Synthesis of linked carbon monolayers: Films, balloons, tubes, and pleated sheets

Abstract

Because of their potential for use in advanced electronic, nanomechanical, and other applications, large two-dimensional, carbon-rich networks have become an important target to the scientific community. Current methods for the synthesis of these materials have many limitations including lack of molecular-level control and poor diversity. Here, we present a method for the synthesis of two-dimensional carbon nanomaterials synthesized by Mo-and Cu-catalyzed cross-linking of alkyne-containing selfassembled monolayers on SiO 2 and Si3N4. When deposited and cross-linked on flat surfaces, spheres, cylinders, or textured substrates, monolayers take the form of these templates and retain their structure on template removal. These nanomaterials can also be transferred from surface to surface and suspended over cavities without tearing. This approach to the synthesis of monolayer carbon networks greatly expands the chemistry, morphology, and size of carbon films accessible for analysis and device applications.networks ͉ nanomaterials ͉ self-assembled I n contrast to carbon nanotubes, fullerenes and various derivatives (1-3), the synthesis of large 2D sheets such as graphene (4), graphyne, and graphdiyne (5, 6) extending over micrometers in lateral dimensions is either in its infancy or has significant limitations. In fact, the synthesis of 2D carbon networks has been recognized as an outstanding challenge in materials chemistry (7).Graphene, the simplest of the 2D conjugated carbon nanomaterials, is produced by micromechanical cleavage of bulk graphite (HOPG) or by thermal decomposition of silicon carbide (8, 9). However, these approaches lack the molecular-level control necessary to define the chemical makeup of these systems. Scholl coupling reactions on oligophenylene precursors (10) produce small (Ͻ15 nm) 2D graphene fragments with improved molecular diversity, and radiation induced modifications of self-assembled (11, 12) or Langmuir-Blodgett (13) monolayers create larger sheets, but with reduced control of the chemistry. Polyelectrolytes (14) represent a different class of chemistry that can form 2D (15) and 3D (16) nanomaterials. These films are formed through deposition of separately synthesized polymers, often in layer-by-layer assemblies, in the form of relatively thick (typically Ͼ5 nm) films governed by electrostatic interactions. These limitations, together with those associated with the planar, radiation-cross-linked monolayers, motivate the need for alternative approaches to these classes of materials.A potential solution to the formation of large 2D conjugated carbon nanomaterials would employ a two-step procedure involving the formation of self-assembled monolayers (SAMs) with highly functionalized monomers followed by chemical crosslinkage of the SAMs to form linked monolayers. Fig. 1 shows the overall process beginning with the formation of SAMs of suitably designed carbon precursors on solid supports, followed by chemical cross-linking to yield covalently bonded networks with monolayer thicknesses. Not...

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