Electroreflectance Studies of the Metal Surface

The reflectivity of a solid/electrolyte interface is often found to change with electrode potential, even in the absence of any faradaic reaction. This change in reflectance with potential, BR/dU, is commonly called electroreflectance (ER). In contrast to semiconductor where the externally applied 

Soon after the first observation of an ER effect for a metal by Feinleib, a systematic investigation of this effect was started at several places. The early results, mainly for polycrystalline Ag and Au surfaces were interpreted in terms of the free-electron model which was developed by Hansen and later refined by Mclntyre. This model assumes that the change in the free-electron concentration at the surface, induced by the potential change, is 

FIGURE 21. (a) Model of the electrochemical double layer, (b) Potential distribution across the double layer. 

FIGURE 22. Surface charge density Ap of a metal, induced by a weak external electric field. X = 0 denotes the edge of the positive-charge background, = Wigner-Seitz radius. After Ref. 67. 

Besides an actual change with potential in the electronic states at the surface due to the very high electric field, which leads to a modulation of the interband transition and hence to a contribution of bound electrons to ER, there can be a noticeable modulation of the interband transition proper, very much like the Franz-Keldysch effect in ER of semiconductors. As was pointed out by Lynch, this may occur via field-induced indirect interband transitions. Because of the high field strength attainable at metal/electrolyte 

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