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Materials Science and Engineering

Paul Voyles

Assistant Professor Paul Voyles studies some of the images of metallic glass revealed through his work with electron microscopes. (15K JPG)

Novel microscopy techniques could clear up glass atom mystery

The atomic structure of glass has long mystified scientists. Atoms in glass are jumbled together — resembling marbles in a jar, for example, as opposed to eggs in a carton. But beyond that, little is known about how atoms order themselves in glass. That's inhibited the development of new glass-based materials.

Assistant Professor Paul Voyles's research promises new insights into the atomic structure of glass. His research earned Voyles a prestigious Faculty Early Career Development Award (CAREER) from the National Science Foundation, which is awarded for innovative and creative projects that effectively integrate research and education.

Voyles plans to use a novel electron microscopy technique he helped develop to study the atomic structure of metallic glass — metals that do not crystallize, and therefore resemble glass, when cooled. Scientists have come to believe that useful properties of metallic glass can be attributed to some level of nanoscale atomic ordering. But such structures have been difficult to measure.

Voyles has proposed using fluctuation electron microscopy, a novel quantitative electron microscopy technique uniquely sensitive to subtle structural order in disordered materials, on metallic glass. He complements his experiments through electron diffraction, electron spectroscopy, and atomistic structural modeling.

Insight into this atomic structure should allow researchers to figure out ways to develop better materials that utilize the desirable properties of metallic glass, such as its strength and magnetic force, according to Voyles.

Project takes fault research to new depths

The San Andreas Fault, bisecting California, is ground zero for some of the country's most powerful earthquakes. It has long drawn the interest of scientists. Professor Bezalel Haimson will be among them, having received a two-year, $190,000 research grant from the Division of Earth Sciences of the National Science Foundation to study brittle fracture, deformability, permeability and seismic anisotropy adjacent to and inside the San Andreas Fault Zone.

Haimson is the lead principal investigator of a collaborative project with Professor Teng-Fong Wong of the State University of New York. The study is part of a new national research program, the San Andreas Fault Observatory at Depth (SAFOD), which consists of drilling a 4-kilometer-deep hole into the fault near Parkfield, California. A coordinated study by national and international scientists will examine core samples from the hole, as well as other geological features unique to the San Andreas Fault.

SAFOD is designed to directly sample fault-zone materials, including both rock and fluids, measure a wide variety of fault-zone properties, and monitor a creeping and seismically active fault zone at depth. The SAFOD project aims to provide new insights into the composition and physical properties of fault zone materials at depth, and the laws governing fault behavior. It also hopes to provide direct knowledge of the stress conditions under which earthquakes initiate and propagate.

Time and fatigue take their toll on ferroelectric memory

While the memory inside electronic devices may often be more reliable than that of humans, it, too, can worsen over time. Now a team of scientists from UW-Madison and Argonne National Laboratory may understand why.

Smart cards, buzzers inside watches and even ultrasound machines all take advantage of ferroelectrics, a family of materials that can retain information, as well as transform electrical pulses into auditory or optical signals, or vice versa. The materials have built-in electronic memory that doesn't require any power explains Assistant Professor Paul Evans, a co-author of a paper published in the journal Nature Materials. But there's a problem preventing many of these materials from being used more widely in other technologies, including computers. Eventually they quit working, according to Evans.

The ability of ferroelectrics to store information resides in their arrangement of atoms. Each structure holds a bit of information, which changes every time the material receives a pulse of electricity, basically switching the arrangement of atoms. However each electric pulse — and corresponding change in structure — gradually diminishes the capability of these materials to store and retrieve information until they either forget the information or quit switching altogether.

Engineers call this problem fatigue. With little evidence for what happens to the structure of ferroelectrics as the material's memory fatigues, Evans and his colleagues decided to look inside this material as its arrangement of atoms, controlled by electrical pulses, switched inside an operating device. To create a detailed picture of how the atoms rearrange themselves inside an operating device during each electrical pulse, the researchers used the Advanced Photon Source — the country's most brilliant source of X-rays for research, located at the Argonne National Laboratory — to measure changes in the location of atoms. By seeing how the atoms changed their positions, the researchers could determine how well the material switched, or remembered information.

The X-rays showed that, as the researchers repeatedly pulsed the device, progressively larger areas of the device ceased working, suggesting that the atoms were switching structures less and less. Researchers eventually hope to fully understand why the atoms stop switching and then manufacturers can start to design better devices.

 





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Date last modified: Thursday, 17-Feb-2005 14:09:29 CST
Date created: 17-Feb-2005