Growth evolution of laser-ablated Sr(2)FeMoO(6) nanostructured films: Effects of substrate-induced strain on the surface morphology and film quality.

Pulsed laser deposition was used to grow Sr(2)FeMoO(6) films of different thicknesses on MgO(100), SrTiO(3)(100), and LaAlO(3)(100) with respective lattice mismatches of +6.2%, -1.2%, and -4.3%. Surface roughness and morphology, and film crystal quality and epitaxy were determined by atomic force microscopy and x-ray diffraction, respectively. Two-dimensional layer-by-layer growth was evident for the Sr(2)FeMoO(6) grown on MgO and SrTiO(3) with the film becoming smoother with increasing thickness. The Sr(2)FeMoO(6) films had more nucleation sites on MgO than SrTiO(3). On LaAlO(3), however, three-dimensional progressive growth of flakelike Sr(2)FeMoO(6) nanostructures was observed for all film thicknesses. High-resolution x-ray diffraction measurements indicated that the Sr(2)FeMoO(6) films are near-epitaxial and c-axis oriented on all the substrates. Reciprocal space maps further revealed that Sr(2)FeMoO(6) grows on MgO with relatively constant lattice parameters with increasing film thickness. For films thicker than 120 nm, the formation of a second phase was observed on SrTiO(3) and LaAlO(3) but not on MgO, suggesting that the formation of a second phase provides an effective strain relief in the former. These results suggested a different growth mechanism for the Sr(2)FeMoO(6) films on MgO compared to the SrTiO(3) and LaAlO(3) substrates.