Experimentally Controlling the Edge Termination of Graphene Nanoribbons

The edges of graphene exhibit several unique features, such as the presence of localized edge states, and are anticipated to be a powerful means of controlling the electronic properties of this two-dimensional material. Understanding such properties, however, requires a precise knowledge of the atomic-scale structure and chemical composition of the edge. In this work, the edges of graphene nanoribbons (GNRs) are controlled by hydrogen plasma and are investigated through a combination of high-resolution scanning tunneling microscopy (STM) and first-principles calculations. We recover the atomic structure of the edge termination in atom-by-atom fashion and establish the chemical nature of terminating functional groups at graphene edge segments of different orientation -- (i.e., zigzag, armchair and chiral). These results allow us to conclude that the edges of hydrogen-plasma-etched GNRs are generally free of structural reconstructions and are terminated by hydrogen atoms with no rehybridization of the outermost carbon edge atoms. Both zigzag and chiral edges show the presence of edge states.