Epitaxial growth and surface metallic nature of LaNiO3 thin films

Abstract

In situ epitaxial growth control of $\mathrm{La}\mathrm{Ni}{\mathrm{O}}_3$ (LNO) films at high oxygen pressure has been successfully achieved using a combination of pulsed laser deposition and high-pressure reflection high-energy electron diffraction (RHEED). RHEED oscillations, indicative of epitaxial layer-by-layer growth, were clearly observed during LNO deposition under optimal conditions. The film surfaces were composed of atomically flat terraces and steps. Detailed photoelectron spectroscopy analysis of LNO grown at the optimal oxygen pressure revealed that Ni ions assume a uniform ${\mathrm{Ni}}^{3+}$ high-valence state and that the resultant metallic properties are preserved even at the surface and in the interface region between LNO and the $\mathrm{La}\mathrm{Al}{\mathrm{O}}_3$ substrate.