Introduction to Inner Shell Spectroscopy

This talk is an introduction to to XAS and XRF aimed at the early graduate student. My intent is to provide a gentle introduction to these sophisticated techniques and give the audience some ideas about how these X-ray techniques might be used in their own research.

Transcript

1. Introduction XAS XRF Experiment Real-world problem XAS Applications Microprobe XAS Community
   Introduction to Inner Shell Spectroscopy
   Bruce Ravel
   Synchrotron Science Group, Materials Measurement Science Division
   Materials Measurement Laboratory
   National Institute of Standards and Technology
   &
   Local Contact, Beamline X23A2
   National Synchrotron Light Source
   SUNY Stonybrook, Physics 518
   13 March 2014
   Introduction to Inner Shell Spectroscopy 1 / 43
   

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2. Introduction XAS XRF Experiment Real-world problem XAS Applications Microprobe XAS Community
   Copyright
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   Introduction to Inner Shell Spectroscopy 2 / 43
   

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3. Introduction XAS XRF Experiment Real-world problem XAS Applications Microprobe XAS Community
   This Talk
   This talk is an introduction to the inner-shell spectroscopies, XAS and
   XRF.
   Outline
   An overview of the basic physics of inner shell spectroscopies
   An introduction to XAS and XRF beamline instrumentation
   A flavor of the sorts of science that can be accomplished with XAS and
   XRF using examples from my own research.
   My hope is that you will leave with a sense of how XAS and XRF might
   be applied to your research.
   Introduction to Inner Shell Spectroscopy 3 / 43
   

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4. Introduction XAS XRF Experiment Real-world problem XAS Applications Microprobe XAS Community
   XAS and XRF
   X-ray Absorption Spectroscopy
   and
   X-Ray Fluorescence spectroscopy
   These are inner shell spectroscopies.
   Inner shell means that an x-ray
   interacts primarily with a deep-core
   electron rather than with a valence
   electron.
   Spectroscopy means that some
   aspect of the interaction changes as
   a function of photon energy.
   Introduction to Inner Shell Spectroscopy 4 / 43
   

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5. Introduction XAS XRF Experiment Real-world problem XAS Applications Microprobe XAS Community
   The basic physical process in XAS and XRF
   X-ray
   in
   n=1 K edge
   n=2 L edges
   n=3 M edges
   n=4 N edges
   n=1 K edge
   n=2 L edges
   n=3 M edges
   n=4 N edges
   n=1 K edge
   n=2 L edges
   n=3 M edges
   n=4 N edges
   X-ray out
   n=1 K edge
   n=2 L edges
   n=3 M edges
   n=4 N edges
   Auger e - out
   1 An incoming photon interacts with a deep-core electron. Shown here, a 1s
   electron is excited for a K-edge spectrum.
   2 The deep-core electron is promoted to some unoccupied state above the
   Fermi energy, propagates away, and leaves behind a core-hole.
   3 A short time later (1 or 2 femtoseconds), a higher-lying electron decays
   into the core-hole and emits a photon.
   4 Alternately, the energy from the higher-lying electron can be used to emit
   an Auger electron.
   Introduction to Inner Shell Spectroscopy 5 / 43
   

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6. Introduction XAS XRF Experiment Real-world problem XAS Applications Microprobe XAS Community
   Characteristic energies
   Each element has a characteristic set of excitation and fluorescence energies.
   Iron: Z=26
   Edge Energy
   K 7112
   L3 706.8
   L2 719.9
   L1 844.6
   Line Transition Energy Strength
   Kα1 K-L3 6405.2 0.580
   Kα2 K-L2 6392.1 0.294
   Kβ1 K-M3 7059.3 0.082
   Kβ3 K-M2 7059.3 0.043
   Kβ5 K-M4,5 7110.0 0.001
   Uranium: Z=92
   Edge Energy
   K 115606
   L3 17166
   L2 20948
   L1 21757
   Line Transition Energy Strength
   Lα1 L3-M5 13614.0 0.686
   Lα2 L3-M4 13438.0 0.077
   Lβ2 L3-N4,5 16387.7 0.181
   Lβ5 L3-O4,5 17063.2 0.038
   Lβ6 L3-N1 15727.0 0.013
   L L3-M1 11618.0 0.005
   Introduction to Inner Shell Spectroscopy 6 / 43
   

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7. Introduction XAS XRF Experiment Real-world problem XAS Applications Microprobe XAS Community
   A simple picture of X-ray absorption
   An incident x-ray of energy E is absorbed, destroying a core electron of
   binding energy E0 and emitting a photo-electron with kinetic energy
   (E − E0
   ). The core state is eventually filled, ejecting a fluorescent x-ray
   or an Auger electron.
   An empty final state is required.
   No available state,
   no absorption!
   When the incident x-ray energy is
   larger than the binding energy,
   there is a sharp increase in
   absorption.
   For an isolated atom, µ(E) has a sharp step at the core-level binding
   energy and is a smooth function of energy above the edge.
   Introduction to Inner Shell Spectroscopy 7 / 43
   

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8. Introduction XAS XRF Experiment Real-world problem XAS Applications Microprobe XAS Community
   X-ray absorption in condensed matter
   The ejected photo-electron can scatter from neighboring atoms. R has
   some relationship to λ and there is a phase shift associated with the
   scattering event. Thus the outgoing and scattered waves interfere.
   The scattering of the photo-electron
   wave function interferes with itself.
   µ(E) depends on the density of
   states with energy (E − E0
   ) at the
   absorbing atom.
   This interference at the absorbing atom will vary with energy, causing
   the oscillations in µ(E).
   Introduction to Inner Shell Spectroscopy 7 / 43
   

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9. Introduction XAS XRF Experiment Real-world problem XAS Applications Microprobe XAS Community
   XAS and Valence State
   As the valence increases
   Mn0→ Mn2+ → Mn3+ → Mn4+
   the edge position shifts to higher
   energy.
   XAS is a direct measure of valence state
   Since each element has its own edge energy, an element’s valence can
   be measured even in a heterogeneous sample
   Since x-rays are deeply penetrating into matter, minimal sample
   preparation is required
   No assumption of symmetry or periodicity is made, so the sample can
   be crystalline, amorphous, thin film, in solution, surface sorbed, · · · ,
   whatever
   Introduction to Inner Shell Spectroscopy 8 / 43
   

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10. Introduction XAS XRF Experiment Real-world problem XAS Applications Microprobe XAS Community
    XAS and Local Atomic Structure
    The different Mn species display big differences
    in the fine structure beyond the edge as the
    valence increases (Mn0
    , Mn2+
    , Mn3+
    , Mn4+
    ).
    The white line and subsequent oscillations are
    quite different.
    The oscillatory portion of the spectrum can be
    isolated and ...
    ... Fourier transformed. This FT function can be
    interpreted to yield partial pair distribution
    functions of atoms about the absorber. The
    Mn-O distances are different for the Mn2+
    ,
    Mn3+
    , and Mn4+
    and clearly different from the
    Mn-Mn distance in Mn metal.
    Introduction to Inner Shell Spectroscopy 9 / 43
    

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11. Introduction XAS XRF Experiment Real-world problem XAS Applications Microprobe XAS Community
    XAS is a direct measure of local structure
    Since each element has its own edge energy, an element’s local structure
    can be measured even in a heterogeneous sample
    Since x-rays are deeply penetrating into matter, minimal sample
    preparation is required
    No assumption of symmetry or periodicity is made, so the sample can be
    crystalline, amorphous, thin film, in solution, surface sorbed, · · · , whatever
    Samples can be measured in situ, which can mean
    cryostat or furnace
    high pressure cell
    electrochemistry cell or fuel cell
    peristaltic or stop-flow pump with liquid samples
    high field magnet
    etc...
    As a result, XAS is used in a very broad array of scientific
    disciplines
    Introduction to Inner Shell Spectroscopy 10 / 43
    

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12. Introduction XAS XRF Experiment Real-world problem XAS Applications Microprobe XAS Community
    Fluorescence from Many Elements
    X-ray fluorescence is a spectroscopy in which the incident energy is
    fixed and the energy dependence of the secondary photons is measured.
    Every element with an edge below the incident energy will fluoresce.
    Glass with every 2nd element Ca–Ge, incident energy = 11153 eV
    Introduction to Inner Shell Spectroscopy 11 / 43
    

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13. Introduction XAS XRF Experiment Real-world problem XAS Applications Microprobe XAS Community
    Fluorescence from A Sediment Sample
    Here are the XRF spectra with incident beams above and below the U
    LIII edge for sediment heavily contaminated with uranium.
    Combined with a standard measured under identical conditions,
    concentrations can be quantified.
    Introduction to Inner Shell Spectroscopy 12 / 43
    

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14. Introduction XAS XRF Experiment Real-world problem XAS Applications Microprobe XAS Community
    Using the Fluorescence Spectrum for XAS
    We can place a region of interest (ROI) around the U Lα peak and
    measure its variation as a function of incident energy.
    In this way, we measure signal only from the absorber and reject all
    other photons entering the detector.
    Introduction to Inner Shell Spectroscopy 13 / 43
    

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15. Introduction XAS XRF Experiment Real-world problem XAS Applications Microprobe XAS Community
    Learning About Your Sample
    I once performed a study to measure the bonding between Hg and
    catalytic DNA molecules. I was given a solution with
    3 mM Hg chlorate
    3 mM DNA
    50 mM cacodylic acid (buffer)
    100 mM NaClO4 (salt)
    Here is the fluorescence spectrum:
    A quick Wikipedia search told me
    that cacodylic acid is:
    The big peak is As Kα (∼10.5 keV), the
    little one is Hg Lα (∼10 keV).
    Introduction to Inner Shell Spectroscopy 14 / 43
    B. Ravel, et al., EXAFS studies of catalytic DNA sensors for mercury
    contamination of water, Radiation Physics and Chemistry 78:10 (2009)
    pp S75-S79 DOI: 10.1016/j.radphyschem.2009.05.024
    

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16. Introduction XAS XRF Experiment Real-world problem XAS Applications Microprobe XAS Community
    A Typical XAS Beamline
    CM
    Mono
    FM
    Hutch
    Fluo
    I
    0
    Slits
    I
    T
    I
    R
    Sample
    CM=Collimating Mirror FM=Focussing Mirror =X-ray Detector
    Monochromator: Si(111) or Si(311) or Si(220) or · · ·
    Introduction to Inner Shell Spectroscopy 15 / 43
    

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17. Introduction XAS XRF Experiment Real-world problem XAS Applications Microprobe XAS Community
    The HXMA Beamline at the CLS
    Introduction to Inner Shell Spectroscopy 16 / 43
    

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18. Introduction XAS XRF Experiment Real-world problem XAS Applications Microprobe XAS Community
    Beamline Optics
    Source The source can be a bend magnet, a wiggler, or an
    undulator. XAS beamlines of each sort exist around
    the world.
    Collimating mirror Correct the vertical divergence of the beam and
    suppress harmonic content.
    Monochromator Use Bragg diffraction from a highly perfect crystal to
    select one energy (i.e. one wavelength) from the
    white light coming from the source. Two crystals are
    needed to direct the beam into the hutch.
    Focussing mirror Change the beam profile from a large rectangle to a
    small circle with minimal reduction of flux.
    Together these deliver a small, monochromatic, tunable beam into
    the hutch for use in an experiment.
    Introduction to Inner Shell Spectroscopy 17 / 43
    

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19. Introduction XAS XRF Experiment Real-world problem XAS Applications Microprobe XAS Community
    Hutch Instrumentation
    Fluo
    I
    0
    Slits
    I
    T
    I
    R
    Sample
    Reference
    mirror
    This is the typical layout of the
    hutch instrumetation. Depending on
    the details of the experiment, the
    sample area might include special
    equipment.
    Furnace or cryostat
    Electrochemistry or fuel cell
    High pressure cell
    High field magnet
    Peristaltic or stop flow fluid pump
    etc...
    Introduction to Inner Shell Spectroscopy 18 / 43
    

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20. Introduction XAS XRF Experiment Real-world problem XAS Applications Microprobe XAS Community
    Hutch Instrumentation: Transmission XAS
    Fluo
    I
    0
    Slits
    I
    T
    I
    R
    Sample
    Reference
    mirror
    In a transmission experiment, we
    measure the direct attenuation of
    the x-ray beam (Beer’s law).
    It
    =I0
    exp(−µt)
    µt = ln
    I0
    It
    Ion chambers are easy to use and
    accurate over many decades of
    intensity.
    X­ray
    Current amplifier
    High Voltage
    Filled with inert gas
    Introduction to Inner Shell Spectroscopy 18 / 43
    

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21. Introduction XAS XRF Experiment Real-world problem XAS Applications Microprobe XAS Community
    Hutch Instrumentation: Fluorescence XAS
    Fluo
    I
    0
    Slits
    I
    T
    I
    R
    Sample
    Reference
    mirror
    The fluorescence detector might be
    an ion chamber or it might be an
    energy discriminating detector.
    If
    ∝µI0
    µ ∝
    If
    I0
    The energy discriminating detector
    is useful for low concentrations or
    very heterogeneous samples.
    Introduction to Inner Shell Spectroscopy 18 / 43
    

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22. Introduction XAS XRF Experiment Real-world problem XAS Applications Microprobe XAS Community
    Elements Measured at a Typical Hard X-Ray
    Beamline
    K-edges, measured with Si(111) monochromator
    K-edges, measured with Si(311) monochromator
    L-edges
    Soft x-ray beamlines exist which deliver photons in the 100 eV to 1 keV
    range (e.g. first row K, transition metal L, actinide N)
    Introduction to Inner Shell Spectroscopy 19 / 43
    

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23. Introduction XAS XRF Experiment Real-world problem XAS Applications Microprobe XAS Community
    My backyard
    When I bought my house, there was a wooden deck off the dining room.
    I replaced this with a paving stone patio and converted the adjacent
    plot of ground into a vegetable garden.
    Introduction to Inner Shell Spectroscopy 20 / 43
    

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24. Introduction XAS XRF Experiment Real-world problem XAS Applications Microprobe XAS Community
    Wood preservative
    The wood used to make the deck was
    treated with the wood preservative
    chromated copper arsentate (CCA), which
    is chromium-bearing analogue of copper
    orthoarsente, Cu3(AsO4)2·4H2O.
    CCA-treated wood is known to leach all three elements into surround-
    ing soils. I had some questions:
    1 How much As is in the soil? Is it higher than elsewhere in the garden?
    (Use XRF)
    2 What chemical species is the As in the soil? (Use XAS)
    Introduction to Inner Shell Spectroscopy 21 / 43
    The orthoarsenate image is from Wikimedia commons and is in the
    public domain.
    

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25. Introduction XAS XRF Experiment Real-world problem XAS Applications Microprobe XAS Community
    XRF spectra
    I took soil samples from a few centimeters below the surface from a spot
    adjecent to the old deck and from a spot 5 meters away and slightly
    uphill.
    Here are the XRF spectra from those two spots:
    There is a clear enhancement of both As and Cr in the soil adjacent to
    the old deck. The As is enhanced roughly two-fold.
    Introduction to Inner Shell Spectroscopy 22 / 43
    

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26. Introduction XAS XRF Experiment Real-world problem XAS Applications Microprobe XAS Community
    As standards
    As a point of reference, here are the XAS spectra from two inorganic As
    standards, As3+
    2 O3 and As5+
    2 O5.
    Note that the edge of As5+
    standard is shifted substantially to higher
    energy and that its white line is much enhanced.
    As5+
    is water soluble, thus more mobile than As3+
    .
    Also As5+
    is quite toxic.
    Introduction to Inner Shell Spectroscopy 23 / 43
    

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27. Introduction XAS XRF Experiment Real-world problem XAS Applications Microprobe XAS Community
    XAS from the soil samples
    Here are the raw µ(E) data from
    the two soil locations. Sure enough,
    the signal from the site adjacent to
    the old deck is enhanced by about
    a factor of 2.
    Here are the normalized data
    compared to standards. The As is
    slightly reduced, but predominantly
    As5+
    . As in soil is well known to
    bind to soil particles as As5+
    .
    Should I be worried about the produce I grow in the garden?
    Introduction to Inner Shell Spectroscopy 24 / 43
    

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28. Introduction XAS XRF Experiment Real-world problem XAS Applications Microprobe XAS Community
    XRF spectra from plant leaves
    Here are XRF spectra from the leaf of a squash plant growing in the
    soil adjacent to the old deck.
    Although toxic As5+
    is present in the soil in elevated quantities, very
    little is taken up by the plants growing that soil.
    The squash were delicious!
    Introduction to Inner Shell Spectroscopy 25 / 43
    

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29. Introduction XAS XRF Experiment Real-world problem XAS Applications Microprobe XAS Community
    XAS Examples
    XAS is used in an amazingly wide variety of disciplines. Here are a few
    examples from my work in the past few years.
    Economic geology Measure the rate of reduction of Au3+
    chloride to
    metallic Au and identify an intermediate species
    Minerology Supporting evidence for a novel U5
    /U6
    mineral
    formed under certain hydrothermal conditions
    Dielectric materials BaTaO2N represents a class of materials with
    tunable dielectric properties
    XAS beamlines regularly see experiments on magnetic materials,
    superconductors, materials for recording media, metallo-organic compounds, metalloproteins, Earth
    mantel materials, extraterrestrial materials, liquids and amorphous solids, etc., etc., etc....
    Introduction to Inner Shell Spectroscopy 26 / 43
    

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30. Introduction XAS XRF Experiment Real-world problem XAS Applications Microprobe XAS Community
    Economic geology (I)
    One way that gold deposits form is by having Au chloride fluids rise
    from the deep earth, wash over cyanobacteria colonies, and reduce to
    metallic gold.
    Au3+Cl
    Before
    Exposed
    After
    We simulated this process at the
    beamline by exposing cyanobacteria
    to an Au3+
    solution and “watching”
    the evolution of the Au XAS from
    Au3+
    to Au0
    .
    Questions
    What is the rate constant?
    Is there an intermediate species?
    Introduction to Inner Shell Spectroscopy 27 / 43
    M. Lengke et el., Mechanisms of Gold Bioaccumulation by Filamentous
    Cyanobacteria from Gold(III)-Chloride Complex, Environ. Sci. Technol.
    40(20) p. 6304-6309. (2006), DOI: 10.1021/es061040r
    

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31. Introduction XAS XRF Experiment Real-world problem XAS Applications Microprobe XAS Community
    Economic geology (II)
    We see that 7 minutes after
    injection, the data strongly
    resemble the Au3+
    Cl. After one
    week, the data resemble Au metal.
    Over the course of the time series,
    the white line ∼ 11921 shrinks
    while the bump ∼ 11945 grows,
    suggesting the reduction to Au
    metal.
    Introduction to Inner Shell Spectroscopy 28 / 43
    M. Lengke et el., Mechanisms of Gold Bioaccumulation by Filamentous
    Cyanobacteria from Gold(III)-Chloride Complex, Environ. Sci. Technol.
    40(20) p. 6304-6309. (2006), DOI: 10.1021/es061040r
    

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32. Introduction XAS XRF Experiment Real-world problem XAS Applications Microprobe XAS Community
    Economic geology (III)
    We can analyze these data as a
    linear combination of species,
    including Au3+
    Cl, Au metal, and
    Au1+
    sulfide.
    We can plot out the contributions
    from these species as a function of
    time to get a sense of reaction rates.
    Introduction to Inner Shell Spectroscopy 29 / 43
    M. Lengke et el., Mechanisms of Gold Bioaccumulation by Filamentous
    Cyanobacteria from Gold(III)-Chloride Complex, Environ. Sci. Technol.
    40(20) p. 6304-6309. (2006), DOI: 10.1021/es061040r
    

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33. Introduction XAS XRF Experiment Real-world problem XAS Applications Microprobe XAS Community
    Minerology (I)
    A deep understanding of the nuclear fuel cycle requires study of “exotic”
    pentavalent uranium minerals that can form under specific mine or
    storage facility conditions. One such mineral,
    UV(H2O)2(UVIO2)2O4(OH)+4·H2O, has recently been synthesized.
    XRD is an indirect measure of valence — XAS is a direct measure!
    Introduction to Inner Shell Spectroscopy 30 / 43
    N. Belai et el., Pentavalent Uranium Oxide via Reduction of [UO2]2+
    Under Hydrothermal Reaction Conditions, Inorg. Chem., 2008, 47 (21),
    pp 10135âĂŞ10140, DOI: 10.1021/ic801534m
    

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34. Introduction XAS XRF Experiment Real-world problem XAS Applications Microprobe XAS Community
    Minerology (II)
    XAS on UV(H2O)2(UVIO2)2O4(OH)+4·H2O
    XANES data
    We see evidence of UV by the
    intermediate edge position between our
    UIV and UVI standards.
    EXAFS analysis
    The crystal structure refined from the
    XRD is consistent with the EXAFS
    data.
    Introduction to Inner Shell Spectroscopy 31 / 43
    N. Belai et el., Pentavalent Uranium Oxide via Reduction of [UO2]2+
    Under Hydrothermal Reaction Conditions, Inorg. Chem., 2008, 47 (21),
    pp 10135âĂŞ10140, DOI: 10.1021/ic801534m
    

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35. Introduction XAS XRF Experiment Real-world problem XAS Applications Microprobe XAS Community
    Dielectric materials (I)
    Tantalum oxynitrides are a class of dielectric materials with high K
    which is tunable by selection of the A cation. By mixing A cations, a
    temperature-constant dielectric is possible.
    First principles DFT suggests that the different ionic radii of O and N
    introduce substantial disorder around the Ta atom.
    Introduction to Inner Shell Spectroscopy 32 / 43
    B. Ravel et el., Role of local disorder in the dielectric response of
    BaTaO2N, Phys. Rev. B73, p. 184121 (2006), DOI:
    10.1103/PhysRevB.73.184121
    

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36. Introduction XAS XRF Experiment Real-world problem XAS Applications Microprobe XAS Community
    Dielectric materials (II)
    The DFT results in a rather complex coordination environment about the
    Ta atom — much more complex than the simple perovskite structure.
    With some effort, this complexity can be incorporated into the data
    analysis. The EXAFS data are shown to be (mostly) consistent with the
    DFT results.
    Introduction to Inner Shell Spectroscopy 33 / 43
    B. Ravel et al., Role of local disorder in the dielectric response of
    BaTaO2N, Phys. Rev. B73, p. 184121 (2006), DOI:
    10.1103/PhysRevB.73.184121
    

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37. Introduction XAS XRF Experiment Real-world problem XAS Applications Microprobe XAS Community
    Hutch Instrumentation: Microprobe
    Fluo
    I
    0
    Slits
    I
    T
    I
    R
    Sample
    Reference
    mirror
    The energy discriminating detector can
    see all elements in a sample with edges
    below the incident energy.
    This is a Vortex 4 element silicon
    drift detector
    Introduction to Inner Shell Spectroscopy 34 / 43
    

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38. Introduction XAS XRF Experiment Real-world problem XAS Applications Microprobe XAS Community
    Focussing optics
    Different types of focussing optics can be matched to the relevant length
    scales of different samples
    1D focussing + slits A total external
    reflection mirror is bent to
    condense the x-rays vertically.
    Slits are used to define the
    horizontal extent. (> 50 µm)
    Kirkpatrick-Baez mirrors Short mirrors
    with excellent figures are used in
    both directions to define a small
    spot. (1–25 µm)
    Refractive optics Fresnel zone plates use
    refraction to define a small first
    order spot (< 1 µm)
    Introduction to Inner Shell Spectroscopy 35 / 43
    

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39. Introduction XAS XRF Experiment Real-world problem XAS Applications Microprobe XAS Community
    X-ray Fluorescence Mapping
    The mapping experiment involves
    placing the sample on an
    3-dimensional stage and in the
    focal spot of the beam.
    The sample is rastered in ˆ
    y and ˆ
    z
    to cover a two-dimensional area.
    At each point xy, the XRF spectrum
    is measured. Integrating the
    elemetal regions of interest yields
    maps of the elemental distributions.
    Introduction to Inner Shell Spectroscopy 36 / 43
    

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40. Introduction XAS XRF Experiment Real-world problem XAS Applications Microprobe XAS Community
    Gravel Contaminated with U
    Gravel embedded in epoxy with a polished surface
    Under a UV lamp, U glows greenish.
    Introduction to Inner Shell Spectroscopy 37 / 43
    D. Phillips et el., Env. Sci. and Tech., 2008, 42 (19), pp 7104âĂŞ7110
    DOI: 10.1021/es8001579
    

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41. Introduction XAS XRF Experiment Real-world problem XAS Applications Microprobe XAS Community
    Gravel Contaminated with U
    Gravel embedded in epoxy with a polished surface
    UV photo + superposed U map — 200 µm probe at APS 10ID.
    Introduction to Inner Shell Spectroscopy 37 / 43
    D. Phillips et el., Env. Sci. and Tech., 2008, 42 (19), pp 7104âĂŞ7110
    DOI: 10.1021/es8001579
    

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42. Introduction XAS XRF Experiment Real-world problem XAS Applications Microprobe XAS Community
    XRF Spectra at each Position
    Here are a few of the XRF spectra from the marked area on the U map
    from the previous page.
    Introduction to Inner Shell Spectroscopy 38 / 43
    D. Phillips et el., Env. Sci. and Tech., 2008, 42 (19), pp 7104âĂŞ7110
    DOI: 10.1021/es8001579
    

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43. Introduction XAS XRF Experiment Real-world problem XAS Applications Microprobe XAS Community
    µ-EXAFS
    High quality XAS data is measured with the
    200 µm probe. We can see the variation in U
    quantity under the spot in the XAS step size.
    Normalizing the data, we see variability in the
    XANES, indicating spatial heterogeneity in U
    speciation.
    The EXAFS is of high quality and can be
    analyzed to uncover the different structural
    environments around the U at the various
    locations.
    Introduction to Inner Shell Spectroscopy 39 / 43
    D. Phillips et el., Env. Sci. and Tech., 2008, 42 (19), pp 7104âĂŞ7110
    DOI: 10.1021/es8001579
    

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44. Introduction XAS XRF Experiment Real-world problem XAS Applications Microprobe XAS Community
    Arsenic Hyper-Accumulating Plant (I)
    An Arabadopsis mutant was plucked from arsenite contaminated medium
    and pressed between two pieces of kapton tape.
    Introduction to Inner Shell Spectroscopy 40 / 43
    M. Pischke and B. Ravel, unpublished
    

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45. Introduction XAS XRF Experiment Real-world problem XAS Applications Microprobe XAS Community
    Arsenic Hyper-Accumulating Plant (II)
    We measured XANES from a vein in the leaf
    with a 20 µm probe at APS 13BM.
    ∼25% As trisglutathiol and ∼75% Arsenite
    Introduction to Inner Shell Spectroscopy 41 / 43
    M. Pischke and B. Ravel, unpublished
    

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46. Introduction XAS XRF Experiment Real-world problem XAS Applications Microprobe XAS Community
    Where to go for more information
    http://xafs.org/
    Introduction to Inner Shell Spectroscopy 42 / 43
    

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47. Introduction XAS XRF Experiment Real-world problem XAS Applications Microprobe XAS Community
    Information about the software
    Ifeffit A suite of interactive programs for XAFS analysis, combining
    high-quality and well-tested XAFS analysis algorithms, tools for
    general data manipulation, and graphical display of data.
    http://cars9.uchicago.edu/ifeffit/
    Athena & Artemis Graphical programs for the processing and analysis
    of XAFS data.
    http://bruceravel.github.io/demeter
    The Ifeffit mailing list Discussion of and related XAFS analysis
    programs. Also covered are general discussions of XAFS, XAFS
    theory, and related spectroscopies.
    http://cars9.uchicago.edu/mailman/listinfo/ifeffit/
    and friends are free software
    free as in beer and free as in speech
    Introduction to Inner Shell Spectroscopy 43 / 43
    

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