Phase and structural characterization of Sr2Nb2O7 and SrNbO3 thin films grown via pulsed laser ablation in O2 or N2 atmospheres

The influence of substrate temperature, process gas, deposition pressure, and substrate type on the phase selection, orientation/epitaxy, and growth morphology of thin films in the SrNbOy (y∼3.0 or 3.5) family was investigated. Pulsed laser deposited films (from a Sr2Nb2O7 target) obtained in both oxygen and nitrogen atmospheres upon various substrates were characterized with X-ray diffraction, energy dispersive spectroscopy, atomic force microscopy, and transmission electron microscopy. In oxygen atmospheres, films adopted the (110)-layered perovskite structure of the target. Higher temperatures, lower pressures of oxygen, and use of (110)-oriented SrTiO3 substrates lead to highly crystalline, epitaxial films of Sr2Nb2O7. The use of nitrogen atmospheres resulted in cubic perovskite SrNbO3 formation: epitaxial, textured, or polycrystalline films were obtained depending on the substrate; no nitrogen incorporation could be observed on the anion sublattice. On SrTiO3, the cubic perovskite films followed a cube-on-cube epitaxy and planar defects were observed to occur on the (110) perovskite planes. - Graphical abstract: Phase selection of SrNbOy films is influenced primarily by the process gas (in the 1-100 mTorr pressure range). In oxygen, films adopt the Sr2Nb2O7 (110)-layered perovskite structure (left). In nitrogen, films adopt the cubic perovskite SrNbO3 structure (right). The films' microstructure depends, however, on the substrate type and temperature