Xu’s laboratory explores the impossible

Thursday, October 4, 2007

Tucked away on the fourth floor of Barus and Holley is Brown’s laboratory of impossible technologies. Led by Jimmy Xu, professor of engineering and physics, the lab’s official name is the Laboratory for Emerging Technologies. Here, students explore the seemingly impossible, such as designing transmission cables from carbon nanotubes and DNA strands. In 2005, the lab generated international press by emitting laser light from silicon – an element that does not emit light.

“We’re not crazy,” said Xu, adding that the lab’s researchers are fully aware of the fundamental reasons silicon cannot emit light. Instead, they began wondering how they could alter silicon to make such a property possible.

Since silicon is one of the most pervasively used materials in electronics manufacturing, the invention of silicon lasers would mark a tremendous breakthrough for the computer industry. Xu and his students began the research in part because working with silicon simply struck them as interesting.

Xu said he got the idea of working with silicon while bored on a 20-hour flight back from Asia. He called up two of his graduate students when he returned, and they began tests.

“Jimmy likes to do something impossible,” said Chih-Hsun Hsu GS. Hsu, who received his master’s degree in Taiwan, explained that the creativity and freedom in Xu’s lab far outweighed the cutting-edge equipment the Taiwanese lab he worked in prided itself on. He said Xu’s lab has a “variety of knowledge,” with graduate students working in chemistry, biology, physics and engineering.

A sign above the entrance to Xu’s lab fittingly reads: “Opportunity Room,” alluding to the lab’s long-running joke that there are simply too many opportunities there for students to pursue.

There are no rules, save one: Anyone late to a group meeting must bring enough pizza and doughnuts for everyone. In fact, the rule resulted in such prompt attendance that lab members considered changing meeting times to try to catch people.

With the exception of the doughnut-and-pizza rule, Xu gives his students complete freedom, and he urges them to pursue their interests. It’s their self-motivation and curiosity that result in the lab’s varied, innovative research.

“When you’re doing things that have never been done before, you can’t follow a model,” Xu said.

“I can explore many things,” said Hongsik Park GS, a former researcher for Samsung who now works in Xu’s lab. “If I want to try something, I can do that.”

The bulk of the silicon research was conducted by Sylvain Cloutier PhD’06, who is currently a professor at the University of Delaware. By drilling billions of microscopic pores in the silicon, he was able to change its atomic structure. “We knew something’s got to be different (about the silicon),” Xu said. “We didn’t know what would be different.”

The result was “a very faint signal in a very messy spectrum,” according to Xu. Though the technology needs years of refinement, it defies decades of convention that silicon cannot give off light.

The problem with the silicon lasers, explained Jeffrey Shainline GS, was that they only worked within the frigid temperature range of 80 Kelvin and below. Shainline, who is refining Cloutier’s silicon-drilling techniques, hopes to improve silicon’s emissive properties by manipulating the spacing of the microscopic pores.

“(A silicon laser) would change computers in a way that few single technologies these days really can,” said Shainline. Though he cautioned that efficient uses for silicon lasers are over a decade away, Shainline described the possibility of 3-D computer processors. Silicon lasers could be built directly onto the processors, allowing each two-dimensional layer to communicate with the others at nearly the speed of light, he said.

Xu remains hesitant to predict any specific applications for light-emitting silicon. “I think it’s like all fundamental breakthroughs in science,” he explained. “Applications will come, but they will come in areas that nobody expected.”

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