Stepwise On-Surface Synthesis of Porous Carbon Nanoribbons with Notched Zigzag Edges

Abstract

Bottom-up synthesis of carbon nanomaterials embedded with periodic arrays of nanoporous structures is of great interest for potential applications in nanotechnology. In limited examples, lateral fusion of polymer chains or armchair/ chevron graphene nanoribbons with phenyl functional groups upon dehydrogenative coupling has been observed for the generation of porous nanoribbons or nanoporous graphene.Here we report a stepwise on-surface synthesis of porous carbon nanoribbons upon hierarchical Ullmann coupling for promoting highly selective inter-ribbon connections, which results in porous carbon nanoribbon structures with a notched zigzag edge and variable widths. By combining scanning tunneling microscopy and atomic force microscopy, the nanoporous structure and the corresponding electronic structures are fully characterized, which shows that localized electronic states are generated at pore−ribbon interfaces and ribbon zigzag edges. Further first principle calculations unveil the observed electronic states near the Fermi level originating from the two flat bands upon nanoporous structure imprinting. Our results provide a promising strategy for the atomically precise synthesis of porous carbon nanoribbons with engineered electronic structures, which can potentially enrich the synthetic routes to porous nanostructures and also expand the variety of carbon nanomaterials with characteristic electronic properties.

Self-Limited Embedding Alternating 585-Ringed Divacancies and Metal Atoms into Graphene Nanoribbons

“…These results directly demonstrate the distinct electronic behaviors between the hydrogenated and the 585-ringed divacancies. The appearance of localized frontier orbitals in the 585/Ag GNRs may suggest their potential applications in GNR-based field effect transistors for exploring correlated physics. ,, …”

“…The appearance of localized frontier orbitals in the 585/Ag GNRs may suggest their potential applications in GNR-based field effect transistors for exploring correlated physics. 14,15,18 Theoretical Insights into the Ag Adatom-Assisted Intramolecular Cyclodehydrogenation. Considering the fact that both in the final 585/Ag GNR superlattices and the intermediates, after annealing at a slightly lower temperature of 810 K (Figure S17), there present Ag atoms embedded at the dehydrogenated divacancies, we can reasonably think of the participation of Ag adatoms in the reactions.…”

“…Periodically embedding structural defects, such as vacancies, , nonhexagonal rings, − and heteroatoms , into the basal hexagonal lattice of graphene, provides a predicable way aiming at electronic property engineering for potential applications . Recent development of on-surface synthesis, − based on rationally designed molecular precursors, has become a remarkable success in atomically precisely fabricating novel graphene superlattices with periodic structural modulations, as exemplified by nanopores in graphene sheets − and graphene nanoribbons (GNRs), − heteroatoms of B , and N − in GNRs, and also a wide range of interesting carbon allotropes − that consist of various nonbenzenoid combinations. One of the interesting nonbenzenoid combinations is the structure of a pair of five-membered rings and an eight-membered ring (585 rings), formed by the loss of two adjacent carbon atoms, also known as divacancy in graphene and carbon nanotubes (CNTs) .…”

Step-Assisted On-Surface Synthesis of Graphene Nanoribbons Embedded with Periodic Divacancies

“…Graphene nanoribbons (GNRs), a family of quasi-one-dimensional (1D) materials with a graphitic lattice and highly tunable electronic properties, have presented great potentials in next-generation electronics, − spintronics, and optoelectronics. , While the band structure engineering of GNRs is sensitive to the edge shapes and ribbon widths, patterning defects/nanopores in GNRs offers another opportunity for tailoring the chemical and electronic functionalities, − extending the applications in water purification, chemical sensing, and ion transport . However, introduction of well-controlled uniform pores in the basal lattice of the sp 2 carbon plane is very difficult following the top-down approach. , The alternative bottom-up approach, using rationally designed molecular precursors via Ullmann polymerization and cyclodehydrogenative graphitization reactions, has provided a promising route to realize atomically precise porous graphene nanostructures, such as nanographenes, − GNRs, − and graphene sheets − , (Figure ). While the size/geometry of the nanopores is a critical parameter to deliver the designer electronic properties and functionalities, the synthesis of periodic monovacancies and divacancies in GNRs remains a great challenge.…”

On-Surface Reaction of 1,4-Dibromo-2,5-Diiodobenzene on Au(111) and Ag(100)

“…The activation temperature of Ullmann coupling mainly depends on types of metal substrates and halogen substituents of molecular precursors. The decreasing bond dissociation energy required for dehalogenation of F, Cl, Br, and I and the enhancing catalytic ability of Au, Ag, and Cu substrates correspond to successively lower activation temperatures. − Through the utilization of these differences in temperature intervals, target products can be synthesized from molecular precursors with different types of halogen substituents according to a temperature-controlled stepwise routine. − For example, sequential Ullmann coupling was demonstrated in precursors with I and Br substituents on Au(111) where deiodination and debromination occurred after RT deposition and further annealing, respectively. − Also, precursors with Br and Cl substituents were reported to fabricate 2D covalent organic frameworks through stepwise debromination and dechlorination at 180–200 and 280–300 °C on Au(111). , In addition, a nonbenzenoid biphenylene network with four- and eight-membered rings had been successfully synthesized from Br- and F-functionalized DHTP precursors through sequential debromination and lateral dehydrofluorination reactions on Au(111) …”