Oxygenation mechanism of YBa_2Cu_3O_(6+x) thin films during growth by pulsed laser deposition

摘要

We have studied the incorporation of oxygen in YBa_2Cu_3O_(6+x) (YBaCuO) thin films during the growth at high temperature by laser ablation. Using a quenching technique, we have demonstrated that it is possible to obtain superconducting films without the need of any oxygen intercalation during the cooling down step. This result reveals that the oxygenation of YBaCuO films during growth is strongly enhanced in comparison to the previsions of the (Pm, T) thermodynamic diagram, due the high reactivity of atomic and ionic oxygen present in the laser plasma. The dependence of the critical temperature of quenched films on the target-to-substrate distance suggests that the concentration of reactive oxygen is not homogeneously distributed within the plume. Furthermore, we have experimentally demonstrated that atomic oxygen plays an important role in the process which governs the reaction kinetics of the YBaCuO phase formation, enhancing the mobility of species incident on the substrate, which leads to an important improvement of the morphological and structural properties of the films. In conclusion, we show that the presence of reactive oxygen in the laser plasma is important to understand the mechanism of growth of YBaCuO films and probably has to be taken into consideration for the growth of new oxide materials by PLD and sputtering.