Factor analysis applied to the study of valence band resonant photoemission spectra in transition‐metal compounds

We have applied factor analysis to the study of the valence band resonant photoemission spectra of a TiO2 thin film. Classical analysis of the photoemission spectra as a function of the photon energy through the Ti 2p → 3d absorption edge does not give a clear understanding of the resonant process, because the resonance phenomenon is present along the valence band and the only differences on the resonance are related to the distribution of cationic d-states. However, factor analysis of the spectra allows a more quantitative analysis of the resonance phenomena. Using theoretical partial Ti 3d and O 2p density of states as starting bases in principal component analysis, it is shown that only the hybridized Ti 3d states at the valence band resonate. The Ti 3d constant initial state (CIS) curve maps the Ti 2p x-ray absorption spectrum. Experimental relative photoemission cross-sections of the Ti 3d states at the absorption edge (455–470 eV) have been obtained. It is shown that resonant photoemission gives a sixfold enhancement of the Ti 3d cross-section at 463 eV with respect to the values at energies off-resonance. Copyright © 2002 John Wiley & Sons, Ltd.