Georg Wahl

High-Tc YBa2Cu3O7-δ prepared by chemical vapour deposition

Deposition experiments were carried out on polycrystalline Y-stabilized ZrO2 (YSZ) and on single crystalline (100)-oriented SrTiO3 substrates. The evaporation temperatures for Y(thd)3, Ba(thd)2 and Cu(thd)2 were 112, 208 and 117 ° C, respectively. All deposition experiments were carried out at a total pressure of 10 mbar, with a flow rate of 18 l/h oxygen for each evaporator and in addition 40 l/h argon for the Ba(thd)2 evaporator. Under these conditions the deposition kinetics is surface-reaction-controlled up to temperatures of 600 ° C. At higher temperatures the growth rate is limited by the mass transport of the precursors towards the substrate surface. The maximum growth rates obtained in this region are about 20 nm/min, which can be increased by increasing the evaporation rates of the source materials. The comparison with the kinetics of the single oxide deposition shows an interdependence of the single oxide deposition kinetics during the YBa2Cu3O7-δ deposition. Assuming a linear superposition of the single oxide deposition processes the diffusion-controlled region for YBa2Cu3O7-δ would be expected at T > 850 ° C. High-quality films can be obtained on YSZ substrates as well as on SrTiO3 substrates with the c-axis perpendicular to the substrate surface at temperatures higher than 850 ° C. The transition temperatures are higher than 90 K with transition widths between 0.5 and 2 K. The maximum critical current densities jc measured for YSZ substrates are jc = 6 X 103A/cm2 at 77 K. In the case of single crystalline (100) SrTiO3 substrates the critical current densities are of the order of 106 A/cm2 in zero field and liquid nitrogen temperature, decreasing to values of 105 A/cm2 in an applied magnetic field of 5.5 T.

Uv Excimer Laser-Induced Deposition of Palladium from Palladium Acetate Films

UV excimer laser-induced deposition of palladium from spin coated palladium acetate films in air is described. We have investigated mainly the deposition of palladium on aluminum oxide and quartz substrates and its dependence on the fluence and the number of excimer laser pulses. The decomposition mechanism was studied by measuring in situ the transmitted pulse energy during the exposure process. We have found that the excimer laser-induced decomposition of palladium acetate films is mainly pyrolytic and a simple model can be used to describe the decomposition process.