•Efforts are taken to deposit WO3 directly on to glass substrate without assistance of seed layer hydrothermal technique.•2D nanoplates like structure of WO3 were synthesized via simple route.•The 2D ...nanoplates of WO3 exhibited excellent and highly selective gas response ∼10 for 5ppm.•The new synthesis route and sensing behavior of as synthesized WO3 nanoplates revealed a promising candidate for fabricating low-consumption gas sensors.
Gas sensors based on a chemiresistive metal oxide semiconductor are widely used including nitrogen dioxide (NO2) at a moderate temperature. In this work efforts are taken to fabricate NO2 gas sensor using thin films of tungsten oxide (WO3) grown directly on to a soda-lime glass substrate without assistance of any seed layer by a simple and a facile hydrothermal technique. As per our knowledge, the deposition of nanostructured WO3 thin films without assistance of any seed layer on the glass substrate was rarely reported. The WO3 thin film samples were synthesized at various deposition times ranging from 3h to 7h and were characterized by X-ray diffraction, Raman spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, UV–vis spectroscopy and Brunauer-Emmett-Teller techniques. The surface morphological and structural characterization showed the two dimensional (2D) nanoplate-like structure of as synthesized WO3 thin films with plate thickness ranging from 90 to 150nm and had an orthorhombic structure, respectively. Moreover, the 2D nanoplates of WO3 exhibited a gas response ∼10 for 5ppm for toxic NO2 gas at relatively low operating temperature. The new synthesis route and sensing behavior of as synthesized WO3 nanoplates revealed a promising candidate for the fabrication of the cost effective gas sensors.
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•Synthesis of Cu-doped rod-like ZnO nanostructured thin films by a simple wet chemical method.•The Cu doping modifies the surface morphology and conductivity of ZnO thin films.•As per ...the author’s knowledge, this is the first report on NO2 gas sensing with Cu doped ZnO Nanorods.•The Cu doped ZnO exhibited the gas response of ˜ 71 for 1 ppm NO2 gas at low operating Temperatures.
In this report, we have prepared Cu-doped ZnO nanorods by a simplistic wet chemical method with subsequent annealing. The phase formation, optical, surface morphological studies along with the electrical properties of the Cu doped ZnO thin films were characterized by X-ray diffraction (XRD), photoluminescence (PL), field emission scanning electron microscopy (FESEM) and Hall measurements, respectively. The addition of copper (Cu) in to the matrix of ZnO influenced the surface morphology of the product dramatically. The regular hexagonal nanorods-like surface morphology of ZnO becomes a broken rod-like morphology, after addition of copper. Owing to the complexes surface morphology of Cu doped ZnO, the system was used to detect the toxic gases like NO2. The effect of doping on the gas-sensing properties of ZnO was slightly counterintuitive in that they initially increased up to Cu concentrations of 1% before beginning to decline. Meanwhile, the Cu doped ZnO exhibited the gas response of ˜ 71 for 1 ppm of NO2 gas at low operating temperatures. This higher gas sensing response is due to the defect states observed in Cu doped ZnO films. In addition to above mentioned findings, the transformation of n-type ZnO to p-type Cu doped ZnO was also observed. The p-type conductivity is attributed to the holes created in the merging of Cu on Zn sites.
Recently, the nanostructured metal oxides are widely attracted for resistive switching memory devices. In this work, nanostructured ZnO thin films were deposited via simple and cost-effective spray ...pyrolysis technique (SPT) onto a glass/FTO substrates at 450 °C by varying the solution quantity such as 40, 80, and 120 ml. The structural, morphological, and compositional properties of the deposited ZnO thin films were investigated using XRD, FESEM, AFM and EDAX characterizations. All the deposited ZnO samples showed crystalline nature with nanoflakes-like morphology. The bipolar resistive switching properties of the Al/ZnO/FTO fabricated memristive devices and its mechanism were investigated. The fabricated memristive device showed two-valued charge–flux relation which confirms non-ideal memristor devices. The data retention property of memristive devices was examined by measuring the low-resistance state (LRS) and high-resistance state (HRS) for every 10 s and it can retain data up to 10
4
s. The ZnO-based memristive device possesses good non-volatile memory properties with reliable device performance that can be advantageous for light-responsive memory, synaptic, sensor devices, etc.
Graphical abstract
Synthesis of nanostructured ZnO thin films by spray pyrolysis technique for resistive switching applications.
Nickel oxide thin films were obtained by a cost-effective chemical spray pyrolysis approach on glass substrates using nickel chloride as starting precursor with different deposition times. The X-ray ...diffraction investigation indicated that the obtained films were polycrystalline cubic structure with preferred orientation along (111) plane. Scanning electron microscopy images for sprayed NiO layers at deposition time of 5 and 10 min exhibit a porous structure with randomly oriented honeycomb like morphology. The optical direct band-gap energy Eg of sprayed NiO films was around 3.4–3.5 eV for all deposited samples and optical transmittance decreases with increasing the deposition time. Gas sensing performance was tested for the detection of nitrogen dioxide (NO2) at different operating temperatures and NO2 concentrations. It was found that the sprayed NiO thin film at deposition time of 5 min shows the maximum sensitivity of 57.3% for 20 ppm NO2 at 200 °C as operating temperature with good stability and selectivity. This study suggests that the sprayed NiO thin film is a good candidate material for NO2 detection at a relatively low operating temperature.
•NiO thin films were successfully fabricated by chemical spray pyrolysis with different thicknesses.•The structural, morphological, optical, and sensing measurements of NiO films were studied.•Operating temperature of NiO gas sensors for NO2 detection was optimized at 200 °C.•Gas sensor based on NiO thin film with the lowest thickness shows the best sensing performance toward NO2 gas.•NiO gas sensor shows maximum sensitivity of 57% for 20 ppm NO2 at 200 °C and the detection limit is 10 ppm gas concentration.
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•Synthesis of 3-D micro flowers structure using simple hydrothermal method.•The structure directing agent (KOH) plays a pivotal role in altering the morphology of WO3 ...nanostructures.•As per the author’s knowledge, this morphology useful for adsorption of target gas and hence to increase the gas sensitivity.
An exotic 3-D tungsten oxide (WO3) microflower was synthesized via low-cost and environmental-friendly hydrothermal strategy. The effect of structure-directing agent on the formation of 3-D microflowers from a 2-D nanosheets of WO3 and its gas sensing behavior are investigated. The as-synthesized WO3 powder was used in morphological, structural and phase studies by X-ray diffraction (XRD), scanning electron microscopy (SEM), FT-Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). The WO3 samples were found to be polycrystalline with monoclinic crystal structure. The SEM micrographs revealed the formation of 3-D microflowers made up of two-dimensional (2-D) multi-directional dendritic nanoplates. The potassium hydroxide (KOH) acts as a structure-directing agent in the formation of 3-D microflowers of WO3 sample. To further understand the formation of 3-D microflowers of WO3 sample, concentration-dependent experiments were carried out by varying KOH concentration and the formation mechanism was investigated. The synthesized WO3 microstructures were subjected to detailed gas sensing tests for different gases at an optimized temperature. A selective, sensitive gas response was obtained for WO3 gas sensor. The lower detection limit is about 1 ppm at 150 °C working temperature for an optimized WO3 gas sensor. The gas sensing results indicate that the 3-D microflower-like WO3 nanostructures are highly promising for applications as gas sensors.
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•ZnO nanorods, Silver-doped ZnO nanoflower and nanoellipsoids were successfully synthesized.•SZO nanoellipsoids had wider optical absorption region than ZnO nanorods.•Silver-doped ZnO ...showed fast gas response and recovery time at 10ppm of ammonia concentration.•Silver-doped ZnO (6%) showed maximum response of 29 for 100ppm at 150°C.
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 (6wt%) showed higher gas response compared with other content of Ag wt%. Ag/ZnO (6wt%) exhibited the highest response of 29.5 when exposed to 100ppm ammonia gas. Interestingly, Ag/ZnO (6wt%) possessed good response and recovery property of 13 and 20s at low concentration of ammonia at 10ppm, respectively. The mechanism of gas sensing and enhanced gas response of pure ZnO and Ag/ZnO composite was discussed.
•Surfactant free In2O3 was synthesized by hydrothermal method.•In2O3 is found to be activated at very low operating temperature of 50 °C.•The porosity boosts the gas sensing performance of ...In2O3.•Sensing mechanism at low operating temperature is proposed.•NO2 gas is detected at ppb level.
In this work, porous indium oxide is synthesized by hydrothermal method. The In2O3 has been structurally and optically characterized by using XRD, XPS, FESEM and TEM techniques. The morphological studies have revealed the growth of self-assembled In2O3 nanoparticles which helpts to form a brick-like structure. The porous In2O3 nanoparticles have provided the large number of active sites for the adsorption of gas molecules which resulted in a quick sensor response of 6877 for 10 ppm of NO2 gas at very low temperature of 50 °C. Remarkably, the In2O3 sensor has shown the detection of NO2 gas down to 60 ppb.
Ammonia is a kind of colorless, pungent gas which is highly toxic to human health when inhaled above the moderate level. Detection of ammonia at low temperature is one of the most challenging tasks. ...In this work, low-temperature ammonia gas sensor using manganese-doped ZnO sphere as sensing material was successfully developed. Undoped ZnO nanorods and Mn-doped ZnO microsphere were successfully synthesized by the simple hydrothermal method and the structural, surface morphological, optical and gas sensing properties were investigated. Field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) revealed that the Mn-doped ZnO has sphere like-morphology decorated with nanoparticles. X-ray photoelectron spectroscopy (XPS) analysis indicated that the Mn-doped ZnO sample is in the Mn2+ valence state. Mn-doped ZnO sphere showed enhanced selectivity towards ammonia compared to other gases at low temperature. Mn-doped ZnO (8 wt%) showed the higher response of 28.58. The response and the recovery time of the fabricated sensor towards 20 ppm ammonia are 4 and 10 s (s).
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•Manganese-doped ZnO microsphere decorated nanoparticles nanostructures were successfully synthesized.•Mn-doped ZnO showed fast gas response, recovery time about 4 and 15 s.•Mn-doped ZnO (8%) showed maximum response of 28.5 for 100 ppm at 150 °C.•Mn-doped ZnO showed long term stability and repeatability.
Detection of the 21-cm signal coming from the epoch of reionization (EoR) is challenging especially because, even after removing the foregrounds, the residual Stokes I maps contain leakage from ...polarized emission that can mimic the signal. Here, we discuss the instrumental polarization of Low Frequency Array (LOFAR) and present realistic simulations of the leakages between Stokes parameters. From the LOFAR observations of polarized emission in the 3C196 field, we have quantified the level of polarization leakage caused by the nominal model beam of LOFAR, and compared it with the EoR signal using power spectrum analysis. We found that at 134–166 MHz, within the central 4° of the field the (Q, U) → I leakage power is lower than the EoR signal at k < 0.3 Mpc−1. The leakage was found to be localized around a Faraday depth of 0, and the rms of the leakage as a fraction of the rms of the polarized emission was shown to vary between 0.2 and 0.3 per cent, both of which could be utilized in the removal of leakage. Moreover, we could define an ‘EoR window’ in terms of the polarization leakage in the cylindrical power spectrum above the point spread function (PSF)-induced wedge and below k
∥ ∼ 0.5 Mpc−1, and the window extended up to k
∥ ∼ 1 Mpc−1 at all k
⊥ when 70 per cent of the leakage had been removed. These LOFAR results show that even a modest polarimetric calibration over a field of view of ≲ 4° in the future arrays like Square Kilometre Array will ensure that the polarization leakage remains well below the expected EoR signal at the scales of 0.02–1 Mpc−1.
•The CBD technique was used to synthesize and alter chemical compositions of CdS thin films.•The Cd contents increase with the rise in the CBD deposition period, which affect the composition of CdS ...thin films and induces defects in the film.•The prolonged deposition time produce a huge CdS micro-balls like morphology.•Such CdS films showed low-temperature gas sensing behavior to NO2 gas with an encouraging outcomes.
A simplistic chemical bath deposition (CBD) technique was used to synthesize the hierarchical morphology of cadmium sulfide (CdS) thin films with altered chemical compositions. The novelty of the work does not lies in the surface morphology of the product, but is found in the influence of the CBD reaction time (mainly after post-optimization) on the Cd contents in the films, subsequently the presence of defects and consequently their electrical conductivity and NO2 gas sensing performance. The morphology of the CdS thin films was characterized by field-effect scanning electron microscopy and defects estimated using photoluminescence spectroscopy. The increment in the deposition time affects the precursor contents in the produced film effectively. In the case of the CdS, the Cd contents increase with the rise in the CBD deposition period. Consequently, it affects the presence of the secondary phase and the conductivity of the compound. As the concentration of the films slightly differs from the standard value, we utilized the films for the sensor application. The low-temperature gas sensing measurements of this Cd-rich CdS structure to NO2 gas were carried out, and we found encouraging outcomes.
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