Friction And Wear Characteristics Of Graphene Nanosheets Studied By Atomic Force Microscopy

Graphene, a new two-dimensional material with excellent mechanical, thermal, and electrical properties, has provided promising applications in many fields. And the research on nanotribological properties of graphene is of great significance for efficient fabrication and reliable operation of graphene-based nanodevices.In this paper, four different types of graphene films, including mechanically exfoliated graphene nanosheets (MEGS), chemical vapor deposition graphene nanosheets (CVDGS), reduced graphene oxide nanosheets (RGOS) and graphene oxide nanosheets (GOS), were characterized by calibrated atomic force microscopy (AFM), raman spectroscopy, X-ray photoelectron spectroscopy (XPS), et al. Furthermore, the adhesive forces between graphene films and tips were measured and analyzed using AFM in ambient conditions. Adhesive forces on different types of graphene films were quite different and affected by the ambient relative humidity. However, they were almost independent of thickness of the graphene films.The friction and wear characteristics of graphene films were detailedly explored using AFM in this study. Four types of graphene films were all found to be able to effectively reduce the friction of SiO2/Si substrate as lubricants. MEGS exhibited the lowest friction and the best anti-wear performance due to its perfect planar lattice. CVDGS was found to have a worse performance both on friction and wear resistance compared to MEGS because of the presence of PMMA residues as well as tiny defects. The surface of GOS was terminated with abundant oxygenous groups, leading to special friction behavior. In contrast with the other types of graphene films, the friction of GOS decreased when relative humidity increased or the sliding velocity exceeded its critical velocity. The friction of RGOS was lower than that of GOS, and this was mainly attributed to the sharp reduction in functional groups after chemical reduction treatment. In addition, there was no significant difference in anti-wear performance between RGOS and GOS. And the existence of many defects in both of the graphene films may be the possible reason.