Surface structure of oxygen annealed donor doped SrTiO3(100) single crystals studied with spectroscopic electron microscopy

Heating 5at.% (on A-site) La-doped SrTiO3(100) single crystal in an ambient atmosphere at 1300°C for 120 h results in the formation of insulating islands on top of the surface with typical dimensions of up to 50 μm. The islands and the surface between them were investigated by spectroscopic Metastable Impact Electron Emission Microscopy (specMIEEM) and Photoelectron Emission Microscopy in order to determine its electronic and geometric structure. The comparison of specMIEEM results with MIES (Metastable Impact Electron Spectroscopy) spectra from stoichiometric SrO shows that the insulating islands, which most likely consist of SrO, are at least partly covered by another species, probably SrO2. All these islands are surrounded by 2-3 μm wide haloes. The electronic structure of these haloes is quite different from that of SrO and SrTiO3 but similar to the electronic structure of TiO2 or Ti2O3. It is suggested that the depletion of SrO from Ruddlesden-Popper (Srn+1TinO3n+1) phases results in the formation of SrO islands.