AFM study of the initial stages of polyaniline growth on ITO electrode
Introduction
In the last decades, the growing interest in the study of conducting polymers has resulted in an extensive number of publications, which established the importance of these systems for different technological applications [1], [2]. The studies concerning electrochemically induced polyaniline (PAni) growth have shown that the deposit characteristics depend on several parameters such as solution composition (including monomer concentration and electrolyte nature) [3], [4], [5], applied potential [6], [7], [8], [9], current density [10] and temperature [11]. Moreover, electrochemical techniques can provide a very useful tool to analyse the nucleation and growth processes, as well as to provide control over some parameters such as film thickness and film density [11].
Several studies concerning conductive polymer nucleation and growth are available in the literature, since the works of Pletcher with polypyrrole [12], [13] and Hillman with polythiophene [14]. The dependence of PAni film morphology on the nature of the substrate has been extensively demonstrated [15], [16], [17], including the variation from fibrilar to globular morphologies. However, such demonstrations only concerned to the best of our knowledge, massive PAni deposits, while the origin of such differences should be better associated with the initial stages of deposition and growth. The results presented in the literature demonstrate that, after the initial stages of nucleation and growth, the film morphology is affected, mainly, by the final thickness of the deposit [11], instead of the substrate nature. In this way, the study of the initial stages of nucleation and growth of PAni is a matter of relevance in order to discuss the effect of the substrate in the film characteristics. However, few papers concerning such a theme can be found in the literature [3], [7], [18]. It was reported that the electrodeposition of PAni includes a nucleation process similar to that for metal deposition, occurring with a 2D or 3D progressive nucleation, depending on the experimental conditions [3], [7], [15].
An important tool that is beginning to be used in the studies of the early stages of electrocrystallisation of metals and polymers is atomic force microscopy (AFM) [19], [20], [21]. A recent publication [22] from one of the authors showed that, at the nuclei scale, scanning electron microscopy (SEM) does not have sufficient resolution to show hemispherical nuclei of the depositing species. On the other hand, by using AFM the authors were able to show the overlay of hemispherical nuclei of Ni and Co on a Au substrate, with a mean diameter of approximately 20 nm.
In this way, the aim of this work is to study the initial stages of PAni electrodeposition on ITO by chronoamperometry and AFM.
Section snippets
Experimental
The electrochemical synthesis of PAni was carried out using cyclic voltammetry and chronoamperometry in aqueous (Milli-Q, Millipore, water) medium, in the presence of aniline (Aldrich 99.5% ACS), using a three-electrode cell. The working electrode was a foil of ITO (geometric area ) (ASAHAI/Japan). A Pt foil (geometric area ) was used as counter electrode and a hydrogen reversible electrode (HRE) was used as reference.
The ITO electrodes were cleaned by
Results and discussion
The voltammetric response of a clean ITO electrode in aniline is presented in Fig. 1. It can be observed that the current for the electro-oxidation of aniline begins to increase at approximately 1.1 V, in the direct sweep. After inversion, at 1.3 V, the anodic current continues to increase in the negative sweep due, mainly, to: (a) the overpotential region relative to the aniline oxidation and (b) the increase in the electrode surface area due to the film formation. The
Conclusions
The AFM analysis of the initial stages of PAni deposition on ITO surfaces showed a strong influence of the substrate in the film morphology. The globular aspect of ITO surface is still present at the first stages of polymer deposition. For the less anodic potential values, the only morphological evidence of film deposition is an increase in the roughness value. The micrographs at higher magnification showed neighboring globular deposits, under these experimental conditions. This aspect is
Acknowledgments
The authors wish to thank Conselho Nacional de Desenvolvimento Cientı́fico e Tecnológico (CNPq) and Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) for financial support.
References (28)
Synth. Met.
(1997)- et al.
Electrochim. Acta
(1997) - et al.
Synth. Met.
(1997) - et al.
Electrochim. Acta
(1998) - et al.
Electrochim. Acta
(1994) - et al.
Electrochim. Acta
(1992) - et al.
Synth. Met.
(1995) - et al.
J. Electroanal. Chem.
(1993) - et al.
J. Electroanal. Chem.
(1992) - et al.
Synth. Met.
(1999)
J. Electroanal. Chem.
J. Electroanal. Chem.
Polymer
J. Electroanal. Chem.
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