Scanning Tunneling and Atomic Force Microscopy Evidence for Covalent and Noncovalent Interactions between Aryl Films and Highly Ordered Pyrolytic Graphite

Abstract

International audienceElectroreduction of 4-nitrobenzenediazonium ions at highly ordered pyrolytic graphite (HOPG) gives a nitrophenyl film that is shown by noncontact atomic force microscopy (AFM) to be continuous and of multilayer thickness. Investigation of the same surface by ultrahigh vacuum scanning tunneling microscopy (UHV-STM) reveals molecular species immobilized on the step edges, but only mobile species on the basal planes. After several scans across an area of basal plane, atomic-level resolution images of clean, defect-free graphite surfaces are obtained. The same behavior is observed with a film deposited by reduction of 4-((triisopropylsilyl)ethynyl)benzenediazonium ion. Throughout extensive STM measurements we find no evidence for covalent attachment of aryl groups to the basal plane and conclude that our results can be best explained by the formation of films of physisorbed oligomeric species. After heating above 300 °C, nitrophenyl films are more stable to STM imaging but no longer contain nitro groups. Increased cross-linking within the film from coupling of radicals formed by thermal decomposition of nitrophenyl groups may be responsible for the more robust film structure

Electrochemistry at highly oriented pyrolytic graphite (HOPG): lower limit for the kinetics of outer-sphere redox processes and general implications for electron transfer models

“…a recent STM study with more than 100 scans failed to find any point defects in the basal plane. 99 Likewise, for the study herein, we also carried out STM measurements on AM grade HOPG, with > 100 images (each of 10 × 10 nm 2 ) obtained in randomly selected areas. We could not find a single defect in any of the images (e.g.…”

Nanoscale Electrochemistry of sp2 Carbon Materials: From Graphite and Graphene to Carbon Nanotubes

“…45 We studied the reduction of carboxybenzenediazonium in aqueous solution and found that the electrochemistry and modification were independent of step edge density. 46 Moreover, with SECCM we were able to confine the electrochemical modification to isolate the contribution of the basal plane alone, showing unambiguously that step edges were not required for modification.…”

Electrochemical Behaviour of HOPG and CVD‐Grown Graphene Electrodes Modified with Thick Anthraquinone Films by Diazonium Reduction

“…Very recently, Kirkman et al also proposed that aryl groups are covalently attached at both basal plane and step edge sites of HOPG [46]. In contrast, Ma et al presented an interesting study on the attachment of aryl groups onto HOPG via diazonium reduction, in which they found no clear evidence for covalent attachment of aryl groups to basal plane HOPG [47].…”