Epitaxial growth of Ruddlesden-Popper La$_{n+1}$Ni$_{n}$O$_{3n+1}$ series using reactive molecular-beam epitaxy

We report the growth of single crystalline La$_{n+1}$Ni$_{n}$O$_{3n+1}$ epitaxial thin films using reactive molecular-beam epitaxy. Ruddlesden-Popper La$_{n+1}$Ni$_{n}$O$_{3n+1}$ compounds, consisting of LaO$^{+}$ and NiO$_{2}$$^{-}$ layers, have been considered a potential candidate for solid-oxide fuel cell cathodes and thermoelectrics. However, the growth of higher order La$_{n+1}$Ni$_{n}$O$_{3n+1}$ single crystals has not been possible so far. We utilize synchrotron x-ray diffraction at the Advanced Photon Source during layer?by?layer deposition together with density functional theory calculations to understand how LaO$^{+}$ and NiO$_{2}$$^{-}$ oxide layers re-arrange dynamically during growth. Using this layer re-arrangement, epitaxial La$_{2}$NiO$_{4}$, La$_{3}$Ni$_{2}$O$_{7}$, and La$_{4}$Ni$_{3}$O$_{10}$ films on (001)-oriented SrTiO$_{3}$ have been synthesized with the proper nickel valance state and structure. Here we will discuss the connection between structure and electrical transport properties. Work at the APS, Argonne is supported by the U.S. Department of Energy, Office of Science, and Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.