A novel NO2 gas sensor based on Bis[phthalocyaninato] samarium complex/silicon hybrid charge-flow transistor

A new kind of sandwich-like bis[2,3,9,10,16,17,23,24-octakis(octyloxy)phthalocyaninato] samarium complex Sm[Pc^*]₂(Pc^*=Pc(OC₈H₁₇)₈) is used as film-forming material. Pure Sm[Pc^*]₂ and mixture of Sm[Pc^*]₂ and octadecanol(OA) deposited from both pure water and 10^-4M Cd²⁺ subphases are investigated. It is found that a mixture of 1:3 Sm[Pc^*]₂:OA forms an excellent material for the fabrication of the gas-sensing Langmuir-Blodgett (LB) film by studying the film-forming characteristics. A new gas sensor has been fabricated by incorporating the multilayer LB film into the gate electrode of a metal-oxide-semiconductor field effect transistor, forming an array of charge-flow transistor. On the application of a gate voltage (V_GS), greater than the threshold voltage (V_TH), a delay was observed in the response of the drain current. This is due to the time taken for the resistive gas-sensing film to charge up to V_GS. This delay characteristic was found to depend on the concentration of NO₂. Results are presented showing that the device can detect reversibly the concentration of NO₂ gas down to 5 ppm at room temperature.