Moir� patterns and their application to the study of the growth of YBa2Cu3O7-? thin films

Abstract

Very thin films of YBa2Cu3O7-δ have been formed directly on specially prepared electron-transparent thin-foil substrates of MgO by pulsed-laser deposition and examined using transmission electron microscopy. The moire fringe pattern visible in the electron micrographs has been used to provide information about film growth and the introduction of defects into the growing film. Individual domains, rotated about the [001] zone axis by small amounts, were detectable in the moire fringe pattern by rotation of the fringes. In the case of small rotations, the fringe spacing varies only slightly. Individual domains rotated by large amounts, about the [001] zone axis, have been identified by the large variation produced in the moire fringe spacing. The ability to identify domain rotation through examination of the moire pattern is a very-fine-scale probe of local misorientations. Furthermore, these rotationally misaligned regions are formed directly at the film/substrate interface during the early stages of film growth. In some regions of the film, discontinuities in the moire fringe pattern were observed. These discontinuities are indicative of growth-related defects, for example, threading dislocations. It was found that the number density of these defects was apparently reduced in films grown at higher substrate temperatures.