Molecular Self‐Assembly on Graphene

Abstract

The formation of ordered arrays of molecules via self-assembly is a rapid, scalable route towards the realization of nanoscale architectures with tailored properties. In recent years, graphene has emerged as an appealing substrate for molecular self-assembly in two dimensions. Here, the first five years of progress in supramolecular organization on graphene are reviewed. The self-assembly process can vary depending on the type of graphene employed: epitaxial graphene, grown in situ on a metal surface, and non-epitaxial graphene, transferred onto an arbitrary substrate, can have different effects on the final structure. On epitaxial graphene, the process is sensitive to the interaction between the graphene and the substrate on which it is grown. In the case of graphene that strongly interacts with its substrate, such as graphene/Ru(0001), the inhomogeneous adsorption landscape of the graphene moiré superlattice provides a unique opportunity for guiding molecular organization, since molecules experience spatially constrained diffusion and adsorption. On weaker-interacting epitaxial graphene films, and on non-epitaxial graphene transferred onto a host substrate, self-assembly leads to films similar to those obtained on graphite surfaces. The efficacy of a graphene layer for facilitating planar adsorption of aromatic molecules has been repeatedly demonstrated, indicating that it can be used to direct molecular adsorption, and therefore carrier transport, in a certain orientation, and suggesting that the use of transferred graphene may allow for predictible molecular self-assembly on a wide range of surfaces.

Adsorption and STM imaging of polycyclic aromatic hydrocarbons on graphene

“…Indeed, a graphene layer may adopt a particular structure once adsorbed, especially on a rough SiO 2 substrate, on SiC [47,48], on metallic surfaces [46,49] such as Ru(0001), Rh(111), Pt(111), Ir(111), or Ni(111), or on h-BN [50]. Even if a moiré pattern was observed on Cu(111) with STM [51], as well as preferential sticking of molecules on some parts of the moiré [52], one anticipates that the reconstruction of the graphene layer is small enough to consider an unperturbed substrate for molecular adsorption. For the Cu surface and the tip we limited the basis set to a single 4s orbital, except for the apex Cu atom which was modeled with two Slater exponents to allow for long-range interactions with the adsorbates in the tunneling junction.…”

Supramolecular heterostructures formed by sequential epitaxial deposition of two-dimensional hydrogen-bonded arrays

“…The formation of two-dimensional supramolecular arrays provides a highly flexible route to the control of the spatial organization, down to the molecular scale, of the chemical functionality of a surface [1][2][3][4] . These molecular networks, which can be formed through selfassembly processes on a variety of different substrates including semiconductors 5,6 , metals 7,8 , insulators [9][10][11] and layered materials [12][13][14][15] , are, in almost all cases, limited to monolayer thickness.…”

Graphene wrinkle effects on molecular resonance states

“…31 Using the highly flexible and reproducible CVD fabrication technique, we fabricated single-layer graphene films on copper foil using methane as the carbon precursor. The electronic and structural properties of molecular adsorbates on epitaxial graphene have been well characterised 23,[32][33][34] and the role of graphene edges on molecular conductance gaps 35 is known. By contrast, the effect of out-of-plane wrinkles (outsized ripples with an aspect ratio larger than 1) 36 present on CVD-grown graphene (commonly used in the fabrication of graphene electrodes) on the energetic states of molecules remain to be fully clarified.…”