The functionalization of carbon electrodes with aryl films can be achieved via the electrochemical reduction of the corresponding diazonium salt. We have previously shown that this deposition procedure will produce multilayer films on ordered graphite under certain conditions. We examine here the formation of multilayer films on glassy carbon (GC) electrodes by potential step electrolysis of diazonium salts for longer periods of time. The deposition of diethylaniline (DEA) is tracked with the use of infrared reflectance absorption spectroscopy and scanning force microscopy. DEA is continually deposited over a 30 min potential step and the film thickness approaches 20 nm. Phenylacetic acid and nitrophenyl films that are 15-25 nm thick can also be deposited in this way. We also find that, despite the presence of a relatively thick DEA film on a GC electrode, electron transfer to benchmark redox systems is not completely blocked. We attribute the compromised blocking to a high density of defects in the film structure.

This paper describes the nucleation and growth of functionalized aryl films on ordered graphite. The attachment of aryl groups to carbon surfaces is induced by the electrochemical reduction of the corresponding diazonium salt. This deposition procedure affords the ability to control film formation by potential cycling in a low concentration of precursor. Electrochemical and scanning probe microscopic techniques were utilized to track film formation. The blocking of Fe(CN)6 3-/4- electron transfer and scanning force microscopy images both indicate that initial nucleation of these films starts at cleavage steps. Continued deposition results in growth on the supposedly nonreactive basal plane. Scanning tunneling microscopy provides clear images of film nucleation on the basal plane, which likely occurs at atomic scale defect sites. The structure of the completed film consists of 3-dimensional features which form via a polymerization type reaction between the bound monolayer and the free radicals in solution.

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Tailoring the surface chemistry of metallic nanoparticles is generally a key step for their use in a wide range of applications. There are few examples of organic films covalently bound to metal nanoparticles. We demonstrate here that aryl films are formed on gold nanoparticles from the spontaneous reduction of diazonium salts. The structure and the bonding of the film is probed with surface-enhanced Raman scattering (SERS). Extinction spectroscopy and SERS show that a nitrobenzene film forms on gold nanoparticles from the corresponding diazonium salt. Comparison of the SERS spectrum with spectra computed from density functional theory models reveals a band characteristic of a Au-C stretch. The observation of this stretch is direct evidence of a covalent bond. A similar band is observed in high-resolution electron energy loss spectra of nitrobenzene layers on planar gold. The bonding of these types of films through a covalent interaction on gold is consistent with their enhanced stability observed in other studies. These findings provide motivation for the use of diazonium-derived films on gold and other metals in applications where high stability and/or strong adsorbate-substrate coupling are required.