SYNCHROTRON-RADIATION PHOTOEMISSION SPECTROSCOPY OF OCTAHEDRALLY COORDINATED LAYER COMPOUNDS

The polarized uv continuum emitted by the University of Wisconsin Storage Ring has been employed to study the electronic structure of SnS2, PbI2, and BiI3 with several different photoemission-spectroscopy techniqùes. For binding energy ∼ 11.5 eV with respect to the top of the valence band, Eν, four valence-band density-of-states peaks have been found for SnS2 and five each for PbI2 and BiI3. In the energy region extending from the vacuum level to ∼ 14 eV above it the photoelectron spectra exhibit six conduction-band density-of-states peaks for SnS2 and PbI2 and four for BiI3. A theoretical analysis of the results shows that in all three materials the anion p states give the main contribution to the valence band and the cation p states to the bottom of the conduction band. The transfer of electrons from cation p states to anion p states leaves two filled s states in each cation which also contribute to the valence-band spectrum. For SnS2 these states have been found ∼ 7.4 eV below Eν, while for PbI2 and BiI3 they combine to some extent with anion (s-p) hybrid orbitals, giving a shallow occupied state with antibonding character as well as a bonding state deep in the valence band. More details about the wave-function symmetry have been provided by photon-polarization effects and by spectra taken in a normal-emission geometry. Little dispersion of the normal emission energydistribution-curves peaks with respect to photon energy variation was observed, and this indicates that the interlayer interactions are weaker here than in the tetrahedrally coordinated III-VI compounds. © 1979 The American Physical Society.