Imaging the Nucleation and Growth of Thin-films of Poly(3,4- ethylenedioxythiophene) (PEDOT) using In-situ Liquid Transmission Electron Microscopy

Conducting polymer thin films have received considerable scientific and commercial interest for a variety of applications like photovoltaics, organic electronics and neural interfaces. (PEDOT) is particularly important due to its chemical and mechanical stability and high charge transport properties. The morphology of electrochemically-polymerized thin-films can be fine-tuned by controlling the early stage nucleation and growth of the oligomeric clusters. We have used in-situ, low dose Transmission Electron Microscopy to obtain a detailed understanding of the fundamental processes occurring at the electrode-solution interface, especially the evolution of the mobile oligomers that precede solid polymer film formation. The total electron doses for our experiments were in the range of 10-20 mC/cm² which is well below the critical dose of PEDOT. We have found that the growth rates of individual nuclei were somewhat irregular. Certain droplets were found to gradually decrease in size and mass thickness, indicating some degree of reversibility of the process. We have also found substantial variations when the chemistry of the monomer is changed, including a dramatic increase in the nucleation density when a more hydrophilic, carboxylic acid substituted EDOT was used as a comonomer.