Structural transformations at interfaces

Transformations of the atomic structure of the CaF 2 Si(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 CaF 2 film during this transition is discussed.