Pacific Nanotechnology Inc.

NanoTribology

Frictional Forces

Friction between two surfaces depends on the chemical and mechanical interaction between the surfaces. Changes in chemical composition giving rise to friction are measurable with the AFM. The technique for measuring these forces is called lateral force, or frictional force microscopy.

As the probe moves over a surface in the AFM, changes in the chemical composition of the surface can give rise to torsions of the cantilever on which the probe is mounted. The torsion of the cantilever is then proportional to the friction between the probe and the surface.

Figure 4: Illustration of the principle that allows lateral force or frictional fore microscope images to be measured. The cantilever will twist as the probe interacts with the surface while scanning.

In an AFM it is possible to simultaneously measure topography and frictional force images. The topography image is derived from monitoring the vertical forces on the cantilever and the friction image is acquired simultaneously by monitoring the lateral motions of the cantilever. Below is a FFM image of a sample illustrating changes in the friction.

Figure 5: (left) Two dimensional view of a composite material measured with the AFM. Barely visible in this image are striation marks derived from a change in chemical composition at the surface.
(right) The lateral force or frictional force image of the composite material clearly shows changes in chemical composition at the surface of the composite material. Both the topography and frictional force image are measured simultaneously with the AFM.