Electrical Control of Plasmon Resonance of Gold Nanoparticles Using Electrochemical Oxidation

Abstract

A large shift of the localized surface plasmon resonance (LSPR) spectrum of gold nanoparticles was attained by electrochemical oxidation of the nanoparticle surface. This oxidation occurred in the cell, which consisted of a pair of indium tin oxide (ITO) electrodes and water medium between the electrodes. On one side of the ITO electrode, the gold nanoparticles were adsorbed. With the application of a voltage of 5 V to the cell, a spectrum shift as large as 68 nm was obtained. Though the spectrum shift has already been observed by changing liquid crystal (LC) orientation surrounding gold nanoparticles, the size of the shift was not large (11 nm). That was because the variation of the effective refractive index of LC was rather small. Our large shift due to electrochemical oxidation resulted from the large refractive index of Au-O. The electrochemical oxidation was confirmed by XPS analysis of the gold nanoparticles with the LSPR spectrum shift. Other possible mechanisms of the shift such as charge localization, aggregation, and adsorption of charged materials proved to have no effect via SEM measurement and so on. This large shift of the resonance spectrum can be expected to lead to further development of spatial light modulators for next-generation optical communications and displays.

Electrochemical Tuning of the Dielectric Function of Au Nanoparticles

“…Because gold oxide has a larger dielectric constant than the electrolyte solution, oxidation of the AuNP surface will cause changes of the index of refraction at the surface of the metal nanoparticle relative to an unoxidized Au particle. [6][7][8]29,35 Further, the refractive index of the surrounding medium could also change due to alignment of dipoles in the electrolyte, as in an electric double layer. 12,16,20,24,26,30 Damping may also be modified by an applied bias because of variations of population or depopulation of electronic surface states at the AuNP surface.…”

“…The Drude model does not take into account other effects that happen in parallel with changes in charge density in a real system, such as changes in electronic surface states due to chemical interactions with the surrounding medium and the resultant changes in damping and index of refraction (e.g., adsorbates, oxidation, electric double layer). 6,8,[10][11][12]16,20,24 Furthermore, using a Drude model to represent a uniform change in charge density in a plasmonic structure does not account for the excess charge residing at the conductor surface. Thus, in order to predict optoelectronic behavior of plasmonic systems, we desire a model that will account not only for changes in charge density, but also for changes in damping, index of refraction, and penetration depth of surface charge and damping.…”

From tunable core-shell nanoparticles to plasmonic drawbridges: Active control of nanoparticle optical properties

“…Researchers in pursuit of in situ active control have used electronic ( 1 , 2 ), chemical ( 3 ), and electrochemical ( 4 – 9 ) approaches. Recent electrochemical efforts have resulted in either small reversible modulations ( 7 , 8 ) or large irreversible plasmon shifts ( 10 , 11 ). One strategy toward achieving larger plasmon resonance shifts is tuning the plasmon coupling strength between adjacent nanostructures.…”

Chemically directed self-assembly of perpendicularly aligned cylinders by a liquid crystalline block copolymer

“…Fig. 40,50,51 These results reveal that Au ions penetrated inside the PEO cylindrical microdomains in the block copolymer thin film were partially reacted by the VUV irradiation intricately, and suggest that zero valence Au 0 was formed simultaneously during the polymer etching process by the VUV treatment. In the spectra of Au-doped PEO 114 -b-PMA(Az) 24 , two peaks were detected at 84.2 and 88.0 eV, which can be assigned as Au 4f 7/2 and 4f 5/2 relating to zero valence Au 0 , respectively.…”