OXYGEN-CONTENT OF YBA2CU3O6-FILMS DURING GROWTH BY PULSED-LASER DEPOSITION(X THIN)

The oxidation ability of the laser plasma plume during in situ formati on of YBa2Cu3O6+x (YBaCuO) thin films has been studied as a function o f the deposition conditions. A quenching technique has been used immed iately after termination of growth to avoid any oxygen in or out-diffu sion during the cooling down step. It is shown that superconducting YB aCuO thin films can be formed without any post-oxygenation procedure, contrary to that expected from the (P-O2, T) thermodynamic diagram. Th is is due to the production of oxygen activated species in the plume, which significantly increases the oxygen potential and, therefore, the oxidation state of the films during deposition. Moreover, it is demon strated that there exits an optimal position of the substrate respecti ng to the visible luminous plume for each O-2 pressure, which leads to the highest T-c and to the best structural and morphological properti es of quenched films. It is concluded that the presence of active oxyg en, which is not homogeneously distributed over space, enhances the su rface reaction kinetics and, thus, plays an important role in the mech anism of growth of laser ablated YBaCuO films. (C) 1998 Elsevier Scien ce B.V.