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本文基于第一性原理和蒙特卡罗模拟方法，系统研究了氧化铝晶体内部O空位缺陷和Al空位缺陷对二次电子发射特性的影响。密度泛函计算结果表明，空位缺陷会导致能带结构发生改变，其中Al空位缺陷的存在使得禁带宽度变窄，费米能级降低至价带内部。在此基础之上，获得了不同晶体结构下的弹性和非弹性平均自由程。氧化铝中存在Al空位缺陷时的弹性平均自由程最大，而存在O空位缺陷时的非弹性平均自由程最大。为了分析不同缺陷浓度下的二次电子发射特性，对已有蒙特卡罗模拟算法进一步优化。模拟结果表明，随着O空位和Al空位缺陷占比的增加，最大二次电子发射系数随之而下降。相比于Al空位缺陷，相同缺陷占比下O空位缺陷导致二次电子发射系数降低更多。Based on first-principles combined Monte Carlo method, the effect of vacancy defect on secondary electron characteristics of Al2O3 are studied in this work. The density functional theory (DFT) calculation results show that the band structure changes when the vacancy defect exists. The existence of Al vacancy defect leads to the narrowing of band gap, which decreases from 5.88 eV to 5.28 eV. At the same time, the Fermi level decreases below the energy of the valence band maximum. Besides, the elastic and inelastic mean free paths of electrons in different crystal structures are also obtained. Compared with Al2O3 without defect and Al2O3 with Al vacancy defect, the inelastic mean free path of electrons in Al2O3 with O vacancy defect is the largest. When the energy of electrons is smaller than 50 eV, the inelastic mean free path of electrons in Al2O3 without defect is larger than that of Al2O3 with Al vacancy defect. The elastic mean free paths of electrons slightly increases when the vacancy defect exists, and that of Al2O3 with Al vacancy defect is the largest. To investigate the secondary electron emission characteristics with different ratio of vacancy defect, an optimized Monte Carlo algorithm is proposed. When the ratio of O vacancy defect and Al vacancy defect increase, the simulation results show that the maximum value of secondary electron yield (SEY) decreases with the increase of the ratio of vacancy defect. The existence of O vacancy defect increases the probability of inelastic scattering of electrons, so electrons are difficult to emit from the surface. As a result, compared with Al vacancy defect, the SEY of Al2O3 decreases more with the same ratio of O vacancy defect.
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Keywords:
- Secondary electron /
- vacancy defects /
- Monte Carlo /
- Density functional theory
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