Observation of proportionality between friction and contact area at the nanometer scale

The nanotribological properties of a hydrogen-terminated diamond(111)/tungs ten-carbide interface have been studied using ultra-high vacuum atomic forc e microscopy. Both friction and local contact conductance were measured as a function of applied load. The contact conductance experiments provide a d irect and independent way of determining the contact area between the condu ctive tungsten-carbide AFM tip and the doped diamond sample. We demonstrate that the friction force is directly proportional to the real area of conta ct at the nanometer-scale. Furthermore, the relation between the contact ar ea and load for this extremely hard heterocontact is found to be in excelle nt agreement with the Derjaguin-Muller-Toporov continuum mechanics model.