Electronic structure of Ni and other transition-metal silicide overlayers on Si

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Abstract
The electronic structure of Ni overlayers on Si (111) has been calculated by the tight-binding method for various possible bonding geometries. Surface EXAFS suggests nickel exists at six- or sevenfold-coordinated, Ni6 or Ni7, sites buried between the topmost layers of Si. The authors results favour the Ni6 geometry for which EF lies in the lower gap, as observed, while bonding at the Ni7 configuration appears to be less stable. A general bonding model for other transition-metal overlayers is developed. The Co5 geometry at CoSi2:Si(111) interfaces is rationalised and an interstitial threefold coordination is suggested for Co monolayers to account for the photoemission data.