High-Energy Surface and Volume Plasmons in Nanopatterned Sub-10 nm Aluminum Nanostructures

Abstract

In this work, we use electron energy-loss spectroscopy to map the complete plasmonic spectrum of aluminum nanodisks with diameters ranging from 3 nm to 120 nm fabricated by highresolution electron-beam lithography. Our nanopatterning approach allows us to produce localized surface plasmon resonances across a wide spectral range spanning 2-8 eV.Electromagnetic simulations using the finite element method support the existence of dipolar, quadrupolar and hexapolar surface plasmon modes as well as centrosymmetric breathing modes depending on the location of the electron-beam excitation. In addition, we have developed an approach using nanolithography that is capable of meV control over the energy and attosecond control over the lifetime of volume plasmons in these nanodisks. The precise measurement of volume plasmon lifetime may also provide an opportunity to probe and control the DC electrical conductivity of highly confined metallic nanostructures. Lastly, we show the strong influence of the nanodisk boundary in determining both the energy and lifetime of surface plasmons and volume plasmons locally across individual aluminum nanodisks, and we have compared these observations to similar effects produced by scaling the nanodisk diameter.High-energy plasmonic nanostructures resonant in the ultraviolet (UV) to vacuum ultraviolet (VUV) region of the spectrum offer routes to channel high-energy radiation into nanoscale volumes thus supporting enhancement of high-energy photochemical reaction pathways at targeted nanoscale locations. Plasmonic nanoparticles resonant at visible and near-infrared frequencies have been used to direct electromagnetic radiation into sub-wavelength volumes known as 'hot spots', lending these nanoparticles to applications in nanoengineered devices for spectroscopy, 1-4 catalysis, 5,6 photodetectors, 7,8 sensors, 9-11 optoelectronics, 12,13 nano-optics, [14][15][16] photocathodes 17-19 and energy harvesting. 20,21 Consequently, high-energy plasmonic nanoparticles may provide a route to extend the spectral range of these applications into the VUV, an energy range where simple gas-phase molecules such as CO, O 2 and H 2 O have electronic absorption bands 22,23 and work functions in solids can be overcome producing reactive photoelectrons.Plasmons in materials take one of two forms: (1) volume plasmons (VPs), which are high-energy longitudinal oscillations of conduction and valence band electrons that propagate through the bulk of a material; and (2) interface plasmons, which are collective oscillations of free electrons at an interface. When an interface plasmon occurs at the surface of a material it is referred to as a surface plasmon (SP). SPs can adopt multiple forms, those being surface plasmon polaritons (SPPs), which are propagating SPs that exist at the interface between a metal and a dielectric, and localized surface plasmon resonances (LSPRs) that exist on sub-wavelength metallic nanoparticles.Controlled engineering of LSPRs and VPs with energies greater than 5 eV has been limited to dat...

Nonlocal quasinormal modes for arbitrarily shaped three-dimensional plasmonic resonators

“…These QNMs are typically computed numerically from the Helmholtz equation with open boundary conditions, for example, with perfectly matched layers (PMLs), whose solution 2334-2536/17/121503-07 Journal © 2017 Optical Society of America can then be used to construct the full photon Green function (GF) of the medium-a function that is well known to connect to many useful quantities in classical and quantum optics [28][29][30][31][32][33][34][35][36][37][38]. The GF can also be used (and indeed is required) to compute electron energy loss spectroscopy (EELS) maps for plasmonic nanostructures [39][40][41][42][43][44][45][46][47][48][49][50], which is a notoriously difficult problem in computational electrodynamics, especially for nanoparticles or arbitrary shape. Despite these successes with QNMs, in the presence of nonlocal effects, it is not known whether such a mode description even applies.…”

The Substrate Effect in Electron Energy-Loss Spectroscopy of Localized Surface Plasmons in Gold and Silver Nanoparticles

“…3 accessible, allowing LSPs to be probed and studied with sub-nanometer spatial resolution 6,8,[22][23][24][25][26] . TEM requires specimens thin enough to be electron transparent (typically below 100 nm) and therefore, plasmonic nanoparticles studied by EELS are typically supported on thin membranes 6,8,27 or buried in a thin embedding material 28 .…”

Effective heat dissipation in an adiabatic near-field transducer for HAMR

“…The Au taper was patterned by electron beam lithography (EBL). Since the dimensions of the NFT varied from 24 µm (the largest L value) to 50 nm (the nominal width of the tip and the layer thickness) the EBL process had to be carefully optimized [26]. We use a Carl Zeiss Electron Beam Lithography SEM -Supra 40 system to do the fabrication, the finest feature is 50 nm is our optimized recipe, and we made 12 samples for each length to test the repeatability of the fabrication and the variation of the length for the tapers is less than 2.5%.…”