Role of step edges in oxygen vacancy transport into SrTiO3(001)

Abstract

Using a combination of oblique-incidence optical reflectivity difference and specular reflection high energy electron diffraction techniques, we studied vacuum annealing of pulsed-laser deposited Nb-doped SrTiO3 monolayers on SrTiO3(100) near 730°C. In oxygen-free ambient, the as-grown monolayers are oxygen deficient. The excess oxygen vacancies in the monolayers are reduced by vacancy diffusion into the bulk. We found that the reduction rate is characterized by an activation energy E=1.0eV. More interestingly, the pre-exponential factor decreases significantly as the annealing time interval increases between two successive monolayer depositions. We propose that the indiffusion of excess surface oxygen vacancies takes place at step edges, and the Oswald ripening governs the density of the latter during vacuum annealing.