Tuning of Localized Surface Plasmons in Vanadium Dioxide Nanoparticles via Size and Insulator–Metal Transition

Vanadium dioxide nanostructures represent a promising phase-changing platform for use in tunable plasmonic devices. However, localized surface plasmon resonances have been investigated in detail only in nanostructure arrays using optical techniques, which did not provide comprehensive information about individual plasmonic modes and their tunability. In this study, we present a comprehensive modal analysis of single-phase and multiphase vanadium dioxide nanoparticles. In situ high-resolution electron energy loss spectroscopy was utilized to resolve the dipole plasmon peak, higher-order and breathing plasmonic modes, and bulk losses as a function of nanoparticle size. Furthermore, the focus is directed toward capturing the dynamic nanoscale optical response throughout the metal–insulator transition. This system possesses the ability to be gradually switched on and off in terms of the emergence of near-infrared plasmonic absorption. The switching is accompanied by a gradual spectral shift of the absorption peak, which is essential for functional nanodevices based on vanadium dioxide.