Localized surface plasmon resonance applications

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]. 

RECENT APPLICATIONS OF THE TUNABLE LOCALIZED SURFACE PLASMON RESONANCE... 

Surprisingly, in the 25 years since the discovery of the SERS effect, there has never been a detailed comparison of the localized surface plasmon resonance (LSPR) spectra of highly ordered, structurally well-defined, nanoparticle surfaces and the surface-enhanced Raman excitation spectra (SERES) even though they are intimately linked through the electromagnetic (EM) enhancement mechanism. There are more than 4000 papers concerning SERS and its many applications however, less than 30 of these address SERES. The paucity of SERES data in the literature is a consequence of the difficulty of SERES experiments, its typically low data point density, and, therefore, its low information content. 

Localized surface plasmon (LSP) The surface plasmon (SP) cannot propagate on the surface of metallic nanoparticles and therefore, is localized and hence known as localized surface plasmon (LSP). The LSP resonance of gold and silver NPs occurs in the visible range of the spectrum, which makes these two metals particularly useful for a number of applications ranging from ultrasensitive diagnostic tools to biosensing devices. 

It is clear from the foregoing considerations that the surface plasmon is shifted by interaction with the oscillatory modes of the adsorbed layer, and new coupled modes are introduced. In fact, the adsorbed layer substantially changes all the dielectric response properties of the substrate in accordance with Eq.(22). In consequence of this, its optical properties are modified, in particular in surface plasmon resonance experiments (as well as in all other probes). Analysis of such modifications reflect on the nature of the oscillatoiy modes of the adsorbate, which can identify it for sensing purposes. It should be noted that the determination of the screening function K (Eq.(22), for example) not only provides the shifted coupled mode spectram in terms of its frequency poles, but it also provides the relative oscillator strengths of the various modes in terms of the residues at the poles. The analytic technique employed here for the adsorbate layer (in interaction with the substrate) can be extended to multiple layers, wire- and dot-like structures, lattices of such, as well as to the case of a few localized molecular oscillators. It can also take account of spatial nonlocality, phonons, etc., and the frequencies of the shifted surface (and other) plasmon resonances can be tuned by the application of a magnetic field. 

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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