Gas sensing measurements and analysis of the optical properties of poly(3-butylthio)thiophene Langmuir-Blodgett films

Films of poly[(3-butylthio)thiophene] were prepared via Langmuir-Blodgett (LB) deposition and casting techniques for applications in gas sensor devices. A description of the preparation of the sensing layer is given for both methods: the LB deposition of the polymer in mixture with arachidic acid and the solvent casting by using directly a solution of the polymer in chloroform. In both cases, alumina substrates equipped with gold interdigitated electrodes have been used. In particular, the samples so prepared show variation in the electrical conductivity when exposed to NO2-oxidising or NH3-reducing agents at a working temperature of about 100 degrees C. The refractive index n and the extinction coefficient ii at normal incidence have been determined in the 400-800 nm spectral range and an energy gap (highest occupied-molecular-orbital or conduction band (HOMO)-lowest unoccupied molecular-orbital or valence band (LUMO) separation) of about 1.9 eV has been estimated.