Microstructure of epitaxial superconductive YB_a2Cu₃O₇thin films prepared at different deposition rates

Abstract

A study is reported on the growth mechanism of YBa2Cu307 with different growth speeds by high resolution transmission microscopy (HRTEM) and analysis of the interface and thin film microstructure. Two thin films were synthesized by pulse laser deposition on [ 1001, miscut 5", SrTi03 substrate at 820 "C, one with a pulse laser frequency of 1 Hz and one with 6 Hz. Crosssections were studied by an H-9000 NAR HRTEM along the [OlO] direction. The growth process of the sample made at 1 Hz was as follows. First, distorted step flow growth occurred on a step-mediated substrate surface of 3 4 cells thickness. Second, about a 15 nm thickness of island shape growth #becomes superimposed on the area of the step flow layer. Finally, thin f i l m growth occurred but with growth fluctuation. The sample made at 6Hz showed the characteristics of island growth; the growth area of island or ball shape was of small size and dense distribution, and seemed to be a confused mosaic stack. The influence of growth speed on YBCO epitaxial f i l m microstructure was studied explicitly by HRTEM.