TRIBOSCOPIC DESCRIPTION OF LOCAL WEAR PHENOMENA UNDER AN AFM TIP

For a better understanding of local wear processes, a method called tr iboscopy has recently been developed. It gives a global representation of interface behaviour during sliding by locating it both in space an d time. Let us consider a classical tribological experiment. A sphere is rubbed against a flat specimen, under a constant load and during N reciprocating cycles along the same track. This method allows the typi cal measurements of the experiment (surface topography, friction force , etc.) to be converted into diagrams where the x axis represents the relative position of the solids and the y axis the number of cycles. T he grey level of each pixel corresponds to the level of the measured v alue. The aim of this work is to extend this method to the nanometric scale, with the help of a leteral force microscope (LFM). Cobalt coati ng on pure silica is chosen as the plane. The sphere is the tip of a c lassical Si3N4 pyramidal probe. When the sample is scanned by the LFM tip, contact pressure is 2.0 GPa. We show that some variation occurs i n its topography and lateral force during the repeated scanning of the surface (250 x 250 nm). Furthermore, in a 128 reciprocating cycle-exp eriment performed along one line (250 nm long), we obtain relevant tri boscopic diagrams of this rubbing track. We discuss them in terms of n anometric-scale wear phenomena.