The temperature dependence of the surface potential at the Al2O3/electrolyte interface

Electrolyte/insulator/silicon structures can be used to measure the variations of surface potential at the insulator/electrolyte interface. We have used this method to measure the temperature dependence of the surface potential Ψ0 at the γ-Al2O3/electrolyte interface. By applying the surface site dissociation model, this measurement can be interpreted in terms of the enthalpy changes of the ionization reactions of OH surface sites. As this theory predicts, it is found that ∂Ψ0ϖT varies linearly with pH. From the slope and intercept of this experimental line, the following enthalpies can be deduced: ΔHa1 = +34.8 ± 2.0 kJ/mole, for the dissociation of a proton from a SOH2+ site, and ΔH2a = +54.0 ± 2.0 kJ/mole, for the dissociation of a proton from a SOH site. These results imply that proton dissociation on Al2O3 surfaces is endothermic, and are in reasonable agreement with those obtained by Griffiths and Furstenau with a colloidal suspension.