Realistic Metal–Graphene Contact Structures

Abstract

The contact resistance of metal–graphene junctions has been actively explored and exhibited inconsistencies in reported values. The interpretation of these electrical data has been based exclusively on a <i>side</i>-contact model, that is, metal slabs sitting on a pristine graphene sheet. Using <i>in</i> <i>situ</i> X-ray photoelectron spectroscopy to study the wetting of metals on as-synthesized graphene on copper foil, we show that side-contact is sometimes a misleading picture. For instance, metals like Pd and Ti readily react with graphitic carbons, resulting in Pd- and Ti-carbides. Carbide formation is associated with C–C bond breaking in graphene, leading to an <i>end</i>-contact geometry between the metals and the periphery of the remaining graphene patches. This work validates the <i>spontaneous</i> formation of the metal–graphene end-contact during the metal deposition process as a result of the metal–graphene reaction instead of a simple carbon diffusion process