Influence of target composition on the quality of YBCO films fabricated byNd : YAG pulsed laser deposition

The influence of target composition on the formation of surface particles a nd the crystallinity of YBCO epitaxial films is studied by pulsed laser abl ation-deposition method using the fourth harmonic of a Nd:YAG laser and by X-ray diffraction, scanning electron microscope, atomic force microscope, a nd electron probe X-ray microanalyzer analysis. Six kinds of targets in whi ch one of the atomic constituents is deviated by +/-5% to +/-1% from stoich iometry were used in addition to the stoichiometric target YBa2Cu3Oy. All f ilms deposited are highly c-axis oriented. Films fabricated from stoichiome tric targets have a high transition temperature (T-c) of 90.0 +/- 0.5 K and a small number of surface particles (mainly droplets), as low as 1.5 parti cles/10 mum(2). By constrast, the films deposited from non-stoichiometric t argets exhibit a large number of outgrowths (CuO and oxides mainly of Ba an d Cu) in addition to droplets and a low T, in the range of 75-89 K. The num ber and the sort of the outgrowths do not depend largely on the kinds of th e non-stoichiometric targets nor on the extent of deviation in the range of +/-1% to +/-5%. These results have been reasonably understood as mainly du e to the targets inhomogeneity from the following experimental evidence. (1 ) The non-stoichiometry of the targets produces much more extent of segrega tion of impurity phases than that expected from the imbalance of +/-5% to /-1%. (2) The extent of segregation is almost identical for every non-stoic hiometric target. The present study indicates clearly that the target shoul d have the stoichiometric ratio (1:2:3) in order to prepare high quality YB CO epitaxial films. (C) 2001 Elsevier Science B.V. All rights reserved.