Many-body effect in the resonant Ti L 23–M 23V Auger-electron spectroscopy spectra and Auger-photoelectron coincidence spectroscopy spectra of Ti oxides

Abstract

Recently Danger et al. [J. Danger, H. Magnan, D. Chandesris, P. Le Fèvre, S. Bourgeois, J. Jupille, A. Verdini, R. Gotter, A. Morgante, Phys. Rev. B 64 (2001) 045110] and Le Fèvre et al. [P. Le Fèvre, J. Danger, H. Magnan, D. Chandesris, J. Jupille, S. Bourgeois, M.-A. Arrio, R. Gotter, A. Verdini, A. Morgante, Phys. Rev. B 69 (2004) 155421] showed the absence of resonant Raman scattering feature in the Ti L 23–M 23V resonant Auger-electron spectroscopy (RAES) spectra of Ti oxides measured across the Ti 2p edges. They attributed the absence to the covalent character of the Ti–O bond which allows an effective delocalization of 3d electrons. It is shown by a many-body theory that when the time scale of relaxation of the resonantly excited core-hole state to the fully relaxed core-hole state is much shorter than that of core-hole decay, any sizeable Raman scattering is absent in the RAES spectra measured across the Ti 2p edges. The relaxation width depends on the hybridization strength and the charge transfer (CT) energy between the two states. The L 2–L 3V Coster–Kronig (CK) decay widths of TiO 2 and TiO 2− x are determined from the L 23–M 23V Auger-photoelectron coincidence spectroscopy (APECS) spectra reported in the aforementioned papers. They are about 0.18 and 0.35 eV, respectively. The CK-decay width in the reduced Ti oxide increases compared to that of TiO 2 in rutile because of filling of the 3d states just below the Fermi level in the former.