Laser-ablated thin films of infinite-layer compounds and related materials

We report laser-ablation studies of highly-oriented thin films of the electon-doped infinite-layer copper-oxide compounds Sr1-xLaxCuO2. The primary synthesis variables were substrate or buffer layer material, temperature, laser fluence, target-substrate distance, and oxygen pressure. The films were characterized by x-ray diffraction, atomic force microscopy (AFM), Rutherford back-scattering (RBS), and electrical resistivity. Films were deposited on strontium titanate (001) or on buffer layers of T'-phase copper oxides, Ln(2)CuO(4) (Ln = Pr, Sm) on SrTiO3 (001). The in-plane lattice constants of such T'-phase materials (a = 0.391-0.396 nm) could provide a structure more amenable to electron doping than strontium titanate (a = 0.390 nm). Extremely flat buffer layers were obtained from stoichiometric targets of Sm2CuO4 and Pr2CuO4. However, ablation from stoichiometric infinite-layer targets onto buffer layers resulted in mixtures of infinite-layer and chain/ladder phases. Non-stoichiometric deposition was confirmed by RES analysis. We thus utilized non-stoichiometric targets to obtain single-phased infinite-layer films. The x-ray rocking curves of highly-oriented epitaxial infinite-layer films exhibited full-widths at half maximum as narrow as 0.05 degrees. Infinite-layer films grown on T'-phase buffer layers exhibited lattice constants closer to those of the bulk superconductor than films grown directly on SrTiO3.