Microstructures and enhancement of critical current density in YBa2Cu3O7 thin films grown by pulsed laser deposition on various single crystal substrates modified by Ag nano-dots

YBa₂Cu₃O₇ (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_c have been studied systematically. Results showed that at fixed physical deposition conditions J_c increased monotonically with number of Ag shots, n, for films grown on both STO and LAO substrates. At 77 K, the J_c increased from 10⁶ to 3.2×10⁶ A/cm² for LAO and from 8×10⁵ to 3.5×106 A/cm² for STO as n increased from 0 to 150. At 5 K, the enhancement of J_c was approximately four times at both low and high fields. However, for films grown on YSZ substrate, J_c increased from 2×10⁵ to 2×10⁶ A/cm² as Ag shots increased from 0 to 30, and decreased to 9×10⁵ for n≥60. Detailed microstructure investigations indicated that the crystallinity and ab alignment gradually improved as the number of Ag-nano-dots increased.