Infinite-layer copper-oxide laser-ablated thin films: substrate, buffer-layer, and processing effects

Laser-ablation studies of highly-oriented thin films of the electon-doped infinite-layer copper-oxide compounds Sr_1-xLa_xCuO₂ are reported. We observe significant variations in film properties with substrate or buffer layer material. X-ray diffraction, atomic force microscopy (AFM), Rutherford back-scattering (RBS), and electrical resistivity were used to characterize the films. Films were deposited on strontium titanate [001] or on buffer layers of T´-phase copper oxides (Ln₂CuO₄ with Ln = Pr, Nd, Sm), Sr₃FeNb₂O₉, and La_1.8Y_0.2CuO₄ on SrTiO₃ [001]. The in-plane lattice constants of such buffer layers (a = 0.390 - 0.400 nm) should provide the bond tension required for electron doping. Extremely flat, epitaxial buffer layers with X-ray rocking curves as narrow as 0.08° were obtained from stoichiometric targets of Ln₂CuO₄; the other buffer layers yielded poor epitaxy. A linear dependence of infinite-layer c-axis plane spacing on substrate or buffer-layer in-plane a-axis lattice constant is observed.