Validity of the free-electron model for Ag—Ge and Au—Ge amorphous metallic alloys

Abstract

Ag—Ge and Au—Ge amorphous alloy films have been prepared by co-evaporation on cold (15–20 K) substrates under ultra-high vacuum for Ge concentrations between 20 and 40 at.%. Changes in short-range order for samples with Ge concentrations larger than 30 at.% were studied by resistance versus temperature measurements during annealing and room-temperature electron diffraction experiments. The d.c. electrical resistivity and the optical properties measured in situ at the deposition temperature are examined in detail. The Drude model with a constant relaxation time is found to reproduce the optical data at low energies satisfactorily. Deviations from this model at higher energies, as well as discrepancies between the average effective number of conduction electrons per atom and the predictions of a rigid-band model, are attributed to s, p-d hybridization. Interband transitions are also discussed.