Localized surface plasmon resonance electromagnetic fields

In recent years, it has become accepted within the SERS community that hot spots primarily arise from intense and highly localized electromagnetic fields caused by local surface plasmon resonances (LSPR). However, questions over the precise magnitude of the enhancement present at such locations have led some to suggest that there must be a chemical aspect to hot spots. In this section, the key results from recent work focusing on the fundamentals of hot spots with regard to these two components are summarized. 

For centuries, metal nanoparticles have never ceased to attract scientists and artists from many diverse cultures. In this section we briefly introduce a phenomenon of metal nanoparticles that still inspires scientists localized surface plasmon resonance (LSPR) (Hutter and Fendler, 2004). Metal nanoparticles show nonlinear electronic transport (single-electron transport of Coulomb blockade) and nonlinear/ultrafast optical response due to the SPR. Conduction electrons (—) and ionic cores (-F) in a metal form a plasma state. When external electric fields (i.e., electromagnetic waves, electron beams etc.) are applied to a metal, electrons move so as to screen perturbed charge distribution, move beyond the neutral states, return to the neutral states, and so on. This collective motion of electrons is called a plasma oscillation. SPR is a collective excitation mode of the plasma localized near the surface. Electrons confined in a nanoparticle conform the LSPR mode. The resonance frequency of the surface plasmon is different... 

Metal nanocrystals also interact strongly with electromagnetic waves and offer remarkable properties due to the localized surface plasmon resonance (SPR) that induces, through optical excitation, very intense local electrical fields. This property can be exploited for surface-enhanced Raman spectroscopy (SERS) and SPR-based... 

Metal nanostructures (such as particles and apertures) can permit local resonances in the optical properties. These local resonances are referred to as localized surface plasmons (LSPs). The simplest version of the LSP resonance comes for a spherical nanoparticle, where the electromagnetic phase-retardation can be neglected in the quasi-static approximation, so that the electric field inside the particle is uniform and given by the usual electrostatic solution [3] ... 

As the simplest nanoantennas, plasmonic nanoparticles can be utilized to enhance the absorption within thin-film solar cells [243]. They couple incoming waves with the localized SPP field, have increased scattering cross-section and strongly localize electromagnetic field just in the thin active region of the detector. Fig. 2.62. The same principle is applicable for infrared detection [321]. This cannot be done with pure noble metal nanoparticles since their surface plasmon resonance is in ultraviolet or visible part of the spectrum. Because of that their response must be redshifted. In this part, two approaches to such redshifting are described. 

---