Photoemission study of pristine and Ni-doped SrTiO 3 thin films

We combined photoelectron spectroscopy with first-principles calculations to investigate electronic properties of ${\mathrm{SrTiO}}_{3}$ doped with Ni impurities. High-quality epitaxial pristine ${\mathrm{SrTiO}}_{3}$ and ${\mathrm{SrTiO}}_{3}$:${\mathrm{Ni}}_{x}$ films with $x=0.06$ and 0.12 were prepared by pulsed laser deposition. Electronic band structure calculations for the ground state, as well as one-step model photoemission calculations, which were obtained by means of the Korringa-Kohn-Rostoker Green's function method, predict the formation of localized $3d$-impurity bands in the band gap of ${\mathrm{SrTiO}}_{3}$ close to the valence band maxima. The measured valence bands at the resonance Ni $2p$ excitation and band dispersion confirm these findings.