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Dispersion and thermal resistivity in silicon nanofilms by molecular dynamics

机译:分子动力学在硅纳米膜中的色散和热阻

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On nanoscale, thermal conduction is affected by system size. The reasons are increased phonon scattering and changes in phonon group velocity. In this paper, the in-plane thermal resistivity of nanoscale silicon thin films is analyzed by molecular dynamics (MD) techniques. Modifications to the dispersion relation are calculated directly with MD methods at high temperature. The results indicate that the dispersion relation starts to change for very thin films, at around two nanometers. The reasons are band folding and phonon confinement. Thermal resistivity is analyzed by the direct non-equilibrium method, and the results are compared to kinetic theory with modified dispersion relations. Thermal resistivity is affected by both surface scattering and dispersion. Moreover, in thin films, the characteristic vibrational frequency decreases, which in standard anharmonic scattering models indicates a longer relaxation time and affects the resistivity. The results indicate that in very thin films, the resistivity becomes highly anisotropic due to differences in surface scattering. In two cases, surface scattering was found to be the most important mechanism for increasing thermal resistivity, while in one case, phonon confinement was found to increase resistivity more than surface scattering.
机译:在纳米级,热传导受系统尺寸的影响。原因是声子散射增加和声子群速度变化。在本文中,通过分子动力学(MD)技术分析了纳米级硅薄膜的面内热阻。分散关系的修改直接在高温下用MD方法计算。结果表明,对于大约两纳米左右的非常薄的薄膜,色散关系开始发生变化。原因是带折叠和声子约束。通过直接非平衡法分析热阻率,并将结果与​​具有修正色散关系的动力学理论进行比较。热阻受表面散射和分散的影响。此外,在薄膜中,特征振动频率降低,这在标准的非谐波散射模型中表明更长的弛豫时间并影响电阻率。结果表明,在非常薄的薄膜中,由于表面散射的差异,电阻率变得高度各向异性。在两种情况下,发现表面散射是增加热阻的最重要机制,而在一种情况下,发现声子限制比表面散射增加了电阻率。

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