CaF2/Si heteroepitaxy: Importance of stoichiometry, interface bonding, and lattice mismatch

Abstract

With use of x-ray standing waves in UHV and synchrotron radiation, the early stages of growth of ${\mathrm{CaF}}_2$ on Si(111) were investigated. A new and subtle arrangement of the Si(111)/${\mathrm{CaF}}_2$ interface emerges from this study. For deposition at high substrate temperatures, the first monolayer of ${\mathrm{CaF}}_2$ dissociates, and CaF is formed at the surface with Ca in the ${\mathit{T}}_4$ and ${\mathit{H}}_3$ sites. At lower temperature, a larger fraction of the ${\mathrm{CaF}}_2$ remains undissociated, and a third Ca site sevenfold F coordinated in addition to ${\mathit{H}}_3$ ${\mathit{T}}_4$ sites is consistent with the standing-wave experiments. These results have a direct bearing on the interfacial electronic behavior and its dependence on deposition conditions.