Electrochemical Optical Spectroscopy

2 X 10 M Pb(N03)2 were added to the solution and one monolayer of lead was deposited during the potential scan from 0 to —0.5 V. As seen from the voltammogram in the inset, between 0 and —0.5 V this reaction has two different steps which correspond to different adsorption energies. This feature is also reflected in the dependence of the SPP excitation energy on the electrode potential. 

Information about the electrode-electrolyte interface can be extracted from electrochemical spectra if one establishes a correlation between its optical 

Another important point of data analysis is to find a relation between the dielectric properties of the electrode-electrolyte interface and its microscopic characteristics. A rigorous treatment of this problem is rather complex and involves large-scale computer calculations. An alternative method is to use semi-phenomenological models which relate the behavior of the dielectric tensor components to different features of the electron spectrum of the system. The mechanisms responsible for modulated electroreflectance can be classified as those arising from the modulation of the electron density in the selvedge region of the electrode (plasma electroreflectance), and from those which are due to a modulation of both interband and intraband optical transi- 

Agranovich, D.L. Mills (Eds.), Surface Polaritons, North-Holland Publishing Company, Amsterdam, 1982. 

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A.M. Brodsky, L.I. Daikhin, M.I. Urbakh, Interpretation of data on electrochemical optical spectroscopy of metals, /. Electroanal. Chem. 1984,171,1. 

Brodsky, A., Daikhin, L., and Urbakh, M. (1985). Electrochemical optical spectroscopy of metals. Uspekhy Khimie, 54 3 - 32. 

Such effects are observed inter alia when a metal is electrochemically deposited on a foreign substrate (e.g. Pb on graphite), a process which requires an additional nucleation overpotential. Thus, in cyclic voltammetry metal is deposited during the reverse scan on an identical metallic surface at thermodynamically favourable potentials, i.e. at positive values relative to the nucleation overpotential. This generates the typical trace-crossing in the current-voltage curve. Hence, Pletcher et al. also view the trace-crossing as proof of the start of the nucleation process of the polymer film, especially as it appears only in experiments with freshly polished electrodes. But this is about as far as we can go with cyclic voltammetry alone. It must be complemented by other techniques the potential step methods and optical spectroscopy have proved suitable. 

The initial stages, notably the formation of a monolayer on a foreign substrate at underpotentials, were mainly studied by classical electrochemical techniques, such as cyclic voltammetry [8, 9], potential-step experiments or impedance spectroscopy [10], and by optical spectroscopies, e.g., by differential reflectance [11-13] or electroreflectance [14] spectroscopy, in an attempt to evaluate the optical and electronic properties of thin metal overlayers as function of their thickness. Competently written reviews on the classic approach to metal deposition, which laid the basis of our present understanding and which still is indispensable for a thorough investigation of plating processes, are found in the literature [15-17]. 

Zhou Y, Itoh H, Uemura T, Naka K, Chujo Y (2002) Preparation, optical spectroscopy, and electrochemical studies of novel pi-conjugated polymer-protected stable PbS colloidal nanoparticles in a nonaqueous solution. Langmuir 18 5287-5292... 

Inspired by these Surface Science studies at the gas-solid interface, the field of electrochemical Surface Science ( Surface Electrochemistry ) has developed similar conceptual and experimental approaches to characterize electrochemical surface processes on the molecular level. Single-crystal electrode surfaces inside liquid electrolytes provide electrochemical interfaces of well-controlled structure and composition [2-9]. In addition, novel in situ surface characterization techniques, such as optical spectroscopies, X-ray scattering, and local probe imaging techniques, have become available and helped to understand electrochemical interfaces at the atomic or molecular level [10-18]. Today, Surface electrochemistry represents an important field of research that has recognized the study of chemical bonding at electrochemical interfaces as the basis for an understanding of structure-reactivity relationships and mechanistic reaction pathways. 

It must be kept in mind that nonelectrochemical techniques are also very useful for assessing electrode materials and more specially optical spectroscopy, x-ray absorption and diffusion, electron microscopy, calorimetry, and quartz crystal microbalance (see, for example, Ref. [6] for a quick insight about these techniques). They are used as a complement to the electrochemical ones. 

Refs. [i] Hoke R (2008) Surface and interface analysis an electrochemists toolbox. Springer, Berlin [ii] Tadjeddine A, Peremans A (1998) Non-linear optical spectroscopy of the electrochemical interface. In Clark RJH, Hester RE (eds) Advances in spectroscopy (spectroscopy for surface science), vol. 26. Wiley, Chichester, p 159 [iii] Shen YR (1990) In Gutierrez C, Melendres C (eds) Spectroscopic and diffraction techniques in interfacial electrochemistry (NATO ASI series C, vol. 320). Kluwer, Dordrecht, p 281 [iv] Shen YR (1986) Applications of optical second-harmonic generation to surface science. In Hall RB, Ellis AB (eds) Chemistry and structure at interfaces. VCH, Deerfield Beach, p 151 [v] Williams CT, Beattie DA (2002) SurfSci 500 545... 

Spectromicroscopy — Most optical spectroscopies probe rather large areas or volumes because the beam of light (whether infrared, UV-Vis, or X-ray etc.) probing the electrochemical interface or the electrolyte solution volume in front of the electrode (the interphase) has a finite diameter ranging from several 10 micrometers to a few millimeters or even more. Thus, spatially or locally resolved information cannot be obtained. Employing confocal or near-field optics very small surface areas can be probed, resolutions down to a few micrometers are possible. 

The need to combine conventional electrochemical measurements of electron transfer (ET) with spectroscopic probes was recognized over 40 years ago [1, 2]. It was quickly realized that optical spectroscopies, first applied to the visible... 

To bridge the gap between ideal and practical catalysts, optical spectroscopies, electron spin resonance (ESR), nuclear magnetic resonance (NMR), and Mossbauer spectroscopy can be used. All have been reviewed recently (373, 396), and some examples have been cited earlier (107, 108). Electron spin resonance has been used in several studies of electroorganic reactions (357,371). It can detect short-lived radicals resulting from electron transfer. Recent application of Mossbauer spectroscopy in situ in electrochemical cells deserves mentioning, although it addressed only the anodic polarization and film stability of Co- and Sn-coated electrodes (397,398). Extension to electrocatalytic studies involving Mossbauer nuclides seems feasible. 

Beyond these obvious roles, the spectroscopic and electrochemical signatures of metal complexes can be used to understand DNA reactivity and to detect DNA structures. In this review, efforts to exploit the redox and photophysical properties of metal complexes to understand DNA reactivity will be discussed (23, 39). Metal complexes provide a special opportunity for these studies, because they exhibit well-defined redox states that can be correlated with redox changes in nucleic acids and nucleotides. In metal complexes, changes in these redox states are coupled to changes in the optical spectroscopy of the metal center. 

Reflection spectroscopy, Raman spectroscopy, and ellipsometry complement the various electrochemical methods to study metal deposition. The optical methods can be used for a direct monitoring of the deposition process. The great advantage of optical spectroscopy... 

Fig. 8 Five optical collection modes in electrochemical Raman spectroscopy, (a) Front collection mode (b) and (c) back-scattering mode (d) and (e) internal and external ATR mode.

Tadjeddine A and Peremans A (1998) In Clark RJH and Hester RE (eds.) Non-linear Optical Spectroscopy of the Electrochemical Interface. Spectroscopy for Surface Science. London Wiley. 

Among the electrochemical techniques and characterization tools, vibrational and optical spectroscopies have been important. Electrochemical charge transfer, an important process in electrochemistry, influences not only the electronic structure of the materials but also their vibrational and optical properties, which are all dependent on the concentration of electrons and holes found in the solid. Therefore, valuable data can be obtained when electrochemistry and in situ Raman spectroscopy are applied simultaneously under the heading of spectro-electrochemistry. Such investigations have been carried out extensively on carbon nanomaterials in order to investigate the effects of electron and hole doping. 

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