ATOMIC-FORCE MICROSCOPY STUDY OF (001)SRTIO3 SURFACES

By means of atomic force microscopy, we have investigated the surfaces of SrTiO3(001) substrates (used for the growth of high-T-c supercondu cting films) after different heat treatments. These treatments were (i ) annealing in O-3, (ii) annealing in O-2, (iii) annealing in O-3 foll owed by deposition of SrTiO3, and (iv) annealing in UHV. Our results s uggest that, independently of the type of annealing, the surfaces of t he polished SrTiO3 substrates rearrange, either by diffusion or desorp tion of atoms, until reaching the energetically most favourable surfac e structure. For vicinal (001) substrates, this equilibrium structure corresponds to atomically flat terraces separated by smooth steps of o ne unit-cell in height, with the orientation and width of the terraces being determined by the miscut of the substrate. However, the kinetic s involved in the reconstruction of the SrTiO3 surface were observed t o be strongly dependent on the annealing conditions. In particular, th e use of O-3 instead of O-2 or UHV was found to accelerate the reconst ruction of the SrTiO3 surface. Finally, this study provides an accurat e characterisation of the defects present on SrTiO3 substrates.