Porous Gold Nanowires: Plasmonic Response and Surface‐Enhanced Infrared Absorption

Abstract

Because of its extended surface area porous gold is of potential interest for surface‐enhanced spectroscopy methods. Optical properties of porous and smooth gold nanowires of similar diameter are analyzed with infrared spectroscopy and modeled with finite‐difference time‐domain simulations. By electrochemical deposition in ion‐track etched polymer smooth gold and gold–silver alloy nanowires are synthesized. Porous gold nanowires are subsequently obtained by dealloying. The porosity clearly affects important plasmonic characteristics, resulting in a strong redshift of the resonant wavelength, and significant line broadening, which can be convincingly explained by effective Drude parameters related to a lowered average electron density and a higher electron scattering in the porous gold, respectively. Finally, the sensing performance of porous wires is tested by surface‐enhanced infrared absorption. The measurements show a similar vibrational signal contrast for smooth and porous wires. This is explained by simulations which reveal that the nanowire near‐field modeled with bulk gold data is higher and thus accordingly the vibrational signal is enhanced compared to nanowires modeled with the effective Drude parameters of porous gold. This means that the advantages offered by the larger surface of porous wires are counterbalanced by lower near‐field strength.