Quantitative characterization of friction coefficient using lateral force microscope in the wearless regime

Absolute quantitative data from atomic force microscopy (AFM)/lateral force microscopy experiments are always difficult to obtain mainly due to the need of the normal force F-N and the friction force F-F calibration. In this article, we developed an experimental method which allows us to extract absolute quantitative friction data without calibrating any force when the relation between F-N and F-F is linear or only calibrating the normal force when the relationship is nonlinear. The technique reported here, is suitable for an atomic force microscope that has the cantilever attached to the piezotube translator and an unguided incident laser beam on the cantilever. We take advantage of the piezotube bending during a large scan (5 mumx5 mum), generally considered as an undesirable effect, to calculate a detection factor that allows the determination of quantitative tribological data. The validity of our experimental method is checked on the extensively AFM studied materials, such as muscovite, silicon, and highly oriented pyrolytic graphite. The experiments are carried out in a load range where the shear stress tau can be expressed as tau=tau(0)+muP, where mu is the friction coefficient, P is the mean contact pressure, and tau(0) is a parameter related to the tip/sample adhesion. The value of mu is found to be independent of the tip geometry and the pull-off force, and always constant for a given tip/sample couple in the load range investigated. (C) 2004 American Institute of Physics.