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International audience; The nanocrystalline hydroxyfluorapatite (HFA) was synthesized by mechanosynthesis with a planetary ball mill (PM200). The disc to jar speed ratio was constant (equal to 0.5). The effect of different milling parameters such as grinding duration, balls number's, initial powder mass and disc rotation speed were studied to apprehend their effects on both the process of grinding/mechanosynthesis and the synthesis of nanocrystalline HFA. Unlike previous studies in which milling parameters have been independently studied, the effects of these parameters on the phase contents were simultaneously studied. Abdellaoui's model was also introduced to analyse the physical milling parameters effect such as the injected shock power, the shock kinetic energy, the shock frequency and the cumulated kinetic energy on the microstructural properties and synthesized phases contents. The results predicted by the model were compared to experimental ones. This study showed that the optimal conditions for the synthesis of nanocrystalline HFA were reached when the mechanosynthesis was carried out with a speed of 450 rpm, 6 balls, 1.2 g of starting material and 24 h of grinding duration. X-ray diffraction characterization confirmed the purity phase of HFA nanocrystalline powders.

In this study, the effects of thermal annealing on the morphological, structural and optical properties of BGaAs/GaAs Quantum Wells (QWs) are investigated for the first time. Atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) show that boron islands nucleate on the surface and their rugosity increases after annealing due to boron segregation phenomenon. The segregation is further validated through high-resolution X-ray diffraction (HR-XRD) measurements, which also confirms a good crystalline quality of the system. After annealing at 710 °C for 10 min a significant compositional increment of boron is also observed. Nevertheless, a negligible enhancement of photoluminescence (PL) intensity and minor shift in PL peak energy are found, which is attributed to the defect density and the spatial reduction of localization effects. Time-resolved photoluminescence (TRPL) results exhibit an initial decay time in the microsecond regime from localization emission, followed by an even slower decay from deep levels states. Our results can be the first step towards the engineering of carriers localization in BGaAs/GaAs SQWs by thermal annealing and can orient the material system to be an active layer in intermediate band solar cells.

International audience; InxGa1-xN/GaN solar cells are ideal candidates for use in extreme temperature applications. The conversion efficiency potential of double heterostructure solar cells was investigated at high temperatures using physical simulation. For a targeted working temperature, optimized efficiency lies in a compromise between the absorber bandgap energy determined by In composition and the band offsets at the heterointerface directly correlated with the capability for the photogenerated carriers to cross through the barrier by thermoionic emission. An optimized efficiency of 18% is obtained for an In content of 50% at 400K and decrease down to 10% for an In content of 35% at 500K. As the operating temperature goes higher, the indium content needs to be reduced in order to limit the detrimental effect of increasing intrinsic carrier concentration. The consequence is a decreasing efficiency due to the reduced covered range of the solar spectrum. In the same time, the band offsets are no more a limiting parameter, as there are reduced as the In content decreases, and as higher temperature increases the thermionic transport probability. This result shows the interest of InxGa1-xN/GaN double heterostructure design for high temperatures applications.

Hydroxyfluorapatite Ca10(PO4)6(OH)F (HFA) powders were prepared by mechanosynthesis method using planetary ball milling with various parameters. X-ray Diffraction (XRD), Infrared (IR) and Raman spectroscopies, Energy Dispersive X-ray (EDX) and Brunauer-Emmett-Teller (BET) methods were employed to characterize the synthesized nanoparticles. Four factors (rotation speeds of disk, mass of balls, initial mass of powder and milling time) were investigated to understand their effect on the milling process and the formation of HFA nanocrystallite. Taguchi's design, with just 16 experiments (an L16 orthogonal array), was used to evaluate the impact of these parameters on six distinct properties, namely the crystallite size (nm), the percentage of crystallinity, the specific surface area (m2/g), the Ca/P atomic ratio, the percentages of the apatite and calcite phases. The average effects of the milling parameters and the signal-to-noise ratio (SN) were discussed. ANOVA analysis was used to determine the importance, the proportion of factor participation and also the influence of process parameters on responses. The Taguchi results indicated that the mass of balls and the rotation speed were found to be the most influential factors on the purity of compounds. The ball to powder weight ratio (BPR) was also introduced to study its effect on the synthesis process. Transmission Electron Microscopy (TEM), Scanning Electronic Microscopy (SEM) and Dynamic Light Scattering (DLS) revealed that milled HFA powders contained a nano-sized agglomerate.

BGaAs/GaAs epilayers and BInGaAs/GaAs quantum well (QW) have been prepared using metal-organic chemical vapor deposition under different growth conditions, and their physical and structural properties have been examined. SEM-EDS investigation showed a dependence of surface properties of the ternary compound on the growth conditions. High-resolution X-ray diffraction evidenced a tensile strain for the ternary alloys whatever the growth condition, while the quaternary QW always shows a compressive strain state. Room temperature optical absorption allowed to follow the variation of the bandgap with boron incorporation. Photoluminescence measurements confirmed the carrier-localization phenomenon and its dependence with the growth conditions. Deposition temperature and diborane (B2H6) flow rate are with particularly significant effects on the optical properties: lower diborane flow rate and high growth temperature enhance the radiative emission. Computer simulation using localized state ensemble model quantitatively relates the lattice inhomogeneity to the optical properties and suggests a way to engineer the localization phenomenon and avoid clustering effects. Electrical investigations by current-voltage, capacitance and conductance methods have been performed for the first time on selected BGaAs samples. The ideality factor of Schottky barriers has been determined, while their height and film doping level could only be approximately estimated. Such physical properties make boron-based alloys very promising for applications in multijunction solar cells.

The paper presents a study of M-doped anatase TiO2 (M = Fe or Au) electronic structures and optical behaviors within the density functional theory using the revised gradient-corrected Perdew–Burke–Ernzerhof (GGA-PBE), GGA + U, and HSE06 functional frame works along with the ab initio pseudo-potentials method. The results showed that the electronic structures are better described with the GGA + U method indicating that Fe and Au into anatase TiO2 incorporation serves to reduce the absorption under visible-light irradiation. Consequently, the incorporation of Fe-doped anatase TiO2 exhibited the enhanced optical absorption under visible-light irradiation compared to Au doped TiO2 and pure TiO2.

The recombination dynamics in BxGa1-xAs alloys on GaAs (001) grown by metal-organic chemical vapor (MOCVD) are investigated using steady-state photoluminescence and Time-Resolved Photoluminescence (TRPL) measurements in the nanosecond range. The decay time as a function of the emission energy and the geometry of the sample (quantum well, epilayer) and post-growth treatment (annealing) is slower for lower-energy emission. In correlation with a systematic study on the photoluminescence features, we have studied the temperature effect on the decay time of the photogenerated carrier. Depending on the geometry of the sample, the exciton dynamics is assisted by the localization phenomenon in the boron-based ternary alloys. It is shown that, at low temperatures, the transfer is mainly ensured by tunneling through localized states where the recombination process is found to be purely radiative in nature. At intermediate temperatures, a competitive process between radiative and non-radiative recombination takes place. For high temperatures, the transfer is assisted by thermal activation, leading to purely non-radiative recombination. We have shown that the unknown state-of-the-art kinetic parameters of the e stage of carrier relaxation and additional carrier recombination dynamics, divulges the particular role of bandgap inhomogeneity and the below-band gap states for the relaxation dynamics that can contribute to the photogeneration mechanisms in BxGa1-xAs/GaAs alloys. Indeed the research findings of this article will help to gain insight into the preliminary carrier relaxation dynamics in boron-based materials.

To detect COVID-19, the reverse transcription-polymerase chain reaction (RT-PCR) is usually used but there is a number of faulty tests or an inexact diagnostic, especially in the primordial period of infection In this regard, the optical response of hybrid quantum dots (QDs): L-serine is presented for the first time as a new and rapid method of detection QDs were further conjugated with anti-infectious viruses' antibodies The detection of a target analyte is increased due to the fact that the final formed hybrid system is exposed to doses of L-serine optically active QDs acts as L-Serine's host This last will trap the virus and emerges less/high photoluminescence (PL) response depending on the L-serine, virus, and doping concentrations Such rapid optical treatment will inform us of the infection state faster and more efficiently than ELISA tests The fluorescence properties of the new hybrid system permit a control of coronavirus with a limit of detection LOD similar to 80 EID/50 mu l thanks to families of clusters induced by L-serine's molecules Families of L-serine clusters with inhomogeneous densities can block the S-protein in COVID-19 Moreover, the detection can be issued by trapping the virus with the same dopant

We investigate a novel grown-MOCVD BGaAs/InGaAs/BGaAs/GaAs heterostructure for the first time using High-Resolution X-Ray Diffraction (HR-XRD), steady state photoluminescence (PL) and time-resolved photoluminescence (TRPL). The strain effects in the InGaAs/GaAs quantum well is compensated due to the additional BGaAs buffer/barrier layer (%B = 7.8%). PL measurements show an extended emission around 1 eV and two emission bands associated with the InGaAs and BGaAs layers and these bands are analyzed theoretically with the help of 10 band k‧p Hamiltonian. Red shifts of about 0.15 eV (InGaAs) and 0.29 eV (BGaAs) are observed, encouraging dual applications in high wavelengths and solar cells. A reduction of the abnormal behavior due to potential fluctuations and carrier localization is quantitatively and qualitatively investigated using the Localized States Exciton model (LSE) model. Our structure appears to be a promising candidate for future-generation ultra high-efficiency three- and four-junction multijunction solar cell devices as well as its applications in the telecommunication wavelength range.

In this paper, we propose an investigation on the graphene monolayer effect, elaborated on Silicon (Si) by atmospheric-pressure chemical vapor deposition (APCVD), on the carrier localization in ternary InGaN nanorods (NRs) grown by metal-organic chemical vapor deposition (MOCVD). The growth has been proved using scanning electron microscopy (SEM) and Raman technic. SEM investigations support NRs size fluctuations and the presence of random coalescence zones. Raman study reveals the graphene self-doping and low tensile strain which constitutes an origin of the random potential fluctuation. The temperature dependent photoluminescence (PL) of InGaN NRs showed the presence of the localization phenomenon due, principally, to the NRs density and size inhomogeneity and composition fluctuations. Carrier localization increases Auger recombination rates more than radiative rates and is therefore detrimental to the internal quantum efficiency (IQE) of nitrides-based emitters. Our work suggests a partial suppression of the phenomenon effects through a partial suppression of random potential fluctuations by the mean of the direct growth of nitride on Graphene-covered Si substrate. Our qualitative investigations show a reduction of the localization effects due the added graphene monolayer which is quantitatively reinterpreted using the Localized State Ensemble model (LSE) for the first time. Our findings are substantial to advance the integration of nitrides-based devices on any substrates of choice, thereby permitting novel designs of nitrides-based heterojunction device concepts.

Electronic transition in BGaAs/GaAs single quantum well (SQW) have been performed combining the dimensional Schrodinger equation, band anticroissing BAC and 10-band k.p models. The modelling results have been validated experimentally by photoluminescence (PL), high resolution-X-ray diffraction (HRXRD) and photoreflectance (PR). The calculated results appeared to be consistent with experiments. Surface photovoltage SPV spectroscopy gives a new way to study the bandgap of the boron based-SQW for the first time. New e1-lh1 transition appeared which is specific to the SQW. The suggested structure looks to be a promising candidate for solar cells and photonic applications as well as a reference for the growth optimization and understanding of the electronic properties of related B(In)GaAs/GaAs quaternary alloys.

Electronic transition in BGaAs/GaAs single quantum well (SQW) have been performed combining the dimensional Schrodinger equation, band anticroissing BAC and 10-band k.p models. The modeling results have been validated experimentally by photoluminescence (PL), high resolution-X-ray diffraction (HRXRD) and photoreflectance (PR). The calculated results appeared to be consistent with experiments. Using secondary-ion mass spectrometry (SIMS) and X-ray photoelectron spectroscopy (XPS), contamination levels have been investigated. Cross-sectional transmission electron microscopy (TEM) reveals the QW growth and the strain, composition and thickness fluctuation in the BGaAs QW. Surface photovoltage SPV spectroscopy gives a new way to study the bandgap of the boron based-SQW for the first time. New e1-lh1 transition appeared which is specific to the SQW. The suggested structure looks to be a promising candidate for solar cells and photonic applications as well as a reference for the growth optimization and understanding of the electronic properties of related B(In)GaAs/GaAs quaternary alloys.