Direct determination of surface potential on sodium chloride single crystals. I. Analysis of measurements

Measurement by a vibrating capacitor probe of the variation with temperature of the surface potential of freshly cleaved surfaces of sodium chloride single crystals confirm the basic characteristics predicted by point defect theory: negative potentials at low temperature, positive potentials at high temperature, and an intermediate isoelectric temperature at which the surface potential is zero. An additional feature not predicted by theory is a substantial surface voltage associated with surface irregularity that can be reduced but not eliminated by annealing. Quantitative analysis of experimental results shows that measurement of the surface potential is, in principal, capable of yielding reliable values for the separate anion and cation vacancy formation parameters.