OBSERVATION OF OXYGEN IN YBCO THIN-FILMS DURING THE COOLING DOWN PROCESS USING O-18 TRACER

We have studied the behavior of oxygen in YBa2Cu3Ox films using O-18 a s a tracer. Pure O-18(2) gas was introduced into a chamber during depo sition. In contrast to O-18(2) gas, O-16(2) gas was used in the subseq uent cooling down process. Though YBCO films certainly contained only O-18 atoms in their oxygen sites during the growth process, almost all the O-18 atoms were replaced with O-16 atoms while the films were coo led down; 95% of O-18 atoms were substituted using rf-plasma, and 85% of O-18 atoms without the plasma. This shows that the rf-plasma strong ly affected the oxygenation of the YBCO films even in the cooling proc ess.