Phase and structural characterization of Sr{sub 2}Nb{sub 2}O{sub 7} and SrNbO{sub 3} thin films grown via pulsed laser ablation in O{sub 2} or N{sub 2} 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 SrNbO{sub y} (y{approx}3.0 or 3.5) family was investigated. Pulsed laser deposited films (from a Sr{sub 2}Nb{sub 2}O{sub 7} 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 SrTiO{sub 3} substrates lead to highly crystalline, epitaxial films of Sr{sub 2}Nb{sub 2}O{sub 7}. The use of nitrogen atmospheres resulted in cubic perovskite SrNbO{sub 3} formation: epitaxial, textured, or polycrystalline films were obtained depending on the substrate; no nitrogen incorporation could be observed on the anion sublattice. On SrTiO{sub 3}, 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 SrNbO{sub y} films is influenced primarily by the process gas (in the 1-100 mTorr pressure range). In oxygen, films adopt the Sr{sub 2}Nb{sub 2}O{sub 7} (110)-layered perovskite structure (left). In nitrogen, films adopt the cubic perovskite SrNbO{sub 3} structure (right). The films' microstructure depends, however, on the substrate type and temperature.