The surface morphology of poly(3,4-ethylenedioxythiophene) (PEDOT) was investigated in the vapor-phase polymerization of the thiophene monomer on a flexible polyethyleneterphthalate (PET) substrate film. The PET surface was modified with ethylene diamine maintaining the surface roughness within 2 nm to create amine and amide groups for the enhanced hydrophilic interaction with Fe(III)-tosylate (Fe(OTs)(3)) and for the desirable hydrogen bonding with thiophene monomer as well as PEDOT. Polymerization rate was reduced by incorporating pyridine as a reaction retardant to control the surface roughness and conductivity of PEDOT thin films. The optimal conditions of pyridine and glycerol were found at a pyridine/Fe(OTs)(3) molar ratio of 0.5 and a glycerol concentration of 4-5 wt.%, respectively, providing the conductivity up to 500 S/cm and the surface roughness < 2 nm. (c) 2007 Elsevier B.V. All rights reserved.