First-principles design of an ultralow frictional interface of a black phosphorus and graphene heterostructure with oxide functionalization and high-pressure conditions

Using first-principles density functional theory (DFT) calculations, we demonstrate that the heterointerface of black phosphorus and graphene (BP/Gr) should be a promising lubricant, especially under high pressure conditions. The ultralow interfacial frictional sliding motion is enabled by graphene oxide (GO) functional groups, such as epoxy and hydroxyl groups. These functional groups significantly modulate the interfacial charge distribution to facilitate interfacial slip. The epoxy functional group enables a reduction in not only the bilayer adhesion but also the shear strength along the armchair direction by approximately 40% compared with that without functionalization. The potential energy surface (PES) calculation shows the possibility of an ultralow friction sliding process in BP/Gr and BP/GO due to the presence of almost frictionless paths. In addition, high-accuracy PES calculations predict an almost frictionless sliding path even under pressure. Interestingly, our calculation shows that the corrugation energy and shear strength of BP/Gr decrease under 10 GPa. We elucidated that the origin of the improved frictional properties under high pressure stems from the unique heterostructure of BP/Gr. These results consistently suggest that BP/Gr is promising lubricants for high-pressure applications, which can be further improved using a design principle of exploring optimal interfaces and functional groups.