空位在金刚石近(001)表面扩散的分子动力学模拟

The vacancy diffusion near diamond (001) surface by molecular dynamics simulation

用分子动力学方法模拟了空位在金刚石近 (0 0 1)表面的扩散过程 ,研究了温度对空位扩散的影响 .结果表明 ,当温度为 10 0 0K左右时 ,位于近表面第二层上的空位开始向表面运动 ;当温度在 140 0— 2 0 0 0K时 ,空位完全扩散到表面 .这与实验结果和其他计算结果符合得很好 .同时发现 ,温度为 140 0— 180 0K时 ,空位的扩散经历了两次迁移运动 ,其分别对应了均方位移图中的两个极大值 .在不施加任何约束的条件下得到了空位的动态扩散路径 ,空位在金刚石近 (0 0 1)表面的扩散势垒约为 0 4 2eV .并探讨了一定温度下空位数目增多及其不同排列方式对空位扩散的影响 .

The diffusion process of the vacancy near diamond(001) surface and the effects of temperature on the vacancy diffusion were investigated by molecular dynamics simulation. The results show that when the temperature is about 1000K, the vacancy in the second layer begins to diffuse to the surface. In the 1400_2000K temperature range, the vacancy can migrate to the surface. This result is in a good agreeement with that of experiment and other calculation. In the temperature range of 1400_1800K, two migration stages are observed in the vacancy diffusion process, which correspond to two maximums in the mean square displacement curves. In addition, the vacancy diffusion path was obtained without any constraints exposed on the atoms and the calculated diffusion barrier of the vacancy near diamond(001) surface is about 0^42 eV. We also discussed the effects of vacancy number and different vacancy arrangement on vacancy diffusion at a certain temperature.