SPM Study of YBCO Films Prepared by Plasma Assisted Laser Ablation

Abstract

High T _c and J _c YBa₂Cu₃O_7-x (YBCO) superconducting thin films have been prepared by DC oxygen discharge plasma assisted excimer laser ablation on MgO (100), SrTiO₃ (100) and yttria-stabilized ZrO₂ (100) substrates. The main improvement obtained with this laser ablation scheme is that laser deposition can be carried out in the oxygen discharge environment. This is achieved by two ring-shaped electrodes which have been placed in the middle between the target and substrate. X-ray diffraction (XRD), atomic force microscopy (AFM) and scanning tunnelling microscopy (STM) techniques have been used to characterise the as-deposited films. A set of narrow (001) peaks in the x-ray diffraction patterns from these films indicate film growth with a preferential c-axis orientation. AFM image observations show that the number of the particulates observed on thin films prepared by this new laser ablation scheme is reduced by comparison with films prepared by the conventional laser ablation method. The majority of growth islands have merged and connected with each other and have formed much larger, denser and smoother flat plateaus. Similar to films fabricated by the conventional laser ablation scheme, STM surface characterisation reveals that the films prepared by oxygen plasma assisted laser ablation are also formed mainly by screw dislocation generated spiral growth.