Surface anisotropic electroreflectance response at an edge-plane pyrolytic graphite electrode

We found that the potential-modulated UV-vis reflectance (electroreflectance, ER) spectrum measured with linearly polarized incident light at an edge-plane graphite (EPG) electrode with adsorbed redox species shows surface anisotropy. At a hemin or methylene blue-adsorbed EPG electrode, s-polarized incident light gave rise to greater ER response than p-polarized when the c axis of the graphite electrode is parallel to the plane of incidence, while when the c axis is perpendicular to the plane of incidence p-polarized light gave rise to greater response. The anisotropy was also observed for an EPG electrode coated with a Nafion film in which adsorptive species was incorporated. In contrast, methylviologen-incorporated Nafion films did not produce the anisotropy. The possible origin of the anisotropy was discussed in light of the surface morphology of the EPG as observed by the SEM.