Y-BA-CU-O FILMS OBTAINED BY EXCIMER LASER ABLATION

Y-Ba-Cu-O films with (001) orientation have been deposited on MgO by laser ablation at 248 and 193 nm wavelengths. Transitions to zero resistance at 87 K and 90 K have been reproducibly achieved in the respective cases. Optical spectroscopy studies of the plume show the importance of molecular species in the ablate if good superconducting films are to be formed. The substrate position in the plume and the substrate temperature are important in determining film quality. The influence of oxygen gas pressure can be significant. Scanning electron microscopy studies show the occurrence of second-phase outcrops with a needle-like morphology aligned over the whole area of the film along two mutually perpendicular directions in the film surface. Film orientation is determined by X-ray diffraction and R vs. T is measured down to 80 K in a hydrogen exchange gas cryostat.