Characterization of Surface Defect Structures

氟化钙（萤石），具有热稳定性和电绝缘性，作为电子轰击的结果，在真空环境中解吸氟原子。在真空度为10 ~ 4 Torr、H_2O浓度为90%的条件下，电子轰击氟化钙晶体后<-8>，表面缺陷立即与残留的H_2O反应生成氧化钙相。X射线光电子能谱分析表明，氧化钙相与基体呈外延生长关系，其111轴与基体共轴。在10 μ Torr下电子轰击后<-9>，表面缺陷相对稳定。X射线光电子能谱测量表明，在约1 mC/cm^2的电子轰击下，2表面两层或三层原子层中的氟原子数量减少。在电子轰击后，Fls的X射线光电子衍射图中特定角度处的特定峰的强度降低。为了将X射线光电子衍射图的变化与表面缺陷结构联系起来，进行了基于单散射方案的理论计算。实验结果用第三原子层中部分氟原子选择性脱附的模型进行了解释。

Calcium fluoride(fluorite), which is thermally stable and electrically insulating., is well known to desorb florine atoms as a result of electron bombardment in ultrahigh vacuum environment. The purpose of this research is to clarify the structure of surface defects created by electron bombardment on a calcium fluoride crystal.After electron bombardment on a calcium fluoride crystal under vacuum of 10^<-8> Torr with 90% of H_2O, the surface defects immediately reacted with residual H_20 to yield calcium oxide phase. Chemicalstate-discriminated X-rgy photoelectron diffraction measurements showed that the calcium oxide phase was in epitaxial relationship with the substrate, in which the 111 axis was common between the substrate and. the overlayer, and the orientation-was 180ﾟ rotated with each other.After electron bombardment under 10^<-9> Torr, surface defects were relatively stable. X-ray photoelectron spectroscopic measurements showed that fluorine atoms in two or three atomic layers from the 2 surface decreased in number by electron bombardment of about 1 mC/cm^2. Intensity of a specific peak at definite angle in an X-ray photoelectron diffraction pattern for Fls decreased after electron bombardment. In order to relate the change in an X-ray photoelectron diffraction pattern with surface defect structure, theoretical calculation based on single scattering scheme was performed. Experimental results were best interpreted by the model in which a part of fluorine atoms in the third atomic layer selectively desorbed.