脉冲激光烧蚀制备纳米Si晶粒成核气压阈值及动力学研究

采用脉冲激光烧蚀技术,在室温、低压Ar气条件下通过改变气体压强及靶与衬底间距,对纳米Si晶粒成核的气压阈值进行了研究.根据扫描电子显微镜图像、拉曼散射谱和X射线衍射谱对制备样品的表征结果,确定了在室温、激光能量密度为4 J/cm²、靶与衬底间距为3 cm条件下形成纳米Si晶粒的阈值气压为0.6 Pa.结合流体力学模型和成核分区模型,对纳米晶粒的成核动力学过程进行了分析.通过Monte Carlo数值模拟,表明在气相成核过程中,烧蚀Si原子的温度和过饱和密度共同影响着纳米晶粒的成核. 关键词： 脉冲激光烧蚀 成核 气压阈值 Monte Carlo数值模拟

Pressure threshold and dynamics of nucleation for Si nano-crystal grains prepared by pulsed laser ablation

Si nano-crystal grains are prepared by pulsed laser ablation in low pressure Ar at room temperature through changing the gas pressure and the distance between target and substrate. The morphologies and compositions of samples are characterized by scanning electron microscopy images, Raman scattering spectra and X-ray diffraction spectra.The pressure threshold for Si grain formation is obtained to be 0.6 Pa at a laser fluence of 4 J/cm², distance between target and substarate of 3 cm, and room temperature.Combining the fluid mechanics model and the nucleation division model, the dynamics process of nucleation is analyzed.The Monte Carlo simulation shows that the nucleation of nano-crystal grains is determined jointly by temperature and supersaturated density.