Electrostatic interaction in scanning probe microscopy when imaging in electrolyte solutions

In scanning force and scanning tunneling microscopy an electrostatic force acts between tip and sample when imaging in electrolyte solutions. This force has been calculated numerically with a modified Poisson-Boltzmann equation. To calculate the force in a scanning tunneling microscope the electric potentials within the tip and on the sample were kept constant. The electrostatic interaction in a scanning force microscope was calculated with constant or regulated surface charge densities. The main parameters determining the electrostatic force are the surface charge density (or the surface potential) of tip and sample, the salt concentration in the electrolyte solution and the tip shape. Practical consequences of the electrostatic interaction in scanning force microscopy are discussed.