TEM studies on the crystal structure of YBa₂Cu₃O_7−x thin films prepared by pulsed laser deposition

Abstract

The crystal structures of YBa₂Cu₃O_7−x thin films deposited on MgO(100) substrates have been investigated by cross-sectional transmission electron microscopy (TEM). At a substrate temperature of 670 °C, Cu–O chains become wavy. Stacking faults are formed between the Cu–O chains. Therefore, the domains with c-axis lattice constants of 15 Å, 27 Å, and 39 Å are observed. By applying a biasing voltage of + 300 V, deviation in the c-axis orientation is reduced compared to that at an unbiased condition; even some grain boundaries remain. Near substrate surfaces, deviation of the c-axis direction from the substrate normal increases with a decreasing substrate temperature from 700 °C to 670 °C. Application of a substrate bias voltage of +300 V improved the heteroepitaxial growth of the c-axis oriented YBa₂Cu₃O_7−x.