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Munetaka Oyama Department of Material Chemistry, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8520, Japan (Received 22 May 2009; accepted 15 July 2009)

Photocatalytic deposition of Ag nanoparticles from a mixed aqueous solution of AgNO3 and polyvinylpyrrolidone (PVP) onto TiO2 film supported on indium-tin oxide-coated glass slide (Ag/TiO2 film) was carried out by using UV light irradiation. The size and shape of the Ag nanoparticles were controlled by the addition of PVP during the photodeposition. In the optical absorption spectra of the Ag/TiO2 film, the localized surface plasmon resonance (LSPR) absorption of the Ag nanoparticles was observed. When the film was immersed in various kinds of alcohols with the refractive index at 20
C (n20 D ), ranging between 1.3292 and 1.4103, the peak LSPR absorption was shifted to longer wavelengths and the peak absorbance increased with increasing n20 D . The spectral change of the Ag/TiO2 film with larger spherical Ag nanoparticles was more prominent than that with smaller ones.

I. INTRODUCTION

Titanium dioxide (TiO2) is well known as a wideband gap semiconductor that has broad applications in a variety of fields such as photovoltaics, catalyst, textiles, paints, cosmetics, and ceramics. In recent years, considerable interest has been devoted to TiO2 composite materials with precious metal nanoparticles. This interest is because TiO2 composite materials inhibit the recombination of photogenerated electrons and holes and enhance the trapping probability of the photogenerated charge carriers. Thus, the attachment of metal nanoparticles to TiO2 improves the photocatalytic efficiency of TiO2.1–3 On the other hand, the absorption coefficients in the visible region of the TiO2 films with Au, Ag, and Pt nanoparticles become large in comparison with that of bare TiO2 film. This effect is due to the localized surface plasmon resonance (LSPR) absorption of the metal nanoparticles, which can have several applications in optical fields. In particular, Au and Ag nanoparticles have attracted much attention for their application to sensing devices, such as SPR sensors and immunoassays. The SPR sensors with Au and Ag nanoparticles avoid the complicated traditional optical instrument in the measurement.4–7 Among the precious metal nanoparticles, special a)

Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2010.0012 J. Mater. Res., Vol. 25, No. 1, Jan 2010

attention has been devoted to Ag nanoparticles. This focus is because Ag is a cheaper and biocompatible metal compared with Au and Pt.8 There is a wide variety of preparation processes of the TiO2 films modified with Ag nanoparticles, such as photoreduction, sputtering, and seed-mediated method. The photoreduction method has been widely investigated because of its in situ preparation and easy processing at room temperature. By using the normal photoreduction method, the aggregated Ag particles with different shapes and large size distribution were formed on TiO2 fil