SENSITIVITY OF FRICTIONAL FORCES TO PH ON A NANOMETER-SCALE - A LATERAL FORCE MICROSCOPY STUDY

An atomic force microscope (AFM) operating in the lateral (frictional) force mode (LFM) was used to investigate the pH dependence of kinetic friction between a silicon nitride tip and an oxidized silicon surfac e under aqueous electrolyte solutions. It was found that, besides the known pH dependence of the normal force curves, the frictional force i s highly sensitive to the pH value of the solution. A linear relations hip between frictional force and adhesion hysteresis (i.e., the dissip ated energy), as recently shown to be valid for some systems by Israel achvili et al., is supported. The implication is that many chemical sp ecies on surfaces can be readily differentiated using AFM-LFM by varyi ng the pH value of the surrounding medium and that a possible nanochem ical imaging method could be developed, based upon this principle.