Plasmonic Fields Focused to Molecular Size

Abstract

Efficient use of light energy is regarded as a key factor in solving energy challenges to create a sustainable society. The highly concentrated photon energy generated by localized surface plasmon resonance excitation in the vicinity of metal nanostructures can enhance light‐matter interaction. Optimization of the interactions between plasmons and electrons in materials can lead to novel light energy applications. To overcome the current limitations for these interactions, the plasmon field must be focused to an extremely small size close to the molecular scale. Formation of the plasmonic field at the quantum limit may cause interesting phenomena with unique photoresponses. Recently, following the development of nanofabrication techniques, detailed investigations have been undertaken to understand these processes. In this focus review, we describe recent advances in the strong interactions between highly localized photons and electrons in nanomaterials, including molecules, nanocarbons, and quantized nanoparticles. First, we outline the plasmonic properties that depend on the metal nanostructures. In addition, we describe surface‐enhanced Raman scattering (SERS), which is used to detect interactions between plasmons and materials. The importance of the resonant electronic excitation process, which is a chemical effect based on the charge transfer contribution, is discussed while considering the unique molecular selectivity in SERS. We then highlight the unique photoresponse properties that are used for ultra‐sensitive detection of single molecules by the localized plasmon field. These properties are major advantages of the plasmon field. Next, we introduce strong coupling between plasmons and excitons. This coupling state is promising because of its ability to modify the intrinsic optical properties of materials via creation of a novel absorption wavelength region to accumulate the light energy. Finally, we discuss the use of plasmon excitation for effective chemical reactions accompanied by electron transfer. We conclude that reduction of light to the molecular scale would open novel routes for energy manipulation required by the next generation.

Multipolar terahertz absorption spectroscopy ignited by graphene plasmons

“…In general, multipolar absorption is inherently small because it ensues from the electromagnetic field spatial variation within the molecule 19 . However, over recent years it has been shown that such "forbidden" transitions can be accessed by the deepsubwavelength scattered field produced by graphene nanostructures [47][48][49][50][51][52][53][54][55] . Note in Figs.…”

Surface‐enhanced Raman scattering probe for molecules strongly coupled with localized surface plasmon under electrochemical potential control

“…[1][2][3] Under the excitation of the LSPR, the strong electric field forms in the vicinity of the metal nanostructure depending on the size or shape of the structure and can induce various unique chemical phenomena. [4][5][6][7] Especially, the strong coupling between the energy quanta in matter, such as the exciton, vibration, or intraband transition, and plasmons has been recognized as the important phenomena because it can modify the property of the materials in exotic way. [8][9][10][11][12][13][14] Under the formation of the strong coupling regime, the energy is coherently exchanged between electrons and plasmons showing new energy hybridized states, which are the upper and lower polaritons form.…”

In Situ Observation of Unique Bianalyte Molecular Behaviors at the Gap of a Single Metal Nanodimer Structure via Electrochemical Surface-Enhanced Raman Scattering Measurements

“…It is widely accepted that surface-enhanced Raman scattering (SERS) observation can be used as the very efficient tool for probing the molecular behavior at interfaces. − The enhancement of Raman scattering can be described as the excitation of the localized surface plasmon resonance (LSPR) at the metal nanostructures. − It has been recognized that the SERS spectrum is the result of the specific interaction between LSPR and molecules. It could be very important to discuss about the information on adsorbed states of molecules to affect the resonant electronic excitation as a result of the electronic interactions .…”