Pt interactions with annealed and chemically-etched Nb-doped SrTiO3(0 0 1) surfaces: Metal/oxide surface chemical effects on band bending behavior

Abstract

XPS and LEED have been used to characterize the interaction of sputter-deposited Pt (maximum coverage <5 ML) with Nb-doped SrTiO3(001) surfaces prepared either by annealing in O2 and then UHV, or by chemical-etching in aqua regia. The annealed surface exhibits an ordered (1×1) LEED pattern, with additional diffraction spots and streaks indicating the presence of oxygen vacancies. Increasing Pt coverage results in the decrease of the observed Pt(4f7/2) binding energy and the uniform shift of the Sr(3d), Ti(2p) and O(1s) levels to smaller binding energies, as expected for Pt cluster growth and surface-to-Pt charge donation on an n-type semiconductor. The etched surface is disordered, and exhibits a hydroxylated surface with a contaminant C film of ∼23Ǻ average thickness. Pt deposition on the etched surface results in an immediate decrease in the intensity of the OH feature in the O(1s) spectrum, and a uniform shift of the Sr(3d), Ti(2p) and O(1s) levels to larger binding energies with increasing Pt coverage. The observed Pt(4f7/2) binding energy on the etched surface (∼72eV) is independent of Pt coverage, and indicates substantial electronic charge donation from the Pt to surface hydroxyl species. The observation of band bending towards higher binding energies upon Pt deposition (behavior normally associated with p-type semiconductors) demonstrates that sub-monolayer quantities of adsorbates can alter metal/oxide interfacial charge transfer and reverse the direction of band bending, with important consequences for Schottky barrier heights and device applications.