Conductive Atomic Force Microscopic (C-AFM) Studies of Au/MoS₂ Nanocomposite Films

Au/MoS₂ nanocomposite films with high Au concentrations (75 to 90 at%), recently developed at The Aerospace Corp., have shown properties that are promising for use in sliding electrical contacts, such as slip rings and relays. For such applications, it is critical to maintain low contact resistance while maintaining low friction with controlled wear (i.e. removal and transfer of material). In this report, we present results from conductive atomic force microscopic (c-AFM) investigations of Au/MoS₂ nanocomposite structures and their dynamic material transfer phenomena under a sliding contact, which are both important in understanding the friction, wear and conducting mechanisms of the films. We have performed c-AFM to obtain topography, friction and current images simultaneously. Remarkable morphological changes were observed in a series of current images which initially showed distinct nanoscale metallic (Au) and semiconducting (MoS₂) phases that were relatively well dispersed, but repeated contact sliding in the same area resulted in gradual disappearance of the metallic phase and reduction of the overall friction. These results reveal that MoS₂ is transferred across the surface to provide lubrication while Au particles at or near the surface provide electrical conductivity. The c-AFM results provide real-time and real-space visualization of the lubrication mechanism occurring inside a nanoscale sliding contact.