FORMATION OF EPITAXIAL COSIX SILICIDE AT THE CO COSI2(111) INTERFACE STUDIED BY PHOTOEMISSION AND BAND-STRUCTURE CALCULATIONS/

The reaction of a few monolayers of Co with a Si-rich CoSi2(111)-Si su rface is investigated in the 300-400 degrees C range. For a Co coverag e of one monolayer, the Si-rich CoSi2 surface is transformed into the bulk-like terminated CoSi2(111) one. This latter surface is characteri zed by a specific surface state whose origin is clearly established wi th the help of band structure calculations using the crystalline exten sion of the extended Huckel theory. Upon increasing the Co coverage (< 5 monolayers), a thin epitaxial CoSix top-layer is formed. The electr onic as well as the crystallographic structure of this thin metastable CoSix layer is discussed in connection with that of recently discover ed CoSix, epitaxially grown on Si(111).