Seamless Staircase Electrical Contact to Semiconducting\nGraphene Nanoribbons

Abstract

Electrical\ncontact to low-dimensional (low-D) materials is a key\nto their electronic applications. Traditional metal contacts to low-D\nsemiconductors typically create gap states that can pin the Fermi\nlevel (<i>E</i>_F). However, low-D metals possessing\na limited density of states at <i>E</i>_F can\nenable gate-tunable work functions and contact barriers. Moreover,\na seamless contact with native bonds at the interface, without localized\ninterfacial states, can serve as an optimal electrode. To realize\nsuch a seamless contact, one needs to develop atomically precise heterojunctions\nfrom the atom up. Here, we demonstrate an all-carbon staircase contact\nto ultranarrow armchair graphene nanoribbons (aGNRs). The coherent\nheterostructures of width-variable aGNRs, consisting of 7, 14, 21,\nand up to 56 carbon atoms across the width, are synthesized by a surface-assisted\nself-assembly process with a single molecular precursor. The aGNRs\nexhibit characteristic vibrational modes in Raman spectroscopy. A\ncombined scanning tunneling microscopy and density functional theory\nstudy reveals the native covalent-bond nature and quasi-metallic contact\ncharacteristics of the interfaces. Our electronic measurements of\nsuch seamless GNR staircase constitute a promising first step toward\nmaking low resistance contacts.