Oxidation in preparation of oxide superconducting films by MBE using NO₂ and O₃ gases

In order to prepare oxide superconducting films by molecular beam epitaxy (MBE), we developed a compact NO₂ supersonic molecular beam source and a new ozone jet generator to supply oxidizing gases with high controllability. Using these sources, oxide superconducting films of REBa₂Cu₃O_x (RE  Nd, Y) were prepared on either MgO or SrTiO₃ substrates. Because of the sufficiently low pressure during deposition, the oxidation process of the metals, especially of copper, by the oxidizing gases and the crystallization and surface flatness of the films were studied in situ by XPS and reflection high‐energy electron diffraction (RHEED) together with effective cleaning of the substrates by the oxidizing gases.