The influence of pH on friction between oxide surfacesin electrolytes, studied with lateral force microscopy:application as a nanochemical imaging technique

We have investigated the lateral force (frictional) signalbetween the Si3N4 tip of an AFM andSiO2 and AlOx surfaces in a 1 mMNaCl solution, as a function of pH. It was found that thefrictional force depends strongly on both the pH and theisoelectric points (IEP) of the materials under investigation.A simple linear model describing the dependence of the lateralforce on the total normal force has been used to accountqualitatively for the observed lateral force signal from the single-asperity contact between tip and surface on a nanometerscale. The observed pH-dependence of the lateral force signalon different oxide surfaces has been applied to reverse thechemical contrast on an appropriate sample composed of twodifferent oxides, thus demonstrating the potential of this method for ``chemical imaging''.