Abstract
Room-temperature gas sensors are attracting attention because of their low power consumption, safe operation, and long-term stability. Herein, ZnO nanorods (NRs) and nanowires (NWs) were on-chip grown via a facile hydrothermal method and used for room-temperature NO2 gas sensor applications. The ZnO NRs were obtained by a one-step hydrothermal process, whereas the NWs were obtained by a two-step hydrothermal process. To obtain ZnO NW sensor, the length of NRs was controlled short enough so that none of the nanorod-nanorod junction was made. Thereafter, the NWs were grown from the tips of no-contact NRs to form nanowire-nanowire junctions. The gas-sensing characteristics of ZnO NRs and NWs were tested against NO2 gas at room temperature for comparison. The gas-sensing characteristics of the sensors were also tested at different applied voltages to evaluate the effect of the self-activated gas-sensing performance. Results show that the diameter of ZnO NRs and NWs is the dominant parameter of their NO2 gas-sensing performance at room temperature. In addition, self-activation by local heating occurred for both sensors, but because the NWs were smaller and sparser than the NRs, local heating thus required a lower applied voltage with maximal response compared with the NRs.
Highlights
In the past decades, the rapid rise of industrialisation and urbanisation has caused severe air pollution, which primarily comes from automobile exhausts and factory emissions
Given that the Zn seed layer is sandwiched between two Pt layers, the ZnO NRs can just start to grow from the edge of the electrode but not on the top
Two electrodes were connected by these ZnO NRs that formed NR-NR junctions, which acted as conducting channels for gas-sensing measurement
Summary
The rapid rise of industrialisation and urbanisation has caused severe air pollution, which primarily comes from automobile exhausts and factory emissions. The gas-sensing properties of the sensors based on ZnO nanostructures are mainly dependent on the operation temperature, which controls the surface reaction kinetics and carrier mobility, resulting in the change in material conductivity [20]. Cui et al used ultraviolet (UV) illumination to trigger the gas-sensing reaction of their ZnO nanostructures to HCHO at room temperature [28]. The use of a noble metal catalyst and/or UV illumination to enable room-temperature sensing characteristics of ZnO leads to high fabrication and energy usage costs. ZnO NRs and NWs were first grown on-chip by a hydrothermal method at atmospheric pressure, and their room-temperature NO2 gas-sensing properties were studied. We discussed in depth the sensing performance of sensors under the size effect and self-activation
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