Electrical conductivity of gold-implanted alumina nanocomposite

We have carried out ion implantation of gold into alumina ceramic substrates and measured the surface resistivity as a function of implantation dose. The Au ion energy was 40 keV and the dose spanned the range 2.7–8.9 × 1016 cm−2. Imaging of the implanted material by transmission electron microscopy revealed that the implanted gold self-assembles into nanoparticles, thus forming a gold-alumina nano-composite. The surface resistivity measurements were compared with the predictions of a model based on percolation theory, in which electron transport through the composite is explained by conduction through a random resistor network formed by the Au nanoparticles. The electrical conductivity of a composite, near the critical conductor–insulator transition, is given by σ ≈ σ0(x−xc)t, where σ0 is the saturation conductivity for which the material still remains a composite, x is the normalized metal atom concentration of the conducting phase, xc is the critical concentration, or percolation threshold and t is the critical exponent. Excellent agreement was found between the experimental results and the predictions of the theory, and the results are consistent with prior related (but more limited) work. The percolation dose was 4.4 × 1016 cm−2, and the critical exponent obtained was t = 1.4 ± 0.1. We conclude that the conductivity process is due to percolation and that the contribution from tunneling conduction is negligible.