Local determination of the terminating layer of SrTiO₃

Abstract

The crystallinity and physical properties of complex oxide films are strongly influenced by the quality of the substrate. This is determined by the bulk microstructure (e.g. grains, twin boundaries, vacancies) and by the surface characteristics. In the case of single-crystal films grown on single-crystal substrates, the latter point becomes extremely important and has to be studied in detail at the nanometer scale. In the case of SrTiO3 (001) substrates, the fabrication process usually leads to samples with different surfaces. The topography itself is very sensitive to process parameters, and has exhaustively been studied in the past few years. The terminating layer can be a mixture of both SrO and TiO2 planes. Only few techniques can determine this surface chemical composition, and so far only on a macroscopic scale. We report here, for the first time, the chemical characterization of such a surface, for which we use a combination of annealing and scanning probe microscopy. We then applied the same technique to the characterization of the surface LaAlO2 (001) and SrLaAlO4 (001) substrates. So far, no friction contrast has been observed on these latter surfaces. In the case of LaAlO3, the characteristic twin structure is clearly revealed.