Hydrogen-passivation modulation on the friction behavior of graphene with vacancy defects under strain engineering

Excellent friction properties of graphene are degraded by the presence of various defects. Such degradation may be suppressed with the help of element passivation. This work investigates the effect of hydrogen (H)-passivation on the friction behavior of graphene containing vacancy defects under strain engineering by molecular dynamics simulations. It is found that the introduction of vacancy defects in graphene by deleting its carbon (C) atoms highly improves the chemical activity of atom initially bonded with the deleted atoms due to the creation of dangling bonds. Such high chemical activity can be reduced by the H-passivation on the dangling bonds of C atoms, which highly increases the critical normal load for onset of covalent bonds formed at the sliding interface. Below the critical load, the friction reduction of graphene is realized by applying the uniaxial in-plane tensile strain to improve the incommensurability between graphene layers. The friction behaviors of H-passivated defective graphene are determined by the combined effects of atomic-level surface roughness at the defect sites and the chemical inertness evaluated by first-principles calculations. This study offers a novel way to control the lubrication performance of graphene-based nanomaterials with various defects in mechanical applications.