Ni-doped ZnO nanorods gas sensor: Enhanced gas-sensing properties, AC and DC electrical behaviors
TL;DR: In this paper, Ni-doped zinc oxide (ZnO) nanorods had been successfully fabricated via a fast microwave-assisted hydrothermal synthesis at 150°C and the morphology and composition were carefully characterized by X-ray diffraction, field emission scanning electronic microscopy, and transmission electron microscopy.
Abstract: Ni-doped zinc oxide (ZnO) nanorods had been successfully fabricated via a fast microwave-assisted hydrothermal synthesis at 150 °C. The morphology and composition were carefully characterized by X-ray diffraction, field emission scanning electronic microscopy, and transmission electron microscopy. Gas-sensing testing results demonstrated that Ni-doped ZnO nanorods had enhanced gas-sensing performance. Furthermore, AC impedance spectroscopy and DC current–voltage curves were observed to investigate the gas-sensing mechanism. Current–voltage curves are approximately close to a linear function, indicating the potential barriers formed at the electron-depleted surface layer occupy a dominant when carriers transport in the gas sensor, and AC impedance spectra indicates the potential barriers height of the electron-depleted surface layer.
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TL;DR: In this paper, a comprehensive report on the microwave-assisted synthesis of metal oxides for applications in the field of gas sensing is given, emphasizing the improved characteristics compared with materials produced by conventional synthesis procedures.
Abstract: This review gives a comprehensive report on the microwave-assisted synthesis of metal oxides for applications in the field of gas sensing. In recent years, microwave heating technology has gained importance in the synthesis of metal oxides because of its faster, cleaner and cost effectiveness than conventional thermal heating. Further, due to the peculiarity of microwave heating mechanism, the synthesis of metal oxides in different nanostructured forms by microwave-assisted methods has been widely pursued and the nanomaterials thus obtained have been applied as sensing elements in chemoresistive gas sensors. Their gas sensing performances are here described and discussed in detail, emphasizing the improved characteristics compared with materials produced by conventional synthesis procedures.
234 citations
TL;DR: In this paper, high sensitivity ammonia gas sensor based on Ag/ZnO composite (SZO) nanostructures and their structural, optical, morphological and gas sensing properties were investigated.
Abstract: High sensitivity ammonia gas sensor based on Ag/ZnO composite (SZO) nanostructures and their structural, optical, morphological and gas sensing properties were investigated. Field- emission scanning electron microscopy and high- resolution transmission electron microscopy revealed that pure ZnO flower-like nanorods transformed into nanoellipsoids upon adding of silver (Ag). Scanning transmission electron microscopy (STEM) analysis showed clear flower-like morphology of Ag/ZnO composite. STEM-mapping measurement showed that Zn, Ag and O were homogeneously distributed. The ammonia gas sensing analysis revealed that the Ag/ZnO (6 wt%) showed higher gas response compared with other content of Ag wt%. Ag/ZnO (6 wt%) exhibited the highest response of 29.5 when exposed to 100 ppm ammonia gas. Interestingly, Ag/ZnO (6 wt%) possessed good response and recovery property of 13 and 20 s at low concentration of ammonia at 10 ppm, respectively. The mechanism of gas sensing and enhanced gas response of pure ZnO and Ag/ZnO composite was discussed.
207 citations
TL;DR: In this paper, an enhanced hydrogen-gas-sensing performance of a Ni-doped ZnO sensor decorated with the optimum concentration of reduced graphene oxide (rGO) was reported.
Abstract: We report enhanced hydrogen-gas-sensing performance of a Ni-doped ZnO sensor decorated with the optimum concentration of reduced graphene oxide (rGO). Ni-doped ZnO nanoplates were grown by radio frequency sputtering, rGO was synthesized by Hummer’s method and decorated by the drop cast method of various concentration of rGO (0–1.5 wt %). The current–voltage characteristics of the rGO-loaded sensor are highly influenced by the loading concentration of rGO, where current conduction decreases and sensor resistance increases as the rGO concentration is increased up to 0.75 wt % because of the formation of various Schottky heterojunctions at rGO/ZnO interfaces. With the combined effect of more active site availability and formation of various p–n heterojunctions due to the optimum loading concentration of rGO (0.75 wt %), the sensor shows the maximum sensing response of ∼63.8% for 100 ppm hydrogen at moderate operating temperature (150 °C). The rGO-loaded sensors were able to detect a minimum of 1 ppm hydrogen...
123 citations
TL;DR: This highly hydrogen selective Pd contacted ZnO nanorods based sensor detecting low concentration even at low operating temperature of 50 °C is reported, which exhibits dual characteristics as metal contact and excellent catalyst to hydrogen molecules.
Abstract: We report highly hydrogen selective Pd contacted ZnO nanorods based sensor detecting low concentration even at low operating temperature of 50 °C. The sensor performance was investigated for various gases such as H2, CH4, H2S and CO2 at different operating temperatures from 50 °C to 175 °C for various gas concentrations ranging from 7 ppm to 10,000 ppm (1%). The sensor is highly efficient as it detects hydrogen even at low concentration of ~7 ppm and at operating temperature of 50 °C. The sensor’s minimum limit of detection and relative response at 175 °C were found 7 ppm with ~38.7% for H2, 110 ppm with ~6.08% for CH4, 500 ppm with ~10.06% for H2S and 1% with ~11.87% for CO2. Here, Pd exhibits dual characteristics as metal contact and excellent catalyst to hydrogen molecules. The activation energy was calculated for all the gases and found lowest ~3.658 kJ/mol for H2. Low activation energy accelerates desorption reactions and enhances the sensor’s performance.
112 citations
TL;DR: In this article, a zinc oxide (ZnO) based thin film sensor was used to enhance the gas response and sensitivity of the sensor towards nitrogen dioxide (NO 2 ) by Ni doping and achieved a sensitivity of around 4.2%/ppm at moderate operating temperature of 200°C.
96 citations
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TL;DR: In this paper, the authors used impedance spectroscopy for unravelling the complexities of such materials, which functions by utilizing the different frequency dependences of the constituent components for their separation, and showed that electrical inhomogeneities in ceramic electrolytes, electrode/electrolyte interfaces, surface layers on glasses, ferroelectricity, positive temperature coefficient of resistance behavior and even ferrimagnetism can all be probed, successfully.
Abstract: Electroceramics are advanced materials whose properties and applications depend on the close control of structure, composition, ceramic texture, dopants and dopant (or defect) distribution. Impedance spectroscopy is a powerful technique for unravelling the complexities of such materials, which functions by utilizing the different frequency dependences of the constituent components for their separation. Thus, electrical inhomogeneities in ceramic electrolytes, electrode/electrolyte interfaces, surface layers on glasses, ferroelectricity, positive temperature coefficient of resistance behavior and even ferrimagnetism can all be probed, successfully, using this technique.
2,004 citations
TL;DR: In this paper, the authors demonstrated that the sensing characteristics of a semiconductor gas sensor using SnO2 can be improved by controlling fundamental factors which affect its receptor and transducer functions.
Abstract: It is demonstrated that the sensing characteristics of a semiconductor gas sensor using SnO2 can be improved by controlling fundamental factors which affect its receptor and transducer functions. The transducer function is deeply related with the microstructure of the elements, i.e., the grain size of SnO2 (D) and the depth of the surface space-charge layer (L). The sensitivity is drastically promoted when D is made comparable to or less than 2L, either by control of D for pure SnO2 elements or by control of the Debye length for impurity-doped elements. On the other hand, the receptor function is drastically modified by the introduction of foreign receptors on the surface of SnO2. In the particular cases of Pd and Ag promoters, the oxides (PdO and Ag2O) formed in air interact with the SnO2 surface to produce an electron-deficient space-charge layer, and this contributes much to promoting the gas sensitivity. For a test gas having a specific reactivity, such specificity can be utilized for exploiting gas-selective receptors, as exemplified by CuOSnO2 and La2O3SnO2 elements, which detect H2S and ethanol gas respectively very sensitively.
1,534 citations
TL;DR: This Review highlights the recent developments and reflects the impact of nanoscience on sensor technology, which can be improved and novel sensor concepts based on bottom-up approaches show that the sensor properties can be controlled by molecular design.
Abstract: Sensor technology is one of the most important key technologies of the future with a constantly increasing number of applications, both in the industrial and in the private sectors. More and more gas sensors are used for the control of technical processes, in environment monitoring, healthcare, and automobiles. Consequently, the development of fast and sensitive gas sensors with small cross sensitivity is the subject of intense research, propelled by strategies based on nanoscience and -technology. Established systems can be improved and novel sensor concepts based on bottom-up approaches show that the sensor properties can be controlled by molecular design. This Review highlights the recent developments and reflects the impact of nanoscience on sensor technology.
1,194 citations
TL;DR: In this paper, the authors investigated the interaction of tin oxide surface with oxygen, water vapor, and hydrogen using temperature-programmed desorption (TPD) chromatograms of oxygen.
736 citations
TL;DR: In this article, the effect of grain size on the sensitivity of chemoresistive nanocrystalline metal-oxide gas sensors was evaluated by calculating the effective carrier concentration as a function of the surface state density for a typical sensing material, SnO2, with different grain sizes between 5 and 80 nm.
Abstract: The effect of grain size on the sensitivity of chemoresistive nanocrystalline metal-oxide gas sensors was evaluated by calculating the effective carrier concentration as a function of the surface state density for a typical sensing material, SnO2, with different grain sizes between 5 and 80 nm. This involved numerical computation of the charge balance equation (the electroneutrality condition) using approximated analytical solutions of Poisson’s equation for small spherical crystallites. The calculations demonstrate a steep decrease in the carrier concentration when the surface state density reaches a critical value that corresponds to a condition of fully depleted grains, namely, when nearly all the electrons are trapped at the surface. Assuming that the variations in the surface state density are induced by surface interactions with ambient gas molecules, these calculations enable us to simulate the response curves of nanocrystalline gas sensors. The simulations show that the conductivity increases line...
561 citations