Point defects assisted NH3 gas sensing properties in ZnO nanostructures
TL;DR: In this paper, the NH 3 gas sensing properties of ZnO nanostructures fabricated by radio frequency magnetron sputtering under various argon sputtering pressures have been investigated under various temperatures.
Abstract: In this report, the NH 3 gas sensing properties of ZnO nanostructures fabricated by radio frequency magnetron sputtering under various argon sputtering pressures have been investigated under various temperatures. The morphological transitions occur from vertical standing nanorods to inclined and tapered nanostructures with increasing the argon sputtering pressure. The dominant green emission at around 2.28 eV in the photoluminescence spectra signifies the presence of oxygen vacancies in the ZnO nanostructures which increases as a function of argon sputtering pressure. Despite low surface area, the nanostructures grown under higher argon sputtering pressure of 10 Pa exhibit excellent NH 3 gas response magnitude since it is exhibiting more oxygen vacancies as compared to other counterparts. For 25 ppm NH 3 gas at room temperature, a response time of 49 s and a fast recovery time of 19 s are attributed to the modification in the intermediate defect states induced by the oxygen vacancies through the adsorption and desorption of gas molecules on the surface of ZnO nanostructures.
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TL;DR: In this paper, the room-temperature gas sensing properties of ZnO-based gas sensors are comprehensively reviewed, and more attention is particularly paid to the effective strategies that create room temperature gas sensing, mainly including surface modification, additive doping and light activation.
Abstract: Novel gas sensors with high sensing properties, simultaneously operating at room temperature are considerably more attractive owing to their low power consumption, high security and long-term stability. Till date, zinc oxide (ZnO) as semiconducting metal oxide is considered as the promising resistive-type gas sensing material, but elevated operating temperature becomes the bottleneck of its extensive applications in the field of real-time gas monitoring, especially in flammable and explosive gas atmosphere. In this respect, worldwide efforts have been devoted to reducing the operating temperature by means of multiple methods In this communication, room-temperature gas sensing properties of ZnO based gas sensors are comprehensively reviewed. Much more attention is particularly paid to the effective strategies that create room-temperature gas sensing of ZnO based gas sensors, mainly including surface modification, additive doping and light activation. Finally, some perspectives for future investigation on room-temperature gas-sensing materials are discussed as well.
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TL;DR: In this article, a novel and highly sensitive two-dimensional (2D) gas sensing material based on metal nanoparticles-reduced graphene oxide (rGO) nanocomposite for the detection of ammonia gas was reported.
119 citations
TL;DR: In this paper, a combination of defect structure analysis based on photoluminescence (PL) and electron paramagnetic resonance (EPR) was employed to detect coexisting oxygen vacancies (V O ) and zinc interstitials (Zn i ) defects in undoped and transition metal doped ZnO systems.
115 citations
TL;DR: In this paper, the authors provided an all-inclusive outline of recent developments on the classification of metal oxide defects based on the dimensions of a host crystal lattice, and the surface modification of metal oxides through 0D (point), 1D (line), 2D (planar), and 3D (volume) defects with their subsequent mechanism and impact on photocatalytic performance.
111 citations
TL;DR: In this paper, ZnO nanofibers (NFs) were synthesized by the simple electrospinning technique for gas sensing studies, and they were irradiated with a high-energy (1 MeV) electron beam (e-beam) at different doses (50, 100, and 150 kGy) to study the effect of the e-beam dose on the sensing performance of the synthesized NNOs.
Abstract: In the present study, ZnO nanofibers (NFs) were synthesized by the simple electrospinning technique for gas sensing studies. ZnO NFs were irradiated with a high-energy (1 MeV) electron beam (e-beam) at different doses (50, 100, and 150 kGy) to study the effect of the e-beam dose on the sensing performance of the synthesized ZnO NFs. H2 sensing studies showed that the sensing properties of the unirradiated and 50 kGy-irradiated sensors were similar, which indicates that this e-beam dose was insufficient. However, the sensing characteristics improved with an increase in the irradiation dose to 100 and 150 kGy. The response of the optimal sensor (150-kGy-irradiated) to 10 ppm H2 was much higher than that to other (interfering) gases (e.g., C2H5OH, C6H6, C7H8, and CO). The observed high gas response of the 150 kGy-irradiated sensor was attributed to its high surface area resulting from the one-dimensional nature of the ZnO NFs, the grain size of ZnO, and the formation of surface defects by e-beam irradiation. The high selectivity of the ZnO NFs toward H2 gas was related mainly to the metallization of ZnO and the concentration gradient of carfbon across the NF surfaces. Overall, the findings demonstrate the effectiveness of high-energy irradiation in enhancing the sensing performance of ZnO NFs. We believe that this approach can be extended to other metal oxides for the enhancement of sensing performance.
98 citations
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TL;DR: The semiconductor ZnO has gained substantial interest in the research community in part because of its large exciton binding energy (60meV) which could lead to lasing action based on exciton recombination even above room temperature.
Abstract: The semiconductor ZnO has gained substantial interest in the research community in part because of its large exciton binding energy (60meV) which could lead to lasing action based on exciton recombination even above room temperature. Even though research focusing on ZnO goes back many decades, the renewed interest is fueled by availability of high-quality substrates and reports of p-type conduction and ferromagnetic behavior when doped with transitions metals, both of which remain controversial. It is this renewed interest in ZnO which forms the basis of this review. As mentioned already, ZnO is not new to the semiconductor field, with studies of its lattice parameter dating back to 1935 by Bunn [Proc. Phys. Soc. London 47, 836 (1935)], studies of its vibrational properties with Raman scattering in 1966 by Damen et al. [Phys. Rev. 142, 570 (1966)], detailed optical studies in 1954 by Mollwo [Z. Angew. Phys. 6, 257 (1954)], and its growth by chemical-vapor transport in 1970 by Galli and Coker [Appl. Phys. ...
10,260 citations
TL;DR: This approach has the potential of converting mechanical, vibrational, and/or hydraulic energy into electricity for powering nanodevices.
Abstract: We have converted nanoscale mechanical energy into electrical energy by means of piezoelectric zinc oxide nanowire (NW) arrays. The aligned NWs are deflected with a conductive atomic force microscope tip in contact mode. The coupling of piezoelectric and semiconducting properties in zinc oxide creates a strain field and charge separation across the NW as a result of its bending. The rectifying characteristic of the Schottky barrier formed between the metal tip and the NW leads to electrical current generation. The efficiency of the NW-based piezoelectric power generator is estimated to be 17 to 30%. This approach has the potential of converting mechanical, vibrational, and/or hydraulic energy into electricity for powering nanodevices.
6,692 citations
TL;DR: The beltlike morphology appears to be a distinctive and common structural characteristic for the family of semiconducting oxides with cations of different valence states and materials of distinct crystallographic structures, which could be an ideal system for fully understanding dimensionally confined transport phenomena in functional oxides.
Abstract: Ultralong beltlike (or ribbonlike) nanostructures (so-called nanobelts) were successfully synthesized for semiconducting oxides of zinc, tin, indium, cadmium, and gallium by simply evaporating the desired commercial metal oxide powders at high temperatures. The as-synthesized oxide nanobelts are pure, structurally uniform, and single crystalline, and most of them are free from defects and dislocations. They have a rectanglelike cross section with typical widths of 30 to 300 nanometers, width-to-thickness ratios of 5 to 10, and lengths of up to a few millimeters. The beltlike morphology appears to be a distinctive and common structural characteristic for the family of semiconducting oxides with cations of different valence states and materials of distinct crystallographic structures. The nanobelts could be an ideal system for fully understanding dimensionally confined transport phenomena in functional oxides and building functional devices along individual nanobelts.
5,677 citations
TL;DR: By combining electron paramagnetic resonance (EPR), optical absorption, and photoluminescence (PL) spectroscopy, a strong correlation is observed between the green 510 nm emission, the free-carrier concentration, and the density of singly ionized oxygen vacancies in commercial ZnO phosphor powders as mentioned in this paper.
Abstract: By combining electron paramagnetic resonance (EPR), optical absorption, and photoluminescence (PL) spectroscopy, a strong correlation is observed between the green 510 nm emission, the free‐carrier concentration, and the density of singly ionized oxygen vacancies in commercial ZnO phosphor powders. From these results, we demonstrate that free‐carrier depletion at the particle surface, and its effect on the ionization state of the oxygen vacancy, can strongly impact the green emission intensity. The relevance of these observations with respect to low‐voltage field emission displays is discussed.
1,888 citations
1,260 citations