Abstracts

The Canadian Light Source Facility and Prospects for an X-Ray Microprobe

Dr. Ronald G. Cavell

Professor of Chemistry, University of Alberta
Senior Scientific Consultant, Canadian Light Source

The Canadian Light Source, a 2.9 GeV, third generation, synchrotron light generator, under construction on the campus of the University of Saskatchewan, Saskatoon, SK will provide high brilliance X-rays suitable for microscopy. Construction of the facility, which is scheduled to commence operations at the beginning of 2004, is well under way. The status of the project and the technical specifications of the facility will be reviewed.

Absorption of photons throughout the electromagnetic spectrum is widely used for qualitative and quantitative analysis of materials in a multitude of circumstances. The development of the third generation synchrotron radiation sources has revolutionized an old but very powerful technique, X-ray absorption spectroscopy.

The utility and power of X-ray absorption spectroscopy arises from the property that each element has a characteristic X-ray absorption edge and precise measurement of that edge allows the determination of the valence state of that element. Furthermore, analysis of the extended absorption fine structure (EXAFS) may be used to determine the local structural environment about individual excited elements. The characteristic edges are generally well separated so that interferences are minimal. The range of sensitivity is large and detection to sub-PPM levels is possible, particularly with the high-flux beams provided by the modern synchrotrons.

Excitation with photons results in far less sample damage than the electrons or ions of the currently used electron or ion microprobes. Higher energy X-rays offer enhanced penetrating power which can be used to analyze, in place, buried components or interfaces and can also be applied to the analysis of materials under process treatments. Surface and bulk signals can be differentiated. Innumerable applications of the capabilities of this technique exist of importance to both research and industrial explorations such as investigation of catalytic surfaces, analyzing matrix inclusions, composite materials, interfaces and joints, electronic materials, stress and corrosion cracks in materials, and microstructures.

Of particular interest in the future for Materials and Earth Sciences applications will be the capability of producing, from small gap insertion devices, very bright X-rays in the 5-40 keV range. These bright X-rays can be focused to small dimensions to provide X-ray spectromicroscopy for analysis of small areas of micrometer to sub-micrometer dimensions. Opportunities for X-ray microscopy to be developed at the Canadian Light Source using the Alberta based support structure will be discussed.

X-ray Absorption Fine Structure Spectroscopy

Dr. E. Daryl Crozier

Professor, Department of Physics, Simon Fraser University, Burnaby, B.C., Canada
Pacific Northwest Consortium Collaborative Access Team
Advanced Photon Source, Argonne National Laboratory, Argonne, Ill.

Synchrotron radiation has permitted rapid development of XAFS, the spectroscopy of the fine structure in the x-ray absorption coefficient above an absorption edge. XAFS encompasses both the extended (EXAFS) and near edge regimes, providing local structural information: interatomic distances, number and identity of coordinating atoms, information about the correlated motion between the absorbing atom and its neighbour, and in some circumstances, bond angles.

XAFS provides the partial pair distribution functions with high spatial resolution. Long range order is not required, so that the local structure of liquids, glasses and amorphous solids can be determined using the same analysis procedures as for crystalline materials. The concentration of the absorbing species can be as low as ppm. An XAFS spectrum can be measured by a variety of detection methods relaxing some constraints on sample preparation, increasing the ease of application to the diverse materials encountered in physics, chemistry, biological sciences, materials science, environmental science, earth and geological sciences.

This talk will provide an introduction to XAFS spectroscopy. It will be illustrated with results from our work on problems in physics, material sciences, environmental and geological sciences.

Some review articles and texts are listed below:

1. T.M. Hayes and J.B. Boyce, in Solid State Physics, ed: H. Ehrenreich, F.Seitz and D. Turnbull (Academic Press, New York, 1982) Vol 37, p. 173.

2. B.K. Teo, EXAFS: Basic Principles and Data Analysis, Pub: Springer-Verlag, 1986.

3. X-ray Absorption: Principles, Applications, Techniques of EXAFS, SEXAFS and XANES; ed: D.C. Koningsberger and R. Prins; pub: J. Wiley, 1988.

4. J. Stohr, NEXAFS Spectroscopy, Pub: Springer-Verlag, 1992, Springer Series in Surface Science: 25.

5. E.D.Crozier, A review of the current status of XAFS spectroscopy, Nuclear Instruments and Methods in Physics Research B133 (1997) 134-144. Abstract TBA

Earth and Environmental Science with X-ray Microprobes

Dr. Matthew G. Newville

Beamline Scientist - X-ray Absorption Spectroscopy
University of Chicago-CARS

The application of x-ray microprobes to experiments in earth and environmental science from the GeoSoilEnviroCARS beamline at the Advanced Photon Source will be presented. The use of bright x-rays beams focused to a few microns for x-ray fluorescence and x-ray absorption spectroscopy provides the ability to do spatially-resolved, in-situ analysis of the chemical composition and oxidation state of metal ions in heterogeneous systems and at low concentrations. This combination of techniques is especially important for studying the interaction at mineral-water interfaces and metal sorption species in soils and contaminated sediments.

Progress in the Theory and Interpretation of XANES

Dr. John J. Rehr

Professor, Department of Physics, University of Washington

There has been dramatic progress in recent years both in ab initio calculations and the interpretation of x-ray absorption near edge structure (XANES) [1]. These developments have led to ab initio codes such as FEFF8 which now yield semi-quantitative results comparable to experiment for XANES, and permit an interpretation of the spectra in terms of geometrical and electronic properties of a material.

We begin with a summary of the key theoretical developments, which have lead to a self-consistent, full multiple scatting real space Green's function treatment implemented in the FEFF8 code. We show that the high-order multiple scattering (MS) theory can often give an approximate treatment of XANES, but this approach can fail close to an edge, where full MS calculations are often necessary.

A fully quantitative treatment of XANES is challenging, due to a number of many-body effects, e.g., core-hole relaxation, multiplet effects, the photoelectron self energy, and inelastic losses, and we review recent progress in accounting for these effects.

Finally natural extensions of the theory to other spectroscopies, e.g., x-ray emission spectra, anomalous x-ray scattering, DAFS (diffraction anomalous fine structure), and XMCD (x-ray magnetic circular dichroism) are briefly discussed. These developments are illustrated with a number of applications.

[1] Real space multiple scattering calculation and interpretation of X-ray absorption near edge structure, A. Ankudinov, B. Ravel, J.J. Rehr, and S. Conradson, Physical Review B 58, 7565 (1998); J. J. Rehr and R. C. Albers, Rev. Mod. Phys. 72, 621 (2000).

Probing Hydrothermal Fluids

Dr. Alan J. Anderson

Professor and Chair of the Department of Geology
St. Francis Xavier University

Mass and energy transport in the Earth's crust is controlled in part by aqueous fluids which are known to occur in all parts of the lithosphere. In general, these fluids are mulitcomponent electrolyte H2O-CO2 solutions, in which the dominant solutes are alkali chlorides. Our understanding of the composition and structure of such fluids at elevated temperatures and pressures is rudimentary due to the paucity of solubility and spectroscopic studies on geologically representative systems.

The unique capabilities of the synchrotron microprobe have opened new opportunities to directly analyze natural fluid inclusions and simple synthetic aqueous systems under hydrothermal conditions. These data are essential for modeling fluid-rock interaction in the crust. Recent developments and applications of the synchrotron X-ray microprobe to the study of hydrothermal fluids will be presented.

About the Speakers

Dr. Ronald G. Cavell

Professor, Department of Chemistry, University of Alberta
President, Canadian Institute for Synchrotron Radiation

Our primary interest lies in the development of phosphorus chemistry to provide novel ligands. Our heterobifunctional phosphorus ligands yield metal complexes that have proven their worth in support of homogeneous catalysis systems. Our ligands are designed to present bifunctional hard/soft binding character to the metal to promote differential reactivity. Oxidation with trimethylsilyl azide introduces the P=N-SiMe₃ functionality. Elimination or migration of this silyl substituent in reactions with metal halides or terminal metal oxides forms N-M bonds. We have used this type of ligand to prepare complexes of highly oxidized metals (e.g., Re^VII and Re^V) which have applications as novel oxidants and radiopharmaceutical binding agents.

Other novel compounds of phosphorus have been prepared, in particular a series of highly oxidized/high coordinate phosphorus compounds which contain internal donor-acceptor bonds to maximize the coordination at phosphorus. Our most recent synthesis gave an unusual cation wherein a pair of P^III atoms are linearly bound to a central, six-coordinate P^V unit.

We also study photoabsorption, photoelectron and Auger spectra of simple, volatile inorganic molecules (SPF₃, OPF₃, PF₅, etc.) with variable photon energy excitation using the Canadian Synchrotron Radiation Facility (CSRF) in Madison, WI, which is an excellent high resolution source of photons through the range 20-3000 eV. These spectra probe the orbital structure of the molecular species to provide information about bonding. Further study of photoabsorption-photoionization coincidence spectroscopy is under way to understand the pathways of molecular photofragmentation. The Stanford Synchrotron Radiation Laboratory (SSRL) provides us with higher photon energies (>5 keV) than CSRF to study, with K-edge X-ray spectroscopy, the electronic (XANES) and physical structure (EXAFS) of simple compounds of Ti, V and Cr. In addition to the photoelectron and photoabsorption spectroscopies we use Secondary Ion Mass Spectroscopy (SIMS), established in our own laboratory, to study molecules absorbed on surfaces, an area of fundamental importance for understanding heterogeneous catalysis.

Dr. E. Daryl Crozier

Professor, Department of Physics, Simon Fraser University

Dr. Matthew G. Newville

Beamline Scientist - X-ray Absorption Spectroscopy
University of Chicago - Consortium for Advanced Radiation Sources (CARS)

Matt Newville is a beamline scientist at the GeoSoilEnviroCARS sector of the Advanced Photon Source, Argonne, IL, specializing in x-ray microprobe, XAFS, and XANES measurements for problems in earth and environmental sciences. He received a PhD in Physics from the University of Washington, Seattle, WA.

Dr. John J. Rehr

Professor of Physics, University of Washington
Consulting Professor at the Stanford Synchrotron Radiation Laboratory
PNL Affiliate Staff Scientist at the Pacific Northwest Laboratory

Professor John J. Rehr received a B.S.E. (magna cum laude) in Science Engineering from the University of Michigan in 1967. He held an NSF Graduate Fellowship at Cornell University (1967-70) and in 1970-71 at the Istitito di Fisica G. Marconi at the University of Rome. He received a Ph.D. in Theoretical Physics from Cornell University in 1972, with a specialty in Condensed Matter Theory and a Ph.D. dissertation on "Thermodynamic Transformations and the Theory of Equilibrium Critical Phenomena." A NATO postdoctoral fellowship at King's College London (1972-73), and a postdoctoral appointment at University of California, San Diego, (1973-1975) followed.

In 1975, he joined the Department of Physics at the University of Washington as an Assistant Professor. He was an Alexander von Humboldt Scholar at the Max Planck Institut for Festkorperforschung, Stuttgart, W. Germany in 1978, a Visiting Scientist at Cornell University in 1986-87 and fall 1988, and a Visiting Professor at Ohio-State University in summer 1988. Rehr held subsequent visiting appointments at the Freie Universitat Berlin (fall 1993) and Lund University (spring 1994).

Rehr is currently Professor of Physics at the University of Washington, Consulting Professor at the Stanford Synchrotron Radiation Laboratory, and a PNL Affiliate Staff Scientist at the Pacific Northwest Laboratory. Professor Rehr's research specialties are in condensed matter theory, encompassing both solid state and statistical physics. His major research interests at present include theories of x-ray absorption and photoemission and electronic structure algorithms, and his group at UW is well known for the x-ray absorption code FEFF. He has about 200 scientific publications.

Dr. Alan J. Anderson

Professor and Chair of the Department of Geology
St. Francis Xavier University, Nova Scotia
Dr. Anderson's home page.

Alan Anderson is currently Professor and Chair of the Department of Geology, St. Francis Xavier University, Nova Scotia. After earning a Ph.D. at Queen's University, he worked for two years as a visiting scientist in the Fluids Research Laboratory at Virginia Tech.

Since joining the faculty at St. F.X.U. in 1989, Anderson has carried out research on fluid-related processes in the lithosphere with emphasis on ore-forming environments. Over the past eight years, he has used synchrotron X-ray microprobes at the National Synchrotron Light Source (NSLS), Brookhaven, the Cornell High Energy Synchrotron Source (CHESS), and the Advanced Photon Source (APS), Argonne National Laboratory, to probe the composition and structural properties of fluid inclusions and model synthetic solutions at high temperatures and pressures.

In 1999, Anderson, together with collaborators R. Mayanovic and S. Bajt, was awarded the Hawley Medal from the Mineralogical Association of Canada for their paper on the application of synchrotron radiation to the study of zinc chlorocomplexing in natural fluid inclusions.

X-ray Microprobe Workshops