The rational bottom-up synthesis of atomically defined graphene nanoribbon (GNR) heterojunctions represents an enabling technology for the design of nanoscale electronic devices. Synthetic strategies used thus far have relied on the random copolymerization of two electronically distinct molecular precursors to yield GNR heterojunctions. Here we report the fabrication and electronic characterization of atomically precise GNR heterojunctions prepared through late-stage functionalization of chevron GNRs obtained from a single precursor. Post-growth excitation of fully cyclized GNRs induces cleavage of sacrificial carbonyl groups, resulting in atomically well-defined heterojunctions within a single GNR. The GNR heterojunction structure was characterized using bond-resolved scanning tunnelling microscopy, which enables chemical bond imaging at T = 4.5 K. Scanning tunnelling spectroscopy reveals that band alignment across the heterojunction interface yields a type II heterojunction, in agreement with first-principles calculations. GNR heterojunction band realignment proceeds over a distance less than 1 nm, leading to extremely large effective fields.
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This research was supported by the Office of Naval Research BRC Program (spectroscopic imaging), by the US Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES), under award no. DE-SC0010409 (design, synthesis, and characterization of molecular precursors) and Nanomachine Program award no. DE-AC02-05CH11231 (surface reaction characterization and band structure calculations), by DARPA, the US Army Research Laboratory and the US Army Research Office under contract/grant no. W911NF-15-1-0237 (tip-based manipulation), and by the National Science Foundation (NSF) under grant no. DMR-1508412 (development of theory formalism and STM analyses). Computational resources were provided by the DOE at Lawrence Berkeley National Laboratory's NERSC facility and by the NSF through XSEDE resources at NICS. Y.S. and J.R.C. acknowledge support from the US DOE under contract no. DOE/DE-FG02-06ER46286 (AFM simulation) and the Welch Foundation under grant F-1837 (image analysis). A.A.O. acknowledges support from the Swiss National Science Foundation (SNSF) Postdoctoral Research Fellowship under grant no. P2ELP2-151852.
About this article
Physica E: Low-dimensional Systems and Nanostructures (2019)