Both bright-field (Fig. (i)) and dark-field (Fig. (ii)-(iii)) mode TEM images show that the flat aqueous side consists of a compact layer of PEDOT nanofibers that run parallel to the ITIES. The diameter of the PEDOT nanofibers varies from < 5 nm to above 50 nm. We propose that the nanofibers with a diameter of < 5 nm are first to be deposited at the ITIES during interfacial electrosynthesis, forming an initial compact layer. Subsequently, the nanofiber diameter increases as the thin film grows down into the organic phase.