Broadband Photo/Gas Dual Sensors Enabled by ZnO Nanorod/Graphene Hybrid Structures

In this study, 2-D graphene was integrated with zinc oxide (ZnO) nanorods (NRs) to form broadband photo/gas dual sensors. Since ZnO-based photodetectors (PDs) perform excellent in ultraviolet (UV) light detection, their inability to sense long-wavelength visible and infrared (IR) light limits the PDs' applications. By combining a 2-D graphene layer on ZnO NRs, the 2-D graphene extended light detection range of device from UV to IR light. In terms of gas sensing, this ZnO NR/graphene-based sensor was capable of sensing hydrogen (H2) carbon monoxide (CO) gases. This device exposed to H2 and CO gases delivered comparable sensitivity of 0.25 under an operated temperature of 300 °C. Multiple material characterizations confirm that a 2-D graphene layer has successfully deposited on ZnO NRs to form a distinct hybrid ZnO NR/graphene nanostructure. Through a series of sensing analyses, results have been demonstrated that the ZnO NR/graphene-based sensor outperformed ZnO-based sensor in response to light illumination. However, ZnO NR/graphene-based sensor exhibited inferior gas sensitivity than the ZnO-based sensor. The coverage of graphene on the surface of ZnO NRs could passivate the surface defects of ZnO NRs. Although the surface passivation was beneficial for reducing the charge recombination and improving the photocurrent, the surface passivation of graphene reduced the adsorption sites of target gas. As a result, the gas sensitivity of ZnO NR/graphene-based sensor was reduced. Although the ZnO NR/graphene-based sensor exhibited a reduced gas sensitivity, the hybrid ZnO/2-D graphene nanocomposites pave the way for broadband PDs and gas sensors with promising applications in various fields.