Formation of CrSi andCrSi2upon annealing of Cr overlayers on Si(111)

Abstract

The evolution of the Cr/Si(111) interface upon thermal processing is investigated by low-energy electron diffraction (LEED), angle-resolved ultraviolet, and x-ray photoemission spectroscopy. Increasing progressively the annealing temperature and time results in the successive formation of CrSi and ${\mathrm{CrSi}}_2$, two well-defined bulk silicides. The silicides are characterized by their valence-band and core-level spectra. It is found that in contrast to ${\mathrm{CrSi}}_2$, CrSi exhibits a high density of states at the Fermi energy, which is reflected in the core-level spectra. As to the silicide film structure, the LEED data indicate that for large Cr-layer thicknesses [≳80 monolayers (ML)] the silicides are apparently polycrystalline but, at lower coverages (≲30 ML), epitaxial domains for both CrSi and ${\mathrm{CrSi}}_2$ can be achieved.