Nanocrystalline ion-irradiated gold Electrical resistivity used to study defects and grain boundaries

Abstract

Thin films of nanocrystalline gold have been prepared by electron-beam deposition on to liquid-nitrogen cooled substrates, giving a grain size of about 8 nm. Some of these films were annealed at 773 K for 1 h, giving a second set of films with a grain size of about 40 nm. These two sets of films, denoted nanocrystalline and polycrystalline, were ion irradiated using 1 MeV Xe²⁺ and 500 keV Ar⁺ with doses up to about 10 displacements per atom. Changes in the electrical resistivity and its temperature dependence were measured. A relatively small resistivity contribution due to grain-boundary scattering was observed, giving no evidence for a strongly disordered grain-boundary phase. The temperature-dependent part of the electrical resistivity was found to be very similar to that of pure bulk gold, suggesting the same characteristic Debye temperature for nanocrystalline thin films and bulk gold (185±10K). The saturation level for irradiation-induced defects at room temperature was found to be similar for the nanocrystalline and polycrystalline thin films. The same saturation concentration, corresponding to a resistivity increase, Δp, of about 1 μΩ cm, was found for both Xe²⁺ and Ar ⁺ irradiation for doses larger than 1 displacement per atom. After ion irradiation, a change in the temperature dependence of the electrical resistivity was found. This change is in agreement with an irradiation-induced reduction by 20% of the characteristic Debye temperature to 150±10K.