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Microbial fuel cell (MFC) is a promising technology for simultaneous wastewater treatment and energy harvesting. The properties of the anode material play a critical role in the performance of the MFC. In this study, graphene oxide was prepared by a modified hummer's method. A thin layer of graphene oxide was incorporated on the carbon brush using an electrophoretic technique. The deoxygenated graphene oxide formed on the surface of the carbon brush (RGO-CB) was investigated as a bio-anode in MFC operated with real wastewater. The performance of the MFC using the RGO-CB was compared with that using plain carbon brush anode (PCB). Results showed that electrophoretic deposition of graphene oxide on the surface of carbon brush significantly enhanced the performance of the MFC, where the power density increased more than 10 times (from 33 mWm−2 to 381 mWm−2). Although the COD removal was nearly similar for the two MFCs, i.e., with PCB and RGO-CB; the columbic efficiency significantly increased in the case of RGO-CB anode. The improved performance in the case of the modified electrode was related to the role of the graphene in improving the electron transfer from the microorganism to the anode surface, as confirmed from the electrochemical impedance spectroscopy measurements.

In this work, Cu2O nanoparticles were successfully prepared onto the surface of two-dimensional graphitic carbon nitride (g-C3N4) by using a simple solution chemistry approach. An environment-friendly reducing agent, glucose, was used for the synthesis of Cu2O NPs onto the surface of g-C3N4 without using any surfactant or additives. The surface composition, crystalline structure, morphology, as well as other properties have been investigated using XPS, XRD, SEM, FTIR, FESEM, EDS, etc. The electrochemical measurements of the prepared materials demonstrated that Cu2O exhibited a weak oxidation activity towards urea, while g-C3N4 has no activity towards urea oxidation. The Cu2O supported on the surface of g-C3N4 (Cu2O-g-C3N4) demonstrated a significant activity towards urea oxidation that reached two times that of the unsupported one. The significant increase in the performance was related to the synergetic effect between the Cu2O and g-C3N4 support. The prepared composite materials demonstrated high stability towards urea oxidation as confirmed from the stable current discharge for around 3 h without any noticeable degradation performance.

A simple electrodeposition technique has been used to synthesize Co nanoparticles with a 3D leaf-like morphology at room temperature. The prepared Co material has a layered sheet structure of a few nanometers thickness. The surface area of the Co leaf-like structure is three times higher than that of the Co nanoparticles. The prepared nanoparticles exhibit high activity towards ethanol oxidation in alkaline media with an onset potential of 0 V vs Ag/AgCl, which is one of the lowest reported potentials for a non-precious catalyst. The current density is observed to increase with increasing ethanol concentration from 0.1 M to 2 M, after which it plateaus. Mixing the Co catalyst with Vulcan carbon (20 wt%) resulted in a 50% increase in current discharge at different ethanol concentrations due to the improvement in mass and charge transfer rates as confirmed by EIS measurements. Also, Co deposited in situ on the surface of nickel foam (NF) exhibited a high activity towards ethanol oxidation as a standalone electrode that is 10 times that of bare NF.

Particulate matter (PM) specimens from a traffic site were sampled on Teflon filters using a low volume sampler. The sampling campaign ran over a one-year period with sampling frequency of twice a week for both PM2.5 and PM10. X-ray diffraction (XRD) methods, which are not commonly used in PM analysis, have been utilized successfully to identify crystalline phases present, including secondary pollutants. XRD data confirmed results obtained by X-ray fluorescence, positive matrix factorization modeling, and scanning electron microscopy. PM2.5 consisted mainly of secondary sulfates, like Mascagnite [(NH4)2SO4], Koktaite [(NH4)2Ca(SO4)2·H2O], and Gypsum [CaSO4·2H2O]. For PM10, it was found that the major phases are mostly originating from natural sources, such as dust storms and sea salts, in addition to secondary compounds, such as sodium nitrate. The main phases identified were Calcite, Quartz, Gypsum, Halite, and Palygorskite.

We report a density functional theory study of ZnO cluster doped with Eu and Mg along with native point defects using the generalized gradient approximation including the Hubbard parameter. The Zn atomic positions are found to be energetically more favorable doping sites than O. The Eu has a lower formation energy than Zn and O vacancies, helps in lowering the formation energy of point defects and induces spin polarization. Mg is less favorable dopant energetically and is not inducing any magnetism in the cluster. Presence of Eu and point defects along with Mg can help in sustaining spin polarization, implying that transition metal and rare earth dopant is a favorable combination to invoke desirable properties in ZnO based materials. Eu–Eu doping pair prefers ferromagnetic orientation and a spin flip is induced by Eu in the Eu–Mg configuration. Further, Eu doping increases the value of static refractive index and optical absorption in the UV region compared to the undoped ZnO cluster.

Nowadays, wind energy is one of the most cost-effective and environmentally friendly energies in high demand due to shortages in fossil fuels and the necessity to reduce global carbon footprint. One of the main goals of wind turbine development is to increase the power output of the turbine either by increasing the turbine blade swept area or increasing the velocity of the wind. In this article, a proprietary augmentation system was introduced to increase the power output of vertical axis wind turbines (VAWT) by increasing the free stream velocity to more than two folds. The system comprises two identical airfoiled casings within which the turbine/turbines are seated. The results showed that the velocity slightly increases when decreasing the gap between the casing. It was also found that changing the angle of attack of the housing has more impact on the augmented airspeed. CFD technique was used to assess the velocity and flow of air around the system.

The magnetic properties of a single crystalline bi-layered La1.15Sr1.85Mn2O7 manganite have been studied using magnetization measurements complemented by low-temperature Raman spectroscopy. The bulk magnetization measurements revealed a magnetic transition at a temperature of Tc = 85 K. The temperature dependence of the inverse magnetization data revealed an upward deviation from the Curie-Weiss law at a temperature of T* = 250 K, which is indicative of the onset of the short-ranged ferromagnetic metallic cluster formation based on the phase separation/coexistence models. Raman spectrum analysis of certain peaks revealed interesting phenomena at around T*. The T* that has been observed in the inverse magnetization data and the Raman spectrum analysis of certain peaks has been discussed. Our observations demonstrate that Raman spectroscopy is a powerful technique for the determination of subtle magnetic phenomena in this group of materials.

One of the important applications in intelligent transportationsystem is path planning for vehicles at urban areas. A driver can reach a destination in a short time with a pleasant ride using less fuel and reach his or her destination safely. However, the destination status may change, and no more becomes a desired destination. In this paper we highlighted, discussed and analyzed related works for vehicle’s path planning using Internet of Things (IoT). A new perspective for the destination was also proposed which defines how important considering the updated information of the destination in real-time using IoT that brings driver’s attention when planning for a trip. A mathematical model for an optimal path planning was introduced which composes of two cost functions; path planning function and destination function. A gas station scenario was introduced as an example to demonstrate the proposed model. Futuristic look at integration design for the proposedsystem was also highlighted.

International audience; Severe acute respiratory syndrome SARS-CoV-2 virus led to notable challenges amongst researchers in view of development of new and fast detecting techniques. In this regard, surface-enhanced Raman spectroscopy (SERS) technique, providing a fingerprint characteristic for each material, would be an interesting approach. The current study encompasses the fabrication of a SERS sensor to study the SARS-CoV-2 S1 (RBD) spike protein of the SARS-CoV-2 virus family. The SERS sensor consists of a silicon nanowires (SiNWs) substrate decorated with plasmonic silver nanoparticles (AgNPs). Both SiNWs fabrication and AgNPs decoration were achieved by a relatively simple wet chemical processing method. The study deliberately projects the factors that influence the growth of silicon nanowires, uniform decoration of AgNPs onto the SiNWs matrix along with detection of Rhodamine-6G (R6G) to optimize the best conditions for enhanced sensing of the spike protein. Increasing the time period of etching process resulted in enhanced SiNWs’ length from 0.55 to 7.34 µm. Furthermore, the variation of the immersion time in the decoration process of AgNPs onto SiNWs ensued the optimum time period for the enhancement in the sensitivity of detection. Tremendous increase in sensitivity of R6G detection was perceived on SiNWs etched for 2 min (length=0.90 µm), followed by 30s of immersion time for their optimal decoration by AgNPs. These SiNWs/AgNPs SERS-based sensors were able to detect the spike protein at a concentration down to 9.3 × 10−12 M. Strong and dominant peaks at 1280, 1404, 1495, 1541 and 1609 cm−1 were spotted at a fraction of a minute. Moreover, direct, ultra-fast, facile, and affordable optoelectronic SiNWs/AgNPs sensors tuned to function as a biosensor for detecting the spike protein even at a trace level (pico molar concentration). The current findings hold great promise for the utilization of SERS as an innovative approach in the diagnosis domain of infections at very early stages.

Oxygen-free copper of >99.95% purity was processed by equal-channel angular pressing at room temperature (RT) for up to 24 passes and then pulled to failure at RT using strain rates from 10−4 to 10−2 s−1. The results show that the microstrain increases with strain at the lower numbers of passes but decreases between 16 and 24 passes. Similar trends were found also for the dislocation density, the Vickers microhardness and the values of the measured yield stresses in tensile testing. X-ray diffraction measurements showed a minor increase in the crystallite size at the high strain imposed by processing through 24 passes. These results demonstrate the occurrence of dynamic recovery at the highest strain. In tensile testing at a strain rate of 10−3 s−1 the results gave a yield stress of ~391 MPa and an elongation to failure of 52% which is consistent with an earlier report using Cu of much higher purity but not consistent with an earlier report using Cu of the same purity.

Oxygen-free copper was processed by equal-channel angular pressing (ECAP) at room temperature for 1, 4 and 8 passes and then the ECAP specimens were further deformed by dynamic testing at 298 K using a strain rate of 10 s−1. Experiments were conducted to investigate the influence of the initial microstructures induced by ECAP on the subsequent grain refinement and mechanical properties after dynamic testing. The results show the strength of copper increased with increasing numbers of ECAP passes and a significant additional grain refinement was produced in the ECAP specimens through the dynamic testing. Thus, the initial grain sizes after ECAP for 1, 4 and 8 passes were ~16, ~4.4 and ~2.9 μm, respectively, and these values were reduced to ~400, ~330 and ~300 nm by dynamic testing, The grains were refined by conventional dislocation processes in the 1-pass specimen but there was evidence for dynamic recrystallization in the specimen processed by 8 passes.

Exploration of novel strategies for fabricating SERS substrates attracted enormous research potential as achieving high sensitivity, reproducibility along with cost effectiveness is really challenging. Herein, we have fabricated hierarchical silver nanoprism/graphene oxide/silicon nanowire (Ag/GO/SiNWs) arrays as surface-enhanced Raman scattering (SERS) sensors for the effective detection of atrazine. Homogenous and vertically aligned SiNWs have been successfully synthesized using silver assisted chemical etching. Further, Ag/GO/SiNWs arrays were assembled by subsequent spin-coating of GO followed by drop-casting deposition of Ag nanoprisms. Micro-structural properties of as-fabricated nano-arrays have been well examined by scanning electron and atomic force microscopic techniques. Nanowire bunches have been decorated by GO layers; which further facilitates homogenous deposition of Ag nanoprisms. Using rhodamin 6G as probe molecule, high SERS activity and excellent reproducibility of as-fabricated substrates have been demonstrated. High efficiency of 3.2 × 108 and was obtained for the fabricated sensors; attributed to the synergetic charge transfer between GO and Ag nanoprisms on high surface area Si nanowires. Charge transfer mechanism that leading to enhanced surface plasmon resonance effect of the as-fabricated array was established as well. Further, these low cost Ag/GO/SiNWs sensors exhibited ultrasensitive detection of pollutants such as methylene blue and atrazine residues down to picomolar levels; these can serve as potential chemical sensors for rapid monitoring of environmental pollutants in trace levels.

This study unravels the soft chemical synthesis of Bi2O3/ZnO (BZO) nanocomposites having nano-cones like morphology with tunable optical and luminescent properties. The prepared BZO samples with varying Bi2O3 concentrations have been characterized for structural, morphological, band gap energy, photoluminescence (PL) and antibacterial characteristics. Structural and morphological investigations revealed the separate single wurtzite phase of ZnO and monoclinic phase of Bi2O3 without any undesired phases with dominant nano-cones like morphology. Optical and PL analysis have depicted the band gap widening, enhanced ultra-violet (UV) emission and decreased defects densities of BZO nanocomposites as compared to pristine ZnO nano-cones. Interestingly, a good correlation between defects and antibacterial activity of ZnO nanostructures has been found.

This paper presents the results obtained for incorporating the Al65Cu24Fe11material with the conventional TiO2 as the electron injection layer in dye-sensitized solar cells. The icosahedral phase of the Al-Cu-Fe system has attractive physical and optical properties at the target composition, and is obtained by synthesizing the material via the facile high energy ball milling process to ensures the highest possible interdiffusion of elemental powders, followed by heat treatment. The evolution of the i-phase is confirmed via X-ray diffraction, scanning electron microscopy and energy dispersive x-ray spectroscopy. The optical absorption and electrical properties of the compound are investigated by spectrometry, four probe measurement and Mott-Schottky analysis, respectively. Different cells with different percentages (x value) of (TiO2)1-x/(Al65Cu24Fe11)xare constructed and tested to obtain the electrical characteristic curves, efficiency and fill factor to quantify the effect of the proposed material mixture.

Mesoporous Co dendrites prepared by electroplating have a surface area of 145 m2g−1, which is three times that of Co nanoparticles. The Co dendrites demonstrate superior urea oxidation activity compared to Ni or Co nanoparticles prepared using chemical reduction. The onset potential with Co dendrites is around 0 V “vs. Ag/AgCl” using 2 M urea, that is remarkably lower than 0.35 V “vs. Ag/AgCl” for Ni catalyst at optimum urea concentration of 0.5 M. The current produced in case of the Co dendrites using 2 M urea at 0.5 V “vs. Ag/AgCl” was six times that obtained using Ni. The in-situ measurements using Co dendrites on the Ni foam as anode and Prussian blue as cathode catalyst demonstrated a 21 mWcm−2 at 20 °C. These are the first reported results for a complete Ni-free nonprecious anode and cathode catalysts under real fuel cell operation with high performance comparable to those obtained using precious catalyst under same conditions.

Graphene is a 2-D carbon material showing considerable prominence in a wide range of optoelectronics, energy storage, thermal and mechanical applications. However, due to its unique features which are typically associated with difficulty in handling (ultra-thin thickness and hydrophobic surface, to name a few), synthesis and subsequent deposition processes are thus critical to the material properties of the prepared graphene films. While existing synthesis approaches such as chemical vapor deposition and epitaxial growth can grow graphene with high degree of order, the costly high temperature and/or high vacuum process prohibit the widespread usage, and the subsequent graphene transfer from the growth substrates for deposition proves to be challenging. Herein, a low-cost one-step synthesis and deposition approach for preparing few-layer graphene (FLG) on flexible copper substrates based on dry ball-free milling of graphite powder is proposed. Different from previous reports, copper substrates are inserted into the milling crucible, thus accomplishing simultaneous synthesis and deposition of FLG and eliminating further deposition step. Furthermore, while all previously reported high energy milling processes involve using balls of various sizes, we adopt a ball-free milling process relying only on centrifugal forces, which significantly reduces the surface damage of the deposition substrates. Sample characterization indicates that the process yields FLG deposited uniformly across all tested specimens. Consequently, this work takes graphene synthesis and deposition a step closer to full automation with simple and low-cost process.

In this work, we show the results of our investigation on the photoelectric properties of heterojunction solar cells based on Au/PS/mc-Si/Al and Au/TiO2/PS/mc-Si/Al structures. Porous silicon (PS) were prepared by an electrochemical etching process with different values of current density. The surface porosity was found to increase with the increase of current density. Pulsed laser deposition was used to deposit 80 nm TiO2 thin films. Surface morphology and structural properties of TiO2/PS were characterized by using scanning electron microscopy (SEM) and atomic force microscopy (AFM). An enhancement of the electrical properties of the TiO2/PS/mc-Si heterojunction was observed after coating with TiO2. As a consequence, the solar cell efficiencies increased from 1.4% for the uncoated PS/mc-Si structure to 5% for the TiO2 coated one. Impedance spectroscopy confirmed the passivation effect of TiO2 through the improvement of the elaborated cells’ electron lifetime and the formation of a TiO2/PS/Au heterojunction with the appearance of a second semi-circle in the Nyquist plot.

ZnO was prepared using room temperature bipolar electrochemical process in deionized water. Electron microscopy, powder X-ray diffraction, and micro-Raman spectroscopy showed crystallization of the material into the wurtzite hexagonal structure of ZnO, self-organized in micro-sized flower-like shapes that are formed out of individual nanorods preferentially grown along the direction. The intrinsic electronic properties were evaluated by potentiodynamic electrochemical impedance spectroscopy using Mott–Schottky analysis of semiconductor/liquid junctions. Because the flat band and carrier density are frequency-dependent, we used an approximation based on fractional order capacitance fitting, and subsequently three different ways to calculate the frequency-independent effective capacitance of the system. The capacitance computed using the four parameters of single-dispersion Randle's model, i.e., pseudocapacitance, dispersion coefficient, and series and parallel resistances, is more recommended for the characterization of the electrochemical system.

This work reports on passivation effect of solar-grade multicrystalline Si (mc-Si) using a TiO2/porous silicon double coating. For this purpose, TiO2 nanoparticles were deposited onto porous silicon (PS)/mc-Si using pulsed laser ablation of titanium target. The structural and optoelectronic properties of the TiO2/PS treated mc-Si substrates were investigated by X-ray diffraction, Raman spectroscopy, optical spectrometry, photo-conductance and photoluminescence (PL). It was found that the minority carrier lifetime (τ eff) of the mc-Si wafer could enhance at a nominal thickness of the TiO2 film (nanoparticle sizes). This was attributed to a surface passivation of the mc-Si wafer via TiO2-passivation of the PS film, whose PL intensity improves consequently. An optimal TiO2 thickness of 80 nm was found to give the highest PL intensity and an enhancement of the minority carrier lifetime from 5 µs for untreated mc-Si wafer to about 391 µs for a TiO2/PS treated wafers.

Pulsed laser deposition has been successfully used to achieve in-situ nitrogen doping of zinc oxide thin films at a temperature as low as 300 °C. Nitrogen-doped zinc oxide (ZnO:N) thin films with a maximum nitrogen content of 0.7 at.% were obtained by varying the nitrogen background pressure in the range of 0–150 mTorr. The ZnO:N thin films were found to present hexagonal crystalline structure with dense and smooth surface. X-ray photoelectron spectroscopy analysis confirms the effective incorporation of nitrogen into ZnO thin films. Optical transmission together with room temperature photoluminescence measurements show that the band gap of the ZnO:N films shifts from 3.3 eV to 3.1 eV as nitrogen concentration varies in the range of 0.2–0.7 at.%. The narrower band gap is obtained at an optimal nitrogen concentration of 0.22 at.%. This band gap narrowing is found to be caused by both nitrogen incorporation and nitrogen-induced defects in the ZnO:N films.

Crystals of CuGaS2 and AgGaS2 with different isotopic compositions have been grown by chemical vapor transport (CVT) using iodine as the transport agent. Before performing the CVT growth, sulfur and copper were purified by sublimation and etching, respectively. 109Ag and the etched 71Ga isotopes were purified from oxides by vacuum annealing. Transparent yellow orange crystals of CuGaS2 and greenish yellow crystals of AgGaS2 were obtained in the shape of platelets, chunks, rods and needles in sizes of up to 8 mm (CuGaS2) and 30 mm (AgGaS2). These crystals were used to study their electronic, vibrational and thermodynamic properties. Higher excitonic states (n=2,3) were observed at low temperatures with wavelength-modulated reflectivity spectroscopy, thus proving an excellent surface and crystal quality. In addition, the experimentally determined non-monotonic temperature dependence of the excitonic energies can be well fitted by using two Bose–Einstein oscillators and their statistical factors, corresponding to characteristic acoustic and optical phonon frequencies. Isotopic shift of excitonic energies has also been successfully observed in these crystals.

The application of 50 VDC cathodic contact glow discharge electrolysis for six hours in 1.0 mol/L KOH + 0.8, 0.4 and 0.08 g/L ammonia results in the removal of 66, 71 and 77% of ammonia, respectively, following pseudo first-order kinetics at ca. 0.3 mol/kWh. The yields of dissolved NO2N and NO3N lie between 9 and 29% and are coupled with ammonia removal suggesting a nitrification process. Based on the near-cathode UV–Vis emissions and ionization products of H2O and NH3 molecules, a mechanism is proposed along with the charge/energy transfer reactions between the plasma-generated free radicals and ionic species. Joule heating and vaporization are also believed to physically remove ammonia.

This paper investigates the effects of post-weld heat treatment (PWHT) and temper bead welding (TBW) on hardness, microstructure and residual stresses in multi-layer welding on low carbon steel specimens made with two different weld geometries, viz. (1) smooth-contoured and (2) U-shaped. It was found that the PWHT technique gave overall lower hardness than the TBW technique, but the hardness values in both techniques were acceptable. Microscopy analysis showed that the TBW technique was more effective in tempering the heat affected zone as the grain size decreased slightly at the fusion line in spite of the higher temperature at the fusion line. Residual stresses measured using the hole-drilling method showed that the residual stress is not reduced below yield stress near the last bead solidified in TBW. Only PWHT gives low residual stress results in this area. High tensile residual stresses may result in sensitivity to fatigue loading.

Copper–tin (CuxSn1−x) nanocluster is a promising system for gas sensing applications, mainly because of its sensitivity and selectivity for H2S. In this work, pure Sn and Cu as well as composite CuxSn1−x nanoclusters were synthesized using the dc magnetron sputtering gas condensation technique. Nanoclusters with different Sn to Cu ratios were produced by changing the ratio of Sn and Cu in the target. The dependence of Sn, Cu, and CuxSn1−x nanoclusters’ size distribution on various source parameters, such as the inert gas flow rate and aggregation length, has been investigated in detail. The results show that as the inert gas flow rate increases, the mean nanocluster size increases for Sn, decreases for Cu, while increases and then decreases for CuxSn1−x. The results could be understood in terms of the contribution percentage of the nanocluster formation mechanism. Furthermore, this work demonstrates the ability of tuning the CuxSn1−x nanoclusters’ size and composition by a proper optimization of the source operation conditions.

The absence of bandgap bowing in the common-anion II–VI semiconductor ternary alloys is investigated. As examples, we consider the C d 1 − x Z n x T e and C d 1 − x Z n x S e alloys. The sp3s* tight-binding method with the inclusion of spin–orbit interactions is employed to calculate the alloy’s band structure and its corresponding constituents’ charge states (ionicities) as a function of composition. The variation is found to be nearly linear. The vanishingly small valence-band offset ( VBO ≃ 0 ) in common-anion compounds would yield a linear scaling of bandgap energy with composition, especially as the conduction-band edge state being a singlet state with spherical symmetry. Furthermore, the two cation atoms (Cd and Zn) are found not to compete in changing their charge states as the composition is varied. The absence of such competition is believed to be the main reason for the absence of bowing. The theoretical results are compared to the available experimental data and found to be in good agreement.

This research investigates the thermal characteristics of a thermal insulation for a pipe with a phase change material (PCM) for an unsteady operating condition. A layer of the PCM located at the inner surface of the insulation is aimed to minimize the heat loss from the pipe by absorbing and storing the heat loss in the form of latent and sensible heats. A convection boundary condition is applied at the inner and outer surfaces of the insulation, and one-dimensional finite element method is utilized to solve the problem. The effectiveness of the insulation with the PCM is evaluated by comparing the heat loss to insulation without a PCM. The effect of the PCM type, the PCM layer thickness, and temperature cycle of the inner surface is studied. The results indicate that heat loss is reduced significantly when the PCM layer is used for a significant amount of time, and the heat loss is reduced more when the quantity of the PCM is increased. The temperature cycle has an insignificant influence on the thermal...

DOI: 10.2514/1.36648 Natural convection flow in a cubical enclosure with a heated strip is solved numerically using the finite element method. The heated strip simulates an array of electronic chips. The heated strip is attached to the front wall and maintained at high temperature, and the entire opposite wall is maintained at low temperature. The Rayleigh numbers of 10 4 ,1 0 5 , and 10 6 are considered in the analysis and the heated strip is either vertically or horizontally attachedtothewall.Theresultsindicatethattheheattransferstronglydependsontheorientationandpositionofthe heated strip. The maximum Nusselt number for the horizontal heated-strip configuration can be achieved if the heater is placed at the lower half of the wall, whereas for the vertical heated-strip case, the maximum Nusselt occurs whenthe heated stripis placed inthe middle of the wall. Increasing the Rayleigh number significantlyincreases heat transfer in the enclosure for the examined case studies.

Single crystals of Cd1?xCaxTe and Cd1?yCaySe ternaries, grown by the Bridgman technique and characterized by microprobe and x-ray techniques, showed the upper limit of x and y to be 0.05. The excitonic energy gap, determined from the derivative signature of free excitons in wavelength modulated reflectivity, shows a linear increase with increasing Ca2+ concentration in both ternary alloys. The near-band gap emissions of donor-bound and of acceptor-bound excitons observed in photoluminescence, investigated as a function of alloy composition, reveal blue shifts of donor-bound excitonic signatures, in good agreement with those observed for free excitons. The Raman spectra of Cd1?xCaxTe reveal the clear presence of CaTe-like LO phonons, confirming that the Ca incorporation has indeed resulted in a ternary Cd1?xCaxTe with a characteristic two-mode behaviour.

Single crystals of the diluted magnetic semiconductor Cd1-xCoxTe grown by the vertical Bridgman technique are characterized by wavelength-modulated reflectivity and magnetization measurements. Low-temperature magnetization and high-temperature magnetic susceptibility analysis were used to extract the exchange integrals for up to third-neighbour Co2+ pairs in the CdTe host: J1/kB = -25pm7 K, J2/kB = -3.0pm1.5 K, and J3/kB = -1.3pm0.3 K. These values correspond well to the values obtained for other Co-based II-VI diluted magnetic semiconductors and are a clear manifestation of the unusually large Co2+-Co2+ antiferromagnetic interaction. The excitonic energy gap Eg(x) of Cd1-xCoxTe in the wavelength-modulated reflectivity shows a linear monotonic increase with increasing x in the composition range studied.

International audience

Single crystals of Cd1-xCoxTe ternaries, grown by the vertical Bridgman technique, are characterized with x-ray diffraction, electron microprobe analysis, wavelength modulated reflectivity, resonant Raman scattering and magnetization measurements. The lattice parameter decreases linearly with increasing x in the range 0≤ x ≤0.022, but not beyond. The Co2+ concentration estimated from magnetic measurements as well as that from microprobe analysis reveals a maximum value of x~0.02, significantly higher than that reported in the literature, suggesting that it is indeed the solubility limit of Co2+ in CdTe. The blue shift of the excitonic energy gap with increasing x, observed in wavelength modulated reflectivity and in resonant Raman scattering, confirms the substitutional incorporation of Co2+ in CdTe.

We report a strongly nonlinear pressure dependence of the band gaps and large downward shifts of the conduction band edges as functions of composition in ZnS xTe (1-x) and ZnSe (y)Te (1-y) alloys. The dependencies are explained by an interaction between localized A1 symmetry states of S or Se atoms and the extended states of the ZnTe matrix. These results, combined with previous studies of III-N-V materials define a new, broad class of semiconductor alloys in which the introduction of highly electronegative atoms leads to dramatic modifications of the conduction band structure. The modifications are well described by the recently introduced band anticrossing model.

The energy of the excitonic signature, E g ( x ), in the wavelength modulated reflectivity spectrum of Zn 1− x Mg x Te shows a monotonic increase with x in contrast to a large downward bowing of E g ( x ) in ZnS x Te 1− x and ZnSe x Te 1− x . Free and bound excitonic signatures in the photoluminescence spectra of the same samples provide additional confirmation for these trends. Raman spectra of these ternaries display a remarkable resonance enhancement of the zone center longitudinal optical (LO) phonon and its overtones when the scattered photon energy approaches the free excitonic transition energy: for a fixed exciting photon energy, the intensities of Raman lines with shifts of 1LO, 2LO, 3LO,… are selectively enhanced in sequence as a function of x , but in the reverse order in Zn 1− x Mg x Te as compared to that in ZnSe x Te 1− x , underscoring the monotonic increase of E g ( x ) in the former and a significant downward bowing in the latter.

Single crystals of Cd1−xMgxSe ternaries grown by the vertical gradient freezing technique are characterized by X-ray diffraction and electron probe microanalysis as well as wavelength-modulated reflectivity and photoluminescence to establish their basic structural and optical properties. In the composition range 0

We present an investigation into the existence and origins of bandgap bowing in compound-semiconductor common-cation ternary alloys. As examples, we consider CdSe(x)Te(1-x) and ZnSe(1-x)Te(x) alloys. A calculation, based on the sp(3)s(*) tight-binding method including spin-orbit coupling within the framework of the virtual crystal approximation, is employed to determine the bandgap energy, local density of states and atomic charge states versus composition and valence-band offset. The results show that (i) in the valence band, the top states are mainly contributed by Te atoms. The degree of ionicity of all atoms is found to vary linearly with mole fraction x. (ii) There is a strong competition between the anions (Se and Te) in trapping/losing charges and this competition is the main reason for the bandgap bowing character. (iii) There is a reasonable agreement between the calculated results and the available photoluminescence data. (iv) The bowing parameter is found to increase with increasing valence-band offset and increasing lattice mismatch.

Laminar forced convection flow past an in-line elliptical cylinder array with inclination is simulated using the finite element method. The inclination of the elliptical cylinders is increased with the number of the cylinder in the array, 0 deg for the first cylinder and 90 deg for the last cylinder. The global objective of this research is to enhance the heat transfer out of the cylinders. A parametric study of heat exchanges between the cylinders and flow (expressed by the Nusselt number) is reported for Reynolds numbers between 125 and 1000, while the Prandtl number is fixed at 0.71. The results are compared with an elliptical cylinder array without inclination to assess the heat transfer enhancement. The problem is solved as transient, and a vortex shedding phenomenon is reported. The results indicated that the Reynolds number has a significant effect on the heat transfer out of the cylinders, and the inclination of the elliptical cylinders enhances heat transfer rate up to 238.59%, but pressure drop is increased as high as 700%. Also, skin-friction coefficient along the five cylinders’ perimeter, plots of the velocity flow field, and temperature contours are presented.

This research studies the fluid flow and heat transfer in a wavy channel with a linearly increasing waviness at the entrance region. The considered model consists of a channel formed by two wavy plates described by a sinusoidal profile and maintained at a uniform temperature. The finite element method is utilized to solve the problem. Reynolds numbers are considered in the range of 125

${\mathrm{Zn}}_{1\ensuremath{-}x}{\mathrm{Fe}}_{x}\mathrm{Te}$, a zinc blende II-VI diluted magnetic semiconductor (DMS), exhibits a temperature independent magnetization at low temperature (van Vleck paramagnetism) as a consequence of the electronic structure of ${\mathrm{Fe}}^{2+}$ in its site symmetry as an isoelectronic replacement of ${\mathrm{Zn}}^{2+}$. The lowest level of its $^{5}\ensuremath{\Gamma}_{3}$ ground state multiplet has a ${\ensuremath{\Gamma}}_{1}$ nonmagnetic level, with a ${\ensuremath{\Gamma}}_{4}$ magnetic level $2.26\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$ above it. The Raman spectrum of this DMS displays the ${\ensuremath{\Gamma}}_{1}\ensuremath{\rightarrow}{\ensuremath{\Gamma}}_{4}$ electronic transition (labeled in this paper ${\ensuremath{\Gamma}}_{1\ensuremath{\rightarrow}4}$), whose Zeeman splitting is interpreted in terms of symmetry considerations and numerical calculations. The magnetic field and temperature dependence of the spin-flip Raman line $({\ensuremath{\omega}}_{\mathit{SFR}})$ of the donor-bound electron in ${\mathrm{Zn}}_{1\ensuremath{-}x}{\mathrm{Fe}}_{x}\mathrm{Te}$ exhibit characteristics typical of the van Vleck paramagnetism and, in combination with magnetization measurements, yield the $s\text{\ensuremath{-}}d$ exchange constant ${N}_{0}\ensuremath{\alpha}=239.0\ifmmode\pm\else\textpm\fi{}10\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$. The Raman spectra also show ${\ensuremath{\Gamma}}_{1\ensuremath{\rightarrow}4}$ in combination with the LO phonons of ${\mathrm{Zn}}_{1\ensuremath{-}x}{\mathrm{Fe}}_{x}\mathrm{Te}$ as a ternary alloy with an intermediate mode behavior.