High-Performance Flexible ZnO Nanorod UV/Gas Dual Sensors Using Ag Nanoparticle Templates

Flexible zinc oxide (ZnO) nanorod (NR) ultraviolet (UV)/gas dual sensors using silver (Ag) nanoparticle (NP) templates were successfully fabricated on a polyimide substrate with nickel electrodes. Arrays of Ag NPs were used as a template for the growth of ZnO NRs, which could enhance the flexibility and the sensing properties of the devices through the localized surface plasmon resonance (LSPR) effect. The Ag NPs were fabricated by the rapid thermal annealing process of Ag thin films, and ZnO NRs were grown on Ag NPs to maximize the surface area and form networks with rod-to-rod contacts. Because of the LSPR effect by Ag NPs, the UV photoresponse of the ZnO NRs was amplified and the depletion region of ZnO NRs was formed quickly because of the Schottky contact with the Ag NPs. As a consequence, ZnO NR UV/gas dual sensors grown on the Ag NP template with a diameter of 28 nm exhibited the outstanding UV-sensing characteristics with a UV on-off ratio of 3628 and a rising time ( t_r) and a decay time ( t_d) of 3.52 and 0.33 s upon UV exposure, along with excellent NO₂-sensing characteristics with a stable gas on-off ratio of 288.5 and a t_r and t_d of 38 and 62 s upon NO₂ exposure. Furthermore, the sensors grown on the Ag NP template exhibited good mechanical flexibility and stable sensing properties without significant degradation even after the bending test up to 10 000 cycles at the bending radius of 5 mm.