BIAS EFFECT ON THE PREPARATION OF YBA2CU3O7-DELTA THIN-FILMS BY LASER ABLATION

Bias effects on the preparation of superconducting thin films by pulsed laser deposition have been investigated by using time-of-flight mass-spectroscopy. Since a large number of electrons were emitted from the target at the same time as ions during ablation, ions in the plume are shielded from the external electric field by electrons and not influenced by substrate biasing. Under postively biased conditions, the electron emission was greatly enchanced. The multi-valence ions (Cu2+ and Cu3+) were also observed in these conditions. It can be understood qualitatively that the rapid extraction of electrons from the target surface by the electric field tends to generate the multi-valenced ions. It was also found that the multi-valenced ions have an energy of more than 250 eV which is a higher value than that of the other atomic ions.