Surface plasmons excitation

Homola, J., "Thin Films Study by Means of Optically Excited Surface Plasmons, Nano 94—International Coirference on Nanometrology Scanning Probe Microscopy and Related Techniques, Proceedings, Nano 94, Bmo, Czech Rep., 1994, pp. 84-87. 

Certain roughened surfaces (Ag or Au colloids) exhibit another nice intensification of the Raman effect of 103 to 106 by exciting surface plasmons in the colloid particles this is surface-enhanced Raman, first seen by Fleischmann54, and explained by van Duyne.55 Combining resonance and surface-enhanced effects in surface-enhanced resonance Raman spectroscopy (SERRS), the Raman intensity can increase by factors as large as 1012, so that solutions of concentration down to 10 12 M can be detected. 

Studies involved with evanescent wave excited surface plasmon coupled fluorescence... 

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). 

No doubt, the present author has his own private consensus which, in spite of his efforts, may inject itself into the review. In order to offset such an undesirable bias, as much as possible, and perhaps putting the cart before the horse, the author will state here his own conclusions and beliefs I am convinced that electric field amplification and enhanced emission near SERS-active surfaces due to resonating metal excitations (surface-plasmon polaritons, plasmonlike modes, shape resonances, or electron-hole pairs) is an active mechanism in most of the systems studied. However, in most systems, this contribution, though an important one, is minor compared to the total enhancement possible in SERS. The major mechanism, in my opinion, must be a resonance mechanism, in the sense of a resonance Raman process, i.e., a mechanism by which a part of the system (molecule, molecule-metal atoms, metal surface) becomes a strong scatterer by virtue of its large resonance polarizability and not as a result of strong fields exerted by the other parts of the system . 

The application of the ATR method in Raman spectroscopy provides a unique way to study essentially mirrorlike polished metals, in particular single crystalline surfaces. The ATR method is used to excite surface plasmon polaritons (SPPs) effectively at the smooth metal surface, to improve the sensitivity in Raman spectroscopy by electromagnetic field enhancement [19]. The enhancement of the ATR configuration, as shown in Figs. 8(d and e), with respect to the normal external reflection geometry spans one to three orders, depending on the electrodes and their crystallographic orientations. 

FIGURE 21-14 Surface plasmon resonance. Laser radiation is coupled into the glass substrate coated with a thin metal film by a half-cylindrical prism. If total internal reflection occurs, an evanescent wave is generated in the medium of lower refractive Index. This wave can excite surface plasmon waves. When the angle is suitable for surface plasmon resonance, a sharp decrease in the reflected intensity is observed at the detector. 

If the internally reflecting interface is coated with a conducting material, such as a thin metal film, the p-polarized component of the evanescent wave may penetrate the metallic layer and excite surface plasmon waves. If the metal is nonmagnetic, such as a gold film, the surface plasmon wave is also p-polarized, which creates an enhanced evanescent wave. Because of the penetration of the electric field into the lower-refractive-index medium, the interaction is quite sensitive to the refractive index at the metal film surface. When the angle is suitable for surface plasmon resonance, a sharp decrease in the reflected intensity is observed, as can be seen in Figure 21-14. The resonance condition can be related to the refractive index of the metal film and can be used to measure this quantity and other properties of the surface. 

Detection of Evanescent Fields on Arachidic Acid LB Films on A1 Films Caused by Resonantly Excited Surface Plasmons... 

In an attempt to overcome this limit of detection we recently introduced surface plasmon field-enhanced fluorescence spectroscopy (SPFS) following an earlier report liy Attridge et al. The basic principle of this approach combines the excitation of a surface plasmon mode as an interfacial light source with the well-established detection schemes of fluorescence spectroscopy the resonantly excited surface plasmon waves excite chromophores that are attached to the analyte either chemically or by genetic engineering techniques. The emitted fluorescence photons are then monitored and analyzed in the usual way to give information about the behavior of the analyte itself. 

For SPR measurement the incident beam should be p-polarized (the electric vector is parallel to the plane of incidence) since s-polarized light will not excite the surface plasmon and will not decrease reflectivity at some angles of incidence. Similarly to a total internal reflection (TIR), the incident beam which excites surface plasmons creates an evanescent field. This evanescent field penetrates the medium next to the metal up to a few hundred nanometers [27-29] and can provide effective excitation of fluorophores. 

Figure 9. Geometries used for SPCE measurements. Top For SPE (Kretschmann configuration, KR). The excitation enters through the coupling prism. Bottom In reverse Kretschmann configuration, RK, the excitafitm directly reaches the sample and does not excite surface plasmons.

Problem 3.10. A light beam of wavelength A = 590 nm falls from a vacuum onto a metal surface with a sinusoidal grating of period d = 1.77 pm. The dielectric function of the metal is e(A) = —9. Find all possible angles of incidence at which light will excite surface plasmon polaritons, provided that the plane of incidence is perpendicular to the grating ruling. 

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