Electrical Control of Plasmon Resonance of Gold Nanoparticles Using Electrochemical Oxidation

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.