Thin polyaniline and polyaniline/carbon nanocomposite films for gas sensing P. Lobotka a, ⁎, P. Kunzo a , E. Kovacova a , I. Vavra a , Z. Krizanova a , V. Smatko a , J. Stejskal b , E.N. Konyushenko b , M. Omastova c , Z. Spitalsky c , M. Micusik c , I. Krupa c a Institute of Electrical Engineering SAS, Dubravska cesta 9, SK-84104 Bratislava, Slovakia b Institute of Macromolecular Chemistry ASCR, Heyrovskeho nam. 2, CZ-162 06 Prague 6, Czech Republic c Polymer Institute SAS, Dubravska cesta 9, SK-84236 Bratislava, Slovakia abstract article info Available online 22 January 2011 Keywords: Gas sensor Polyaniline thin film Nanocomposite Carbon nanotube We have studied the gas sensing properties of five polyaniline-based materials—thick and thin PANI films, nanocomposite PANI/MWNT and PANI/SWNT films, and PANI nanogranules embedded in a polyvinylpyrro- lidone matrix. The films (except for the latter) were deposited within the induction period of the polymerization process on gold interdigitated micro electrodes. Their sensitivity to NH 3 ,H 2 , ethanol, methanol, and acetone was measured. The thin PANI film (~100 nm thick) prepared by a lift-off process had the sensitivity to ammonia below 0.5 ppm, which was higher than that of nanocomposite films. Two materials —thick PANI film and nanocomposite PANI/MWNT film—exhibited a shallow minimum in the temperature dependence of resistance (at 313 K and 319 K), which is a feature exploitable in practical applications, since the gas sensors should be insensitive to small temperature fluctuations at these temperatures. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Although metaloxide gas sensors are quite popular, there has been an effort to replace them because of their relatively high operational temperature (200–400 °C), which implies higher energy consumption compared with that of sensors working at room temperature [1]. One of the new candidates are sensors based on conductive polymers, such as polyaniline (PANI) or polypyrrole. They can be combined with carbon particles of nanometre size (nanotubes, flakes of expanded graphite, etc.), which leads to nanocomposite materials [2]. Electrical resistivity is a quantity that is usually measured to obtain information on concentrations of gases or vapours in the ambient. The measure- ment of resistance is simple, and it does not require complicated electronic circuits with high energy consumption. It is known that both constituents of the carbon/polymer nanocomposites are sensitive to gases and vapours of organic liquids [3–5]. However, the sensitivity of a nanocomposite can be even higher [6,7]. The most attractive features of sensors based on conductive polymers are (i) good gas sensitivity at room temperature and (ii) simple sensor fabrication even on flexible substrates [8]. In this paper, we report on sensing properties of thick and thin PANI films, two carbon/polymer nanocomposite SWNT/PANI and MWNT/PANI films, and a film that consists of PANI nanoparticles embedded in a polyvinylpyrrolidone (PVP) matrix. The last film can be viewed as a polymer/polymer nanocomposite. Simple chemi- resistors with gold interdigitated electrodes were fabricated from the materials to test their sensitivities to ammonia, hydrogen, acetone, ethanol, and methanol. To obtain some insight into the transport mechanism in the films, we also measured current–voltage (I–V) curves and temperature dependences of resistivity (R–T) of the materials. 2. Experimental procedure 2.1. Preparation of the interdigitated electrodes All films were deposited on interdigitated electrodes. They were fabricated using a lift-off process of a titanium adhesion layer (5 nm) and a gold layer (100 nm) deposited on oxidized Si wafers by vacuum evaporation. The width of the digit was 10, 15 or 25 μm, and the spacing between the digits varied from 3 to 25 μm. The total area of the electrodes was 1 mm 2 . 2.2. Thick film PANI A sample with a thick PANI film was prepared by dropping a tiny droplet of freshly-prepared polymerization solution in the middle of the electrodes. The solution was prepared according to a procedure described in detail in Ref. [9]. It is well-known that the induction period of the PANI polymerization process takes about 5 min at room temperature [9]. This is sufficient to be able to deposit the polymerizing solution manually onto the electrodes. However, the polymerization starts at any interface: on the substrate as well as on top of the droplet, and it continues inside, even in the solid state, until Thin Solid Films 519 (2011) 4123–4127 ⁎ Corresponding author. E-mail address: eleklobo@savba.sk (P. Lobotka). 0040-6090/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2011.01.177 Contents lists available at ScienceDirect Thin Solid Films journal homepage: www.elsevier.com/locate/tsf