TRIBOSCOPIC DESCRIPTION OF LOCAL WEAR PHENOMENA UNDER AN AFM TIP

For a better understanding of local wear processes, a method called triboscopy has recently been developed. It gives a global representation of interface behaviour during sliding by locating it both in space and 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 typical 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. The grey level of each pixel corresponds to the level of the measured value. The aim of this work is to extend this method to the nanometric scale, with the help of a leteral force microscope (LFM). Cobalt coating on pure silica is chosen as the plane. The sphere is the tip of a classical Si3N4 pyramidal probe. When the sample is scanned by the LFM tip, contact pressure is 2.0 GPa. We show that some variation occurs in its topography and lateral force during the repeated scanning of the surface (250 x 250 nm). Furthermore, in a 128 reciprocating cycle-experiment performed along one line (250 nm long), we obtain relevant triboscopic diagrams of this rubbing track. We discuss them in terms of nanometric-scale wear phenomena.