Structure of Lattice-Matched Fluoride Films

用<1-x>X射线驻波技术测定了生长在GaAs（111）B表面的Ca_xSr_ F_2（x = 0.43）单晶薄膜的原子结构。一种新的方法已被应用，它允许使用一个单一的标本失配结构的完整分析。(Ca发现界面处的（Sr）原子为七配位，支持了先前提出的立方氟化物薄膜外延生长模型。与<Ang>由体键长计算的结果相比，界面原子层间距收缩了0.37。在室温下，尽管体混合氟化物与GaAs晶格完全匹配，但薄膜的应变使（111）晶面间距收缩了0.28%。本研究是基于对吸收非中心对称晶体中驻波相对于原子平面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.