晶界几何结构对纳晶ZnO材料导热过程的影响

为了探究晶界几何结构对纳晶ZnO材料导热性能的影响,将晶界表面抽象出几种典型几何形状,深入讨论了晶界表面粗糙度的计算以及声子入射角对镜面反射率的影响,改进了晶界镜面反射率的计算模型。采用PhonTS软件,用迭代法求解玻尔兹曼输运方程模拟计算得到了纳晶ZnO晶格热导率。基于分子动力学理论计算了ZnO完美材料的热导率,分析了镜面反射率、声子入射角、晶粒尺寸等因素对热导率的影响。结果表明:晶界表面粗糙度的减小或声子入射角的增大会使晶界镜面反射率增大;声子在晶界发生镜面反射不会产生热阻,纳晶材料的热导率会随着镜面反射率的增大而增大;纳晶ZnO材料的热导率表现出强烈的尺寸效应,尺寸效应随着晶粒尺寸的增大而减小。

Liu Yingguang, Han Xiao, Hao Jiangshuai

Nanocrystalline ZnO is widely used in the field of microelectronics, and its thermal conductivity has an important effect on the performance of electronic devices. In order to explore the effect of grain boundary geometry on the thermal conduction of nanocrystalline ZnO,,the grain boundary geometries were abstracted into several typical structures. On this basis, the calculation of grain boundary surface roughness and the effect of phonons incident angle on specular reflectance were discussed, and the calculation model of grain boundary specular reflectance was improved. PhonTS software was used to solve the boltzmann transport equation iteratively to obtain the perfect lattice thermal conductivity of nanocrystalline ZnO. The thermal conductivity of nanocrystal ZnO was calculated based on the molecular dynamics theory, and effects of specular reflectance, phonon incidence angle and grain size on the thermal conductivity were analyzed. The results showed that: (1) the decreases of grain boundary surface roughness or the increases of phonon incidence angle will increase the specular reflectance of grain boundary; (2) phonons specular reflectance at grain boundary will not generate thermal resistance, and the thermal conductivity of nanocrystalline materials increases with the increase of specular reflectance; (3) the thermal conductivity of nanocrystalline ZnO shows a strong size effect, which decreases with the increasing of grain size.