For highly efficient thermoelectric devices with Si nanostructures, we have fabricated and characterized micro/nanometer-scaled Si wires preserving the phonon-drag effect in order to observe the impact of phonon-boundary scattering on the phonon-drag factor in its Seebeck coefficient. The observed phonon-drag factor in the Seebeck coefficient decreases with a decrease in the wire width, which is considered due to an increase in the boundary scattering of phonons. Since the boundary scattering is characterized by the specularity parameter, we measured the surface roughness of the wire and evaluated the specularity. It was found that the top surface of the Si wire has higher specularity compared with the sidewall of the wire in the range of phonon wavelength contributing to the phonon drag. This result qualitatively explains the fact that the phonon drag in the Seebeck coefficient is hardly affected by the wire thickness with a nanometer order, whereas the wire width influences it significantly even on a micrometer scale. Moreover, it is demonstrated that the phonon-drag effect in the Seebeck coefficient of Si nanostructures can be preserved while their thermal conductivity is lowered.

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声子边界散射对硅丝塞贝克系数中声子拖曳因子的影响

对于具有Si纳米结构的高效热电器件，我们已经制造并表征了保留声子拖曳效应的微米/纳米级Si线，以观察声子边界散射对其声贝克系数中声子拖曳因子的影响。塞贝克系数中观察到的声子拖曳因子随导线宽度的减小而减小，这被认为是由于声子边界散射的增加。由于边界散射的特征在于镜面反射参数，因此我们测量了导线的表面粗糙度并评估了镜面反射率。已经发现，在声子波长范围内，硅线的顶面与线的侧壁相比具有更高的镜面反射率，这有助于声子的阻力。该结果定性地解释了塞贝克系数中的声子阻力几乎不受纳米级线径的影响，而线宽甚至在微米尺度上也对其影响显着。此外，证明了可以保持Si纳米结构的塞贝克系数中的声子-拖曳效应，同时降低其热导率。