Suppression of oxygen diffusion by thin Al 2 O 3 films grown on Sr Ti O 3 studied using a monoenergetic positron beam J. Appl. Phys. 97, 033508 (2005); 10.1063/1.1836010 Defects in CeO 2 / SrTiO 3 fabricated by automatic feeding epitaxy probed using positron annihilation J. Appl. Phys. 94, 5193 (2003); 10.1063/1.1606112Vacancy-type defects in BaTiO 3 / SrTiO 3 structures probed by monoenergetic positron beams Oxygen vacancies introduced by homoepitaxial growth of thin films on strontium titanate (SrTiO 3 ) substrates were studied by means of positron annihilation. The SrTiO 3 films were grown by molecular-beam epitaxy without using an oxidant. The Doppler broadening spectra of the annihilation radiation were measured as a function of incident positron energy for the SrTiO 3 /SrTiO 3 samples fabricated by various growth conditions. The line shape parameter S, corresponding to the annihilation of positrons in the substrate, was found to be increased by the growth of the film. This increase was attributed to the diffusion of oxygen from the substrate into the film, and the resultant introduction of oxygen vacancies in the substrate. Two different types of defects in the substrate were identified: one is oxygen multivacancies, such as oxygen divacancies, and the other is their complexes with Sr vacancies. The concentration of oxygen vacancies in the subsurface region increased as the substrate temperature during the growth decreased (р320°C). This fact was attributed to the decrease in the diffusion length of oxygen at low temperatures, and the resultant accumulation of oxygen vacancies in the subsurface region.