Microchim. Acta 143, 147–153 (2003) DOI 10.1007/s00604-003-0063-8 Original Paper Morphology of Electropolymerized Poly(N-Methylaniline) Films Qingli Hao 1 , Michael Rahm 2 , Dieter Weiss 2 , and Vladimir M. Mirsky 1; 1 Institute of Analytical Chemistry, Chemo- and Biosensors, University of Regensburg, 93040 Regensburg, Germany 2 Institute of Experimental and Applied Physics, University of Regensburg, 93040 Regensburg, Germany Received May 18, 2003; accepted June 12, 2003; published online November 17, 2003 # Springer-Verlag 2003 Abstract. The influence of polymerization conditions on the morphology of thin films of poly-(N-methylani- line) (PNMA) was studied. The films were prepared by electropolymerization on gold and platinum electrodes and studied by optical and electron microscopy. It was demonstrated that the film morphology does not depend on the polymerization rate or on the electrode metal. However, it is sensitive to the kind of counter ion of PNMA. The polymers containing acetate or chloride do not form stable films. Polymer films containing phosphate or sulfate display inhomogeneous struc- tures. A formation of sprouts and ‘‘nanotubes’’ was observed for PNMA sulfate. The films formed by PNMA perchlorate are smooth and transparent (glass-like structure). A sublayer of 4-aminothiophenol increases the adhesion of polymers to the gold surface. Key words: Poly-(N-methylaniline); polyaniline derivatives; elec- tropolymerization; film morphology. The knowledge about the application potential of polyaniline and other conductive polymers in organic electronics, chemical sensors, or as antistatic, corro- sion protective or electrochromic coatings [1–8] resulted in extensive investigations during the last decade. Substituted polyanilines, including poly(N- methylaniline) (PNMA) [9–15], belong to the com- pounds of interest. Optical properties [16–19] and their modification during protonation and deprotona- tion of the PNMA [15, 16], correlation of optical, electrical and structural properties of PNMA-sulfate [17] were studied. The polymers could be promising for applications in conductometric sensors [20], gas sensors [21] and in potentiometry [18]. However, exploring the unique conductive proper- ties of this polymer requires information on its mor- phology after deposition on electrodes. In this paper we studied the effect of counter ions, polymeriza- tion conditions, electrode materials and adhesive sublayers on the morphology of these polymers, as evaluated by means of optical and electron micro- scopy in the micrometer scale. Experimental N-Methylaniline (analytical grade; from Fluka) was distilled under low pressure and stored in a refrigerator before use. Other chemicals (H 2 SO 4 , HClO 4 , HCl, H 3 PO 4 and CH 3 COOH) were of analytical grade from Merck and used as received. Millipore water was used to prepare all the solutions and to wash the electrodes. Thin film electrodes on glass or silicon support formed by deposi- tion of gold or platinum were provided by R. Bosch GmbH (Germany). The thickness of the metal layer was about 250 nm, and the electrode area was 0.38mm 2 for circle electrodes or 0.25mm 2 for interdigital electrodes. Electropolymerization of poly(N-methylaniline) (PNMA) was performed with a potentio=galvanostat Autolab PGSTAT-12 (Eco- Chemie). A three-electrode cell containing the working electrode, a saturated calomel electrode (SCE) as the reference electrode and a platinum wire as the counter electrode was used. A group of gold electrodes was pre-coated by a sublayer of 4-aminothiolphenol [22]  Author for correspondence. E-mail: vladimir@mirsky.de