Electrochemical and Atomic Force Microscopy Study of Carbon Surface Modification via Diazonium Reduction in Aqueous and Acetonitrile Solutions

Abstract

Electrochemical reduction of the diazonium salts of 4-nitrobenzene and 4-nitroazobenzene-4'- has been investigated in aqueous acid and acetonitrile media at carbon surfaces. Using pyrolyzed photoresist films as the substrate, we have examined the deposited films using electrochemistry and atomic force microscopy (AFM). Film thicknesses were measured by scratching through the film with an AFM tip. The procedure employed two AFM cantilevers with different lengths, located on the one device. When the shorter cantilever engages the surface in tapping mode, the longer cantilever (which is not resonating) imbeds into the surface with a constant force. For both modifiers and modification media, film thicknesses increase with deposition time to a limiting value. With equivalent modification conditions, films prepared in aqueous acid medium have lower limiting thicknesses than those prepared in acetonitrile. For nitrophenyl (NP) films, the same trends are found when calculating surface coverages from the charge associated with the reduction of surface -Ar-NO2 groups. Lower limiting film thicknesses and surface coverages for films prepared in aqueous conditions is attributed to growth of inherently more blocking films and is supported by examination of the response of the Fe(CN)6(3-/4-) couple at NP-modified surfaces. Combination of voltammetrically determined surface coverage and film thickness data yields a surface coverage of -Ar-NO2 groups of (2.5 +/- 0.5) x 10(-10) mol cm(-2) for a film thickness equivalent to a monolayer of NP groups.

Covalent modification of graphitic carbon substrates by non-electrochemical methods

“…AFM depth profiling of films grafted to PPF showed a maximum thickness of 3.8 nm, and a linear relationship between surface concentration of nitrophenyl groups and film thickness. The surface concentration per monolayer thickness of nitrophenyl groups was (3.2 ± 0.5) x 10 -10 mol cm -2 , close to that previously determined for electrochemically grafted layers [28], suggesting a similar film structure after spontaneous and electrochemical grafting. Spontaneous grafting of carboxyphenyl groups to PPF from acidic solutions of the corresponding diazonium salt was also successful.…”

“…It is well-established that electroreduction of aryldiazonium salts on carbon can lead to multilayer film growth [26,27,28,33]. The thickness of the layer (typically ranging from one monolayer, ca.…”

“…A second consideration is that different film structures (monolayer vs multilayer or closepacked vs loosely packed) may result from different modification strategies. For example, electrochemical grafting tends to lead to multilayer or polymeric films, and it may be difficult to limit the grafting to a monolayer [26,27,28]. Different attachment strategies also lend themselves more or less easily to patterning, an important consideration for applications of modified carbon surfaces in areas such as sensors and molecular electronics.…”

Electrografting of calix[4]arenediazonium salts to form versatile robust platforms for spatially controlled surface functionalization

“…Gold substrates (gold layer onto Si substrates) were purchased from Aldrich and thoroughly cleaned before surface functionalization (piranha solution). PPF samples were prepared according to previously published procedure 57 . Surface modification by electrochemical reduction of in situ generated diazonium cations was carried out in an ice bath.…”

Nanoscale films covalently attached to conducting substrates: structure and dynamic behaviour of the layers

“…The depth profiling technique involves using an AFM tip to remove a section of film grafted to a PPF substrate, and then scanning across the scratch to determine its depth and hence the film thickness [25]. Figure 2a shows a cyclic voltammogram of a PPF surface with a film grafted from pnitrobenzenediazonium salt [25]. In acid solution, the reduction of nitrophenyl groups at E pc § -0.7 V affords the aminophenyl and hydroxylaminophenyl groups through the reactions described in equations 1 and 2.…”