Surface electromagnetic wave spectroscopy

Figure 10. The two prism method for surface electromagnetic wave spectroscopy as developed by Schoenwaid, Burstein, and Elson (14)...

Another interesting variant of the total reflection technique is the so-called Surface Electromagnetic Wave Spectroscopy (SEWS), which consists of the generation of a surface plasmon on a substrate by frustrated total internal reflection in a prism located a few microns from the surface. This plasmon is decoupled by a second prism. Some interesting data relating to surface modes on alumina have been reported with this technique [30]. 

SEMPA Scanning Electron Microscopy with Polarisation Analysis, 37 SERS Surface Enhanced Raman Scattering, 32 SEW Surface Electromagnetic Waves Spectroscopy, 40 SEXAFS Surface EXAFS, 49... 

Ishino, Y. and Ishida, H. (1990) Spectral simulation for infrared surface electromagnetic wave spectroscopy. Surf. ScL, 230, 299-310. 

Figure 4. A typical experimental configuration of surface electromagnetic wave propagation spectroscopy. A surface wave is launched along the surface of a metal using a coupling prism separated by an air gap. The light is coupled out to a detector through another prism.

In materials investigations surface-sensitive techniques are of special interest. The major contribution of infrared spectroscopy to this field is internal reflection spectroscopy (IRS), often called the "attenuated total reflection" (ATR) technique. To describe theory and principle, electromagnetic wave theory must be apphed [33]. 

Alternatively, various analytical methods based on SPR phenomenon have been developed, including surface plasmon field-enhanced Raman scattering (SERS) [7], surface plasmon field-enhanced fluorescence spectroscopy (SPFS) [8-11], surface enhanced second harmonic generation (SHG) [12], surface enhanced infrared absorption (SEIRA) [13], surface plasmon field-enhanced diffraction spectroscopy (SPDS) [14-18], Most of these methods take advantage of the greatly enhanced electromagnetic field of surface plasmon waves, in order to excite a chromophoric molecule, e.g., a Raman molecule or a fluorescent dye. Therefore, a better sensitivity is expected. 

At the surface of metals, the surface plasmon-polaritons, also called "surface plasmons," are not the same as the "bulk" plasmons these surface plasmons are affected (i.e., shifted slightly in energy) by monolayer adsorbates thus Surface Plasmon Resonance (SPR) spectroscopy yields information about the nature of the binding of the adsorbates onto a metal surface. The surface plasmons are excited by a p-polarized electromagnetic wave (polarized in the plane of the film) that crosses a glass medium (1), such as a prism, and is partially reflected by a metallic film (2) and back into the glass medium the dispersion relation is... 

On metal surfaces, two additional selection mles apply. The first is that only vibrations perpendicular to the surface are HREELS active. This mle follows from two phenomena unique at metal surfaces " (i) Electromagnetic waves polarized perpendicularly to the plane of incidence (parallel to the plane of the surface) undergo a 180° phase shift upon reflection. That is, at the metal surface, the out-of-phase electric-field vectors of the incident and reflected waves cancel each other as a result, no field exists that can couple with dipoles that oscillate parallel to the surface, (ii) The dynamic dipole moment generated by an oscillator that vibrates in the surface-parallel direction is cancelled by that of its image dipole (Figure 1) hence, there the net dynamic dipole moment is zero. On the other hand, if the real dipole is oriented perpendicularly to the surface, its dynamic dipole moment is reinforced by that of its image dipole. This selection mle is the same as that for infrared reflection-absorption spectroscopy (1RAS).°... 

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... 

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