Metals Raman spectroscopy

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

Vibrational Spectroscopy. Infrared absorption spectra may be obtained using convention IR or FTIR instrumentation the catalyst may be present as a compressed disk, allowing transmission spectroscopy. If the surface area is high, there can be enough chemisorbed species for their spectra to be recorded. This approach is widely used to follow actual catalyzed reactions see, for example. Refs. 26 (metal oxide catalysts) and 27 (zeolitic catalysts). Diffuse reflectance infrared reflection spectroscopy (DRIFT S) may be used on films [e.g.. Ref. 28—Si02 films on Mo(llO)]. Laser Raman spectroscopy (e.g.. Refs. 29, 30) and infrared emission spectroscopy may give greater detail [31]. 

Al-Obaidi A H R, Rigby S J, Hegarty J N M, Bell S E J and McGarvey J J 1996 Direct formation of silver and gold metal liquid-like films (MELLFS) from thiols and sols without organic solvents SERS and AFM studies ICORS 96 XVth Int. Conf on Raman Spectroscopy ed S A Asher and P B Stein (New York Wiley) pp 590-1... 

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. 

Laser stimulation of a silver surface results in a reflected signal over a million times stronger than that of other metals. Called laser-enhanced Raman spectroscopy, this procedure is useful in catalysis. The large neutron cross section of silver (see Fig. 2), makes this element useful as a thermal neutron flux monitor for reactor surveillance programs (see Nuclearreactors). 

Raman spectroscopy has provided information on catalytically active transition metal oxide species (e. g. V, Nb, Cr, Mo, W, and Re) present on the surface of different oxide supports (e.g. alumina, titania, zirconia, niobia, and silica). The structures of the surface metal oxide species were reflected in the terminal M=0 and bridging M-O-M vibrations. The location of the surface metal oxide species on the oxide supports was determined by monitoring the specific surface hydroxyls of the support that were being titrated. The surface coverage of the metal oxide species on the oxide supports could be quantitatively obtained, because at monolayer coverage all the reactive surface hydroxyls were titrated and additional metal oxide resulted in the formation of crystalline metal oxide particles. The nature of surface Lewis and Bronsted acid sites in supported metal oxide catalysts has been determined by adsorbing probe mole-... 

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. 

Today we have some understanding of the first lithium intercalation step into carbon and of the processes taking place on the lithium metal anode. A combination of a variety of analytical tools including di-latometry, STM, AFM, XPS, EDS, SEM, XRD, QCMB, FTIR, NMR, EPR, Raman spectroscopy, and DSC is needed in order to understand better the processes occurring at the anode/electrolyte interphase. This understanding is crucial for the development of safer and better lithium-based batteries. 

Many of the compounds in higher oxidation states are reactive, and for moisture-sensitive solids that cannot be crystallized, some of the bond lengths quoted in Table 2.1 are from EXAFS measurements [24], Raman spectroscopy is likewise well suited to studying such reactive compounds, and vibrational data for halometallates are given in Table 2.2 trends illustrated include the decrease in frequency as the oxidation state of the metal decreases, and similarly a decrease in vibrational frequency, for a given oxidation state, with increasing mass of the halogen. 

Of special Interest as O2 reduction electrocatalysts are the transition metal macrocycles In the form of layers adsorptlvely attached, chemically bonded or simply physically deposited on an electrode substrate Some of these complexes catalyze the 4-electron reduction of O2 to H2O or 0H while others catalyze principally the 2-electron reduction to the peroxide and/or the peroxide elimination reactions. Various situ spectroscopic techniques have been used to examine the state of these transition metal macrocycle layers on carbon, graphite and metal substrates under various electrochemical conditions. These techniques have Included (a) visible reflectance spectroscopy (b) laser Raman spectroscopy, utilizing surface enhanced Raman scattering and resonant Raman and (c) Mossbauer spectroscopy. This paper will focus on principally the cobalt and Iron phthalocyanlnes and porphyrins. 

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., In situ Raman spectroscopy at metal electrodes, in Adsorption of Molecules at Metal Electrodes, 1. Lipkowski and P. N. Ross, Eds., VCH, New York, 1992, p. 285. 

The combination of atomic force microscopy (AFM) and Raman spectroscopy is another approach to attain high spatial resolution. AFM also employs a sharp tip close to a sample surface. When the tip is made of metal and light is irradiated onto the tip and surface, Raman scattering is largely enhanced. In this way, a spatial resolution of 15 nm is achieved [2]. 

STM-Raman spectroscopy utilizes the effect that Raman scattering is enhanced for a molecule in the vicinity of a metal nanostructure. This enhancement effect is generally called surface-enhanced Raman scattering (SERS). When a sharp scanning probe, such as a tunneling tip for STM, is used as a metal nanostructure to enhance Raman intensity, it is called tip-enhanced Raman scattering (TERS). The concept of STM combined with Raman spectroscopy is presented in Figure 1.1. 

Pettinger, B., Picardi, G., Schuster, R. and Ertl, G. (2002) Surface-enhanced and STM-Tip-enhanced Raman spectroscopy at metal surfaces. Single Mol., 5-6, 285—294. 

In 1994, we proposed that a metallic needle having a nano-tip at its apex be employed as a nano-light-source for microscopy attaining nanometric spatial resolution [2]. Later, we expanded the technique to Raman spectroscopy for molecular nano-identification, nano-analysis and nano-imaging. In this chapter, we give a brief introduction to local plasmons and microscopy using a metallic nano-needle to produce the local plasmons. Then, we describe the microscope that we built and... 

A nano-light-source generated on the metallic nano-tip induces a variety of optical phenomena in a nano-volume. Hence, nano-analysis, nano-identification and nanoimaging are achieved by combining the near-field technique with many kinds of spectroscopy. The use of a metallic nano-tip applied to nanoscale spectroscopy, for example, Raman spectroscopy [9], two-photon fluorescence spectroscopy [13] and infrared absorption spectroscopy [14], was reported in 1999. We have incorporated Raman spectroscopy with tip-enhanced near-field microscopy for the direct observation of molecules. In this section, we will give a brief introduction to Raman spectroscopy and demonstrate our experimental nano-Raman spectroscopy and imaging results. Furthermore, we will describe the improvement of spatial resolution... 

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. 

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