what can technology do for you? what can you do with the aid of technology?
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What can technology do for you?
What can you do with the aid of technology?
Why look at surfaces at high magnification?
Description and identification of constituent phases by morphology, emission and absorption properties, or other physical responses.
Observation of features which give you insight into processes and the relevant mechanisms.
What is chemical microanalysis all about and why do it?
Phase identification by element ID and stoichiometry.
Identify and quantify chemical processes.
Establish qualitatively and quantitatively the distribution of elements in a sample at the micro-scale, and quantify kinetic processes.
Provide quantitative data for thermodynamically constrained processes (establish the temperature, pressure, solution activities, etc. of chemical reactions in nature.)
Use technology to gain insights into the processes of nature…
How? Examine controlled physical interactions between matter and energymicroscopy spectroscopy
Resources and engineering
Planetary processes
The array of microanalysis tools…sorting through the acronyms
EPMA
SEM-EDS
STEM
TEM
SHRIMP
EELS
AESEBSD
FTIR
UV-VIS
μ-XRF
XPS
SIMS
LA-ICP-MS
μ-XRD
AFM
STM
TAP
nanoSIMS
XANES
SPM
LE
XE
SESCA
MFM
IRA
S
FIM
CFM
ARPES
HAS
LEIS
LEED
PE
EM
PIXE
XAFS
SCEMH
IM
LRS
The array of microanalysis tools…
Photon ablationLA-ICP-MS – Laser ablation inductively coupled plasma mass spectrometry
Ion ablation and activation(focused ion beam techniques) SIMS-Ion Microprobe – Secondary ion mass spectrometry SHRIMP – sensitive high resolution ion microprobenanoSIMSHe-ion microscopy
OtherSPM – Scanning probe microscopies
STM – Scanning tunneling microscopyAFM – Atomic force microscopyMFM – Magnetic force microscopy
Atom probe (TAP) tomographic atom probe or atom probe microscopy (APM)
LA-WATAP (laser assisted wide angle)PIXE – proton induced x-ray emission
Electron excitation and absorption techniquesSEM – Scanning electron microscopyEPMA – Electron probe microanalysisLEXES – low energy electron induced x-ray emission spectroscopyTEM-STEM – Transmission electron microscopy (and scanning transmission electron microscopy or “analytical electron microscopy” = AEM)EELS – electron energy loss spectroscopyEBSD – electron backscatter diffraction in SEMAES – Auger electron spectroscopy
Photon excitation and absorption techniquesOptical MicroscopyXPS – X-ray photoelectron microscopy (or ESCA = electron spectroscopy for chemical analysis)FTIR – fourier transform infrared analysisUV-VISLaser Raman Spectroscopyμ-XRF – micro-X-ray fluorescenceX-ray microdiffractionSynchrotron techniques
XANESXAFS
The array of microanalysis tools…
Electron excitation and absorption techniquesSEM – Scanning electron microscopyEPMA – Electron probe microanalysisLEXES – low energy electron induced x-ray emission spectroscopyTEM-STEM – Transmission electron microscopy (and scanning transmission electron microscopy or “analytical electron microscopy” = AEM)EELS – electron energy loss spectroscopyEBSD – electron backscatter diffraction in SEMAES – Auger electron spectroscopy
Photon excitation and absorption techniquesOptical MicroscopyXPS – X-ray photoelectron microscopy (or ESCA = electron spectroscopy for chemical analysis)FTIR – fourier transform infrared analysisUV-VISLaser Raman Spectroscopyμ-XRF – micro-X-ray fluorescenceX-ray microdiffractionSynchrotron techniques
XANESXAFS
Surface imaging down to a few Å (or less) – primarily morphologyQuantitative microanalysis and compositional imagingUltra low kV X-ray microanalysis (10’s of μm) at low voltage
Imaging by electron transmission for extreme magnification of internal structure.
Compositional analysis, bonding and valence (low Z)Microstructural analysisUltra low energy surface analysis for elemental composition Similar to XPS, but higher spatial resolution (10-100nm)
Microstructural observation, including polarization propertiesSurface (upper few nm) chemical analysis (parts per thousand) Spatial resolution 100’s of μmMolecular fingerprintingAnalysis of transition metal ions, organic compoundsVibrational modes – molecular identification via bond info.Quantitative analysis of major and minor elements, 100s of μmMicrostructural analysis
Valence and coordination, material band structureScattering of photoelectrons from surrounding atoms = local structure.
The array of microanalysis tools…
Photon ablationLA-ICP-MS – Laser ablation inductively coupled plasma mass spectrometry
Ion ablation and activation(focused ion beam techniques) SIMS-Ion Microprobe – Secondary ion mass spectrometry SHRIMP – sensitive high resolution ion microprobenanoSIMSHe-ion microscopy (HIM)
OtherSPM – Scanning probe microscopies
STM – Scanning tunneling microscopyAFM – Atomic force microscopyMFM – Magnetic force microscopy
Atom probe (TAP) tomographic atom probe or atom probe microscopy (APM)
LA-WATAP (laser assisted wide angle)PIXE – proton induced x-ray emission
Trace elements and isotopic compositions, 10’s to 100’s of microns (ppt in some cases), destructive.
Ion mass/charge ratios, 10-30 microns, ppm-ppb sensitivity, isotope ratios and geochronology (destructive)Isotope ratios (limited range, 10’s of nanometers)Ultra high resolution surface imaging – RBS possible
Surface atomic imaging (conductors) – nm or less, indirectSurface atomic imaging – 0.1nm – directSurface magnetic structureAtom scale 3D composition (destructive)
TAP on insulatorsCompositional analysis down to μm scale (accelerator)
Chemical analysis of microvolumesElemental concentrationsSEM - EDSEPMA (WDS)LA-ICP-MSμ-XRFSIMSPIXEFTIR (bonding, functional groups)
Chemical analysis of microvolumesIsotopic concentrationsLA-ICP-MSSIMS
Surface imagingSEMSTM - atomicAFM - atomicEBSD - SEMAESXPSSIMS
Surface chemistrySIMSAESXPSTAP-APMEPMA – LEXES (WDS)
Analysis of microstructureTEM-STEMEBSD - SEMX-ray microdiffractionSTMAFMTAP-APM
Micro-scaleSEM - EDSEPMASIMS (ablation)AES (surface)XPS (surface)
Nano-scaleHR-SEM-EDSHe-ion microscopeEPMA (special)TEM-STEM-EDSSTM (atomic scale)AFM (atomic scale)NanoSIMS (ablation)TAP-APM (atomic scale)
Electron…Elementary particle (no internal structure)Fermion (Half integer spin, constrained by Pauli Exclusion principle)Lepton (do not interact through the color force = no strong interaction) of charge -1, mass = 0.511 MeV/c2
Electron properties and interaction with matterWavelength (0.01-0.04nm) much shorter than visible light (400-650nm)Charged, so will interact with EM fields – can be focusedInteract with matter
Elastically -BackscatterInelastically – to produce
Secondary electronslightX-raysheat (phonon excitation/lattice oscillation)
Observations…Size, shape, relationships of objects(What does what you “see” actually represent?)
Paleotemperature, pressure, solution activities, age, etc.Calculated results with assumptions…
Elemental concentration…do we actually measure this?
Measured…Intensities of X-rays at specified wavelengthsMass ratios
Data?
Scanning Electron Microscopy and Electron Microprobe Analysis
• High magnification surface imaging• Chemical analysis of materials on a
scale of microns (or less)
Focused electron beam generates detectable signals from specimen
• Secondary electrons• Backscattered electrons• X-rays
• Non-destructive• In-situ analysis
Scanning Electron Microscope
Focused electron beam is scanned over surface - excites atoms of target – signals emitted and detected
High magnification surface imaging with resolution of few nm to sub-nm for secondary electrons
Scanning Electron Microscope
Artificial artery
foraminifera
V-oxide
Zeolite surface
Electron Microprobe (Electron Probe Microanalysis - EPMA) quantitative chemical microanalysis and compositional imaging
Primarily designed for precise characteristic X-ray detectionX-ray wavelengths relate to electronic structure – can identify specific elements.
Intensity variation in specimen relates to spatial distribution of these elementsX-ray counts from specimen compared to standards of known composition →
computed elemental concentrations
PURPOSE
Analysis of individual mineral grains or amorphous solid phases
In-situ (preserve textural relationships!)
Compositional imaging and spatial distribution of elements in the scanned area.
Quantitative chemical variation within mineral grains or discrete phases - zoning and growth histories
Mg Kα
Ag distribution in solder
Y distribution in natural monazite
Solder bumps on IC
50 μm
GENERAL “LIMITATIONS”
Spatial resolution – it dependsElectron beam focused to 0.01 to 0.2 μm diameterScattering → electron interaction volume and signal emission volume.Imaging (SEM) – from few nm to hundreds of nmChemical analysis (EPMA) - Silicates 1 to 3 μm diameter volume
Compositional sensitivity (detection limits) – it depends 50-200 ppm (a few ppm in some special cases)
For EPMA, mostly major and minor elementsElement rangeRoutinely Na and heavier – but it depends…Also B, C, N, O (special circumstances)
ELECTRONS
λ shorter than visible light → higher image resolution(light 400-650nm, electrons ~ 0.04 -.01nm,1-10kV)
Charged particles - can be electromagnetically focused
Interact with specimen to produce detectable signalsBSESEX-Rays
ELECTRON OPTICS
Electron source (gun)Cathode + AnodeControls beam voltage
Condenser lensesControls beam current
Objective lensControls beam size, shape, depth of field at specimen
Result = electron beam of specified voltage, current and diameter.
Wavelength dispersive, X-ray spectrometer
Vacuum System - mean path length of electrons must be greater than column length10-3 to 10-5 pa (~10-5 to 10-7 torr)
specimen
Raimond Castaing
What happens when beam reaches specimen?
Beam/Specimen interactions
1) Some beam electrons scattered back out-More effectively by heavier target atoms-Results in BSE signal
2) Some beam electrons interact inelastically with atoms in the targetEnergy is transferred
A) Can result in ejection of some weakly bound outer shell electrons → secondary electron signal (low energy)
B) Some cause inner shell ionizations leading to characteristic X-ray emission
15 kV
10 kV
1 mm
Electron trajectory modeling - Casino
Labradorite (Z = 11)
INNER SHELL IONIZATION
1) If energy equal or greater than critical excitation potential…
Can eject inner shell electron
2) Atom wants to return to ground stateouter shell electron fills vacancy – relaxation
Outer shell electron in higher energy state relative to inner shell electron
some energy surplus in the transition → photon emission (X-ray)
X-ray is characteristic of the target element
Example: E SiKα = 1.740 KeV (7.125Å)
E FeKα =6.404 KeV (1.936Å)
Kα
ψp
ψ1sψp2
ψp1
Kβ
ψp
ψ1sψp2
ψp1
Also produce background spectrum
Originates from deceleration reactions of insufficient energy to ionize the target atom
Produce overall X-ray spectrumCharacteristic peaks superimposed on a background
How are X-rays detected?
Discriminated by energy (EDS) Or wavelength (WDS)
EDS DetectorsSolid state semiconductor detectorsSee entire spectrum at onceFastRelatively low resolution
WDS Select analytical lines by diffraction
nλ = 2d sin θ
Relatively high resolution
WDS used for most quantitative analysisEDS for qualitative evaluation
crystal
detector (counter)
sample
Wavelength Dispersive Spectrometry (WDS)
Bragg Law:
θ
nλ = 2d sinθ
d
At certain θ, rays will be in phase,
otherwise out of phase = destructive interference
DetectorsUsually gas filled counter tubes
1) ionize counter gas (Xe, Ar)2) eject photoelectron3) photoelectron ionizes other gas atoms4) electrons collected by wire5) output pulse = x-ray count
pulse height proportional to x-ray energy
Measure counts per second of a particular X-raycompare to standard of known composition to get concentration
Must correct for matrix effectsZ atomic #A absorptionF secondary fluorescence
I
I % S i
S iK (un k )
S iK (std )std un co rr. w t%
Ci / C(i) = [ZAF] [Ii / I(i)]
IMAGING
Secondary electron detectorelectron strikes scintillator and converted to light pulse - Amplified and displayed
Raster the beam over sample and display at the same time and get image (basically an intensity map)
Scan smaller and smaller areas to increase magnification
Object: Convert radiation into an electrical signal which is then amplified
SelectSecondary electronsBackscattered electronsX-raysAuger electronsPhotons from CathodoluminescenceAbsorbed electron current
Incident beamLight
(cathodoluminescence)
BremsstrahlungSecondary electrons
Backscattered electrons
heat
Elastically scattered electrons
Transmitted electrons
Specimen current
Auger electrons
Characteristic X-rays
Sample
Any of the collected signals can be displayed as an image if you either scan the beam or the specimen stage
5 mm
Electron Backscatter
Backscattering more efficient with heavier elements
Can get qualitative estimate of average atomic number of target
Image will reveal different phases
Brighter = higher average Z
Garnet, Grand Canyon MgKα
X-ray mapping display spatial distribution of characteristic X-ray intensity to get qualitative compositional information
Garnet - Moretown Formation, MA CaKα
Garnet - Italy MgKα Garnet – Grand Canyon MnKα
Corona texture - CaKα Saskatchewan
Originalopx
Cpx + qtz
opx
plag
opx+plag+ mt
garnet
matrixplag
Lobster cuticle – composite element map
calcite
100 μm
Monazite – thorium map
Monazite Geochronology
Quantitative Analysis – Geosciences applications
Mineral chemistry – in-situ, single phase characterizationmicroscale compositional changes within phases - zoning
Crystallization paths and evolution of magmatic systems
Geothermometry
Geobarometry
Geochronology
Low-temperature geochemistryclay mineralogymass transfer / weathering reactionspaleoclimate applications – speleothem microchemistry
Fundamental geochemical processesPhase equilibria
Kineticsdistribution coefficients
Two generations of garnet growthBlack Hills, SD
grossular
spessartine
0 10 20 30 40 50 60 70 80 90 100 110 120
20
25
30
35
40
45
Mg
/Ca
*(1
03 )
Age KY B.P.
0.2
0.4
0.6
0.8
1.0
1.2
Sr/C
a*(1
03)
980
960
940
920
900
880
860
840
820
Fe
b. in
sola
tion
(30
0S)
-6
-4
-2
0
(d)
(c)
(b)
(a)
18
O
Paleoclimate
20 30 40 50 60 70 80 90 1000
2
4
6
8
10
12
14
16
GeO2
Tm2O3
microns
wt.
%
Element concentrations in optical fiber
CoreCladding Cladding
Geochronology – traditionally using isotopic/mass-spectrometric techniques• IDTIMS• Ion Probe
Electron Microprobe (EPMA)• High spatial resolution
access to ultra-thin rims,micro-domains, and inclusions
• In-situ: relate composition (and age) tomicro/macro-structure and mineral paragenesis
• Non-destructive• Integrated spatial / compositional / age relationships
Monazite: LREE-phosphate with Th and U (→ radiogenic Pb)Common accessory phase in many rocksFabric formerDissolution/re-precipitation reactions result in polygenetic
nature, and ties into overall reaction history
ThMα
Dating events{
Map, map, map…
Map compositional domains, then quantitatively measure Th, U, and Pb concentrations. Compute age via:
The Ultrachron Project
Electron optics• Optimize analytical resolution
(Smaller phase analysis) for a range of kV and current
• High, stable current for trace element analysis
• Minimize excitation volume in high Z material
Detection
BSE and X-Ray optics• Improve precision (Optimize
counting - PbMα)• Integrate spectrometers• Improve accuracy – background
estimation
Techniques• Minimize beam damage• Background• Analytical protocols
Improve dynamic range of BSE amplifier
BSE shielding for high current applications
New high intensity crystals (VLPET) + VL detectors
Counters optimized (gas mixture, pressure, HV)
Completely dry vacuum system
Anticontamination
CeB6 /LaB6
New HV power supply
Decouple operation of condensers to optimize brightness down column
Current regulation up to 1 microamp
ψp
ψ1sψp
ψp
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