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Controlling the atomic configurations of structural defects in graphene nanostructures is crucial for achieving desired functionalities. Here, we report the controlled fabrication of high-quality single-crystal and bicrystal graphene nanoislands (GNI) through a unique top-down etching and post-annealing procedure on a graphite surface. Low-temperature scanning tunneling microscopy (STM) combined with density functional theory calculations reveal that most of grain boundaries (GBs) formed on the bicrystal GNIs are 5-7-5-7 GBs. Two nanodomains separated by a 5-7-5-7 GB are AB stacking and twisted stacking with respect to the underlying graphite substrate and exhibit distinct electronic properties, forming a graphene homojunction. In addition, we construct homojunctions with alternative AB/twisted stacking nanodomains separated by parallel 5-7-5-7 GBs. Remarkably, the stacking orders of homojunctions are manipulated from AB/twist into twist/twist type through a STM tip. The controllable fabrication and manipulation of graphene homojunctions with 5-7-5-7 GBs and distinct stacking orders open an avenue for the construction of GBs-based devices in valleytronics and twistronics.
We thank Sokrates T. Pantelides and Min Ouyang for constructive suggestions. We acknowledge financial support from the National Key Research & Development Projects of China (Nos. 2016YFA0202300 and 2019YFA0308500), the National Natural Science Foundation of China (Nos. 61888102, 51872284, 51922011, 11974045, and 51761135130), the CAS Pioneer Hundred Talents Program, Strategic Priority Research Program of the Chinese Academy of Sciences (No. XDB30000000), and China Postdoctoral Science Foundation (Nos. 2018M641511, 2018M630217, and 2019T120148). A portion of the research was performed in CAS Key Laboratory of Vacuum Physics.