Localized surface plasmon resonance local-field enhancement, metallic

Localized surface plasmon resonance (LSPR) at the metal surface has been exploited to enhance the signal obtained from optical biochips and thereby lower the limits of detection. There are two main enhancement factors (i) an increase in the excitation of the fluorophore by localizing the optical field on the nanoparticles near the fluorophore and (ii) an increase in quantum efficiency of the fluorophore. The plasmon resonance wavelength should coincide with the fluorophore absorption band to obtain the maximum emission efficiency. Several parameters concerning the signal detection enhancement are as follows (84)... 

There are two types of SERS mechanisms, which are responsible for the observation of the SERS enhancement [8] one type is the long-range EM effect and the other is the short-range CHEM effect. The EM effect is believed to be the result of localized surface plasmon resonance electric fields (hot spot) set up onto the roughened metallic surfaces [9, 10, 31]. The probe molecules residing within these hot spots will be strongly excited and subsequently emit amplified Raman... 

As already mentioned for aperture arrays, the periodicity of the structure can lead to significant local field enhancement by resonantly exciting surface plasmons. To translate this resonance effect to an isolated aperture, the metal surface surrounding the ajjerture can be structured in a periodic maiuier in order to efficiency excite the SPP. Most designs use concentric grooves around a central nanoajjerture, which is called bull s eye aperture (56, 70, 71). 

Metal nanoparticles have attracted considerable interest due to their properties and applications related to size effects, which can be appropriately studied in the framework of nanophotonics [1]. Metal nanoparticles such as silver, gold and copper can scatter light elastically with remarkable efficiency because of a collective resonance of the conduction electrons in the metal (i.e., the Dipole Plasmon Resonance or Localized Surface Plasmon Resonance). Plasmonics is quickly becoming a dominant science-based technology for the twenty-first century, with enormous potential in the fields of optical computing, novel optical devices, and more recently, biological and medical research [2]. In particular, silver nanoparticles have attracted particular interest due to their applications in fluorescence enhancement [3-5]. 

Another approach has been proposed to enhance the optical nonlinearity of semiconductor nanoclusters based on surface plasmon resonance [99,100], In the proposed method, the semiconductor nanocluster is coated with metals such as silver. The local electric field inside the cluster can be enhanced because of the surface plasmon resonance of the metal particles. The local field enhancement effect on nonresonant xl3) of CdS clusters has already been demonstrated using the third harmonic generation technique [17, 84, 85]. In this case enhancement in the local field originates from the difference in dielectric properties between the clusters and the host. The proposed enhancement of x 3) of metal-coated semiconductor nanoclusters owing to surface plasmon resonance has not been demonstrated experimentally. 

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. 

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