Stress relaxation in c(perpendicular to)-c(parallel to) YBaCuO thin films on MgO substrate studied by LACBED

Thin films of YBaCuO grown by in situ pulsed laser deposition on MgO substr ate are studied by means of high resolution transmission electron microscop y imaging and large angle convergent beam electron diffraction experiments. Both c(parallel to) and c(perpendicular to) YBaCuO crystals coexist in the film. The diffraction experiments are performed on the MgO substrate along the interface with the YBaCuO film. Some of the Bragg lines exhibit a dram atic broadening when the electron probe is just below the c(parallel to) or iented crystal. This result is interpreted in terms of lattice strain relax ation due to the thinning of the TEM sample. This relaxation phenomenon ind icates that the c(parallel to) oriented grains embedded in a c(perpendicula r to) oriented host matrix of YBaCuO, are under stress. (C) 2000 Elsevier S cience S.A. AU rights reserved.