Scanning Electron Microscopy and X-Ray Microanalysis Joseph I

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Scanning Electron Microscopy and X-Ray Microanalysis Joseph I. Goldstein Dale E. Newbury Joseph R. Michael Nicholas W.M. Ritchie John Henry J. Scott David C. Joy

Scanning Electron Microscopy and X-Ray Microanalysis

Fourth Edition Joseph I. Goldstein Dale E. Newbury University of Massachusetts National Institute of Standards and Technology Amherst, MA, USA Gaithersburg, MD, USA Joseph R. Michael Nicholas W.M. Ritchie Sandia National Laboratories National Institute of Standards and Technology Albuquerque, NM, USA Gaithersburg, MD, USA John Henry J. Scott David C. Joy National Institute of Standards and Technology University of Tennessee Gaithersburg, MD, USA Knoxville, TN, USA

ISBN 978-1-4939-6674-5 ISBN 978-1-4939-6676-9 (eBook) https://doi.org/10.1007/978-1-4939-6676-9

Library of Congress Control Number: 2017943045

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Preface

This is not your father’s, your mother’s, or your is that a reader seeking specific information can grandparent’s Scanning Electron Microscopy and select a topic from the list and obtain a good X-Ray Microanalysis (SEMXM). But that is not to understanding of the topic from that module say that there is no continuity or to deny a family alone. While each topic is supported by informa- resemblance. SEMXM4 is the fourth in the series tion in other modules, we acknowledge the like- of textbooks with this title, and continues a tradi- lihood that not all users of SEMXM4 will “read tion that extends back to the “zero-th edition” in it all.” This approach inevitably leads to a degree 1975 published under the title, “Practical Scanning of overlap and repetition since similar informa- Electron Microscopy” (Plenum Press, New York). tion may appear in two or more places, and this is However, the latest edition differs sharply from entirely intentional. its predecessors, which attempted an encyclope- dic approach to the subject by providing extensive In recognition of these fundamental changes, the details on how the SEM and its associated devices authors have chosen to modify SEMXM4 exten- actually work, for example, electron sources, lenses, sively to provide a guide on the actual use of the electron detectors, X-ray spectrometers, and so on. instrument without overwhelming the reader with the burden of details on the physics of the opera- In constructing this new edition, the authors have tion of the instrument and its various attachments. chosen a different approach. Modern SEMs and the Our guiding principle is that the microscopist- associated X-ray spectrometry and crystallography microanalyst must understand which parameters measurement functions operate under such exten- can be adjusted and what is an effective strategy to sive computer control and automation that it is select those parameters to solve a particular prob- actually difficult for the microscopist-microanalyst lem. The modern SEM is an extraordinarily flex- to interact with the instrument except within care- ible tool, capable of operating over a wide range fully prescribed boundaries. Much of the flexibility of electron optical parameters and producing of parameter selection that early instruments pro- images from electron detectors with different sig- vided has now been lost, as instrumental operation nal characteristics. Those users who restrict them- functions have been folded into software control. selves to a single set of operating parameters may Thus, electron sources are merely turned “on,” with be able to solve certain problems, but they may the computer control optimizing the operation, or never know what they are missing by not explor- for the thermally assisted field emission gun, the ing the range of parameter space available to them. electron source may be permanently “on.” The user SEMXM4 seeks to provide sufficient understand- can certainly adjust the lenses to focus the image, ing of the technique for a user to become a com- but this focusing action often involves complex petent and efficient problem solver. That is not to interactions of two or more lenses, which formerly say that there are only a few things to learn. To would have required individual adjustment. More- help the reader to approach the considerable body over, the nature of the SEM field has fundamentally of knowledge needed to operate at a high degree changed. What was once a very specialized instru- of competency, a new feature of SEMXM-4 is the ment system that required a high level of training summary checklist provided for each of the major and knowledge on the part of the user has become areas of operation: SEM imaging, elemental X-ray much more of a routine tool. The SEM is now sim- microanalysis, and backscatter-diffraction crystal- ply one of a considerable suite of instruments that lography. can be employed to solve problems in the physical and biological sciences, in engineering, in technol- Readers familiar with earlier editions of SEMXM ogy, in manufacturing and quality control, in fail- will notice the absence of the extensive material ure analysis, in forensic science, and other fields. previously provided on specimen preparation. Proper specimen preparation is a critical step in The authors also recognize the profound changes solving most problems, but with the vast range of that have occurred in the manner in which peo- applications to materials of diverse character, the ple obtain information. The units of SEMXM4, topic of specimen preparation itself has become whether referred to as chapters or modules, are the subject of entire books, often devoted to just meant to be relatively self-contained. Our hope one specialized area. VI Preface

Throughout their history, the authors of the Finally, the author team sadly notes the passing in SEMXM textbooks have been closely associated 2015 of Professor Joseph I. Goldstein (University as lecturers with the Lehigh University Summer of Massachusetts, Amherst) who was the “found- Microscopy School. The opportunity to teach and ing father” of the Lehigh University Summer interact with each year’s students has provided a Microscopy School in 1970, and who organized very useful experience in understanding the com- and contributed so extensively to the microscopy munity of users of the technique and its evolution courses and to the SEMXM textbooks throughout over time. We hope that these interactions have the ensuing 45 years. Joe provided the stimulus to improved our written presentation of the subject the production of SEMXM4 with his indefatigable as a benefit to newcomers as well as established spirit, and his technical contributions are embed- practitioners. ded in the X-ray microanalysis sections.

Dale E. Newbury Nicholas W.M. Ritchie John Henry J. Scott Gaithersburg, MD, USA

Joseph R. Michael Albuquerque, NM, USA

David C. Joy Knoxville, TN, USA

The original version of this book was revised. Index has been updated. VII

Scanning Electron Microscopy and Associated Techniques: Overview

Imaging Microscopic Features location on the sample is digitized and recorded into computer memory, and is subsequently used The scanning electron microscope (SEM) is an to determine the gray level at the corresponding instrument that creates magnified images which X-Y location of a computer display screen, form- reveal microscopic-scale information on the size, ing a single picture element (or pixel). In a con- shape, composition, crystallography, and other ventional-vacuum SEM, the electron-optical physical and chemical properties of a specimen. column and the specimen chamber must operate The principle of the SEM was originally demon- under high vacuum conditions (<10−4 Pa) to min- strated by Knoll (1935; Knoll and Theile 1939) imize the unwanted scattering that beam elec- with the first true SEM being developed by von trons as well as the BSEs and SEs would suffer by Ardenne (1938). The modern commercial SEM encountering atoms and molecules of atmo- emerged from extensive development in the 1950s spheric gasses. Insulating specimens that would and 1960s by Prof. Sir Charles Oatley and his develop surface electrical charge because of many students at the University of Cambridge impact of the beam electrons must be given a con- (Oatley 1972). The basic operating principle of ductive coating that is properly grounded to pro- the SEM involves the creation of a finely focused vide an electrical discharge path. In the variable beam of energetic electrons by means of emission pressure SEM (VPSEM), specimen chamber pres- from an electron source. The energy of the elec- sures can range from 1 Pa to 2000 Pa (derived trons in this beam, E0, is typically selected in the from atmospheric gas or a supplied gas such as range from E0 = 0.1 to 30 keV). After emission water vapor), which provides automatic discharg- from the source and acceleration to high energy, ing of uncoated insulating specimens through the the electron beam is modified by apertures, mag- ionized gas atoms and free electrons generated by netic and/or electrostatic lenses, and electromag- beam, BSE, and SE interactions. At the high end netic coils which act to successively reduce the of this VPSEM pressure range with modest speci- beam diameter and to scan the focused beam in a men cooling (2–5 °C), water can be maintained in raster (x-y) pattern to place it sequentially at a a gas–liquid equilibrium, enabling direct exami- series of closely spaced but discrete locations on nation of wet specimens. the specimen. At each one of these discrete locations in the scan pattern, the interaction of the SEM electron-optical parameters can be optimized electron beam with the specimen produces two for different operational modes: outgoing electron products: (1) backscattered 1. A small beam diameter can be selected for high electrons (BSEs), which are beam electrons that spatial resolution imaging, with extremely fine emerge from the specimen with a large fraction of scale detail revealed by possible imaging strate- their incident energy intact after experiencing gies employing high beam energy, for example,

Fig 1a scattering and deflection by the electric fields of . . (E0 = 15 keV) and low beam energy,

Fig 1b Fig 1c the atoms in the sample; and (2) secondary elec- . . (E0 = 0.8 keV), . . (E0 = 0.5 keV),

Fig 1d trons (SEs), which are electrons that escape the and . . (E0 = 0.3 keV). However, a nega- specimen surface after beam electrons have tive consequence of choosing a small beam ejected them from atoms in the sample. Even size is that the beam current is reduced as the though the beam electrons are typically at high inverse square of the beam diameter. Low beam energy, these secondary electrons experience low current means that visibility is compromised kinetic energy transfer and subsequently escape for features that produce weak contrast. the specimen surface with very low kinetic ener- 2. A high beam current improves visibility of low gies, in the range 0–50 eV, with the majority below contrast objects (e.g., . Fig. 2). For any combi- 5 eV in energy. At each beam location, these out- nation of beam current, pixel dwell time, and going electron signals are measured using one or detector efficiency there is always a threshold more electron detectors, usually an Everhart– contrast below which features of the speci- Thornley “secondary electron” detector (which is men will not be visible. This threshold contrast actually sensitive to both SEs and BSEs) and a depends on the relative size and shape of the “dedicated backscattered electron detector” that is feature of interest. The visibility of large objects insensitive to SEs. For each of these detectors, the and extended linear objects persists when signal measured at each individual raster scan small objects have dropped below the visibility VIII Scanning Electron Microscopy and Associated Techniques: Overview

a b

100 nm EHT - 15.00 kV Signal A = InlLens Mag - 94.28 K XWidth - 1.213 mm Date: 19 Oct 2015 YK WD - 1.7 mm Signal B = InlLens I Probe - 135 pA ESB Grid = 800 V Image Pixel Size - 1.184 nm c

HV mag HFW WD 500 nm 800.00 V 100 000 x 1.49 µm 990.7 µm Helios d

SU8200 0.50kV-D 1.6mm X 200k SE+BSE(TU) 200nm

10nm JEOL x500,000 0.30kV UED GBSH WD 2.0mm

SU8200 0.50kV-D 1.6mm X 500k SE+BSE(TU) 100nm

.. Fig. 1 a High resolution SEM image taken at high (image courtesy of Trevan Landin, FEI); Bar = 500 nm. c beam energy (E0 = 15 keV) of a finFET transistor (16-nm Mesoporous silica nanosphere showing 5-nm-diameter technology) using an in-lens secondary electron detector. pores imaged with a landing energy of 0.5 keV (specimen This cross section was prepared by inverted Ga FIB milling courtesy of T. Yokoi, Tokyo Institute of Technology; images from backside (Zeiss Auriga Cross beam; image courtesy courtesy of A. Muto, Hitachi High Technologies); Upper image of John Notte, Carl Zeiss); Bar = 100 nm. b High resolu- Bar = 200 nm, Lower image Bar = 100 nm. d Si nanoparticle tion SEM image taken at low beam energy (E0 = 0.8 keV) of imaged with a landing energy of 0.3 keV; Bar = 10 nm zeolite (uncoated) using a through-the-lens SE detector (image courtesy V. Robertson, JEOL)

threshold. This threshold can only be lowered 3. The beam divergence angle can be minimized

by increasing beam current, pixel dwell time, to increase the depth-of-field (e.g.,. Fig. 3). and/or detector efficiency. Selecting higher With optimized selection of aperture size and beam current means a larger beam size, caus- specimen-to-objective lens distance (working resolution to deteriorate. Thus, there is a ing distance), it is generally possible to achieve dynamic contest between resolution and visibil- small beam convergence angles and therefore ity leading to inevitable limitations on feature effective focus along the beam axis that is at size and feature visibility that can be achieved. least equal to the horizontal width of the image. IX Scanning Electron Microscopy and Associated Techniques: Overview

0.5 nA 20 nA

20 mm 20 mm BSE MAG: 1000 x HV: 20.0 kV WD: 11.0 mm BSE MAG: 1000 x HV: 20.0 kV WD: 11.0 mm

.. Fig. 2 Effect of increasing beam current (at constant pixel dwell time) to improve visibility of low contrast features.

Al-Si eutectic alloy; E0 = 20 keV; semiconductor BSE detector (sum mode): (left) 0.5 nA; (right) 20 nA; Bar = 20 µm

1 2

10 mm BSE MAG: 750 x HV: 20.0 kV WD: 11.0mm

.. Fig. 4 Atomic number contrast with backscattered HV WD magdet mode HFW 4 mm electrons. Raney nickel alloy, polished cross section; 20.00 kV 8.0 mm 12 711 x ETD Custom 11.7 mm NIST FEG ESEM E0 = 20 keV; semiconductor BSE (sum mode) detector. Note that four different phases corresponding to different com- .. Fig. 3 Large the depth-of-focus; Sn spheres; positions can be discerned; Bar = 10 µm E0 = 20 keV; Everhart–Thornley(positive bias) detector; Bar = 4 µm (Scott Wight, NIST)

A negative consequence of using a small aper- limited to approximately 10–100 nm depend- ture to reduce the convergence/divergence angle ing on the specimen composition and the is a reduction in beam current. beam energy selected.

2. Topography (shape) (e.g., . Fig. 5). Topo- Vendor software supports collection, dynamic graphic structure can be imaged with varia- processing, and interpretation of SEM images, tions in local surface inclination as small as including extensive spatial measurements. Open a few degrees. The edges of structures can source software such as ImageJ-Fiji, which is be localized with a spatial resolution rang- highlighted in this textbook, further extends these ing from the incident beam diameter (which digital image processing capabilities and provides can be 1 nm or less, depending on the elec- the user access to a large microscopy community tron source) up to 10 nm or greater, depend- effort that supports advanced image processing. ing on the material and the geometric nature General specimen property information that of the edge (vertical, rounded, tapered, re- can be obtained from SEM images: entrant, etc.).

1. Compositional microstructure (e.g., . Fig. 4). 3. Visualizing the third dimension (e.g., . Fig. 6). Compositional variations of 1 unit differ- Optimizing for a large depth-of-field permits ence in average atomic number (Z) can be visualizing the three-dimensional structure observed generally with BSE detection, with of a specimen. However, in conventional X-Y even greater sensitivity (ΔZ = 0.1) for low image presentation, the resulting image is a (Z = 6) and intermediate (Z = 30) atomic num- projection of the three dimensional informa- bers. The lateral spatial resolution is generally tion onto a two dimensional plane, suffering X Scanning Electron Microscopy and Associated Techniques: Overview

20 mm20 mm SE MAG: 500 X HV: 20.0 kV WD: 11.0 mm BSE MAG: 500 X HV: 20.0 kV WD: 11.0 mm

.. Fig. 5 Topographic contrast as viewed with different detectors: Everhart–Thornley (positive bias) and semiconductor

BSE (sum mode); silver crystals; E0 = 20 keV; Bar = 20 µm

Measuring the Elemental Composition

The beam interaction with the specimen produces two types of X-ray photon emissions which com- pose the X-ray spectrum: (1) characteristic X-rays, whose specific energies provide a fingerprint that is specific to each element, with the exception of H and He, which do not emit X-rays; and (2) continuum X-rays, which occur at all photon energies

from the measurement threshold to E0 and form a background beneath the characteristic X-rays. This X-ray spectrum can be used to identify and quantify the specific elements (excepting H and He, which do not produce X-rays) present within the beam-excited interaction volume, which has SEM HV: 15.0 kV WD: 9.42 mm dimensions ranging from approximately 100 nm View field: 439 mm Det: SE 100 mm to 10 μm depending on composition and beam .. Fig. 6 Visualizing the third dimension. Anaglyph ste- energy, over a wide range of concentrations (C, reo pair (red filter over left eye) of pollen grains on plant expressed in mass fraction): fibers; E0 = 15 keV; coated with Au-Pd; Bar = 100 µm “Major constituent”: 0.1 < C ≤ 1 “Minor constituent”: 0.01 ≤ C ≤ 0.1 spatial distortion due to foreshortening. The “Trace constituent”: C < 0.01 true three-dimensional nature of the specimen can be recovered by applying the tech- The X-ray spectrum is measured with the semi- niques of stereomicroscopy, which invokes conductor energy dispersive X-ray spectrometer the natural human visual process for stereo (EDS), which can detect photons from a threshold imaging by combining two independent views of approximately 40 eV to E0 (which can be as high of the same area made with small angular dif- as 30 keV). Vendor software supports collection ferences. and analysis of spectra, and these tools can be aug- 4. Other properties which can be accessed by mented significantly with the open source software SEM imaging: (1) crystal structure, including National Institute of Standards and Technology grain boundaries, crystal defects, and crystal DTSA II for quantitative spectral processing and

deformation effects (e.g.,. Fig. 8); (2) mag- simulation, discussed in this textbook. netic microstructure, including magnetic Analytical software supports qualitative X-ray domains and interfaces; (3) applied electri- microanalysis which involves assigning the char- cal fields in engineered microstructures; (4) acteristic peaks recognized in the spectrum to electron-stimulated optical emission (cath- specific elements. Qualitative analysis presents odoluminescence), which is sensitive to low significant challenges because of mutual peak energy electronic structure. interferences that can occur between certain XI Scanning Electron Microscopy and Associated Techniques: Overview combinations of elements, for example, Ti and standard spectra can be effectively used if a quality Ba; S, Mo, and Pb; and many others, especially measurement program is implemented to ensure when the peaks of major constituents interfere the constancy of measurement conditions, includ- with the peaks of minor or trace constituents. ing spectrometer performance parameters. With Operator knowledge of the physical rules govern- such a standards-based measurement protocol and ing X-ray generation and detection is needed to ZAFc matrix corrections, the accuracy of the anal- perform a careful review of software-generated ysis can be expressed as a relative deviation from peak identifications, and this careful review must expected value (RDEV): always be performed to achieve a robust measurement result. RDEV ()%%=´[]()Measured-True / True 100 (2) After a successful qualitative analysis has been performed, quantitative analysis can proceed. Based on extensive testing of homogeneous The characteristic intensity for each peak is auto- binary and multiple component compositions, matically determined by peak fitting procedures, the distribution of RDEV values for major con- such as the multiple linear least squares method. stituents is such that a range of ±5 % relative cap- The intensity measured for each element is pro- tures 95 % of all analyses. The use of stable, high portional to the concentration of that element, integrated count spectra (>1 million total counts but that intensity is also modified by all other ele- from threshold to E ) now possible with the sili- ments present in the interaction volume through 0 con drift detector EDS (SDD-EDS), enables this their influence on the electron scattering and level of accuracy to be achieved for major and retardation (“atomic number” matrix effect, Z), minor constituents even when severe peak inter- X-ray absorption within the specimen (“absorp- ference occurs and there is also a large concen- tion” matrix effect, A), and X-ray generation tration ratio, for example, a major constituent induced by absorption of X-rays (“secondary flu- interfering with a minor constituent. Trace con- orescence” matrix effects, F, induced by charac- stituents that do not suffer severe interference teristic X-rays and c, induced by continuum can be measured to limits of detection as low as X-rays). The complex physics of these “ZAFc” C = 0.0002 (200 parts per million) with spectra matrix corrections has been rendered into algo- containing >10 million counts. For interference rithms by a combined theoretical and empirical situations, much higher count spectra (>100 approach. The basis of quantitative electron- million counts) are required. excited X-ray microanalysis is the “k-ratio proto- An alternative “standardless analysis” protocol col”: measurement under identical conditions uses libraries of standard spectra (“remote stan- (beam energy, known electron dose, and spec- dards”) measured on a different SEM platform trometer performance) of the characteristic with a similar EDS spectrometer, ideally over a intensities for all elements recognized in the wide range of beam energy and detector parame- unknown spectrum against a suite of standards ters (resolution). These library spectra are then containing those same elements, producing a set adjusted to the local measurement conditions of k-ratios, where through comparison of one or more key spectra (e.g., locally measured spectra of particular ele- kI= / I (1) UnknownStandard ments such as Si and Ni). Interpolation/extrapola- tion is used to supply estimated spectral intensities for each element in the unknown. Standards are for elements not present in or at a beam energy not materials of known composition that are tested to represented in the library elemental suite. Testing be homogeneous at the microscopic scale, and of the standardless analysis method has shown preferably homogeneous at the nanoscale. that an RDEV range of ±25 % relative is needed to Standards can be as simple as pure elements—e.g., capture 95 % of all analyses. C, Al, Si, Ti, Cr, Fe, Ni, Cu, Ag, Au, etc.—but for High throughput (>100 kHz) EDS enables col- those elements that are not stable in a vacuum lection of X-ray intensity maps with gray scale rep- (e.g., gaseous elements such as O) or which resentation of different concentration levels (e.g., degrade during electron bombardment (e.g., S, P, . Fig. 7a). Compositional mapping by spectrum and Ga), stable stoichiometric compounds can be imaging (SI) collects a full EDS spectrum at each used instead, e.g., MgO for O; FeS2 for S; and GaP pixel of an x-y array, and after applying the quanti- for Ga and P. The most accurate analysis is per- tative analysis procedure at each pixel, images are formed with standards measured on the same created for each element where the gray (or color) instrument as the unknown(s), ideally in the same level is assigned based on the measured concentra- measurement campaign, although archived tion (e.g., . Fig. 7b). XII Scanning Electron Microscopy and Associated Techniques: Overview

Al Fe

20µm

Ni Al Fe Ni

BSE Al

20 mm BSE MAG: 1000 x HV: 20.0 kV WD: 11.0 mm

Ni Fe

20µm 0.001 0.01 0.1 1.0 b 0.1 1.010 100 wt%

.. Fig. 7 a EDS X-ray intensity maps for Al, Fe, and Ni and color overlay; Raney nickel alloy; E0 = 20 keV. b SEM/BSE (sum) image and compositional maps corresponding to a XIII Scanning Electron Microscopy and Associated Techniques: Overview

Measuring the Crystal Structure Dual-Beam Platforms: Combined Electron and Ion Beams An electron beam incident on a crystal can undergo electron channeling in a shallow near-surface layer A “dual-beam” instrument combines a fully func- which increases the initial beam penetration for tional SEM with a focused ion beam (FIB), typi- certain orientations of the beam relative to the cally gallium or argon. This combination provides crystal planes. The additional penetration results in a flexible platform for in situ specimen modifica- a slight reduction in the electron backscattering tion through precision ion beam milling and/or coefficient, which creates weak crystallographic ion beam mediated material deposition with contrast (a few percent) in SEM images by which sequential or simultaneous electron beam tech- differences in local crystallographic orientation nique characterization of the newly revealed can be directly observed: grain boundaries, defor- specimen surfaces. Precision material removal mations bands, and so on (e.g., . Fig. 8). enables detailed study of the third dimension of a The backscattered electrons exiting the speci- specimen with nanoscale resolution along the men are subject to crystallographic diffraction depth axis. An example of ion beam milling of a effects, producing small modulations in the intensi- directionally solidified Al-Cu is shown in. Fig. 9, ties scattered to different angles that are superim- as imaged with the SEM column on the dual- posed on the overall angular distribution that an beam instrument. Additionally, ion-beam amorphous target would produce. The resulting induced secondary electron emission provides “electron backscatter diffraction (EBSD)” pattern scanning ion microscopy (SIM) imaging to com- provides extensive information on the local orienta- plement SEM imaging. For imaging certain speci- tion, as shown in . Fig. 8b for a crystal of hematite. men properties, such as crystallographic EBSD pattern angular separations provide mea- structure, SIM produces stronger contrast than surements of the crystal plane spacing, while the SEM. There is also an important class of stand- overall EBSD pattern reveals symmetry elements. alone SIM instruments, such as the helium ion This crystallographic information combined with microscope (HIM), that are optimized for high elemental analysis information obtained simultane- resolution/high depth-of-field imaging perfor- ously from the same specimen region can be used to mance (e.g., the same area as viewed by HIM is identify the crystal structure of an unknown. also shown in . Fig. 9).

a b

40 mm BSE MAG: 400 x HV: 20.0 kV WD: 11.0 mm

.. Fig. 8 a Electron channeling contrast revealing grain boundaries in Ti-alloy (nominal composition: Ti-15Mo-3Nb-3Al-

0.2Si); E0 = 20 keV. b Electron backscatter diffraction (EBSD) pattern from hematite atE 0 = 40 keV XIV Scanning Electron Microscopy and Associated Techniques: Overview

Field of view Dwell Time Mag (4x5 Polaroid) 50.00 um 5.00 um 50.0 us 2,540.00 X magHVWDHFW curr 20 µm Working Dist Image Size Blankar Current Detector 5 000 x15.00 kV 3.9 mm 51.2 µm 86 pA 12.1 mm 1024x1024 0.7 9A PrimaryETDetector

.. Fig. 9 Directionally-solidified Al-Cu eutectic alloy after ion beam milling in a dual-beam instrument, as imaged by the SEM column (left image); same region imaged in the HIM (right image)

Modeling Electron and Ion References Interactions Knoll M (1935) Static potential and secondary emission of bodies under electron radiation. Z Tech Physik 16:467 An important component of modern Scanning Knoll M, Theile R (1939) Scanning electron microscope for Electron Microscopy and X-ray Microanalysis determining the topography of surfaces and thin is modeling the interaction of beam electrons layers. Z Physik 113:260 and ions with the atoms of the specimen and its Oatley C (1972) The scanning electron microscope: part 1, environment. Such modeling supports image the instrument. Cambridge University Press, Cambridge von Ardenne M (1938) The scanning electron microscope. interpretation, X-ray microanalysis of challeng- Theoretical fundamentals. Z Physik 109:553 ing specimens, electron crystallography methods, and many other issues. Software tools for this pur- pose, including Monte Carlo electron trajectory simulation, are discussed within the text. These tools are complemented by the extensive database of Electron-Solid Interactions (e.g., electron scattering and ionization cross sections, secondary electron and backscattered electron coefficients, etc.), developed by Prof. David Joy, can be found in chapter 3 on SpringerLink: http://link.springer. com/chapter/10.1007/978-1-4939-6676-9_3. XV

Contents

1 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 XVI Contents

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 XVII Contents

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 XVIII Contents

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 XIX Contents

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 XX Contents

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 XXI Contents

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 XXII Contents

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 XXIII Contents

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