Takehiko Kawasaki

Effect of metal cluster ions on the low-temperature growth of YBa2Cu3Oy thin films

Abstract Using the reactive ionized cluster beam method, the roles of Y, BaO x , and Cu clusters in YBa 2 Cu 3 O y (YBCO) thin-film growth are investigated. This method utilizes ionized and accelerated Y, BaO x , and Cu clusters consisting of loosely coupled aggregates of 10 2 –10 3 atoms. It is found that, at substrate temperatures below 400°C, each ionized cluster has a different effect on the formation of YBCO. Namely, ionized and accelerated Cu and BaO x clusters with an average energy of less than approximately 2.0 eV significantly promote the oxidation of the YBCO films. In particular, the use of ionized BaO x clusters facilitates crystal growth. On the other hand, ionized Y clusters exhibit an obviously negative effect on YBCO growth. These results suggest that it may be difficult to obtain completely ortho-I films in situ at substrate temperatures below 400°C because of the trade-off for the effect of ionized Y clusters and the other two ones. At temperatures above 500°C, there is no significant observable difference between the films grown by this method and those grown using a conventional method. As a result, it seems that, at higher temperatures, YBCO film growth is dominated by the thermal energy supplied from a heated substrate.