Two-phase separation in epitaxial (001) SrTiO3 thin films on LaAlO3 substrates

An epitaxial (001) SrTiO3 thin film, pulsed laser deposited on a LaAlO3 substrate, has been investigated using analytical transmission electron microscopy and x-ray diffraction. The film contained two different phases, with sharp compositional boundaries between the phases. One phase was 18% Sr-deficient, exhibited a columnar subgrain morphology, and had a large spread in the lattice parameter values. The other phase was stoichiometric SrTiO3, single crystalline, and defect-free. The results show that film stoichiometry is important if interfacial strain and columnar growth is to be avoided. A Sr-rich target and high-temperature annealing are two suggested precautions to improve homogeneity and stoichiometry.