Energy-band structure ofCoSi2epitaxially grown on Si(111)

Angle-resolved photoemission experiments performed with synchrotron radiation allow us to map the energy-band structure along the Γ-L symmetry direction of the bulk Brillouin zone for ${\mathrm{CoSi}}_2$ epitaxially grown on Si(111). Two kinds of epitaxial crystals with either Co-rich or Si-rich surfaces were investigated in order to identify unambiguously the photoemission transitions from bulk electronic states. Within a direct transition model assuming a free-electron-like final-state band, the experimental band dispersions are in fairly good agreement with a recent self-consistent band-structure calculation for the free-electron-like ${\Lambda }_1$ bands. However, measured binding energies for Co 3d–like states such as ${\Gamma }_{25}^{\mathcal{’}}$ (3.5 eV) and the upper nonbonding ${\Lambda }_3$ band (∼1.4 eV) are systematically smaller than those calculated (typically by 20% at ${\Gamma }_{12}$). It is suggested that these discrepancies may be explained in terms of correlation effects for band states with strong d character. A distortion of the lower ${\Lambda }_3$ band near L, observed on a ${\mathrm{CoSi}}_2$(111) silicon-rich surface, is attributed to a surface-structure-induced effect.