Stefan investigates the properties of strontium titanate surfaces. Strontium titanate belongs to the class of perovskite oxides. These materials are used as cathode materials in solid oxide fuel cells, in photocatalysis, and as a substrate for the growth of high-temperature superconductors. In the last year Stefan and his colleagues have been investigating how water interacts with the (110) surface of strontium titanate. In addition to this, the formation of a two-dimensional electron gas at the (110) surface after doping with oxygen vacancies was addressed.