COMBINATION OF IBA TECHNIQUES AND RAMAN-SPECTROSCOPY TO STUDY DEFECTSIN O-18 LABELED YBACUO THIN-FILMS

We have studied the annealing conditions leading to the selective O-18 labelling of oxygen sites in the Cu-O chain-planes of a-axis oriented superconducting YBaCuO thin films. The labelling is performed by a co mbination of two processes: (i) O-18 uptake due to the reoxidation, an d (ii) isotopic O-18 <--> O-16 exchange. The annealing conditions (P(O 2) = 0.13 mbar and T = 400-degrees-C), chosen according to the thermod ynamical diagram (P(O)2, T), correspond to an oxygen composition of O6 .6. The complete oxygenation to O7 was reached by increasing the O-18 pressure to 200 mbar at the same temperature. Due to the reoxidation f rom the O6.6 composition, it is expected that 40% of the Cu-O chain-pl anes will be labelled by O-18 atoms. Moreover, additional labelling du e to the O-18 <--> O-16 exchange also takes place at 0.13 and 200 mbar . The composition of the films was determined by RBS and the total O-1 8 content was measured by NRA. The O-18 concentration depth profile wa s determined by the O-18(p, alpha)N-15 nuclear reaction resonance at 6 29 keV. It was found, by combining NRA and Raman spectroscopy, that th e O-18 atoms are only located in the Cu-O chain-planes. The O-18 label ling of the Cu-O chain-planes induced by reoxidation and by isotopic e xchange is incomplete and ranges from 58% to 85%. A second annealing i n the same conditions leads to obtain a 100% labelling of the Cu-O cha in-planes. The defects in the surface region of the O-18 labelled Cu-O chain-planes were studied by channeling using the O-18(p, alpha)N-15 nuclear reaction resonance at 629 keV. Some correlation was found betw een the mechanism of O-18 labelling and the presence of defects. The r esults are discussed.