Pure and Mg-doped ZnO (3 at. %) nanoparticles were prepared based to sol–gel route under supercritical conditions of ethyl alcohol. The samples were characterized by certain techniques. XRD patterns ...showed the hexagonal wurtzite crystalline structure of ZnO and Mg-doped ZnO nanoparticles. The TEM image demonstrates the hexagonal shape and the nanometric size of the nanostructures. SEM images show the presence of hexagonal like shape nanoparticles and the increase of grain size for the Mg doped sample. The corresponding EDX analysis proves the existence of Mg with low concentrations and shows coherent distribution of high concentrations of Zn and O elements. The UV–Vis–NIR spectroscopy exhibits high absorbance of the prepared samples in the UV range. Thereafter, the effect of doping ZnO by Mg on sensing properties has been investigated. The obtained results outline an enhancement in sensing performances for Mg doped ZnO based sensor, which exhibits, competitive response and recovery times, high and linear response at working temperature 300 °C toward low and high ethanol concentrations with detection limit less than 1 ppm. Long term stability has been also investigated and sensor exhibits after one year, similar and reproducible responses.
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•Pure and Mg (3 at.%) doped ZnO nanoparticles have been synthesized using sol–gel technique.•The TEM observation shows prismatic shape and nanosized particles confirming the XRD results.•3 at% Mg doped ZnO (M3ZO) based gas sensor exhibits high sensitivity and excellent response to ethanol.•M3ZO has highest Response/ppm ratio compared to literature results at 300 °C and 50%RH.•M3ZO sensor Response exhibits, good linear relationship with concentration, and excellent long term stability.
Ca-doped ZnO (CZO) nanopowders were synthesized via a simple sol–gel method. The effects of calcium on the structural, morphological, and optical properties of the resultant powders were ...investigated. The XRD patterns showed that calcium has been incorporated into the ZnO lattice and the crystallites have nanometric size in the range of 50 nm. TEM observations depicted that crystallites possess spherical shape and confirm the nanometric size. UV–Vis–NIR characterization revealed an absorption band in the UV range with a decrease in optical band gap from 3.24 to 3.2 eV with increasing Ca concentration. Pure ZnO- and Ca-doped ZnO nanoparticles were used as active layer and tested for their sensing performance to formaldehyde. The most performed prepared sensor exhibits good formaldehyde sensing properties, including a high response of 5.28 (5 ppm, 250 °C) and low detection limit (≤ 1 ppm).
Probabilistic design factors for pipes used for hydrogen transport are proposed for 3 locations: urban, peri-urban and rural areas.
The used method involves a risk equation defined as the product of ...probability of leakage after failure, probability to have a gas flow greater than a prescribed value, probability of ignition, probability of lethal effects greater than a threshold value and probability of the presence of a person corrected by an environment factor and a risk reduction coefficient. The results obtained are less conservative than the deterministic values provided by ASME code.
•Probabilistic design factors for pipes have been established.•The used method involves a risk equation.•This approach is based on assumption of a risk 10−5 probability.•The results obtained are less conservative than values provided by ASME code.
Zinc oxide nanopowder was made using an auto-combustion method, and oxygen vacancies were formed using a thermally activated procedure under vacuum treatment. The structural and morphological ...properties of ZnO
1-X
samples were determined by using X ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and scanning electronic microscope (SEM) characterizations. XRD studies revealed that the ZnO
1-X
samples had a hexagonal wurtzite structure, with nanoparticle sizes ranging from 40 to 47 nm. The growing quantity of oxygen vacancies was confirmed by XPS tests. SEM images showed a spherical nanometric particle with high porosity especially for ZnO
0.90
. Optical measurements with spectroscopy UV–Visible revealed that oxygen vacancies increase absorption of the material in the visible region. Also, the photoluminescence properties of the prepared samples were investigated by PL and PLE measurement, which indicate a high presence of oxygen vacancies and other defaults in the structure of ZnO
0.90
more than pure zinc oxide. The electrical conductivity proportional to the temperature showed that the conduction process was thermally activated and that the carriers had long-distance mobility. Thus, we found that the conductivity of ZnO
0.90
was lower than that of ZnO, which can be explained by the introduction of oxygen vacancies which allows the creation of electron trapping centers localized by the presence of the deep-levels. Spraying an aqueous solution of ZnO
1-X
nanoparticles over alumina substrates with pre-deposited gold interdigitated electrodes resulted in gas sensors. At ambient temperature and under white light illumination, the manufactured sensors showed excellent sensing responses to 0.5 ppm NO
2
. The presence of oxygen vacancies improves sensor performance, which the sensor based on ZnO
0.90
showed a high response of 76.
ZnO nanoparticles have been prepared by auto-combustion method. Morphological and structural properties of the prepared samples were investigated by SEM, XRD, Raman and XPS characterizations. The XRD ...diffractogram of the sample indicates that ZnO has a hexagonal wurtzite structure. The crystallites average size, calculated from the Williamson–Hall plot, was 69.3 nm and the estimated by the SEM image (76.86 nm). Raman investigation indicates different modes of atomic displacement which correspond to longitudinal/transversal optical components with different frequencies. These modes are due to the macroscopic electric fields associated with the basic phonon of hexagonal ZnO. The XPS spectra indicate the presence of Zn and O in the structure with a small number of interstitial Zn
2+
, oxygen vacancies (
V
o
), and a negligible amount of chemical bonds with carbon (=CO …), confirmed by FTIR spectroscopy. The UV absorbance and reflectance spectra show a high absorbance with gap energy of 3.17 eV, estimated by Tauc's model. The a.c. electrical spectroscopy can be described by the Jonscher universal power-law. The charge carriers move according to the correlated barrier hopping pattern over the dispersive region. At room temperature, the conductivity of ZnO is high (~ 8 × 10
–6
S.m
−1
) making it promises for gas detection applications. The sensor was prepared by spraying the suspension of ZnO nanopowders on alumina substrates with pre-deposited gold interdigitated electrodes. The sensor responses of NO
2
, for concentrations of 0.5, 0.75 and 1 ppm, were investigated at room temperature under illumination with different wavelengths. The best response of the sensor was obtained for a concentration of 1 ppm NO
2
excited by 400 nm (purple) and 380 nm (UV) wavelengths, which were 91 and 88 with response/recovery times equal to 4/6.7 min and 4.4/3.3 min. Higher responses at the lower wavelength are due to the higher excitation energy which tends to excite more electrons, at the material surface, subsequently participating in the detection mechanism with gas molecules
•RPCVD growth of GeSn alloys was explored in H2 and N2 carrier gas.•Growth in N2 results in increased growth rate but decreased Sn-incorporation.•Fully-relaxed GeSn layers up to ∼1.1μm thick were ...realized.•Thick layer growth results in unique compositional profile due to strain relaxation.•TEM shows that dislocations in thick layers are confined to the GeSn/Ge interface.
High quality, thick (up to 1.1μm), strain relaxed GeSn alloys were grown on Ge-buffered Si (100) in an ASM Epsilon® chemical vapor deposition system using SnCl4 and low-cost commercial GeH4 precursors. The significance of surface chemistry in regards to growth rate and Sn-incorporation is discussed by comparing growth kinetics data in H2 and N2 carrier gas. The role of carrier gas is also explored in the suppression of Sn surface segregation and evolution of layer composition and strain profiles via secondary ion mass spectrometry and X-ray diffraction. Transmission electron microscopy revealed the spontaneous compositional splitting and formation of a thin intermediate layer in which dislocations are pinned. This intermediate layer enables the growth of a thick, strain relaxed, and defect-free epitaxial layer on its top. Last, we present photoluminescence results which indicate that both N2 and H2 growth methods produce optoelectronic device quality material.
A high-performance 1.3 μm InAs/GaAs quantum-dot laser directly grown on Si substrates has been achieved by using InAlAs/GaAs strained-layer superlattice serving as dislocation filter layers (DFLs). ...The Si-based laser achieves lasing operation up to 111°C with a threshold current density of 200 A/cm2 and an output power exceeding 100 mW at room temperature.
Maghemite (γ-Fe
2
O
3
) nanopowder was prepared by the sol–gel method. The microstructural and morphological properties of the prepared sample were studied by X-ray diffraction (XRD) and scanning ...electron microscopy (SEM). The electrical investigation was performed by impedance spectroscopy and the temperature/magnetic field dependence of magnetization was investigated using a magnetometer. The characterization results confirmed that the reflection peaks indexed by XRD correspond to the γ-Fe
2
O
3
material with a crystallite size of 8 nm. The nanoparticles of the sample we prepared present a spherical shape and small size with high porosity. The electrical conductivity is in good agreement with Jonscher's law. Consequently, the displacement of charge carriers corresponds to the pattern of correlated barrier jumps over the dispersive region generated by interstitial defects and vacancies. The Nyquist diagram shows the presence of grains and grain boundary effects on the electrical transport in the structure of our material. The dielectric behavior was correlated with the polarization effect and a small dielectric loss. The saturation magnetization shows a high value for our sample, corresponding to 57 emu/g at room temperature (300 K) and 65 emu/g at a temperature of 5 K.
Microcystins (MCs) are the most common cyanotoxins with more than 200 variants. Among these cyanotoxins, microcystin-LR (MC-LR) and microcystin-RR (MC-RR) are the most studied congeners due to their ...high toxicity and frequent occurrence in surface waters. MC-LR has been detected in more than 75% of natural cyanobacteria bloom, along with other toxic and less toxic congeners. Accumulation of several microcystins variants (MC-LR and MC-RR) has been confirmed in aquatic snails exposed naturally or in the laboratory to toxic blooms. Thus, this paper aims to compare the biochemical and histological impact of both toxic variants (microcystin-LR and microcystin-RR) and their mixed form on a bioindicator, the land snail Helix aspersa. During experiments, snails were gavaged with a single acute dose (0.5 μg/g) of purified MC-LR, MC-RR, or mixed MC-LR + MC-RR (0.25 + 0.25 μg/g). After 96 h of exposure, effects on the hepatopancreas, kidney, intestine and lungs were assessed by histological observations and analysis of oxidative stress biomarkers. The results show that a small dose of MCs variants can increase the non-enzymatic antioxidant glutathione (GSH), inhibit glutathione-s-transferase (GST) level and trigger a defense system by activating glutathione peroxidase (GPx), catalase (CAT) and superoxide dismutase (SOD). Microcystin-RR causes serious anomalies in the hepatopancreas and kidney than Microcystin-LR. The organ most affected is the kidney. The damage caused by MC-LR + MC-RR is greater than that caused by single variants.
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•MC-RR exposure induced necrosis and degeneration cells in H. aspersa hepatopancreas.•MC-LR + MC-RR mixture could induce hyperplasia, degeneration, and necrosis in nephrocytes.•MC-RR triggered the defense system by activating; GPx, CAT, and SOD enzymes.•The most affected organ by MCs variants was the kidney, and the less one was the lung.
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