Influence of deposition conditions and ion irradiation on thin films of amorphous Cu-Zr superconductors

Amorphous films of Cu-Zr have been prepared by electron-beam (e-beam) codeposition and ion beam mixing. Various treatments, such as deposition onto liquid nitrogen cooled substrates and ion irradiation with 1 MeV Xe2+ ions or 500 keV Ar+ ions at 100 K and at 300 K, were used to vary the level of disorder in the amorphous state. The residual resistance ratio, the relative resistance change after irradiation, the temperature and width of the superconducting transition, and the upper critical field were measured and used to compare qualitatively the level of disorder and homogeneity. The following observations could be made: (1) amorphous thin films, e-beam deposited at 300 K and below, are more disordered than amorphous ribbons; (2) ion irradiation with Xe and Ar ions performed at 100 K and 300 K only leads to a slightly increased disorder level even for doses corresponding to about one displacement per atom; (3) ion irradiation gives rise to a homogenization of the specimens as evidenced by a decreasing width of the superconducting transition; and (4) a significantly increased level of disorder is achieved by low-temperature deposition of very thin films.