Electronic structure of SnS deduced from photoelectron spectra and band-structure calculations

SnS is a layer compound with a phase transition from a high-temperature {β} phase to a low-temperature {α} phase with a lower symmetry. Ab initio band-structure calculations are presented for both phases. The calculations show that the charge distributions in the two phases are very similar. However, the band gap is much larger in the {α} phase. The calculations are used to discuss the chemical bonding in the {α} and the {β} phase. Energy-dependent photoelectron spectra, using synchrotron radiation, and angle-resolved photoelectron spectra were obtained for {α}-SnS. The energy versus wave-vector curves deduced from the spectra are in good agreement with the band-structure calculations. Photoemission from the top of the valence band shows a resonance and an interference effect at photon energies of 25--30 eV.