The 'graphene rush' that started almost a decade ago is far from over. The dazzling properties of graphene have long warranted a number of applications in various domains of science and technology. Harnessing the exceptional properties of graphene for practical applications however has proved to be a massive task. Apart from the challenges associated with the large-scale production of the material, the intrinsic zero band gap, the inherently low reactivity and solubility of pristine graphene preclude its use in several high- as well as low-end applications. One of the potential solutions to these problems is the surface functionalization of graphene using organic building blocks. The 'surface-only' nature of graphene allows the manipulation of its properties not only by covalent chemical modification but also via non-covalent interactions with organic molecules. Significant amount of research efforts have been directed towards the development of functionalization protocols for modifying the structural, electronic, and chemical properties of graphene. This feature article provides a glimpse of recent progress in the molecular functionalization of surface supported graphene using non-covalent as well as covalent chemistry.

One current key challenge in graphene research is to tune its charge carrier concentration, i.e., p- and n-type doping of graphene. An attractive approach in this respect is offered by controlled doping via well-ordered self-assembled networks physisorbed on the graphene surface. We report on tunable n-type doping of graphene using self-assembled networks of alkyl-amines that have varying chain lengths. The doping magnitude is modulated by controlling the density of the strong n-type doping amine groups on the surface. As revealed by scanning tunneling and atomic force microscopy, this density is governed by the length of the alkyl chain which acts as a spacer within the self-assembled network. The modulation of the doping magnitude depending on the chain length was demonstrated using Raman spectroscopy and electrical measurements on graphene field effect devices. This supramolecular functionalization approach offers new possibilities for controlling the properties of graphene and other two-dimensional materials at the nanoscale.

Thin MoS 2 films continue to be of key interest for numerous applications; however, effective doping and high metal to MoS 2 contact resistance are challenges for future applications. We report on the self-assembly of oleylamine on top of MoS 2 thin-films and the effective doping of MoS 2 thin-film field effect transistors by oleylamine. Atomic force microscopy revealed that oleylamine organizes in lamellae domains on MoS 2 thin films with similar characteristics of those previously observed on highly ordered pyrolytic graphite. A carrier concentration increase from 7.1 Â 10 11 cm À2 up to 1.9 Â 10 13 cm À2 at 0 V gate voltage is achieved together with a reduction of the contact resistance by a factor of 5 when using gold as metal contact. Furthermore, this noncovalent doping proves to be removable and reproducible among different flakes and does not degrade the electron mobility. Thus, this work opens the path for future works on controlling the doping of MoS 2 by proper selection of the self-assembled species. Published by AIP Publishing.

Graphene-based two-dimensional (2D) materials are promising candidates for a number of different energy applications. A particularly interesting one is in next generation supercapacitors where graphene is being explored as an electrode material in combination with room temperature ionic liquids (ILs) as electrolytes. Since the amount of energy that can be stored in such supercapacitors critically depends on the electrode-electrolyte interface, there is considerable interest in understanding the structure and properties of the graphene/IL interface. Here we report on the changes in the properties of graphene upon adsorption of a homologous series of alkyl imidazolium tetrafluoroborate ILs using a combination of experimental and theoretical tools. Raman spectroscopy reveals that these ILs cause n-type doping of graphene and the magnitude of doping increases with increasing cation chain length despite the expected decrease in the density of surfaceadsorbed ions. Molecular modelling simulations show that doping originates from the changes in the electrostatic potential at the graphene/IL interface. The findings described here represent an important step in developing a comprehensive understanding of the graphene/IL interface.

Doping of graphene by self-assembled molecular network of uncharged dibenzyl viologen (DBV0) generated in situ.