Surface analysis on superconductors is reviewed in the field of the fabrication of Josephson junction and the preparation of high Tc superconductors. The surface oxide and tunnel barrier of Pb alloys, Nb metal, and Nb compounds (Nb
3Sn, Nb
3Ge, Nb
3Al, and NbN etc.) are characterized by using XPS, UPS, AES, TEM, ellipsometer techniques. Among many surface analysis techniques, XPS is used as the most powerful tool for the surface analysis of superconductors. The mechanism of oxide formation on the Nb surface is interpreted. The oxidation mechanism of Pb alloy and A 15 compounds is explained by selective ionic diffusion due to the difference of contact potential between superconductor and the absorbed oxygen layer on it, and the difference of ionization potential between constituent elements.
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