Electronic and Optical Properties of Atomically Precise Graphene Nanoribbons and Heterojunctions
Among graphene related materials, nanoribbons (GNRs) narrow stripes of graphene have emerged as promising building blocks for nanoelectronic devices. The lateral confinement in GNRs opens a bandgap that sensitively depends on the ribbon width, allowing in principle for the design of GNR based structures with tunable properties. However, structuring with atomic precision is required to avoid detrimental effects induced by edge defects. Recently, we have introduced a versatile route for the bottom up fabrication of GNRs [1] allowing for the atomically precise synthesis of ribbons with different shapes as well as heterojunctions be tween doped and undoped ribbon segments [2,3] Here, we report on detailed experimental and computational investigations of the structural, electronic and optical properties of selected GNRs and heterojunctions [1 3] For the case of armchair GNRs of width N=7, the electronic band gap and band dispersion have been determined with high precision [4,5] Optical characterization has revealed important excitonic effects [6] which are in good agreement with ab initio calculations including many body effects. For the case of heterojunctions, consisting of seamlessly assembled segments of pristine (undoped) graphene nanoribbons and deterministically nitrogen doped graphene nanoribbons, we find a behavior similar to traditional p n junctions. With a band shift of 0.5 eV and an electric field of 2 x 108 V m 1 at the heterojunction, these materials bear a high potential for applications in photovoltaics and electronics. Finally, we will discuss the potential of the bottom up approach with regard to the fabrication of GNRs exhibiting zigzag edges, which are predicted to exhibit spin polarized edge states.