Room temperature toluene sensing using phthalocyanine Langmuir-Blodgett films

Organic thin films, produced by the Langmuir-Blodgett (LB) technique were used to sense toluene gas at levels of 5–9 p.p.m.(parts per million). The interaction of the gas with the surface of the thin films led to significant changes in the electrical conductivity of the film. Since surface reaction is vital in these sensors, it is expected that films produced by the LB technique would provide the necessary surface uniformity to improve the performances of these devices. Most thin film sensors are operated at elevated temperatures to obtain higher efficiencies. A major problem associated with the use of LB films at elevated temperatures is the probability of disintegration and distortion of the layered structure. Thin films (thickness 100–120 nm) of specially substituted phthalocyanine molecules were investigated as possible sensors of toluene gas for room-temperature operation. The preliminary results indicated instantaneous response and recovery times, and the saturation value was reached within 2–3 s when the film was exposed to the gas at intervals of 2 min. The results thus offer potential for using such versatile organic materials as microsensors, even at room temperature.