Grain orientation in thick laser-deposited Y1Ba2Cu3O7−δ films: Adjustment of <i>c</i>-axis orientation

Abstract

Y1Ba2Cu3O7−δ films with a thickness between 0.5 and 5 μm were grown on Si covered with an amorphous SiO2 layer, on Zr foils, and on a single-crystalline MgO substrates by KrF laser ablation. The influence of film thickness and substrate temperature on the structure, texture, and microstructure of the as-grown films was investigated by x-ray diffraction and scanning electron microscopy. At an appropriate, substrate-dependent temperature, on all three substrate materials, the films grow c-axis oriented up to a thickness of about 2 μm (critical thickness), followed by a sharp transition to a-axis-oriented growth occurring within about 100 nm. Similar changes could be observed by lowering the substrate temperature by 120 °C. Therefore, the hypothesis was propounded that the thickness dependence of the growth orientation of the film is due to a decrease of the surface temperature. To prove this the influence of raising the substrate temperature during the growth process was investigated. It could be shown that a linear increase of the substrate temperature leads to completely c-axis-oriented films up to thicknesses of 5 μm. A change of the thermal emissivity of the film surface as a possible cooling mechanism is discussed.