  In this paper, the effect of Ar+ bombardment of SrTiO3:Nb surface layers is
investigated on the macro- and nanoscale using surface-sensitive methods. After
bombardment, the stoichiometry and electronic structure are changed distinctly
leading to an insulator-to-metal transition related to the change of the Ti "d"
electron from d0 to d1 and d2. During bombardment, conducting islands are
formed on the surface. The induced metallic state is not stable and can be
reversed due to a redox process by external oxidation and even by
self-reoxidation upon heating the sample to temperatures of 300{\deg}C.
