ATMOSPHERIC DETERIORATION OF CLEAN SURFACE OF EPITAXIAL (001)-YBACUO FILMS STUDIED BY LOW-ENERGY ELECTRON-DIFFRACTION

The effects of gas exposure on the clean surface of the epitaxial YBaCuO thin films were closely investigated using the low-energy electron diffraction (LEED) method. The clean surface was obtained by in-vacuum annealing at 500-degrees-C. Once the clean surface was exposed to air, even at room temperature, the LEED spots disappeared or sometimes became faint. To ensure the degradation mechanism of the YBaCuO clean surface, the specimens were exposed to pure O2 and N2 gases separately and measured by LEED. As a result, it was found that O2 is very safe but N2 serves as a poisonous gas for the YBaCuO clean surface.