Electrical Percolation and Aging of Gold Films

Electric transport in ultrathin metallic films can be either “percolative” or “conductive” depending on the links between the islands that constitute the film. Once the formation of long-range connections is established within the film, the overlayer reaches the so-called percolation threshold. This work describes a quantitative study of the electrical resistance of Au films, as a function of coverage. Film resistance displays a universal scaling law dependence with a critical exponent of 1.9 before percolation, which changes to 1.5 after percolation. These values are between the theoretical predictions for the evolution of growth as 2D or 3D systems. Results also indicate deposition parameters have a defining role in the evolution of the resistance during fabrication. A rise in pressure or deposition rate results in a lowering of the thicknesses at which percolation occurs. A decrease in the substrate temperature modified the typical resistance behavior of the Volmer–Weber growth mode to a trend of 2D growth mode. Finally, results describing the effect of film’s aging on the electrical resistance are presented. Aging is responsible for an important reduction in the film resistance after percolation, a process mainly mediated by material diffusion.