For Peidong Yang,

it's a small world

Suzhou and Zhuzhou are two cities in China with similar names, but very little else in common — except that both are central to Peidong Yang and his family.

Suzhou has been called China's garden city, the "Venice of the East." Located near Shanghai, Suzhou's beauty inspired the Manchu rulers to build a model of its canals on the grounds of the Summer Palace in Beijing. Suzhou is where Yang was raised.

Zhuzhou is not so famous. It is a growing commercial and transportation center in Hunan province, the region known for its red earth, fertile countryside, and its fiery cuisine. Zhuzhou was home for Mei Wang, who would become Yang's wife.

The couple met between the two cities, in Hefei, when they both attended the University of Science and Technology of China (USTC). Yang, now 35, studied chemistry at USTC from 1988 to 1993 as part of the university's rigorous five-year degree program.

In 1993 Yang departed from China for a Ph.D. program in chemistry at Harvard. Wang left soon after for a physics Ph.D. program at Yale. They kept in touch and were married in 1996.

At Harvard, Yang wrote his dissertation on high-temperature superconductors under Charles Lieber. He then came to California in 1997 as a postdoctoral researcher at UC Santa Barbara, where he studied nanostructures and high-surface area silica for a year and a half in the group of Galen D. Stucky.

In 1998, Yang made a fateful decision. As he applied for academic positions, he needed to formulate a research program. "My dissertation research had been in the area of high-temperature superconductors," he says, "but academic interest had declined in that topic by 1998, and most of the research had moved over to industrial labs."

Yang next considered carbon nanotubes. Richard E. Smalley of Rice University had won the Nobel Prize in 1996 for his role in the discovery of "buckeyballs" and other fullerenes. "By 1998, carbon nanotubes were a very hot research topic," according to Yang. "I asked myself, should I jump into the crowd or try something different?"

In the end, Yang moved in a different direction. By sleuthing the research literature, he discovered that a team at Bell Labs had learned how to construct what they called "whiskers" out of silicon in the 1960s. Another group at Hitachi flirted with the nanowire concept in the early 1990s, but they did not continue their research.

Yang developed a research plan in nanowire fabrication, and he was hired as an assistant professor in the UC Berkeley Department of Chemistry in 1999. Since then his research has blossomed, and Yang, an associate professor since 2004, oversees the West Coast's leading research group in nanowire fabrication. Ironically, the East Coast's leading research group is that of his dissertation advisor at Harvard, Charles Lieber. "My old advisor is now my main competitor," Yang says with a smile.

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Yang's nanowires are long thin structures less than 100 nanometers (billionths of a meter) in diameter, typically made of a semiconductor material like silicon, germanium, zinc oxide or gallium nitride. These nanowires are grown by chemical vapor deposition (CVD) or by the vapor liquid solid (VLS) process. In these processes, the material of the nanowire is deposited from a gas vapor onto a solid substrate (CVD) or onto a nanoscale droplet of liquid catalyst on a solid surface (VLS). Yang's group is about 30-people strong, and they have coaxed a variety of applications from nanowires.

"Cheaper solar power cells are a good example of what can be done with nanowires," says Yang. "The advantage of nanowire solar cells is that they are made from low-cost material, the production techniques are inexpensive, and the production process is environmentally benign. And most important, they can achieve better energy conversion efficiency."

Conventional solar panels are large sheets of extremely pure silicon, similar to the material used in computer chips. When light strikes a solar panel, electrons are knocked out of place in the material, leaving "holes." The electrons must reach an electrode, where they are gathered in the billions and billions to produce a current. The electrons flow from the solar panel to do work — power a light bulb or run a refrigerator — and return to the solar panel, where they reunite with the holes.

"The problem with a conventional solar cell," says Yang, "is that an electron must hop from particle to particle inside the silicon semiconductor material in a random way until it reaches the electrode. It's like trying to get from San Francisco to San Jose by following city streets. Any imperfection in the material acts as a roadblock, and the electrons get stuck."

A solar cell made of an array of nanowires allows the light-energized electrons to flow directly to the electrode via the nanowire. "It's like traveling on a highway instead of a city street," says Yang.

For now the efficiency of the nanowire solar cells remains low, at about 3.5 percent, compared to up to 20 percent for commercial silicon solar panels. Yang's goal is to raise efficiency to 10 percent in the next few years.

Several empty bottles of champagne rest atop one of Yang's bookcases. There is one bottle for each of his students who has passed the qualifying exam. Yang is proud to have three of his Ph.D. students graduate this year. One will go to academia, two to postdoctoral positions.

"The interest in nanowires is growing" says Yang, "and many major electronics firms like HP, IBM, GE and Intel have nanowire labs." One of his students, Matthew Law, was one of six graduating doctoral students to win the International Union of Pure and Applied Chemistry award for the best Ph.D. thesis in the chemical sciences.

Yang is especially proud of the youngest member of his "group," his daughter, who arrived in 2004. Wife Mei completed her Ph.D. in physics at Yale but returned to school at Berkeley's Haas Business School and now works in finance. Together they return to China with their daughter to visit both pairs of her grandparents, one pair in Suzhou and one in Zhuzhou.

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