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International audience; Titanium nitride (TiN) films were grown by CVD (Chemical Vapor Deposition) from 11 titanium chlorides generated in situ by direct chlorination of titanium metal, ammonia (NH3) and 12 hydrogen (H2) as carrier gas on single crystal c-plane sapphire (Al2O3), cemented carbides (WC-Co), 13 stainless steel (AFNOR Z150CDV12) and amorphous graphite substrates. Kinetic pathways 14 involving four surface reactions has been proposed to simulate the growth rate. The proposed 15 model has been validated by experiments performed at different temperatures (650-1400 °C), 16 pressures (300-1000 Pa), with different amount of precursors (N/Ti ratio in gas phase) and on 17 different substrates. The study shows that on polycrystalline materials, the crystal orientation 18 depends on supersaturation while (111) preferred orientation is forced by underlying c-plane 19 sapphire whatever the supersaturation. The low N/Ti ratio in gas phase leads to low growth rate 20 and dense TiN film which is the key to obtain golden TiN. The high growth rate corresponds to 21 brown TiN. Globally, the study shows that golden color is independent from texture and is just the 22 natural aspect of a dense stoichiometric TiN layer. 23

International audience; We propose an innovative process coupling powder bed additive manufacturing by Electron Beam Melting (EBM) with Chemical Vapor Deposition (CVD) and Atomic Layer Deposition (ALD) to develop 3D Ti-6Al-4V structures covered with AlN coating. Despite of the high reactivity of Ti-6Al-4V with nitrogen, thick (~10 μm) and conformal AlN films are deposited by CVD on Ti-6Al-4V substrates with high surface roughness. An AlN underlayer deposited by ALD is necessary to mitigate the reaction between Ti-6Al-4V and the nitrogen precursor NH 3(g) and to limit the formation of brittle titanium nitride phases. We have thus achieved an adherent coating without any modification of the Ti-6Al-4V microstructure at the core of the substrate. We show that a 7 μm thick AlN coating is efficient in protecting Ti-6Al-4V against cyclic oxidation at 650 • C for at least 650 h. This study opens new opportunities for the design of coated 3D Ti-6Al-4V structures for use in high temperature oxidizing environments.

International audience; A comprehensive model to predict the stress evolution in a multilayer coating during its use in solar receivers is proposed. The model takes into account residual stress in the coatings, thermal gradient in the structure and high temperature phenomena like oxide scale growth and creep relaxation. The numerical tool developed in this work can help to understand the complex interplay of these phenomena occurring in all the materials involved. Additionally, the present model can be used to assess high temperature data like creep when it is compared with an experimental case.

Processing of Ti1-xAlxN thin films by the reactive chemical vapor deposition (R-CVD) technique has been performed from the reaction between a titanium tetrachloride (TiCl4-H-2) gas mixture and (0001) c-plane monocrystalline aluminium nitride (AlN) films at high temperatures, in the 800-1200 degrees C range. As a typical result, the growth of epitaxial 70 nm thick layers of (111)-fcc Ti1-xAlxN (0.05 = x = 0.65) has been processed. Multicomponent mass transport and diffusion modelling is proposed to assess the experimental results. A good agreement is found between the experimental thickness of the transformed zones and the calculated titanium diffusion length in AlN. Fcc-Ti1-xAlxN phase formation can be regarded as a diffusion-controlled mechanism. The novel experimental methodology developed in this work could help in understanding the complex formation and stability of this technologically important material.

International audience; Direct liquid injection – metalorganic chemical vapor deposition (DLI-MOCVD) is the most advanced process dedicated to the internal protection of nuclear fuel cladding in accident conditions such as loss of coolant. It allows the deposition of an amorphous, glassy-like chromium carbide CrCx coating which is resistant against high-temperature oxidation in air and steam. Since the above-mentioned material characterizations demonstrated that coatings possessed the appropriate protection properties, the DLI-MOCVD process was scaled-up. First, a joint development between experimental and numerical studies led to a deposition inside a 1 m long cladding segment with a coating of sufficiently large and uniform thickness. Optimized reactor parameters consist in a combination of low temperature (~600 K) and low pressure (~600 Pa) with a high vapor flow rate of reactive species in the reactor ensuring a short residence time. The second phase of the scale-up consisted in coating simultaneously three, then sixteen segments in a single run. 3D computational simulations of the deposition process assisted the development of specific flanges designed to distribute homogeneously the reactive vapor into the three or sixteen cladding tubes. Experimental conditions have been extrapolated from one to three and to sixteen cladding segments, resulting in the deposition of the CrCx coating inside all segments with a relatively uniform partition. Overall, this paper demonstrates the feasibility of the deposition of CrCx coating in a bundle of several, up to sixteen, nuclear fuel cladding segments of 1 m in length (ID 8 mm), in order to protect them during accident conditions. This “batch demonstration” is a first step in the course of DLI-MOCVD technological transfer. Next step will be the deposition in a full-length cladding tube (4 m) that is already supported by numerical predictions.

Boron Nitride is a promising group 13-group 15 compound material that exhibits various interesting properties like wide band gap, chemical stability, attractive mechanical properties and other. The growth behavior of this material has not been investigated in sufficient details to tailor properties of the resulting films. In this work we present the results on the growth of turbostratic boron nitride (t-BN) thin films at a relatively high growth rate of 3 mu m/h with the aim to investigate the potential use of boron trichloride in combination with ammonia as precursors for growth. Deposition experiments were conducted in a vertical cold wall high temperature chemical vapor deposition reactor in the temperature range 1000 degrees C-1700 degrees C depending on the substrate used. Templates of w-AlN (0001), 4 degrees off-cut 4H-SiC (0001), Cr (110) and W (110) were employed as substrates for the BN growth. As-grown BN layers were characterized by Scanning Electron Microscopy, X-Ray Diffraction, Electron Diffraction and Raman Spectroscopy. The results indicate that temperature and N/B ratio have a great influence on the crystallinity of the deposited films. For AlN and SiC substrates, a temperature of 1600 degrees C and N/B ratio in range between 3 and 7.5 were identified as the best parameters for the growth of a 2 mu m thick t-BN layer with a spacing between basal planes of about 3.36 angstrom compare to the 3.33 angstrom spacing between basal planes of hexagonal or rhombohedral BN (h-BN or r-BN). For Cr and W substrates which have a lower mismatch with h-BN (1 and 8.8 %), layers of t-BN were deposited at much lower temperature (1000 degrees C-1150 degrees C) with a spacing between basal planes of 3.5 angstrom and morphology similar to that observed on SiC substrates. We obtained t-BN layers with in plane strong disorder but out of plane orientation (c-axis normal to the surface).

Plasma enhanced atomic layer deposition (PE-ALD) of aluminum nitride (AlN) thin films often utilizes NH3 or a mixture of N2 and H2 as a plasma source. However, the possibility of separating the activation step from the nitridation step by using H2 alone as the plasma source has never been explored. In this paper, we study the deposition of AlN by PE-ALD by using trimethylaluminum, H2 plasma and NH3 for deposition temperatures below 400 °C. The self-limiting ALD growth was achieved between 325 °C and 350 °C. As a comparison, AlN was also deposited by thermal ALD (T-ALD), where surface reactions between TMA and NH3 occurred with reasonable growth rates only at temperatures above 400 °C. The PE-ALD films showed low oxygen (1.5 at.%) and carbon contaminations (1 at.%). The T-ALD films contained carbon (5 at.%) mainly attributed to the presence of C Al bonds that was insignificant in PE-ALD films. The flow rate of H2 used in H2 plasma was found to have a significant impact on the preferred orientation of AlN films, where higher H2 flow rate promoted the (002) preferred orientation. Besides, the electrical resistivities were probed to be 108 Ω cm, as expected in an insulating material. As an example, AlN was used to infiltrate porous sintered silicon carbide (SiC). Both AlN deposited by PE-ALD and by T-ALD operating with exposure mode deposited at 400 °C were attempted. Even though, there is a greater risk for TMA precursor to decompose at 400 °C, infiltration of AlN was more successful by T-ALD operating with exposure mode.

International audience; The effect of direct recycling of effluents on the quality of CrxCy coatings grown by MOCVD using direct liquid injection (DLI) of bis(ethylbenzene)chromium(0) in toluene was investigated. The results are compared with those obtained using non-recycled solutions of precursor. Both types of coatings exhibit the same features. They are amorphous in the temperature range 673–823 K. They exhibit a dense and glassy-like microstructure and a high hardness (> 23 GPa). Analyses at the nanoscale revealed a nanocomposite microstructure consisting of free-C domains embedded in an amorphous Cr7C3 matrix characterized by strong interfaces and leading to an overall composition slightly higher than Cr7C3. The stiffness and strength of these interfaces are mainly due to at least two types of chemical bonds between Cr atoms and free-C: (i) Cr intercalation between graphene sheets and (ii) hexahapto η6-Cr bonding on the external graphene sheets of the free-C domains. The density of these interactions was found increasing by decreasing the concentration of the injected solution, as this occurred using a recycled solution. As a result, “recycled” coatings exhibit a higher nanohardness (29 GPa) than “new” coatings (23 GPa). This work demonstrates that using bis(arene)M(0) precursors, direct recycling of effluents is an efficient route to improve the conversion yield of DLI-MOCVD process making it cost-effective and competitive to produce protective carbide coatings of transition metals which share the same metal zero chemistry.

International audience; Cr deposits are widely used as protective coatings but multifunctional performances are required in harsh environments motivating research on new processes. MOCVD of Cr metal coatings was carried out by direct liquid injection (DLI) of a unique solution containing bis(ethylbenzene)chromium as metal source and thiophenol as inhibitor of carbide formation. A low amount (

International audience; One mu m-thick (0001) t-BN layers have been grown on w-AlN template by HT-HVPE (High Temperature Hydride Vapor Phase Epitaxy). The experimental set-up consists of a vertical cold-wall quartz reactor working at low pressure with an inductively heated graphite susceptor. The used reactants are ammonia (NH3) and boron trichloride (BCl3). As-grown BN layers have been characterized by XRD and TEM. The influence of the temperature and the N/B ratio of precursors in the gas phase, on the c-lattice parameter of BN layer, have been investigated in order to optimize the crystalline quality. For a deposition at a temperature of 1600 degrees C and a N/B ratio of 7.5, the growth of a 2 mu m-thick t-BN layer with lattice parameters (a and c) of 2.50 and 6.78 angstrom has been achieved.

There is a growing interest in producing tantalum nitride (TaN) thin films for various industrial applications. For example, in microelectronics, the development of IC technology is driven by the need to increase both performance and functionality while reducing power and cost. This goal can be achieved by several solutions among which the introduction of architecture enhancements such as 3D integration. The most challenging step is the deposition of a conformal, continuous, and adherent diffusion barrier. In this work, atomic layer deposition (ALD) of TaN thin films is explored using the combination between the thermodynamical behavior of the precursor, mass transfer in the reactor, and the operating conditions. TaN thin film deposition on very complex shape substrates, such as nanodots, TSV, silicon nanowires, and carbon nanotubes, has been evaluated.

The residual porosity of structural silicon carbide (SiC) composites limits their use in advanced nuclear systems. The use of thick coatings of high-Z materials like tungsten (W) or tungsten alloys (W1−xRex) is a promising solution to overcome such problems. However, solid-state reactions occur between SiC and metals at high temperatures. An intermediate layer is therefore selected, based on thermodynamic computation. It is shown that aluminum nitride (AlN) could limit the interface reactivity at temperatures close to 1000 °C. Duplex AlN/W1−xRex coatings were fabricated in two steps by chemical vapor deposition on bulk silicon carbide to verify experimentally the theoretical material solution approach. Electron probe micro-analyses showed that, at the micrometer level, there was no interface reaction during the growth process. It is the first time that such a material stack has been fabricated, and it seems promising for the high-temperature use of SiC with tungsten alloys.

Chromium carbide layers were deposited using liquid-injection metal-organic chemical vapor deposition inside long (0.3 to 1 m) and narrow (8 to 24 mm in diameter) metallic tubes. The deposition was carried out using a molecular single-source, bis(benzene)chromium (BBC), as representative of the bis(arene)metal family diluted in toluene and injected with N2 as carrier gas. A multicomponent mass transport model for the simulation of the coupled fluid flow, heat transfer and chemistry was built. The kinetic mechanism of the growth of CrCx films was developed with the help of large-scale experiments to study the depletion of the precursors along the inner wall of the tube. The model fits well in the 400&ndash, 550 &deg, C temperature range and in the 1.3 &times, 102 to 7 &times, 103 Pa pressure range. The pressure is shown to have a pronounced effect on the deposition rate and thickness uniformity of the resulting coating. Below 525 &deg, C the structure, composition and morphology of the films are not affected by changes of total pressure or deposition temperature. The coatings are amorphous and their Cr:C ratio is about 2:1, i.e., intermediate between Cr7C3 and Cr3C2. The model was applied to the design of a long reactor (1 m), with a double injection successively and alternatively undertaken at each end to ensure the best uniformity with sufficient thickness. This innovative concept can be used to optimize industrial deposition processes inside long and narrow tubes and channels.

International audience; Despite its real advantages compared to seeded sublimation growth, SiC solution growth has never given convincing results. The difficulty of stabilizing the growth front, and thus avoiding any polycrystal formation results from a poor description and understanding of the coupled phenomena that occur in the crucible. This paper addresses the coupled heat transfer and fluid dynamic modeling of the SiC solution growth process, with special attention being paid to the different convective flows in the liquid. It is demonstrated that both Marangoni and electromagnetic convections have to be avoided. The configuration where the flow patterns in front of the crystal are driven only by crystal rotation, insures the most stable growth front. The correlation between calculated results and experiments is presented and a 3C-SiC wafer grown by the optimized process is shown.

In this paper, AlN synthesis is achieved by High Temperature CVD which consists of a graphite susceptor heated by induction in a home-built vertical cold-wall reactor working at low pressure. The reactants used are ammonia NH3 and aluminium chlorides AlClx species formed in situ via Cl2 reaction with high purity Al wire. AlN films were deposited on a 55 mm diameter graphite susceptor between 1200{degree sign}C and 1600{degree sign}C. The influence of deposition temperature on growth rate, surface morphology, grain size and crystalline state is presented. Growth rates of up to 230 µm.h-1 were reached. AlN layers were characterized by SEM, X-ray Diffraction, Raman spectroscopy and Optical Profilometry.

Modeling and simulation of the SiC growth processes, Physical Vapor Transport (PVT), Chemical Vapor Deposition (CVD), are sufficiently mature to help building new process equipment or up-scaling old ones. It is possible (i) to simulate accurately temperature and deposition distributions, as well as doping (ii) to quantify the limiting phenomena, (iii) to understand the important role of different precursors in CVD and hydrogen additions in PVT. The first conclusion of this paper is the importance of the "effective" C/Si ratio during CVD epitaxy in hot-wall reactors and its capability to explain the doping concentrations. The second conclusion is the influence of the C/Si ratio in alternative bulk growth technique involving gas additions.

This paper reviews research on advanced bulk crystal growth of SiC. A brief review highlights the benefits of the so called Modified Physical Vapor Transport Technique which uses an additional gas pipe for fine tuning of the growth cell of a conventional Physical Vapor Transport setup with additional gases. Main emphasis, however, will be laid on a systematic dislocation evolution study for various growth parameter sets. Besides doping, growth temperature was considered. Two main results were found: (i) In p-type SiC, irrespective of the incorporation of aluminum or boron acceptors, basal plane dislocations that are harmful for bipolar power devices appear less pronounced or are even absent compared to n-type SiC. (ii) Growth at elevated seed temperature (i.e. 2300 °C and higher) is beneficial for low dislocation densities. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Silicon carbide is interesting for high power, high temperature and high frequency applications but its development is limited by the low quality and high cost of single-crystalline wafers. The transfer by wafer-bonding of single-crystalline SiC thin films to a polycrystalline SiC support is an attractive way for lowering the cost. This transfer requires high quality polycrystalline substrates fabricated with high growth rate, controlled morphology (columnar, dense, well-oriented layers), and very low surface roughness (RMS

Natural gas appears to be a fuel of great interest for SOFC systems. The principal component of natural gas is methane, which can be converted into hydrogen by direct or gradual internal reforming (DIR or GIR) within the SOFC anode. However, DIR requires a large amount of steam to produce hydrogen. If the injected mixture contains very small quantities of steam, GIR is then obtained. With GIR, the risk of carbon formation is even greater. This paper proposes a model and simulation, using the CFD-Ace software package, of the behaviour of a tubular SOFC using GIR and a comparison between utilization in DIR and GIR. A thermal study is included in the model and a detailed thermodynamic analysis is carried out to predict the carbon formation boundary for SOFCs fuelled by methane. Thermodynamic equilibrium calculations taking into account Boudouard and methane cracking reactions allowed us to investigate the occurrence of carbon formation. Simulations were used to calculate the distributions of partial pressures for all the gas species ( CH 4 , H 2 , CO, CO 2 , H 2 O ), current densities and potentials in both electronic and ionic phases within the anode part (i.e., gas channel and cermet anode). The simulations indicate that there is no decrease in electrochemical performance if GIR is used rather than DIR. A thermal study appears to confirm that the cooling effect due to the endothermic reforming reaction is eliminated in GIR, but the thermodynamic study indicates that carbon formation can be suspected for x H 2 O / x CH 4 ratios lower than one.

International audience; Photovoltaic (PV) modules are generally installed by the application of empirical rules aimed at reducing shadows during the periods of high solar irradiation. A traditional installation on a horizontal surface results in largely spaced rows of modules with a relatively low tilt angle. The addition of interrow reflectors results in more direct and diffuse flux transmitted to the cells. The Amélioration de l'Efficacité Photovoltaïque (Aleph) project aims to define clear rules for optimal settings of systems of PV module rows with fixed interrow planar reflectors in a given location and under a given climate. Two PV technologies are tested for performance with this type of system: amorphous silicon (a-Si) and polycrystalline silicon (p-Si). This study combines experiments on panel behavior in an outdoor environment on the Site Instrumental de Recherche par Télédétection Atmosphérique (SIRTA) meteorology platform and a multiphysics numerical model used to couple all the important physical phenomena and accurately describe the system behavior. The model includes a ray tracing radiation/optics module based on the Monte-Carlo method, as well as an electrical module simulated in SPICE. This study presents the influence of the string mismatch losses, which is present at periods of heterogeneous illumination, on the yield of PV modules augmented by static planar reflectors.

Recently, in some silicon carbide single crystals, some micropipes associated with screw dislocation have been observed by X-ray topography and the strain field around them produced images similar to those of screw dislocations with a very large Burgers vector, about 667 nm. The radius of the hole in the centre of the micropipe is less than 10 'm. This value and the theoretical predictions by Frank (about 7.8 mm) using the Burgers vector magnitude show a large discrepancy. In this paper we present Atomic Force Microscopy experiments around this kind of defects. The Burgers vector magnitude of the screw dislocation and the value of the radius have been measured by this technique. Not only one dislocation, but several have been observed around the micropipe. We concluded that it is in better agreement with the Frank theory modified by Cabrera and Levine concerning kinetic effects during the growth.

We have studied the impact of the chemical nature of additional gases fed into the modified physical vapor transport (M-PVT) growth cell. In particular experiments were carried out using helium, argon, nitrogen and propane in the growth setup. Numerical modeling was used to address the underlying physical and chemical effects that impact the global temperature field. It is found that chemical decomposition of complex gases plays a secondary role as heat source or sink. However, temperature variations related to varying gas compositions fed to the systems are primarily induced by changes of the graphite foam isolation properties.

Because of the formation of DPB (Double Positioning Boundary) when starting from a hexagonal seed, DPB-free 3C-SiC single crystals have never been reported up to now. In a recent work we showed that, using adapted nucleation conditions, one could grow thick 3C-SiC single crystal almost free of DPB [1]. In this work we present the results of a multi-scale investigation of such crystals. Using birefringence microscopy, EBSD and HR-TEM, we find evidence of a continuous improvement of the crystal quality with increasing thickness in the most defected area, at the sample periphery. On the contrary, in the large DPB-free area, the SF density remains rather constant from the interface to the surface. The LTPL spectra collected at 5K on the upper part of samples present a nice resolution of multiple bound exciton features (up to m=5) which clearly shows the high (electronic) quality of our 3C-SiC material.

Natural gas appears to be a fuel of great interest for solid oxide fuel cell (SOFC) systems. It mainly consists of methane, which can be converted into hydrogen by direct internal reforming (DIR) within the SOFC anode. However, a major limitation to DIR is carbon formation within the ceramic layers at intermediate temperatures. This paper proposes a model solution using the CFD-ACE software package to simulate the behavior of a tubular SOFC. A detailed thermodynamic analysis is carried out to predict the boundary of carbon formation for SOFCs fueled by methane. Thermodynamic equilibrium calculations that take into account Boudouard and methane cracking reactions allow us to investigate the occurrence of carbon formation. This possibility is discussed from the values of driving forces for carbon deposition defined as α=PCO2∕(KBPCO2) and β=PH22∕(KCPCH4), from the equilibrium constants KB and KC of the Boudouard and cracking reactions, and from the partial pressure Pi of species i. Simulations allow the calculation of the distributions of partial pressures for all the gas species (CH4, H2, CO, CO2, and H2O), current densities, and potentials of both electronic and ionic phases within the anode part (i.e., gas channel and Cermet anode). Finally, a mapping of α and β values enables us to predict the predominant zones where carbon formation is favorable (α or β1) according to the calculation based on thermodynamic equilibrium. With regard to the values of these different coefficients, we can say that a carbon formation can be supposed for temperature less than 800°C and for ratios xH2O∕xCH4 smaller than 1.

The deposition of hybrid a-SiOC:H dielectric films from decamethylcyclopentasiloxane/cyclohexene oxide/helium (D5/CHO/He) plasmas has been investigated in various operating conditions. In order to understand the influence of molecule fragmentation on the film formation, the species in the plasma were monitored by optical emission spectroscopy and mass spectroscopy. The films were analyzed with spectroscopic ellipsometry and Fourier transform infrared spectroscopy. The CHO molecule loss rate under fragmentation and film formation was always much higher than that of D5, with the ratio depending on the plasma conditions. The CHO was found to lose at least CO, CH, H and C"3 groups whereas D5 main reactions in plasma occurred through Si-CH"3 and C-H bond dissociation, leaving its cyclic structure unaltered. This suggested that different hydrocarbon fragments got incorporated in the film thanks to the presence of CHO in the gas feed compared to D5 alone deposited films. Moreover some Si-O-Si structure indicated a high level of the D5 cycle preservation in the film. The deposition rate increased linearly with RF plasma power for D5 films and for D5/CHO films. It was enhanced by the presence of CHO in the plasma.

This paper summarizes recent experimental and simulation results on etching, growth rates and nitrogen incorporation in silicon carbide epitaxial layers grown in a horizontal hot-wall chemical vapor deposition reactor. The combination of heat and mass transfer modeling, process simulation and experimental studies allows the identification and the quantification of the growth and doping histories. It is demonstrated that, in this high temperature technology, (a) it is difficult to optimize the deposition rate uniformity for large-scale substrates and (b) hydrogen etching during growth is of great importance. Finally, new results concerning the influence of hydrogen etched nitrogen on the nitrogen doping profile in the epilayer are shown. A simple model taking only into account N 2 adsorption is not sufficient to correctly explain the doping variations. Specific experiments have been realized to identify and quantify additional phenomena such as the etching of nitrogen by H 2 during the deposition process.

High temperature epitaxial processes for SiC bulk and thin films by physical vapour transport and chemical vapour deposition are reviewed from an academic point of view using heat and mass transfer modelling and simulation. The objective is to show that this modelling approach could provide information on fabrication and characterization for the improvement of the knowledge of the growth history. Recent results of our integrated research programme on SiC, taking into account the fabrication, process modelling and characterization, will be presented.

Two-dimensional simulations of 3C–SiC growth from SiH4/C3H8/Ar/H2 mixtures in a cold-wall CVD reactor have been performed. The impingement rate of the species incoming at the surface can be extracted from a reactor simulation and used as input data in an atomic-scale growth modeling. However, only a restricted number of species can be considered in such a multiscale approach combining several numerical codes. For this reason, two rather simple reaction schemes are selected in the present reactor modeling work. The predicted deposition rate profiles obtained using both schemes are compared to the experimental profiles. The relative contributions of the various species in the deposition process are calculated, and the most important species are identified. The strong influence of thermal diffusion is also emphasized.

In view of its excellent thermal, mechanical and electronic properties, silicon carbide is the reference semiconductor material for high-temperature, high-frequency and high-power devices. Ingots of monocrystalline SiC which are currently grown by the seeded sublimation growth technique have opened the path to the production of large-area SiC wafers. Despite constant progress in crystal growth, the development of industrial applications has been up to now severely limited by the insufficient quality and size of the substrates. This situation results mainly from the fact that the growing process is quite complex. As a consequence, it is quite difficult to control the growth of a given polytype and the doping level while decreasing the number of defects such as misoriented domains, inclusions, macrodefects and micropipes. This paper is mainly devoted to a review of our work on the influence of the seed characteristics and the growth process parameters, such as the thermal field and the pressure, on the occurrence of defects in the as grown ingot and on the enlargement process. Polytype identification and morphology, structural perfection and defect analyses have been carried out using mainly polarized light microscopy and x-ray white-beam synchrotron topography.

In order to characterize the estrogenic activity of chemicals, we established complementary in vitro recombinant receptor-reporter gene assays in stably transfected MCF-7 and HeLa cells. MCF-7 cells which express the endogenous estrogen receptor alpha (ER alpha) were stably transfected with only an estrogen-regulated luciferase gene. These cells enable the detection of compounds which bind to ER alpha or interfere with the induction of ER alpha mediated gene expression. Furthermore, HeLa cells, which do not express endogenous ERs, were transfected with an ER alpha or an ER beta construct together with an estrogen-regulated luciferase gene, or a chimeric GAL4-ER alpha receptor and the corresponding luciferase reporter gene. Finally, we tested these four cellular models as tools to check the estrogenic activities of several potential xenoestrogens and to detect estrogenic activity in wastewater sewage treatment effluents. In all of the models, nonylphenol mixture (NPm), 4n-nonylphenol (4nNP), 2,4'-DDE, 4,4'-DDE and wastewater sewage treatment effluent were active, while PCB mixture (Aroclor 1254), PCB 77, atrazine and lindane (gamma hexachlorocyclohexane) were inactive. Dioxin partially activates the estrogen receptor in MCF-7 cells while in HeLa-derived cell lines, it decreased the estrogenic-induced expression of luciferase.

The exponential increase in computing power realized over the past three decades has required devices of ever-decreasing dimensions. With these reductions in feature size, each generation of circuit technology creates a new set of materials-science challenges, as exemplified by the use of silicide-based diffusion barriers.The use of transition-metal silicides in the semiconductor industry began in the early 1980s with (in retrospect) fairly thick films, simple compositions, and minimal microstructural requirements. The implementation of thin-film binary silicides in integrated circuit (IC) applications required the development of appropriate modeling techniques to select the deposited metal, its gaseous precursor, and the Silicon precursor. These vectors were used to define experimental conditions to yield desired films. Chemical-vapor-deposition (CVD) experiments were simulated and CVD phase diagrams were used to describe the changing film properties with different thermodynamic conditions.In the early 1990s, research began to focus on CVD of ternary Systems (Ta-Si-N, Ti-Si-N). Modeling these complex Systems required optimization of the thermodynamic data and careful evaluation of the ternary phase diagrams.Current-generation materials are deposited in extremely thin layers (ULSI, or ultralarge-scale integration), composed of multiple elements from a variety of gas sources, an d have tailored micro-structures. As described in this article, early thermodynamic modeis helped develop deposition techniques for early-generation silicides. As the technological requirements increased, the modeling method s evolved in parallel, yielding continued insight into the relevant processes. Current work on CVD modeling couples thermodynamic calculations with heat and mass transfer. Incorporating both kinetic and thermodynamic effects, these methods provide a more realistic description of the CVD reactor.

The deposition of single SiC crystals has been processed inside a sealed enclosure at temperatures above 2300 K and pressures lower than 5 × 103 Pa by the modified Lely method. The purpose of this work is to present different optimized macroscopic models, thermodynamics, heat and mass transfers used in the simulation of the growth of such crystals. Thermodynamic modelling has been used to determine the most important reactive species involved in equilibrium conditions. Induction heating modelling has allowed the calculation of the actual temperatures inside the reactor which are not well known because of the difficulty associated with their measurement. Finally, mass transport modelling provided the calculated deposition rate. It was found that the calculated growth rates were close to the experimental ones which may indicate a good representation of the actual phenomena involved in the crucible. Moreover, defect formation, which is the primary obstacle to the production of large area devices, is explained by local sublimation of the growing ingot and related to the temperature gradients existing within the crystal and graphite holder.

International audience; The application of AlN films in optoelectronics, sensors and high temperature coatings is strongly dependent on the nano-micro-structure of the film, impurity level and defect density. AlN epitaxial thin (0.5-10 mu m) and thick polycrystalline (>10 mu m) films were grown on different foreign substrates (sapphire, silicon carbide, graphite) and single AlN crystals by Chemical Vapor Deposition (CVD), also called Hydride Vapor Phase Epitaxy (HVPE), at high temperature (1200-1750 degrees C). In the first part of this paper, polycrystalline growth of thick films (>10 mu m) prepared at high growth rate (>100 mu m.h(-1)) was performed on graphite substrates to study the preferential orientation of the films. AlN/W multilayers were deposited on silicon carbide composites to increase their performance at high temperature in aggressive conditions. Such multilayer materials can be used for the cladding of nuclear fuel. The second part of this paper concerns the characterization of epitaxial films, including their crystalline state, surface morphology, and inherent and thermally induced stress which inevitably leads to high defect densities and even cracking. The full-width at half-maximum (FWHM) of X-ray rocking curves of the grown AlN layers exhibited very large values (several thousand arcsec), and they became steeply deteriorated with increasing growth rate. To improve the crystalline quality of AlN layer, well-known growth techniques, such as multi-step growth using buffer layers, were used at temperatures above 1200 degrees C in order to lower the disorientation to 300 arcsec. The applications of such "templates" for deep UV light emitting diodes (UV LED) and surface acoustic wave sensors (SAW) are discussed. (C) 2013 Published by Elsevier B.V

The deposition of single SiC crystals has been processed inside a sealed enclosure at temperatures above 2300 K and pressures lower than 5 ⋅ 103 Pa by the modified Lely method. The purpose of this work is to examine the potentialities of different macroscopic models, thermodynamics, heat, and mass transfers on the simulation of the growth of such crystals with a special emphasis on their coupling mechanism. Thermodynamic modeling has been used to determine the most important reactive species involved in equilibrium conditions. Induction heating modeling has allowed the calculation of the actual temperatures inside the reactor which are not well known because of the difficulty associated with their measurements. Finally, mass transport modeling provided the calculated deposition rate. It was found that the calculated growth rates were close to the experimental ones which may indicate a good representation of the actual phenomena involved in the crucible. As a matter of fact each of the proposed models has contributed to a better knowledge of the process.

Mutation of isoleucine 747 to threonine in the C-terminal part of the ligand-binding domain (LBD) of the human glucocorticoid receptor (GR) alters the ligand specificity for transactivation. Natural glucocorticoids such as cortisol or corticosterone were completely inactive with the mutant 1747T, whereas synthetic steroids like dexamethasone efficiently stimulated GR 1747T-mediated transactivation. However, the corresponding ligand dose-response curve for dexamethasone-induced transactivation was shifted to higher concentrations when compared with that obtained with the wild type GR. Neither this shift nor the inability of cortisol to activate the 1747T mutant was due to an altered in vitro ligand-binding affinity. In the canonical three-dimensional structure of nuclear receptor LBDs, isoleucine 747 is in the direct vicinity of residues that contribute to the ligand-binding pocket. Moreover, it is located in the C-terminal LBD region, which harbors the conserved core of the activation function AF-2 and undergoes a ligand-induce transconformation, required to generate the surface interacting with putative transcriptional intermediary factors/coactivators of AF-2. The phenotype of 1747T mutant is discussed in view of the possible consequences of the mutation on the various events which, according to the model, lead to a transcriptionally competent AF-2.

In order to improve the sliding wear resistance of stainless steel components, carbide-hardened surfaces were produced on AISI 316L austenitic stainless steel by laser surface alloying. Different powdered precursors (Cr3C2, a mixture of Cr3C2 and Cr and a mixture of Ti and SiC) were applied to the steel surface and irradiated using a continuous wave, 300 W, Nd-YAG laser. The surface alloys resulting from the incorporation of Cr3C2 alone or mixed with chromium were composed of austenite (y) dendrites surrounded by a γ-M7C3 eutectic (M≡Fe or Cr); their microhardness ranged from 380 to 450 HV. Superficial hardening by titanium carbide was obtained using a mixture of Ti and SiC powders as precursors; Ti and SiC particles dissolved in the melted pool, leading to the precipitation of fine TiC particles during solidification. The microhardness of the surface alloy was about 350 HV. For both chromium carbide and titanium carbide surface alloying treatments, the processing conditions were determined which led to a noticeable improvement of the sliding wear resistance of AISI 316L stainless steel without any detrimental effect on its high temperature oxidation resistance.

In order to improve the sliding wear resistance of stainless steel components, carbide-hardened surfaces were produced on AISI 316 L austenitic stainless steel by laser surface alloying. Cr 3 C 2 or TiC powder was applied to the steel surface and irradiated using a continuous wave, 300 W, Nd-YAG laser. Surface alloys resulting from the incorporation of Cr 3 C 2 were found to be composed of austenite and M 7 C 3 (M≡Fe or Cr). By varying the thickness of the initial Cr 3 C 2 coating, alloys with different compositions and microstructures were produced, with related microhardnesses in the range 450–900 Hv. Superficial hardening by titanium carbide was obtained using coarse TiC powder which was incorporated into the melted layer with no, or very little, dissolution: the microhardness of the surface composite was about 450 Hv. For the wear conditions used in this study, a greater improvement in the sliding wear behaviour of the 316 L substrate was achieved with TiC as the hard phase.

The goal of this study is to investigate different hardening routes for 316L stainless steel by laser surface alloying. We have investigated the formation of iron-chromium carbides by SiC or carbon incorporation, the alloying with submicronic particles of TiC and the precipitation of titanium carbide from mixtures of Ti and SiC. For each hardening route we present the microstructures and the hardness of the processed surface alloys and the conditions leading to the best compromise between highest hardness, best homogeneity and lowest occurrence of cracks. From these results it can be reasoned that hardening by iron-chromium carbides is the best hardening route and that this surface alloy might be a good candidate for tribological applications.

In transfection experiments performed with wild-type MR, the maximal transcriptional activation of a mineralocorticoid response induced by glucocorticoid was generally similar to that of aldosterone, the natural mineralocorticoid hormone. However, compared to aldosterone, glucocorticoid activity decreased when the A/B region of MR was absent. We describe in this study the synthesis and biological activities of seven mutated MRs differently truncated in the N-terminal region. Using transient expression conditions in MCF-7 cells, the N-terminal domain of MR has been shown to contain a region (residues 254-390) whose deletion led to an apparent "aldosterone selectivity". These results suggest that this region could help to maintain the most transcriptionally active conformation of MR even in the presence of ligands which are not by themselves able to fully induce such a conformation.

Surface alloys are of great interest for improving the mechanical and/or chemical properties of the near-surface region of metallic materials. A new method is described to produce surface alloys under laser irradiation using submicronic powders suspended in a polymeric mixture. By this process, Fe-TiC composite surface alloys were achieved on mild steel; they exhibited increased hardness, the value of which may be varied by controlling the TiC fraction incorporated.

Iron silicide (FesSi) coatings of composition Fe-16 at% Si and Fe-25 at% Si have been produced by laser surface alloying on pure iron substrates with predeposited silicon powder. The coatings showed excellent adherence without any pores or cracks. They were compositionally and microstructuraly homogeneous, exhibiting two to three times higher surface hardness values than pure iron. High temperature oxidation resistance of the coatings were tested in the temperature range 1173-1273 K in static pure oxygen ( P ~ , = 13.3 k ~ a ) . Their superiority compared to bulk alloys and CVD coatings is discussed.

We previously established a stable expression system in MCF-7 cells for the detection of (anti)estrogenic activity by assaying the reporter enzyme activity of firefly luciferase. In this cell line (called MVLN), the bioluminescent response can be measured either in the cellular homogenate, or in intact living cells. Here we present various potential experimental uses of this cellular model. First, we used this cell line to screen natural or synthetic molecules classified as full or partial (anti)estrogens and observed that their behavior towards our model was identical to that expected. Moreover, the bioluminescent response was in agreement with the natural responses like cellular proliferation or stimulation of the progesterone receptor. We then demonstrated the inhibitory effects of retinoic acid and 1,25 dihydroxyvitamin D 3 , two molecules which do not compete with estradiol for its receptor. We thus deduced that with this cell line an “antiestrogenic” effect which occured at any step of the estrogenic action, might be detected. Finally, we showed that detection of luciferase activity in intact living cells was particularly helpful for investigating the evolution of estrogenic activity. For instance, we observed that long-term treatment of MVLN cells with an antiestrogen irreversibly decreased the bioluminescent response by more than 90%. This phenomenon affected all cells equally and could not be reversed, even by long-term estradiol treatment. We therefore conclude that this chineric response faithfully reflects estrogenic action in the cell and can be used to develop different aspects of the endocrine research.

Boron was incorporated in the near surface region of iron samples by three different methods: ion implantation, laser alloying and pack cementation. The behaviour of these different surface alloys was studied thermogravimetrically between 400 and 600°C in static SO 2 atmospheres at the pressure of 133 hPa. Implanted samples were obtained near room temperature at a dose of 10 17 B + cm −2 . The boron amount (∼ 2 μ g cm −2 ) and the thickness involved (∼ 300 nm) although small, induced a noticeable reduction of the corrosion rate. At low temperatures (T ≤ 450°C), the rate law was paralinear and the only product formed was iron (II) sulphate in good agreement with thermochemical provisions. In this temperature range, boron was thought to have a catalytic effect as, when absent, iron (II) sulphate did not appear. At higher temperatures a duplex layer containing iron oxide and sulphide grew parabolically. Surface alloys obtained by laser alloying were 50–100 μm in thickness and exhibited compositions lying in the FeFe 2 B region of the phase diagram. Different microstructures were observed, depending on the irradiation conditions. The kinetic laws were parabolic or cubic, showing a greater protection when compared to implanted samples. Eutectic surface alloys exhibited the best behaviour for high temperatures or long times of oxidation. Pack-boronization at 950°C for 2 h in a powder mixture containing boron, ammonium fluoride and alumina led to a layer consisting mainly of Fe 2 B. Kinetic experiments showed that such a coating exhibited the best protection at the lowest temperatures.

International audience; AlN growth by HTCVD (High Temperature Chemical Vapor Deposition) from AlCl3 and NH3 is currently a promising way to obtain thick, compact layers of aluminum nitride. This study focused on the development of a kinetic mechanism that models AlN growth with only 7 gas-phase reactions and 4 surface reactions. Ab initio estimation of the thermodynamic data of the AlCl2NH2, AlClNH, AlCl(NH2)2 and Al(NH2)3 intermediates suspected to be involved in the gas-phase reactions is proposed. It was found that only AlCl2NH2 is present in noticeable concentrations under our experimental conditions. Experiments made at different temperatures and N/Al ratios, carried out in a cold wall HTCVD reactor, were used to validate the proposed model. Finally, the N/Al ratio in the gas phase was observed to play a key role in the AlN surface quality. Possible explanations of this influence and future experiments that will confirm this trend are discussed.

A specific approach based on a “tendecy model”, intermediate between the “black-box” and the “detailed analytical” models, has been developed. It makes it possible to predict both the amount of polymer produced in the autoclave process, and the quality of the polymer, expressed in terms of molecular structure: molecular-weight distribution (MWD), average molecular weights, long- and short-branching indices, double-bond indices. The prediction of conversion requires an appropriate representation of partial segregation of the initiator feedstream. The prediction of quality is based on a kinetic model taking into account the most important mechanism recognized for this reaction. Several kinds of free radicals are involved to which the quasi-steady-state assumption is applied. Processes giving rise to new chains are identified and the statistical moments for the corresponding distributions are derived. The moments of the overall dead polymer population are finally derived,thanks to a mixing theorem. In spite of the difficulties caused by transfer to polymer and scission of free radicals, equations for the moments are obtained in a closed form and this constituents a remarkable property of the present model. An expression for the MWD can then be obtained from its statistical moments by an original method based on the deformation of a known distribution.

The surface of Ti-6Al-4V precoated with silicon powders was irradiated by a YAG: Nd 3+ laser to produce a homogeneous and uniform alloy layer. The surface hardness measured was 730 HV 0.1 and the oxidation resistance was greatly improved. This improvement is mostly due to the diminution of the inward diffusion of O 2− and the outward diffusion of Ti 4+ by the presence of silica and a little alumina on the top surface of the oxide scale.

We recently developed the cellular model MVLN-15 in which estrogenic action can be detected by bioluminescence. Using this cellular model, we characterized the inhibitory effect of retinoic acid on the estrogen-dependent induction of luciferase transcription. We present evidence that i) the inhibitory effect of retinoic acid is not due to a simple competition between retinoic acid and estradiol for binding to the estrogen receptor, ii) a DNA sequence restricted to an estrogen-responsive element (ERE) was sufficient for the antiestrogenic effect of retinoic acid, and iii) retinoic acid does not act via a cryptic AP-1 binding site associated with this ERE. Therefore, we conclude that the antiestrogenic effect of retinoic acid is due to an inhibition of estrogen receptor activity, for example by altering the amount of estrogen receptor protein bound to the ERE or affecting the transcriptional efficiency of this complex.

In order to achieve AlN bulk growth, HTCVD chlorinated process is investigated. High growth rate and high crystalline quality are targeted for AlN films grown on (0001) 4H SiC at 1750 °C. The precursors used are ammonia NH3 and aluminium chlorides AlClx species formed in situ by action of Cl2 on high purity Al wire. Influence of total pressure, Cl2 flow rate and NH3 flow rate on AlN growth rate, crystalline state and microstructure are presented. Growth rates of up to 200 μm.h–1 have been reached for polycrystalline layers. Thermodynamic calculations were carried out and correlated to the experimental results. As-grown AlN layers were characterized by SEM and X-ray Diffraction. Surface morphology was studied by SEM and FEG-SEM and crystallographic orientations were obtained by X-ray diffraction on θ/2θ. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

In order to achieve AlN bulk growth, HTCVD chlorinated process is investigated. High growth rate and high crystalline quality are targeted for AlN films grown on (0001) 4H SiC at 1750°C. The precursors used are ammonia NH3 and aluminium chlorides AlClx species formed in situ by action of Cl2 on high purity Al wire. Influences of N/Al ratio in the gas phase on growth rate, crystalline state and microstructure are presented. Growth rates of up to 200 µm/h have been reached for polycrystalline layers. Thermodynamic calculations were carried out and correlated to the experimental results. As-grown AlN layers were characterized by SEM and X-ray Diffraction. Surface morphology is studied by SEM and FEG-SEM and crystallographic orientations were obtained by X-ray diffraction on θ/2θ.