Electrochemical tuning of the optical properties of nanoporous gold

Abstract

Using optical in-situ measurements in an electrochemical environment, we study the electrochemical tuning of the transmission spectrum of films from the nanoporous gold (NPG) based optical metamaterial, including the effect of the ligament size. The long wavelength part of the transmission spectrum around 800 nm can be reversibly tuned via the applied electrode potential. The NPG behaves as diluted metal with its transition from dielectric to metallic response shifted to longer wavelengths. We find that the applied potential alters the charge carrier density to a comparable extent as in experiments on gold nanoparticles. However, compared to nanoparticles, a NPG optical metamaterial, due to its connected structure, shows a much stronger and more broadband change in optical transmission for the same change in charge carrier density. We were able to tune the transmission through an only 200 nm thin sample by 30%. In combination with an electrolyte the tunable NPG based optical metamaterial, which employs a very large surface-to-volume ratio is expected to play an important role in sensor applications, for photoelectrochemical water splitting into hydrogen and oxygen and for solar water purification.

Structure and Applications of Gold in Nanoporous Form

“…The reason for enhancement in SPR response is attributed to excitation of local plasmon field and an increased surface area for the reaction. In the absorption spectra, two characteristic LSPR peaks can be observed for np-Au, one near 490 nm and other around 550-650 nm [91,92]. The LSPR peak of np-Au at 490 nm is nearly independent of change in refractive index [92] and the peak at 550-650 nm is relatively wider compared to that obtained from Au nanoparticles and nanorods.…”

Recent Progress in Active Optical Metasurfaces

“…Particularly, chemical changes due to electrochemical reactions offer a unique approach for electrically controllable plasmonics that are sensitive to the chemical constituent and the surface carrier properties of the nanostructures. Electrochemical potential controlled plasmonic devices have recently been reported and should prove useful for active and fine tuning of plasmonic properties of metallic metasurfaces . Dramatic plasmonic resonance tuning based on surface‐charge density modulation was first observed in arrays consisting of 10 nm thick gold SRR and has been recently reidentified in gold nanoporous systems with remarkable surface‐to‐volume ratios .…”

“…Electrochemical potential controlled plasmonic devices have recently been reported and should prove useful for active and fine tuning of plasmonic properties of metallic metasurfaces . Dramatic plasmonic resonance tuning based on surface‐charge density modulation was first observed in arrays consisting of 10 nm thick gold SRR and has been recently reidentified in gold nanoporous systems with remarkable surface‐to‐volume ratios . Moreover, electrochemical processes can also directly result in changes in constituent material properties, which may lead to dramatic variation in the associated plasmonic response.…”

Nanoporous Metals with Structural Hierarchy: A Review

“…Local processes at the surface of the pores or at their interface with a fluid are exploited for applications in fields such as catalysis, [11,[47][48][49][50] sensing, [11,51,52] actuation (see below), optical switching, [140][141][142] electropumping for microfluidic devices, [143] integrated circuit contacting, [144] biological implants, [145][146][147][148] and as electrodes where a large surface area is needed. Local processes at the surface of the pores or at their interface with a fluid are exploited for applications in fields such as catalysis, [11,[47][48][49][50] sensing, [11,51,52] actuation (see below), optical switching, [140][141][142] electropumping for microfluidic devices, [143] integrated circuit contacting, [144] biological implants, [145][146][147][148] and as electrodes where a large surface area is needed.…”