平均自由程
声子
热导率
材料科学
热流
散射
凝聚态物理
热电效应
波长
玻尔兹曼方程
计算物理学
光学
光电子学
物理
热力学
复合材料
作者
S. Aria Hosseini,Alathea Davies,Ian Dickey,Neophytos Neophytou,P. Alex Greaney,Laura de Sousa Oliveira
标识
DOI:10.1016/j.mtphys.2022.100719
摘要
The ability to minimize the thermal conductivity of dielectrics with minimal structural intervention that could affect electrical properties is an important capability for engineering thermoelectric efficiency in low-cost materials such as Si. We recently reported the discovery of special arrangements for nanoscale pores in Si that produce a particularly large reduction in thermal conductivity accompanied by strongly anticorrelated heat current fluctuations [1] – a phenomenon that is missed by the diffuse adiabatic boundary conditions conventionally used in Boltzmann transport models. This manuscript presents the results of molecular dynamics simulations and a Monte Carlo ray tracing model that teases apart this phenomenon to reveal that special pore layouts elastically backscatter long-wavelength heat-carrying phonons. This means that heat carriage by a phonon before scattering is undone by the scattered phonon, resulting in an effective mean-free-path that is significantly shorter than the geometric line-of-sight due to the pores. This effect is particularly noticeable for the long-wavelength, long mean-free-path phonons whose transport is impeded drastically more than is expected purely from the usual considerations of scattering defined by the distance between defects. This “super-suppression” of the mean-free-path below the characteristic length scale of the nanostructuring offers a route for minimizing thermal conductivity with minimal structural impact, while the stronger impact on long wavelengths offers possibilities for the design of band-pass phonon filtering. Moreover, the ray tracing model developed in this paper shows that different forms of correlated scattering imprint a unique signature in the heat current autocorrelation function that could be used as a diagnostic in other nanostructured systems. • Large-scale MD calculations show that special arrangements of nanopores result in anticorrelated heat flux fluctuations. • Thermal conductivity is reduced by 80% beyond that expected by porosity alone, due to super-suppression of long MFP phonons. • Different forms of correlated scattering imprint a unique signature in the heat current autocorrelation function. • Monte Carlo simulations show that these phenomena can occur in experimentally realizable systems. • The super-suppression of long MFP phonons provides opportunities for these porous systems to act as phonon band-pass filters.
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