However the on-going challenge for scientists and engineers has been to make thermoelectric materials that are efficient enough to be practical. The goal is a value of 1.0 or more for a performance measurement called the thermoelectric figure of merit or ZT, which combines the electric and thermal conductivities of a material with its capacity to generate electricity from heat. Because these parameters are generally interdependent, attaining this goal has proven extremely difficult.
In recent years, ZT values of one or more have been achieved in thin films and nanostructures made from the semiconductor bismuth telluride and its alloys, but such materials are expensive, difficult to work with, and do not lend themselves to large-scale energy conversions.
Bulk silicon is a poor thermoelectric material at room temperature, but by substantially reducing the thermal conductivity of our silicon nanowires without significantly reducing electrical conductivity, we have obtained ZT values of 0.60 at room temperatures in wires that were approximately 50 nanometers in diameter, said Yang. By reducing the diameter of the wires in combination with optimized doping and roughness control, we should be able to obtain ZT values of 1.0 or higher at room temperature.
The ability to dip a wafer into solution and grow on its surface a forest of vertically aligned nanowires that are consistent in size opens the door to the creation of thermoelectric modules which could be used in a wide variety of situations. For example, such modules could convert the heat from automotive exhaust into supplemental power for a Freedom CAR-type vehicle, or provide the electricity a conventional vehicle needs to run its radio, air conditioner, power windows, etc.
When scaled up, thermoelectric modules could eventually be used in co-generating power with gas or steam turbines.
You can siphon electrical power from just about any situation in which heat
|Contact: Lynn Yarris|
DOE/Lawrence Berkeley National Laboratory