Electrical Control of LSPR from Gold Nanoparticles Using Electrochemical Oxidation
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1208-O10-04
Electrical Control of LSPR from Gold Nanoparticles Using Electrochemical Oxidation Takashi Miyazaki1, Rei Hasegawa1, Hajime Yamaguchi1, Hitoshi Nagato1, Haruhi Oh-oka1, Isao Amemiya1 and Shuichi Uchikoga2 1 Corporate Research & Development Center, Toshiba Corporation. 1, Komukai Toshiba-cho, Saiwai-ku, Kawasaki, 212-8582, Japan. 2 Toshiba Research Europe Limited, Toshiba Corporation, Cambridge, United Kingdom ABSTRACT Large shift of localized surface plasmon resonance (LSPR) spectrum of gold nanoparticles was attained by electrochemical oxidation of the nanoparticle surface. This oxidation occurred in a cell consisting of a pair of indium tin oxide (ITO) electrodes with water medium between the electrodes. On one side of the ITO electrode, the gold nanoparticles were adsorbed. The LSPR spectrum was moved consecutively to the red by increasing the applied positive voltage. By the application of 5 V to the cell, the spectrum shift as large as 55 nm was obtained. Though the spectrum shift has already been observed by changing liquid crystal (LC) orientation surrounding gold nanoparticles, the amount 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 upper limit of the LSPR spectrum shift by our method is estimated to be 138 nm.
INTRODUCTION Surface plasmon resonance (SPR) is a charge-density oscillation that may exist at the interface of two media with dielectric constants of opposite signs, for instance, a metal and a dielectric. Many industrial applications of SPR such as light-emitting devices and molecular sensors have been proposed and actively developed. These applications are referred to as plasmonics. Another possible application is considered to be spatial light modulators. Localized surface plasmon resonance (LSPR) excited on nanoparticle surface results in wavelengthselective absorption with extremely large molar extinction coefficients. If the resonance wavelength can be electrically modulated over a wide range, spatial light modulators with large tunable range will be realized and attractive applications such as reflective displays can be expected. Moreover, condition of incident angle is not severe and no polarizers are required for LSPR excitation, which is also favorable for practical use. In our study, we found that the shift of LSPR spectrum was voltage controllable and nearly reversible. It was confirmed by XPS analysis that the mechanism of the spectrum shift was refractive index change due to electrochemical oxidation of gold nanoparticles. In order to determine whether this method can be applied to reflective displays, the maximum shift of the LSPR spectrum was calculated based on the thickness of gold oxide estimated from the XPS analysis.
EXPERIMENT The shift of the LSPR spectrum due to voltage application was measured with a cell structure composed of a pair of indium tin oxide (ITO) electrodes formed on
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