Tuning Nanoscale Adhesive Contact Behavior To A Near Ideal Hertzian State Via Graphene Coverage

We carry out molecular statics (MS) simulations to study the indentation process of Pt (1 1 1) surfaces using an indenter with the radius of 5-20 nm. The substrate and indenter surfaces are either bare or graphene-covered. Our simulations show that the influence of the adhesion between the bare substrate and indenter tip can be significantly reduced by decreasing the adhesion strength and adhesion range between the atoms on the substrate and indenter, or by enhancing the substrate stiffness. Our results suggest that the elastic response of the substrate exhibits weaker adhesion after the coating of graphene layers on either side of the contacting interface, which is attributed to the weak interaction between the graphene layers. Based on these principles obtained for the bare substrate, the nanoscale contact behavior of the substrate can be tuned into a near-ideal Hertzian state by increasing the number of graphene layers, applying pre-strains to graphene on substrate, or using large indenters. Therefore, even for strong adhesion between tip, graphene, and substrate, mechanical properties of substrate can be determined by nanoindentation using graphene coverage. Our research provides theoretical guidance for designing adhesion-less coatings for AFM probes and MEMS/NEMS systems.