CO gas sensor devices plasma‐polymerized from tetramethyltin

Abstract

SynopsisThin films plasma-polymerized from tetramethyltin was applied for CO gas sensor device. The films formed from tetramethyltin contains alkyl chains with organic tin moieties, and pyrolysis of them at 350-500°C yields carbonized films with SnO, moieties. The electrical resistance for the films pyrolized at 350-500°C decreases in exposing to CO gas. The sensitivity, the ratio of the electrical resistance between in air and in CO atmasphere, is enhanced by catalytic actions of palladium chloride, specially in operation at low temperatures below 50°C. The gas sensitivity between CO and other gases such as ethanol, methane, and propane gases is good. The possible determination of CO gas concentration by the sensor device is in ranges from 10 to loo0 ppm. INTRODUCTIONSnO, is an n-type semiconductor. The SnO, surface is of interest in electrochemical behavior. When the SnO, surface is exposed to reducible gases, the oxidation of them occurs at the SnO, surface, and, consequently, the electrical resistance of the SnO, surface decreases. This is a basic mechanism to detect propane gas with a gas sensor device.' Essentially, the detection of gases from decrease in electrical resistance of the SnO, surface is not restricted to propane gas, but is extend to other reducible gases. CO gas, which is a hazardous material because of rapid reactions with hemoglobin of human blood, is one of reducible gases.Plasma polymerization is a polymer-forming process and has many characteristics including: (1) Volatile-organic molecules, even if they have no functional groups to be polymerized, are plasma-polymerized easily in the discharge state and (2) thin films deposit directly on the substrate surface without fabrication. Therefore, we are able to obtain films with many metals using plasma polymerization technique. The preparation and physical properties of plasma polymers containing metals were reported. They involve germanium,6 copper? Tin-containing polymers are obtained easily from plasma polymerization of tetramethyltin and show semiconductive ~roperties.~ This study is a preliminary application of plasma films prepared from tetramethyltin to CO gas sensor device. EXPERIMENTAL Plasma PolymerizationThe apparatus for plasma polymerization and the experimental procedures are similar to those reported elsewhere! The reaction chamber (100 mm i.d., 2342 INAGAKI, TASAKA, AND MASE 400 mm long) made of Pyrex glass is equipped with a monomer inlet, a pressure gauge, a vacuum system, and a matching network for the inductive coupling of a 13.56 MHz radio frequency (rf) source. Prior to performing plasma polymerization surfaces of the substrates on which plasma polymers would deposit were exposed to argon plasma for 10 min to eliminate water adsorbed on them. Afterwards plasma polymerization was performed under discharge conditions of an rf power of 25 W, a monomer flow rate of 1.87 cm3 (STP)/min, and a Tressure in the reaction chamber of 1.3 Pa. This operating condition of the plasma polymerization corresponds to a W / F M value of 100 ...

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