Fabrication of high-quality YBCO epitaxial films by ablation using the fourth harmonic of the Nd : YAG laser

A pulsed laser deposition technique is investigated for fabricating high-qu ality epitaxial films of YBa2Cu3Oy superconductor using fourth harmonic of the YAG laser. The harmonic has a photon energy comparable to the KrF excim er laser and has potential for industrial use because of its effectiveness, safety and low running cost. High-quality films have been reproducibly pre pared on SrTiO3(100) and MgO(100) single crystal substrates by optimizing t he experimental conditions. Films on the respective substrates have critica l temperatures T-c= 90 K and 85(+/-1) K and critical currents 0.6 x 10(6) a nd 0.5 x 10(6) A cm(-1). X-ray diffraction revealed a spectrum composed ent irely of (001) diffraction peaks (I = 1-13) which are sharply resolved by K -alpha 1 and K-alpha 2 X-rays of copper isotopes, indicating formation of e pitaxial films having good crystallinity with c-axis orientation. Scanning electron microscopy and atomic force microscopy showed good surface morphol ogy: only a small number (0.5 mu m(-2)) and small sizes (< 0.2 mu m diamete r) of particles, and a good surface flatness (similar to +/- 20 nm). Optimu m conditions in the present method differ from previous reports using excim er lasers and require a lower pulse frequency, lower deposition energy, hig her substrate temperature and higher oxygen pressure. This may be due to hi gh densities of particles in the ablation plume, which are produced by irra diation with YAG pulsed laser having a shorter pulse width than the excimer laser. (C) 1999 Elsevier Science B.V. All rights reserved.