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Controlled functionalization of graphene

Opening a gap by photocycloaddition

par Guy Molénat - publié le , mis à jour le

Surfaces of graphene on Cu (111) or on mica can be functionalized in a controlled manner by photo-cycloaddition reactions with a monolayer of a maleimide dienophile. These molecules are transferred to the graphene surface under ultra-high vacuum and organize themselves in an orderly manner into a supramolecular assembly via intermolecular hydrogen bonds. The formation of covalent bonds between the molecules and the graphene substrate by cycloadditions [2 + 2] or [2 + 4] is activated by irradiation in ultra-violet. This grafting modifies the properties of graphene with the formation of an electronic gap.

The controlled functionalization of graphene is a subject of major interest because it should open the door to the modification of the electronic properties of this 2D material, for example by opening a gap, or to add functionalities (chemical, optical, biochemical) provided by the anchored molecule. However, this grafting is difficult because graphene is a poorly reactive material, except at its defects. A solution to this problem is to use cycloaddition reactions between the double bond activated of a molecule (a dienophile) and one or two "double bonds" (ene or diene) of graphene in the Kékulé representation. We showed in 2017 [Ref 2] that the formation of these covalent bonds with graphene locally disturbed the electronic properties of graphene. However, this grafting was randomly distributed on the surface and the article concluded by suggesting a possibility of controlling the organization of these reactive sites on the surface using supramolecular self-assembly. This second hedge has just been crossed in the frame of an international cooperation involving four other countries, China, Denmark, Canada and the United Kingdom. In these experiments, the maleimide molecule is functionalized with a phenyl-3,5-dicarboxylic group. After sublimation under ultra-high vacuum on a graphene surface on Cu (111) or on mica, the molecules organize themselves in a very ordered six-fold fashion on the surface to form hexagons held by hydrogen bonds between the carboxylic acid functions. These supramolecular structures, which do not involve covalent bonds between the molecules and graphene, are relatively fragile. The reaction can then be photochemically activated by ultraviolet irradiation. Here again, it leads to [2 + 2] or [2 + 4] cycloadditions but in a totally controlled geometry over areas of several hundred square nanometers. The molecules are then covalently linked and this robust grafting confers a great thermal stability to the system. The electronic properties of these modified surfaces have been studied by tunneling microscopy and numerous surface spectroscopic techniques and we have been able to show the opening of a gap of around 170 meV in the irradiated areas.

This result opens the way to prospects for local control of the electronic structure of functionalized graphene, for example using masks during the irradiation phase.



1 - Thèse de Cristina Mattioli (Synthesis and study of molecules for graphene functionalization, 2014) http://thesesups.ups-tlse.fr/2362/ dans le cadre de ANR ChimGraphN (coordinateur : L. Simon)

2 - Covalent functionalization by cycloaddition reactions of pristine, defect-free graphene. L. Daukiya et al. ACS Nano (2017) 11 (1), 627–634 DOI : http://pubs.acs.org/doi/abs/10.1021/acsnano.6b06913


Long-range ordered and atomic-scale control of graphene hybridizationby photocycloaddition

Miao Yu,* Chong ChenQi Liu, Cristina Mattioli, Hongqian Sang, Guoqiang Shi, Wujun Huang, Kongchao, Shen, Zhuo Li, Pengcheng Ding, Pengfei Guan, Shaoshan Wang, Ye Sun, Jinping Hu, André Gourdon,* Lev Kantorovich,* Flemming Besenbacher*, Mingshu Chen, Fei Song, Federico Rosei, and Xueming Yang

Nature Chemistry (2020) https://www.nature.com/articles/s41557-020-0540-2

 Contact : Andre Gourdon (andre.gourdon chez cemes.fr)