Two-step modification of phonon mean free paths for thermal conductivity predictions of thin-film-based nanostructures
Two-step modification of phonon mean free paths for thermal conductivity predictions of thin-film-based nanostructures
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DOI：
10.1016/j.ijheatmasstransfer.2020.119636
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发表时间：
2020-06-01
影响因子：
5.2
通讯作者：
Wang, Sien
中科院分区：
文献类型：
--
作者：
Hao, Qing;Xiao, Yue;Wang, Sien
作为一种简单的超材料，纳米材料通常在薄膜上制造，以便可以控制热传输。这些纳米结构的蚀刻侧壁通常是粗糙的，这是由于在纳米加工过程中引入的表面缺陷，而顶部和底部膜表面更光滑。在现有的分析模型中，这些表面之间的对比度还没有得到解决，所有的边界被假定为声子反射扩散。在本文中，一个新的两步方法来解决这个问题，提出了一般的薄膜为基础的结构的声子输运建模。在这种方法中，有效的面内声子平均自由路径（λ（膜））首先从体声子MFP修改，以考虑顶部/底部膜表面的影响，在低温下镜面声子反射的可能性增强。该λ（膜）被进一步修改以包括通过蚀刻侧壁的散射，其具有几乎完全扩散的声子散射。这样的两步声子平均自由程修改产生几乎相同的结果作为频率依赖的声子蒙特卡罗模拟蚀刻纳米线和代表性的纳米多孔薄膜。这个简单而准确的分析模型可以应用到一般的薄膜基纳米结构的联合收割机的声子尺寸效应沿着正交方向。(C)2020爱思唯尔有限公司保留所有权利。
As one simple metamaterial, nanopatterns are often fabricated across a thin film so that the thermal transport can be manipulated. The etched sidewalls for these nanostructures are usually rough due to surface defects introduced during the nanofabrication, whereas the top and bottom film surfaces are smoother. In existing analytical models, the contrast between these surfaces has not been addressed and all boundaries are assumed to be diffusive for phonon reflection. In this paper, a new two-step approach to address this issue is proposed for phonon transport modeling of general thin-film-based structures. In this approach, the effective in-plane phonon mean free paths (Lambda(Film)) are first modified from the bulk phonon MFPs to account for the influence of the top/bottom film surfaces, with possibly enhanced probability of specular phonon reflection at cryogenic temperatures. This Lambda(Film), is further modified to include the scattering by etched sidewalls with almost completely diffusive phonon scattering. Such a two-step phonon mean free path modification yields almost identical results as frequency-dependent phonon Monte Carlo simulations for etched nanowires and representative nanoporous thin films. This simple yet accurate analytical model can be applied to general thin-film-based nanostructures to combine the phonon size effects along orthogonal directions. (C) 2020 Elsevier Ltd. All rights reserved.