Bernhard Steinhauser
Johannes Kepler University Linz - Institute of Applied Physics
Bernhard Steinhauser is currently a PhD student at the Johannes Kepler University Linz, where he is part of the nanoplasmonics group of Prof. Thomas Klar. His research focuses on the combination of nanoplasmonics and electrochemistry.
Extraordinary chemical stability and unique optical properties render gold as excellent material for all kinds of plasmonic sensing applications. These attributes allowed the development of localized plasmon voltammetry (LPV), where the optical response of a plasmonic nanostructure is monitored while applying an electrochemical potential sweep. This technique is capable to optically detect the electrochemical charging of plasmonic nanostructures as well as the adsorption of ionic species. However, for large electrochemical potentials, the region of stability of elemental gold is exceeded and gold oxides are formed on the surface. As plasmonic sensing is based on the dielectric properties of the interface region, it is of great necessity to investigate the plasmonic response during surface oxide formation.
Therefore, we report LPV measurements on a plasmonic gold nanowire array with electrolytes of different pH values. The plasmonic gold nanowire arrays are produced by oblique evaporation of gold on a nanostructured poly-ethylene terephthalate foil. The plasmonic nanowires exhibit transverse localized plasmon resonance modes at a resonance wavelength of ca. 800nm and are used as nanometer-sized working electrodes in an electrochemical three electrode cell.
To correlate the optical response with redox processes we concurrently measure the electrical current through the electrochemical cell. By changing the pH values of the electrolyte solutions, we tune the oxidation and reduction potentials of the gold redox system. We observe an excellent agreement for the oxidation and reduction potentials determined optically with the LPV method or with the current measured by cyclic voltammetry for all tested pH values.
Furthermore, we apply electrochemical potentials that exceed the applicable potential region for electrical current measurements in aqueous solutions, i.e. potentials where currents from the formation of elemental hydrogen and oxygen gas cover currents originating from other sources. Our results show that the evolution of gaseous species has little to no influence on optical signals detected by the LPV method. Moreover, they reveal an additional redox reaction happening on the plasmonic electrode.
[1] Dondapati et.al. Nano Lett.,2012,12(3),1247
[2] Dahlin et.al. Nanoscale,2012,4,2339
[3] Brown et.al. ACS Photonics,2015,2(4),459
[4] Byers et.al. Nano Lett,2016,16(4),2314
Photonic & plasmonic nanomaterials , Enhanced spectroscopy and sensing
