▎ 摘　　要

Localized surface plasmon resonance of metallic nanoparticles has been widely employed for gas sensing applications. Since the response of bare nanoparticles is usually weak, it is possible to improve their responses by utilizing the high gas adsorption capability of 2-D materials. In this paper, we developed an optical gas sensor by decorating reduced graphene oxide (rGO) sheets with Ag nanoparticles for the detection of ethanol vapor at the room temperature. We showed that the gas sensitivity of bare Ag nanoparticles can he enhanced by utilizing rCO sheets. We observed improved responses for structures in which rGO was fabricated above the nanoparticles (rGO(up)/Ag) compared with the structures with rGO below the nanoparticles (Ag/rGO(down)). Gas sensitivity was improved 1.47 and 2.75 times, respectively, in the Ag/rGO(down) and rGO(up)/Ag structures compared with the bare Ag nanoparticles. Our results demonstrate that the adsorption of ethanol molecules on the Ag nanoparticles/rGO hybrids leads to not only a plasmonic shift occurring in bare Ag nanoparticles but also an intensity change in the extinction spectrum. In other words, alteration of rGO conductivity due to the gas adsorption leads to an intensity variation in optical spectrum, which can be utilized for improving gas sensing. Finally, we performed a finite-element analysis by assuming the electron exchange between Ag nanoparticles/rGO hybrids and target gas through redox reactions to assess the validity of observed experimental results. Our numerical results confirmed the observed experimental results.