Covalent Modification of Graphene and Graphite Using Diazonium Chemistry: Tunable Grafting and Nanomanipulation

Abstract

We shine light on the covalent modification of graphite and graphene substrates using diazonium chemistry under ambient conditions. We report on the nature of the chemical modification of these graphitic substrates, the relation between molecular structure and film morphology, and the impact of the covalent modification on the properties of the substrates, as revealed by local microscopy and spectroscopy techniques and electrochemistry. By careful selection of the reagents and optimizing reaction conditions, a high density of covalently grafted molecules is obtained, a result that is demonstrated in an unprecedented way by scanning tunneling microscopy (STM) under ambient conditions. With nanomanipulation, i.e., nanoshaving using STM, surface structuring and functionalization at the nanoscale is achieved. This manipulation leads to the removal of the covalently anchored molecules, regenerating pristine sp(2) hybridized graphene or graphite patches, as proven by space-resolved Raman microscopy and molecular self-assembly studies.

Electrochemical Functionalization of Graphene at the Nanoscale with Self-Assembling Diazonium Salts

“…However, a major shortcoming of diazonium chemistry is the limited covalent grafting density in combination with multilayer formation or dendritic growth. 20 Application of electrochemical bias can greatly enhance grafting yield by tuning the Fermi level of graphene, thereby increasing the rate of the electron transfer reaction. The negative potential applied to graphene also concentrates the diazonium cations within the double layer to accelerate the reaction, but the position of the grafted molecules is always random.…”

Nanoscale Electrocatalysis of Hydrazine Electro-Oxidation at Blistered Graphite Electrodes

“…There are 3 broad, and somewhat interrelated, approaches and effects to consider: (i) selective doping of sp 2 materials by various heteroatoms (e.g. N, 22 B, 23 S, 24 and P 25 ); (ii) surface modification with different functional groups by chemical oxidation, or grafting 26,27 and (iii) defects, which may promote electrocatalysis. 28,29 An interesting way to introduce defects is by the intercalation of anions (ClO 4 − , NO 3 − , and SO 4 2− ) during the electrochemical oxidation of sp 2 carbon materials (e.g.…”

Confined polydiacetylene polymerization reactions for programmed length control

“…Covalent modification involves chemisorption of aryl radicals generated electrochemically from diazonium precursors. 15,16 The covalently bound aryl molecules are removed in a systematic manner from the surface during a process called 'nanoshaving'. In the nanoshaved corrals self-assembly can occur on freshly exposed graphite.…”

“…Further experimental details are described in previous works. 16,19,22 Nanocorrals are created within the dense monolayer of grafted aryls by raster scanning the desired area with the STM tip at high current (I t = 200 pA) and low sample bias (V s = À1 mV). These aggressive scanning conditions bring the tip in close proximity to the HOPG surface atoms allowing removal of the covalently bound aryl molecules.…”