Palladium-free hydrogen sensor based on oxygen-plasma-treated polyaniline thin film

Sensing properties of a chemiresistor gas sensor based on a thin polyaniline (PANI) film are reported. The sensor contains a thin PANI film defined by lift-off on interdigitated micro-electrodes pre-processed on a silicon chip. The sensor sensitivity to hydrogen and ammonia was measured. It was then shortly treated by oxygen plasma, which remarkably enhanced the sensitivity, mainly to hydrogen, and shortened the sensor response and recovery times. The plasma treatment changed the composition, thickness and morphology of the PANI films, which was studied using XPS, FTIR, and AFM. The study necessitated very smooth PANI film surfaces that were achieved by mild sonication of a solution during the chemical polymerization process. The sensor treated by oxygen plasma for 60 s showed a reproducible sensitivity to 10 ppm hydrogen pulses via ∼30% increase in resistance. We believe that this result makes the sensor useful for several room temperature applications.