Surface enhanced effects

In contrast to Raman scattering, the absorption of infrared (IR) radiation is a first-order process, and in principle a surface or an interface can generate a sufficiently strong signal to yield good IR spectra [6]. However, most solvents, in particular water, absorb strongly in the infrared. There is no special surface enhancement effect, and the signal from the interface must be separated from that of the bulk of the solution. 

The extension of continuum models to complex environments is further analyzed by Ferrarini and Corni Frediani, respectively. In the first contribution the use of PCM models in anisotropic dielectric media such as liquid crystals is presented in relation to the calculation of response properties and spectroscopies. In the second contribution, PCM formulations to account for gas-liquid or liquid-liquid interfaces, as well for the presence of a meso- or nano-scopic metal body, are presented. In the case of molecular systems close to metal bodies, particular attention is devoted to the description of the surface enhanced effects on their spectroscopic properties. 

When the phase boundary of a liquid is given by a metal, other phenomena occur. We have so far examined the case of specimens with the metal in a nanoparticle aggregation, with the opportune morphology of the metal subsystem (noble metals are more appropriate) Surface enhancement effects on the spectroscopic property of a chromophore have been evidenced, in agreement with the available experimental findings (especially for SERS, but also for other spectroscopic signals) [9]. In some experiments of this type, the metal is covered by a substance with a dielectric response differing from that of the bulk liquid, Which has also been introduced in PCM [9],... 

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. 

It is possible that surface enhancement effects, similar to the observations made earlier in metal-fluorophore systems [11, 83-85] may occur. Metal surfaces are known to have effects on fluorophores such as increasing or decreasing rates of radiative decay or resonance energy transfer. A similar effect may take place in ZnO nanomaterial platforms. However, decay lengths of fluorescence enhancement observed in the semiconducting ZnO NRs are not commensurate with the length scale seen on metals such as Au or Ag. For effective metal enhanced fluorescence, fluorophores should be placed approximately between 5-20 nm away from the metal surface. However, fluorescence enhancement effect on ZnO NRs is observed even when fluorophores are located well beyond 20 nm away from the NR surface. At the same time, no quenching effec en when they are placed directly onto ZnO NR surfaces. In addition, there overlap between the absorption and emission... 

When surface-enhanced Raman spectroscopy (SERS) was discovered in 1974 by Eleischman, Hendra, and McQuillan, it was initially attributed to a surface concentration effect rather than to a surface enhancement effect [8]. The foundations of the... 

Since the discovery of the surface enhancement effect, it has been the subject of much debate as to what the origins of the effect are. It is generally understood that there are several mechanisms which are responsible for the observed enhancement. There are two main theories electromagnetic enhancement and charge-transfer or chemical enhancement which will be mentioned only briefly here. 

Plasmonic nanostructures that are materials consisting of noble metal nanoparticles with sizes of 1-100 nm are known as specific substrates for surface enhanced Raman scattering and luminescence enhancement [1-4]. These effects are stimulated by the localized surface plasmon absorption (LSPA) and may be controlled by the change of metal nanoparticle sizes, their concentration and a substrate choice [5]. New opportunities for surface-enhanced effect realization and optimization are now discussed in connection with bimetallic nanostructures [6]. At the technological aspect one of the simplest types of a binary nanostructure is a stratified system made of two different monolayers, each is consisted of definite metal nanoparticles. The LSPA properties of these binary close-packed planar nanostructures are the subject of the paper. 

Keywords Nanophotonics Biosensors Sensors Surface plasmons Surface enhanced effects Metallic nanostructures... 

Sensing Based on Localized Surface Plasmons and Surface Enhanced Effects.89... 

The present author can only reiterate his conclusion, stated in the Introduction, based on the evaluation of theory and experiment as given above There is no one mechanism at the root of SERS however, there is a mechanism which, in the large majority of systems, is the main contributor to the surface enhancement effect. That mechanism is a resonance mechanism. It is felt there is not enough evidence, yet, to determine which of the mechanisms belonging to this group is the important one, or which can be ruled out. The LFE mechanism certainly has a role, but a more minor one. Note, however, that a minor factor in SERS is a factor of a 100 or so, which may be the difference between a detectable and a nondetectable signal ... 

We have applied these solid surface enhancement effects to the measurement of hydrogen peroxide (H2O2). In Fig. 2, the relationship between relative CL intensity and absolute amount (mole) of peroxide is shown. As Fig. 2 shows, the lowest... 

Yoshinaga T, Tanaka Y, Ichimura T, Hiratsuka H, Kobayashi M, Hoshi T. Solid surface enhancement effects on chemiluminescence diaryloxalate and polymers as media solids. J Luminescence 1998 78 221-9. 

The selection rales for SERS are essentially the same as those for the linear Raman effect However, because the local electrical field at the surface is highest in the direction normal to the surface, only vibrations perpendicular to the surface are stron y enhanced. In order to optimise the surface enhancement effect, the laser frequency has to match the frequency of a plasma resonance. A large variety of SERS substrates are reported in the literature. The most common substrates are electrodes, colloids, metal films and silver island metal films. 

This model explains why SEIRA is observed in both s- and p- polarized IRRAS [384] and ATR [391, 405] spectra and in normal-incidence transmission spectra [377] and why the enhancement is not uniformly spread over each metal island but occurs mainly on the lateral faces of the metal islands [378, 384, 385]. The quasi-static interpretation of the SEIRA also defines the material parameters necessary for excitation and observation of SPR (1) The resonance frequency determined from the general Mie condition must be as low as possible and (2) Ime((Ures) must be as small as possible. The maximum enhancement effect should be observed for the absorption bands near the Mie (resonance) frequency of the particle. As mentioned in Section 3.9.1, the resonance frequencies of metal particles lie in the visual or near-IR range. However, they can be shifted into the mid-IR range by (1) increasing the aspect ratio of the ellipsoids, (2) adding the support to an immersion medium, (3) coating the particles by a dielectric shell [24, 406], or (4) varying the optical properties of the support [24, 349, 350, 384]. As emphasized by Metiu [299], the surface enhancement effect is not restricted to metals but can also be observed for such semiconductors as SiC and InSb. 

In another work, silica nano helices have been prepared from the organic self-assemblies of -tartrate amphiphiles by sol-gel transcription. Then this chiral nanostructures were functionalized with (3-aminopropyl)-trietho)y-silane (APTES) or (3-mercaptopropyl)triethoxysilane (MPTES) and decorated with gold nanoparticles of various diameters (1-15 nm) resulting in nanohelix hybrid structures (Fig. 25). ° It was found that the surface plasmon resonance intensity of these nanohybrid systems increased with gold particle size. Gold nanoparticles of 10-14 nm diameter have clearly showed a surface enhanced effect on Raman spectroscopy. This sj tem is a unique example of the 3D hybrid network that could be used as ultrasensitive chemical and biological sensors for detection of molecules of interest in liquids by accumulation under flow. 

SERS was initially observed in 1974 [5], and in 1977 [6,7] the role of the surface enhancement effect was discovered. Since then much efforts have been concentrated to explain the phenomenon, and it was not before the beginning of the 80s when people started to realize the analytical qualities of SERS for apphed research. The SERS effect can be briefly described as up to a 10 enhancement of the Raman scattering cross section of adsorbates on the roughened metal surfaces. This enormous enhancement makes SERS to a very sensitive technique for detecting adsorbed species on metal surfaces, even in submonolayer coverage. 

In 1984, Tran [73] reported the first use of SERS identification and detection of structurally similar dyes for TLC. The separation paper was prepared for SERS detection by spraying the TLC paper with silver hydrosols after the paper had been spotted by the analyte or by adding the silver hydrosols and analyte together in a premixed solution to the paper. As noted in another 1984 publication by Tran [89], the detection levels of dyes corresponded well with their molar absortivity, thus giving a possible a priori means of determining detection limits of unstudied dyes. In this article, detection limits for various dyes varied from 0.500 to 240 ng, but only a 3-mW He-Ne laser was used for Raman excitation. Such low laser power was possible because approximately a 9-10 order-of-magnitude increase in Raman cross sections occurs as a result of the surface-enhanced effect. In addition, Rau [42] has shown the use of near-IR excitation with SERS, which further eliminates the possibility of fluorescence problems arising in TLC experiments. 

This is a really complete book that covers topics ranging from the basics of light-matter interaction through practical and theoretical methods to understand and characterize the optical response of nanoparticles and molecules, as well as their interaction and related surface enhancement effects. The theoretical description is complemented by experimental examples and applications. The book will he very useful to researchers entering the field of molecular plasmonics, particularly those who are less familiar with the basic concepts, which are usually skipped in more specialized books or reviews. "... 

The crystal violet used as a sample has an absorption band around 250 nm, originating from benzene rings in the molecular structure. The wavelength of 244 nm used for Raman excitation nearly matches the DUV absorption of crystal violet, allowing the resonance Raman spectrum to be measured. They observed a change in the resonance Raman spectral shape when the molecules were placed on aluminum, which they attributed to a manifestation of the surface enhancement effect of aluminum. 

We note that surface-enhanced infrared absorption can also be used for near-field probing of chemical constitution with a local resolution of less than 100 nm (Knoll and Kellmann 1999). In fact, fortunately one finds in many different cases, surface enhancement effects caused by the scanning tip, which should allow one to use a variety of traditionally far-field spectroscopies in the near-field regime. 

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