Control of surface particle density in pulsed laser deposition of superconducting YBa₂Cu₃O₇ and diamondlike carbon thin films

We have investigated the effects of target preparation and modification in controlling the particle density of films fabricated by the pulsed laser deposition (PLD) technique. YBa₂Cu₃O₇ targets, prepared by unique processing conditions, were used to experimentally study the factors controlling surface morphology of PLD films. By varying the nature of the target processing conditions, the particle density can be considerably reduced in superconducting thin films and completely eliminated in diamondlike carbon thin films. Cold pressed and sintered bulk superconducting targets were subjected to controlled continuous wave (cw) CO₂ laser irradiation for compacting and densifying the target. Another method employed was the incorporation of silver into the superconductor targets to improve its thermal conductivity, optical absorption coefficient, and bulk density. The particle density was found to significantly reduce for films deposited from cw CO ₂ laser processed YBa₂Cu₃O₇ targets. The experimental results were in agreement with the subsurface superheating model which predicts that the particle density in PLD films can be considerably reduced by (i) increasing the absorption coefficient, (ii) thermal conductivity, and (iii) cohesion of the target grains. The first two factors decrease subsurface superheating effects while the third increases the barrier for particle removal.