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.

原子定义的石墨烯纳米带（GNR）异质结的合理的自下而上的合成代表了一种用于设计纳米级电子设备的技术。迄今为止，所使用的合成策略依赖于两种电子上不同的分子前体的无规共聚，以产生GNR异质结。在这里，我们报告了通过从单个前体获得的V形GNR的后期功能化制备的原子精确GNR异质结的制备和电子表征。完全环化的GNR的生长后激发诱导牺牲性羰基的裂解，从而在单个GNR中产生原子上明确定义的异质结。GNR异质结结构的特征在于使用了键分辨扫描隧道显微镜，从而能够在T  = 4.5K。扫描隧道光谱显示，跨异质结界面的能带对准产生II型异质结，与第一性原理计算一致。GNR异质结带重新排列在小于1 nm的距离内进行，从而导致非常大的有效场。