MOIRE PATTERNS AND THEIR APPLICATION TO THE STUDY OF THE GROWTH OF YBA2CU3O7-DELTA THIN-FILMS

Very thin films of YBa2Cu3O7-delta have been formed directly on specia lly prepared electron-transparent thin-foil substrates of MgO by pulse d-laser deposition and examined using transmission electron microscopy . The moire fringe pattern visible in the electron micrographs has bee n used to provide information about film growth and the introduction o f 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, t he 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 i dentify domain rotation through examination of the moire pattern is a very-fine-scale probe of local misorientations. Furthermore, these rot ationally 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. T hese discontinuities are indicative of growth-related defects, for exa mple, threading dislocations. It was found that the number density of these defects was apparently reduced in films grown at higher substrat e temperatures.