Fano Transparency in Rounded Nanocube Dimers Induced by Gap Plasmon Coupling

Abstract

Homodimers of noble metal nanocubes form model plasmonic systems where the localized plasmon resonances sustained by each particle not only hybridize but also coexist with excitations of a different nature: surface plasmon polaritons confined within the Fabry-Perot cavity delimited by facing cube surfaces (i.e., gap plasmons). Destructive interference in the strong coupling between one of these highly localized modes and the highly radiating longitudinal dipolar plasmon of the dimer is responsible for the formation of a Fano resonance profile and the opening of a spectral window of anomalous transparency for the exciting light. We report on the clear experimental evidence of this effect in the case of 50 nm silver and 160 nm gold nanocube dimers studied by spatial modulation spectroscopy at the single particle level. A numerical study based on a plasmon mode analysis leads us to unambiguously identify the main cavity mode involved in this process and especially the major role played by its symmetry. The Fano depletion dip is red-shifted when the gap size is decreasing. It is also blue-shifted and all the more pronounced that the cube edge rounding is large. Combining nanopatch antenna and plasmon hybridization descriptions, we quantify the key role of the face-to-face distance and the cube edge morphology on the spectral profile of the transparency dip.

Tunable Fano Resonances in an Ultra-Small Gap

“…Recently, Fano resonances were observed in silver nanocube dimers [31,32], where small spacer separations occur via surfactants. However, precise control of these small nanogaps is challenging and the silver nanocube dimers are easily misaligned.…”

Correlating Single-Molecule Sers Statistics to Plasmonic Nanocluster Structure and Near-Field Properties

“…For instance, the coupling between two silver nanocubes may present an asymmetrical lineshape due to out-of-phase interaction of plasmon modes. 42,43 Such plasmon resonance, also known as Fano resonance, leads to observable SERS spectral signatures regarding relative intensities. 44,45 Also, since the plasmon resonance wavelength is dependent on the cluster structure, it is possible to extract qualitative information about the nanoparticle aggregation state from sm-SERS experiments.…”

Plasmonic Nanocomposites Based on Silver Nanocube–Polymer Blends Displaying Nearly Perfect Absorption in the UV Region

“…First, inter-cube coupling mode appears in the visible range that leads to red-shifted absorption bands when reducing inter-cube distance. 8,[16][17][18][19] This limits the possibility to reach strong light absorption in the spectral region of the dipolar resonance. Secondly, the light absorption in the UV is enhanced by a blue-shift of the dipolar mode.…”

“…Plasmonic inter-cube couplings (also referred as gap plasmon) appear within NCs assemblies and trigger an enlargement and red-shift of the absorption, with the appearance of a new large peak at 500 nm. 8,[16][17][18][19] Furthermore, the absorption spectra in Figure 3a concentration. In contrast, the absorption of the dipolar mode at 450 nm increases only in a linear way up to sample C and derives strongly into saturation for sample E-G, due to its slight blueshift, reaching a maximum of 80% in absorption even for the highest NCs concentration.…”

“…due to the rounding of the cube (corner sharpness). 12,18 Concerning the peak at 380 nm, the origin is mostly attributed to a quadrupolar mode 18,38 or quadrupolar-dipolar hybrid mode. 36 In order to produce p-PNCs with highly dispersed NCs, PVP was used as polymer host,…”