Surface plasmon resonance dielectric constant

Surface plasmons, also known as surface plasmon polaritons or packets of electrons, are surface electromagnetic waves that propagate parallel along a metal-dielectric interface [69,70], Surface plasmons exist where the complex dielectric constants of the two media are of opposite sign. The excitation of surface plasmons by light of a wavelength matching the resonant frequency of the electrons is termed surface plasmon resonance (SPR) for planar surfaces and localized surface plasmon resonance where nanometer-sized metallic structures are concerned [71,72],... 

The field reaches its maximum at the surface plasmon resonance frequency when e = -2 Co where Co is the dielectric constant of the medium surrounding the particle surface. This induced field of the metallic nanoparticies provides an external field for the fluorescence excitation of the molecules in addition to the electric field of the incident light and thus increases the absorption rate which is responsible for the enhanced fluorescence intensity. 

In Chap. 1 by J. Homola of this volume [1] surface plasmons were introduced as modes of dielectric/metal planar waveguides and their properties were estabhshed. It was demonstrated that the propagation constant of a surface plasmon is sensitive to variations in the refractive index at the surface of a metal film supporting the surface plasmon. In this chapter, it is shown how this phenomenon can be used to create a sensing device. The concept of optical sensors based on surface plasmons, commonly referred as to surface plasmon resonance (SPR) sensors, is described and the main approaches to SPR sensing are presented. In addition, the concept of affinity biosensors is introduced and the main performance characteristics of SPR biosensors are defined. 

In addition to the plasmon resonance displayed by AuNPs, gold films also exhibit a surface plasmon resonance (SPR) that fluctuates in response to surface-bound molecules. Using SPR, surface-sensitive analytical techniques have been designed based on the ability of SPR to detect changes in the dielectric constant induced by molecular adsorption onto the metal surface. SPR has been used for the detection of a variety of... 

The ultraviolet (UV) - visible spectrophotometer is another important tool in the characterisation of vegetable oil-based polymer nanocomposites and is particularly effective for metal nanocomposites. The formation of metal nanoparticles in the matrix can be easily detected by UV-visible spectroscopy. Every metal nanoparticle has its own characteristic surface plasmon resonance value. This band is attributed to the collective oscillation of electron gas in the nanoparticles, with a periodic change in the electronic density at the surface. Parameters such as particle size, shape and dielectric constant of the medium and surface adsorbed species determine the position and shape of the plasmon absorption. When the particles become significantly smaller than the mean free path of electrons in the bulk metal, the plasmon oscillation is dampened. The plasmon absorption peak shifts to a higher wavelength than expected with an increase in aggregation of the nanoparticles. The sharpness of the peak indicates the narrow size distribution. 

Another area of growing importance in optical sensing is the surface plasmon resonance (SPR). This technique makes use of the surface plasma wave (SPW) that may exist at the interface of two media with dielectric constants of opposite signs, e.g., a metal and a dielectric. The excitation of the SPW by... 

Optical techniques can be used to monitor optical thickness and dielectric constant parameters. This includes ellipsometry, multiple reflection interferometry (74), evanescent wave (75), and surface plasmon resonance spectroscopy techniques (43). Ellipsometry has been used widely and routinely to investigate film thickness of pol3mier brush films (76). For optical properties of films, it is important that the average film roughness and imiformity is specified. Often, sampling is localized by the spot size, such that it is necessary to probe and average different areas of a sample. 

Mahmoud MA, Chamanzar M, Adihi A, El-Sayed MA. Effect of the dielectric constant of the surrounding medium and the substrate on the surface plasmon resonance spectrum and sensitivity factors of highly symmetric systems silver nanocubes. J Am Chem Soc 2012 134 6434-6442. 

Figure 6.3. Schematic of the surface plasmon resonance (SPR) technique for the study of SAM structures changes in the inter-phase dielectric constant produce shifts in the angle of minimum reflectivity...

Optical waveguide lightmode spectroscopy and surface plasmon resonance spectroscopy can also be used to measure the rate of absorption, besides optical film thickness, dielectric constant, and anisotropy. 

By means of this combination of the cross section for an ellipsoid with the Drude dielectric function we arrive at resonance absorption where there is no comparable structure in the bulk metal absorption. The absorption cross section is a maximum at co = ojs and falls to approximately one-half its maximum value at the frequencies = us y/2 (provided that v2 ). That is, the surface mode frequency is us or, in quantum-mechanical language, the surface plasmon energy is hcos. We have assumed that the dielectric function of the surrounding medium is constant or weakly dependent on frequency. 

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