Large and uniform optical emission shifts in quantum dots externally strained along their growth axis

We introduce a method which enables to directly compare the impact of elastic strain on the optical properties of distinct quantum dots (QDs). Specifically, the QDs are integrated in a cross-section of a semiconductor core wire which is surrounded by an amorphous straining shell. Detailed numerical simulations show that, thanks to the mechanical isotropy of the shell, the strain field in a core section is homogeneous. Furthermore, we use the core material as an in situ strain gauge, yielding reliable values for the emitter energy tuning slope. This calibration technique is applied to self-assembled InAs QDs submitted to incremental tensile strain along their growth axis. In contrast to recent studies conducted on similar QDs stressed perpendicularly to their growth axis, optical spectroscopy reveals 5-10 times larger tuning slopes, with a moderate dispersion. These results highlight the importance of the stress direction to optimise QD response to applied strain, with implications both in static and dynamic regimes. As such, they are in particular relevant for the development of wavelength-tunable single photon sources or hybrid QD opto-mechanical systems

Developmental defects in zebrafish for classification of EGF pathway inhibitors.

AbstractOne of the major challenges when testing drug candidates targeted at a specific pathway in whole animals is the discrimination between specific effects and unwanted, off-target effects. Here we used the zebrafish to define several developmental defects caused by impairment of Egf signaling, a major pathway of interest in tumor biology. We inactivated Egf signaling by genetically blocking Egf expression or using specific inhibitors of the Egf receptor function. We show that the combined occurrence of defects in cartilage formation, disturbance of blood flow in the trunk and a decrease of myelin basic protein expression represent good indicators for impairment of Egf signaling. Finally, we present a classification of known tyrosine kinase inhibitors according to their specificity for the Egf pathway.In conclusion, we show that developmental indicators can help to discriminate between specific effects on the target pathway from off-target effects in molecularly targeted drug screening experiments in whole animal systems

La matrice minérale de l'eau influence la perception de la flaveur chlore

poster exposé au 5e Congrès Vitagora Goût-Nutrition-Santé les 23-24 mars 2010 à Dijon (FRANCE)Objectif de l’étude : Le traitement par le chlore garantit une qualité bactériologique irréprochable à l’eau de réseau. La flaveur du chlore est un des reproches majeurs à l’encontre de l’eau du robinet. Le goût d’une eau est influencé par : a) la quantité totale de minéraux présents dans celle-ci (Teillet et al., 2007) [1] ; b) La nature et la proportion relative de ces minéraux (Puget, Curé et al., 2009) [2]. L’objectif de cette étude est de déterminer si le goût intrinsèque de l’eau, induit par sa matrice minérale, peut avoir une influence sur la perception de la flaveur chlore

Effects of some controversial food additives on zebrafish embryonic development

Background information: There are rising concerns about potential hazardous properties of food additives, forcing legislator to tighten management policy and requiring extensive, yet animal- minimized, testing strategies. The zebrafish embryo is an emerging model system for chemical testing with many advantages that made it amenable to high-throughput assays at the in vivo level. In this study, we applied a panel of tests to evaluate toxicity, particularly neurobehavioral effects, of seven substances including standard compounds and controversial food additives. Methods: Zebrafish wildtype and transgenic fluorescent embryos were exposed to different concentrations of four food additives: Sodium benzoate (SB), Monosodium glutamate (MSG), Tartrazine (TTZ), and Quinoline yellow (QY). Method validation was carried out using three other substances: Ethanol (EtOH), Dimethyl sulfoxide (DMSO), 3,4-Dichloroaniline (DCA). Morphological and lethal effects were recorded and the data were analysed to determine median lethal concentration (LC50), median effective concentration (EC50), effective concentration 10% (EC10), and teratogenic index (TI) values as well as concentration-response equations. Delayed effects of substances on larval locomotion were inspected using the light/dark challenge. Gene expression analysis was carried out using transgenic fluorescent lines. Results: LC50 values of three standard compounds (EtOH, DMSO, and DCA) reveal a high correlation with previously validated data, proving the reliability of our method. Effects of each substance on zebrafish embryonic morphology and lethality were determined as well as the corresponding concentration-response curves. Calculated toxicological indexes revealed that SB belongs to Cat.3 aquatic toxicity class, while QY is the most teratogenic substance. At EC10, all additives exhibited a delayed effect on zebrafish larval locomotion in compound-specific patterns. Observation of transgenic fluorescent embryos and locomotion analysis of hatched larvae reveal that SB could decrease the zebrafish motoneuron differentiation rate, while TTZ exhibited anti-angiogenic effects. Conclusion: Our results demonstrate that our test panel is reliable as a means to assess and categorise chemical toxicity. Also, our data suggest the need to reconsider the safety of food additives SB, TTZ, and QY as well as other controversial food additives in further studies

II-VI semiconductors and derivated kesterites structures for photovoltaic conversion

International audienceCuZnSnSSe (CZTSSe) semiconductor devices are nowadays one of the approaches to achieve thin film solar cells of the third generation. However, up to now, they do not allow to reach power conversion efficiencies as high as the ones obtained with similar absorber materials such as CuInGaSSe, typically 12% instead of 22%: more precisely, the limited open-circuit voltage (Voc) commonly reported on CZTS based solar cells is still an important issue and remains a main drawback for the former compounds, made from earth-abundant elements. This is probably due to the presence of strong potential fluctuations which are induced by a large amount of intrinsic point defects. As predicted by the density functional theory calculations, the major part of these point defects in CZTSSe compounds is coming from the exchange between Cu and Zn which induces CuZn and which are stabilized by the formation of self-compensated defect clusters (see S. Chen, X.G. Gong, A. Walsh, S.H. Wei, Phys. Rev. B 79, 165211 (2009); S. Chen et al. Phys. Rev. B 81,245204 (2010). A high concentration of these neutral defect complexes locally induces a band gap shift of the conduction and valence band edges, directly responsible for potential fluctuations and consequently for the VOC reduction due to the induced band tailing. This band tail is studied here by optical spectroscopy, combining three types of measurements, namely emission spectra compared to photoluminescence excitation spectroscopy, emission spectra as function of excitation power, and time resolved photoluminescence spectra. All these data converge to show that both the bandgaps and the band tail of localized states just below are depending on the order/disorder degree in the Cu/Zn cation sublattice of the quaternary structure: in the more ordered structures, the bandgap is increasing by about 50 meV and the energy range of the band tail is decreased from about 110 meV to 70 meV. The impact of this localized states band tail on the admittance response is also considered. The admittance model which was developed shows that the potential fluctuations can well explain the anomalous stretching of the capacitance step which is observed, and that they have to be considered to precisely extract the energy trap position. All these data show that both the bandgaps and the band tail of localized states just below, are depending on the order/disorder degree in the quaternary structure

The taste system can discriminate mixtures of water dissolved minerals varying on cations proportion

International audienceThe taste of water depends on the total dissolved solids (TDS) namely the quantity of minerals dissolved in water (Teillet et al., 2007). However, it remains unclear whether the Human taste system is able to discriminate between two water samples with the same TDS but different proportions of minerals. In other words, has our gustatory system the ability to reflect a difference in taste quality due to a difference in the proportion of minerals in mixture? We addressed this question using 7 water samples containting a mixture of Na+, K+, Ca2+, Mg2+, HCO3 -, SO4 2- and Cl-. These 7 samples contained the same total amount of dissolved solids but varied in ions proportion. 62 subjects compared these 7 samples following a pair comparison procedure. Differences between the samples were evaluated using the binomial law and a Bonferroni correction. The results indicated that the panel discriminated the sample including a higher amount of Na+ from those including a higher amount of Mg2+ or K+ and the sample with a higher proportion of K+ from the one boosted in Ca2+. These findings evidenced that, beyond total dissolved solids variations, our taste system is able to differentiate between the proportions of cations in mixture. As a consequence,the taste of water appeared to be driven both by the total amount of dissolved solids but also by their respective proportion. We thank ANRT(CIFRE number 372/2006) for financial support. Teillet E, Urbano C, Cordelle S, Schlich P. (2007) A study of the sensory perception of tap waters versus bottled mineral waters using a combined sorting, descriptive and hedonic task carried out by 389 French consumers. 7th Pangborn Sensory Science Symposium. Minneapolis, USA

Biomineralization of magnetic nanoparticles in stem cells

International audienceIron is one of the most common metals in the human body, with an intrinsic metabolism including proteins involved in its transport, storage, and redox mechanisms. A less explored singularity is the presence of magnetic iron in the organism, especially in the brain. The capacity of human stem cells to biosynthesize magnetic nanoparticles was recently demonstrated, using iron released by the degradation of synthetic magnetic nanoparticles. To evidence a magnetic biomineralization in mammalian cells, it is required to address the biosynthesis of magnetic nanoparticles in cells supplied exclusively with non-magnetic iron salt precursors. Herein, mouse and human mesenchymal stem cells were incubated with ferric quinate for up to 36 days. By optimizing the concentration and culture time, and by measuring both total intracellular iron content and cellular magnetic signals, the biosynthesis of magnetic nanoparticles was found to occur from 14 days of continuous iron incubation and was correlated with important doses of intracellular iron. The local electronic structure and chemical environment of intracellular iron were further characterized by XAS spectroscopy at the Fe K-edge, showing a total conversion of Fe2+ to Fe3+ when using ferrous salts (ascorbate and sulfate), and a transformation towards ferrihydrite as well as a small proportion of a magnetic phase

AlGaN Nanostructures for Electron Beam Pumped UV Emitters

International audienceUV disinfection is receiving renewed attention due to the global pandemic, as an immediately deployable and cost-effective option. The common sources used for this application are low-pressure arc lamps, emitting at 254 nm and containing toxic mercury, which Europe is trying to phase out. Furthermore, this radiation is highly carcinogenic and cataractogenic, which represents a health hazard. Recently different replacements for mercury lamps have been proposed, e.g. excimer lamps that emit at 222 nm, supposedly harmless. However, most of the focus is now on AlGaN-based UV LEDs, with numerous advantages (fast on/off switching, longer lifetime, reduced ozone generation, wider wavelength selection). Yet the wall plug efficiency of commercial LEDs at 260 nm is WPE < 1%, far below that of mercury lamps, and drops dramatically at shorter wavelengths. Therefore, there is still a need and opportunity for alternative UV sources.This work proposes electron-beam pumped UV lamps as an alternative to LEDs to overcome issues related to doping, transport and contacting. This approach obviates the need for p-type doping and efficient and homogeneous carrier injection is achieved without an electron blocking layer. Furthermore, the WPE should not vary much over 210−350 nm. Here, we study the performance of AlGaN/AlN dots-in-a-wire [1] and Stranski-Krastanov quantum dot superlattices [2], whose UV emission can be tailored in the 230-330 nm range. The three-dimensional (3D) carrier confinement in such nanostructures results in high internal quantum efficiency (IQE = 50% on average) and promising external quantum efficiency (EQE up to 5% for as-grown structures). Studies conducted under operation conditions (high injection) show no degradation of the IQE for excitation power densities up to 1 MW/cm2, obtained by pumping with a pulsed Nd-YAG laser. With e-beam excitation, the emission efficiency remains stable up to 10 kV of acceleration voltage and 0.5 mA of injected current (current limit of our setup). E-beam pumping offers also an interesting alternative for the fabrication of UV lasers, highly demanded in the fields of medicine and biotechnology, as well as in 3D printing and non-line-of-sight communication. Today, this spectral range is covered by gas lasers (ArF, KrF, XeF) or lasers based on frequency conversion (Nd:YAG). III-nitride semiconductor laser diodes are promising candidates to provide an efficient semiconductor-based alternative, but current injection is a major problem for wavelengths shorter than 360 nm.For this application, advantages of the e-beam pumping include higher flexibility in the choice of materials for the active medium due to the absence of doping or electrical contacts, as well as higher radiative recombination efficiency since the electrons and holes generated by impact ionization share the same distribution in the active medium. This technology has enabled the fabrication of ZnSe-based pulsed lasers that emit up to 600 W at 535 nm. There are some studies of e-beam pumped UV lasers using AlGaN/GaN separate confinement heterostructures (SCH), but they are limited to pulsed electron beam excitation at cryogenic temperatures [3,4]. New device architectures are required with the prospect of achieving room temperature lasers. Here, we present a study of undoped AlGaN/GaN SCHs designed to operate under e-beam injection with an acceleration voltage 10 kV. We discuss the effect of spontaneous and piezoelectric polarization on the carrier diffusion and demonstrate that the performance is improved using an asymmetric graded-index separate-confinement heterostructure (GRINSCH).[1] H. Arkumar et al., Nanotechnology 31 505205 (2020).[2] I. Dimkou et al., Nanotechnology 31 204001 (2020).[3] T. Wunderer et al., IEEE Photonics Technology Letters 29 1344 (2017).[4] T. Hayashi et al., Scientific Reports 7 2944 (2017)