Microstructures and Enhancement of Critical Current Density in<tex>$rm YBa_2rm Cu_3rm O_7$</tex>Thin Films Grown by Pulsed Laser Deposition on Various Single Crystal Substrates Modified by Ag Nano-Dots

Abstract

YBa/sub 2/Cu/sub 3/O/sub 7/ (Y123) thin films were grown by pulsed laser deposition (PLD) on YSZ (100), SrTiO3 (100), and LaAlO3 (100) single crystal substrates. Prior to the film deposition, a discontinuous layer of Ag nano-dots was deposited on the substrates. The Y123 films grown on such surfaces modified with Ag nano-dots were characterized by Atomic Force Microscopy (AFM), X-ray diffraction (XRD), scanning electron microscopy (SEM), AC susceptibility and DC magnetization. The effects of the density of Ag nano-dots, which was controlled by the numbers of PLD shots, on the microstructures and resultant critical current density J/sub c/ have been studied systematically. Results showed that at fixed physical deposition conditions J/sub c/ increased monotonically with number of Ag shots, n, for films grown on both STO and LAO substrates. At 77 K, the J/sub c/ increased from 10/sup 6/ to 3.2/spl times/10/sup 6/ A/cm/sup 2/ for LAO and from 8/spl times/10/sup 5/ to 3.5/spl times/106 A/cm/sup 2/ for STO as n increased from 0 to 150. At 5 K, the enhancement of J/sub c/ was approximately four times at both low and high fields. However, for films grown on YSZ substrate, J/sub c/ increased from 2/spl times/10/sup 5/ to 2/spl times/10/sup 6/ A/cm/sup 2/ as Ag shots increased from 0 to 30, and decreased to 9/spl times/10/sup 5/ for n/spl ges/60. Detailed microstructure investigations indicated that the crystallinity and ab alignment gradually improved as the number of Ag-nano-dots increased.