Resistivity and phonon softening in ion-irradiated epitaxial gold films

Abstract

The influence of ion irradiation-induced defects on the temperature dependence of the resistivity of epitaxial, thin (25nm), and ultrathin (7nm) gold films was investigated. To include surface scattering properly, the analysis was performed with the classical size-effect model of Fuchs–Sondheimer. Values for the residual resistivity, the specularity parameter p, and the Debye temperature were obtained. It turned out that ion irradiation not only leads to an expected increase of the resistivity but also to a modification of electron-phonon scattering. With increasing defect density, the effective Debye temperature was significantly reduced. This reduction was less pronounced for He+ as compared to Ar+ irradiation pointing towards vacancy clustering in the latter case. In ultrathin films (7nm), the Debye temperature is reduced already in the as-prepared state due to an increased surface-to-volume ratio, and ion irradiation-induced defects do not lead to a further reduction.