Plasmonic Nanogaps: From Fabrications to Optical Applications

Abstract

Metallic nanostructures with nanogap features are proved to be highly effective building blocks for plasmonic systems, as they can provide ultrastrong electromagnetic (EM) fields and controllable optical properties. A wide range of fields, including surface enhanced spectroscopy, sensing, imaging, nonlinear optics, optical trapping, and metamaterials, are benefited from these enhanced EM fields. This review outlines the latest development of the fabrication methods for nanogap structures (metal nanoparticle assembly, nanosphere lithography, electron beam lithography (EBL), focused ion beam (FIB) lithography, oblique angle shadow evaporation, edge lithography, and so on), followed by a summary of their optical applications. The present review will inspire more ingenious designs and fabrications of plasmonic nanogap structures with lithography‐free fabrication techniques, and promote their applications in optics and electronics.

Massively Parallel Arrays of Size‐Controlled Metallic Nanogaps with Gap‐Widths Down to the Sub‐3‐nm Level

“…It is well known that regular arrays of sub-wavelength holes or slits in metal films allow optical energy to be efficiently coupled into SPPs-electromagnetic excitations that propagate in a wave-like manner along the planar interface between a metal and a dielectric-or into localized surface plasmons. [7,46,60] The confinement of the electromagnetic wave to the vicinity of the metal/dielectric interface results in a substantial enhancement of the electromagnetic field and accounts for many useful surface-enhanced optical properties, for example increased absorption, fluorescence, Raman scattering, second-harmonic generation, and chiroptical behavior. [6,10,46,60] The RSN arrays are therefore of potential interest for a variety of plasmonic applications.…”

Selective switching of multiple plexcitons in colloidal materials: directing the energy flow at the nanoscale

“…We suggest that the peculiar behavior in the Q bands region could be attributed to the formation of plasmon nanogaps 72 where the H 2 -TPPS 2− molecules are trapped between two closely adjacent metal nanostructures. Similar geometries have already been suggested for NPs coupled to quantum dots.…”

A Programmable DNA‐Silicification‐Based Nanocavity for Single‐Molecule Plasmonic Sensing

“…[6,7] Hence, enormous efforts have been devoted to engineering plasmonic nanocavities through either cleanroom-dominated top-down or selfassembly-based bottom-up techniques, particularly by harnessing customized DNA-origami nanoassembly. [8][9][10][11][12][13][14][15][16][17][18][19] The modal properties of the plasmonic hotspots are then probed by either near-field scanning optical spectroscopy (NSOM) or high-energy electron-beam-based electron energy loss spectroscopy (EELS). [20][21][22] Despite considerable progress in the design of metallic nanoassemblies, [23] it still remains profoundly challenging to fabricate structurally resilient hierarchical plasmonic nanocavities of a few nanometers with high fidelity, which harbor intense and well-distributed plasmonic hotspots.…”

“…[ 6,7 ] Hence, enormous efforts have been devoted to engineering plasmonic nanocavities through either cleanroom‐dominated top‐down or self‐assembly‐based bottom‐up techniques, particularly by harnessing customized DNA‐origami nanoassembly. [ 8–19 ] The modal properties of the plasmonic hotspots are then probed by either near‐field scanning optical spectroscopy (NSOM) or high‐energy electron‐beam‐based electron energy loss spectroscopy (EELS). [ 20–22 ]…”