1. Nanowire Thermoelectrics for Energy Conversion
Xuan Gao, Department of Physics, Case Western Reserve University
30K 2K
Confining electrons in nanoscale materials may be used to tailor the electronic structure and tune the thermoelectric properties of nanowires to achieve improved thermoelectric energy conversion efficiency. Electric conductance and thermopower are two important parameters relevant for characterizing thermoelectric figure of merit. We have performed electrical transport measurements of InAs nanowires with small (20nm) diameter in which quantum confinement could be significant. Through temperature and magnetic field dependent conductance study, we showed that electrons have long quantum coherence length (longer than nanowire diameter) in InAs nanowires and interference between electron diffusion paths makes electron wavefunction being localized in a one-dimensional fashion.
A magnetic field destroys quantum interference effect and increases nanowire’s conductance. Furthermore, a perpendicular magnetic field is shown to be more effective than parallel magnetic field in suppressing the weak localization, again due to the small cross-section and wire geometry. One-dimensional effect on controlling the thermopower of nanowire is being investigated, to complement the electric conductance study.
Another interesting property of semiconductor nanowires is the existence of surface state and the use of surface state conduction for enhanced sensor response. Bulk InAs is known to have electron accumulation at surface due to surface states. With large surface-to-volume ratio, the surface electron layer plays a dominant role in the electrical properties of nanowire and may be exploited for sensing molecules adsorbed on surface. Indeed, we found that gas molecule adsorption onto InAs nanowire surface induces strong change in nanowire’s conductance, making this material ideal for sensing applications.