Oxidation of c-axis-oriented epitaxial YBa₂Cu₃O_7-δ thin films in ozone-containing atmospheres

Oxygen diffusion into c-axis-oriented YBa₂Cu₃O_7-δ epitaxial thin films was observed using real-time spectroscopic ellipsometry. The experiments were conducted under controlled atmospheres of 10% O₃/90% O₂ and 80% O₃/20% O₂. At 2 × 10^-5 torr, oxidation of the films began at temperatures as low as 100-125 °C for heating rates ≤3 °C/min. Full oxidation was seen by 190 °C at these rates. Based on these data, the activation energy of oxygen diffusion into YBa₂Cu₃O_7-δ from an ozone/oxygen atmosphere was found to be between 0.43 and 0.52 eV. This was appreciably smaller than for in-diffusion in a molecular oxygen atmosphere. Higher ozone content atmospheres did not improve the oxidation kinetics. These atmospheres did, however, delay the onset of reduction in the films by 60-70 °C at higher temperatures.