An ultraviolet-enhanced (UV-enhanced) nitric oxide (NO) sensor based on silver-doped zinc oxide (ZnO) nanoflowers is developed using a low-cost hydrothermal method. The results indicate that silver (Ag) ions were doped into the ZnO nanostructure successfully, thus changing the morphology. In the high-resolution transmission electron microscopy images, we also found that some Ag ions were separated out onto the surface of the ZnO nanoflowers and that the Ag-doped and Ag nanoparticles improved the sensing property. The NO sensing property increased from 73.91 to 89.04% through the use of a UV light-emitting diode (UV-LED). The response time was approximately 120 s without the UV-LED, and the UV-enhanced Ag-doped ZnO nanoflower sensor exhibited a reduced response time (60 s). The best working temperature could be reduced from 200 to 150 °C using UV light illumination, and it was found that the NO response increased by 15.13% at 150 °C. The UV photoresponse of the Ag-doped ZnO nanoflowers and the mechanisms by which the improvement of NO sensing property occurred through the use of UV light illumination are discussed. The property of the gas sensor can be calibrated using a self-photoelectric effect under UV light illumination. These interesting UV-enhanced Ag-doped ZnO nanoflowers are viable candidates for practical applications.

In this paper, 100 nm-thick zinc oxide (ZnO) films were deposited as a seed layer on Corning glass substrates via a radio frequency (RF) magnetron sputtering technique, and vertical well-aligned Fe-doped ZnO (FZO) nanorod (NR) arrays were then grown on the seed layer-coated substrates via a low-temperature solution method. FZO NR arrays were annealed at 600 °C and characterized by using field emission scanning microscopy (FE-SEM) and X-ray diffraction spectrum (XRD) analysis. FZO NRs grew along the preferred (002) orientation with good crystal quality and hexagonal wurtzite structure. The main ultraviolet (UV) peak of 378 nm exhibited a red-shifted phenomenon with Fe-doping by photoluminescence (PL) emission. Furthermore, FZO photodetectors (PDs) based on metal–semiconductor–metal (MSM) structure were successfully manufactured through a photolithography procedure for UV detection. Results revealed that compared with pure ZnO NRs, FZO NRs exhibited a remarkable photosensitivity for UV PD applications and a fast rise/decay time. The sensitivities of prepared pure ZnO and FZO PDs were 43.1, and 471.1 for a 3 V applied bias and 380 nm UV illumination, respectively.

In this investigation, gas sensors based on zinc oxide (ZnO) nanorods (NRs) with Co concentration were successfully fabricated and explored. A 100 nm-thick ZnO film was deposited as a seed layer onto Corning glass substrate via radio frequency (RF) magnetron sputtering technique. Then, Co-doped ZnO (CZO) NR arrays were grown by using a simple chemical bath deposition (CBD) method at 95 °C for 3 h and annealing at 450 °C, in which the Co-doping contents are 0, 5, and 10 mM. The surface-to-volume ratio of CZO NRs was higher than that of the pure ZnO structure. X-ray diffraction (XRD) results showed that the synthesised NRs were a single crystalline of the hexagonal wurtzite structure with uniform growth orientation of the c -axis. In addition, increasing ethanol (C ₂ H ₅ OH) response depends on O vacancy (V _O ) adsorption, which is measured via photoluminescence (PL) emission. Compared with pure ZnO NRs, the results showed that the CZO-5 (with 5 mM Co solution) NRs exhibited a superior sensitivity in C ₂ H ₅ OH gas applications and a fast response/recovery time. Meanwhile, the CZO-5 gas sensor presented a high response rate of 90.71% at 300 °C operating temperature when the concentration of ambient C ₂ H ₅ OH gas was 100 ppm.

In this work, we use gold (Au) nanoparticles (NPs) to modify zinc oxide (ZnO) nanostructures and improve the performance of ultraviolet (UV) metal–semiconductor–metal (MSM) photodetectors (PDs). The surface morphology, crystal performance, optical characteristic, and electrical property of the nanostructures were determined by using several instruments [e.g. X-ray diffractometer, field-emission scanning electron microscopy, photoluminescence spectroscopy, X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, and semiconductor parameter analyser]. Single-crystalline one-dimensional (1-D) nanorods (NRs) with hexagonal wurtzite structures were obtained via a facile hydrothermal synthetic route. The ZnO and Au/ZnO NRs with direct current magnetron sputtering times (i.e. 0 and 10 s) were labelled ZOA-0 and ZOA-1 samples, respectively. When the applied voltage was 1 V, ZOA-0 and ZOA-1 samples had dark currents ( ${I} _{dark}$ ) of $2.21\times10$ ⁻⁸ and $3.28\times10$ ⁻⁹ A, respectively, in the photocurrents ( ${I} _{ph}$ ) of $1.35\times10$ ⁻⁷ and $4.33\times10$ ⁻⁶ A, respectively, under UV irradiation. The ${I} _{ph}/{I} _{dark}$ ratios of ZOA-0 and ZOA-1 NRs were 6 and 1320, respectively. As a result, the adsorption of Au on ZnO NRs can increase the conductivity of UV MSM PDs and improve the responsivity of devices for UV-sensing.

In this study, the crystallinities, structures, and optical properties of zinc oxide (ZnO) and platinum nanoparticles (Pt NPs)-decorated ZnO nanorods (Pt/ZnO NRs) were investigated by an X-ray diffraction, a field-emission scanning electron microscopy, and a photoluminescence spectrometry. The Pt NPs-decorated ZnO NRs were prepared by direct current (DC) magnetron sputtering for 0 and 30 s. The ZnO and Pt/ZnO NR-based gas sensors are consistent, stable, and repeatable. The sensitivities of the ZnO and Pt/ZnO NR sensors were 1.34% and 121.03%, respectively, at a concentration of 1000 ppm methanol gas and at an operating temperature of 270 °C. The Pt NPs-decorated ZnO NRs exhibit enhanced sensor characteristics of methanol gas.

The high-density and well-aligned zinc oxide (ZnO) nanostructures with adsorbed gold (Au) nanoparticles (NPs) grown on indium-tin-oxide (ITO) glass substrates were used as a gas-sensing material. The Au NPs-adsorbed nanorod (NR) arrays were successfully grown on the substrates via the simple hydrothermal method at various Au NP sputter deposition times (0 and 30 s). The crystal characteristics, surface morphologies, and elemental distributions were studied by using the X-ray diffraction (XRD) spectrometry, the field-emission scanning electron microscopy (FE-SEM), and the high-resolution transmission electron microscopy (HR-TEM) with an energy dispersive X-ray (EDX) elemental mapping analysis, respectively. The NR structures were vertical to the substrate surface with hexagonal wurtzite structure and single-crystalline performance. All sensors were prepared in a self-made chamber, indicating that the response of the sample toward methanol (CH ₃ OH) vapor at different working temperatures was enhanced by Au adsorption. Additionally, the sensor showed a remarkably enhanced response (62.65%) to 1000 ppm CH ₃ OH at the optimal operating temperature of 150 °C. Simultaneously, the sensor evidently displayed stable and repeatable behavior, and selectivity toward the CH ₃ OH vapor with no substantial response to isopropyl alcohol, acetone, and ethanol vapors. The designed sensor in this investigation may detect harmful gas in the Internet of Thing applications.