Comparison of NO2 Gas-Sensing Properties of Three Different ZnO Nanostructures Synthesized by On-Chip Low-Temperature Hydrothermal Growth

Abstract

Three different ZnO nanostructures, dense nanorods, dense nanowires, and sparse nanowires, were synthesized between Pt electrodes by on-chip hydrothermal growth at 90°C and below. The three nanostructures were characterized by scanning electron microscopy and x-ray diffraction to identify their morphologies and crystal structures. The three ZnO nanostructures were confirmed to have the same crystal type, but their dimensions and densities differed. The NO 2 gas-sensing performance of the three ZnO nanostructures was investigated at different operation temperatures. ZnO nanorods had the lowest response to NO 2 along with the longest response/recovery time, whereas sparse ZnO nanowires had the highest response to NO 2 and the shortest response/recovery time. Sparse ZnO nanowires also performed best at 300°C and still work well and fast at 200°C. The current-voltage curves of the three ZnO nanostructures were obtained at various temperatures, and the results clearly showed that sparse ZnO nanowires did not have the linear characteristics of the others. Analysis of this phenomenon in connection with the highly sensitive behavior of sparse ZnO nanowires is also presented.

New Design of ZnO Nanorod- and Nanowire-Based NO2 Room-Temperature Sensors Prepared by Hydrothermal Method

“…Furthermore, the resistance values of the ZnO NW sensors were considerably higher than those of the ZnO NR sensors. This finding was attributed to the smaller diameters of the NWs compared with the NRs [33,41]. Here, the diameter of the NWs was approximately twice the Debye length, whereas the diameter of the NRs was much larger than the Debye length.…”

“…The morphologies of the ZnO NRs hydrothermally grown between the patterned electrodes were investigated by SEM, as shown in Figure 2. The sensor designed with head-tohead electrodes with no heater stipulates a simple fabrication process [33]. Patterning of the electrodes has been reported elsewhere, except for the deposition of a Zn seed layer of 20 nm [36].…”

“…Two types of sensors are fabricated, namely, NR-NR and NW-NW sensors (Figure 1(b)). The ZnO NRs and NWs were grown by a hydrothermal process [33,34] using zinc nitrate hexahydrate (Zn(NO 3 ) 2 ⋅6H 2 O) and hexamethylenetetramine (HMTA) as precursors. The chemicals were of analytical grade (Sigma-Aldrich) and used without any further purification.…”

Remote Tracking Gas Molecular via the Standalone-Like Nanosensor-Based Tele-Monitoring System

“…An effective approach to achieve the research objective is to employ specific-deigned sensing material which would be sensitive and selective to NO 2 . One of the promising candidates is ZnO, since ZnO with unique morphologies (e.g., nanorods, nanosheets, nanowries, and nanoneedles) have been frequently reported to give relatively high response signal under even harsh conditions [1,4,[27][28][29][30][31][32][33][34][35][36][37][38]. Nevertheless, most of these ZnOs suffer the problem of poor selectivity to NO 2 and/or unstable performance at the operating temperature of higher than 300 °C, thereby hindering their broader application.…”

Stable Electrochemical Measurements of Platinum Screen-Printed Electrodes Modified with Vertical ZnO Nanorods for Bacterial Detection

“…The circular working electrode has a diameter of 4 mm, and the area covered by the electrodes is 12.56 mm 2 , as in our previous publication [28]. A 20 nm of Zn seed layer was deposited by direct current (DC) sputtering on the Pt layer of the circular working electrode in order to grow the ZnO NRs thanks to our experience published previously [29,30] (Figure 1(a)). Figure 1 describes the whole preparation of ZnO NRmodified Pt SPEs for electrochemical detection of bacterial pathogens.…”