Structural transformations at CaF2Si(111) interfaces

Transformations of the atomic structure of the CaF2Si(111) interface during annealing have been studied by reflection high energy electron diffraction (RHEED) and X-ray crystal truncation rod (CTR) scattering. The surface morphology after annealing has been studied by atomic force microscopy (AFM). A conversion of the epitaxial relation of the film with respect to the substrate, from type-A (nonrotated) to type-B (with the axes of the film rotated by 180°C around the interface normal), is monitored by RHEED during annealing of the films. On the basis of RHEED, CTR and AFM data, a model of the conversion is suggested. In addition, a spontaneous transition of the type-B interface formed during the growth to the interface with another atomic arrangement has been studied with CTR. The possible role of point defect motion in the CaF2 film during this transition is discussed.