Atomic structure of CaF2/MnF2-Si(1 1 1) superlattices from X-ray diffraction

X-ray reflectivity and non-specular crystal truncation rod scans have been used to determine the three-dimensional atomic structure of the buried CaF2-Si(1 1 1) interface and ultrathin films of MnF2 and CaF2 within a superlattice. We show that ultrathin films of MnF2, below a critical thickness of approximately four monolayers, are crystalline, pseudomorphic, and adopt the fluorite structure of CaF2. High temperature deposition of the CaF2 buffer layer produces a fully reacted, CaF2-Si(1 1 1) type-B interface. The mature, 'long' interface is shown to consist of a partially occupied layer of CaF bonded to the Si substrate, followed by a distorted CaF layer. Our atomistic, semi-kinematical scattering method extends the slab reflectivity method by providing in-plane structural information