Semiconducting, gas-sensing properties of Europium bisphthalocyanine Langmuir-Blodgett thin films

In this article, Europium bisphthalocyanine (EuPc'(2)) ten-layer Langmuir-Blodgett films transferred to an interdigital electrode has been prepared. The LB films are fabricated microsensors for halogen gases. The sensor incorporates a microheater and a diode to control the temperature of the film. The gas concentration is measured by the conductance change. The film temperature effects on sensitivity, response and recovery time. When the sensor was operated at above 120 degrees C, the response had a slow downward drift, indicating the bond formation between the Cl-2 and the Pc rings which caused the ring to become chlorinated and lose its conductivity. The interaction between EuPc'(2) and Cl-2 in the LB films was monitored by UV-vis spectroscopy. LB films exposed to Cl-2 gave a red-shifted Q band which is similar to the electrochemical oxidation of the macrocycle. The response time of ten-layer LB films is 45 s and the recovery time is 1 min in the vapor of 50 ppm Cl-2 in room temperature. (C) 1997 American Vacuum Society.