Superconductivity in ion-beam-mixed layered Au-Si thin films

The superconducting properties of thin films made by mixing alternating layers of Au and Si using ion-beam bombardment correlate with the formation of metastable metallic phases in what is otherwise a simple eutectic system. Transmission-electron-microscopy measurements reveal the superconducting phases to be amorphous. Compound formation and the nature of Au--Si bonding in these metastable phases are demonstrated from X-ray photoelectron spectroscopy and from a previous study of X-ray-absorption spectroscopy. After mixing with a beam of Xe ions, multilayered films with an average nominal composition Au sub x Si sub 1--x , where x = 0.2, 0.4, 0.5, 0.72, and 0.8, exhibited superconducting transition temperatures 0.2-1.2K. A double transition feature in the magnetic field dependence of the resistivity is attributed to the formation of more than one metastable metallic phase in the same sample as the ion dose increases.