Synthetic Metals 145 (2004) 147–151 AFM studies of poly (5-amino-1-naphthol) ultrathin films obtained by associating Langmuir–Schaefer and Langmuir–Blodgett methods C.P.L. Rubinger a , R.L. Moreira a,∗ , B.R.A. Neves a , L.A. Cury a , C.A. Ferreira b , A. Meneguzzi b a Departamento de F´ ısica, ICEx, Universidade Federal de Minas Gerais, Caixa Postal 702, 30123-970 Belo Horizonte, MG, Brazil b Departamento de Materiais, UFRGS, 90035-190 Porto Alegre, RS, Brazil Received 15 September 2003; received in revised form 23 December 2003; accepted 23 April 2004 Available online 19 June 2004 Abstract Atomic force microscopy (AFM) was used to investigate ultrathin films of poly (5-amino-1-naphthol) (PAN) deposited by Langmuir– Schaefer (LS) and Langmuir–Blodgett (LB) on silicon substrates. The AFM probe was also used to perform nano-indentation and nano-delamination of the polymeric film. By measuring the applied vertical force at the beginning of the delamination process and by using an appropriate model for micro-indentation of elastic continuous systems, we estimate the critical interfacial shear strength for the PAN/Si interface as being approximately 160MPa, which indicates that the polymer adheres well to the substrate. The conditions to obtain multiple depositions of the polymeric film on Si substrates are also described. The multilayer PAN films obtained by associating the LS and LB methods were very smooth and uniform, with approximately 5 nm/monolayer. © 2004 Elsevier B.V. All rights reserved. PACS: 68.18.+p; 61.41.+e; 61.16.Ch; 68.35.Gy Keywords: Langmuir-Schaefer; Langmuir-Blodgett; Poly(amino-naphthol); Conjugated polymers; Atomic force microscopy; Adhesion 1. Introduction Poly (5-amino-1-naphthol) (PAN) is a conjugated polymer with good electrical conductivity and chem- ical anti-corrosive properties [1–3]. This material is usually obtained by electrochemical polymerization of 5-amino-1-naphthol (C 10 H 6 NH 2 OH) on metallic electrodes in acidic aqueous or organic media, via the oxidation of the amine group [1–4]. The structure of PAN, showed in Fig. 1, is very similar to the emeraldine form of polyaniline, which is well known for its good passivating property with respect to iron [5,6]. Moreover, the presence of the free reactive –OH groups in the polymeric chain permits further surface reactions, allowing the use of PAN films as a primer coat- ing, with good compatibility with other polymeric materials [2,4]. On the other hand, PAN films have proved to be useful for molecular electronic applications, owing to their semiconductive response and high chemical stability [7]. In view of any of these applications, well-adhered smooth ∗ Corresponding author. Tel.: +55 31 3499 5629; fax: +55 31 3499 5600. E-mail address: bmoreira@fisica.ufmg.br (R.L. Moreira). films of controlled thickness and high substrate coverage are desirable. The presence of the hydroxyl groups in the PAN molecule provides it with a hydrophilic moiety, which is a good de- parture condition for using the Langmuir–Blodgett (LB) technique. This method is usually applied to produce ultra- thin solid films of amphiphilic molecules with controlled architecture and molecular structure [8,9]. In recent years, its use has been extended to prepare ultrathin films of dif- ferent non-amphiphilic molecules of interest in molecular electronics, such as conjugated polymers and fullerenes [8,10–13]. In general, these materials need either to be mixed with classical surfactants (fatty acids) or to be chemically modified. Nevertheless, we showed recently that Langmuir films of PAN can be obtained in the air/water interface, without addition of surfactant molecules or chemical aids. We have also established the conditions of transferring rel- atively uniform Langmuir–Schafer (LS) monolayers of this polymer on silicon substrates [14]. In the present work, we report on our investigations about the formation of PAN multilayer films either by using the LS method alone or by associating the LS and LB methods. The latter procedure allowed us to obtain a better control of the film thickness and roughness. Atomic force microscopy 0379-6779/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.synthmet.2004.04.023