Extreme nanophotonics from ultrathin metallic gaps

Abstract

Ultrathin dielectric gaps between metals can trap plasmonic optical modes with surprisingly low loss and with volumes below 1nm 3 . We review the origin and subtle properties of these modes, and show how they can be well accounted for by simple models. Particularly important is the mixing between radiating antenna and confined nanogap modes, which is extremely sensitive to precise nano-geometry, right down to the single atom level. Coupling nanogap plasmons to electronic and vibronic transitions yields a host of phenomena including single-molecule strong coupling and molecular optomechanics, opening access to atomic-scale chemistry and material science, and quantum metamaterials. Ultimate low-energy devices such as robust bottom-up assembled single-atom switches are thus in prospect.

Towards Reliable and Quantitative Surface‐Enhanced Raman Scattering (SERS): From Key Parameters to Good Analytical Practice

“…The first question that we need to keep in mind—and try to answer using these methods and techniques—is: where is the signal in our SERS measurements coming from? It is generally accepted that the SERS signal predominantly arises from molecules located in very small (few nm 3 or even less) regions with extremely high local electric field, so‐called hot spots. A simple calculation of an elongated Ag nanoparticle shows that 12 % of the total surface area is responsible for 80 % of the collected SERS signal.…”

“…Although usually provided by the SERS spectrum itself,X -ray photoelectron spectroscopy (XPS) and electrochemical approaches can be used to evaluate the interactions at the interface between the plasmonic nanostructure and the molecules to greater detail. Importantly,t he interaction with light can be simulated for most of the cases,giving insight into,for example,the spectral response,e lectric-field confinement, and polarization-dependence.H owever,t he information provided by these characterization techniques depends on the system under study and should be judged critically.T he first question that we need to keep in mind-and try to answer using these methods and techniques-is:where is the signal in our SERS measurements coming from?Itisgenerally accepted that the SERS signal predominantly arises from molecules located in very small (few nm 3 or even less [20] )r egions with extremely high local electric field, so-called hot spots.Asimple calculation of an elongated Ag nanoparticle shows that 12 %o ft he total surface area is responsible for 80 %o ft he collected SERS signal. These numbers can be even more striking when considering Ag sphere dimers with ag ap of 2nm(see Figure 3, right).…”

Recent Advances in Quantum Effects of 2D Materials

“…[201,202] Therefore, with the employment of 2DLMs, numbers of investigations with novel observations in the field of strong coupling are performed. [203][204][205][206][207][208][209][210][211][212][213][214][215] Figure 10c illustrates the representative strong coupling systems constructed by 2DLMs and plasmonic nanocavities, where the TMDs together with a single plasmonic nanostructure or the nanoparticle on nanofilm structure are chosen. [203][204][205][206] Except for the advantage of large dipole momentum, the 2DLMs also exhibit the merit of controllable excitonic transition energy via the approaches of electrostatic grating, thermal scanning, or optical pumping.…”

Low‐Loss Hybrid High‐Index Dielectric Particles on a Mirror for Extreme Light Confinement

“…They are often based on coupled particles, Fano resonators, or complex‐shaped nanoparticles . However, probably the simplest, most efficient, and flexible platform able to confine light is a nanoparticle located on top of a metallic mirror . For these so‐called particle‐on‐mirror (PoM) structures, if the distance between the mirror and the optical antenna or their array is on the order of several tens or hundreds of nanometers, several exotic effects take place .…”

“…[16] However, probably the simplest, most efficient, and flexible platform able to confine light is a nanoparticle located on top of a metallic mirror. [17][18][19][20] For these so-called particle-on-mirror (PoM) structures, if the distance between the mirror and the optical antenna or their array is on the order of several tens or hundreds of nanometers, several exotic effects take place. [21] Relevant examples, which have found applications, are coupling to surface plasmons launched on the metallic film below, [22] or far-field interference which boosts the absorption of the particle layer.…”