Multilayer Nitroazobenzene Films Covalently Attached to Carbon. An AFM and Electrochemical Study

Abstract

Nitroazobenzene films have been grafted to pyrolyzed photoresist films by electrochemical reduction of the corresponding diazonium salt in acetonitrile solution. Two component films were also prepared by electrochemically grafting methylbenzene layers to preformed NAB films. Voltammetric investigation of the films in aqueous acid medium and the measurement of film thickness using atomic force microscopy (AFM) lead to new insights into film structure. In aqueous acid solution, the azobenzene groups have no detectable electroactivity and not all nitro groups in the films can be reduced. These findings point to a compact film structure in which proton diffusion is limited. There may also be spatial inhibition of the conformational changes that accompany azobenzene reduction. For increasingly thick NAB films, the peak for reduction of the nitro groups moves to more negative potentials and the peaks become more asymmetric in shape. These changes are interpreted in terms of the dielectric properties and the rate of proton diffusion in the films. Film thickness was measured by ploughing through the film with an AFM tip. When an NAB film prepared in acetonitrile solution is reduced in aqueous acid, the film thickness decreases by more than 50%. The changes can be partially reversed by treatment in acetonitrile-electrolyte solution and hence are attributed to ion-solvent induced swelling and shrinking. Thus, the large decrease in thickness detected by AFM after treatment of the film in aqueous acid is consistent with the compact film structure revealed by electrochemistry.

Determination of the Quinone-loading of a Modified Carbon Powder-based Electrode for Electrochemical Capacitor

“…Firstly, with this procedure one assumes that all the immobilized anthraquinone species are electrochemically accessible. This might not be always the case as previously demonstrated for nitrophenyl-modified carbon 18 and although the surface coverage of an electrochemically modified Au electrode with anthraquinone groups was found to vary linearly with film thickness. 19 Secondly, in one of our recent study, the electrochemical behavior of anthraquinone-modified Black Pearls was investigated in electrolyte of various pHs ranging from acidic (0.1 M H 2 SO 4 ) to alkaline (0.1 M KOH) media.…”

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

“…When the same electrochemical and AFM analysis decribed above for nitrophenyl films was applied to films grafted from p-nitroazobenzenediazonium salt, the surface concentration vs film thickness plot shown in Figure 3a was obtained [26]. For this modifier, the relationship between electrochemically-determined surface concentration and film thickness is not linear and it appears that while film thickness increases from 4 to 6 nm, the surface concentration remains constant at approximately 8.…”

Covalent modification of graphitic carbon substrates by non-electrochemical methods

“…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.…”