Spectral modulation of single plasmonic nanostructures

We discuss in this paper the feasibility of dynamically modulating both resonance wavelength and spectral width of single nanostructures exhibiting plasmonic effects by cycling through a metal-insulator transition (MIT) in vanadium dioxide (VO₂). Using full-field 3D finite-difference time domain (FDTD) simulation method with nonuniform mesh techniques, we study the effects of this modulation by varying the lateral dimensions of these nanostructures from 40 nm to 120 nm radially and changing its configuration as well, that is VO₂ nanodisk on gold one and vice-versa. As an initial step towards fabricating those single composite nanostructures showing the greatest modulating effect, we start by making single NPs of VO₂ and single gold NPs embedded between two 60 nm layers of VO₂. The samples are fabricated on 130 μm thin glass substrates by electron-beam lithography, pulsed laser deposition of VO₂ and electron-beam evaporation of gold. Using confocal extinction spectroscopy, we hereafter provide for the first time experimental observations of spectral tuning in these lithographically prepared single nanostructures. However, we discussed the variability in spectra obtained. Indeed, as the gold NP size decreases, it becomes comparable to the domain sizes of the embedding VO₂ and this prevent the correct acquisition of the flat field. Hence the study of the tunability of gold particle plasmon resonance is imparted. However, we conclude that this study will be feasible for truly hybridized NP, that is gold nanodisk stacked on VO₂ nanodisk and vice-versa. As hinted by our simulation studies and preliminary experimental results, these hybridized composite NPs could potentially be used in the dynamic spectral tuning of plasmonic waveguides.