Synthesis of structurally well-defined and liquid-phase-processable graphene nanoribbons

Abstract

Graphene nanoribbons (GNRs) are excellent candidates for next-generation electronic materials. Unlike GNRs produced by "top-down" methods such as lithographical patterning of graphene and unzipping of carbon nanotubes that cannot reach structural perfection, the fabrication of structurally well-defined GNRs has been achieved by a "bottom-up" organic synthesis via solution-mediated or surface-assisted cyclodehydrogenation. Specifically, non-planar polyphenylene precursors were first "build up" from small molecules, and then "graphitized" and "planarized" to yield GNRs. However, fabrication of processable and longitudinally well-extended GNRs has remained a major challenge. Here we report a "bottom-up" solution synthesis of long (>200 nm), liquid-phase processable GNRs with well-defined structure and a large optical bandgap of 1.88 eV. Scanning probe microscopy demonstrates self-assembled monolayers of GNRs, and non-contact, time-resolved Terahertz conductivity measurements reveal excellent charge-carrier mobility within individual GNRs. Such structurally well-defined GNRs offer great opportunities for fundamental studies into graphene nanostructures, as well as development of GNR-based nanoelectronics.DOI: 10.1038/NCHEM.1819 http://www.nature.com/nchem/journal/v6/n2/abs/nchem.1819.html 2 Graphene nanoribbons (GNRs), defined as nanometre-wide strips of graphene, are attracting increasing attention as highly promising candidates for next generation semiconductor materials 1,2,3,4 . Quantum confinement effects impart GNRs with semiconducting properties, i.e. with a finite bandgap, which critically depends on the ribbon width and its edge structure 1,3 . Fabrication of GNRs has been primarily carried out by "top-down" approaches such as lithographical patterning of graphene 5,6 and unzipping of carbon nanotubes 7,8 , revealing their semiconducting nature and excellent transport properties 1 . However, these methods are generally limited by low yields and lack of structural precision, leading to GNRs with uncontrolled edge structures.In contrast, a "bottom-up" chemical synthetic approach based on solution-mediated 9,10,11,12,13 or surface-assisted 14 cyclodehydrogenation, namely "graphitization" and "planarization", of tailor-made three-dimensional polyphenylene precursors offers an appealing strategy for making structurally well-defined and homogeneous GNRs. The polyphenylene precursors are built up from small molecules, and thus their structures can be tailored within the capabilities of modern synthetic chemistry 15 . However, GNRs (>30 nm) produced by solution-mediated methods have been precluded from unambiguous structural characterization, i.e. microscopic visualization, due to their limited processability 9,12 . On the other hand, GNRs produced by the surface-assisted protocol have been characterized to be atomically precise using scanning tunnelling microscopy (STM) 14 . Nevertheless, this method can only provide a limited amount of GNR material, which is further bound to a metal surface, impeding wide...

Evolution of Graphene Molecules: Structural and Functional Complexity as Driving Forces behind Nanoscience

“…Since 2010, we have introduced a whole new class of GNRs with polymer 4a as the most recent example 49 (Scheme 5). The synthesis included the twisted precursor polymer 13a which was obtained by a repetitive Diels-Alder cycloaddition of the AB-type monomer 13.…”

Bulk properties of solution-synthesized chevron-like graphene nanoribbons

“…Several recent studies have focused on the synthesis of GNRs by the bottom-up approaches that rely on building GNRs from smaller molecular species. [7][8][9][10][11][12][13][14][15][16][17][18][19][20] The resulting GNRs are very narrow (typically with widths, w < 2 nm) and have atomically precise edges, which is very important for potential applications. [3][4][5][6]21,22 One type of synthetic GNRs that has received considerable theoretical [23][24][25] and experimental attention 9,16,19,20,26 is the chevron-like GNR that has a very distinct periodic structure (Fig.…”

Graphene based metal and metal oxide nanocomposites: synthesis, properties and their applications

“…29 The bottom-up growth of graphene sheets is an alternative to the mechanical exfoliation of the bulk graphite. In bottom-up processes, graphene is synthesized by a variety of methods such as chemical vapor deposition (CVD), 45,46 arc discharge, 47 epitaxial growth on SiC, 48 chemical conversion, 49 reduction of CO, 50 unzipping carbon nanotubes 51,52 and self-assembly of surfactants. 53 The CVD approach to produce graphene relies on dissolving carbon into metal surfaces, such as Ni and Cu that act as catalysts 54,55 and then forcing it to separate by cooling the metal.…”