dr. nilanjan chatterjeedspace.mit.edu/bitstream/handle/1721.1/82646/12-141-january-iap-2… ·...
TRANSCRIPT
Dr. Nilanjan Chatterjee
©Massachusetts Institute of Technology
Electron Probe MicroElectron Probe Micro--AnalysisAnalysis(EPMA)(EPMA)
Imaging and micrometerImaging and micrometer--scale scale chemical compositional chemical compositional
analysis of solidsanalysis of solids
Secondary electron (SE)
Back-scatteredelectron (BSE)Cathodoluminescence
(CL)
Characteristic X-ray
Electronbeam
Specimen
Signals produced inSignals produced inThe Electron MicroprobeThe Electron Microprobe
Qualitative analysis: phase identificationQualitative analysis: phase identificationBackBack--scattered electron (BSE) image: spatial variations in scattered electron (BSE) image: spatial variations in chemical compositionchemical composition
XX--ray spectra with energy dispersive spectrometer (EDS): ray spectra with energy dispersive spectrometer (EDS): element identificationelement identification
Elemental XElemental X--ray maps with EDS or wavelength dispersive ray maps with EDS or wavelength dispersive spectrometer (WDS)spectrometer (WDS)
SemiSemi--quantitative analysis: phase quantitative analysis: phase abundanceabundance
•• Polished surfacePolished surface•• BackBack--scattered electron scattered electron
imageimage•• Function of Function of
compositioncomposition
•• Thin sectionThin section•• Polarized transmitted Polarized transmitted
light imagelight image•• Function of optical Function of optical
propertiesproperties
Optical MicroscopeOptical Microscopeversusversus
Scanning Electron MicroscopeScanning Electron Microscope
ElectronElectron--specimen interactionsspecimen interactions
Elastic ScatteringElastic Scattering Inelastic ScatteringInelastic ScatteringEE11 = = EE00 , large , large φφee EE11<<EE0 0 , small , small φφii
-- BackBack--scatteredscattered -- Characteristic XCharacteristic X--raysrayselectronelectron -- Secondary electronSecondary electron
-- CathodoluminescenceCathodoluminescence
Beam electronSpecimen atom
Scattered beam electron
Elastic scattering crossElastic scattering cross--sectionsection
QQ(>(>φφee)) = = 1.62x101.62x10--2020 ((ZZ22//EE22)cot)cot22((φφee/2)/2)
QQ: cross section (events.cm: cross section (events.cm22/e/e--.atom).atom)
φφee: elastic scattering angle: elastic scattering angle
ZZ: : atomic numberatomic number
EE: beam energy: beam energyEE11 = = EE00 , large , large φφee
Electron BackElectron Back--scatteringscattering(High angle elastic scattering)(High angle elastic scattering)
η = nBSE/nB
where nB: # beam electrons, nBSE: # back-scattered electronsFor compounds, η = Σ cjηj
where cj : concentration of element ‘j ’
BSE image of rockBSE image of rock
BSE compositional contrastBSE compositional contrast
Electrongun
Condenserlens
OpticalMicroscope
WDS
LN2
EDSSE
Objective lens
BSE
Stage
JEOL JXAJEOL JXA--8200 8200 SuperprobeSuperprobe
Highvacuum
WDS
Liq N2for
EDS
Sampleexchange
Perpendicular geometry
Electron gun: W or LaB6 filament, thermionic emissionAccelerating voltage: 1-40 kV (typical: 10-25 kV)
Electron lenses (condenser and objective):Beam diameter: 1 nm-1 μm (typical: 0.1-1 μm)Beam current: 1 pA-1 μA (typical: 10-100 nA)
Scanning electron imaging:Back-scattered electron (BSE): compositional imaging, 40-4000xSecondary electron (SE): topographic imaging, 40-360,000x
X-ray spectrometry:Energy dispersive (EDS): element detection5 Wavelength dispersive (WDS): concentration measurement
Features:Features:
Capabilities:Capabilities:
BackBack--scattered electron detectorscattered electron detector
Top view of specimenAnnular, Annular, solidsolid--state state diode, split diode, split into two into two semisemi--circles, circles, A and B.A and B.
Compositional and topographic Compositional and topographic imaging with BSE detectorimaging with BSE detector
A+BA+BCompositionalCompositional
modemode
AA--BBTopographicTopographic
modemode
BSE image resolution:BSE image resolution:electron interaction volumeelectron interaction volume
Electron Range Electron Range ((KanayaKanaya--Okayama)Okayama)::
RR = = KKEE00nn//ρρ
where,where, KK = 0.0276 = 0.0276 AA//ZZ 0.8890.889
nn = 1.67;= 1.67; ρρ = density= density
Typical ranges (Typical ranges (15 kV15 kV, perpendicular beam):, perpendicular beam):CC 1.8 1.8 μμmmFeFe 1.1 1.1 μμmmUU 0.8 0.8 μμmm
Phase identification: EDS XPhase identification: EDS X--ray spectraray spectraIlmenite (ilm):
FeTiO3
hbl: hydrousCa-Fe-Mg-Al-silicate
plg:Na-Ca-Al-silicate
Ato# 1 8 11 12 13 14 19 20 22 26ilm: O Ti Fegrt: O Mg Al Si Ca Febt: H O Mg Al Si K Fehbl: H O Mg Al Si Ca Feplg: O Na Al Si Ca
Energy Dispersive XEnergy Dispersive X--ray ray Spectrometer (EDS)Spectrometer (EDS)
EDS detector: a EDS detector: a ‘‘pp--nn’’ layer of layer of intrinsic intrinsic Si(LiSi(Li)) semiconductor; semiconductor; Be windowBe window(Si is usually electron deficient because it (Si is usually electron deficient because it contains B, a contains B, a pp--typetype impurity. It is coated impurity. It is coated with Li, an with Li, an nn--typetype dopantdopant with excess with excess electrons to create a electrons to create a ‘‘pp--nn’’ intrinsic intrinsic semiconductor)semiconductor)
Multichannel analyzer (MCA) Multichannel analyzer (MCA) processes the Xprocesses the X--ray signalray signal
Phase abundance: BSE & XPhase abundance: BSE & X--ray mapsray maps
Scale bar: 4 mmScale bar: 4 mm
BSEBSE OO MgMg CaCa
•• Olivine (Mg,Fe)Olivine (Mg,Fe)22SiOSiO4 4 -- light in O and Mg maps light in O and Mg maps –– 19.9%19.9%•• AugiteAugite Ca(Mg,Fe)SiCa(Mg,Fe)Si22OO6 6 -- light in Ca map light in Ca map –– 19.6%19.6%•• Crystallized fineCrystallized fine--grained matrix grained matrix –– 60.5%60.5%
Other imaging techniques: Other imaging techniques: secondary electron (SE)secondary electron (SE)
(Inelastic scattering)(Inelastic scattering)
Electrons from specimen surface are mobilized by beam electrons(useful in studying surface features)
Emitted at low energies (typical: <10 eV)EE11<<EE0 0 , small , small φφii
Secondary electron detectorSecondary electron detector
Side view of specimen
Imaging with secondary electron Imaging with secondary electron detectordetector
--veve Faraday cage biasFaraday cage biasless SEless SE
less topographic contrastless topographic contrast
++veve Faraday cage biasFaraday cage biasmore SEmore SE
better topographic contrastbetter topographic contrast
Other imaging techniques:Other imaging techniques:CathodoluminescenceCathodoluminescence (CL)(CL)
Band gap energy, Band gap energy, EEgapgap, is a property of the semiconductor, is a property of the semiconductorTrace impurities change Trace impurities change EEgapgap by adding additional energy by adding additional energy states in the band gapstates in the band gap
CathodoluminescenceCathodoluminescence imagingimagingLight from CL is intercepted at the optical
microscope and analyzed with a wavelength discriminating spectrometer
JXA-733
Auto focus
Zircon
JXA-8200
Optical gratingspectrometer
MIT OpenCourseWarehttp://ocw.mit.edu
12.141 Electron Microprobe Analysis by Wavelength Dispersive X-ray SpectrometryJanuary (IAP) 2010
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