A Novel Frictional Force Microscope with 3-Dimensional Force Detection

It has long been recognized that the tip-on-flat geometry of an atomic force microscope (AFM) closely resembles a realistic nanocontact, which can serve as a model in the investigation of friction at the atomic scale.1 AFM’s have been adapted to measure lateral forces down to the nanometer and nanonewton regimes by measuring the torsional response of the force probe. In the past, frictional force microscopes (FFM’s) have produced predominantly qualitative results although recently some groups have produced quantitative nanotribology results.2,3 Even as the techniques in traditional FFM become more refined, the basic problem remains that this method uses a force probe designed to be most sensitive to normal forces. One of the ramifications of this is that most cantilevers snap into contact as the tip-to-sample distance approaches the near contact regime so that hard contact is always made when measuring lateral forces. This near contact regime is of great technological importance as fly heights in disk drives decrease and as the length scales in MEMS are reduced. Cantilevers that do not suffer from the “snap-to-contact” problem have high torsional spring constants so that very small lateral forces are not detectable. In addition, significant coupling exists between torsional and normal motions of the cantilevers.4 Finally, in most FFM’s only one component of the lateral force is measured.