TED-AJ03-652 Thermophysical Property Measurement of Si and Bi_2Te_3 Nanowires

概要

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Theoretical studies have predicted that for Si nanowires with a diameter less than 20 nm, the thermal conductivity could be more than one order of magnitude lower than the bulk value due to boundary scattering and phonon confinement effects. To investigate these predictions, individual Si and Bi_2Te_3 nanowires are isolated and their thermal conductivity and Seebeck coefficient are measured over 10 K to 320 K temperature range. All measurements are made using a microfabricated device consisting of two suspended SiN_x membranes with integrated Pt heaters and resistance thermometers. A separate Pt electrode is patterned on each membrane, allowing electrical contact to the nanowire sample. Amorphous carbon and platinum films are locally deposited at the junction between the wire and the Pt electrode to reduce the thermal contact resistance. Thermal conductivities for Si nanowires of different diameters are found to be much lower than the bulk value, which indicates that the boundary scattering has a strong effect on the phonon transport in the nanowires. Comparison of experimental results with theoretical predictions shows good agreement. Moreover, thermal conductivities and Seebeck coefficient of polycrystalline Bi_2Te_3 nanowires were measured and the results suggested that the synthesis conditions might have strong effects on the properties of the Bi_2Te_3 nanowires.