- •Preface
- •Imaging Microscopic Features
- •Measuring the Crystal Structure
- •References
- •Contents
- •1.4 Simulating the Effects of Elastic Scattering: Monte Carlo Calculations
- •What Are the Main Features of the Beam Electron Interaction Volume?
- •How Does the Interaction Volume Change with Composition?
- •How Does the Interaction Volume Change with Incident Beam Energy?
- •How Does the Interaction Volume Change with Specimen Tilt?
- •1.5 A Range Equation To Estimate the Size of the Interaction Volume
- •References
- •2: Backscattered Electrons
- •2.1 Origin
- •2.2.1 BSE Response to Specimen Composition (η vs. Atomic Number, Z)
- •SEM Image Contrast with BSE: “Atomic Number Contrast”
- •SEM Image Contrast: “BSE Topographic Contrast—Number Effects”
- •2.2.3 Angular Distribution of Backscattering
- •Beam Incident at an Acute Angle to the Specimen Surface (Specimen Tilt > 0°)
- •SEM Image Contrast: “BSE Topographic Contrast—Trajectory Effects”
- •2.2.4 Spatial Distribution of Backscattering
- •Depth Distribution of Backscattering
- •Radial Distribution of Backscattered Electrons
- •2.3 Summary
- •References
- •3: Secondary Electrons
- •3.1 Origin
- •3.2 Energy Distribution
- •3.3 Escape Depth of Secondary Electrons
- •3.8 Spatial Characteristics of Secondary Electrons
- •References
- •4: X-Rays
- •4.1 Overview
- •4.2 Characteristic X-Rays
- •4.2.1 Origin
- •4.2.2 Fluorescence Yield
- •4.2.3 X-Ray Families
- •4.2.4 X-Ray Nomenclature
- •4.2.6 Characteristic X-Ray Intensity
- •Isolated Atoms
- •X-Ray Production in Thin Foils
- •X-Ray Intensity Emitted from Thick, Solid Specimens
- •4.3 X-Ray Continuum (bremsstrahlung)
- •4.3.1 X-Ray Continuum Intensity
- •4.3.3 Range of X-ray Production
- •4.4 X-Ray Absorption
- •4.5 X-Ray Fluorescence
- •References
- •5.1 Electron Beam Parameters
- •5.2 Electron Optical Parameters
- •5.2.1 Beam Energy
- •Landing Energy
- •5.2.2 Beam Diameter
- •5.2.3 Beam Current
- •5.2.4 Beam Current Density
- •5.2.5 Beam Convergence Angle, α
- •5.2.6 Beam Solid Angle
- •5.2.7 Electron Optical Brightness, β
- •Brightness Equation
- •5.2.8 Focus
- •Astigmatism
- •5.3 SEM Imaging Modes
- •5.3.1 High Depth-of-Field Mode
- •5.3.2 High-Current Mode
- •5.3.3 Resolution Mode
- •5.3.4 Low-Voltage Mode
- •5.4 Electron Detectors
- •5.4.1 Important Properties of BSE and SE for Detector Design and Operation
- •Abundance
- •Angular Distribution
- •Kinetic Energy Response
- •5.4.2 Detector Characteristics
- •Angular Measures for Electron Detectors
- •Elevation (Take-Off) Angle, ψ, and Azimuthal Angle, ζ
- •Solid Angle, Ω
- •Energy Response
- •Bandwidth
- •5.4.3 Common Types of Electron Detectors
- •Backscattered Electrons
- •Passive Detectors
- •Scintillation Detectors
- •Semiconductor BSE Detectors
- •5.4.4 Secondary Electron Detectors
- •Everhart–Thornley Detector
- •Through-the-Lens (TTL) Electron Detectors
- •TTL SE Detector
- •TTL BSE Detector
- •Measuring the DQE: BSE Semiconductor Detector
- •References
- •6: Image Formation
- •6.1 Image Construction by Scanning Action
- •6.2 Magnification
- •6.3 Making Dimensional Measurements With the SEM: How Big Is That Feature?
- •Using a Calibrated Structure in ImageJ-Fiji
- •6.4 Image Defects
- •6.4.1 Projection Distortion (Foreshortening)
- •6.4.2 Image Defocusing (Blurring)
- •6.5 Making Measurements on Surfaces With Arbitrary Topography: Stereomicroscopy
- •6.5.1 Qualitative Stereomicroscopy
- •Fixed beam, Specimen Position Altered
- •Fixed Specimen, Beam Incidence Angle Changed
- •6.5.2 Quantitative Stereomicroscopy
- •Measuring a Simple Vertical Displacement
- •References
- •7: SEM Image Interpretation
- •7.1 Information in SEM Images
- •7.2.2 Calculating Atomic Number Contrast
- •Establishing a Robust Light-Optical Analogy
- •Getting It Wrong: Breaking the Light-Optical Analogy of the Everhart–Thornley (Positive Bias) Detector
- •Deconstructing the SEM/E–T Image of Topography
- •SUM Mode (A + B)
- •DIFFERENCE Mode (A−B)
- •References
- •References
- •9: Image Defects
- •9.1 Charging
- •9.1.1 What Is Specimen Charging?
- •9.1.3 Techniques to Control Charging Artifacts (High Vacuum Instruments)
- •Observing Uncoated Specimens
- •Coating an Insulating Specimen for Charge Dissipation
- •Choosing the Coating for Imaging Morphology
- •9.2 Radiation Damage
- •9.3 Contamination
- •References
- •10: High Resolution Imaging
- •10.2 Instrumentation Considerations
- •10.4.1 SE Range Effects Produce Bright Edges (Isolated Edges)
- •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
- •10.5.1 Beam Energy Strategies
- •Low Beam Energy Strategy
- •High Beam Energy Strategy
- •Making More SE1: Apply a Thin High-δ Metal Coating
- •Making Fewer BSEs, SE2, and SE3 by Eliminating Bulk Scattering From the Substrate
- •10.6 Factors That Hinder Achieving High Resolution
- •10.6.2 Pathological Specimen Behavior
- •Contamination
- •Instabilities
- •References
- •11: Low Beam Energy SEM
- •11.3 Selecting the Beam Energy to Control the Spatial Sampling of Imaging Signals
- •11.3.1 Low Beam Energy for High Lateral Resolution SEM
- •11.3.2 Low Beam Energy for High Depth Resolution SEM
- •11.3.3 Extremely Low Beam Energy Imaging
- •References
- •12.1.1 Stable Electron Source Operation
- •12.1.2 Maintaining Beam Integrity
- •12.1.4 Minimizing Contamination
- •12.3.1 Control of Specimen Charging
- •12.5 VPSEM Image Resolution
- •References
- •13: ImageJ and Fiji
- •13.1 The ImageJ Universe
- •13.2 Fiji
- •13.3 Plugins
- •13.4 Where to Learn More
- •References
- •14: SEM Imaging Checklist
- •14.1.1 Conducting or Semiconducting Specimens
- •14.1.2 Insulating Specimens
- •14.2 Electron Signals Available
- •14.2.1 Beam Electron Range
- •14.2.2 Backscattered Electrons
- •14.2.3 Secondary Electrons
- •14.3 Selecting the Electron Detector
- •14.3.2 Backscattered Electron Detectors
- •14.3.3 “Through-the-Lens” Detectors
- •14.4 Selecting the Beam Energy for SEM Imaging
- •14.4.4 High Resolution SEM Imaging
- •Strategy 1
- •Strategy 2
- •14.5 Selecting the Beam Current
- •14.5.1 High Resolution Imaging
- •14.5.2 Low Contrast Features Require High Beam Current and/or Long Frame Time to Establish Visibility
- •14.6 Image Presentation
- •14.6.1 “Live” Display Adjustments
- •14.6.2 Post-Collection Processing
- •14.7 Image Interpretation
- •14.7.1 Observer’s Point of View
- •14.7.3 Contrast Encoding
- •14.8.1 VPSEM Advantages
- •14.8.2 VPSEM Disadvantages
- •15: SEM Case Studies
- •15.1 Case Study: How High Is That Feature Relative to Another?
- •15.2 Revealing Shallow Surface Relief
- •16.1.2 Minor Artifacts: The Si-Escape Peak
- •16.1.3 Minor Artifacts: Coincidence Peaks
- •16.1.4 Minor Artifacts: Si Absorption Edge and Si Internal Fluorescence Peak
- •16.2 “Best Practices” for Electron-Excited EDS Operation
- •16.2.1 Operation of the EDS System
- •Choosing the EDS Time Constant (Resolution and Throughput)
- •Choosing the Solid Angle of the EDS
- •Selecting a Beam Current for an Acceptable Level of System Dead-Time
- •16.3.1 Detector Geometry
- •16.3.2 Process Time
- •16.3.3 Optimal Working Distance
- •16.3.4 Detector Orientation
- •16.3.5 Count Rate Linearity
- •16.3.6 Energy Calibration Linearity
- •16.3.7 Other Items
- •16.3.8 Setting Up a Quality Control Program
- •Using the QC Tools Within DTSA-II
- •Creating a QC Project
- •Linearity of Output Count Rate with Live-Time Dose
- •Resolution and Peak Position Stability with Count Rate
- •Solid Angle for Low X-ray Flux
- •Maximizing Throughput at Moderate Resolution
- •References
- •17: DTSA-II EDS Software
- •17.1 Getting Started With NIST DTSA-II
- •17.1.1 Motivation
- •17.1.2 Platform
- •17.1.3 Overview
- •17.1.4 Design
- •Simulation
- •Quantification
- •Experiment Design
- •Modeled Detectors (. Fig. 17.1)
- •Window Type (. Fig. 17.2)
- •The Optimal Working Distance (. Figs. 17.3 and 17.4)
- •Elevation Angle
- •Sample-to-Detector Distance
- •Detector Area
- •Crystal Thickness
- •Number of Channels, Energy Scale, and Zero Offset
- •Resolution at Mn Kα (Approximate)
- •Azimuthal Angle
- •Gold Layer, Aluminum Layer, Nickel Layer
- •Dead Layer
- •Zero Strobe Discriminator (. Figs. 17.7 and 17.8)
- •Material Editor Dialog (. Figs. 17.9, 17.10, 17.11, 17.12, 17.13, and 17.14)
- •17.2.1 Introduction
- •17.2.2 Monte Carlo Simulation
- •17.2.4 Optional Tables
- •References
- •18: Qualitative Elemental Analysis by Energy Dispersive X-Ray Spectrometry
- •18.1 Quality Assurance Issues for Qualitative Analysis: EDS Calibration
- •18.2 Principles of Qualitative EDS Analysis
- •Exciting Characteristic X-Rays
- •Fluorescence Yield
- •X-ray Absorption
- •Si Escape Peak
- •Coincidence Peaks
- •18.3 Performing Manual Qualitative Analysis
- •Beam Energy
- •Choosing the EDS Resolution (Detector Time Constant)
- •Obtaining Adequate Counts
- •18.4.1 Employ the Available Software Tools
- •18.4.3 Lower Photon Energy Region
- •18.4.5 Checking Your Work
- •18.5 A Worked Example of Manual Peak Identification
- •References
- •19.1 What Is a k-ratio?
- •19.3 Sets of k-ratios
- •19.5 The Analytical Total
- •19.6 Normalization
- •19.7.1 Oxygen by Assumed Stoichiometry
- •19.7.3 Element by Difference
- •19.8 Ways of Reporting Composition
- •19.8.1 Mass Fraction
- •19.8.2 Atomic Fraction
- •19.8.3 Stoichiometry
- •19.8.4 Oxide Fractions
- •Example Calculations
- •19.9 The Accuracy of Quantitative Electron-Excited X-ray Microanalysis
- •19.9.1 Standards-Based k-ratio Protocol
- •19.9.2 “Standardless Analysis”
- •19.10 Appendix
- •19.10.1 The Need for Matrix Corrections To Achieve Quantitative Analysis
- •19.10.2 The Physical Origin of Matrix Effects
- •19.10.3 ZAF Factors in Microanalysis
- •X-ray Generation With Depth, φ(ρz)
- •X-ray Absorption Effect, A
- •X-ray Fluorescence, F
- •References
- •20.2 Instrumentation Requirements
- •20.2.1 Choosing the EDS Parameters
- •EDS Spectrum Channel Energy Width and Spectrum Energy Span
- •EDS Time Constant (Resolution and Throughput)
- •EDS Calibration
- •EDS Solid Angle
- •20.2.2 Choosing the Beam Energy, E0
- •20.2.3 Measuring the Beam Current
- •20.2.4 Choosing the Beam Current
- •Optimizing Analysis Strategy
- •20.3.4 Ba-Ti Interference in BaTiSi3O9
- •20.4 The Need for an Iterative Qualitative and Quantitative Analysis Strategy
- •20.4.2 Analysis of a Stainless Steel
- •20.5 Is the Specimen Homogeneous?
- •20.6 Beam-Sensitive Specimens
- •20.6.1 Alkali Element Migration
- •20.6.2 Materials Subject to Mass Loss During Electron Bombardment—the Marshall-Hall Method
- •Thin Section Analysis
- •Bulk Biological and Organic Specimens
- •References
- •21: Trace Analysis by SEM/EDS
- •21.1 Limits of Detection for SEM/EDS Microanalysis
- •21.2.1 Estimating CDL from a Trace or Minor Constituent from Measuring a Known Standard
- •21.2.2 Estimating CDL After Determination of a Minor or Trace Constituent with Severe Peak Interference from a Major Constituent
- •21.3 Measurements of Trace Constituents by Electron-Excited Energy Dispersive X-ray Spectrometry
- •The Inevitable Physics of Remote Excitation Within the Specimen: Secondary Fluorescence Beyond the Electron Interaction Volume
- •Simulation of Long-Range Secondary X-ray Fluorescence
- •NIST DTSA II Simulation: Vertical Interface Between Two Regions of Different Composition in a Flat Bulk Target
- •NIST DTSA II Simulation: Cubic Particle Embedded in a Bulk Matrix
- •21.5 Summary
- •References
- •22.1.2 Low Beam Energy Analysis Range
- •22.2 Advantage of Low Beam Energy X-Ray Microanalysis
- •22.2.1 Improved Spatial Resolution
- •22.3 Challenges and Limitations of Low Beam Energy X-Ray Microanalysis
- •22.3.1 Reduced Access to Elements
- •22.3.3 At Low Beam Energy, Almost Everything Is Found To Be Layered
- •Analysis of Surface Contamination
- •References
- •23: Analysis of Specimens with Special Geometry: Irregular Bulk Objects and Particles
- •23.2.1 No Chemical Etching
- •23.3 Consequences of Attempting Analysis of Bulk Materials With Rough Surfaces
- •23.4.1 The Raw Analytical Total
- •23.4.2 The Shape of the EDS Spectrum
- •23.5 Best Practices for Analysis of Rough Bulk Samples
- •23.6 Particle Analysis
- •Particle Sample Preparation: Bulk Substrate
- •The Importance of Beam Placement
- •Overscanning
- •“Particle Mass Effect”
- •“Particle Absorption Effect”
- •The Analytical Total Reveals the Impact of Particle Effects
- •Does Overscanning Help?
- •23.6.6 Peak-to-Background (P/B) Method
- •Specimen Geometry Severely Affects the k-ratio, but Not the P/B
- •Using the P/B Correspondence
- •23.7 Summary
- •References
- •24: Compositional Mapping
- •24.2 X-Ray Spectrum Imaging
- •24.2.1 Utilizing XSI Datacubes
- •24.2.2 Derived Spectra
- •SUM Spectrum
- •MAXIMUM PIXEL Spectrum
- •24.3 Quantitative Compositional Mapping
- •24.4 Strategy for XSI Elemental Mapping Data Collection
- •24.4.1 Choosing the EDS Dead-Time
- •24.4.2 Choosing the Pixel Density
- •24.4.3 Choosing the Pixel Dwell Time
- •“Flash Mapping”
- •High Count Mapping
- •References
- •25.1 Gas Scattering Effects in the VPSEM
- •25.1.1 Why Doesn’t the EDS Collimator Exclude the Remote Skirt X-Rays?
- •25.2 What Can Be Done To Minimize gas Scattering in VPSEM?
- •25.2.2 Favorable Sample Characteristics
- •Particle Analysis
- •25.2.3 Unfavorable Sample Characteristics
- •References
- •26.1 Instrumentation
- •26.1.2 EDS Detector
- •26.1.3 Probe Current Measurement Device
- •Direct Measurement: Using a Faraday Cup and Picoammeter
- •A Faraday Cup
- •Electrically Isolated Stage
- •Indirect Measurement: Using a Calibration Spectrum
- •26.1.4 Conductive Coating
- •26.2 Sample Preparation
- •26.2.1 Standard Materials
- •26.2.2 Peak Reference Materials
- •26.3 Initial Set-Up
- •26.3.1 Calibrating the EDS Detector
- •Selecting a Pulse Process Time Constant
- •Energy Calibration
- •Quality Control
- •Sample Orientation
- •Detector Position
- •Probe Current
- •26.4 Collecting Data
- •26.4.1 Exploratory Spectrum
- •26.4.2 Experiment Optimization
- •26.4.3 Selecting Standards
- •26.4.4 Reference Spectra
- •26.4.5 Collecting Standards
- •26.4.6 Collecting Peak-Fitting References
- •26.5 Data Analysis
- •26.5.2 Quantification
- •26.6 Quality Check
- •Reference
- •27.2 Case Study: Aluminum Wire Failures in Residential Wiring
- •References
- •28: Cathodoluminescence
- •28.1 Origin
- •28.2 Measuring Cathodoluminescence
- •28.3 Applications of CL
- •28.3.1 Geology
- •Carbonado Diamond
- •Ancient Impact Zircons
- •28.3.2 Materials Science
- •Semiconductors
- •Lead-Acid Battery Plate Reactions
- •28.3.3 Organic Compounds
- •References
- •29.1.1 Single Crystals
- •29.1.2 Polycrystalline Materials
- •29.1.3 Conditions for Detecting Electron Channeling Contrast
- •Specimen Preparation
- •Instrument Conditions
- •29.2.1 Origin of EBSD Patterns
- •29.2.2 Cameras for EBSD Pattern Detection
- •29.2.3 EBSD Spatial Resolution
- •29.2.5 Steps in Typical EBSD Measurements
- •Sample Preparation for EBSD
- •Align Sample in the SEM
- •Check for EBSD Patterns
- •Adjust SEM and Select EBSD Map Parameters
- •Run the Automated Map
- •29.2.6 Display of the Acquired Data
- •29.2.7 Other Map Components
- •29.2.10 Application Example
- •Application of EBSD To Understand Meteorite Formation
- •29.2.11 Summary
- •Specimen Considerations
- •EBSD Detector
- •Selection of Candidate Crystallographic Phases
- •Microscope Operating Conditions and Pattern Optimization
- •Selection of EBSD Acquisition Parameters
- •Collect the Orientation Map
- •References
- •30.1 Introduction
- •30.2 Ion–Solid Interactions
- •30.3 Focused Ion Beam Systems
- •30.5 Preparation of Samples for SEM
- •30.5.1 Cross-Section Preparation
- •30.5.2 FIB Sample Preparation for 3D Techniques and Imaging
- •30.6 Summary
- •References
- •31: Ion Beam Microscopy
- •31.1 What Is So Useful About Ions?
- •31.2 Generating Ion Beams
- •31.3 Signal Generation in the HIM
- •31.5 Patterning with Ion Beams
- •31.7 Chemical Microanalysis with Ion Beams
- •References
- •Appendix
- •A Database of Electron–Solid Interactions
- •A Database of Electron–Solid Interactions
- •Introduction
- •Backscattered Electrons
- •Secondary Yields
- •Stopping Powers
- •X-ray Ionization Cross Sections
- •Conclusions
- •References
- •Index
- •Reference List
- •Index
373 |
22 |
22.3 · Challenges and Limitations of Low Beam Energy X-Ray Microanalysis
22.3.3\ At Low Beam Energy, Almost Everything Is Found To Be Layered
Most “pure” elements have surface layers such as native oxide, hydration layers, and others that compromise the requirement for uniform composition throughout the electron- excited volume of both the unknown and the standard(s). For example, when “pure” silicon is used as a standard, the inten-
sity of the O K-L2,3 peak, which arises from the SiO2 layer on Si, increases relative to the Si K-L2,3 peak as the beam energy
is lowered, as seen in . Fig. 22.19. In conventional analysis with E0 ≥10 keV, the deviation from “pure” silicon that this surface oxide represents does not constitute a significant source of error since the range is so much greater than the native oxide thickness. However, for low beam energy analysis, the surface oxide constitutes an increasingly significant fraction of the beam excitation volume as the beam energy is reduced, introducing an increasingly larger error because of the uncertainty in the standard composition.
The presence of the O K-L2,3 peak from a surface oxide is especially problematic when it interferes with the characteristic peak of interest, such as the Ti L-family, as shown in. Fig. 22.20. O K-L2,3 (0.525 keV) is separated from Ti L1-M2 (0.529 keV) by
4 eV. Note the large increase in intensity in this region as the beam energy is lowered from 10 keV to 2.5 keV due to the increased contribution from O K-L2,3 as the fraction of the interaction volume represented by the surface oxide increases. Obtaining an adequate standard and peak reference for Ti for low beam energy analysis is thus problematic. Even when a compound expected to be oxygen-free such as TiSi2 is selected, there still appears to be excess intensity due to O K-L2,3, as shown in. Fig. 22.20. Thus, it may be necessary to use advanced preparation, such as in situ ion milling to clean the surface of Ti to reduce the oxygen contribution to the spectrum.
The conductive coating that is applied to eliminate surface charging in insulating specimens becomes more significant as the beam energy is decreased. This effect is illustrated in
. Fig. 22.21 for spectra of the mineral benitoite (BaTiSi3O9) recorded over a wide range of incident beam energies, where
the peak for C K-L2,3 is barely detectable at E0 = 20 keV but becomes one of the most prominent peaks in the spectrum at
E0 = 2.5 keV. The analyst should try to minimize the carbon contribution to the spectrum by using the thinnest acceptable carbon layer, less than 10 nm thick, and it may be necessary to explore the use of ultrathin (~1 nm) heavy metal coatings as an alternative if it is desired to analyze for carbon.
Si_3keV
Si_2.8keV
Si_2.6keV
Si_2.4keV
Si_2.2keV
Si_2.0keV
Si_1.9keV
Counts
0.0 |
0.2 |
0.4 |
0.6 |
0.8 |
1.0 |
1.2 |
1.4 |
1.6 |
1.8 |
2.0 |
2.2 |
2.4 |
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Photon energy (keV) |
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Counts
Si |
Si_3keV |
Si_2.8keV |
|
1.9 keV |
Si_2.6keV |
Si_2.4keV |
|
2.0 keV |
Si_2.2keV |
Si_2.0keV |
|
2.2 keV |
Si_1.9keV |
|
|
2.4 keV |
|
2.6 keV |
|
2.8 keV |
|
3.0 keV |
|
0.0 |
0.2 |
0.4 |
0.6 |
0.8 |
1.0 |
1.2 |
1.4 |
1.6 |
1.8 |
2.0 |
2.2 |
2.4 |
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Photon energy (keV) |
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. Fig. 22.19 EDS spectra of Si over a range of beam energies, showing increase in the O K-L2 peak relative to Si K-L2; all spectra scaled to Si K-L2
\374 Chapter 22 · Low Beam Energy X-Ray Microanalysis
Counts
Ti_2.5kV50nA%DT
Ti_5kV30nA3%DT
Ti_10kV20nA6%DT
Ti
E0 = 2.5 keV E0 = 5 keV E0 = 10 keV
0.00 |
0.10 |
0.20 |
0.30 |
0.40 |
0.50 |
0.60 |
0.70 |
0.80 |
0.90 |
1.00 |
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Photon energy (keV) |
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Counts
Ti_2.5kV50nA2%DT TiSi2_2.5kV50nA1%DT
E0 = 2.5 keV Ti
TiSi2
0.0 |
0.2 |
0.4 |
0.6 |
0.8 |
1.0 |
1.2 |
1.4 |
1.6 |
1.8 |
2.0 |
2.2 |
2.4 |
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Photon energy (keV) |
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||
. Fig. 22.20 (Upper) EDS spectra of Ti at various beam energies showing increase in the O K-L2 peak relative to Ti L-family peaks; (lower) EDS spectra of Ti and TiSi2 at E0 = 2.5 keV
Finding an unexpected composition due to surface modification is a common experience when performing low beam energy analysis of materials that must be analyzed in the as- received condition. Without special surface preparation to expose the interior of the material, such as grinding and polishing or ion beam milling, the modified surface region dominates the analysis. . Figure 22.22 (upper spectrum) shows an example of TiB2, where inspection of the fitting residual after analyzing for B and Ti shows significant peaks for C and O. When these elements are included in the analysis, the fitting residual shown in . Fig. 22.22 (lower spectrum) is
obtained, showing no further undiscovered constituents. The analysis results presented in . Table 22.6 reveal significant concentrations of C and O in the TiB2. Note the greater variance in the C and O contaminants compared to the B and Ti host elements.
Analysis of Surface Contamination
Low beam energy analysis samples such a shallow near- surface region that unexpected contamination layers can dominate an analysis. This can lead to the confounding situation where the analysis can be correct, but what is being
22
375 |
22 |
22.3 · Challenges and Limitations of Low Beam Energy X-Ray Microanalysis
Counts
|
Benitoite_10kV20nA7%DT |
Benitoite |
Benitoite_5kV30nA4%DT |
Benitoite_2.5kV50nA2%DT |
|
BaTiSi3O9 |
Benitoite_20kV10nA7%DT |
|
|
2.5 keV |
|
5 keV |
|
10 keV |
|
20 keV |
|
0.0 |
1.0 |
2.0 |
3.0 |
4.0 |
5.0 |
6.0 |
7.0 |
8.0 |
9.0 |
10.0 |
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Photon energy (keV) |
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Benitoite_10kV20nA7%DT |
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Benitoite_5kV30nA4%DT |
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Benitoite_2.5kV50nA2%DT |
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Benitoite_20kV10nA7%DT |
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Counts
0.0 |
0.2 |
0.4 |
0.6 |
0.8 |
1.0 |
1.2 |
1.4 |
1.6 |
1.8 |
2.0 |
2.2 |
2.4 |
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Photon energy (keV) |
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. Fig. 22.21 EDS Spectra of benitoite (BaTiSi3O9) over arrange of beam energies showing relative increase in the C K-L2 peak as the beam energy decreases
measured is unanticipated. An example is shown in
. Fig. 22.23, which shows a low beam energy SDD-EDS spectrum of NIST SRM 481 (alloy 20Au-80Ag) where the surface was prepared metallographically more than 30 years earlier. The spectrum shows distinct peaks due to S and Cl from the formation of a surface tarnish layer. Quantitative X-ray microanalysis with DTSA-II confirms the high concentrations of S and Cl and very large RDEV values for Ag and Au, as shown in . Table 22.7a. The specimen mount was re-pol- ished with 0.25-μm diamond abrasive, which eliminated the S- and Clrich layer, as seen in the spectrum in . Fig. 22.23.
The results of the quantitative analysis after this first repolishing, which are presented in . Table 22.7b, show analytical totals near unity but large RDEV values for Ag and Au, especially for the 20Au-80Ag alloy. This large deviation from the SRM values is likely to be a consequence of the tarnish formation process selectively removing Ag from the alloy. After two additional repolishing steps with 1 μm and 0.25 μm diamond abrasives (. Tables 22.7c and 22.7d), this perturbed surface layer was finally removed, exposing the SRM alloy, with the DTSA-II analysis values closely matching the SRM certificate values.
\376 Chapter 22 · Low Beam Energy X-Ray Microanalysis
Counts
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TiB2_2p5kV50nA2%DT |
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40000 |
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Residual_TiB2_2p5kV50nA2%DT |
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30000 |
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E0 = 2.5 keV |
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TiB2 |
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Residual: B and Ti L fitting |
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20000 |
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10000 |
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0 |
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0.00 |
0.10 |
0.20 |
0.30 |
0.40 |
0.50 |
0.60 |
0.70 |
0.80 |
0.90 |
1.00 |
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Photon energy (keV) |
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Counts
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TiB2_2p5kV50nA2%DT |
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40000 |
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Residual_TiB2_2p5kV50nA2%DT |
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ResidualTiB2_fit_B_C_O_Ti |
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30000 |
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E0 = 2.5 keV |
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TiB2 |
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Residual: B and Ti L fitting |
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20000 |
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Residual: B, C, O and Ti L fitting |
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10000 |
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0 |
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0.00 |
0.10 |
0.20 |
0.30 |
0.40 |
0.50 |
0.60 |
0.70 |
0.80 |
0.90 |
1.00 |
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Photon energy (keV)
. Fig. 22.22 (Upper) EDS spectrum of TiB2 and residual spectrum after fitting for B K-L2 and Ti L-family revealing peaks for C K-L2and O K-L2; (lower) after fitting for C K-L2and O K-L2; E0 = 2.5 keV
. Table 22.6 Analysis of TiB2 at E0 = 2.5 keV |
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B (atomic concentration) |
C (atomic concentration) |
O (atomic concentration) |
Ti (atomic concentration) |
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Mean (5 analyses) |
0.5110 |
0.0708 |
0.1011 |
0.3171 |
σrel, % |
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2.7 |
27 |
11 |
2.7 |
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22
22.3 · Challenges and Limitations of Low Beam Energy X-Ray Microanalysis
Counts
Counts
20000
15000
10000
5 000
0
0
15000
10000
5000
0
1
1 |
2 |
3 |
Photon energy (keV)
NIST DTSA-II Quantitative analysis
20Au80Ag, 1st-repolishing E0 = 5 keV
2
Photon energy (keV)
377 |
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22 |
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20Au-80Ag alloy, original surface 20Au-80Ag alloy, 1st-repolishing (0.25 µm) E0 = 5 keV
4 |
5 |
20Au80Ag_repolished 20Au80Ag_residual
3 |
4 |
. Fig. 22.23 NIST SRM 481 (Au-Ag alloys). Analysis of an old (>30 years) metallographic preparation at E0 = 5 keV, and the spectrum after repolishing with 0.25 μm diamond abrasive
22
. Table 22.7a Analysis of SRM 481 (Au-Ag alloys); 1970s metallographic preparation, original surface; E0=5 keV; standards: S (FeS2); Cl (KCl); Ag, Au
Alloy |
Raw analytical |
S (norm mass |
σ(%)5 |
Cl (norm mass |
σ(%) 5 |
Au (norm mass |
σ(%)5 loc |
RDEV(%) |
Ag (norm mass |
σ(%) 5 loc |
RDEV (%) |
|
total |
conc) |
loc |
conc) |
loc |
conc) |
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conc) |
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20Au–80Ag |
0.9855 |
0.0934 |
4.4 |
0.1061 |
12 |
0.0796 |
12 |
−64 |
0.7210 |
0.44 |
−7 |
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−14 |
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40Au–60Ag |
0.9959 |
0.0311 |
5.7 |
0.0965 |
10 |
0.3440 |
6.1 |
0.5284 |
2.2 |
−12 |
|
60Au–40Ag |
0.9951 |
0.0094 |
5 |
0.045 |
22 |
0.5754 |
4.7 |
−4.2 |
0.3706 |
4.6 |
−7.2 |
80Au–20Ag |
1.005 |
0.0051 |
8.3 |
0.0365 |
4.5 |
0.7340 |
0.67 |
−8.3 |
0.2244 |
1.6 |
+12 |
. Table 22.7b Analysis of SRM 481 (Au-Ag alloys); surface after first repolishing with 0.25-μm diamond; E0=5 keV; standards: Ag, Au |
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Alloy |
Raw analytical |
Au (norm) |
σ(%) 5 loc |
RDEV (%) |
DTSA-II error |
Ag (norm) |
σ(%) 5 loc |
RDEV (%) |
DTSA-II error |
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total |
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budget (%) |
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budget (%) |
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−10.4 |
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20Au–80Ag |
0.9731 |
0.3050 |
7.1 |
+36 |
0.34 |
0.6950 |
3.1 |
0.75 |
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−7.6 |
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40Au–60Ag |
0.9920 |
0.4460 |
0.96 |
+11.4 |
0.25 |
0.5540 |
0.77 |
1.1 |
|
60Au–40Ag |
0.9907 |
0.6322 |
1.0 |
+5.3 |
0.21 |
0.3678 |
1.8 |
−7.9 |
1.5 |
80Au–20Ag |
0.9930 |
0.8264 |
0.24 |
3.2 |
0.17 |
0.1736 |
1.1 |
−13 |
2.1 |
Microanalysis Ray-X Energy Beam Low · 22 Chapter 378\
. Table 22.7c Analysis of SRM 481 (Au-Ag alloys); surface after second repolishing with 1- and 0.25-μm diamond; E05= keV; standards: Ag, Au
Alloy |
Raw analytical |
Au (norm) |
σ(%) 5 loc |
RDEV (%) |
DTSA-II error |
Ag (norm) |
σ(%) 5 loc |
RDEV (%) |
DTSA-II error |
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total |
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budget (%) |
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budget (%) |
20Au–80Ag |
1.005 |
0.2398 |
0.87 % |
+6.9 % |
0.38 % |
0.7602 |
0.28 % |
−2.0 % |
0.64 % |
40Au–60Ag |
0.9983 |
0.4045 |
0.23 |
+1.1 |
0.27 |
0.5955 |
0.16 |
−0.64 |
0.98 |
60Au–40Ag |
0.9897 |
0.6084 |
0.13 |
+1.3 |
0.21 |
0.3916 |
0.21 |
−1.9 |
1.4 |
80Au–20Ag |
0.9998 |
0.8055 |
0.26 |
+0.62 |
0.19 |
0.1945 |
1.1 |
−2.5 |
1.9 |
20Au–80Ag |
1.005 |
0.2398 |
0.87 |
+6.9 |
0.38 |
0.7602 |
0.28 |
−2.0 |
0.64 |
. Table 22.7d Analysis of SRM 481 (Au-Ag alloys); surface after third repolishing with 1- and 0.25-μm diamond; E05= keV; standards: Ag, Au
Alloy |
Raw analytical |
Au (norm) |
σ(%) 5 loc |
RDEV (%) |
DTSA-II error |
Ag (norm) |
σ(%) 5 loc |
RDEV (%) |
DTSA-II error |
|
total |
|
|
|
budget (%) |
|
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|
budget (%) |
20Au–80Ag |
1.017 |
0.2251 |
0.13 |
−0.11 |
0.39 |
0.7749 |
0.13 |
+0.35 |
0.61 |
40Au–60Ag |
0.9988 |
0.3909 |
0.25 |
−2.3 |
0.28 |
0.6091 |
0.16 |
+1.6 |
0.93 |
60Au–40Ag |
0.9931 |
0.5931 |
0.12 |
−1.2 |
0.22 |
0.4069 |
0.18 |
+1.9 |
1.4 |
80Au–20Ag |
0.9957 |
0.7979 |
0.17 |
−0.32 |
0.18 |
0.2021 |
0.68 |
+1.2 |
1.9 |
Microanalysis Ray-X Energy Beam Low of Limitations and Challenges · 3.22
379
22