Oxidation and reduction during fabrication of high quality Nd/sub 1.85/Ce/sub 0.15/CuO/sub 4-y/ superconducting thin films

Using pulsed-laser deposition and N/sub 2/O reactive gas, the authors have fabricated very high quality c-axis n-type Nd/sub 1.85/Ce/sub 0.15/CuO/sub 4-y/ (NCCO) oxide epitaxial superconducting thin films on different substrates. The film shows a superconducting transition temperature T/sub c/ (R=0 Omega ) of 22.4 K and a transition width of 0.2 K from AC susceptibility measurements. The critical current density J/sub c/ is 8*10/sup 5/ A/cm/sup 2/ at 4.2 K in zero magnetic field. The microwave surface resistance measured at 9.6 GHz shows a value of 3 m Omega at 4.2 K in 500-nm-thick NCCO film, the best result reported so far for NCCO thin films. The oxygen deficiency is necessary to achieve the superconductivity in NCCO, and the oxygen reduction during and after film deposition is critical. The oxidation and reduction processes are studied systematically for various substrate temperatures, atmospheres, and annealing durations.<
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