Related Enhanced Techniques

Plasmon-assisted RS can operate in different modalities depicted in Eig. 3.17. The first modality is represented by bare Au NPs deposited as a film on a solid support and the molecules to be probed are in direct contact with the metal surface (Pig. 3.17a). This contact mode also applies to transition metal-coated NPs (Pig. 3.17b), which extend the SERS application to other wavelength regions and transition-metal catalyzed reactions. In contrast, tip-enhanced Raman scattering (TERS) operates in a noncontact mode the Au tip, acting as the Raman signal amplifier and the probed molecules on the surface are separated from each other (Pig. 3.17c). With this powerful approach of chemical imaging at the nanometre scale, any substrate can be probed without additional constraints on material composition and surface topography. 

Interaction of an EM field with a nanostructured metal surface also strongly influences other optical phenomena, namely absorption and luminescence. Surface-enhanced infrared absorption (SEIRA) of monolayers of benzoic acids on thin Ag island films was first observed in 1980s (Hartstein et al. 1980). The EM mechanisms is attributed to a local field enhancement and, correspondingly, to an enhancement of the absorption cross-section. Absorption can be enhanced generally by a factor of 10 -10 (Osawa 2001 Aroca 2006) and SEIRA is used as a complementary technique to SERS in some cases (Aroca 2006). 

Fluorescence (which is a special case of luminescence) in the vicinity of plas-monic metal can be both surface-enhanced and surface-quenched (Weitz et al. 1983). The fluorescence is a stepwise process involving first absorption which is enhanced by EM mechanism. For the second step (emission), the presence of metal 

3 Basics of Surface-Enhanced Raman Scattering (SERS) 

Abdelsalam, P.N. Bartlett, J.J. Baumberg, S. Cintra, T.A. Keif, A.E. Russell, Electrochemical SERS at a structured gold surface. Electrochem. Comm. 7, 740 (2005) 

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The data matrix is preprocessed using any signal enhancement technique to obtain the spectroscopic data of greatest interest as it relates to the spatial characteristics of the material or sample surface under study. In this particular case each data point represents the absorbance difference between a no absorbing wavelength for the paper surface and an absorbing wavelength for the transparent ink added to the paper. The difference in... 

In the neck, time of flight techniques are preferred over phase contrast techniques due to the longer scan times of phase contrast techniques needed to provide the same coverage and spatial resolution. 2D TOF MRA provides superior flow-related enhancement and allows coverage of the entire neck. Compared to 2D TOF MRA, 3D TOF MRA provides superior spatial resolution and is less susceptible to phase dispersion artifacts, but is more susceptible to saturation effects and cannot cover a large area. 3D TOF flight techniqnes are, therefore, used to delineate the carotid bifurcation only. 2D PC techniques are used to evaluate flow direction in the vertebral arteries when subclavian steal is... 

Over the past 60 years, a great deal of applied and theoretical research has been carried out on both polymer and surfactant DRAs because of their potential useful applications and the influence of the additives on both turbulent structure and rheology. Important results include the identification of maximum drag reduction asymptotes (MDRAs) both Virk s MDRA for polymer solutions [Virk et al., 1970 see Eq. (2.5)] and Zakin et al. s MDRA for surfactant solutions [Zakin et al., 1996 see Eq. (2.6)], relating solution nanostructures and rheological properties to macroscopic DR phenomena hypotheses on the influence of DRAs on turbulent structures, mechanisms for turbulent drag reduction, developing heat transfer enhancement techniques, and so on. 

On the topics of solute-solvent and solute-solute clustering, there is a significant number of publications by research groups from around the world, demonstrating the tremendous interest of the international research community. This chapter is a review of representative literature results, especially those based on molecular spectroscopy and related experimental techniques. Discussion of the fundamental properties of supercritical fluids will be within the context of enhanced solute-solvent and solute-solute interactions in supercritical fluid solutions, and the current understanding of the reasonably well-established solute-solvent clustering model and the somewhat controversial solute-solute clustering concept will be presented. 

In principle, the nonmining recovery of bitumen from tar sand deposits is an enhanced oil recovery technique and requires the injection of a fluid into the formation through an injection weU. This leads to the in situ displacement of the bitumen from the reservoir and bitumen production at the surface through an egress (production) weU. There are, however, several serious constraints that are particularly important and relate to the bulk properties of the tar sand and the bitumen. In fact, both recovery by fluid injection and the serious constraints on it must be considered in toto in the context of bitumen recovery by nonmining techniques (see PETROLEUM, ENHANCED OIL RECOVERY). 

As an example, PL can be used to precisely measure the alloy composition xof a number of direct-gap III-V semiconductor compounds such as Alj Gai j, Inj Gai jfAs, and GaAsjfPj j(, since the band gap is directly related to x. This is possible in extremely thin layers that would be difficult to measure by other techniques. A calibration curve of composition versus band gap is used for quantification. Cooling the sample to cryogenic temperatures can narrow the peaks and enhance the precision. A precision of 1 meV in bandgap peak position corresponds to a value of 0.001 for xin AljfGai j, which may be usefiil for comparative purposes even if it exceeds the accuracy of the x-versus-bandgap calibration. 

Solid-surface room-temperature phosphorescence (RTF) is a relatively new technique which has been used for organic trace analysis in several fields. However, the fundamental interactions needed for RTF are only partly understood. To clarify some of the interactions required for strong RTF, organic compounds adsorbed on several surfaces are being studied. Fluorescence quantum yield values, phosphorescence quantum yield values, and phosphorescence lifetime values were obtained for model compounds adsorbed on sodiiun acetate-sodium chloride mixtures and on a-cyclodextrin-sodium chloride mixtures. With the data obtained, the triplet formation efficiency and some of the rate constants related to the luminescence processes were calculated. This information clarified several of the interactions responsible for RTF from organic compounds adsorbed on sodium acetate-sodium chloride and a-cyclodextrin-sodium chloride mixtures. Work with silica gel chromatoplates has involved studying the effects of moisture, gases, and various solvents on the fluorescence and phosphorescence intensities. The net result of the study has been to improve the experimental conditions for enhanced sensitivity and selectivity in solid-surface luminescence analysis. 

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