Super‐Elasticity and Ultralow Friction of Hydrogenated Fullerene‐Like Carbon Films: Associated with the Size of Graphene Sheets

Hydrogenated fullerene-like carbon (FLC:H) films would be a widely used material with a unique combination of properties including high-hardness/strength, excellent elasticity, and ultralow friction. The nanostructure of graphene sheets and the number of cross-linking sites between them may be two main structural factors determining these properties. Exploring the structure-properties relationship is crucial to effectively tailor these properties for potentially more applications. In this study it is demonstrated that FLC:H films can yield exceptional and tunable mechanical properties by controlling the nanostructure of graphene sheets, similar to those of architectured materials. And the graphene sheets have a critical size (11-13 nm) endowing FLC:H films with super-elastic recovery ability (an elastic recovery rate of 98%), ultralow friction (a friction coefficient of 0.012), and low wear (a wear rate of 10(-17)m(3) (N m)(-1)). The quadratic dependence of the energy loss factors of FLC:H films during load-upload cycles on the size of graphene sheets are well consistent with these experimental results. This work provides a new perspective on the mechanics and friction behavior of FLC:H films and will motivate the design of more novel carbon-based films with superelasticity and superlubricity for engineering applications.