Photoelectrochemical and Optical Behavior of Single Upright Ag Nanoplates on a TiO2 Film

Changes in morphology and optical properties of single Ag nanoplates on a nanoparticulate TiO2 film were studied, by means of combined atomic force microscopy and optical dark-field microscopy with the aid of discrete dipole approximation-based spectral simulation. Photocatalytic reduction of Ag+ ions under diffusion-controlled conditions grows hexagonal and triangular Ag nanoplates mostly in vertical orientation. The Ag nanoplates absorb and scatter light at different wavelengths on the basis of three different localized surface plasmon resonance modes, the in-plane longitudinal (IPL), in-plane transverse (IPT), and out-of-plane modes. Typical upright nanoplates scatter orthogonally polarized green and near-infrared (NIR) light on the basis of the IPT and IPL modes, respectively. Sufficient irradiation with visible and/or NIR light topples the standing nanoplates over by photo electrochemical reactions, and typical overturned nanoplates scatter NIR light. Such photoelectrochemical behavior is applied to orientation-selective overturn and polarization-selective control of the optical properties by irradiation with polarized visible or NIR light.