Measurements of Thermoelectric Properties of Bismuth Telluride Nanowires

Theoretical calculations have predicted that nanowire materials may have enhanced thermoelectric figure of merit compared to their bulk counterparts due to classical and quantum size effects. We have measured the thermoelectric properties of bismuth telluride nanowires deposited using an electrochemical deposition method in porous anodized alumina templates with the average pore size of about 60 nm. Transmission electron microscopy results of these nanowires showed that the nanowires were single crystalline with a composition of 54% Te and 46% Bi and the thickness of the surface oxide layer was in the range of 5–10 nm. The thermal conductance and Seebeck coefficient of the nanowires were measured using a microfabricated device that consists of two suspended membranes, across which the nanowire sample was placed. The obtained Seebeck coefficient of a bundle consisting of two 100 nm bismuth telluride nanowires increased with increasing temperature from 160 K to 360 K, and the room temperature value was 260 μV/K, which was 60% higher than the bulk value. The thermal conductance of the sample also increased with increasing temperature from 25 K to 360 K. Current design of the microdevice does not allow for four-probe electrical resistance measurement of the nanowire. We have measured the four-probe electrical resistance of a 57 nm diameter and a 43 nm diameter bismuth telluride nanowires from the same template, and found that the room-temperature electrical conductivity of the nanowires was close to the bulk value and showed much weaker temperature dependence than bulk electrical conductivity.