Electron Probe X-Ray Microanalysis (EPMA) 1.3.5 Electron Probe X-Ray Microanalysis (EPMA)is an elemental analysis technique based upon bombarding a specimen with a focused beam of energetic electrons (beam energy 5-30 keV)to induce emission of characteristic X rays(energy range 0.1-15 keV).The X rays are measured by Energy-Dispersive (EDS)or Wave- length-Dispersive (WDS)X-ray spectromete rs.Ou ntitative matrix (interelement) tion procedur upon firs t pr es physical ng unknown samples of arbitrary composition;the standard suite can be as simple as pure elements or binary compounds.Typical error distri- butions are such that relative concentration errors lie within 4%for 95%of cases when the analysis is performed with pure element standards.Spatial distributions of elemental constituents can be visualized qualitatively by X-ray area scans (dot maps)and quantitatively by digital compositional maps. Range ofelements Beryllium to the actinides Destructive No,except for electron beam damage Chemical bonding In rare cases:from light-element X-ray peak shifts Depth profiling Rarely,by changing incident beam energy Quantification Standardless or;pure element standards Accuracy t4%relative in 95%of cases;flat,polished sample Detection limits WDS,100 ppm;EDS,1000 ppm Sampling depth Energy and matrix dependent,100 nm-5 um Lateral resolution Energy and matrix dependent,100 nm-5 um Imaging/mapping Yes,compositional mapping and SEM imaging Sample requirements Solid conducte rs and insulat eter aces,indnhi Major uses tructive quantita tive ater Instrument cost $300,000-$800,000 Size 3mx 1.5mx 2m high 15
Electron Probe X-Ray Microanalysis (EPMA) 1.3.5 Electron Probe X-Ray Microanalysis (EPMA) is an elemental analysis technique based upon bombarding a specimen with a focused beam of energetic electrons (beam energy 5-30 kev) to induce emission of characteristic X rays (energy range 0.1-15 kev). The X rays are measured by Energy-Dispersive (EDS) or Wavelength-Dispersive (WDS) X-ray spectrometers. Quantitative matrix (interelement) correction procedures based upon first principles physical models provide great flexibility in attacking unknown samples of arbitrary composition; the standards suite can be as simple as pure elements or binary compounds. Typical error distributions are such that relative concentration errors lie within &4% for 95% of cases when the analysis is performed with pure element standards. Spatial distributions of elemental constituents can be visualized qualitatively by X-ray area scans (dot maps) and quantitatively by digital compositional maps. Range of elements Beryllium to the actinides Destructive No, except for electron beam damage Chemical bonding In rare cases: from light-element X-ray peak shifts Depth profiling Rarely, by changing incident beam energy Quantification Standardless or; pure element standards Accuracy &4% relative in 95% of cases; flat, polished samples Detection limits WDS, 100 ppm; EDS, 1000 ppm Sampling depth Energy and matrix dependent, 100 nm-5 pm Lateral resolution Energy and matrix dependent, 100 nm-5 pm Imaging/mapping Yes, compositional mapping and SEM imaging Sample requirements Solid conductors and insulators; typically, e 2.5 cm in diameter, and e 1 cm thick, polished flat; particles, rough surfldces, and thin films Major uses Accurate, nondestructive quantitative analysis of major, minor, and trace constituents of materials Instrument cost $300,000-$800,000 Size 3 mx 1.5 mx 2 m high 15
X-Ray Diffraction (XRD) 1.4.1 In X-Ray Diffraction (XRD)a collimated beam of X rays,with wavelength A-0.5- 2 A,is incident on a specimen and is diffracted by the crystalline phases in the spec imen according to Bragg's law (=2dsin0,where dis the spacing between atomic phase).The in vs is angle 20 an nd the spec n.This diffra tion pattern is used to identify the specimen's crystalline phases and to measure its structural properties,including strain(which is measured with great accuracy),epi- taxy,and the size and orientation of crystallites(small crystalline regions).XRD can also determine concentration profiles,film thicknesses,and atomic arrangements in am Ir als chara erize defects.To obtain this structura ph sical info m thin films, XRD techniques are de signed to maximize the diffracted X-ray intensities,since the dif fracting power of thin films is small. Range of elements All,but not element specific.Low-Zelements may be difficult to detect Probing depth Typically a few um but material dependent;mono- layer sensitivity with synchrotron radiation Detection Limits Material dependent,but-3%in a two phase mixture; with synchrotron radiation can be-0.1% Destructive No.for most materials Depth profiling Normally no;but this can be achieved. Sample requirements Any material,greater than-0.5 cm,although smaller with microfocus Lateral resolution Normally none;although-10 um with microfocus Main use Identification of crystalline phases;determination of strain,and crystallite orientation and size;accurate determination of atomic arrangements Specialized uses Defect imaging and characterization;atomic arrange ments in amorp us ma measurements Instrument cost $70,000-$200,000 Size Varies with instrument,greater than-70ft.2 INTRODUCTION AND SUMMARIES Chapter 1
X-Ray Diffraction (XRD) 1.4.1 In X-Ray Diffraction (XRD) a collimated beam ofX rays, with wavelength h- 0.5- 2 8, is incident on a specimen and is diffracted by the crystalline phases in the specimen according to Bragg's law (h = 2dsin0, where dis the spacing between atomic planes in the crystalline phase). The intensity of the diffracted X rays is measured as a hnction of the diffraction angle 28 and the specimen's orientation. This diffraction pattern is used to identify the specimen's crystalline phases and to measure its structural properties, including strain (which is measured with great accuracy), epitaxy, and the size and orientation of crystallites (small crystalline regions). XRD can also determine concentration profiles, film thicknesses, and atomic arrangements in amorphous materials and multilayers. It as0 can characterize d&ts. To obtain this structural and physical information ftom thin films, XRD instruments and techniques are designed to maximize the diffracted X-ray intensities, since the diffracting power of thin films is small. Range of elements Probing depth Detection Limits Destructive Depth profiling All, but not element specific. Low-Zelements may be difficult to detect Typically a few pm but material dependent; monolayer sensitivity with synchrotron radiation Material dependent, but -3% in a two phase mixture; with synchrotron radiation can be -0.1% No, for most materials Normally no; but this can be achieved. Sample requirements Any material, greater than -0.5 an, although smaller Lateral resolution Normally none; although 10 pm with microfbcus Main use with microfocus Identification of crystalline phases; determination of strain, and crystallite orientation and size; accurate determination of atomic arrangements Defect imaging and characterization; atomic arrangements in amorphous materials and multilayers; concentration profiles with depth; film thickness measurements Specialized uses Instrument cost $70,000-$200,000 Size Varies with instrument, greater than -70 fc.2 16 INTRODUCTION AND SUMMARIES Chapter 1
Extended X-Ray Absorption Fine Structure (EXAFS) 1.4.2 An EXAFS experiment involves the irradiation of a sample with a tunable source of monochromatic X rays from a synchrotron radiation facility.As the X-ray energy is scanned from just below to well above the binding energy of a core-shell electron (e-B K or L)of a selected element,the X-ray ph process ismo tored.When tron binding energy,X-ray absorption occurs and a steeply rising absorption edge is observed For energies greater than the binding energy,oscillations of the absorption with incident X-ray energy (i.e.,EXAFS)are observed.EXAFS data are characteristic of the structural distribution of atoms in the immediate vicinity(-5 A)of the X-ray absorbing clen ent.The frequency of the EXAFS is related to the int tance orbing andn cighbo ng a ms. The amplitude of the EXAFS is related to the number,type,and order of neighboring atoms. Range of elements Lithium through uranium Destructive No Bonding Yes,interatomic distances,coordination numbers,atom information types,and structural disorder;oxidation stare by inference Accuracy 1-2%for interatomic distances;10-25%for coordi- nation numbers Detection limits Surface,monolayer sensitivity;bulk,>100 ppm Depth probed Variable,from A to um Depth profiling Yes,with glancing incidence angles;electron-and ion-yield detection Lateral resolution Not yet developed Imaging/mapping Not yet developed Sample requirements Virtually any material;solids,liquids,gas Main use Local atomic environments of elements in materials Instrument cost Laboratory y,<$300,000;synchrotron beam Size Small attachment to synchrotron beam line 17
Extended X-Ray Absorption Fine Structure (EXAFS) 1.4.2 An EXAFS experiment involves the irradiation of a sample with a tunable source of monochromatic X rays from a synchrotron radiation facility. As the X-ray energy is scanned from just below to well above the binding energy of a core-shell electron (e.g., K or L) of a selected element, the X-ray photoabsorption process is monitored. When the energy of the incident X-rays is equal to the electron binding energy, X-ray absorption occurs and a steeply rising absorption edge is observed. For energies greater than the binding energy, oscillations of the absorption with incident X-ray energy (i.e., EXAFS) are observed. EXAFS data are characteristic of the structural distribution of atoms in the immediate vicinity (-5 A) of the X-ray absorbing element. The frequency of the EMS is related to the interatomic distance between the absorbing and neighboring atoms. The amplitude of the EXAFS is related to the number, type, and order of neighboring atoms. Range of elements Destructive No Bonding information Accuracy Detection limits Depth probed Depth profiling Lateral resolution Not yet developed Imaging/mapping Not yet developed Sample requirements Virtually any material; solids, liquids, gas Main use Instrument cost Lithium through uranium Yes, interatomic distances, coordination numbers, atom types, and structural disorder; oxidation state by inference 1-2% for interatomic distances; 10-25% for coordination numbers Surface, monolayer sensitivity; bulk, > 100 ppm Variable, from 8, to pm Yes, with glancing incidence angles; electron- and ion-yield detection Local atomic environments of elements in materials Laboratory Facility, c $300,000; synchrotron beam line, > $1,000,000 Size Small attachment to synchrotron beam line 17
Surface Extended X-Ray Absorption Fine Structure and Near Edge X-Ray Absorption Fine Structure (SEXAFS/NEXAFS) 1.4.3 In Surface Extended X-Ray Absorption Fine Structure and Near Edge X-Ray Abso i Fine Structure(SEXAFS/NEXAFS)mpe uually paced a tunable beam of X rays from a syn ron radi ation source.A spectrum is collected by varying the photon energy of the X rays and measuring the yield of emitted electrons or fluorescent X rays.Analysis of the wig- gles in the observed spectrum(the SEXAFS features)gives information on nearest neighbor bond lengths and coordination numbers for atoms at or near the surface ge (NEXAFS)are n cl eristic of theo etc.)or oxidati state For a adsorbed m cules,NEXAFS resonances characterize the type of bonding.On a flat surface,the angular variation of intensity of the resonances gives the orientation of the mole- cule. Range ofelements Almost all.from C to U Destructive No Chemical bonding Yes,through NEXAFS information Accuracy In nearest neighbor distance,+.01 A with care Surface sensitivity Top few monolayers Detection limits 0.05 monolayer Lateral resolution -0.5mm Imaging/mapping No Sample requirements Vacuum-compatible solids Main use of Adsorbate-substrate bond lengths sexAes Main use of Orientation of molecular adsorbates NEXAFS Instrument cost S400,000,plus cost of synchrotron Size Small attachment to synchrotron beam line 18 INTRODUCTION AND SUMMARIES Chapter 1
Surface Extended X-Ray Absorption Fine Structure and Near Edge X-Ray Absorption Fine Structure (SEXAFS/NEXAFS) 1.4.3 In Surface Extended X-Ray Absorption Fine Structure and Near Edge X-Ray Absorption Fine Structure (SEXAFS/NEXAFS) a solid sample, usually placed in ultrahigh vacuum, is exposed to a tunable beam of X rays from a synchrotron radiation source. A spectrum is collected by varying the photon energy of the X rays and measuring the yield of emitted electrons or fluorescent X rays. Analysis of the wiggles in the observed spectrum (the SEXAFS features) gives information on nearest neighbor bond lengths and coordination numbers for atoms at or near the surface. Features near an absorption edge (NEXAFS) are often characteristic of the local coordination (octahedral, tetrahedral, etc.) or oxidation state. For adsorbed molecules, NEXAFS resonances characterize the type of bonding. On a flat surface, the angular variation of intensity of the resonances gives the orientation of the molecule. Range of elements Destructive No Chemical bonding Yes, through NEXAFS information Accuracy In nearest neighbor distance, M.01 with care Surface sensitivity Top few monolayers Detection limits 0.05 monolayer Lateral resolution -0.5 mm Imaging/mapping No Sample requirements Vacuum-compatible solids Main use of SEXAFS Main use of NEXAFS Instrument cost Size Almost all, from C to U Adsorbatesubstrate bond lengths Orientation of molecular adsorbates $400,000, plus cost of synchrotron Small attachment to synchrotron beam line 18 INTRODUCTION AND SUMMARIES Chapter 1
X-Ray Photoelectron and Auger Electron Diffraction(XPD and AED) 1.4.4 In X-Ray Photoelectron Diffraction (XPD)and Auger Electron Diffraction (AED),a single crystal or a textured polycrystalline sample is struck by photons or electrons to produce outgoing electrons that contain surface chemical and struc- tural information.The focus of XPD and AED is structural information,which originates from effects as the outbound electrons from a particular mare scattered by neighboring atoms in the solid.Thee process strongly increases the electron intensity in the forward direction,lead uing to the simple observation that intensity maxima occur in directions corresponding to rows of atoms.An energy dispersive angle-resolved analyzer is used to map the intensity distribution as a function of angle for elements of interest. Range of elements All except H and He Destructive XPD no;AED may cause e-beam damage Element specific Yes Chemical state Yes,XPD is better than AED specific Accuracy Site symmetry Yes,and usually quickly Depth Probed 5-50A Depth profiling Yes,to 30 A beneath the surface Detection limits 0.2at.% Lateral resolution 150 A (AED),150 Hm (XPD) Imaging/mapping Sample requirements Primarily single crystals,but also textured samples Main use To determine adso ption sites and thin-film growth specific manner Instrument cost 5300,000-$600,000 Size 4m×4m×3m
X-Ray Photoelectron and Auger Electron Diffraction (XPD and AED) 1.4.4 In X-Ray Photoelectron Diffraction (XPD) and Auger Electron Diffraction (AED), a single crystal or a textured polycrystalline sample is struck by photons or electrons to produce outgoing electrons that contain surface chemical and structural information. The focus of XPD and AED is structural information, which originates from interference effects as the outbound electrons from a particular atom are scattered by neighboring atoms in the solid. The electron-atom scattering process strongly increases the electron intensity in the forward direction, leading to the simple observation that intensity maxima occur in directions corresponding to rows of atoms. An energy dispersive angle-resolved analyzer is used to map the intensity distribution as a function of angle for elements of interest. Range of elements Destructive Element specific Chemical state specific Accuracy Site symmetry Depth Probed Depth profiling Detection limits Lateral resolution Imaging/ mapping All except H and He XPD no; AED may cause e-beam damage YeS Yes, XPD is better than AED Bond angles to within lo; atomic positions to within 0.05 A Yes, and usually quickly 5-50 A Yes, to 30 A beneath the surface 0.2 at.% 150 A (AED), 150 pm (XPD) Yes Sample requirements Primarily single crystals, but also textured samples Main use To determine adsorption sites and thin-film growth modes in a chemically specific manner Instrument cost $300,000-$600,000 Size 4mx4mx3m 19