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The recent demonstration of thermal conductivity of rough electrolessly etched Si nanowire (Hochbaum et al., Nature, 451:163, ) attracted a lot of interest, because it could not be explained by the existing theory; thermal conductivity of rough Si nanowires falls below the boundary scattering of the thermal conductivity. However, nanoscale pores presented in the nanowires (Hochbaum et al., Nano Letters, 9:3550-3554, ) hinder one to be fully convinced that the surface roughness solely made a contribution to the significant reduction in thermal conductivity. In this study, we synthesized vapor-liquid-solid (VLS) grown rough SiGe nanowire and measured and theoretically simulated thermal conductivity of the nanowire. The thermal conductivity of rough SiGe nanowire is an order of magnitude lower than that of bulk SiGe and around a factor of four times lower than that of smooth SiGe nanowire. This significant reduction could be explained by the fact that the surface roughness scatters medium-wavelength phonons, whereas the long-wavelength phonons are scattered by phonon boundary scattering, and the short-wavelength phonons are scattered by alloy scattering. [ABSTRACT FROM AUTHOR]

In this paper, we synthesize VLS-grown rough Si nanowires using Mn as a catalyst with various surface roughnesses and diameters and measured their thermal conductivities. We grew the nanowires by a combination vapor-liquid-solid and vapor-solid mechanism for longitudinal and radial growth, respectively. The surface roughness was controlled from smooth up to about 37 nm by the radial growth. Our measurements showed that the thermal conductivity of rough surface Si nanowires is significantly lower than that of smooth surface nanowires and decreased with increasing surface roughness even though the diameter of the smooth nanowire was lower than that of the rough nanowires. Considering both nanowires were grown via the same growth mechanism, these outcomes clearly demonstrate that the rough surface induces phonon scattering and reduces thermal conductivity with this nanoscale-hole-free nanowires. Control of roughness induced phonon scattering in Si nanowires holds promise for novel thermoelectric devices with high figures of merit. [ABSTRACT FROM AUTHOR]

Abstract: Silicon nanowires were grown on a stainless steel substrate using a vapor–liquid–solid mechanism in self-catalytic mode. The multi-component Fe–Cr–Ni–Mn–Si catalyst that was formed from the substrate leads the growth of single-crystal Si nanowires with lengths of several micrometers and diameters ranging from 100 to 150nm. A systematic investigation of the processing parameters revealed that the hydrogen flow rate is critical to the growth of the nanowires. At a high flow rate that exceeds 1000sccm, the substrate is embrittled by H2, and liquid droplets, which lead the growth of nanowires by the vapor–liquid–solid mechanism, are formed on the substrate. Electrical transport measurements indicated that the nanowires grown with the multi-component catalyst have electrical properties comparable to those grown by a single-component Ti catalyst. [Copyright &y& Elsevier]