ROOM-TEMPERATURE TOLUENE SENSING USING PHTHALOCYANINE LANGMUIR-BLODGETT-FILMS

Organic thin films, produced by the Langmuir-Blodgett (LB) technique w ere used to sense toluene gas at levels of 5-9 p.p.m.(parts per millio n). The interaction of the gas with the surface of the thin films led to significant changes in the electrical conductivity of the film. Sin ce surface reaction is vital in these sensors, it is expected that fil ms produced by the LB technique would provide the necessary surface un iformity to improve the performances of these devices. Most thin film sensors are operated at elevated temperatures to obtain higher efficie ncies. A major problem associated with the use of LB films at elevated temperatures is the probability of disintegration and distortion of t he layered structure. Thin films (thickness similar to 100-120 nm) of specially substituted phthalocyanine molecules were investigated as po ssible sensors of toluene gas for room-temperature operation. The prel iminary results indicated instantaneous response and recovery times, a nd the saturation value was reached within 2-3 s when the film was exp osed to the gas at intervals of 2 min. The results thus offer potentia l for using such versatile organic materials as microsensors, even at room temperature.