Observation of core-level binding energy shifts between (100) surface and bulk atoms of epitaxial CuInSe₂

Synchrotron radiation soft x-ray photoemission spectroscopy was used to directly observe Se 3d core-level binding energy shifts from surface atoms of the (100) face of epitaxial CuInSe₂/ GaAs(100). High-resolution spectra show two sets of Se 3d_5/2,3/2 spin-orbit components separated by 0.6 eV, with the low-binding-energy peaks being associated with the surface atoms. However, surface state emission from Se p states in the valence band was not observed due to the low photoionization cross sections. Cation bonding-antibonding states were observed in the valence band and are centered at about 1.0 and 3.1 eV below the valence band edge.