Atomic scale friction and charge transport properties of graphene

Abstract

Since energy dissipation in friction is mediated by basic elements, including phonon and electron-hole excitation, understanding the relationship between friction and charge transport properties is an important subject in the field of nanotribology. In this talk, I will highlight the recent works of domain imaging based on friction and current mapping with current sensing atomic (friction) force microscopy. Graphene, a single layer of graphite, is attracting great interest due to its remarkable electrical and mechanical properties and possible applications in emerging electronic devices. Mechanical exfoliation, however, may induce strain on the graphene layer during deposition on a substrate and can create wrinkled films and other defects due to interactions with the substrate that might introduce uneven compressive and tensile stresses. I will show the observation of domains on exfoliated monolayer graphene with differing friction characteristics, as measured by friction force microscopy. Angle-dependent scanning revealed friction anisotropy with a periodicity of 180° on each friction domain. The origin of the friction domains can be explained in light of ripple distortions that give rise to anisotropic friction in each domain as a result of the anisotropic puckering of the graphene. The recent experiments on charge transport properties of mechanically stressed graphene will be discussed. Current mapping on single layer graphene prepared using inductively-coupled plasma chemical vapor deposition revealed nanoscale domain boundaries. The conductance on the domain boundary is lower than that inside the domain structure, which is associated with atomic-scale disorder on the boundary. The influence of chemical modification of graphene on friction and charge transport properties will be discussed.