A surface topography-independent friction measurement technique using torsionalresonance mode in an AFM

Abstract

The recently introduced torsional resonance mode (TR mode) technique has been appliedfor friction force measurements at the micro/nanoscale. In this technique, an atomic forcemicroscope (AFM) with a vibrating cantilever tip in torsional mode is used, andthe contact torsional vibration amplitude of the tip motion (TR amplitude) ismonitored at a contact resonance frequency under constant normal load. In thispaper, the TR mode friction force images are compared to the friction force imagesacquired by conventional contact mode friction force microscopy on three samples:a self-assembled monolayer (SAM) with two phase structure, a silicon ruler, and a metalevaporated (ME) tape. The results from those samples show that the TR mode frictionforce images are much less affected by the surface topography and are almostindependent of the scanning direction of the tip, whereas this is not the case forthe contact mode friction force measurements. Mechanisms responsible for theseobservations are also discussed in the paper. In order to predict coefficient of frictionas a function of the change in the TR amplitude, an energy balance model isproposed.