Nanoprobing Friction and Charge Transport Properties of Chemically Modified Graphene

Abstract

Atomically thin graphene is the ideal model system for studying nanoscale friction due to its intrinsic two-dimensional anisotropy. Furthermore, modulating its tribological properties could be an important milestone for graphene-based micro- and nano-mechanical devices. Here, report the correlation between electrical transport property and mechanical deformation of graphene layer grown on Cu substrate by chemical vapor deposition method was studied with conductive probe AFM / friction force microscopy in ultra-high vacuum. We studied the nanoscale friction and charge transport properties of pristine and chemically modified graphene. Current mapping reveals the domain and domain boundaries on the graphene surface. We found that the friction of graphene increased by a factor of 6 after fluorination, while the adhesion force is reduced by 25 percent. Results of density functional theory (DFT) calculations show that the out-of-plane stiffness of graphene is sensitive to fluorination, in contrast to the rather insensitive in-plane stiffness. The FFM experiment and DFT simulation suggest that nanoscale lateral friction of the two-dimensional atomic sheet is dominated by normal stiffness, and the frictional energy mainly dissipates through the softest transverse-acoustic (TA) phonons, which can be readily modified by chemical treatment of the surface.