Bismuth NanoWires and Ohmic Contacts
We have developed a reproducible method to synthesize single crystalline Bismuth nanowires (BiNWs), 40nm in diameter, with embedded quantum point contacts. We have also developed methods to characterize the ZT values of individual wires, i.e., free of any averaging of ensemble measurements, and we show that our BiNWs have superior thermoelectric properties at low temperatures (77K), with ZT>3.
Thermoelectric materials convert thermal gradients and electric fields for power conversion and refrigeration, respectively. Despite their many advantages, devices based on thermoelectric materials are used today only in a few applications, due to their low efficiency, as determined by their figure of merit ZT. While common household refrigerators are operating with a cooling efficiency which corresponds to ZT=3, state of the art thermoelectric materials are typically characterized by ZT=1-1.5.
Theoretical studies predict that scaling down of these materials to the nanometric scale should enhance their efficiency mainly due to two complimentary effects: i) quantum confinement which should result in high Seebeck coefficient, and ii) decreased lattice thermal conductivity.
Stage of Development and Suggested Next Steps
A scalable fabrication of BiNWs has been established.
We are currently seeking to expand our capabilities and demonstrate similar high ZT values at room temperature.
- Bismuth nanowires with very low lattice thermal conductivity as revealed by the 3ω method; A. Holtzman, E Shapira and Y Selzer; Nanotechnology 23, 495711 (2012).
- Very high thermopower of Bi nanowires with embedded quantum point contacts; E. Shapira, A. Holtzman, D. Marchak, Y. Selzer; Nano Lett 12(2):808-12 (2012)