Abstract
An experimental chamber was connected to the 2.5 MV Van de Graaff accelerator allowing in situ sample annealing at T ≤ 700° C and under pO 2 ranging from 10-8 to 1 bar. For the first time to our knowledge the 16 O (3 He ,α)15 O nuclear reaction has been employed to monitor in situ the oxygen loss and uptake in Y 1 Ba 2 Cu 3 O 7-x (YBCO) thin films as a function of oxygen pressure and temperature ( T ≤ 500° C ). The role played by the presence of carbon contamination on YBCO surface was elucidated. Using the 12 C(d,p) 13 C nuclear reaction the carbon loss was observed for T ≥ 250° C and it was associated with the oxygen loss enhancement in YBCO. It is found that in absence of carbon contamination, oxygen in-diffusion rate in YBCO is much faster than the out-diffusion rate, the later being surface reaction limited. The oxygen diffusion coefficients and the surface exchange coefficients of YBCO films have been evaluated. These results will be discussed in relation with the mechanism of high temperature YBCO thin film growth by cathodic sputtering and with the mechanism of the oxygen loss and/or uptake during the sample cooling.
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