On-Surface Growth Dynamics of Graphene Nanoribbons: The Role of Halogen Functionalization

Abstract

On-surface synthesis is a powerful route toward the fabrication of specific graphene-like nanostructures confined in two dimensions. This strategy has been successfully applied to the growth of graphene nanoribbons of diverse width and edge morphology. Here, we investigate the mechanisms driving the growth of 9-atom wide armchair graphene nanoribbons by using scanning tunneling microscopy, fast X-ray photoelectron spectroscopy, and temperature-programmed desorption techniques. Particular attention is given to the role of halogen functionalization (Br or I) of the molecular precursors. We show that the use of iodine-containing monomers fosters the growth of longer graphene nanoribbons (average length of 45 nm) due to a larger separation of the polymerization and cyclodehydrogenation temperatures. Detailed insight into the growth process is obtained by analysis of kinetic curves extracted from the fast X-ray photoelectron spectroscopy data. Our study provides fundamental details of relevance to the production of future electronic devices and highlights the importance of not only the rational design of molecular precursors but also the most suitable reaction pathways to achieve the desired final structures.

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.…”

“…[20] On the one hand, on-surface synthesis requires simple halogenated, aromatic building blocks that can be assembled in one-dimension array of molecules. [21][22][23][24][25][26] TheG NRs thus obtained are often defect-free,a llowing the comprehensive study of their electronic properties.H owever,s ophisticated microscopy tools are needed to follow the reaction and study the properties,a nd very low amount of materials can be produced. On the other hand, solution-phase synthesis requires more complex building blocks,m ore synthetic steps and sometimes tedious purification processes,b ut allows the production of large quantity of materials.…”

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

“…M. Di Giovannantonio et al. explored the mechanisms of extending GNR via changing monomer of the different halogen functionalization units . Figure a is showing on‐surface synthesis of 9‐ AGNRs using halogen functionalization (Br or I) of the molecular precursors.…”

“… Real‐time investigation of dehalogenation . (a) On‐surface synthesis of 9 ‐AGNRs by debromination and deiodination.…”

Effect of Edge Functionalization on the Bottom‐Up Synthesis of Nano‐Graphenes

“…The preliminary demonstration of electronic devices was also reported, in which GNRs without intentional doping were used in the channel. While the effect of halogen, substrate, and impurities as well as growth kinetics in on‐surface Ullman coupling have been reported so far, the mechanism of on‐surface polymerization is not yet thoroughly investigated. Without comprehensive understanding of the mechanism, the on‐surface synthesis has largely relied on the haphazard trial and errors.…”