Graphene Functionalization by O₂, H₂, and Ar Plasma Treatments for Improved NH₃ Gas Sensing

Graphene-based materials have gained attention for their promise in various applications owing to their two-dimensional structure. Functionalizing the graphene surface can help realize materials with noble properties. In this study, graphene was functionalized by plasma treatment in O₂, H₂, and Ar environments, and the effects on the NH₃ gas-sensing performance were evaluated. The O₂ plasma treatment induced oxidation of the graphene (i.e., graphoxide), while the H₂ plasma treatment induced hydrogenation (i.e., graphane). Raman scattering spectroscopy suggested that graphoxide had vacancy-type defects and graphane had sp³-type defects, while Ar-treated graphene had both types of defects. Graphane had the highest sheet resistance followed by graphoxide, Ar-treated graphene, and pristine graphene, which can be attributed to the large bandgap of 3.0 eV for graphane. In contrast, graphoxide had the best NH₃ gas-sensing performance, which indicates that NH₃ gas interacts more strongly with vacancy-type defects than with sp³-type defects. The results showed that functionalizing the graphene structure generated noble materials with a superior NH₃ gas-sensing performance compared with pristine graphene.