Passivation Species Suppress Atom-by-Atom Wear of Microcrystalline Diamond

Despite its supreme hardness, (synthetic) diamond wears. Due to the small volume loss involved, diamond wear is challenging to quantify, specifically for multicontact interfaces. Consequently, identifying which wear mechanisms dominate the degradation of macroscopically loaded diamond interfaces has remained an open challenge. Using a topography difference method based on atomic force microscopy imaging, we observe the wear of multi-asperity microcrystalline diamond (MCD) surfaces sliding nonrepeatedly against silicon nitride (Si₃N₄)-coated silicon wafers. By examining the wear scars on Si₃N₄, which can be seen as footprints of the MCD surface, we are uniquely able to track the nanoscale wear of individual MCD crystallites. Our MCD wear measurements show that the diamond wears atom-by-atom and that this wear is accelerated in the absence of passivation species in the environment. This conclusion is confirmed by ab initio molecular dynamics simulations, highlighting how diamond surface passivation suppresses interfacial bonding. Our results thus demonstrate that atom-by-atom wear occurs even in realistic, multi-asperity diamond contacts and that environmental passivation provides a practical and effective means to control interfacial degradation in advanced tribological systems.