Room-temperature formation and oxidation properties of the Cr/Si(111) interface

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Abstract
The structural and electronic properties of the Cr/Si(111) interface formed at room temperature (RT) are investigated by low-energy electron diffraction, x-ray photoelectron spectroscopy and angle resolved ultraviolet photoemission spectroscopy, and work function measurements. The data indicate strong reactive behavior in agreement with a previous study by Franciosi et al. The data show intermixing up to ∼25 monolayer (ML) Cr coverage with an overlayer stoichiometry evolving gradually from Si rich to Cr rich phases with increasing Cr coverage. The reacted phases are metastable and definitely different from any known bulk silicide. Above ∼30-ML Cr coverage, polycrystalline bulk Cr metal is formed. Further insight into the nature of the intermixed layer comes from oxidation studies of the interface as a function of Cr coverage. A progressive shift of the oxidized Cr 3d, Cr 2p3/2, and Si 2p lines with Cr coverage in the 0–25 ML range implies different oxidation states for Si and Cr species at various steps of the interface formation, and in turn, indicates a composition gradient normal to the surface. The data also demonstrate that above ∼2-ML Cr coverage the oxygen uptake of the interface is up to 10 times faster than for definite silicides such as CrSi or CrSi2. The enhanced interface reactivity of the metallic RT grown Si–Cr phases apparently originates in their unique metastable bulk and surface composition and structure.

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