Surface electronic structure ofCoSi2(111)

The surface electronic structure of ${\mathrm{CoSi}}_2$(111) surfaces is studied by angle-resolved photoemission using synchrotron radiation in the energy range 10≤ħω≤60 eV. Depending on preparation technique the crystal termination is either a Co or a Si(111) plane. The ${\mathrm{CoSi}}_2$(111)-Co terminated surface exhibits two surface-related features at Γ¯ at -1.4 and -2.7 eV. The prominent low-lying peak is a true surface state of the Shockley type located in an absolute Si3s3p–Co 3d hybridization gap of the projected bulk band structure at Γ¯ and shows an oscillating emission intensity in reciprocal space. The relevant surface-state band disperses toward the Fermi level with increasing $k_{?}$ and corresponds to bonding states of surface Co atoms with a reduced coordination shell. In contrast, the -1.4-eV feature is rather a Tamm surface state or resonance derived from surface Co 3d nonbonding orbitals. On ${\mathrm{CoSi}}_2$(111)-Si terminated surfaces only weak surface-related features can be identified.