扫描透射电镜中厚样品的电子散射与透过率特性的模拟研究

Simulation of Electron Scattering and Transmission in Characterization of Thick Films by Scanning Transmission Electron Microscopy

电子散射和电子透过率是影响厚膜样品扫描透射电镜成像及其检测应用的重要因素。本文根据样品材料中电子的弹性散射和非弹性散射模型,采用蒙特卡罗方法模拟了能量为100~300 keV的电子在微米级厚非晶薄膜样品中的散射过程,并计算了在扫描透射电镜明场模式下的电子透过率特性。电子透射厚样品的散射次数和出射角分布都由于样品厚度的增大而明显增大且展宽。所获得的电子透过率随样品厚度的变化规律与文献中实验报道一致。分析了入射电子能量、接收半张角及样品材料类型等参数对电子透过率的影响。结果表明电子透过率随着电子能量的提高而增大,随着样品材料的原子序数和密度的增大而减小。模拟结果还证实,部分电子经多重弹性散射而返回接收半张角会使电子透过率的减小偏离指数线性变化。

The electron scattering and transmission characteristics in the studies of thick amorphous films,by scanning transmission electron microscopy in bright-field mode,were simulated in Monte Carlo method.The influence of the incident-electron energy（100~300 keV）,acceptance half-angle,and content of the micron-thick films,on the electron transmission rate were evaluated.The simulated results show that the electron transmission rate significantly depends on the film thickness,electron energy,and specimen of the sample.For instance,as the film thickness,the scattering number of the transmitted electron markedly increases with an increasingly widened angular distribution.Besides,the electron transmission rate increases with an increase of electron energy,but decreases with the increases of the density and atomic number of the sample.We found that the deviation from the linearity originates from some electron scattered back to the acceptance half-angle by elastic multi-scattering.The simulated results agree fairly well with experimental data reported in the literature.