Layer Contributions to Electroreflectance

The ER effect of the metal/electrolyte interface is usually dominated by contributions from the metal surface, especially in the interband transition region. The potential-induced changes in the optical properties of the Helmholtz layer proper, which constitutes a purely dielectric film in the photon energy range under study, are expected to give rise to AR/R values which are orders of magnitude smaller than those of the metal surface. This is readily demonstrated with the help of the linear approximation equations (29a) and (29b). 

Attempts have been made in the past to unravel these two types of contributions for polycrystalline surfaces of Pb and Au and for The separation procedure rested largely upon two simple correlations derived from the linear approximation equations for a three-phase model (a) when the optical properties of the metal surface are only slightly different from those of the bulk (that is to say, the perturbation causing a reflectance change arises from the metal side), then at tpx = 45°, R/R)p 2(AR/R), (as a direct consequence of Abeles relation Rp = R] at (pi = 45°) (b) if, on the other hand, a dielectric film on top of a metal substrate is the cause for a AR/R effect, we find (AR/R) 0 and (AR/R) 0 for tpi = 45°, while (AR/R)p increases markedly for higher angles of incidence, say, 70°. It was therefore concluded that the ER effect at pi = 45° represents the metal contribution only (especially since one indeed often finds (AR/R) twice as large as (AR/R)J, 

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