Surface study of YBa2Cu3O7−δ epitaxial films cleaned by an atomic oxygen beam

An atomic oxygen beam generated by a microwave plasma source has been used to clean the surface of high-Tc superconducting a- and c-axis oriented YBa2Cu3O7−δ (YBCO) epitaxial thin films. The crystallinity and electronic structure of the cleaned films have been characterized in situ using reflection high energy electron diffraction, low energy electron diffraction (LEED), and ultraviolet and x-ray photoemission spectroscopies (UPS, XPS). Exposure of the surface at 350 °C to the atomic oxygen beam yields sharp LEED spots and a metallic feature at the Fermi level. For a-axis films, clear LEED patterns and a Fermi edge in UPS spectra of a recleaned surface are simultaneously observed. The contact resistance between a cleaned a-axis YBCO film and in situ deposited gold was found to be in the range of 10−10–10−9 Ω cm2.