Gas sensing properties of the composite Langmuir-Blodgett films:: effects of the film thickness and the Cd2+ addition into the subphase

It was discovered in the previous studies that the kinetic response of NO sensors based on copper tetra-tert-butyl phthalocyanine (CuTTBPc) Langmuir-Blodgett films (LB films) could be greatly improved if CuTTBPc mixed with arachidic acid (AA) in optimized molar ratios was used instead of the phthalocyanine derivative alone. In this paper we investigate the effects of the film thickness and the ionic content of the subphase on gas-sensitive properties of CuTTBPc:AA (1:1 molar ratio) LB films with respect to NO. It was shown that both the sensitivity and the kinetic response of the LB films were influenced by the Cd2+ addition into the subphase. These distinctions, being rather small for the thinnest films, became much more pronounced for thicker ones. If "pure"water was used as a subphase, experimental data could be explained mainly by the gas diffusion into the film bulk whereas the surface adsorption was a predominant process in the case of the Cd2+-ntaining subphase. Obtained results are discussed as regards the sensor performance optimization. (C) 1999 Elsevier Science S.A. All rights reserved.