Hybrid Graphene-Supported Aluminum Plasmonics

Abstract

Controlled fabrication of devices for plasmonics on suspended graphene enables obtaining tunable localized surface plasmon resonances (LSPRs), reducing the red-shift of LSPRs, and creating hybrid 3D–2D systems promising for adjustable dipole–dipole coupling and plasmon-mediated catalysis. Here, we apply a low-cost fabrication methodology to produce patterned aluminum nanostructures (bowties and tetramers) on graphene monolayers via electron-beam lithography and trap platinum (Pt) nanoclusters (NCs) within their hotspots by thermal annealing. We reveal the LSPRs of aluminum plasmonics on graphene using electron energy-loss spectroscopy (EELS) and energy-filtered transmission electron microscopy (EFTEM) in a monochromated scanning transmission electron microscope (STEM). The LSPRs of these nanostructures are measured to be between visible and ultraviolet regions of the spectrum and are confirmed by electromagnetic simulations. The antibonding dipole and bonding dipole modes of both structures are tuned by controlling their gap size. The tetramers enable the simultaneous excitation of both antibonding and bonding dipole modes at the poles of nanoprisms, while bowties allow us to excite these modes separately either at the poles or within the hotspot. We further show that the hybrid nanocavity–NC systems are in the intermediate coupling regime providing an enhanced plasmon absorption in the Pt NCs via the energy transfer from the antibonding dipole mode to the Pt NCs. The dipole LSPR of Pt NCs also couples to the bonding-type breathing mode in bowties. Our findings suggest that these hybrid nanocavity–graphene systems are of high application potential for plasmon-mediated catalysis, surface-enhanced fluorescence, and quantum technologies.

Electron Beam Induced Circularly Polarized Light Emission of Chiral Gold Nanohelices

“…49 To obtain spatially resolved spectral information about the localized plasmons, spectrum images were acquired with a spatial sampling of 7 nm, providing a three-dimensional data cube, where each voxel contains a low-loss spectrum with an energy resolution of approximately 80 meV, as determined by the full width at half-maximum (fwhm) of the zero-loss peak (ZLP). The EELS findings are confirmed through simulations based on the boundary element method (BEM), 50,51 which solve Maxwell's equations with respect to the real threedimensional shape of the sample. The distinct architecture of the helix comprises two full windings with a consistent pitch of 105 nm and a clearly defined outer helical diameter of 135 nm.…”

Resonance mechanisms of coupled-particle plasmonic nano-antennas to maximize UV fluorescence enhancement of biological molecules

“…Despite of efforts in the design of aluminum (Al) BNAs, the EF factors remain significantly smaller than in the visible range [29,31,34,[36][37][38]. The challenges of achieving high EF factors in the UV range are caused by the inherent characteristics of BNA resonances.…”

“…Our solution to overcome this challenge is to use quadrupole modes for excitation enhancement at higher photon energy and dipole modes for emission enhancement at lower photon energy. Quadrupole modes are of higher photon energy and possess larger quality factor than dipole modes but are considered 'dark' modes for 'small' plasmonic particles [38]. Phase retardation of an oblique incidence light has been shown to excite quadrupole and higher order modes in small particles [40].…”

Nanoscale mapping of shifts in dark plasmon modes in sub 10 nm aluminum nanoantennas

“…In the last decade, there has been an increased interest in developing plasmonic materials and devices based on more sustainable and earth-abundant materials than conventionally used noble metals [13][14][15][16]. In particular, aluminum (Al) can generate plasmon resonances across the ultraviolet (UV) region of the spectrum [4,13,17]. Plasmonic Al nanostructures can therefore find applications in photocatalysis and sensing where LSPRs in the nanostructures can couple to electronic transitions in the UV [18][19][20][21][22].…”