Preparation of Gas Sensors Based on Poly pyrrole Films

3 Preparation of Gas Sensors Based on Poly(pyrrole) Films 

The resistance gas sensor design consisted of two coplanar chromium contacts which were evaporated onto an insulating glass substrate and a PPy film was placed on top of them, bridging the gap, see Fig. 7.2. This architecture allows to monitor the resistivity change of the sensing material, which connects the two separated electrodes, as a response to gases or solvent vapors. 

A first batch of sensors was assembled in the following way. First an as-deposited PPy film prepared on one of the usually used FTO-coated substrates was coated with a thick layer of high molecular weight poly(styrene) dissolved in xylene. After drying the sample on a hotplate at 50°C the combined film was carefully peeling off and transferred onto a chromium-patterned substrates. Finally the poly(styrene) was dissolved by washing in xylene for several hours. 

A second, more sophisticated type of devices was fabricated in the following way. First a temporary gold layer, which closed the nonconducting gap between the two chromium electrodes, was evaporated. Subsequently a voided double-gyroid-structured template was prepared on this continuously metal-coated substrate and refilled with PPy. Then the redundant template was dissolved with xylene. Finally the superficial gold layer was etched with a wet gold etchant, which reestablished the gap between the chromium electrodes. 

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