2D Abrupt Nano-Junctions Blending sp-sp² Bonds on Atomically Precise Heterostructures

Two-dimensional heterostructures combining sp-sp ${}^2$ hybridization-blending graphene with graphyne-based allotropes-offer substantial potential for enhancing the tunability of electronic and transport properties while providing significant structural flexibility, which are desirable characteristics for next-generation nanoscale electronics. Despite such potential, their experimental realization remains elusive, as synthesized carbon heterostructures are limited to doped, graphene-based systems exhibiting exclusively sp ${}^2$ hybridization. Here, the on-surface synthesis of covalently bonded sp-sp ${}^2$ lateral heterostructures between graphene nanoribbons and graphdiyne networks on Au(111) is demonstrated. Atomic-resolution scanning tunneling microscopy, combined with density functional theory, reveals the formation mechanism of the covalent interfacial bonds between nanoribbons and graphdiynes, also highlighting the key role of surface chemistry. Bromine atoms, deriving from the molecules dehalogenation and chemisorbed along the nanoribbon, inhibit junction formation, but bonding efficiency can be boosted up to 66% by controlled removal of these byproducts. Electronic structure and transport calculations show that the 2D heterostructure by itself is characterized by disentangled properties for the two subsystems, forming an atomically narrow junction, enabling voltage-tunable spatial current separation in two dimensions. These results define a viable strategy for engineering graphene-based sp-sp ${}^2$ heterostructures, paving the way for the design and synthesis of all-carbon nanoscale electronic architectures.