Electromagnetic enhancement surface plasmon waves

Alternatively, various analytical methods based on SPR phenomenon have been developed, including surface plasmon field-enhanced Raman scattering (SERS) [7], surface plasmon field-enhanced fluorescence spectroscopy (SPFS) [8-11], surface enhanced second harmonic generation (SHG) [12], surface enhanced infrared absorption (SEIRA) [13], surface plasmon field-enhanced diffraction spectroscopy (SPDS) [14-18], Most of these methods take advantage of the greatly enhanced electromagnetic field of surface plasmon waves, in order to excite a chromophoric molecule, e.g., a Raman molecule or a fluorescent dye. Therefore, a better sensitivity is expected. 

The surface enhancement is ascribed to the occurrence of two separate effects, electromagnetic and chemical (70). The electromagnetic effect arises from small surface structures arising in the ORC that cause strong local increases of the electric fields of the excitation and scattered radiation via surface plasmon waves. The chemical effect is attributed to interactions between the adsorbed molecule and the metal surface which lead to electronic (charge-transfer) transitions between molecule and metal. The result is a res-onance-Raman-like effect. Since both effects operate only over very small distances, SERS is specific for molecules at the electrode surface. 

The SERS electromagnetic enhancement originates from the resonance between incident radiation and electronic excitation wave on the metal surface, called surface plasmon band, as explained below. The resonance condition depends on the dielectric constant of the metal s (co) = Sj + i 2, which is a complex function of the frequency co. The enhancement factor can be expressed as ... 

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... 

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. 

Additional applications of the SPR phenomenon include using the surface plasmon electromagnetic waves to excite emission of surface-bound chromo-phores, to enhance Raman spectra (surface-enhanced Raman spectroscopy), and as surface-bound light in optical microscopy. 

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