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Sushi and Acoustic Waves — INEEL Materials Scientist Back from Japan Sojourn

Materials scientist David Hurley recently returned from a three-month sojourn to Hokkaido University located in the northern Japanese city of Sapporo. And while there was some visiting with in-laws involved, Hurley’s purpose was to use ultrahigh frequency acoustic waves to characterize a variety of material properties at the University’s Applied Solid State Physics Laboratory, one of top research labs for such work in the world.

In some ways, this trip was a little like going back home. Hurley spent a year at Hokkaido University as a National Science Foundation postdoctoral fellow in 1998 working with professor Oliver Wright, a physicist originally from the United Kingdom.

One of Hurley's first impressions of Japan was how much the landscape resembled Montana.

Before setting foot on Japanese soil for the first time, the extent of his exposure to the Japanese language was “what I’d studied from a Berlitz language book during the flight over,” said Hurley.

While it was easier this time around, there were still periods when communicating was especially frustrating. Hurley admits that sometimes it was tiring to concentrate on understanding native Japanese. As a consequence he reverted to a mixture of Japanese and English (Jinglish) something he reflexively does when chatting on the phone with his Japanese wife, Miho.

David Hurley, Ph.D., in his laboratory at the INEEL.

"For me, it’s hard to study Japanese and science at the same time," said Hurley. "The language work is mostly memorizing, whereas science is more creative—and I have a hard time combining the two."

After two research trips to Japan, he’s firmly convinced that nouns are the secret to communicating. "If you can just get the nouns down, you’re going to be able to get your point across," Hurley said. "Complete sentences are a luxury that will take more time to develop."

Still, these kinds of exchanges "should be encouraged at the INEEL," said Hurley. "The language barriers can be overcome and the benefits of exposure to new ideas are incredible."

Long days—significant results

Hurley’s research focus is materials characterization using picosecond acoustic waves. Translated into layman’s terms, this means he uses short bursts of laser light to create a picosecond sound pulse that travels through solid material (a picosecond is one million millionth of a second). Picosecond acoustic pulses typically have a wavelength of about 10 nanometers (about 1/10,000 of the thickness of a human hair) and a frequency of 100 gigahertz (10,000,000 times higher than the audible range).

This photo shows a Wavelength-Tunable Dual Femtosecond Laser System (Ti:sapphire). Photo courtesy of the Applied Solid State Physics Laboratory, Hokkaido University.

Hurley then uses another pulse of light derived from the same laser to detect and measure the acoustic ripples in the material. The spatial and temporal sensitivity provided by picosecond acoustics has allowed Hurley and others in the field to study the interaction of acoustic waves with a variety of atomic sized creatures such as electrons, phonon and dislocations. This work has a host of current and potential applications. For instance understanding the physical exchange between acoustic waves and material microstructure such as dislocations holds the potential to determine the state of a structural material along its Road to Failure. This information then could be used to design materials with precisely chosen properties. Along these lines, Hurley and his Japanese collaborators successfully imaged the interaction of GHz surface acoustic waves with material grain boundaries in aluminum and copper samples.

"This is quite exciting because this imaging technique provides the ability to see dynamic changes in material microstructure on length scales comparable to individual features," said Hurley.

Hurley explored another field of materials characterization while in Japan that involved gauging the interaction between acoustic waves and particles that carry energy in semiconducting materials (carriers). Understanding how carriers such as electrons and phonons lose and gain energy and on what length scale and time scale has important consequences in the field of solid-state physics. While in Japan, Hurley and his Japanese collaborators successfully monitored the interaction of electrons and phonons in GaAs, a technologically important piezoelectric semiconductor. What does this all mean: Hurley hopes to harness the interaction between electrons and phonons to direct electrons along well-defined paths, i.e. acoustic circuits. The transient nature of acoustic circuits hold the potential of continually modifying the quantum mechanical nature of the electrons by changing the characteristics of the acoustic waves. This in turn might lead to such far out things as the creation of new computing paradigms.

Sharing stories and sake at a mountain hut in Taisetsu National Park.

While at Hokkaido, Hurley kept graduate student hours, working from 11:00 a.m. to 10:00 p.m. 6 days a week, and at one point was conducting experiments in three labs at the same time. Hurley readily acknowledges that that his degree of productivity was only possible with the dedicated help of Dr. Osamu Matsuda, an Associate Professor, Dr. Yoshihiro "Yoshipi" Sugawara, a post doctoral fellow, and Motonobu "boss" Tomoda a research assistant. "With all the help, I was easily able to get a year’s worth of work done," he said. "And the equipment was amazing." More information about the laboratory capabilities at Hokkaido.

His work at Hokkaido advances research goals for both a DOE Office of Science Basic Energy Sciences project titled Microstructure Nondestructive Evaluation using Imaging Laser Ultrasonics (SAW interaction with grain boundaries), and an INEEL Laboratory Directed Research and Development sponsored project titled Nanostructure Characterization for Sensing (Carrier interaction in semiconductors). Hurley hopes to begin submitting papers for publication within three months.

"The opportunity to forge this collaboration would not have been possible without the support and encouragement of Ken Telschow, Helen Farrell, David Miller and Richard Wright from the INEEL and Timothy Fitzsimmons from DOE headquarters," said Hurley.