Electrical and NO2 sensing properties of liquid crystalline phthalocyanine thin films

In this study, the electrical and nitrogen dioxide (NO2) sensing properties of a series liquid-crystalline octakisalkylthiophthalocyanine (C6S)8PcM [M = 2H, Ni, Cu, Zn] thin film were investigated. The thin films were coated on to the Interdigital Transducer (IDT) with gold electrodes, using jet-spray technique in an inert ambient from a solution of phthalocyanines in chloroform. The electrical properties of liquid-crystalline phthalocyanines were studied within wide temperature range from 293 to 423 K under the high purity nitrogen (N2) flow and in the frequency range from 500 Hz to 1 MHz for ac electrical measurements. It was observed that the I-V curves of all phthalocyanines showed a significant hysteresis at low temperature and the maximum dc conductivity obtained for (C6S)8PcZn thin film. The ac conduction mechanism of all thin films could be explained with quantum-mechanical tunneling (QMT) model. The NO2 gas sensing measurements were done in the concentration range of 1-10 ppm at the temperatures of 100 °C and 150 °C. The maximum sensor response (%) was obtained as approximately 10,000 and the response time was observed to be a few seconds for (C6S)8PcH2 thin film at 150 °C.