Surface morphology and critical current density of high quality YBa/sub 2/Cu/sub 3/O/sub 7/ thin films on sapphire substrates

Pulsed laser deposition has been used to prepare YBa/sub 2/Cu/sub 3/O/sub 7/ (YBCO) film on CeO/sub 2/ buffer layers on single crystal Al/sub 2/O/sub 3/ (11~02) substrates. High quality YBCO films have been obtained when 500-/spl Aring/-thick CeO/sub 2/ buffer layers were deposited with fluence of 1.5 J/cm/sup 2/ and oxygen pressure of 50 mTorr. Surface morphology of the c-axis oriented YBCO films were strongly dependent on the preparation conditions of CeO/sub 2/ buffer layers, resulting in significant changes of critical current densities. Critical current densities of YBCO films increased with the increase of the substrate temperature for CeO/sub 2/ buffer layer deposition in the range 400/spl deg/C/spl les/T/sub s//spl les/800/spl deg/C. Superconducting properties in YBCO/CeO/sub 2//Al/sub 2/O/sub 3/ exhibit T/sub c/=89.5 K, /spl Delta/T/sub c//spl les/0.5 K, and J/sub c/>3/spl times/10/sup 6/ A/cm/sup 2/ at 77 K.