TARGET MODIFICATION IN THE EXCIMER LASER DEPOSITION OF YBA2CU3O7-X THIN-FILMS

Under conditions used for pulsed laser deposition (308 nm, 20 ns, 2-8 J/cm2) of Y-Ba-Cu-O superconducting thin films, we have measured a pronounced decrease in deposition rate with cumulative laser exposure of the target. This decay in rate is accompanied by evolution on the target surface of microscopic columnar structures, having yttrium-enriched surfaces, which are aligned in the direction of the incident laser beam (45-degrees). Neither the vapor plume direction nor film stoichiometry is affected by the presence of these oriented, chemically altered surface features.