Conductive polymers (CP) belong to an attractive class of materials with plastic-like mechanical properties and electric conductivity typical of metals, which have awakened an increasing interest for several applications, e.g. sensing, electronic and energy. One of the most studied CP is the Poly(3,4-ethylenedioxythiophene) (PEDOT) due to its well-known properties and the advantage of being synthesized as thin-film directly on the substrates of interest. PEDOT thin films can be realized by electrochemical synthesis performed in an aqueous media containing a small quantity of the monomer 3,4-ethylenedioxythiophene (EDOT) and a suitable supporting electrolyte [1-2]. It is known that the process parameters influence both the structural and the electrical properties but further studies on the nucleation and growth mechanisms of the film formation are still required. Thus, it can be useful to monitor in real-time the synthesis process of PEDOT films in order to tune the process parameters and produce films with reproducible specific properties. Up to now, atomic force microscopy (AFM) based techniques have been employed to underlying the morphological features of the films at different steps of the deposition process and their related conductive properties but results of an in situ AFM investigation are not yet reported.
In this work, the growth mechanism of electrodeposited PEDOT films are investigated by using the electrochemical atomic force microscopy (EC-AFM) in order to determine the correlation between their morphological features and the electrochemical parameters of the process. In EC-AFM, a standard AFM apparatus is equipped with a three-electrode electrochemical cell whose working electrode is the sample surface where the electrodeposition takes place. Thus, a real time study of the electrochemical reactions occurring at the surface of the sample is achieved and the in situ surface morphology evolution is monitored by using an unbiased AFM probe. In particular, the electropolymerization of EDOT is observed performing a cyclic voltammetry and controlling the evolution of current flowing through the electrode surface, together with a standard AFM image. By varying the supporting electrolyte concentration, the voltammetry scan rate and the working electrode surface, the nucleation and growth mechanisms of the film are investigated and the results are compared with the already hypothesized growth model.
Overall, this work demonstrates the capability of the EC-AFM to deepen the growth mechanism of electrodeposited polymeric films with tunable and reproducible properties.
[1] E. Tamburri et al., Synthetic Metals, 159 (2009) 406–414.
[2] V. Castagnola et al., Synthetic Metals, 189 (2014) 7–16.