Overview - UMass Geosciences

Report
What can technology do for you?
What can you do with the aid of technology?
Use technology to gain insights into the processes of nature…
How? Examine controlled physical interactions between matter and energy
microscopy
spectroscopy
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.)
Resources and
engineering
Planetary processes
The array of microanalysis tools…sorting
through the acronyms
XPS
The array of microanalysis tools…
Electron excitation and absorption techniques
SEM – Scanning electron microscopy
EPMA – Electron probe microanalysis
LEXES – low energy electron induced x-ray emission
spectroscopy
TEM-STEM – Transmission electron microscopy (and
scanning transmission electron microscopy or
“analytical electron microscopy” = AEM)
EELS – electron energy loss spectroscopy
EBSD – electron backscatter diffraction in SEM
AES – Auger electron spectroscopy
Photon excitation and absorption techniques
Optical Microscopy
XPS – X-ray photoelectron microscopy (or ESCA =
electron spectroscopy for chemical analysis)
FTIR – fourier transform infrared analysis
UV-VIS
Laser Raman Spectroscopy
μ-XRF – micro-X-ray fluorescence
X-ray microdiffraction
Synchrotron techniques
XANES
XAFS
Photon ablation
LA-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 microprobe
nanoSIMS
He-ion microscopy
Other
SPM – Scanning probe microscopies
STM – Scanning tunneling microscopy
AFM – Atomic force microscopy
MFM – 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
The array of microanalysis tools…
Electron excitation and absorption techniques
SEM – Scanning electron microscopy
EPMA – Electron probe microanalysis
LEXES – low energy electron induced x-ray emission
spectroscopy
TEM-STEM – Transmission electron microscopy (and
scanning transmission electron microscopy or
“analytical electron microscopy” = AEM)
EELS – electron energy loss spectroscopy
EBSD – electron backscatter diffraction in SEM
AES – Auger electron spectroscopy
Photon excitation and absorption techniques
Optical Microscopy
XPS – X-ray photoelectron microscopy (or ESCA =
electron spectroscopy for chemical analysis)
FTIR – fourier transform infrared analysis
UV-VIS
Laser Raman Spectroscopy
μ-XRF – micro-X-ray fluorescence
X-ray microdiffraction
Synchrotron techniques
XANES
XAFS
Surface imaging down to a few Å (or less) – primarily morphology
Quantitative microanalysis and compositional imaging
Ultra 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 analysis
Ultra low energy surface analysis for elemental composition
Similar to XPS, but higher spatial resolution (10-100nm)
Microstructural observation, including polarization properties
Surface (upper few nm) chemical analysis (parts per thousand)
Spatial resolution 100’s of μm
Molecular fingerprinting
Analysis of transition metal ions, organic compounds
Vibrational modes – molecular identification via bond info.
Quantitative analysis of major and minor elements, 100s of μm
Microstructural analysis
Valence and coordination, material band structure
Scattering of photoelectrons from surrounding atoms = local
structure.
The array of microanalysis tools…
Photon ablation
LA-ICP-MS – Laser ablation inductively coupled plasma
mass spectrometry
Trace elements and isotopic compositions, 10’s to 100’s of
microns (ppt in some cases), destructive.
Ion ablation and activation
(focused ion beam techniques)
SIMS-Ion Microprobe – Secondary ion mass spectrometry
SHRIMP – sensitive high resolution ion microprobe
nanoSIMS
He-ion microscopy (HIM)
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
Other
SPM – Scanning probe microscopies
STM – Scanning tunneling microscopy
AFM – Atomic force microscopy
MFM – 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
Surface atomic imaging (conductors) – nm or less, indirect
Surface atomic imaging – 0.1nm – direct
Surface magnetic structure
Atom scale 3D composition (destructive)
TAP on insulators
Compositional analysis down to μm scale (accelerator)
Surface imaging
SEM
STM - atomic
AFM - atomic
EBSD - SEM
AES
XPS
SIMS
Surface chemistry
SIMS
AES
XPS
TAP-APM
EPMA – LEXES (WDS)
Chemical analysis of microvolumes
Elemental concentrations
SEM - EDS
EPMA (WDS)
LA-ICP-MS
μ-XRF
SIMS
PIXE
FTIR (bonding, functional groups)
Chemical analysis of microvolumes
Isotopic concentrations
LA-ICP-MS
SIMS
Analysis of microstructure
TEM-STEM
EBSD - SEM
X-ray microdiffraction
STM
AFM
TAP-APM
Micro-scale
SEM - EDS
EPMA
SIMS (ablation)
AES (surface)
XPS (surface)
Nano-scale
HR-SEM-EDS
He-ion microscope
EPMA (special)
TEM-STEM-EDS
STM (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 matter
Wavelength (0.01-0.04nm) much shorter than visible light (400-650nm)
Charged, so will interact with EM fields – can be focused
Interact with matter
Elastically -Backscatter
Inelastically – to produce
Secondary electrons
light
X-rays
heat (phonon excitation/lattice oscillation)
Data?
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 wavelengths
Mass ratios
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
V-oxide
Artificial artery
Zeolite surface
foraminifera
Electron Microprobe (Electron Probe Microanalysis - EPMA)
quantitative chemical microanalysis and compositional imaging
Primarily designed for precise characteristic X-ray detection
X-ray wavelengths relate to electronic structure – can identify specific elements.
Intensity variation in specimen relates to spatial distribution of these elements
X-ray counts from specimen compared to standards of known composition →
computed elemental concentrations
PURPOSE
Analysis of individual mineral grains or
amorphous solid phases
Mg Kα
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
Ag distribution in solder
50 μm
Y distribution in natural monazite
Solder bumps on IC
GENERAL “LIMITATIONS”
Spatial resolution – it depends
Electron beam focused to 0.01 to 0.2 μm diameter
Scattering → electron interaction volume and signal emission
volume.
Imaging (SEM) – from few nm to hundreds of nm
Chemical 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 elements
Element range
Routinely 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 signals
BSE
SE
X-Rays
ELECTRON OPTICS
Electron source (gun)
Cathode + Anode
Controls beam voltage
Condenser lenses
Controls beam current
Objective lens
Controls 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 length
10-3 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
15 kV
2)
1 mm
Some beam electrons interact inelastically with atoms
in the target
Energy 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
10 kV
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 state
outer 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 =
E FeKα =
1.740 KeV (7.125Å)
6.404 KeV (1.936Å)
Kα
ψp1
ψp
ψp2
ψ1s
Kβ
ψp1
ψp
ψp2
ψ1s
Also produce background spectrum
Originates from deceleration reactions of insufficient energy to
ionize the target atom
Produce overall X-ray spectrum
Characteristic peaks superimposed on a background
How are X-rays detected?
Discriminated by energy (EDS)
Or wavelength (WDS)
EDS Detectors
Solid state semiconductor detectors
See entire spectrum at once
Fast
Relatively low resolution
crystal
WDS
Select analytical lines by diffraction
nλ = 2d sin θ
Relatively high resolution
WDS used for most quantitative analysis
EDS for qualitative evaluation
detector
(counter)
sample
Wavelength Dispersive Spectrometry (WDS)
Bragg Law:
nλ = 2d sinθ
θ
d
At certain θ, rays will be in phase,
otherwise out of phase = destructive interference
Detectors
Usually gas filled counter tubes
1)
2)
3)
4)
5)
ionize counter gas (Xe, Ar)
eject photoelectron
photoelectron ionizes other gas atoms
electrons collected by wire
output pulse = x-ray count
pulse height proportional to x-ray energy
Measure counts per second of a particular X-ray
compare to standard of known composition to
get concentration
ISiK (unk)
 %Sistd  uncorr. wt%
ISiK (std)
Must correct for matrix effects
Z
atomic #
A
absorption
F
secondary fluorescence
Ci / C(i) = [ZAF] [Ii / I(i)]
IMAGING
Object: Convert radiation into an electrical
signal which is then amplified
Select
Secondary electrons
Backscattered electrons
X-rays
Auger electrons
Photons from Cathodoluminescence
Absorbed electron current
Incident
Light
beam Auger
(cathodoluminescence)
electrons
Secondary
electrons
Bremsstrahlung
Characteristic
X-rays
Backscattered
electrons
Sample
heat
Any of the collected signals can be
displayed as an image if you either scan
the beam or the specimen stage
Specimen
current
Elastically
scattered
electrons
Transmitted
electrons
Secondary electron detector
electron 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
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
X-ray mapping
display spatial distribution of characteristic X-ray intensity to get
qualitative compositional information
Garnet, Grand Canyon MgKα
Garnet - Italy MgKα
Garnet - Moretown Formation, MA CaKα
Garnet – Grand Canyon MnKα
plag
matrix
plag
opx
Cpx
+ qtz
garnet
opx+plag+
mt
Original
opx
Corona texture - CaKα Saskatchewan
calcite
100 μm
Monazite – thorium map
Lobster cuticle – composite
element map
Monazite Geochronology
Quantitative Analysis – Geosciences applications
Mineral chemistry –
in-situ, single phase characterization
microscale compositional changes within phases - zoning
Crystallization paths and evolution of magmatic systems
Geothermometry
Geobarometry
Geochronology
Low-temperature geochemistry
clay mineralogy
mass transfer / weathering reactions
paleoclimate applications – speleothem microchemistry
Fundamental geochemical processes
Phase equilibria
Kinetics
distribution coefficients
Two generations of garnet growth
Black Hills, SD
grossular
spessartine
820
(a)
840
860
Paleoclimate
900
920
(b)
940
0
0
Feb. insolation (30 S)
880
960
980
18
 O
-2
(c)
1.2
-4
1.0
45
0.4
40
0.2
3
Mg/Ca*(10 )
35
30
25
20
0
10
20
30
40
50
60
70
Age KY B.P.
80
90 100 110 120
3
0.6
(d)
Sr/Ca*(10 )
0.8
-6
16
Cladding
14
Core
Cladding
GeO2
12
wt.%
10
Tm2O3
8
6
4
2
0
20
30
40
50
60
70
80
microns
Element concentrations in optical fiber
90
100
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) to
micro/macro-structure and mineral
paragenesis
• Non-destructive
• Integrated spatial / compositional / age relationships
Monazite:
Dating events
{
ThMα
LREE-phosphate with Th and U (→ radiogenic Pb)
Common accessory phase in many rocks
Fabric former
Dissolution/re-precipitation reactions result in polygenetic nature,
and ties into overall reaction history
Map, map, map…
Map compositional domains, then quantitatively measure
Th, U, and Pb concentrations. Compute age via:
CeB6 /LaB6
The Ultrachron Project
New HV power
supply
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
•
•
•
Decouple operation
of condensers to
optimize brightness
down column
Current regulation
up to 1 microamp
Improve dynamic
range of BSE
amplifier
Improve precision (Optimize
counting - PbMα)
Integrate spectrometers
Improve accuracy – background
estimation
BSE shielding for
high current
applications
Techniques
•
•
•
Minimize beam damage
Background
Analytical protocols
New high intensity crystals
(VLPET) + VL detectors
Counters optimized (gas
mixture, pressure, HV)
Completely dry
vacuum system
Anticontamination
ψp
ψp
ψp
ψ1s

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