蒙特卡洛方法计算材料表面激发参数

电子非弹性散射平均自由程（IMFP）是用表面电子能谱进行表面化学定量分析时极为重要的一个参数，它可以用测量的弹性峰电子能谱分析以及蒙特卡洛模拟来确定.为了更加精确地确定电子非弹性散射平均自由程，必须对弹性峰电子能谱中的表面激发效应进行修正，通常使用介电响应理论方法计算得到的表面激发参数.然而，通过理论计算得到的表面激发参数不能包含电子在材料内部输运过程中弹性散射的影响，进而影响所测的电子非弹性散射平均自由程的准确度.在这个工作中，我们采用蒙特卡洛方法来确定包含弹性散射效应时的表面激发参数.所得到的表面激发参数在不同能量、角度情况下，尤其是在弹性散射效应显著的60°以上的大角度入射、出射情况下，都与实验测量值符合得非常好.基于这些新确定的表面激发参数，可以在弹性峰电子能谱测量中获得更为准确的电子非弹性散射平均自由程数据.

Calculation of Surface Excitation Parameters by a Monte Carlo Method

Electron inelastic mean free path (IMFP) is an important parameter for surface chemical quantification by surface electron spectroscopy techniques. It can be obtained from analysis of elastic peak electron spectroscopy (EPES) spectra measured on samples and a Monte Carlo simulation method. To obtain IMFP parameters with high accuracy, the surface excitation effect on the measured EPES spectra has to be quantified as a surface excitation parameter (SEP), which can be calculated via a dielectric response theory. However, such calculated SEP does not include influence of elastic scattering of electrons inside samples during their incidence and emission processes, which should not be neglected simply in determining IMFP by an EPES method. In this work a Monte Carlo simulation method is employed to determine surface excitation parameter by taking account of the elastic scattering effect. The simulated SEPs for different primary energies are found to be in good agreement with the experiments particularly for larger incident or emission angles above 60° where the elastic scattering effect plays a more important role than those in smaller incident or emission angles. Based on these new SEPs, the IMFP measurement by EPES technique can provide more accurate data.