Structure of CaF2/Si(111) long interface

We have investigated the structure and morphology of a type-B CaF2/Si(111) interface (CaF2 structure rotated by 180 degrees in the plane of the interface) by means of X-ray diffractometry. From the analysis of the crystal truncation-rod (CTR) scattering, we obtained parameters for the interface spacing, roughness, and crystalline quality and confirmed that the interface has a long interface spacing (4.58 Angstrom from the middle of the Si bilayer to Ca atom). In particular, from the non-specular CTR scattering, we obtained the result that Ca atoms occupy T-sites at the interface (atop the atoms of the first Si layer). This structure is the same as that of a type-A CaF2/Si(111) interface investigated previously, but it is different from that of the type-B interface with a short interface spacing.