The characterization of SrTiO3(001) with MIES, UPS(HeI) and first-principles calculations

The metastable impact electron spectra (MIES) and photoelectron spectra (UPS(HeI)) of undoped SrTiO3 (001) single crystals are presented. The work function is 2.6 eV; the top of the valence band is located 3.1 eV below the Fermi level which coincides with the bottom of the conduction band. An interpretation of the spectra is made on the basis of first-principles electronic structure results, also presented in this paper. We find that the HeI spectra can be well described by the bulk density of states of the SrTiO3 (0 0 1) valence band. The MIES spectra are best understood when assuming that the He 2s electron localizes at surface cations after its resonant transfer to the surface. This He-induced "dynamical" cation reduction greatly affects the He-surface interaction. The MIES spectra are similar to Auger deexcitation spectra, but are shifted by about 1.2 eV towards smaller kinetic energies. The shape of the spectra is best described by the density of states at about 4 a.u. in front of the surface. (C) 2002 Elsevier Science B.V. All rights reserved.