Self-regulated growth of CaVO₃ by hybrid molecular beam epitaxy

The authors report on the growth of stoichiometric CaVO₃ thin films on LaSrAlO₄ (001) using hybrid molecular beam epitaxy approach, whereby the metalorganic vanadium oxytriisopropoxide (VTIP) and Ca was cosupplied from a gas injector and a conventional effusion cell, respectively. Films were grown using a fixed Ca flux while varying the VTIP flux. Reflection high energy electron diffraction, x-ray diffraction, atomic force microscopy, energy-dispersive x-ray spectroscopy, and high resolution transmission electron microscopy were employed to relate film quality to growth conditions. A wide growth window was discovered in which the films were stoichiometric and film lattice parameter was found independent of the Ca/VTIP flux ratio, allowing more than 10% unintentional deviation in the Ca flux while maintaining stoichiometric growth conditions. Films grown within the growth window showed atomically smooth surfaces with stepped terrace morphology and narrow rocking curves in x-ray diffraction with a full width of half maximum of 8 arc sec, similar to that of the substrate. For growth conditions outside of this window, excess Ca and V nonstoichiometric defects were incorporated into the lattice. The effect of film microstructure and stoichiometry on temperature dependent electrical conductivity is discussed. The ability to produce high quality CaVO₃ films without precise control of cation fluxes opens a robust synthesis route to explore the intrinsic physics of strongly correlated metals with reduced dimensionality.