Localized surface plasmon resonance wave scattering

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. 

On smooth surfaces, surface plasmons exist as waves of electrons bound and confined to the metal surface. However, on a roughened metal surface, the plasmons become localized and are no longer confined and the resulting electric field can radiate both in a parallel and in a perpendicular direction. When an incident photon falls on the roughened surface, excitation of the plasmon resonance of the metal may occur, causing the electric field to be increased both parallel and perpendicular to the surface. The adsorbate is bathed in this field and the Raman scattering is amplified. This mechanism has been studied and reviewed by Weitz, Moskovits and Creighton. 

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