The Center for Advanced Radiation Sources (CARS)

Faculty Research Summaries | Executive Director's Introduction

Keith Brister

CARS CARS at the APS provides a unique laboratory where a variety of techniques and scientific communities come together. By drawing on the biological crystallographic community and the resources of BioCARS, ChemMatCARS, GSECARS, and a neighboring sector, I am developing a research program to study biological macromolecules at high pressures. With the collaboration of colleagues from The Scripps Research Institute, the behavior of crystals of several viruses has been studied under pressures as high as 5 kbar. The early results suggest that the application of high-pressure could lead to another tool in the crystallographers “tool kit” to solve virus structures. This technique also lends itself to the study of dynamic protein folding and to understanding the action of proteins in deep-sea animals.

Peter Eng

Though the combined development of novel instrumentation (e.g.,. microfocusing x-ray optics, detectors and diffractometers) and techniques (e.g., interface diffraction, inelastic x-ray scattering and tomography) that exploit the brilliance of the second and third generation x-ray sources we have studied the bulk and lower dimensional properties of condensed matter and earth science systems. In particular, by applying the technique of lower dimensional x-ray diffraction as well as x-ray absorption fine structure, x-ray standing waves, x-ray fluorescence microprobe, microtomography and microcrystallography we have studied important problems in earth and environmental science. One of the main thrusts of this work is to better understand the transport and bioavailability of toxic species in the Earth's crust. Through the combination of these six techniques we have been able to study such problems as: the nature of the aqueous solid interface; the short and intermediate range structure of cation and anion coordination environments in adsorbates on mineral surfaces; the microdistribution of chemical species in rocks, soil and plants; the role of micro-organisms in controlling metal speciation and reactions; the efficacy of waste encapsulation materials; the crystal chemistry of strategic and toxic elements; and the fluid transport mechanisms in rocks.

Timothy Graber

Photochemical reactions in which light induced structural changes in a molecule occur upon laser irradiation can be used to study processes such as electron transfer (charge separation) which, for example, is one of the key mechanisms in the photosynthesis reaction. We are developing methods to measure these excited-state molecular structures (life times of ~100 psec or greater) with atomic resolution using monochromatic crystallographic techniques. Small-molecule crystallography measurements traditionally yield ground state molecular structures. However, the large increase in x-ray spectral brilliance at third generation synchrotrons has enabled the study of transient molecular species using modified crystallographic methods with crystals of average dimension ~10 m. A laser-pump x-ray-probe technique has been developed at ChemMatCARS which effectively takes a snap shot of the molecule at a fraction-of-an-excited-state-life-time after laser excitation. Small crystal size is very advantageous for these experiments since a large excited state conversion percentage can be achieved while at the same time undesirable diffraction effects are reduced. To date, thermally equilibrated excited states in molecules such as Cu(I)(dmp)(diphos)+(dmp = dimethylphenanthroline) (diphos = 1,2-bis(diphenylphosphino)ethane), which exhibit intramolecular metal-to-ligand charge transfer, have been measured and significant structural changes have been observed.

Binhua Lin

The high-brilliance third generation synchrotron source at the APS provides a powerful and indispensable tool to study the structural and dynamic properties in the field of soft-condensed matter science at a length-scale ranging from sub-nanometers to micrometers. Systems of my interests belong to two categories: one includes Langmuir monolayers (monolayers supported at the air/water interface) of amphiphilic polymers or nanometer metal spheres; and the other includes bulks or thin films of polymer nano-composites. The focus of the research is on the characterization of the structure and phase separation or transitions of the systems; on the transport properties of two-dimensional systems (Langmuir monolayers); and on the kinetics and diffusion of nanoparticles in polymers. My research also includes the study of diffusion, hydrodynamic coupling and structural properties of quasi-one-dimensional colloidal suspensions using video microscopy. Our initial results have shown that the structural and transport properties of fluids quasi-one-dimension are drastically different from those of fluids in higher dimensions. Understanding the physics of quasi-one-dimensional fluids will provide insight into the behavior of real quasi-one-dimensional systems, many of which occurs naturally. Some well-known systems are molecular and supermolecular fluids or solids in porous materials (e.g. zeolites, membranes, and carbon nanotubes), charge carriers in one-dimensional conducting polymers, and highway traffic flows.

Mati Meron

New synchrotron light sources can generate extremely intense X-ray beams to be used as experimental probes in various areas of basic and applied research. However, in order to make a full use of the high flux density and very high brilliance (i.e. phase space density) of these beams there is a pressing need to develop new X-ray optics schemes. Within CARS we are working on the development of focusing, brilliance-preserving X-ray optics devices, capable of withstanding very high heat loads without degradation of performance. One of the consequences of the high brilliance of synchrotron beams is that experiments which traditionally belonged in the realm of visible optics, especially those depending on coherence properties of the radiation wave front can now in principle be performed using X-rays. This can be extremely valuable, especially in the study of surfaces, but serious studies of this subject are still in their infancy. A subgroup of CARS (including Jim Viccaro, Binhua Lin and myself) has engaged in a long-term study of coherent beam propagation and reflection off structured surfaces. The results of this study, which did already yield several publications, are being used to refine optics designs and to plan future experiments.

Keith Moffat

Our research focuses on the development of techniques for time-resolved X-ray crystallography and their application to systems of interest to structural biologists. The experimentally accessible time range spans nanoseconds to seconds. Reaction initiation in large single crystals of excellent diffraction quality is generally achieved by pulsed or CW laser stimulation, and progress along the reaction coordinate is monitored both by the change in the diffracted X-ray intensities and in another crystal parameter such as its optical absorption. We are developing mathematical techniques for the analysis of time-resolved crystallographic data, such as singular value decomposition and cluster analysis. Our main biological interest lies in the molecular mechanisms of light-friven signal transduction. Systems under study include a simple bacterial photosensor known as photoactive yellow protein, blue light photoreceptors based on flavin photochemistry, the carbon monoxide complexes of heme proteins, and enzymes whose activity is controlled by light.

Matthew Newville

I am interested in the relationship between the atomic and electronic structure of disordered materials with their physical and chemical properties of materials, and in the use and development of synchrotron x-ray spectroscopies such as x-ray fluorescence and x-ray absorption fine-structure (XAFS) to study these relationships. My research focuses on the application of x-ray absorption spectroscopy to identify the chemical and physical properties of metal ions in highly disordered systems including impurities and trace elements in crystals and glasses, ions in solution, and at mineral surfaces, Such applications are particularly important for systems of interest in the geological and environmental sciences. My work includes the development of state-of-the-art instrumentation to use the brilliance of the APS for x-ray spectroscopies and x-ray scattering with microfocussed x-ray beams. I am also active in the development and advancement of the theoretical and analytical tools for XAFS and related spectroscopies, and the application of these advancing techniques to problems in material, earth, and environmental sciences.

Joe Pluth

(See Department of Geophysical Sciences)

Stuart A. Rice

(See Department of Chemistry)

Mark Rivers

(See Department of Geophysical Sciences)

Guoyin Shen

My research focuses on studying material properties under the conditions of high pressure and high temperature. My current research interest is to provide experimental constraints on the thermal, chemical, and dynamic structures of the Earth and other terrestrial planets. The deep pressure-temperature conditions are simulated with the use of the diamond anvil cell technique. In recent years, efforts have been put on the development of techniques for in situ x-ray measurements at various temperatures (10 – 5000 K) under pressure. Because extreme static pressure-temperature conditions are generally achieved at the cost of reducing sample volume – e.g., at the Earth’s core-mantle boundary condition the sample size in a diamond anvil cell is typically in an order of ~10 micrometers – the high brilliant x-ray beam at the APS is ideal for studying the behavior of materials at extreme conditions. Systems under study include iron and its alloys known as the major composition of the Earth’s core, and major lower mantle minerals (silicate perovskites and ferropericlase). X-ray measurements on the materials provide information on crystal structure, structure of melts, equations of state, melting curve, lattice dynamics, elasticity, rheology, and electronic and magnetic structure.

Joseph V. Smith

(See Department of Geophysical Sciences)

Stephen Sutton

(See Department of Geophysical Sciences)

P. James Viccaro

X-rays have traditionally been very powerful probes of the properties of matter. Many current techniques based on synchrotron X-ray sources can in fact be traced to early experiments using in-laboratory generators. One new area with high potential at the APS relies on the coherent property of high brilliance sources. Of particular interest is the development of brilliance-driven instrumentation for techniques such as time-resolved crystallography and surface science. My current scientific interest involves the characterization of the properties of complex coherent X-ray sources and, in collaboration with Mati Meron and Binhua Lin, the applications of coherent radiation to the study of structured surfaces and nanoscale phenomena. A recent focus of the research has been the nano-scale structural properties of nearly 2-D films.

Yanbin Wang

The combination of large-volume high-pressure apparatus and the high-brilliance X-ray source at the APS provides a unique powerful tool for studies of materials under extreme pressure and temperature conditions. The focus of my research is primarily on physical properties of materials relevant to the Earth’s deep interior, aiming at understanding the current state, the dynamics, as well as evolution of the Earth. Through collaborations with GSECARS colleagues and users, we have designed and built two large-volume presses at the GSECARS beamlines and developed techniques to study phase relations, transformation kinetics, pressure-volume-temperature (P-V-T) equations of state, and crystal chemistry. Many studies involve a combination X-ray diffraction (energy or angle dispersive) and development of other physical property measurement techniques and instrumentation. These include (1) acoustic velocities of mantle minerals, using ultrasonic interferometry, with simultaneous P-V-T measurements, to understand seismic structure and composition of the Earth’s mantle, (2) viscosities of molten silicates and iron alloys with radiography, to help model magmatic activities and state of the Earth’s core, (3) separation processes of iron melt in silicates using microtomography, to constrain models for the formation of the core, and (4) quantitative high pressure deformation for measuring rheological properties of high-pressure minerals (with development of a new deformation apparatus), to understand mantle dynamics and deep seismic activities.