Interface creation on a mixed-terminated perovskite surface

In the field of complex oxide heterostructures, understanding of the initial substrate surface can be critical to fundamental studies regarding the development of emergent properties at the film–substrate interface. For this reason, a considerable amount of effort has gone into the development of techniques to achieve surfaces with single termination for a variety of perovskite single crystals. However, a decisive understanding of how an interface is created when epitaxial growth occurs on a mixed terminated surface remains lacking. Employing in situ synchrotron X-ray scattering during thin film growth by molecular beam epitaxy, we investigate the initial stages of growth on (LaAlO3)(Sr2AlTaO6) (001) substrates with mixed termination. Using LaNiO3 as a model system, we find that the surface layers of the substrate restructure during deposition such that while a NiO2 monolayer is weakly bound, a LaO monolayer bonds strongly, effectively incorporating with (Al, Ta)O2 from the surface and forming a La(Al, Ta)O3 ultrathin film.