硅纳米薄膜中声子弹道扩散导热的蒙特卡罗模拟

通过建立声子散射概率函数描述声子在输运过程中的散射，提出了一种模拟声子弹道扩散导热的蒙特卡罗方法，并将其应用于硅纳米薄膜中的稳态和瞬态弹道扩散导热过程的研究. 提出的蒙特卡罗方法对边界发射的声子束进行跟踪，根据散射概率函数模拟声子束在传播区域内经历的散射过程，并通过统计声子束的分布得到温度分布. 稳态导热过程的模拟发现，尺寸效应会引起边界温度跳跃，其值随着Knudsen数的增大而增大；计算的硅纳米薄膜的热导率随着厚度的增大而增大，与文献中的实验数据和理论模型相符. 通过瞬态导热过程的模拟得到了纳米薄膜内的温度分布随时间的变化，发现瞬态导热过程中的热波现象与空间尺度相关，材料尺寸越小，弹道输运越强，薄膜中的热波现象也越显著.关键词：纳米薄膜弹道扩散导热蒙特卡罗模拟尺寸效应

Monte Carlo simulation of phonon ballistic diffusive heat conduction in silicon nanofilm

A Monte Carlo (MC) method is proposed by establishing a new model of phonon scattering processes with random sampling according to a scattering probability function. The MC scheme is used to simulate steady and transient ballistic-diffusive heat conduction in silicon nanofilm. In the MC simulations, we trace the phonon bundles that emit into media from the boundaries, and obtain the temperature profiles through statistics of the distribution of phonon bundles. It is found that the size effect of phonon transport leads to a boundary temperature jump which increases with the Knudsen number increasing. The thermal conductivity of the silicon nanofilm is calculated and the results suggest that nanofilm thermal conductivity increases with film thickness increasing, which is in good agreement with the experimental data as well as the results from the theoretical model. The temperature profiles vary with time in the transient simulations, which shows that the heat wave is related to not only time scale but also spatial scale. When the spatial scale becomes smaller, the ballistic transport is more dominant, which leads to stronger heat waves.
Keywords：nanofilmballistic-diffusive heat conductionMonte Carlo simulationsize effect