Circumventing the stability problems of graphene nanoribbon zigzag edges

Abstract

Carbon nanostructures with zigzag edges exhibit unique properties—such as localized electronic states and spins—with exciting potential applications. Such nanostructures however are generally synthesized under vacuum because their zigzag edges are unstable under ambient conditions: a barrier that must be surmounted to achieve their scalable integration into devices for practical purposes. Here we show two chemical protection/deprotection strategies, demonstrated on labile, air-sensitive chiral graphene nanoribbons. Upon hydrogenation, the chiral graphene nanoribbons survive exposure to air, after which they are easily converted back to their original structure by annealing. We also approach the problem from another angle by synthesizing a form of the chiral graphene nanoribbons that is functionalized with ketone side groups. This oxidized form is chemically stable and can be converted to the pristine hydrocarbon form by hydrogenation and annealing. In both cases, the deprotected chiral graphene nanoribbons regain electronic properties similar to those of the pristine nanoribbons. We believe both approaches may be extended to other graphene nanoribbons and carbon-based nanostructures.

Aza-Triangulene: On-Surface Synthesis and Electronic and Magnetic Properties

“…In our previous work, the combination of atomic hydrogen reduction followed by annealing was shown efficient in removing the oxygen atoms on ketone-substituted graphene nanoribbons on Au(111). 29 Inspired by this, we employed a similar procedure for molecule 1. Hydrogen reduction followed by annealing resulted in partial (2) or complete (5) deoxygenation of the precursor 1.…”

“…The sample held at RT was then hydrogenated by exposing to atomic hydrogen. As a result, a considerable number of sp 3 -hybridized carbon atoms were generated (Figure S3), which turned most of the molecules three-dimensional . Subsequent annealing at 250 °C caused a notable desorption and planarized most of the remaining molecular species (>70%; Figure b).…”

“…As a result, a considerable number of sp 3 hybridized carbon atoms were generated (Figure S3), which turned most of the molecules three-dimensional. 29 Subsequent annealing at 250 °C caused a notable desorption and planarized most of the remaining molecular species (>70%; Figure 2b). Figure 2c shows a representative constant-height STM image of the most abundant product in Figure 2b.…”

“…These molecules retain a residual ketone group (2; Figure 1), and the trimer structure is apparently stabilized via O•••Au coordination interactions and hydrogen bonds (see details in Figures S5−S7), as reported previously for other ketonefunctionalized carbon nanostructures. 29,39 Using similar tip manipulation procedures as described above, products 3 and 4 (Figure 1b) can be obtained hierarchically as well (Figures S5 and S6).…”

“…Figure b shows the reaction procedure starting from the corresponding precursor, that is, the ketone-substituted aza-triangulene 1 . In our previous work, the combination of atomic hydrogen reduction followed by annealing was shown efficient in removing the oxygen atoms on ketone-substituted graphene nanoribbons on Au(111) . Inspired by this, we employed a similar procedure for molecule 1 .…”