Transport gap engineering by contact geometry in graphene nanoribbons: Experimental and theoretical studies on artificial materials

摘要

Electron transport in small graphene nanoribbons is studied by microwave emulation experiments and tightbindingcalculations. In particular, it is investigated under which conditions a transport gap can be observed. Ourexperiments provide evidence that armchair ribbons of width 3m + 2 with integer m are metallic and otherwisesemiconducting, whereas zigzag ribbons are metallic independent of their width. The contact geometry, definingto which atoms at the ribbon edges the source and drain leads are attached, has strong effects on the transport.If leads are attached only to the inner atoms of zigzag edges, broad transport gaps can be observed in allarmchair ribbons as well as in rhomboid-shaped zigzag ribbons. All experimental results agree qualitatively withtight-binding calculations using the nonequilibrium Green’s function method.