Effects of electric potentials on surface forces in electrolyte solutions

Atomic force microscopy was employed to analyze the electric double layer on an Au film electrode deposited on mica. An Au-covered or a bare Si3N4 tip was used as a probe. An electrolyte solution was aqueous NaOH of pH 10.9. The electrode and the tip potentials were controlled electrochemically by a potentiostat. Repulsive forces were always observed regardless of the polarity of the potential, i.e., the positive and the negative side of the point of zero charge. The result indicates that the strongly adsorbed OH- anions overcompensated the positive charge at the Au surface. The potential of the outer Heimholtz plane at an electrode potential was estimated from the force-distance curves. (C) 1996 American Vacuum Society.