Structure of Lattice-Matched Fluoride Films

用x射线驻波技术测定了生长在GaAs(111)B表面的Ca_xSr_<1-x>F_2 （x = 0.43）单晶薄膜的原子结构。应用了一种新方法，可以使用单个样品对不匹配结构进行完整分析。在界面处发现（Ca, Sr）原子为七配位，支持了之前提出的外延立方氟化膜生长模型。与体键长计算结果相比，界面原子层间距缩小了0.37 <Ang>。尽管块状混合氟化物在室温下与GaAs晶格完全匹配，但薄膜的（111）面间距离收缩了0.28%。该研究是基于对吸收非中心对称晶体时原子面驻波位置的理论重新研究。

The atomic structure of a single-crystal Ca_xSr_<1-x>F_2 (x = 0.43) film grown on GaAs(111)B surface has been determined with the X-ray standing-wave technique. A new method has been applied which allows complete analysis of mismatched structures using a single specimen. (Ca, Sr) atoms at the interface are found seven-coordinated, supporting the previously proposed growth model of epitaxial cubic fluoride films. The atomic layer spacing across the interface is contracted by 0.37 <Ang> compared with that calculated from the bulk bond lengths. The film is strained in such a way that the (111) interplanar distance is contracted by 0.28 %, although bulk mixed fluoride exactly lattice matches GaAs at room temperature, The study is based on a theoretical re-investigation of the standing-wave position with respect to atomic planes in absorbing non-centrosymmetric crystals.