Preparation and gas-sensing properties of bis[phthalocyaninato] Sm[Pc*]2 LB films

Bis[phthalocyaninato] Sm[P_c*]₂ [P_c*=P_c(OC₈H₁₇)₈] has a sandwich-type structure with samarium at the center of two phthalocyanine ligands each other in a staggered form. Spreading solution of 0.42 mg/ml was prepared by dissolving Sm[P_c*]₂ in chloroform before Sm[P_c*]₂ Langmuir-Blodgett (LB) films were deposited on silicon substrate. In order to produce stable LB films, Sm[P_c*]₂ was mixed with octadecanol (OA) at different molar ratios of 1:1, 1:3 ,1:6 and 1:9. It is found that a mixture of 1(Sm[P_c*]₂):3(OA) generates an excellent material for the fabrication of gas-sensing LB films resulting from the optimization of film-forming characteristics. A new gas sensor has been fabricated by incorporating the multiplayer LB film into the gate electrode of charge-flow transistor (CFT), forming an array of charge-flow transistor. Given a gate voltage (VGs) which is greater than threshold voltage (VTH), 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 VGS. This characteristic delay was found to depend on the concentration of NO₂ gas. Results are presented showing that the device can detect reversibly the concentration of NO₂ gas down to 5ppm at room temperature.