Plasmon-sampled surface-enhanced

Haynes CL, Van Duyne RP. Plasmon-sampled surface-enhanced Raman excitation spectroscopy. Journal of Physical Chemistry B 2003, 107, 7426-7433. 

Haynes, C. L., and Van Duyne, R. P. (2003). Plasmon-Sampled Surface-Enhanced Raman Excitation Spectroscopy. J. Phys. Chem. B, 107 7426-7433. 

Plasmon-Sampled Surface-Enhanced Raman Excitation Spectroscopy... 

The small cross sections in multiphoton processes are of course a weakness of nonlinear spectroscopy. Especially in microscopy, this problem becomes serious because of the small volume of a sample. By the use of the signal enhancement techniques, however, the disadvantage can be turned into an advantage of back-ground-free selective measurements. For example, the combined use of HRS with the plasmonic enhancement provides us a chemical imaging with nanoscale spatial resolution when a laser-illuminated metal tip is located adjacent to a sample surface, signal enhancement is locally induced near the tip. This spatial resolution is expected to overcome optical diffraction limit. Such tip-enhanced spectroscopy has already been reported in conventional CARS [15]. 

Figure 16. Raman scattering signal from A1-A lOx-4-pyridine-COOH-A g tunneling junctions with three different thicknesses of CaFs evaporated on the substrates before making the samples ("451. Thicker CaFs films have larger roughness amplitudes. The rougher Ag films couple better to surface plasmons and give larger Raman scattering enhancements.

Again, the emission pattern from a glass substrate is also shown for reference. Figure 17.18 shows the fluorescence output as a function of incidence angle for the passivated sample. At the surface-plasmon incidence angle, the total fluorescence enhancement compared to the reference is 12 (normalized to the 3.1% fill-fraction of the bottom surface of the nanoapertures), which is comparable to the enhancement obtained under full interior surface coverage (Figure 17.14). Therefore, the fluorescence enhancement (per unit area) is comparable for fluorophores on the bottom as for fluorophores on the sidewalls with backside detection, as before with individual apertures. 

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