Optical properties, spectroscopy electroreflectance

Kolb and Franke have demonstrated how surface reconstruction phenomena can be studied in situ with the help of potential-induced surface states using electroreflectance (ER) spectroscopy.449,488,543,544 The optical properties of reconstructed and unreconstructed Au(100) have been found to be remarkably different. In recent model calculations it was shown that the accumulation of negative charges at a metal surface favors surface reconstruction because the increased sp-electron density at the surface gives rise to an increased compressive stress between surface atoms, forcing them into a densely packed structure.532... 

Specular reflection spectroscopy has been actively used in in situ studies of the formation and optical behaviour of monolayer films on surfaces, and for detecting intermediates and products of heterogeneous chemical and electrochemical reactions. The vibrational spectra of the adsorbed species at electrode surfaces are obtained by surface-enhanced Raman scattering and infrared reflectance spectroscopies. Since the mid-1960s, modulated reflection spectroscopy techniques have been employed in elucidating the optical properties and band structure of solids. In the semiconductor electroreflectance, the reflectance change at the semiconductor surface caused by the perturbation of the dielectric properties of... 

Valence Band Spectroscopy. Optical and electronic properties of UPD metal flms on metal electrodes have been studied in situ by means of differential- and electroreflectance spectroscopy [98], Optical absorption bands, however, reflect a combined density of electronic states at a photon energy which is the energetic difference of... 

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]. 

The first studies by UV-visible transmission spectroscopy were carried out using an optically transparent electrode (OTE) such as indium oxide [140,141]. Unfortunately an OTE does not allow the nature and the structure of the electrode material to be changed and these play a key role in electrocatalytic processes. Only reflectance spectroscopy is able to investigate in situ, various electrode materials [142], This was effectively checked for the first time with cobalt porphyrin-doped polypyrrole films using the electroreflectance technique [106,143]. This allowed the characterization of the redox properties of the modified PPy electrode and the determination of the redox potential of the Co"VCo" couple. The catalytic effect towards the ORR was also... 

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