Tunable plasmonics with Au nanoparticles coupled to thin film vanadium dioxide

Abstract

The development of active devices featuring dynamic tunable plasmonic resonances is vital for wide implementation in many optoelectronic devices. By coupling plasmonic nanoparticles to an underlying thin film of phase change material vanadium dioxide (VO2), dynamic tuning of the plasmon resonance can be achieved within the visible and near IR spectral regions. It is shown through selection of single nanoparticle or dimer structures, the plasmon resonances can be tuned over a large spectral range, the scattering cross-section can be increased, and the E-field enhancement and spatial profile can be controlled via the VO2 phase transition. Hybrid Au nanocuboid–VO­2 structures exhibit larger reversible wavelength shifts than rounded nanoparticles, such as rods and discs, of similar dimensions. A plasmon resonance shift of over 600 nm is observed in the near-IR after the semiconducting to metallic VO2 phase transition. The largest increases in the scattering cross-section are achieved with a VO2 thin film thickness of 30–50 nm. Disc, rod, bowtie and cuboid dimers show larger increases of the scattering cross-section at lower wavelengths, even extending into the visible spectral range. On VO2 phase transition the bowtie dimers can provide an increase in the scattering cross-section of over 70% and 3.6-fold increase in the E-field intensity within the dimer gap. Additionally, the near-field enhancement spreads over the entire height of the dimer gap, and in particular, there is a large enhancement at the surface of the dimers. The increased scattering cross-section and modification of the spatial profile of the E-field enhancement provides mechanisms for tunable metasurfaces.