The early stages of interface formation between the fluoride and Si(111) were studied in situ  by using a combination of reflection high-energy electron diffraction, X-ray diffraction, and core-level photo-emission techniques. The results were combined with transmission electron microscopic measurements, and this showed that the initial growth mode changed from Volmer-Weber to Stranski-Krastanov; depending upon the substrate temperature. The cross-over was related to a sub-monolayer transition, of Si(111) reconstruction, from (7 x 7) to (3 x 1). This was accompanied by F2 dissociation at the interface. Both of the initial growth modes produced a uniform CaF2 epilayer, and subsequent growth on the surface was of layer-by-layer type. An X-ray crystal truncation-rod analysis was used to examine the CaF2/Si(111) surface and the interface structure. In films which had been grown at temperatures above the (7 x 7) to (3 x 1) transition, the Ca atom in the fluoride layer at the interface was located in a single T4 bonding site. A structural transition at the interface, from the as-grown structure to a (3 x 3)R30 reconstruction, was observed and appeared to be incommensurate.

C.A.Lucas, D.Loretto, G.C.L.Wong: Physical Review B, 1994, 50[19], 14340-53