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基于Stillinger-Weber势对硅纳米晶体薄膜的热膨胀性质进行了分子动力学模拟.研究表明,硅纳米晶体薄膜表面层原子的二聚现象引起薄膜收缩,而原子之间的非和谐势能引起薄膜膨胀;在约400K以下的低温段,由于硅纳米晶体薄膜表面层原子发生二聚的原子数目随温度的升高而明显增多,而原子间非和谐势能很小,故此时二聚主导热膨胀性质,热膨胀系数为负;在高温段(约400K以上),由于发生二聚的原子数目随温度升高不再显著地增加并渐趋于稳定,而原子间非和谐势能逐渐显著并主导热膨胀性质,故热膨胀系数为正.
Based on the Stillinger-Weber potential, the molecular dynamics simulation of the thermal expansion of silicon nanocrystal films has been carried out. The results show that the dimerization of atoms on the silicon nanocrystal films causes the film shrinkage, while the non-harmonic potential between atoms causes the film to expand. In the low temperature range of about 400K, the number of atoms dimerized on the surface of silicon nanocrystal film increases with the increase of temperature, and the non-harmonic potential energy of atoms is very small. Therefore, the properties of dimerization-dominant thermal expansion, thermal expansion coefficient Is negative; at high temperature (above 400K), since the number of dimerized atoms no longer increases remarkably and stabilizes with the increase of temperature, but the non-harmonic potential between atoms gradually becomes dominant and dominates the thermal expansion property Positive.