Changes in the chemical state of monocrystalline SrTiO surface 3 by argon ion bombardment

High-resolution X-ray photoemission spectroscopy XPS. of single crystalline SrTiO3, SrTiO3:La and SrTiO3:Nb fractured in situ in ultrahigh vacuum UHV.with Arq bombardment revealed that the bombardment caused reduction of Tiq4, Srq2, Laq3 and Nbq5 to the lower valence states at surfaces. Formation of Tiq3 state can be ascribed to the partial occupation of the conduction band; some electrons transfer into Ti 3d band due to the lack of O 2p states. Similarly, the partial occupation of the La 5d orbitals due to the lack of O 2p states was observed for the bombarded SrTiO3:La surface. Loss of surrounding oxygen due to the bombardment also resulted in the states of Nbq3 and Sr0 at the surfaces. To our knowledge, there was no report on reduction of Srq2, Laq3 and Nbq5 in SrTiO3, SrTiO3:La and SrTiO3:Nb. q1999 Elsevier Science B.V. All rights reserved