Compound formation and superconductivity in Au-Si: X-ray absorption measurements on ion-beam-mixed Au-Si films

Multilayered Au-Si thin films have been deposited with the net compositions ‘‘${\mathrm{Au}}_{1\mathrm{-}\mathrm{x}}$ ${\mathrm{Si}}_{\mathrm{x}}$,’’ x=0.29, 0.5, and 0.8. After ion-beam mixing these films exhibited superconductivity in the 0.3–1.2 K range despite the nonsuperconducting character of both Au and Si. Near-edge x-ray absorption spectroscopy (XAS) measurements on the Au $L_3$ edge in these films indicate that metastable Au-Si compound formation occurs in these ion-mixed materials. Specifically, the XAS measurements indicate changes in Au 5d-orbital occupancy and changes in the local Au structural environment which are both consistent with local compound formation.