AFM phase imaging of electropolymerized polybithiophene films at different stages of their growthстатья
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Дата последнего поиска статьи во внешних источниках: 7 ноября 2016 г.
Аннотация:The degree of crystallinity in electronically conducting polymers can affect a variety of important properties such as the work function, conductivity, and charge mobility. In out-previous work (O'Neil, K. D.; Shaw, B.; Semenikhin, O. A. J. Phys. Chem. B 2007, 111, 9253), we studied the distribution of the local conductivity and doping level of conducting polymers with nanometer resolution using Kelvin probe microscopy (KFM) and current-sensing atomic force microscopy (CS-AFM). An unambiguous correlation was found between the polymer morphology, the local oxidation degree (related to the work function), and the local conductivity. One of the possible explanations leading to this behavior was a variation in the crystallinity of polymer films during their nucleation and growth. In this work, direct measurements of the local crystallinity of a conducting polymer, polybithiophene, are performed at different stages of the electropolymerization process using phase imaging atomic force microscopy (AFM). It was found that, at the early stages of the polymer nucleation and growth, the polymer films were predominantly crystalline. At the later stages, the polymer contained both crystalline and amorphous phases, with the crystalline polymer located in the grain cores and the amorphous phase found at the grain periphery. These results are in remarkable agreement with the results of the KFM and CS-AFM measurements reported in our previous work, which relates such inhomogeneity to the presence of both high and low molecular weight polymer fractions in the electropolymerization solution (polydispersity). Furthermore, our data show that the inhomogeneity is not only longitudinal (different crystallinity of grain cores and grain periphery), but also latitudinal (there is a pronounced change in crystallinity between the inner and outer layers of the polymer films).