CORE EXCITONS AND INNER WELL RESONANCES IN SURFACE SOFT-X-RAY ABSORPTION (SSXA) SPECTRA

The surface soft X-ray absorption (SSXA) spectra of about one monolayer of Al2O3 and of SiO2 has been measured. We demonstrate that the near L2,3 edge structures (Kossel strructures), due to core excitons" and "inner well resonances" can give both structural and electronic information of local character which are important in surface physics. A comparison with the structural information which can be extracted from SEXAFS structures appearing at higher photon energies is discussed. We have found that the local structure of the oxide monolayers is formed by SiO4 and AlO6 complexes. The binding energy of surface and bulk core excitons are the same in spite of the shift of the initial state energy. Information on the surface density of states of the conduction band of the Si(111) surface have been extracted from the SSXA spectrum of the clean Si surface. © 1979."