SrTiO3 surface modification upon low energy Ar+ bombardment studied by XPS

Abstract

Segregation processes occurring in the vicinity of the SrTiO3 (100) single crystal surface induced by low energy Ar+ ion etching was studied with the use of X-ray Photoelectron Spectroscopy (XPS). The etching is selective and after the process the near surface region is depleted in both oxygen and strontium relative to titanium. However, photoemission data show an unexpected effect: the surface of the treated crystal after its exposure to air was re-enriched not only in oxygen but also in strontium. The preferential sputtering leads to formation of titanium oxides with lower oxidation states and insulator to metal transition in the surface vicinity of strontium titanate crystals. XPS data indicate that the process of conductive layer formation is less effective when ion sputtering of the crystal takes place at an elevated temperature. The effect is explained by the enhanced oxygen diffusion rate and the process of self-oxidation in the heated sample.