Plasmonic Interactions in Gold::Vanadium Dioxide Hybrid Nanostructures

Abstract

Hybrid nanocomposites consisting of arrays of gold (Au) nanoparticles (NPs) and vanadium dioxide (VO2) were fabricated on indium-tin-oxide coated glass substrates. The Au NPs, with radii from 100 to 180nm and 20nm in thickness, were created by electron beam lithography; subsequently, a VO2 thin film was deposited over the arrays by pulsed laser deposition. The localized surface plasmon resonances in the nanocomposite occur at visible to near-infrared (VS-NIR) wavelengths. At VS-NIR wavelengths, these Au::VO2 nanocomposites present a unique opportunity to study the interactions between the fundamental free-electron excitation of a metal, the plasmon, and the strongly-correlated electronic excitations that give rise to the VO2 semiconductor-to-metal phase transition (SMT). In particular, for Au NP arrays and VO2 thin films at wavelengths between 600 and 1200nm, the electromagnetic coupling between the Au plasmon and the VO2 interband transitions crucially determine the optical characteristics of Au::VO2 structures. For arrays of single NPs, coupling between the plasmon and the VO2 interband transitions allows the NPs to serve as nanoantennas for probing the SMT, leading to a 30% reduction in plasmon dephasing time as the split 3d|| and 3dπ bands reduce in energy to form the metallic VO2 conduction band. By studying the interparticle interactions within pairs of interacting NPs, or nanodimers (NDs) embedded in VO2, we show that plasmon coupling to the vox interband transitions leads to a reduction in coupling strength over NDs in air. Finally, by using a 1550nm CW laser and transient absorption spectrometry, the presence of Au NPs in a VO2 film is shown to enhance the photochromic response of the film to low-intensity irradiation by reducing the critical intensity necessary to induce the phase transition with a 785nm CW laser. This enhancement results from an increased in absorption within the film due to the Au plasmon.