Electrode SERS

Surface enhanced Raman signals from the electrode can be observed using different pretreatment procedures  

A demonstration of the advantage of high sensitivity in SERS spectroscopy is given in Fig. 3. This figure displays the SERS spectrum of the DNA base cytosine The laser power used to excite the sample was only 10 mW at 514.5 nm from an argon ion laser. An important observation is that the band positions obtained in SERS spectra are essentially the same as in NSRS spectra. The largest frequency shift 

NRS spectrum of cytosine (below). Conditions laser excitation hne 

1) The oxidation of the Ag electrode Ag - Ag + e where the amount of Ag oxidation is monitored by the total charge passed through the electrode. 

2) During the reduction half cycle, a roughened silver surface is reformed by Ag -I- e Ag°. Scanning electron microscopy (SEM) of electrode surfaces after this oxidation-reduction procedure have revealed that the initially smooth surfaces have acquired bumps on the scale of 25 to 500 nm These bumps can be approximated as speres, hemispheres and prolate spheroids 

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Surface-enhanced Raman scattering (SERS) has emerged as a powerful technique for studying species adsorbed on metal films, colloidal dispersions, and working electrodes. SERS occurs when molecules are adsorbed on certain metal surfaces, where Raman intensity enhancements of ca. 105-106 may be observed. The enhancement is primarily due to plasmon excitation at the metal surface, thus the effect is limited to Cu, Ag, and Au, and a few other metals for which surface plasmons are excited by visible radiation. 

Absorbates, effect of surface interaction, 138 Absorption at electrodes, SERS monitoring, 135—1 7 Absorption spectra... 

Electrochemical performance of Ag electrode SERS study of passivating film on Ag electrode in lithium batteries... 

Micro-electrode/SERS spectra were obtained with an Instrument S. A. MOLE-S-3000 spectrometer. The MOLE-S-3000 is a new, fully computerized, triple spectrometer system with multichaimel (E-IRY 1024) acquisition of data. The excitation sources were the lines of an argon-ion laser or an He-Ne laser (Spectra physics, model 2020-03 and 127). The actual laser focus used in... 

To illustrate the high sensitivity of SERS spectroscopy we have selected the guanine molecule, because this molecule has a very low solubility in H2O (5 x 10 g in 100 g H2O). Therefore, under these conditions it is impossible to obtain a normal Raman spectrum of this important molecule in biochemical research. But by means of electrode SERS-spectroscopy such a very insoluble molecule shows a very strong vibration spectrum (cf. Figure 1). Thus, SERS spectroscopy opened up a new field of vibration spectroscopy for very low solubility molecules in water. 

Another striking feature of the electrode SERS spectra of N-methylated guanines is the dependence of the carbonyl stretching vibration on the site of methylation. In Table 1 it is observed that the SERS spectra of 9-Me-Gua and 3-Me-Gua depart substantially from the spectra of 1-Me-Gua and 7-Me-Gua in the 1700 cm region (the Ce=0 stretching vibration is missing in the 3-Me-Gua and 9-Me-Gua spectra). 

The substrate is, of course, a necessary component of any SERS experiment. A wide variety of substrate surfaces have been prepared for SERS studies by an equally wide range of teclmiques [ ]. Two important substrates are electrocheniically prepared electrodes and colloidal surfaces (either deposited or in solution). 

The first SERS experiments were performed with electrochemically roughened electrodes and metal colloids, and many other types of suitable SERS substrates are known - e.g. metal island films, metal films over nanoparticles (see Fig. 4.58, below) or rough substrates, gratings, and sputter-deposited metal particles. 

Because silver, gold and copper electrodes are easily activated for SERS by roughening by use of reduction-oxidation cycles, SERS has been widely applied in electrochemistry to monitor the adsorption, orientation, and reactions of molecules at those electrodes in-situ. Special cells for SERS spectroelectrochemistry have been manufactured from chemically resistant materials and with a working electrode accessible to the laser radiation. The versatility of such a cell has been demonstrated in electrochemical reactions of corrosive, moisture-sensitive materials such as oxyhalide electrolytes [4.299]. 

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... 

S. Boghosian, S. Bebelis, C.G. Vayenas, and G.N. Papatheodorou, In Situ High Temperature SERS on Ag Catalysts and Electrodes during Ethylene Epoxidation, J. Catal. 117,561-565 (1989). 

L. Basini, C.A. Cavalca, and G.L. Haller, Electrochemical Promotion of Oxygen Atom Back-Spillover from Yttria-Stabilized Zirconia onto a Porous Platinum Electrode Detection of SERS Signals,/. Phys. Chem. 98, 10853-10856 (1994). 

Since its discovery, SERS has received attention both from theoretical and experimental viewpoints (13). The large enhancement has been observed only for certain metals such as Ag, Cu and Au. The enhancement mechanism Is not quantitatively understood. Even so, very useful Information concerning adsorbed species of some electrode surfaces can be obtained In-sltu with this effect. With... 

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., 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. 

Love B, Lipkowski J. 1988. Effect of surface crystallography on electrocatalytic oxidation of carbon monoxide on Pt electrodes. ACS Symp Ser 378 484. 

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