Silica Nanowires Decorated with Metal Nanoparticles for Refractive Index Sensors: Three-Dimensional Metal Arrays and Light Trapping at Plasmonic Resonances

We report the fabrication of silica nanowires (NWs) decorated with Au or Ag nanoparticles (NPs) by dewetting thin metal films evaporated on the NWs. The Au or Ag NPs, displaced along the NWs, form a three-dimensional (3D) ensemble of metallic NPs in a macroporous structure. Their optical behavior results from the combination of the high white-light scattering of silica NWs with the selective absorption of the localized surface plasmon resonances (LSPRs) of the NPs, causing light trapping just at the LSPR wavelengths. Such a 3D plasmonic structure shows a strong dependence of the LSPR wavelength on the refractive index of the environment in which the 3D NP ensemble is immersed, a feature that makes them morphologically and optically peculiar materials appealing for sensing applications.