Characterization of the Effect of Film Thickness on the Electrochemical Impedance of Nanoporous Gold

Graphs are generated characterizing the effect of film thickness on the electro­ chemical impedance of nanoporous gold. Twelve-karat white gold (50% Ag, 50% Au) leaves were dealloyed to make a total of 12 nanoporous gold samples from 100­ 300 nm thick. Scanning electron microscopy (SEM) was used to determine the pore diameter distributions and an electrochemical cell was used to collect impedance data for each sample. Analysis of the SEM micrographs shows the pore morphology ranges from shallow spherical pores to deep interconnected pores, and the diameter distributions were between 10 nm and 20 nm for all of the samples. A linearized graph of impedance |Z| versus frequency shows that the breakpoint frequency decreases with increasing film thickness. Below the breakpoint frequency, the data support an idealized model that assumes through-thickness pores with uniform diameters. Above the breakpoint frequency, however, the ideal model predicts a drastic imped­ance decrease, whereas the data show only a slight impedance decrease.