Morphology and porosity of nanoporous Au thin films formed by dealloying of Au_xSi_1-x

We have investigated the morphology, structure, and annealing response of nanoporous Au films synthesized via electrochemical dealloying of amorphous Au_xSi_1-x co-deposited films on Si substrates. The starting Au alloy film concentrations were varied from x=0.09 to 0.41 and the resulting nanoscale porous films were characterized by electron microscopy and Rutherford backscattering techniques. Our observations provide a systematic description of the nanoporous Au film morphology, porosity, and degree of collapse as a function of starting Au_xSi_1-x alloy composition. The characteristic pore sizes increased from 10 to 45 nm and the porosity increased from 45% to 70% for the nanoporous Au films with decrease in the starting Au concentrations. The degree of film collapse due to dealloying also increased with decreasing Au concentration. The electrochemical dealloying process for nanoporous film formation was observed to change from a layer-by-layer dealloying process to a localized, percolation-dominated process as the Au concentration was decreased from 40 to 9 at.%. The thin film porous synthesis approach presented here enables the integration of bottom up dealloying self-assembly with top down microelectronics-based fabrication techniques, making it a useful new approach for Si-based microsystem applications.