Initial stages of MBE growth and formation of CaF2/Si(001) high-temperature interface

It has been recently shown [Appl. Surf. Sci. 175-176 (2001) 619] that growth modes and epitaxial relations of CaF2 on Si(0 0 1) drastically depend on the growth temperature: below 500 degreesC 3D nucleation and CaF2(0 0 1)/Si(0 0 1) growth were observed; above 650 degreesC a wetting layer followed by the formation of CaF2 stripes and CaF2(1 1 0)/Si(0 0 1) growth have been found. In this work, electron diffraction, atomic force microscopy (AFM) and photoemission spectroscopy with use of synchrotron radiation were applied to study initial stages of growth and formation of the interface during CaF2 deposition on Si(0 0 1) surface at high temperature. AFM showed that initial (2 x 1 + 1 x 2) Si(0 0 1) surface transforms into anisotropic wetting layer serving as template for subsequent CaF2(1 1 0) growth. Photoelectron spectroscopy showed reduction of Ca2+ and electron transfer from the reduced calcium to the interface Si atoms with formation of negatively charged interface Si layer.