Plasmonic Interactions between Gold Nanoantennas and Vanadium Dioxide at Near Infrared Energies

Nanocomposites made of noble metals and phase-changing materials are an interesting class of switchable metamaterials, as the localized surface plasmon resonance (LSPR) frequency of the nanocomposite can be modulated by the phase transition. Of this class of nanocomposites, gold nanoparticle (NP) arrays embedded in a vanadium dioxide (VO$_{2}$) film has several unique advantages, including the ability to induce the semiconductor-to-metal (SMT) phase transition of the VO$_{2}$ at a critical temperature of only 68$^{\circ}$C. For lithographically produced arrays of NPs between 140~nm and 180~nm, the LSPR has significant overlap with the 1.4~eV electronic transitions of the VO$_{2}$ 3d band. These electrons become strongly-correlated during the phase transition and delocalize to form the metallic conduction band at higher temperatures. Here we use an array of 180-nm diameter Au NPs embedded in a 60-nm VO$_{2}$ film as a nanoscale probe of the SMT in the VO$_{2}$. Temperature-dependent extinction measurements were carried out on the nanocomposite array using the plain VO$_{2}$ film as a reference to observe the hysteresis of the LSPR energy and linewidth. The interaction resulted in a 30\% reduction in plasmon dephasing time as the effective dielectric function of the VO$_{2}$ transitions from Lorentzian resonance to a Drude metal near 1.4~eV. Also, an array of 140-nm diameter Au NPs were used toincrease the efficiency of low-intensity laser switching in the nanocomposite compared to a plain 60-nm thick VO$_{2}$ film. An analytical model of laser heating was developed and suggests that the nanocomposite can be optimized to tune both optical and photothermal switching properties of an active metamaterial.