Raman spectroscopy surface-enhanced

Surface-enhanced Raman spectroscopy or surface-enhanced Raman scattering (SERS) is another technique for obtaining strong Raman signals from surfaces and interfaces, including 

First excited electronic state with 4 vibratioiml levels shown 

Ground electronic state with 4 vibrational levels shown 

Preparing metal surfaces requires expertise and can be expensive. Commercial sources for SERS substrates, colloids, and sample holders are available from companies such as Thermo Fisher Scientific, Renishaw, and Real-Time Analyzers (www.rta.biz), which focuses on high-throughput needs with SERS 96 well plates. 

More than 30 years ago, the phenomenon known as surface-enhanced Raman scattering (SERS) was predicted [16], discovered [17], and identified [18]. The literature on this subject is dominated by reports of research aimed at elucidating the details of the mechanism by which the Raman cross section of a molecule located next to the surface of a particle of gold or silver is increased as much as 1 million times [19-21]. Significantly fewer publications describe the investigation and 

Real-Time Analyzers has developed a compact FT-Raman spectrometer weighing about 15 kg that allows this SERS technology to be applied to measurements of analytes such as methyl phosphonic acid (the hydrolysis product of the nerve agents), cyanide ion, pesticides, the DNA bases, cocaine, and several barbiturates all in water, while uric acid and creatinine have been measured in urine. The interferometer in this instrument is the same as the one shown in Figme 5.15 and is equipped with a quartz beamsplitter. The Nd YVO4 laser emits at 1064 nm and the detector is TE-cooled InGaAs. 

Benner, and L. Smith, Continuous lasers for Raman spectrometry, in Handbook of Vibrational Spectroscopy, J. C. Chalmers and P. R. Griffiths, Eds., Wiley, Chichester, West Sussex, England, 2002, Vol. 1, p. 490. 

When monochromatic light passes through a group of molecules, a very small porhon of that light will shift its wavelength due to an interaction with different vibrational modes of the molecules. This type of light-molecule interaction phenomenon is known as Raman scattering. Like IRAS, the locations of the Raman 

A summary of the different nanodiagnostics techniques is presented in Table 5.1. 

SPR White light Reflection wavelength Nanoparticles Recognition agent required 

LSPR White light Absorbance Nanoparticles Nanoparticle surfaces Recognition agent required 

MEF Laser Fluorescence Nanoparticle surfaces Fractal structures Nanostructure arrays Recognition agent required 

Vibrational spectroscopies such as Raman and infrared are useful methods for the identification of chemical species. Raman scattering [4] is a second-order process, and the intensities are comparatively low. A quick estimate shows that normal Raman signals generated by species at a surface or an interface are too low to be observable. Furthermore, in the electrochemical situation Raman signals from the interface may be obscured by signals from the bulk of the electrolyte, a problem that also occurs in electrochemical infrared spectroscopy (see Section 15.3) 

Fortunately, in favorable cases enhancement mechanisms operate which increase the signal from the interface by a factor of 105 — 106, so that spectra of good quality can be observed - hence the name surface-enhanced Raman spectroscopy (SERS). However, these mechanisms seem to operate only on metals with broad free-electron-like bands, in particular on the sp metals copper, silver and gold. Furthermore, the electrodes must be roughened on a microscopic scale. These conditions severely limit the applicability of Raman spectroscopy to electrochemical interfaces. Nevertheless, SERS is a fascinating phenomenon, and though not universally applicable, it can yield valuable information on many interesting systems, and its usefulness is expected to increase as instrumentation and preparation techniques improve. 

The necessary roughening of the electrodes is usually produced by oxidation-reduction cycles. For this purpose the electrode surface is first oxidized, so that metal cations or poorly soluble salts like AgCl 

The other mechanism involves atomic-size roughness (i.e., single adatoms or small adatom clusters), and is caused by electronic transitions between the metal and the adsorbate. One of the possible mechanisms, photoassisted metal to adsorbate charge transfer, is illustrated in Fig. 15.4. It depends on the presence of a vacant, broadened adsorbate orbital above the Fermi level of the metal (cf. Chapter 3). In this process the incident photon of frequency cjq excites an electron in the metal, which subsequently undergoes a virtual transition to the adsorbate orbital, where it excites a molecular vibration of frequency lj. When the electron returns to the Fermi level of the metal, a photon of frequency (u o — us) is emitted. The presence of the metal adatoms enhances the metal-adsorbate interaction, and hence increases the cross 

Though the existence of these enhancement mechanisms is well established, their details are not well understood, and await further clarification. 

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SERS Surface-enhanced Raman spectroscopy [214-217] Same as RS but with roughened metal (usually silver) substrate Greatly enhanced intensity... 

See Refs. 80 and 81 for other examples. Surface-enhanced Raman spectroscopy is discussed in Section XVI-4C. 

Freunscht P, Van Duyne R P and Schneider S 1997 Surface-enhanced Raman spectroscopy of trans-stilbene adsorbed on platinum- or self-assembled monolayer-modified silver film over nanosphere surfaces Chem. Phys. Lett. 281 372-8... 

Nie S and Emory S R 1997 Near-field surface-enhanced Raman spectroscopy on single silver nanoparticles Anal. Chem. 69 2631-5... 

Ruperez A and Laserna J J 1996 Surface-enhanced Raman spectroscopy Modern Techniques in Raman Spectroscopy ed J J Laserna (New York Wley) pp 227-64... 

Zeisel D, Deckert V, Zenobi R and Vo-Dinh T 1998 Near-field surface-enhanced Raman spectroscopy of dye molecules adsorbed on silver island films Chem. Phys. Lett. 283 381... 

Michaels A M, Nirmal M and Brus L E 1999 Surface enhanced Raman spectroscopy of individual rhodamine 6G molecules on large Ag nanocrystals J. Am. Chem. See. 121 9932-9... 

MOLE, however, is more sensitive than ETIR (<1 samples compared to about 100 p.m ). With surface-enhanced Raman spectroscopy the Raman signal is enhanced by several orders of magnitude. This requires that the sample be absorbed on a metal surface (eg, Ag, Cu, or Au). It also yields sophisticated characterization data for the polytypes of siUcon carbide, graphite, etc. 

Intensity enhancement takes place on rough silver surfaces. Under such conditions, Raman scattering can be measured from monolayers of molecular substances adsorbed on the silver (pyridine was the original test case), a technique known as surface-enhanced Raman spectroscopy. More recendy it has been found that sur-fiice enhancement also occurs when a thin layer of silver is sputtered onto a solid sample and the Raman scattering is observed through the silver. 

Recent developments in the mechanisms of corrosion inhibition have been discussed in reviews dealing with acid solutions " and neutral solu-tions - . Novel and improved experimental techniques, e.g. surface enhanced Raman spectroscopy , infrared spectroscopy. Auger electron spectroscopyX-ray photoelectron spectroscopyand a.c. impedance analysis have been used to study the adsorption, interaction and reaction of inhibitors at metal surfaces. 

QCMB RAM SBR SEI SEM SERS SFL SHE SLI SNIFTIRS quartz crystal microbalance rechargeable alkaline manganese dioxide-zinc styrene-butadiene rubber solid electrolyte interphase scanning electron microscopy surface enhanced Raman spectroscopy sulfolane-based electrolyte standard hydrogen electrode starter-light-ignition subtractively normalized interfacial Fourier transform infrared... 

Substituted 2-naphthols, as azo coupling components 356ff., 362 Sulfanilic acid 14, 71 Sulfidomolybdenum dimer anion, complex with diazonium ions 117 Surface-enhanced Raman spectroscopy 280... 

AC Impedance spectroscopy, 237 Auger electron spectroscopy, AES, 254 High resolution electron energy loss spectroscopy, HREELS, 43, 69 Infrared spectroscopy, IRS, 39, 69 Surface enhanced Raman spectroscopy, SERS, 256... 

The physical methods mostly require ultra high vacuum conditions having the disadvantage of not being applicable directly to solvent swollen films, but recent developments of in situ measurements in SIMS X-ray diffraction surface enhanced Raman spectroscopy (SERS) and scanning electrochemical tunneling microscopy... 

Well-defined CdS/CdSe superlattices have been formed by means of ECALE [74]. In these structures the CdS component - and not CdSe - suffered from substantial crystallographic strain as was evidenced by surface-enhanced Raman spectroscopy (SERS) - a valuable tool for characterizing the superlattice phonons in electrochemical or other ambient environments. Torimoto et al. reported quantum confinement in superlattices of ZnS/CdS grown by ECALE [75]. 

Zou S, Weaver MJ (1999) Surface-enhanced Raman spectroscopy of cadmium sulfide/cadmium selenide superlattices formed on gold by electrochemical atomic-layer epitaxy. Chem Phys Lett 312 101-107... 

Surface Enhanced Raman Spectroscopy" Chang, R.K. Furtak, T. E., Eds. Plenum Press New York, 1982. 

Possible applications include optical coatings [98], catalysts [99-101], substrates for Surface Enhanced Raman spectroscopy [102] or biosensor electrodes [103], Mesoporous gold can be prepared by de-aHoying a suitable precursor such as a... 

Fedchenfeld, H. and Weaver, M.J. (1989) Binding of alkynes to silver, gold, and underpotential deposited silver electrodes as deduced by surface-enhanced Raman spectroscopy. The Journal of Physical Chemistry, 93, 4276—4282. 

In most work on electrochemical systems, use is made of two effects that greatly enhance the Raman signals. One is resonance Raman spectroscopy (RRS), wherein the excitation wavelength corresponds to an electronic transition in an adsorbed molecule on an electrode surface. The other effect is surface-enhanced Raman spectroscopy (SERS), which occurs on certain surfaces, such as electrochemically roughened silver and gold. This effect, discovered by Fleischmann et al. (1974), yields enhancements of 10 to 10 . The vast majority of publications on Raman studies of electrochemical systems use SERS. The limitations of SERS are that it occurs on only a few metals and the mechanism of the enhancement is not understood. There is speculation that only a small part of the surface is involved in the effect. There is a very good review of SERS (Pemberton, 1991). 

Pettinger, B., Picardi, G., Schuster, R. and Ertl, G. (2000) Surface enhanced Raman spectroscopy towards single molecule spectroscopy. Electrochemistry, 68, 942-949. 

Interfacial water molecules play important roles in many physical, chemical and biological processes. A molecular-level understanding of the structural arrangement of water molecules at electrode/electrolyte solution interfaces is one of the most important issues in electrochemistry. The presence of oriented water molecules, induced by interactions between water dipoles and electrode and by the strong electric field within the double layer has been proposed [39-41]. It has also been proposed that water molecules are present at electrode surfaces in the form of clusters [42, 43]. Despite the numerous studies on the structure of water at metal electrode surfaces using various techniques such as surface enhanced Raman spectroscopy [44, 45], surface infrared spectroscopy [46, 47[, surface enhanced infrared spectroscopy [7, 8] and X-ray diffraction [48, 49[, the exact nature of the structure of water at an electrode/solution interface is still not fully understood. 

Pettinger, B., Philpott, M. R. and Gordon, J. G. (1981) Contribution of specifically adsorbed ions, water, and impurities to the surface enhanced Raman spectroscopy (SERS) of Ag electrodes. 

Weaver MJ. 2002. Surface-enhanced Raman spectroscopy as a versatile in situ probe of chemisorption in catalytic electrochemical and gaseous environments. J Raman Spectrosc 33 309. 

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