Hierarchical On-Surface Synthesis of Graphene Nanoribbon Heterojunctions

Abstract

Bottom-up graphene nanoribbon (GNR) heterojunctions are nanoscale strips of graphene whose electronic structure abruptly changes across a covalently bonded interface. Their rational design offers opportunities for profound technological advancements enabled by their extraordinary structural and electronic properties. Thus far, the most critical aspect of their synthesis, the control over sequence and position of heterojunctions along the length of a ribbon, has been plagued by randomness in monomer sequences emerging from step-growth copolymerization of distinct monomers. All bottom-up GNR heterojunction structures created so far have exhibited random sequences of heterojunctions and, while useful for fundamental scientific studies, are difficult to incorporate into functional nanodevices as a result. In contrast, we describe a hierarchical fabrication strategy that allows the growth of bottom-up GNRs that preferentially exhibit a single heterojunction interface rather than a random statistical sequence of junctions along the ribbon. Such heterojunctions provide a viable platform that could be directly used in functional GNR-based device applications at the molecular scale. Our hierarchical GNR fabrication strategy is based on differences in the dissociation energies of C-Br and C-I bonds that allow control over the growth sequence of the block copolymers from which GNRs are formed and consequently yields a significantly higher proportion of single-junction GNR heterostructures. Scanning tunneling spectroscopy and density functional theory calculations confirm that hierarchically grown heterojunctions between chevron GNR (cGNR) and binaphthyl-cGNR segments exhibit straddling Type I band alignment in structures that are only one atomic layer thick and 3 nm in width.

Emerging Bottom‐Up Strategies for the Synthesis of Graphene Nanoribbons and Related Structures

“…[80] In the past 10 years,the Katz-modified Mallory reaction has been used to prepare aw ide variety of PA Hs,t he most popular examples being coronenes [81][82][83][84][85] and fused perylenediimides (PDIs). [86][87][88][89][90][91][92][93][94][95] Despite the success of this reaction to prepare nanographenes in high yields,t here are rare examples of its use for the synthesis of GNRs.Nuckolls and co-workers were the first to report the use of the Mallory reaction for the synthesis of finite-length GNRs.Starting from monobromo,dibromo and monostannane derivatives (21-23,S cheme 5), the PDI units were linked together through aS tille coupling using an iterative approach and the rigid ribbon structures were formed by aM allory reaction (compounds [24][25][26]. [96] Theoretical calculations suggest that these ribbons adopt ac onformation that is either waggling or helical.…”

Design of Atomically Precise Nanoscale Negative Differential Resistance Devices

“…[2][3][4][5][6][7][8][9][10][11][12][13] The recent development of graphene and graphene nanoribbons (GNRs) offers new opportunities to design nanoscale devices and to test NDR at the atomic scale. [15][16][17][18][19][20][21][22][23] In particular, controllable polymer-to-GNR conversion reaction was demonstrated using charge injection from a scanning tunneling microscope (STM) tip. [15][16][17][18][19][20][21][22][23] In particular, controllable polymer-to-GNR conversion reaction was demonstrated using charge injection from a scanning tunneling microscope (STM) tip.…”

Tuning the Electronic Properties of Atomically Precise Graphene Nanoribbons by Bottom‐Up Fabrication

“…has fabricated chevron GNR(CGNR)/binaphthyl‐ CGNR heterojunction (Figure f) using three precursors, they are molecule 23b, 32a and 32b, respectively. This heterojunction between CGNR and binaph‐ CGNR segments exhibit straddling Type I band alignment as shown in Figure g . Similarly, C et al.…”

“…(c), (d) and (e) Chemical structure, dI/dV spectra and theoretical calculation of the fluorenone/unfunctionalized chevron GNR heterojunction, respectively. (f) and (g) Chemical structure and dI/dV spectra of CGNR/binaph‐CGNR heterojunction, respectively . (h) STM image and corresponding atomistic model of a 7/5+/7 heterojunction .…”

“…In recent years, GNRs have been extensively investigated as promising building blocks for nanoelectronics and spintronics . Moreover, the electronic properties of GNRs can be modulated at atomic level by changing width of AGNRs, “doping” with heteroatoms and formation of heterojunctions . At the same time, introduction of non‐benzenoid rings into the honeycomb lattice is an effective way to modulate the electronic structures properties of two dimensional carbon‐based structures .…”