Characterization of Surface Defect Structures

氟化钙(萤石)具有热稳定性和电绝缘性，在超高真空环境中，由于电子轰击而使氟原子解吸，这是众所周知的。为了弄清电子轰击氟化钙晶体产生的表面缺陷的结构，在真空度为10℃、水含量为90%的真空度下对氟化钙晶体进行电子轰击后，表面缺陷立即与残留的氢气反应生成氧化钙相。化学状态分辨X-射线光电子衍射测量表明，氧化钙相与衬底呈外延关系，其中111轴是衬底与衬底的共轴。电子轰击后，表面缺陷相对稳定，表面缺陷相对较稳定。X射线光电子能谱测量表明，当电子轰击强度约为1mC/cm2时，FLS表面2~3个原子层中的氟原子数目减少。电子轰击后，FLS X射线光电子衍射图中某一特定角度的峰强度降低。为了将X射线光电子衍射谱的变化与表面缺陷结构联系起来，进行了基于单次散射的理论计算。实验结果可以用第三原子层中部分氟原子选择性脱附的模型来解释。

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.