PH-dependent charge density at the insulator-electrolyte interface probed by a scanning force microscope

Abstract

This paper deals with the use of a scanning force microscope in the ‘force versus distance mode’, to detect the charge densities on the surfaces of insulators immersed in electrolyte solutions. The results of experiments on mica, Si 3N 4 and Al 2O 3, under various pH conditions, are compared with those of computer simulations performed to calculate the electrostatic forces acting between tip and insulator surface. The considered charge densities include a pH-dependent component, which is taken into account according to the site-binding theory. Simulation results are in good agreement with experimental ones, thus indicating the feasibility of the approach for the characterization of the surface charges of potentiometric microelectronic sensors.