Chemistry graduate student Heng Yu (right) and William E. Buhro, Ph.D., professor of chemistry in Arts & Sciences, examine nanowire specimens in an inert-atmosphere glove box, which stores moisture- and oxygen-sensitive chemicals. The glove box allows manipulation of sensitive reagents and nanostructured materials in a continuously scrubbed nitrogen atmosphere. |
By Tony Fitzpatrick
William E. Buhro, Ph.D., professor of chemistry in Arts & Sciences, sweats the small stuff. In his world, it's all small stuff.
That's because Buhro and his group are immersed in the Lilliputian world of nanoparticles and nanowires, which are invisible to the naked eye and hold promise in making stronger and tougher materials for a wide range of products and applications, and for enabling advances in nanoelectronics.
Buhro is making steady advances that have gained him wide respect nationally as he develops materials and understands properties, structures and functions of nanostructures for the looming enterprise of nanotechnology.
How small is this world? One nanometer is one one-thousandth of a micrometer. In comparison, a strand of human hair is typically 50 micrometers to 100 micrometers thick.
Why small? For years, engineers have constructed parts made of such conventional materials as metals and ceramics having grain sizes on the order of hundreds of micrometers large --nearly big enough to see with the naked eye.
With such large grain sizes, a trade-off exists between strength and fracture toughness --i.e., damage tolerance. Alterations in a material that increase its strength unfortunately also typically increase its brittleness. Conversely, alterations that increase fracture toughness typically decrease strength.
But reducing grain sizes to nanometer dimensions simultan-eously increases the strength and fracture toughness of materials.
In his 14 years at the University, Buhro has collaborated with many researchers across disciplines, both here and at other universities. The longest collaboration is with Patrick Gibbons, Ph.D., professor of physics, who has helped Buhro right from the start with transmission electron microscopy, data interpretation and advising of Buhro's students.
Buhro also has enjoyed a long-standing collaboration with Mark Conradi, Ph.D., professor of physics in Arts & Sciences. Buhro's collaboration with Kenneth Kelton, Ph.D., professor of physics, goes back a long while, too.
Buhro and Kelton collaborated with Richard L. Axelbaum, Ph.D., associate professor of mechanical engineering, and Shankar M.L. Sastry, Ph.D., the Catherine M. and Christopher I. Byrnes Professor of Engineering, in the early '90s on making nanostructured materials for potential applications in the aerospace, defense, medical, and sports and recreation industries.
Their method was to make nanocrystalline powders and then consolidate them into discs for testing. But they found that in compacting and consolidating the nanoparticles, they trapped pores and other defects, so the materials didn't have the toughness they'd hoped for.
William Buhro and Regina Frey are married to each other, parents of a fifth-grade son and colleagues in the chemistry department. |
"What we're trying to do now is the reverse of the original concept," Buhro said. "We are consolidating the material first and then creating the nanostructure. In the beginning, the material has no grain structure, and then we create the nanoscale grain structure."
The material Buhro and Kelton are aiming to make can be referred to as a metallic glass. If that seems to be an oxymoron, it's because the term "glass" doesn't refer to transparency but its underlying structure, Buhro explained. In a crystal, atoms are lined up in periodic rows, row after row in a very ordered, beautiful lattice. In a glass, the structure is jumbled and irregular.
A liquid has the same irregular order as glass, which itself is a liquid. If you doubt that, Buhro suggests you go to a 100-year-old home and remove a pane of original glass. The glass will be thicker at the bottom than the top because the liquid has flowed gradually downward over all those decades.
"If one cools a metallic liquid rapidly --tens of thousands of degrees a second --the structure is trapped in its irregular, liquid-like state," Buhro explained. "It forms a substance that to your hand feels like a solid, but in fact is a liquid structure and shares some properties with viscous liquids.
"This is how we first consolidate the materials. Then we induce them to begin crystallizing on a very small-length scale, which will give a nanocrystalline material."
There is at least one commercially available metallic glass on the market today, in Liquidmetal Golf clubs. The Professional Golfers' Association of America's Paul Azinger uses these clubs, which drive a ball farther because, to put it simply, there is less energy loss upon the impact of the club with a ball.
The goal of this area of Buhro and Kelton's research is to make metallic materials become stronger without losing their toughness.
Similarly, nanocrystals and nanowires are valued for their conducting and semiconducting properties. Microelectronic devices are getting smaller and smaller at a steady rate. Since the 1960s, this shrinking has allowed the number of transistors engineers can fit on a computer chip to double every 18 months.
Many researchers speculate that photolithography, the technology that allows this proliferation, will not be able to fabricate devices smaller than about 100 nanometers. This limit could be reached in five to 10 years from now.
But if nanoscience and nanotechnology can make great leaps and bounds in that span, the "small" revolution can continue.
Since the early '90s, Buhro and his group have been making many kinds of nanowires and nanotubes that might ultimately be incorporated into nano-electronic devices. Nanowires and nanotubes are receiving much attention as potential transistors, wires and switches for ultra-small circuits and devices, to be built from such nanostructures on almost a molecular scale.
"If you want to make electronics smaller and smaller, you have to make the component devices and the wires that interconnect them smaller and smaller," Buhro said.
Carbon nanotubes have been highly touted for their ability to serve in these roles. But a stumbling block is that carbon nanotubes exhibit a variety of wall structures, which means that every sample contains nanotubes having a wide range of different electrical properties.
In contrast, the nanotubes and nanowires the Buhro group makes --of semiconductors such as gallium arsenide, boron nitride and even elemental boron --will have more uniform and controllable properties.
A key collaboration has just begun with Jia Lu, Ph.D., assistant professor of electrical engineering. Together, Lu, Buhro and their students will measure the electrical properties of nanowires that Buhro and his group make, and learn to assemble rudimentary nanoscale devices.
"We are trying to build the scientific infrastructure for electronic nanotechnology and to understand the basic principles involved," Buhro said. "We have to find out how these nanowires work and how to connect them into circuits and functional devices. Even when we have that, nobody yet knows how a computer chip will be made that uses these things. That is a wide-open, unsolved problem.
"But the fundamental science to be done is potentially important and is going to be very fun. Before you can have a nanotechnology, you have to have a nanoscience, and that's what we're trying to help provide."
Buhro's prominence in nanostructures and inorganic chemistry has its roots in his childhood. His father, William L., was a junior-high science and mathematics teacher in Comstock, Mich. (near Kalamazoo), public schools.
Buhro grew up in nearby Portage, and he often accompanied his father to his classroom/laboratory on weekends. He remembers many conversations about the periodic table, sketching models of its atoms and viewing his father's lesson demonstrations.
In high school, an outstanding chemistry teacher, Charles J. Harmon, got Buhro interested in a chemistry career. With Harmon's encouragement and advice, Buhro chose Hope College, a Holland, Mich., small, private liberal arts school with a good chemistry program. There he conducted under-graduate research with chemistry professor Michael P. Doyle.
Buhro went on to pursue a doctorate in organic chemistry at the University of California, Los Angeles, in 1980, but relocated to Salt Lake City and the University of Utah in 1982 because his research director, John A. Gladysz, Ph.D., took a position there.
At Utah, he met a first-year chemistry graduate student, a theoretical chemist named Regina Frey. They married right after Frey received her doctorate in 1986.
Buhro spent almost two years as a postdoctoral research associate in inorganic chemistry with Malcolm H. Chisholm, Ph.D., at Indiana University before coming to Washington University in 1987.
Frey became a lecturer in chemistry in 1994. Numerous times, Buhro and Frey have taught Chemistry 111 concurrently in the fall semester. That makes for interesting dinner conversations that their son, Walter, an 11-year-old fifth-grader, must endure, because the couple has to agree on course content, test questions and procedures.
Buhro is very highly regarded for his teaching as well as his research. At the University, he won the Council of Students of Arts & Sciences Faculty Award for Teaching in 1990 and 1996. He was a National Science Foundation Presidential Young Investigator Award winner (1991-96). And he received the Emerson Electric Co. Excellence in Teaching Award in 1996.
"Bill's contributions to the chemistry department at Washington University have been extraordinary," said Joseph J.H. Ackerman, Ph.D., the William Greenleaf Eliot Professor of Chemistry and department chair. "He is acknowledged as one of the finest teachers in Arts & Sciences --be it a large section of general chemistry or an advanced graduate-level offering --and he has brought us high visibility among chemists nationwide for his nanomaterials research.
"In every way, Bill is the complete package, and we are very fortunate to have him as a colleague."
| Front Page |
Medical News |
Calendar | Notables | Campus Watch |
Email Us! |
| Sports | More Campus News |
Record Staff |
Hilltop Jobs Medical Jobs |
WU Home Page |
