Formation of Y1Ba2Cu3O7-x thin films by pulsed ruby laser ablation

Abstract

Thin films of the superconductor Y1Ba2Cu3O7-x have been grown on MgO (100) substrates by pulsed ruby laser ablation. The heatflow in the Y1Ba2Cu3O7-x target irradiated with the pulsed ruby laser was simulated. The laser energies required for the onset of melting and vaporization were determined, and compared with experimentally determined values. Rutherford backscattering spectrometry was used to measure the thickness and stoichiometry of the deposited layers, while X-ray diffraction was employed to extract phase and orientational information. It was found that the ruby laser can deposit superconducting material with near ideal stoichiometry. The spatial distribution of the deposited films displays a cosn( theta ) dependence (8<n<12) which is consistent with the high degree of forward peaking usually found in pulsed laser deposition. The amount of material deposited in an oxygen ambient of 10-1 mbar with an incident energy density of 2 Jcm-2 was between 1.0 and 1.5 nm per pulse for a target-substrate separation of 15 mm. Resistivity measurements of films deposited at 200 degrees C and post annealed at 850 degrees C revealed a Tc (onset) of 84 K and a transition width Delta T of 2 K. Susceptibility measurements gave a depressed temperature of 80 K and a broader transition width of 7.5 K pointing to weak intergranular links.