Atomistic Near-Field Nanoplasmonics: Reaching Atomic-Scale Resolution in Nanooptics

Abstract

Electromagnetic field localization in nanoantennas is one of the leitmotivs that drives the development of plasmonics. The near-fields in these plasmonic nanoantennas are commonly addressed theoretically within classical frameworks that neglect atomic-scale features. This approach is often appropriate since the irregularities produced at the atomic scale are typically hidden in far-field optical spectroscopies. However, a variety of physical and chemical processes rely on the fine distribution of the local fields at this ultraconfined scale. We use time-dependent density functional theory and perform atomistic quantum mechanical calculations of the optical response of plasmonic nanoparticles, and their dimers, characterized by the presence of crystallographic planes, facets, vertices, and steps. Using sodium clusters as an example, we show that the atomistic details of the nanoparticles morphologies determine the presence of subnanometric near-field hot spots that are further enhanced by the action of the underlying nanometric plasmonic fields. This situation is analogue to a self-similar nanoantenna cascade effect, scaled down to atomic dimensions, and it provides new insights into the limits of field enhancement and confinement, with important implications in the optical resolution of field-enhanced spectroscopies and microscopies.

Plasmon-resonant Raman spectroscopy in metallic nanoparticles: Surface-enhanced scattering by electronic excitations

“…(14) with s as the only adjustable parameter. The agreement with the model is excellent as shown in Figs 6,7,8,9, and 11(a). Our modeling of the electron-hole spectra contrasts with all previous attempts that do not consider the whole frequency range [5,21].…”

“…Its activation is thus always linked to the lack of translational invariance of the metallic surface and its spectral shape is governed by an associated spatial "size" D. Second, at thermal and electronic equilibrium, the spectral and temperature background dependence follows Bose statistics as any inelastic scattering process, as a consequence of the principle of detailed balance in thermodynamics. Third, if any absorption or emission process from real direct single electron-hole transitions can be excluded, the background shape of the signal presents a universal shape with an affine linear dependence at low frequency, a broad maximum and a slowly decreasing tail at high frequency [Figs 6,7,8,9, and 11(a)].…”

“…The impressive enhancement, up to 10 8 , of the vibrational fingerprint of molecules located at specific sites ("hot spots") on the surface of metallic particles is responsible of a further huge development of Raman spectrometry [2]. The possibilities of acquiring vibrational information down to a single molecule [3,4] and controlling a single hot spot with high spatial resolution using tip-enhanced Raman spectroscopy (TERS) [5][6][7][8] have led to new insights on local mechanisms at the origin of SERS. From the beginning, these mechanisms have been commonly referred to as electromagnetic (EM) [9] when due to local electromagnetic inductive effects, or chemical (CM) [10] when due to resonant charge transfer effects, the first one giving the largest contribution to the enhancement factor [11].…”

Tracking Optical Welding through Groove Modes in Plasmonic Nanocavities

“…Also, the energy can be accumulated at other sharp features of the nanoparticle (i.e. away from the mirror), 5 which eventually leads to a smoother (less faceted) nanoparticle (see SEM of Fig. S2b,c).…”

Quantum description of the optical response of charged monolayer–thick metallic patch nanoantennas

“…The conclusions derived from the JM calculations have been later confirmed by the experimental data 40,[66][67][68][69] , and ab-initio calculations at a full atomistic level [70][71][72] .…”