Plasmonic Interactions in Gold::Vanadium Dioxide Hybrid Nanostructures
Ferrara, Davon Wayne
Hybrid nanocomposites consisting of arrays of gold (Au) nanoparticles (NPs) and vanadium dioxide (VO<sub>2</sub>) 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 VO<sub>2</sub> 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::VO<sub>2</sub> 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 VO<sub>2</sub> semiconductor-to-metal phase transition (SMT). In particular, for Au NP arrays and VO<sub>2</sub> thin films at wavelengths between 600 and 1200nm, the electromagnetic coupling between the Au plasmon and the VO<sub>2</sub> interband transitions crucially determine the optical characteristics of Au::VO<sub>2</sub> structures. For arrays of single NPs, coupling between the plasmon and the VO<sub>2</sub> 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 3<i>d</i><sub>||</sub> and 3<i>d</i><sub>π</sub> bands reduce in energy to form the metallic VO<sub>2</sub> conduction band. By studying the interparticle interactions within pairs of interacting NPs, or nanodimers (NDs) embedded in VO<sub>2</sub>, 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 VO<sub>2</sub> 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.