Changes in the chemical state of monocrystalline SrTiO3 surface by argon ion bombardment

High-resolution X-ray photoemission spectroscopy (NPS) of single crystalline SrTiO3. SrTiO3:La and SrTiO3:Nb fractured in situ in ultrahigh vacuum (UHV) with Ar+ bombardment revealed that the bombardment caused reduction of Ti+4, Sr+2, La+3 and Nb+5 to the lower valence states at surfaces. Formation of Ti+3 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 Nb+3 and Sr-0 at the surfaces, To our knowledge, there was no report on reduction of Sr+2, La+3 and Nb+5 in SrTiO3, SrTiO3:La and SrTiO3:Nb. (C) 1999 Elsevier Science B.V. All rights reserved.