CHEMICAL DECORATION OF GRAPHENE AND 2D-MATERIALS: AN AFM OUTLOOK

Session

Poster Session 2

Authors

Dr Vladimir Korolkov (1)

Affiliations

1. Park Systems UK Ltd

Keywords

graphene, self-assembly, molecules, high resolution, supramolecular, surface, 2D-materials

Abstract text

The formation of two-dimensional (2D) supramolecular arrays has been proven as a highly versatile route to the control of the spatial organization, down to the molecular scale, of the chemical functionality of a surface. These molecular networks, which can be formed through self-assembly processes on a variety of different substrates, including semiconductors, metals, insulators and layered materials, are, in almost all cases, limited to surfaces of bulk crystals. Progress towards chemical decoration of graphene and other 2D-materials, that have a thickness of an atom, has been quite limited so far. Likewise, the growth of higher layers on such materials has not even been reported. Although, similar inorganic structures – Van-der-Waals heterostructures – are a very popular research subject. Specifically, the additional functional control, which may be achieved through the formation of heterostructures realized by placing one supramolecular layer on another to result in growth into the third dimension perpendicular to the substrate, has not been widely explored for these materials. Here we describe the successful formation of heterostructures formed by the sequential growth of distinct 1D and 2D arrays on graphene. It is possible, using high-resolution atomic force microscopy (AFM), to determine an epitaxial alignment between successive layers. We chose to investigate a combination of a bicomponent hexagonal network (CAM) formed by cyanuric acid (CA) and melamine (M), and monocomponent honeycomb and linear arrays formed by, respectively, trimesic acid (TMA) and 2,6-Naphthalenedicarboxylic acid (NDA). The heterostructures are formed by first depositing a CAM monolayer that is then used as the substrate for a further deposition cycle whereby monolayers of TMA or NDA are adsorbed to form a heterostructure. The layers are deposited via sequential immersion in solutions, and we have investigated heterostructure formation on the surface of graphene. We use ambient AFM to acquire images of the molecular arrangements in adsorbed networks. This work represents a significant advance in chemical decoration of graphene and the application of AFM to imaging such networks through the acquisition of images, under ambient conditions, with sufficiently high resolution to identify the relative placement of molecules in different layers of the resulting heterostructures. 

In the future, we envisage that this approach to chemical decoration of graphene and building supramolecular heterostructures will provide the foundation for the growth of much more complex materials in which multiple layers can be deposited sequentially with the possibilities to tune the chemical, optical and electronic properties of the resulting organic/inorganic heterostructure. The exploitation of hydrogen bonding stabilizes the growth of 2D sheets that have highly parallel interfaces. The use of graphene as a substrate suggests that this approach can be combined with 2D materials to introduce molecular functionality into stacked device architectures, and may also provide a complete molecular analogue approach to the stacking of layered materials.