COMPOSITION OF PULSED-LASER-DEPOSITED Y-BA-CU-O AND BA-K-BI-O THIN-FILMS

The composition of pulsed-laser-deposited Y-Ba-Cu-O and Ba-K-Bi-O thin films is shown to be strongly affected by target conditioning, gas pr essure, and target-substrate distance. For both compounds, ablation fr om a freshly sanded target surface results in films with an excess of the more volatile elements. The concentration of these volatile elemen ts in the films decreases until the system reaches a steady state afte r sufficient ablation from the target. Y-Ba-Cu-O film composition is a lso affected by oxygen pressure and target-substrate distance. Increas ing pressure or distance results in relative copper and barium depleti on in the central region of deposition, presumably due to differences in the efficacy of oxygen in scattering the different elements. This r elationship between pressure, distance, and composition is shown to be significant for the growth of optimal superconducting Y-Ba-Cu-O thin films. The composition of Ba-K-Bi-O is also affected strongly by backg round gas pressure. Ba-K-Bi-O deposited in vacuum is potassium deficie nt in the film center. A background argon pressure of 1 Torr, however, increases the potassium concentration and results in films with unifo rm composition over a broad area. We argue that this effect is signifi cant in explaining a successful growth method for superconducting Ba-K -Bi-O films.