Correlating surface structures and nanoscale friction of CVD Multi-Layered graphene

Abstract

Surface structures on chemical vapor deposition (CVD) grown graphene determine its functional properties, and thus, in-depth understanding about the relationship between the structures and the properties is essential to investigate CVD graphene in a variety of scientific and engineering applications. Here, we correlate surface structures with nanoscale friction of a multi-layered graphene island. By cleaning graphene surface utilizing mechanical scratching of polymeric surface contamination, we unveiled the surface structures such as small-scale and large-scale (folded) wrinkles on graphene using atomic force microscopy (AFM) and investigated their effect on nanoscale friction. The formation of such surface structures induced twisting of the top-most graphene layer as confirmed by Raman spectroscopic analysis, and the twisted top-most graphene layer influenced the layer dependency of nanoscale friction depending on the applied normal load as revealed by friction force microscopy (FFM) measurements. No identifiable layer-dependency was observed at the low normal load due to the increased interlayer distance between the twisted top-most graphene layer and the underlying AB-stacked layers. Increasing the normal load resulted in the decrease of the interlayer distance and made the contribution of different lateral bending stiffness more dominant to nanoscale friction, resulting in the strong layer-dependency of nanoscale friction on multi-layered graphene.