A study was made of c-axis oriented films with superconducting transition temperatures of up to 89K. These were prepared by ion beam sputter-deposition onto monocrystalline (100) MgO or (100) SrTiO3 substrates. The variation in the O concentration during annealing in vacuum or O was measured,  in situ  and in real time, by means of spectroscopic ellipsometry. Changes in O concentration of less than 1% could be resolved. Measurements on films with thicknesses ranging from 15 to 100nm were used to elucidate the mechanisms of O out-diffusion and in-diffusion. It was found that the O out-diffusion rate depended upon the layer thickness; thus confirming the operation of a bulk diffusion mechanism. The O in-diffusion was relatively independent of the layer thickness; thus suggesting that a surface cum grain-boundary diffusion mechanism predominated in this case. It was noted that H2O enhanced O out-diffusion, while the in-diffusion remained unchanged; or even decreased.

A.Michaelis, E.A.Irene, O.Auciello, A.R.Krauss: Journal of Applied Physics, 1998, 83[12], 7736-43