Study on the optimization of graphene sensors using Ag-nanostructures decoration

Highlights: •Ag-nanostructures decorated on graphene serve as n-typed dopants to graphene. •Sensitivity of graphene sensor to NO₂ is optimized by control of decorated Ag-nanostructures. •Enhanced sensing performance of hybrid structure is due to modification of electric structures. -- Abstract: In this work, we carried out a systematic study of the effects of morphology and coverage of decorated silver (Ag) nanostructures on the sensing performance of monolayer graphene. Ag nanowires (AgNWs) and Ag nanoparticles (AgNPs) were uniformly coated on the chemical vapor deposition-grown graphene. Raman spectra showed that both AgNPs and AgNWs served as n-type dopants to graphene. After decoration of the Ag nanostructures, the sensing performance of the graphene towards NO₂ gas at room temperature was significantly improved. For a graphene and AgNWs hybrid sensor, the sensitivity was approximately 2 time higher and the recovery time was ~10 times shorter than the pristine graphene. In addition, we found that the behavior of NO₂ adsorption depends on the shape of the decorated Ag nanostructures. The surface coverage ratio of the Ag nanostructures on graphene presented a contrary trend, in that lower coverage of AgNWs and higher coverage of AgNPs on graphene exhibited better sensing properties. The effect of each nanostructure on improving graphene sensing is discussed in terms of the surface energy of different facets of Ag nanostructures and the electronic properties of the hybrid structures.