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International audience; Aluminum-droplet combustion is studied in solid-propellant flame environment at 1.0 MPa. Al vapor is observed during the combustion process with high-speed Al-PLIF and visible-emission images. A onedimensional quasi-steady model of aluminum combustion is used to simulate Al-atom concentration and temperature profiles around the droplet. Al-PLIF image simulation has been developed to generate synthetic fluorescence images that reproduce the experimental images. A comparison approach is initiated between experimental and numerical Al-PLIF images and applied to the study of a specific droplet observed during the experiments with a diameter larger than 120 µm. A reasonable consistency is observed between simulated and experimental data, which is promising to provide validation data for the development of more representative aluminum-combustion models.; La combustion de gouttes d'aluminium en flammes de propergols solides à 1,0 MPa est étudiée expérimentalement au moyen de la technique d'imagerie LIF à haute cadence de l'atome d'aluminium en phase vapeur. La technique PLIF-Al est couplée à de l'imagerie directe des gouttes. Dans une première approche, un modèle 1D quasi-stationnaire de combustion d'une goutte isolée est utilisé pour simuler les profils spatiaux de température et de concentration des atomes Al autour de la goutte. Ces données de température et de concentration de Al sont injectées dans le code de simulation des images de fluorescence de Al. Cet article propose une démarche de comparaison entre les images de fluorescence simulées et les images expérimentales pour un cas de goutte de diamètre supérieur à 120 µm. La première comparaison est prometteuse pour de futures validations de modèles de combustion plus réalistes.

International audience; sp 2-hybridized boron nitride is identified as a strategic material for many purposes related to the integration of graphene and 2D materials in devices and the fabrication of van der Waals heterostructures. Thus, it becomes mandatory to have scalable synthesis and characterization procedures for providing suitable and reliable boron nitride material according to these identified needs. We report here on the growth of sp 2-hybridized boron nitride film on polycrystalline nickel substrate by chemical vapor deposition with borazine as precursor. We propose a complete study of the influence of the underlying nickel grain orientation on the BN structure layers, in terms of thickness, crystallographic orientation, domain size and stacking. We show the heteroepitaxial growth of continuous, single crystalline hexagonal boron nitride multilayer film on nickel (111)-like grains. We highlight its ABC stacking sequence with AB stacking faults and show how it impacts the Raman and cathodoluminescence spectra.

In this study, quantitative model of two-photon excitation and fluorescence spectra of carbon monoxide based on up-to-date spectroscopic constants collected during an extensive literature survey was developed. This semi-classical model takes into account Hönl–London factors, quenching effects (collisional broadening and shift), ionization and stark effect (broadening and shift), whereas predissociation is neglected. It was specifically developed to first reproduce with a high confidence level the behavior of our experimental spectra obtained from laser-induced fluorescence (LIF) measurements, and then to allow us to extrapolate the fluorescence signal amplitude in other conditions than those used in these experiments. Synthetic two-photon excitation and fluorescence spectra of CO were calculated to predict the fluorescence signal at high pressures and temperatures, which are representative of gas turbine operating conditions. Comparison between experimental and calculated spectra is presented. Influence of temperature on both excitation and fluorescence spectra shapes and amplitudes is well reproduced by the simulated ones. It is then possible to estimate flame temperature from the comparison between experimental and calculated shapes of numerical excitation spectra. Influence of pressure on both excitation and fluorescence spectra was also investigated. Results show that for temperature below 600 K and pressure above 0.1 MPa, the usual Voigt profile is not suitable to reproduce the shape of the excitation spectrum. We found that the Lindholm profile is well suited to reproduce the pressure-dependence of the spectrum in the range 0.1 to 0.5 MPa at 300 K, and 0.1 to 0.7 MPa at 860 K. Beyond 0.7 MPa, in this temperature range, it is shown that the Lindholm profile does no longer match the spectral profiles, in particularly the red wing. Further analyses taking into account the line mixing phenomenon at higher pressure are thus discussed.

International audience; The oxidation behaviour of ZrB 2-SiC, HfB 2-SiC and HfB 2-SiC-Y 2 O 3 is studied using the real-time Laser-Induced Fluorescence (LIF) detection of BO 2 (g) evaporated from samples heated up to 1873 K in dry air. For each composition, the relevant steps of oxidation (silica formation, volatilization, etc.) can be precisely determined. Moreover, the influence of composition on the oxidation behaviour, and more precisely on the B 2 O 3 /SiO 2 ratio in the glassy phase, can be understood and described by monitoring the LIF signal from the BO 2 (g) radical. Thus, this technique has confirmed the potential of the HfB 2-SiC-Y 2 O 3 composition as a Ultra High Temperature Ceramic (UHTC) material.

International audience; In this study, the Laser Induced Fluorescence (LIF) technique is used to detect BO2 radicals in the gas phase above heated ZrB2 and ZrB2-20 vol. % SiC samples in air, in order to provide an in situ and real-time monitoring of their thermal oxidation. Samples are heated up to 1923 K in air flow with a 2 kW CO2 laser. The BO2 fluorescence and the laser transmission signals are monitored throughout the temperature ramp. This technique allows to detect the key steps of the oxidation (silica formation,...) and to propose more precise oxidation mechanisms as a function of temperature.; Dans cette étude, la Fluorescence Induite par Laser (LIF) est utilisée pour suivre des espèces gazeuses telles que BO2(g) émises lors de l'oxydation de matériaux tels que ZrB2 ou ZrB2-SiC. Des échantillons de compositions ZrB2 etZrB2-20 vol % SiC sont chauffés dans une enceinte spécifique à la pression atmosphérique, sous air et jusqu'à 1650°C grâce à un laser CO2 de 2kW.La LIF de BO2(g) est étudiée dans le système électronique A2u - X2g avec un laser d'excitation à 547nm et une détection de la fluorescence à 580nm. Les signaux de fluorescence et d'absorption enregistrés lors de la chauffe nous ont permis de détecter les étapes clés de l'oxydation comme, le début de l'oxydation de SiC, le remplissage de la couche vitreuse ou encore l'évaporation catastrophique de la couche vitreuse.Le signal LIF a été corrélé aux réactions possibles de B2O3 avec l'air. Ce diagnostic in situ nous a permis de proposer des mécanismes d'oxydation plus précis au cours de la montée en température.

International audience; Two-photon excitation laser-induced fluorescence of carbon monoxide (CO-LIF) is investigated experimentally in order to determine the applicability of this technique for imaging CO concentration in aeronautical combustors. Experiments are carried out in a high temperature, high-pressure test cell, and in a laminar premixed CH4/air flame. Influence of temperature and pressure on CO-LIF spectra intensity and shape is reported. The experimental results show that as pressure increases, the CO-LIF excitation spectrum becomes asymmetric. Additionally, the spectrum strongly shifts to the red with a quadratic dependence of the collisional shift upon pressure, which is different from the classical behavior where the collisional shift is proportional to pressure. Moreover, pressure line broadening cannot be reproduced by a Lorenztian profile in the temperature range investigated here (300–1750 K) and, therefore, an alternative line shape is suggested.; Une étude expérimentale de spectroscopie LIF à deux photons de la molécule CO (CO-LIF) est menée afin d'évaluer sa faisabilité en mode imagerie dans des moteurs aéronautiques. Les expériences sont réalisées d'une part dans une cellule à hautes température et pression et dans une flamme de prémélange CH4/air. Nous présentons l'influence de la température et de la pression sur l'intensité et la forme des spectres LIF de CO. Le spectre d'excitation devient asymétrique quand la pression augmente. Il est fortement décalé vers le rouge avec une dépendance quadratique du décalage collisionnel avec la pression, ce qui diffère de la classique dépendance linéaire. L'élargissement par pression du spectre n'est pas reproduit avec la fonction Lorentzienne et un profil collisionnel de Lindholm est utilisé pour simuler les spectres dans une certaine gamme de pression et températures.

A comparative study was made of sorted semi-conducting single walled carbon nanotube (SWCNT) films and unsorted SWCNT films for gas sensing applications. The transmission line method is used to monitor separately the SWCNTs film resistance and the contact resistance between electrodes and the SWCNTs, thus revealing that the sensing mechanism mainly relies on a modification of the tube conductivity during gas exposure. The fabricated sensors demonstrate a detection limit of 20 ppb NO2 and 600 ppb NH3 mainly attributed to experimental setup limitations. Moreover, semi-conducting nanotubes happened to be 2.5 times more sensitive to NH3 than unsorted ones, thus proving that selectivity can be improved by sorting the SWCNTs. The temperature dependence of the sensor sensitivity was studied, and a good agreement was found between experimental results and the Langmuir adsorption model.

International audience; Planar laser-induced fluorescence on atomic iron is investigated in this paper, and a measurement strategy is proposed to monitor the fluorescence of iron atoms with good sensitivity. A model is proposed to fit the experimental fluorescence spectra, and good agreement is found between simulated and experimental spectra. Emission and laser-induced fluorescence measurements are performed in the flames of ammonium perchlorate composite propellants containing iron-based catalysts. A fluorescence signal from iron atoms after excitation at 248 nm is observed for the first time in propellant flames. Images of the spatial distribution of iron atoms are recorded in the flame in which turbulent structures are generated. Iron fluorescence is detected up to 1.0 MPa, which opens the way to application in propellant combustion.; L'imagerie de fluorescence induite par laser est appliquée aux atomes de fer et une stratégie pour leurs mesurer avec une bonne sensibilité est présentée dans cet article. Un modèle est développé pour calculer les spectres de fluorescence et un bon accord est trouvé entre les spectres calculés et expérimentaux. Les mesures en émission et en fluorescence induite par laser sont effectuées dans des flammes de propergols composites à base de perchlorate d'ammonium dopés avec des catalyseurs ferriques.Le signal de fluorescence induit par l'excitation laser à 248 nm des atomes de fer est observé pour la première fois dans les flammes de propergol. La répartition spatiale des atomes de fer est visualisée en flamme dont les structures turbulentes sont forcées. La fluorescence du fer est détectée jusqu'à 1,0 MPa, ce qui ouvre des perspectives de visualisation d'écoulements de gaz de combustion de propergols solides.

After the discovery of graphene and its consequences in the field of nanoscience and nanomaterials, there has been a growing interest in 2D materials and also their vertical stacking due to unique properties and potential applications.[1] For instance, it was shown the transport properties of exfoliated graphene supported by hexagonal boron nitride (h-BN) could approach the intrinsic graphene limits.[2] Nevertheless, studying the structural properties of 2D materials and 2D heterostructures is crucial to understand their physical and chemical properties. Our motivations have been to exploit state of the art aberration-corrected high resolution transmission electron microscopy (HRTEM) and scanning tunneling microscopy (STM) to study the structure and electronic properties of graphene (G), h-BN and G/h-BN heterostructures. HRTEM analyses were conducted with a JEOL ARM microscope equipped together with a cold FEG, an aberration corrector for the objective lens and a One view camera (Gatan). Notably, we used high-speed atomic-scale imaging to study with unprecedented dynamics (up to 25 fps) the nucleation and growth mechanisms of triangular holes in h-BN under beam irradiation (Figure 1). The direct observation of B and N atom sputtering and surface reconstruction processes allow understanding how the triangular shape and orientation of holes are maintained during the growth. Interestingly, by studying the effects of the electron dose and the number of BN layers, we demonstrate that these atomic-scale processes are simultaneously driven by kinetic and thermodynamic effects. Further works are in progress to study the stability of h-BN/G stacking under electron-beam irradiation. STM analyses were carried out with low temperature STM at 4 K, on 2D heterostructures that consist in a few layers of graphene doped with nitrogen on thick exfoliated flakes of BN deposited on SiO2. Remarkably, we show that STM allows identifying and characterizing ionization defects within the BN flakes below the graphene layers (Figure 2). This study opens new avenues to probe the electronic interactions between this two stacked materials. Keywords: hexagonal boron nitride; aberration-corrected TEM; electron beam irradiation; van der walls heterostructures

The main consequence of the interaction between cells and pulsed electric fields is the destabilization of the plasma membrane leading to its permeabilization. Previous vibrational spectroscopy studies (S.M. Gruenbaum et al., J. Chem. Phys., 135, 2011) have shown that interfacial water is highly organized around the phospholipids of the membrane. Moreover, various numerical studies (such as Molecular Dynamics simulations) have shown that the interfacial water is highly disturbed by the pulsed electric field. We detail here a study of the behavior of the interfacial water around biological objects, before and after exposition to intense pulsed electric fields, by Coherent Anti-stokes Raman Scattering (CARS) spectroscopy.

In situ measurements were executed in the continuous wave CO 2 -laser vaporization synthesis of single-walled carbon nanotubes (SWCNTs). The results were compared with the findings of the ex situ analysis of the product. Different catalysts (Co, Ni, Co/Ni, Ni/Y and Co/Y) were used and the temperature of the target surface (T s ) changed to compare the efficiency of the synthesis process. Our main results are related to the SWCNTs diameter which is depending on T, and on the catalysts nature. The targets containing Y with Co or Ni atoms produce more and larger SWCNTs than Co/Ni targets. The SWCNTs' diameter is seen to increase with T s .

Laser-induced fluorescence spectroscopy is used to measure spatially resolved SiH radical densities in pure and radio-frequency glow discharges devoted to amorphous silicon thin-film deposition. Absolute density calibration is achieved by a Rayleigh scattering measurement in . Typical SiH densities of some are measured on the plasma axis with a detection limit of . The experimental results are compared to the SiH densities calculated by a two-dimensional numerical model of the plasma. A good agreement is found both in hydrogen-diluted and pure silane plasmas.

The boron nitride nanotubes (BNNTs) synthesis, using CO2-laser vaporization of a BN target under nitrogen gas, is investigated by UV-laser induced fluorescence (LIF) of the vapor phase and UV-Rayleigh scattering (RS) of the gas-suspended nanoparticles. The LIF signal from B atoms is mainly detected in the 1.5 mm-thick region above the BN target. It originates from a boron-rich vapor region confined near the hot boron droplet formed at the target surface. Then, recombination between hot boron and N2 gas occurs through a fast condensation process as revealed by both the depletion of B atoms from the vapor phase and the RS signal arising from the grown BN nanoparticles. Fluorescence spectra exhibit a strong peak at 250 nm due to boron fluorescence and mainly to nanoparticles Rayleigh scattering. A narrow peak is observed at 210 nm and a broader peak at 189 nm. These bands are tentatively assigned to fluorescence or photoluminescence (PL) from gaseous or solid BN species respectively since both gas and solid phases coexist in the plume due to the rapid cooling process. Two very weak bands occur at 308 nm and 350 nm. They are related to PL of defects bands from BN nanostructures on the basis of ex situ PL spectra of h-BN crystallites and multi-wall BNNTs. Detection of oxygen impurities is shown feasible through LIF from BO radical which is detected just above the BN target evaporated under vacuum pressure (∼1 mbar). An optical diagnosticstrategy is demonstrated from these first in situ observations during BNNTs synthesis.