A NEW LASER ABLATION GEOMETRY FOR THE PRODUCTION OF SMOOTH THIN SINGLE-LAYER YBA2CU3O7-X AND MULTILAYER YBA2CU3O7-X/PRBA2CU3O7-X FILMS

The advantages and results of a new geometry for laser ablation are presented. The laser beam enters the ablation chamber via a computer controlled scanning mirror and is x-y rastered across the target surface. The laser beam hits the target at normal incidence through the ablation plume. The ablation products are allowed to thermalize in a 200 mTorr oxygen atmosphere before being deposited on a heated substrate (750-degrees-C, SrTiO3, LaAlO3, yttria-stabilized zirconia) facing 180-degrees to the initial plume direction. This overcomes the problem of molten rocks and blobs ejected from the target being deposited on the substrate and results in very smooth films ( +/- 50 angstrom for 5000 angstrom thickness). The high temperature resistivities of YBa2CU3O7-x were linear with temperature with their extensions passing through zero resistivity at 0 K. Typical T(c) values of 90-92 K with 1 K widths were regularly obtained. No oxygen anneal either in situ or post-deposition was required. X-ray analysis shows the films to be c axis oriented. The technique has been extended to the growth of very high quality YBa2Cu3O7-x/PrBa2CU3O7-x multilayer films. Their X-ray spectra are presented for various thicknesses of the individual layers.