Effect of Ion Implantation on YBCO Superconductor Thin Film
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EFFECT OF ION IMPLANTATION ON YBCO SUPERCONDUCTOR THIN FILM Zuhua Zhang, Jiarui Liu, Ki Bui Ma, J. Wu, Ning Yu, Yuan-Jun Zhao, W.A. Lam, P.Y. Hsieh and Wei-Kan Chu Texas Center for Superconductivity and Physics Department, Denes Marton, Chemistry Department, University of Houston, Texas 77204-5506, USA ABSTRACT The effects of the H+, C+, N+, F+, and Ne+ (25-200 keV)ion irradiations have been investigated by means of SEM, room temperature resistance measurement and aqueous degradation test. The room temperature resistance increases exponentially with irradiation doses. At lower dose, the annealing process is dominent, while at higher dose, the resistance increasing process is dominent. A reduction in the thickness induced by ion irradiation has been observed. The aqueous experiment shows that passing current will speed up the degredation and N+ implantations can increase the resistance of the YBCO thin film against attack by water. 1. INTRODUCTION Since the discovery of the high Tc superconductor [1] and the subsequent synthesis of the YBCO superconductor[2], intensive research activities on high Tc superconductors(HTS) have been carried out on the subject of radiation effects. Researchs concerning radiation effects on the HTS materials were carried out in many laboratories, mostly with MeV ions [3-7] for which the nuclear stopping can be neglected as compared with the electron stopping. The detailed mechanism of the superconductivity change induced by radiation are still obscure and need further investigation. This paper will report the effects of the ion irradiation on YBCO thin films with the ion energy below 200 keV where the nuclear stopping is comparable to the electron stopping. The dependence of the room temperature resistance( will be shorted as RT resistance in the following text) on the ion doses has been investigated in this work. In this area, Marwick et al. had carried out a series of detailed works with MeV ions [4-6, 8] which shows that the RT resistance increase with dose follows a exponential relationship. The changs in surface morphology has been observed by using scanning electron spectroscopy (SEM). High dose of nitrogen has been implanted into the surface layer of a YBCO thin film to test for the water resistance of the implanted layer. 2. EXPERIMENTALS YBCO thin films on SrTiO 3 or MgO substrates were made with an inverted cylindrical magnetron sputtering system. The Tc of the films
Mat. Res. Soc. Symp. Proc. Vol. 201. c 1991 Materials Research Society
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are between 82 K to 86 K For RT resistance measurement, the thicknesses of the films chosen are less than 2000 A to ensure that the films can be penetrated by 200 keV neon ions. For the SEM measurement and aqueous degradation test, the thicknesses are about 4500 A. H, C , N, F and Ne ions of the energy ranging from 25 keV to 220 keV were used. The beams were scanned electrostatically over the surface of the sample. The uniformity of the scanned beam is 3%. The beam current density is kept below 75 nA/cm 2 and the average beam power densi
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