PH-DEPENDENT CHARGE-DENSITY AT THE INSULATOR-ELECTROLYTE INTERFACE PROBED BY A SCANNING FORCE MICROSCOPE

This paper deals with the use of a scanning force microscope in the 'f orce versus distance mode', to detect the charge densities on the surf aces of insulators immersed in electrolyte solutions. The results of e xperiments on mica, Si3N4 and Al2O3, under various pH conditions, are compared with those of computer simulations performed to calculate the electrostatic forces acting between tip and insulator surface. The co nsidered charge densities include a pH-dependent component, which is t aken into account according to the site-binding theory. Simulation res ults are in good agreement with experimental ones, thus indicating the feasibility of the approach for the characterization of the surface c harges of potentiometric microelectronic sensors. (C) 1996 Elsevier Sc ience Limited.