Adjustment of oxygen vacancy states in ZnO and its application in ppb-level NO2 gas sensor

Li, Gaoda; Zhang, Heng; Meng, Leixin; Sun, Zhe; Zhao, Chen; Huang, Xiaoyu; Qin, Yong

doi:10.1016/j.scib.2020.05.027

Cited by 68 publications

(29 citation statements)

References 82 publications

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“…A high concentration of V o •• would result in a high responsivity to xylene. Because the binding energy of O 2 on V o (2.97 eV) is larger than that on V o •• (1.36 eV), the concentration of carriers depleted by adsorbed O 2 would increase when oxygen vacancies observed with the doubly ionized states than that of singly ionized states. Consequently, pure ZnO nanorods with high amount of V o •• has the larger initial resistance. When pure ZnO nanorods with a high amount of V o •• are exposed in air, more oxygen molecules can be adsorbed on the surface, and more electrons will be captured form negative oxygen species, resulting in a rather thicker electron depletion layer (L D ).…”

Section: Results and Discussionmentioning

confidence: 99%

ZnO Nanorods with Doubly Positive Oxygen Vacancies for Efficient Xylene Sensing

Yang

Zhao

et al. 2022

ACS Appl. Nano Mater.

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Because of their structural flexibility, earth abundance, and environmental friendliness, ZnO nanomaterials have been widely utilized for gas sensors. ZnO-based sensors showed a high gas response performance, which can be essentially attributed to the effect of oxygen vacancies. However, rare research has focused on the type of oxygen deficiency for regulating gas sensing properties. In this work, we first synthesized ZnO nanorods with a low BET surface area of 6.8 m2/g, presenting superior normalized gas sensitivity toward 200 ppm xylene. This was attributed to very high amounts of doubly positively charged oxygen vacancies forming in these nanorods by creating a highly anoxic environment for oxygen-deficient ZnO growth. In contrast, Ga doping can serve as active sites that are beneficial for adsorbing more oxygen into the lattices of ZnO, resulting in a reduced number of doubly positively charged oxygen vacancies, lower oxygen vacancy-related photoluminescence intensity, and worse xylene sensing performance. Therefore, the doubly positively charged oxygen vacancies play an important role in the gas sensing performance of metal-oxide semiconductors. The results obtained can provide a strategy and facilitate research on the design of other metal-oxide semiconductors with gas sensing properties.

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Section: Results and Discussionmentioning

confidence: 99%

ZnO Nanorods with Doubly Positive Oxygen Vacancies for Efficient Xylene Sensing

Yang

Zhao

et al. 2022

ACS Appl. Nano Mater.

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“…The reaction of oxygen with the ZnO matrix can be divided into three steps, mainly due to chemisorbed oxygen, lattice oxygen, and oxygen vacancy Reactions – depict the generation of electrons due to lattice oxygen, chemisorbed, and oxygen vacancy: − …”

Section: Resultsmentioning

confidence: 99%

Design, Fabrication, and Packaging of an Optothermally Activated Nanocrystalline Pd–ZnO-Based Selective CO Sensor on a Screen-Printed In-Plane Heater

Anjitha

Ahirwar

et al. 2022

ACS Appl. Electron. Mater.

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Continuous monitoring of gases at low concentrations is necessary for keeping track of emanations from coal mines as gas emissions prove to be a detrimental factor for people working in such environments. Therefore, there is a requirement to develop a selective CO sensor which can go down to the ppm level for initiating the triggering of an alarm system. With this objective, a selective CO (up to 20 ppm) sensor has been investigated with the exploration of different material combinations (Pd−ZnO) and optothermal activation techniques. The selectivity of target gases such as CO, CH 4 , and NH 3 has been a controversial topic among researchers as the sensing mechanism is almost similar in all the three cases. The major challenge to be addressed while designing a micro-electromechanical system-based gas sensor is the problem of reliability, cross-sensitivity, and selectivity, which stagnates the overall performance of the system. The optothermally activated sensor platform with suitable nanomaterials play a significant role in curtailing the above-mentioned issues. The present work implements Pd-doped nanocrystalline ZnO with defect-oriented active sites which are found to be highly efficacious in providing a sensor with a strong adsorption reaction and propelling the surface conversion kinetics. The sensor is optimized for selective CO sensing due to the interplay between the defect states on Pd−ZnO with optical and thermal activation. As a direct consequence, a reliable, robust, cost-effective, and CO-selective packaged gas sensor at approximately 3.5 W is realized. Simulation, optimization of the sensing nanomaterial, fabrication of a screen-printed integrated heater and sensing electrodes, thermo-optical excitation, detailed packaging, and characterization are discussed in this study. Thus, the present methodology to fabricate the CO-selective sensor is suitable for various applications where a robust, reliable, selective sensing performance is required. Detailed material characterization has been performed to analyze the sensing behavior of the grown nanomaterials (Pd−ZnO).

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“…For instance, ZnO nanowires with V o rich surface were photoactivated using a UV lamp with a wavelength of 360 nm and optimal irradiance of 0. [50]. ZnO films composed of hierarchically porous nanorods also showed response (6.6 %) to 2.5 ppb of NO 2 under UV illumination (λ = 365 nm), with response and recovery times in the range of seconds, 19 s and 32 s, respectively [51].…”

Section: Single or Non-modified Photoactive Materials (Oxides Dichalcogenides Graphene)mentioning

confidence: 95%

“…ZnO, on the top of the list, is an n-type semiconductor with a broad direct band gap (3.1-3.3 eV), and optical/electrical properties that are significantly influenced by the presence of defects, e.g., oxygen vacancies (V o ), zinc interstitials and zinc vacancies [47,48]. Previously, various ZnO structures in the form of nanowires [49], nanofilms [50], and macro/mesoporous [51] or porous coatings [52] have proved appropriate for NO 2 sensing under photoactivation. For instance, ZnO nanowires with V o rich surface were photoactivated using a UV lamp with a wavelength of 360 nm and optimal irradiance of 0.…”

Section: Single or Non-modified Photoactive Materials (Oxides Dichalcogenides Graphene)mentioning

confidence: 99%