  We propose a theoretical model of friction under electrochemical conditions
focusing on the interaction of a force microscope tip with adsorbed polar
molecules of which the orientation depends on the applied electric field. We
demonstrate that the dependence of friction force on the electric field is
determined by the interplay of two channels of energy dissipation: (i) the
rotation of dipoles and (ii) slips of the tip over potential barriers. We
suggest a promising strategy to achieve a strong dependence of nanoscopic
friction on the external field based on the competition between long range
electrostatic interactions and short range chemical interactions between tip
and adsorbed polar molecules.
