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Research opportunities expand at nation's premier X-ray facility

DOE/Argonne National Laboratory : 04 March, 2007  (Technical Article)
The Advanced Photon Source, located at Argonne National Laboratory and the premier hard X-ray research facility in the nation, each year hosts thousands of experimenters who carry out research that impacts nearly every aspect of our lives. Now, the outlook for this essential U.S. Department of Energy-funded program is even brighter as changes in the way scientists access the APS are significantly increasing opportunities for experimentation.
Access to those APS X-ray beamlines funded, like the APS itself, by the DOE's Office of Basic Energy Sciences has more than tripled since they came under the auspices of the X-ray Operations and Research group in Argonne's Experimental Facilities Division. It's all part of a concerted effort by APS and DOE to make this national scientific asset even more open to experimenters whose research proposals can pass a competitive, peer-reviewed proposal evaluation process.

When the APS began operations in 1996, 25 percent of the research time on most beamlines was available for open, peer-reviewed research. With the creation of XOR, the availability at XOR-operated beamlines has soared to 80 percent. At the same time, the number of XOR-operated sectors has grown from four to 10 and will continue to increase.

DOE's Office of Basic Energy Sciences set out to improve access to beamlines at the APS and other federally funded U.S. light sources to maximize the facilities' scientific and technical impact. At the APS, XOR was formed within the Experimental Facilities Division to operate the BES beamlines, to build new ones and to pioneer new fields of X-ray research.

“It is a natural choice for us to operate these beamlines,” said Experimental Facilities Division Director Efim Gluskin. “Our division has conceptualized, designed and developed innovative instrumentation for APS users. This instrumentation includes insertion devices that provide the extreme-brilliance X-rays, monochromators and mirrors that select the required X-ray wavelength while withstanding extremely high heat loads, and X-ray optics that focus the X-ray beam to spots smaller than a millionth of a meter.” This work remains a main focus of the division.

Experiments at XOR-managed beamlines are uncovering new knowledge in chemistry, geoscience, bioscience and materials science. This research uncovers how sub-microscopic structural changes can lead to large changes in the properties of technologically important materials and develops pioneering research techniques that are expected to lead to new advances in chemistry, materials science and geologically important materials.

“Many research techniques available at the XOR-operated beamlines serve multiple scientific communities,” explained Gabrielle Long, Associate Director of the Experimental Facilities Division. “It is intriguing that the same research technique that delivers geological information about the Earth's core can also provide critical information about systems as delicate as biological tissues.”

Recent research at XOR beamlines

Recent research at XOR beamlines has led to new findings about the properties of ferroelectric materials, the way porphyrins, key molecules in photosynthesis, respond to light under different chemical conditions, and the difficulties of cleaning up contaminated soil at U.S. weapons-production sites.

Our current information technology relies on devices that process information as binary ones and zeroes. Ferroelectric materials are of special interest to developers of the next generation of such devices because they exhibit polarized electronic states that can represent bits of information. Moreover, these materials retain their polarization states without consuming electrical power, which makes ferroelectrics the subject of intense study for nonvolatile memory applications that can store data even when the power is turned off. One problem, however, is polarization fatigue: After a number of cycles, the ability to switch polarization tapers off, rendering the device unusable. Researchers used synchrotron radiation from the APS to study the micrometer-scale details of polarization fatigue in ferroelectric oxides. This research could help lead to computer RAM and other memory devices that retain data even when turned off.

Recent research at an XOR-operated beamline also showed that ferroelectric materials can retain their ability to function even when made into extremely thin films. The results show that a thin film of one particular ferroelectric material, lead titanate, is still stable even in a layer that is a mere 1.2 nanometers (three unit cells) thick. This tiny thickness limit for ferroelectricity bodes well for fabricating submicroscopic layers for use in various novel applications.

Square, flat molecules known as porphyrins are at the heart of natural and artificial photosynthesis, the conversion of sunlight into chemical energy. They provide a molecular springboard that captures photons of sunlight and bounces out energetic electrons. Porphyrins also have potential as light-powered catalysts and as components of photonics devices, such as information storage materials, that use light, rather than electrons to store data. Researchers used an XOR beamline to determine how different porphyrin molecules respond to being excited by light under different chemical conditions. Their findings could help scientists fine tune the chemical structure of porphyrins by changing the attached side groups and the metal ions at their center to respond to different wavelengths of light. Such modified porphyrins may one day form the building blocks of novel catalysts, photonic devices and efficient solar-power units.

Accidental releases of liquid waste from U.S. nuclear weapons production facilities have included large quantities of radionuclides, such as cesium, cobalt, europium, strontium, technetium, and uranium. These leaks at underground waste storage tanks, first built in the 1940s, have caused complex plumes of soil contamination. Researchers from Stanford University, Stanford Synchrotron Radiation Laboratory, Pacific Northwest National Laboratory and Argonne used an XOR beamline to study the properties and behavior of uranium in sediment samples from a contaminated site. The researchers concluded that the distribution and various chemical forms of uranium would likely make environmental remediation of the site difficult. But they also concluded that future release of uranium from these sediments would be minimal.

Building beamlines

A number of new beamlines currently under construction at the APS will be operated by XOR. Chief among them is the nanoprobe beamline for Argonne's new Center for Nanoscale Materials. The nanoprobe will be a hard X-ray microscopy beamline with the highest spatial resolution in the world.

Nanomaterials contain structures only a few atoms across and exhibit properties different from bulk materials. While used in only a few products now, nanomaterials are predicted to grow into a trillion dollar industry. Nanotechnology is expected to open new possibilities in areas as diverse as superconductivity, computer memory media, electrical and thermal transmission, micro-switching devices and highly sensitive free-radical detectors. The nanoprobe beamline will combine fluorescence, diffraction and transmission imaging at a spatial resolution of 30 nanometers or better. The X-ray beam will probe samples under in situ conditions and provide information about the internal structure of nanomaterials.

Another innovative beamline will be a premier facility for inelastic X-ray scattering. This technique can, for example, measure the velocity of sound in liquid metals of importance to geoscience. Finally, a dedicated beamline is under construction to serve the needs of the X-ray powder diffraction community.

XOR is also playing a major role in strategic planning for future scientific development at the APS to attract new groups of researchers with exciting ideas for innovative X-ray science. These concepts will be the foundation for exciting new research at the remaining, uncommitted APS beamlines.
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