硅纳米晶体薄膜热膨胀性质的分子动力学研究

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。

Molecular Dynamics Study on the Thermal Expansion Property of Si Nanocrystal Film

The thermal expansion property of silicon nanocrystal film is simulated by molecular dynamics with the Stillinger-Weber potential. The results show that the dimerization of silicon atoms on the surface of the nanocrystal film results the film contraction, and the interatomic anharmonic potential results the film expansion. When the temperature is lower than about 400K, the number of the dimerized atoms grows significantly with the increase of temperature, and the interatomic anharmonic potentials are very small, so the dimerization dominates the thermal expansion property, and the thermal expansion coefficient is negative; When the temperature is higher than about 400K, the number of dimerized atoms grows not significantly with the increase of temperature and tends to a constant, but the interatomic anharmonic potentials become notable and dominate the thermal expansion property, so the thermal expansion coefficient is positive.