Ronggui Yang, 34

Thermoelectric materials, which generate electricity from heat otherwise lost through vehicle exhaust pipes, industrial equipment, and computer chips, could do a lot to help conserve energy and reduce greenhouse-gas emissions. So far, however, they have been too inefficient and expensive to be widely used. Some newer thermo­electric materials might more effectively convert waste heat into useful electricity, but they require expensive and impractical layer-by-layer assembly.

Mechanical engineer Ronggui Yang has created an easy-to-make alternative: nanocomposites made of semiconductors such as silicon-germanium alloys and bismuth telluride alloys. Because thermoelectrics generate a current when exposed to a heat differential, they must have the unusual property of conducting electricity well but heat poorly. Yang is improving the thermoelectric performance of the materials he uses by turning them into nano­particles and nanowires, which he then fuses to create composite materials. The nanoscale components help inhibit the flow of heat, which is conveyed by atomic vibrations. That increases the thermoelectric efficiency of the finished material. Yang's theoretical work shows that the materials can match or improve on the efficiency of today's best thermoelectrics.

The biggest advantage of Yang's nanocomposites is that they could be mass-produced using a common industrial process. Yang has produced prototypes in conjunction with MIT, Boston College, and NASA's Jet Propulsion Laboratory at Caltech. Eventually, low-cost nanocomposites could offer big payoffs--for instance, significantly boosting the fuel efficiency of cars. --David Talbot