Selective 18O labelling in a-axis oriented YBaCuO thin films

Abstract Superconducting YBaCuO thin films were deposited on SrTiO 3 substrate by inverted cylindrical magnetron sputtering of a stoichiometric target. The composition and the structure of the films were studied by Rutherford Backscattering Spectrometry (RBS) and Nuclear Reaction Analysis (NRA), in random and channeling geometries. Annealing treatments, allowing the selective 18 O → 16 O exchange in the CuO chain-planes, were performed in 18 O 2 atmosphere. In order to accelerate the oxygen diffusion during the annealing, we used, on the one hand, a-axis oriented films and, on the other hand, we adopted thermodynamical conditions corresponding to an oxygen composition of O 6.6 (p O2 = 0.13 mbar and T = 400°C). The full oxygenation was accomplished by increasing the oxygen partial pressure to p O2 = 200 mbar at T = 400°C, during 30 minutes. The absolute 18 O content, determined by NRA, showed a partial and a non uniform 18 O → 16 O exchange. In spite of the fact that the RBS spectra were identical for different points on the sample, the NRA results confirmed that the absolute 18 O content varies from point to point. Moreover, Raman spectroscopy revealed some inhomogeneities concerning the oxygen site occupation by the 18 O tracer atoms in the YBaCuO lattice: In the center of the sample, 18 O atoms are present only in the CuO chain-planes, whereas few mm away of the center, we found the 18 O atoms also in the CuO 2 planes. These results are discussed.