Plasma-Modification of graphene oxide for advanced ammonia sensing

The exceptional tailoriability of electrical properties in reduced graphene oxide (rGO) is a pivotal factor in unleashing its advanced gas sensing capabilities. Amidst various chemically/thermally-driven techniques, plasma reduction emerges as the fastest method with the potential for scalable treatment. This paper demonstrates a controlled plasma-enabled approach for swift and green surface reduction of graphene oxide (GO) films, specifically tailored for room-temperature ammonia (NH3) detection at ppm levels. Employing a mild hydrogen plasma treatment on a thin GO layer deposited on copper electrodes by drop casting, we were able to tailor the sensor's sensitivity and reversibility due to the great impact of treatment time. The GO reduction experiments were conducted in a low-pressure mild hydrogen plasma discharged at 100 W, and the treatment time varied between 10 and 240 s. Structural and chemical analyses reveal an instantaneous reduction in oxygen content, dropping from approximately 30 to 20 atomic percentages within the initial 20 s. Sensitivity and recovery tradeoffs are explored for different treatment durations, with the 'rGO - 20 s' sensor demonstrating the highest sensitivity at 23.9 % (100 ppm) and 47.1 % (1049 ppm) of NH3, albeit with a recovery time approximately four times longer than the '240s-rGO' sample. This double-play behavior, attributed to chemisorption-dominated and physisorption-dominated interactions of NH3-rGO, elucidates the sensitivity and recovery time dynamics. Proposing a scalable, environmental-friendly and room-temperature H2-plasma reduction process enables one of the fastest approaches for designing advanced rGO sensors with controllable sensing behaviour towards ammonia.