Polarity on the SrTiO3(111) and (110) surfaces
Résumé
Relying on the results obtained by a total energy, semi-empirical Hartree-Fock method, we discuss polarity effects at the (111) and (110) surfaces of SrTiO3. For these orientations, we consider some prototypical (1×1) configurations, which differ by their surface composition and the coordination number of the surface atoms. We argue that the compensation for these polar orientations is achieved through anomalous fillings of surface states, which, in principle, should be detectable by surface spectroscopies. The compensation does not imply a partial filling, so that all these surfaces keep their insulating character. The thermodynamic stability of the different configurations is also analyzed, and we conclude that, consistently with the experimental observations, these surfaces are relatively stable, especially when compared with polar faces of more ionic oxides, such as MgO(111). The efficiency of SrTiO3 for screening the strong electrostatic perturbation associated to the polar orientations is invoked to explain such a behavior.