Photoemission study of bonding at theCaF2-on-Si(111) interface

The bonding at the interface between calcium fluoride and the silicon (111) surface has been studied with surface-sensitive core-level photoemission spectroscopy. The interface is found to consist of predominately Si—Ca bonds, with a dissociation of the ${\mathrm{CaF}}_2$ molecule at the interface resulting in depletion of fluorine atoms. When the interface is grown at temperatures below the optimal epitaxial growth temperatures, there is both more fluorine and more disorder at the interface. This affects the valence-band offset between the two materials, which ranges between about 7.3 and 8.3 eV. When the interface is annealed at 700–800 °C, the ${\mathrm{CaF}}_2$ film reevaporates until a 3×1 reconstruction is obtained on which there is calcium but no fluorine. The bonding at this surface is similar to that at the ${\mathrm{CaF}}_2$-on-Si(111) interface.