Interfacial Spatial Heterogeneity-Associated Mesoscale Friction Instability at a Diamond-Cu Interface

Mesoscale interfacial sliding responses bridge nanoscale single-asperity sliding mechanisms and macroscopically averaged frictional responses, enabling local pinning-depinning processes to be resolved within a finite contact region. Recent studies on strongly disordered rough interfaces have revealed statistical features of mesoscale stick-slip, but how such interfacial sliding responses are affected by environmental and mechanical conditions, and how they relate to interfacial morphology, remain unclear. Here, we investigate mesoscale stick-slip at a diamond-Cu interface using a custom-built probe sliding system under controlled environments and loading conditions. Air-vacuum comparison revealed that ambient exposure amplified and destabilized the interfacial response, motivating subsequent vacuum-based measurements. Under vacuum, normal preload and sliding speed mainly changed the absolute force response of stick-slip, while the recurrence length and dominant spectral scale remained within a similar micrometer-scale range. Further comparison with Cu surface topography showed that the main spectral band of the sliding response overlapped with weak topographic features and fell within the autocorrelation-based surface correlation range. These results indicate that mesoscale stick-slip recurrence is associated with interfacial spatial heterogeneity, providing insight into the link between interfacial morphology and sliding stability at diamond-metal contacts.