The role of epitaxial strain and chemical termination in selected interfaces of perovskite oxide heterostructures is under intensive investigation because of emerging novel electronic properties. SrTiO (STO) is one of the most used substrates for these compounds, and along its direction allows for two nonpolar chemical terminations: TiO2 and SrO. In this paper, we investigate the surface morphology and crystal structure of SrO epitaxial ultrathin films: from 1 to about 25 layers grown onto TiO -terminated STO substrates. X-ray diffraction and transmission electron microscopy analysis reveal that SrO grows along its direction with a 4% out-of-plane elongation. This large strain may underlay the mechanism of the formation of self-organized pattern of stripes that we observed in the initial growth. We found that the distance between the TiO plane and the first deposited SrO layer is nm, a value which is about 40% bigger than in the STO bulk. We demonstrate that a single SrO-deposited layer has a different morphology compared to an ideal atomically flat chemical termination.
Keywords: 10 Engineering and Structural materials; 101 Self-assembly / Self-organized materials; 202 Dielectrics / Piezoelectrics / Insulators; 212 Surface and interfaces; 306 Thin film / Coatings; Pulsed laser deposition; epitaxial film; perovskite; surface termination; ultrathin film.