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X-ray Absorption Spectroscopy at GSECARS
Matt Newville, Steve Sutton, Peter Eng, Mark Rivers
Design Team: Glenn Waychunas (LBNL), Gordon Brown (Stanford),
Paul Bertsch (SREL, U Georgia), Francois Farges (U Marne la vallee, Paris)
• Techniques:
XANES
chemical speciation and oxidation state
EXAFS
near-neighbor distances and coordination numbers
Micro-Beam
spatial sensitivity at the micron scale, high sensitivity
• Selected Applications:
As speciation and distribution in Bangladesh groundwater sediments
Cr oxidation state in Hanford core samples
Pu speciation in Yucca Mountain Tuff
Sr coordination in coral used as a paleothermometer
Mn, Cu, Zn speciation around plant hyphae and roots
Cu speciation and coordination in hydrothermal fluid inclusions
Pb speciation in biofilms on mineral surfaces
Eu oxidation state distribution in apatites
Au speciation and coordination in ore deposits
V oxidation state in meteoric fassaite
GeoSoilEnviroCARS
03-Mar-2001
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GSECARS Fluorescence and XAFS Microprobe Station
Beamline13-ID-C is a world-class micro-beam facility for x-ray fluorescence
(XRF) and x-ray absorption spectroscopy (XAS) studies:
Incident Beam:
Monochromatic x-rays
from LN2 cooled Si (111)
Sample Stage: x-y-z stage, 0.1mm resolution
Fluorescence detector:
16-element Ge detector
[shown], Si(Li) detector,
Lytle Detector, or
Wavelength Dispersive
o
Spectrometer at 90
to incident beam
Optical Microscope:
(5x to 50x) with
external video system
Data Collection:
Flexible software for
x-y mapping, traditional
XAFS scans, XAFS
scans vs. sample position.
GeoSoilEnviroCARS
Focusing: Horizontal and Vertical Kirkpatrick-Baez mirrors
03-Mar-2001
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Kirkpatrick-Baez focusing mirrors
The table-top Kirkpatrick-Baez mirrors use a four-point
bender and flat, trapezoidal mirror to dynamically form
an ellipsis. They will focus a 300x300mm beam down to
1x1mm - a flux density gain of 105.
With a typical working distance of 100mm, and an
energy-independent focal distance and spot size, they
are ideal for micro-XRF and micro-EXAFS.
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We use Rh-coated silicon for horizontal and vertical
mirrors to routinely produce 3x3mm beams for XRF,
XANES, and EXAFS.
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03-Mar-2001
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Metals distribution at Root/Soil Interface
Andreas Scheinost, Ruben Kretzschmar (ETH Zurich)
Zn-rich
Metal oxide dust was introduced to a
forest topsoil resulting in 5000 ppm Zn
and 2500 ppm Cu in the soil.
Fe-rich
Mn-rich
stele
cortex
Cu-rich
Zn
Cu
Fe
Mn
These mXRF maps show the distribution
of Zn, Cu, Fe and Mn near a barley root
growing in the contaminated soil. Close
to a Zn oxide particle, the root is strongly
enriched in Zn.
Arrows mark regions where Zn m-XAFS
spectra were collected.
Optical microscope image of root
GeoSoilEnviroCARS
03-Mar-2001
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Normalized Absorption
Zn EXAFS and speciation at Rhizosphere
(k) k
RSF
3
Zn oxide
Zn-rich
Cu-rich
Mn-rich
Fe-rich
stele
cortex
Zn on Fh
aqueous Zn
9.6
9.7
9.8
9.9
Energy [keV]
4
6
8
10
0
2
4
6
2+
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R [Å]
-1
k [Å ]
The Zn-richZBand
Cu-rich areas consist of Zn oxide. The remaining areas lack a strong
Rhizosphere 5a. Zn-K m-XAFS at GSE-CARS. Data transformation: 7/3, 1.5 - 10 A , Bessel 4.
second shell, and show tetrahedral Zn-O coordination, suggesting that Zn dissolved from
the oxide is sorbed by the root cortex and by Fe and Mn hydroxides.
-1
GeoSoilEnviroCARS
03-Mar-2001
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Cr redox in Boreholes below Hanford Waste Tanks
Sam Traina, Isao Yamakawa (Ohio State Univ.),
Gordon Brown, Jeff Warner, Jeff Catalano (Stanford Univ.)
Borehole samples collected from the vadose zone under
leaking waste tanks, containing highly alkaline fluids.
Radioactive (~10 mCi/g Cs-137) soil sections were
embedded in epoxy, and sent for synchrotron analysis
during January, 2001.
mXRF mapping and Cr XAS were studied at GSECARS,
bulk Cr XAS SSRL beamline 11-2, and Cs and Cr XAS at
PNC-CAT (APS 20-ID)
Chromium
Barium
Iron
300 x 300 mm
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03-Mar-2001
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Cr redox in boreholes below Hanford Waste Tanks
Correlation of 3+ and 6+ Peaks
Hanford Soil Chromium Redox State
400
Typical Uncertainty
350
Height of Cr6+ Peak
300
Prelminary analysis of the Cr XANES from a few
different core samples shows some variability of
the Cr6+ / Cr3+ ,ratio, but fairly significant
reduction of Cr6+ to Cr3+.
Cr EXAFS measurements are still being
processed (but seem to be typical Cr3+-oxide)
250
200
150
Line 8_a.001
Spot 8-A
Spot 8-B
Spot 8-C
Spot 8-D
Spot 7-B
Spot 7-C
Spot 7-D
Line 7.003
Spot 7abc-D
Line 7abc.001
Line 7abc.002
Spot 6ab-B
Line 6ab.002
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50
0
10 15 20 25 30 35 40 45 50 55 60 65 70 75 80
Low Peak Height (3+)
GeoSoilEnviroCARS
03-Mar-2001
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Cu speciation in Hydrothermal Fluid Inclusions
John Mavrogenes, Andrew Berry (Australian National University)
Understanding the metal complexes
trapped in hydrothermal solutions is
key to understanding the formation of
ore deposits.
mXRF and mXAFS are important tools
for studying the chemical speciation
and form of these fluid inclusions.
o
Cu 25 C
o
Cu 495 C
Cu and Fe-rich fluid inclusions in granites were examined
at room temperature and elevated temperatures by XRF
mapping and XAFS.
Expectation: chalcopyrite precipitate at low temperature
would dissolve into solution at high temperature.
o
Fe 25 C
o
Fe 495 C
Result: uniform Cu2+ solution at low temperature, not
associated with Fe, and Cu1+ at high temperatures, with
a less uniform spatial distribution.
GeoSoilEnviroCARS
03-Mar-2001
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High Resolution X-ray Fluorescence and EXAFS
A complication in measuring fluorescence
and EXAFS in many natural samples is the
prescence of fluorescence lines from other
elements near the line of interest:
The
resolution of a solid-state fluorescence
detector (~150eV) is sometimes not good
enough to resolve nearby fluorescence lines
The Wavelength Dispersive Spectrometer
has much better resolution (~20eV) than
a solid-state detector, and a much smaller
solid angle. It uses a Rowland circle, not
electronics, to select energies of interest.
It needs the brightness of an undulator,
but complements the Ge detectors, and
allows XRF and even EXAFS on systems
with overlapping fluorescence lines.
GeoSoilEnviroCARS
03-Mar-2001
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Sector Zoning of Rare Earth Elements in Apatites
John Rakovan (Miami University)
.
Apatites have a high affinity for Rare Earth Elements (REE), and
are often used to study petrogenesis. Heterogeneities in crystal
surface structure during apatite growth can strongly alter REE
incorporation.
011 vicinal
face
011 vicinal
face
Most REE show sectoral zoning in apatite based on ionic size.
Ions larger than Ca2+ (La3+) preferring growth along the 001 face,
and those smaller than Ca2+ (Sm3+) preferring the 011 face
Subsector
boundry
011 subsector
001 subsector
3000
520.000000
2500
470.000000
420.000000
2000
370.000000
1500
320.000000
270.000000
78.35
78.15
77.95
77.75
77.55
Linescan distance (mm)
GeoSoilEnviroCARS
1000
77.35
La Concentration (ppm)
Sm Concentration (ppm)
570.000000
001 vicinal
face
Eu is the only REE showing no zonation,
but it has two valence states and two ionic
sizes that straddle the size of Ca2+.
Is there a partitioning of Eu based on
valence state/ionic size?
03-Mar-2001
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Sector Zoning of Rare Earth Elements in Apatites
Since Eu has two valence states with different
ionic sizes (Eu2+ / 1.2 Å, Eu3+ / 1.3 Å), it was
suggested that there may be a valence/ionic size
variation in different growth zones.
.
X-ray counts
The bad news: There is way too much Mn in the
apatite to separate from the Eu fluorescence line
with a solid state detector.
Using the high resolution WDS and the
microprobe, we measured the Eu XANES
on several spots in the different sectors,
and across a <011> / <001> boundary.
Result: We see almost no change at all in
Eu2+ / Eu3+ across the zone boundary: the
ratio is ~17% Eu2+ throughout the apatite.
Energy (keV)
GeoSoilEnviroCARS
03-Mar-2001
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Eu sorption on Fe/Cr oxides
Chia Chen, Sam Traina (Ohio State Univ.)
.
The local structure and coordination chemistry of sorbed
species at mineral-water interfaces greatly influence their
stability -- XAFS plays a key role in understanding the
interactions interactions between sorbent and surface.
-Fe2O3
-Fe1.93Cr0.07O3
The sorption of Eu on minerals such as Fe-and Cr-oxides
is especially relevant to DOE concerns, as Eu is a
common fission product and a chemical analog of Am.
There is way too much Fe/Cr for a solid-state detector.
-Cr2O3
(k) x k3
Several model Eu on Fe/Cr oxide sorption samples were
made to determine the local structure of sorbed Eu as a
function of Cr concentration, pH, and sample aging.
-Fe1.69Cr0.31O3
0.1M Eu liquid
Eu2O3(s)
The Eu LIII edge can’t be used: it gives only 150 eV of
EXAFS before the Fe K-edge
Eu precipitate
These EXAFS measurements were made with the Eu LII
edge, monitoring the Eu Lb fluorescence line with the
Wavelength Dispersive Spectrometer.
2
Bulk EXAFS that requires an undulator.
GeoSoilEnviroCARS
4
6
8
10
k
03-Mar-2001
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Eu sorption on Fe/Cr oxides: Results
.
Fourier Transform Magnitude
-Fe2O3
-Fe1.93Cr0.07O3
-Fe1.69Cr0.31O3
Sample
CN
1st Shell
2
R
-Fe2O3
-Fe1.93Cr0.07O3
-Fe1.69Cr0.31O3
-Cr2O3
Eu liquid
Eu2O3(s)
Eu ppt
7.8
9.4
9.0
8.9
9.1
7.0
9.0
2.39 0.008
2.43 0.014
2.42 0.01
2.41 0.01
2.43 0.007
2.31 0.01
2.43 0.01
E0
-3.59
-1.44
-2.04
-3.30
-1.89
-5.79
-1.36
2nd Shell
2
CN R
1.0
0.4
0.7
0.9
3.47
3.45
3.59
3.53
0.0025
0.0025
0.0025
0.0025
9.0 3.62 0.0081
1.9 3.21 0.0087
-Cr2O3
Eu are sorbed to the Fe/Cr oxide surfaces.
0.1M Eu liquid
Eu2O3(s)
Eu precipitate
0
2
4
Cr substitution for Fe does not impact the sorbed
Eu surface structures.
No significant aging effects were seen.
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R+Å
GeoSoilEnviroCARS
03-Mar-2001