other Map Components …………………………………………………………………………………………………………………………………… 508
29.2.8 Dangers and Practice of “Cleaning” EBSD Data ……………………………………………………………………………………………… 508
29.2.9 Transmission Kikuchi Diffraction in the SEM ………………………………………………………………………………………………….. 509
29.2.10 Application Example …………………………………………………………………………………………………………………………………………. 510
29.2.11 Summary ……………………………………………………………………………………………………………………………………………………………. 513
29.2.12 Electron Backscatter Diffraction Checklist ……………………………………………………………………………………………………… 513
References ………………………………………………………………………………………………………………………………………………………….. 514
30 Focused Ion Beam Applications in the SEM Laboratory ……………………………………………………… 517
30.1 Introduction ……………………………………………………………………………………………………………………………………………………… 518
30.2 Ion–Solid Interactions……………………………………………………………………………………………………………………………………… 518
30.3 Focused Ion Beam Systems …………………………………………………………………………………………………………………………….. 519
30.4 Imaging with Ions …………………………………………………………………………………………………………………………………………….. 520
30.5 Preparation of Samples for SEM ……………………………………………………………………………………………………………………. 521
30.5.1 Cross-Section Preparation………………………………………………………………………………………………………………………………… 522
30.5.2 FIB Sample Preparation for 3D Techniques and Imaging ……………………………………………………………………………… 524
30.6 Summary ……………………………………………………………………………………………………………………………………………………………. 526
References ………………………………………………………………………………………………………………………………………………………….. 528
31 Ion Beam Microscopy ………………………………………………………………………………………………………………….. 529
31.1 What Is So Useful About Ions? ……………………………………………………………………………………………………………………….. 530
31.2 Generating Ion Beams …………………………………………………………………………………………………………………………………….. 533
31.3 Signal Generation in the HIM …………………………………………………………………………………………………………………………. 534
31.4 Current Generation and Data Collection in the HIM ………………………………………………………………………………….. 536
31.5 Patterning with Ion Beams …………………………………………………………………………………………………………………………….. 537
31.6 Operating the HIM …………………………………………………………………………………………………………………………………………… 538
31.7 Chemical Microanalysis with Ion Beams ………………………………………………………………………………………………………. 538
References ………………………………………………………………………………………………………………………………………………………….. 539
Supplementary Information ……………………………………………………………………………………………………… 541
Appendix ……………………………………………………………………………………………………………………………………………………………. 542
Index …………………………………………………………………………………………………………………………………………………………………… 547

 

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