ENGINEERING C E LS EV I E R Materials Science and Engineering C 5 (1998) 203-207 Characterization of polypyrrole containing Langmuir-Blodgett films by surface specific techniques C. Gerardi *, F. DeRiccardis, E. Milella PASTIS-CNRSM, Centro Nazionale Ricerca e Svihtppo Mareriali, Strada Statale 7 'Appia ', km 714, 1-72100 Brindisi, Italy Received 11 November t996 Abstract Ferric stearate Langmuir-Blodgett films modified by solid state reaction have been characterized with the purpose of investigating the formation of polypyrrole confined in the ordered structure. We have used X-ray photoelectron spectroscopy and seconda U ion mass spectrometry for the chemical analysis of the surface. Such analyses give evidence of the formation of polypyrrole in the modified Langmuir- Blodgett multilayer and allow us to deduce the oxidation state of the polymer. Furthermore, by means of scanning electron microscopy and SIMS imaging, we have studied the morphology and the chemicaI mapping of the conducting polymer formed in the film. After the solid state reaction, samples exhibit a structure consisting of small clusters with sizes from 50 to 300 nm embedded in a stearic acid matrix. Finally the clusters show a highly conductive behavior if compared with the insulating remaining part of the fihn, further confirming the formation of the conducting polypyrrole domains. © 1998 Elsevier Science S.A. Keywords: Langmuir-Blodgett film; Polypyrrole; SIMS; XPS; SEM 1. Introduction There is a great interest in conducting polymers due to their multiple potential applications [I,2]. Polypyrrole (PPy) belongs to the poly(heterocycles) group [3] and exhibits both polymeric and electroactive properties. The rnain advan- tages which make polypyrrole a promising electroactive material are the high conductivity and the enviromentaI stability. In view of its applications in micro-electronic devices, it is fundamental to address efforts towards the fabrication of structures with reduced geometrical dimensions and ultra- thin films. The Langmuir-Blodgett (LB) technique appears to be particularly suited for the fabrication of low-dimensional materials [ 4,5 ]. Actually, the use of this deposition technique to confine electro-active polymers in ordered thin structures has provided promising results [6,7]. In this work we have characterized LB films which have been manipulated by solid state reaction to confine polypyr- role between the planes of the multilayers. To this aim we have used high surface sensitivity techniques such as second- ary ion mass spectrometry (SIMS), X-ray photoelectron * Corresponding author. Tel.: +39 831 507263; fax: +39 83t 507379; e-math cosimo.gerardi@ st.com 0928-4931/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved PIIS0928-493 I ( 97 ) 00044- 1 spectroscopy (XPS) and scanning electron microscopy (SEM). The confinement of polypyrrole in the LB structure was attained by exposing ferric stearate LB films to hydrogen chloride gas; such a process involves the precipitation of ferric chloride within the planes of a muItilayer. The precip- itated salt acts to polymerize the pyrrole monomers, which are introduced into the film by vapor diffusion and dope the resultant polypyrrole [6]. As a consequence, polypyrrole forms conductive domains confined in between the planes of the insuIating fatty acid multilayer. 2. Experimental For LB deposition a 1 mg/ml solution of stearic acid in chloroform was spread onto a subphase of deionized water containing 4 x 10- 5 M of ferric chloride. The pH of the sub- phase was kept at a value of 5.6 and the temperature was fixed at 15°C. The pressure-area (~r-A) isotherms and the multilayer deposition were performed with a KSV 5000 LB system. The resultant layers were compressed with a barrier rate of 5 mm/min up to a pressure of 35 mN/m. Silicon (100) slides were used as substrates after treatment with hydrofluoric acid. 20 Y-type monolayers were deposited with a dipping rate of 1 mm/min. The transfer ratio was close to