Graphene\nFunctionalization\nby O<sub>2</sub>, H<sub>2</sub>, and Ar Plasma Treatments for Improved\nNH<sub>3</sub> Gas\nSensing

Graphene-based materials\nhave gained attention for their\npromise\nin various applications owing to their two-dimensional structure.\nFunctionalizing the graphene surface can help realize materials with\nnoble properties. In this study, graphene was functionalized by plasma\ntreatment in O<sub>2</sub>, H<sub>2</sub>, and Ar environments, and\nthe effects on the NH<sub>3</sub> gas-sensing performance were evaluated.\nThe O<sub>2</sub> plasma treatment induced oxidation of the graphene\n(i.e., graphoxide), while the H<sub>2</sub> plasma treatment induced\nhydrogenation (i.e., graphane). Raman scattering spectroscopy suggested\nthat graphoxide had vacancy-type defects and graphane had sp<sup>3</sup>-type defects, while Ar-treated graphene had both types of defects.\nGraphane had the highest sheet resistance followed by graphoxide,\nAr-treated graphene, and pristine graphene, which can be attributed\nto the large bandgap of 3.0 eV for graphane. In contrast, graphoxide\nhad the best NH<sub>3</sub> gas-sensing performance, which indicates\nthat NH<sub>3</sub> gas interacts more strongly with vacancy-type\ndefects than with sp<sup>3</sup>-type defects. The results showed\nthat functionalizing the graphene structure generated noble materials\nwith a superior NH<sub>3</sub> gas-sensing performance compared with\npristine graphene.