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International audience; With an aim to enhance the stability and volatility of the heterometallic derivative [SnCl4(µ-OEt)2Ti(OEt)2(HOEt)2] (A), obtained conveniently and quantitatively as a simple adduct formula from the equivalent reaction of commercially available SnCl4 and Ti(OEt)4 in toluene/ethanol, its modification with 2,2,6,6-heptane-3,5-dione (thdH) is reported. The modified precursor [SnCl4(µ-OEt)2Ti(thd)(OEt)(HOEt)] (1), obtained from equimolar reaction of A and thdH, is stable at room temperature but rearranges on heating into A and [SnCl4(µ-OEt)2Ti(thd)2] (2), as confirmed by the vapor pressure measurements and DFT calculations. The heterometallic 2 can be obtained in excellent yield from the reaction of A and thdH in 1:2 molar ratio and is stable in solid and solution phase up to 200 °C. However, the asymmetric nature of its structure consisting of fragments of titanium β-diketonate and tin chloride connected by bridging ethoxo groups, leads to breakdown into two homometallic components in gas phase, leading to deposition of tin-rich metal oxide films on the substrate.

International audience; The present study is a critical assessment of thermochemical data for gaseous ruthenium oxides based on available experimental data. A full critical analysis and a reinterpretation of data are presented with a proposition for new accurate standard formation enthalpies values: Δ f H°2 98 (RuO 4 , g) =-197.6 ± 5.5 kJ mol-1 , Δ f H°2 98 (RuO 3 , g) =-53.0 ± 10 kJ mol-1 , Δ f H°2 98 (RuO 2 , g,) =158 ± 20 kJ mol-1 and Δ f H°2 98 (RuO, g) = 301 ± 28 kJ mol-1 .

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International audience; Identification of species in the gaseous phase of hydride materials and their mixtures (e.g. LiBH4–MgH2) is crucial for understanding the reactional mechanisms and diffusion kinetics of hydrogen across the different interfaces of phase segregation. This phase separation makes the characterization by conventional gas analysis techniques complicated and some analytical information could not be accessible. To overcome this surface/interface related issue, the study of the evolution of the gas phase emitted by the complex hydrides during ball-milling is considered. In this respect, an experimental set-up is designed by coupling a milling reactor with a mass spectrometer through a capillary tubing and an effusion Knudsen cell. A gas flow study (from molecular to viscous regimes) is performed in order to propose a suitable architecture of the entire device (ball-mill, capillary tubing, pipes, effusion cell compartment and pumping system) compatible with the mass spectrometric detection in terms of effused flow and molecular beam. Simulation of the flows and definition of their regimes nature at each stage of the pipes and vessels system is addressed as function of geometric parameters, upstream pressures, and pumping capacity on the downstream side (effusion cell). The study highlights the advantage of using a capillary tubing for the connection and ensure an optimal detection. Different working pressure conditions are demonstrated and associated to its length, meanwhile the diameter of the capillary has been demonstrated to be too sensitive to be varied.

The current energy transition imposes a rapid implementation of energy storage systems with high energy density and eminent regeneration and cycling efficiency. Metal hydrides are potential candidates for generalized energy storage, when coupled with fuel cell units and/or batteries. An overview of ongoing research is reported and discussed in this review work on the light of application as hydrogen and heat storage matrices, as well as thin films for hydrogen optical sensors. These include a selection of single-metal hydrides, Ti-V(Fe) based intermetallics, multi-principal element alloys (high-entropy alloys), and a series of novel synthetically accessible metal borohydrides. Metal hydride materials can be as well of important usefulness for MH-based electrodes with high capacity (e.g. MgH2 ~ 2000 mAh g-1) and solid-state electrolytes displaying high ionic conductivity suitable, respectively, for Li-ion and Li/Mg battery technologies. To boost further research and development directions some characterization techniques dedicated to the study of M-H interactions, their equilibrium reactions, and additional quantification of hydrogen concentration in thin film and bulk hydrides are presented at the end of this manuscript.

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International audience; Within the framework of purification of molten silicon for solar cells, phosphorus is one of few impurities that remains problematic. The present purpose is to develop a new method that leads to a final phosphorus concentration around 0.5 wppm. We have first focused on the main thermodynamic parameters that control the process: relevant thermodynamic parameters are taken from literature, such as activities, partial pressures and interaction coefficients. According to our results, distillation of phosphorus under vacuum occurs at high temperatures. Yet, the residual oxygen present in the vacuum is a hindrance to the distillation, since it evaporates in the form of silicon oxides. (C) 2015 The Electrochemical Society. All rights reserved.

International audience; A complete thermodynamic description of the Ca-O system is proposed including 3 rd generation modelling of crystalline CaO, liquid and amorphous CaO, and crystalline CaO2. Compared to previous modellings, a more robust description of the thermodynamic properties of the binary phases is achieved using data recently obtained by density functional theory calculations and molecular dynamics simulations. The heat capacity of crystalline CaO is reassessed, leading to a noticeably higher value below the melting point compared to previous modellings and resulting in a slightly higher standard entropy. It is highlighted that the parameters given in terms of polynomial functions of temperature that were employed so far in 3 rd generation models to describe anharmonic contributions in the heat capacity of compounds were not suited to satisfactorily describe the thermodynamic properties of crystalline CaO. It is suggested that this observation can be generalized to most refractory oxides. Alternative terms are proposed in the Gibbs energy function that give more flexibility in fitting the experimental data and lead to more numerically reasonable values for the parameters. The liquid and amorphous CaO phase is described using the two-state model, leading to a significant improvement in the description of its heat capacity. The description of crystalline CaO2 is also improved as only estimates of the thermodynamic properties of the compound were available in previous modellings of the system. Finally, phase equilibria data on the Ca-CaO liquidus is reviewed, and it is highlighted that slight discrepancies in the relatively low temperature measurements can lead to significantly different descriptions of the liquid phase. 2

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Thermodynamic data for the ruthenium oxide RuO2(s) are basic data for the calculation of gaseous release in the case of severe nuclear accident. The present study is a critical analysis of thermochemical data for RuO2(s) based on available published experimental data from calorimetry, vapor pressures in equilibrium with the diphasic Ru RuO2 and Electromotive Force Measurements EMF. A full critical review and reinterpretation of data are presented in this work with a proposition of new and accurate data for RuO2(s): C°p (RuO2, s, 298.15 K) = 56.42 ± 0.08 J·K-1 ·mol-1, S°298.15 (RuO2,s) = 46.15 ± 0.05 J·K-1 ·mol-1, and Δ; fH298 (RuO2,s) = −312.3 ± 1.6 kJ.mol-1

The present study focuses on a specific step of the metallurgical path of purification to provide solar-grade silicon: the removal of boron through the injection of H2O(g)-H2(g)-Ar(g) (cold gas process) or of Ar-H2-O2 plasma (plasma process) on stirred liquid silicon. We propose a way to predict silicon and boron flows from the liquid silicon surface by using a CFD model (©Ansys Fluent) combined with some results on one-dimensional diffusive-reactive models to consider the formation of silica aerosols in a layer above the liquid silicon. The comparison of the model with experimental results on cold gas processes provided satisfying results for cases with low and high concentrations of oxidants. This confirms that the choices of thermodynamic data of HBO(g) and the activity coefficient of boron in liquid silicon are suitable and that the hypotheses regarding similar diffusion mechanisms at the surface for HBO(g) and SiO(g) are appropriate. The reasons for similar diffusion mechanisms need further enquiry. We also studied the effect of pressure and geometric variations in the cold gas process. For some cases with high injection flows, the model slightly overestimates the boron extraction rate, and the overestimation increases with increasing injection flow. A single plasma experiment from SIMaP (France) was modeled, and the model results fit the experimental data on purification if we suppose that aerosols form, but it is not enough to draw conclusions about the formation of aerosols for plasma experiments. This is a post-peer-review, pre-copyedit version of an article published in [Metallurgical and Materials Transactions B] Locked until 16.3.2019 due to copyright restrictions. The final authenticated version is available online at: https://doi.org/10.1007/s11663-018-1228-5

Rationale This study analyzes molecular beam sampling by mass spectrometry by the Knudsen method using the so-called " restricted collimation device" . This device, defined by the field and source apertures, was proposed in order to eliminate any additional contribution to the genuine molecular beam of surface vaporizations coming from the vicinity of the effusion orifice as usually detected by the ion source of a mass spectrometer. Methods The molecular transmission of the " restricted collimation device" was calculated using a vaporization law under vacuum taking into account the real surface where the molecules are emitted, i.e., the sample evaporation surface in the Knudsen cell or the effusion orifice section, towards the ion source inlet by integration of elementary solid angles. Results An optimum is observed depending on the pair of selected apertures that define the restricted collimation device, i.e., the field and source apertures. This optimum is different from that previously calculated when taking into account only the solid angle, as defined by the restricted collimation device. Conclusions This difference is attributed to the previously approximate assumption that optimizing the restricted collimation solid angle automatically optimizes the sampling of the effused beam included in the restricted collimation angle. Moreover, the location of the evaporating surface for molecules traveling through the collimation device towards the ionization chamber remains an important factor: the distance between the sample evaporation surface and the field aperture is of paramount importance as it changes the molecular transmission to the mass spectrometer or to any target collection device in the conventional Knudsen method.

International audience; The gas phase of the CsI + CsOH system is analyzed by high temperature Knudsen cell mass spectrometry in order to confirm the existence of the Cs2IOH(g) complex molecule. The mass spectrometric analysis is quite complex since such molecules undergo dissociative ionization into fragment ions that mix with the same ions from dimers of the pure compounds in the same vapor phase. Varying the chemical conditions for vaporization by using different CsI + CsOH mixture contents showed that the ionization of the Cs2IOH(g) molecule led to five different fragment ions, Cs2OH+, Cs2I+, Cs+, CsOH+ and CsI+. This complex ionization pattern was studied in relation with previous assessed values for the vaporization of CsOH and CsI pure compounds in which monomer and dimer molecules are predominant. The equilibrium constant for the reaction CsI(g) + CsOH(g) = Cs2IOH(g) was determined and, after modeling the structure of the Cs2IOH molecule, the enthalpy of formation was determined using the third law of thermodynamics, as follows: Delta H-f degrees(Cs2IOH, g, 298.15 K) = -578 +/- 14.7 kJ.mole(-1). (c) 2013 Published by Elsevier Ltd.

Non-equilibrium vaporizations in Knudsen cells occur when the net rate of vaporization at the surface of the sample is slower than the rate of effusion. In such a situation, the description of the molecular flow exchanges in an effusion cell according to the Motzfeldt equation allows the determination of the evaporation coefficients from different pressure determinations of the same sample performed with different cell geometries. Further, the chemical signification of the value of the evaporation coefficients was not very often explained. Different thermodynamic analyses are presented on experimental results in order to explain the origin of retarded vaporizations of Al2O3 , SiO2 , AlN , BN and mixtures Si-SiO2 as well as amorphous SiO.

L’evaluation thermodynamique de la phase gazeuse des precurseurs pour les procedes de depots de couches atomiques (ALD) permet de definir les conditions operatoires optimales, de prevoir toutes les reactions possibles et d’estimer la consommation d'energie associee a d’eventuelles transformations. Cet article offre a l’ingenieur qui utilise le procede ALD avec des precurseurs organometalliques une methode de construction des proprietes de la phase gazeuse a partir des donnees structurelles des molecules. Les techniques experimentales qui permettent d’obtenir directement les informations sur la phase gazeuse et l’illustration d’exploitation de ces donnees thermodynamiques sont donnees.

International audience; The present study is a thermodynamic analysis of the different molecular flows occurring during the vacuum brazing of electrical vacuum bottles also called Vacuum In-terrupters (mentioned later as VI). Among the available impurities either coming from the Vacuum Interrupters components materials or from vacuum technology, the analysis is fo-cused on the oxygen since this impurity leads to formation of the more stable compounds, i.e. oxides. During the brazing cycles the resistors of the vacuum furnace and the VI materials including some braze components are the main sources of vapours that partly escape or make deposits on colder parts of the furnace. Vaporization and condensation processes are evaluated, their matter flows quantified and finally their interaction with residual oxygen calculated through a balance between input oxygen from vacuum or neutral gas and the different sources of oxygen coming from the parts under treatment. The enrichment of the VI materials and deposits with oxygen is evaluated as well as the limits required for vacuum conditions. The main conclusion is that present vacuum conditions allow correct working of the brazing sequence but in any other temperature steps or ramps, oxygen is trapped as oxides at the surface of the parts or accumulated in the bulk materials of the furnace.

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.

In the pursuit of smaller and faster devices manufacture, integration of new materials exhibiting a high dielectric permittivity is going on to replace silicon oxide SiO2 in Metal/Insulator/Metal (MIM) capacitors and in Dynamic Random Access Memory (DRAM). Among these materials, the zirconium oxide, ZrO2, in its highest dielectric permittivity phase (the high temperature tetragonal one) is investigated. Atomic Layer Deposition (ALD) of out-of-equilibrium ZrO2 thin films in 3D architectures is explored using various approaches: evaluation of the zirconium gaseous precursor, influence of operating conditions, thermal behavior of the deposited films. Thermodynamic models are used to better understand the film growth.

The most commonly use for gaseous precursors in CVD and ALD processes are organometallic molecules. These ones are generally thermally unstable at low temperatures (100 - 300{degree sign}C) and requires an understanding of its gas-phase chemical behavior. The thermal cracking of the gaseous precursor PDMAT has been studied by Mass Spectrometry. Ta[N(CH3)2]5(g), Ta[N(CH3)2]4(g), N(CH3)2(g) together with TaO[N(CH3)2]4(g) have been found to be the main molecules observed in the vapor phase originated from the PDMAT vaporization. The thermodynamic data of the O-free molecules have been evaluated from literature and statistical calculations. Comparison between experiments and thermodynamic simulations performed at different temperatures and pressures, evidenced kinetic limitations in the decomposition processes: ligand rupture and ligand decomposition. Furthermore, the experimental gas-phase study confirms the presence of oxygen containing molecules in the PDMAT cracking gaseous phase which explains the presence of oxygen in the deposited ALD TaN films. Thermodynamic simulations were also used to evaluate the use of hydrogen addition to the process.

International audience; Organometallic molecules are commonly used as gaseous precursors in Atomic Layer Deposition/Chemical Vapor Deposition (ALD/CVD) processes. However, the use of these molecules, which are generally thermally unstable at temperatures close to the deposition temperature, requires an understanding of their gas-phase chemical behavior. The thermal cracking of the gaseous precursor, pentakis(dimethylamino) tantalum (PDMAT), generally adopted in the ALD/CVD TaN deposition processes, has been studied in the temperature range from 343 to 723K using a specific reactor coupled with a high-temperature mass spectrometer. This reactor-built as tandem Knudsen cells - consists of two superimposed cells. The first stage reactor - an evaporation cell - provides an input saturated vapor flow operating from room temperature to 333K. The second stage cell, named the cracking cell, operated from 333 to 723K in the present study. Experiments showed the appearance of many gaseous species when the cracking temperature increased and, in particular, dimethylamine, corresponding to the saturated organic branches of PDMAT. Decomposition products of the HNC2H6 branch were observed at relatively high temperature, namely above 633K. This gas-phase study - as for the preceding saturated one - shows the presence of oxygen-containing molecules in PDMAT cracked vapor. Thus, it explains the systematic presence of oxygen contamination in the deposited TaN films observed in ALD/CVD industrial processes.

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.

The volatility of pentakis(dimethylamido) tantalum (PDMAT) has been studied in the temperature range from − 15 to 60 °C. A special Knudsen cell reactor coupled to a high temperature mass spectrometer, was specifically designed for the study of organometallic precursors. It is composed of an evaporation/sublimation chamber (− 30 to 200 °C), which can be tight closed – like a vacuum chamber – in order to protect the precursors which are likely to be very unstable vs. moisture and atmospheric components. This chamber can be independently weighted for calibration purpose of the mass spectrometric experiments. During experiments, the effusion orifice is externally opened for direct mass spectrometric measurements of saturated vapour pressures. The device has been tested using the well-known mercury vapour pressure. First results obtained for the vaporization of PDMAT are presented.

Thermodynamic properties of condensed and gas phases of the CsOH compound are assessed. Thermal functions of the condensed phase are those already selected in a preceding compilation with some important modification concerning the melting temperature of CsOH(s, γ) that has been re-evaluated to be T = 649 ± 2 K from recent mass spectrometric determination certifying the total lack of water impurity and from a comparison between the CsOH–H2O and the RbOH–H2O phase diagram shapes. The vapor phase thermodynamic properties – dealing mainly with the CsOH(g) and Cs2O2H2(g) molecules – are re-evaluated from the selection of a new dimerization equilibrium constant and a thorough analysis of preceding vaporization experiments. Besides, flame studies that give directly the dissociation energies of the Cs OH bond are analyzed from the main assumed reactions as well as considering the different analytical methods as used. The reliability of flame results have also been analyzed in this work by thermodynamic adiabatic calculations of the flame. The mean formation enthalpies as retained in the present analysis are: Δ f H ° ( CsOH,g, 298.15 K ) = - 252.7 ± 7.0 kJ · mol - 1 , and Δ f H ° ( Cs 2 O 2 H 2 ,g, 298.15 K ) = - 652.0 ± 11.7 kJ · mol - 1 .

The dissolution of aluminium in cryolitic melts is the major cause of the loss in current efficiency during the industrial process of aluminium electrolysis. These melts are corrosive and not easy to handle experimentally. Using the laser-heated device, associated with a tightly closed crucible, we have studied different compositions of the NaF–AlF3–Al system by 27Al, 23Na and 19F in situ NMR at 1030 °C. The samples were also characterized after rapid cooling at room temperature by MAS NMR, X-rays diffraction and microscopy in order to describe the structure of the solidified phases. To cite this article: I. Nuta et al., C. R. Chimie 7 (2004).

This study analyzes molecular beam sampling by mass spectrometry by the Knudsen method using the so-called " restricted collimation device" . This device, defined by the field and source apertures, was proposed in order to eliminate any additional contribution to the genuine molecular beam of surface vaporizations coming from the vicinity of the effusion orifice as usually detected by the ion source of a mass spectrometer.The molecular transmission of the " restricted collimation device" was calculated using a vaporization law under vacuum taking into account the real surface where the molecules are emitted, i.e., the sample evaporation surface in the Knudsen cell or the effusion orifice section, towards the ion source inlet by integration of elementary solid angles.An optimum is observed depending on the pair of selected apertures that define the restricted collimation device, i.e., the field and source apertures. This optimum is different from that previously calculated when taking into account only the solid angle, as defined by the restricted collimation device.This difference is attributed to the previously approximate assumption that optimizing the restricted collimation solid angle automatically optimizes the sampling of the effused beam included in the restricted collimation angle. Moreover, the location of the evaporating surface for molecules traveling through the collimation device towards the ionization chamber remains an important factor: the distance between the sample evaporation surface and the field aperture is of paramount importance as it changes the molecular transmission to the mass spectrometer or to any target collection device in the conventional Knudsen method.

Thermodynamic data for the CsI compound, including solid, liquid and are important for the calculation of iodine release in the case of severe nuclear accident: – (i) for accurate evaluation of the nature of iodine containing volatile compounds, and – (ii) for scaling kinetic data that are important in the calculations of intermediate states at short release time. The present study is a critical analysis of thermochemical data for the CsI compound based on available literature data. Revised values of the heat capacity for the liquid phase are proposed within the range of available experimental thermodynamic determinations. Vapor pressure data are assessed and accurate values of the standard enthalpies of formation of the gaseous monomer CsI(g) and dimer Cs2I2(g) are proposed: Δ f H ∘ ( CsI,g, 298.15 K ) = - 153.3 ± 1.8 kJ · mol - 1 , Δ f H ∘ ( Cs 2 I 2 ,g, 298.15 K ) = - 469.2 ± 5 kJ · mol - 1 . The trimer Cs3I3(g) also exists as well as tetramer species in smaller amounts, less than 0.1% up to 1500 K.

The development and the design of materials and/or the processes of their fabrication are generally very time consumer and with expensive operations. Various methods of development can be conceived. Often, "empirical" approaches are adopted: the choice of the experimental parameters is established either on technological or commercial criteria, the optimization being the results of a “trial and error” approach, or on the results of design of experiments (DOE) approach targeted at a property of a material or a parameter of a very particular process. Another approach is to use process modeling: to simulate the process by a more or less simplified model. The modeling of gas-solid materials fabrication processes brings together several physical and chemical fields with variable complexity, starting from thermodynamics and\or kinetics studies up to the mass and heat transport coupled with databases and with thermodynamic and/or kinetics transport properties.

International audience; Previous work has established that when a few volume percent of transition metal-based particles are dispersed in nano-grained MgH2 powders, H-sorption times are reduced to a few minutes at temperatures near 300 degrees C. We report H-sorption cycles performed in a mini-tank of Mg powders containing such particle dispersions placed in monochromatised synchrotron light going through the powders for in situ X-ray diffraction in transmission at the European Synchrotron Radiation Facility. The three selected catalyst particle dispersions were Nb2O5, FeF3 and amorphous Ti0.7Ni0.3. The main result is that these very different 2nd phase particle additions have a similar impact on H-sorption in the sense that in all three MgH2 powders, H-sorption goes to completion as T approximate to 270 degrees C reached during heating. The commonality of the three selected particle dispersions, two crystalline and one amorphous, is that their thermodynamic properties are consistent with the chemical conditions of immiscibility and H-attractive interfaces within MgH2 powders. Once this condition is satisfied, the acceleration of the kinetics of sorption is likely dominated by the extent (specific area) of such internal interfaces.

In situ high temperature NMR spectroscopy has been used to characterize the interactions between aluminum metal and cryolitic melts. (27)Al, (23)Na, and (19)F NMR spectra have been acquired in NaF-AlF(3) and NaF-AlF(3)-Al melts over a wide range of compositions. The evolution of the signals evidence a chemical reaction between the metal and the salt. The different samples have been also described after solidification at room temperature by Environmental Scanning Electronic Microscopy, high resolution solid state NMR, and X-ray diffraction. The combination of in situ high temperature NMR characterization of the melts, with experimental description of solidified samples after cooling, evidence an enrichment of the melts with AlF(3) and different reactions with metallic aluminum depending on the initial bath composition.

International audience; New calorimetric determinations of molar heat capacity C(p,m) of lithium tetrahydroborate (LiBH(4)) were performed in order to analyze the origin of the previously observed "anomaly" before the polymorphous transition at 386 K. The above room temperature dependence of LiBH(4) C(p,m) was measured until approaching the melting point of the compound at 553 K and the abnormal behaviour was attributed to lattice defects independent of the main crystalline phase transition. As a result, lower entropy of the transition Delta(trs)S = 13.11 +/- 0.23J K(-1) mol(-1) than that proposed in literature was obtained, which is in agreement with the observed anisotropy and crystal density decrease before the transition from recent X-ray diffraction indexing. An estimate of the liquid C(p,m) of LiBH(4) "molten salt" is proposed. (C) 2011 Elsevier B.V. All rights reserved.

In this study, we report the TaN ALD film growth from PDMAT, in Through-Silicon Vias with NH3 as nitrogen precursor and H2 as reducing agent. We report deposits on planar and patterned substrates with high aspect ratios (5 to 20). As a reference, TaN was deposited from PDMAT and NH3 only, and the influence of H2 injections as reducing agent is reported. H2 was introduced in two manners: either during the PDMAT pulse or during the NH3 pulse. The samples obtained when H2 is introduced during the PDMAT pulse show a lower amount of oxygen than the reference deposited with only PDMAT and NH3 as precursors. Unexpectedly, when H2 is introduced during the NH3 pulse, the oxygen content increases compared to the reference. An experimental study of the deposition parameters was carried out by in situ microgravimetry to explain the H2 influence on the TaN deposition.

A special reactor coupled to a high-temperature mass spectrometer was specifically designed for the study of vaporization and thermal cracking of organometallic precursors. This reactor has two kinds of settings. One is a single Knudsen effusion cell which enables the analysis of the composition of saturated vapors and the determination of the partial pressure of each gaseous molecule in equilibrium with its condensed phase. This cell is an evaporation/sublimation cell (operating from 243 to 473 K), which can be tightly closed – like a vacuum chamber – in order to protect organometallic compounds against moisture and atmospheric components. This cell can be independently weighed usefully to evaluate the equilibrium vapor pressures of the sample using the mass-loss method. During experiments, the effusion aperture is externally opened for direct mass spectrometric measurements. The other setting dedicated to the study of thermal decomposition of gaseous molecules consists of a set of tandem cells: the previously described Knudsen cell and a cracking cell (operating from 293 to 973 K). Copyright © 2009 John Wiley & Sons, Ltd.

International audience; The development of an ALD process, which is based on the sequential self-limiting surface reactions from generally two gaseous precursors, requires knowledge of the reactions mechanisms. Most of the studies of ALD modeling have been focused on the surface reactions. However, the most common use of organometallic molecule as gaseous precursors which are generally thermally unstable at temperatures close to the deposition one requires also an understanding of the gas-phase chemical reactions, as for the usual CVD processes. This presentation describes specific examples of the application of mass spectrometry to the determination of the thermal stability and behavior of organometallic precursors used for the ALD deposition of TaN and ZrO2 ultra thin layers.

The thermal stability of the pentakis(dimethylamino) tantalum (PDMAT) precursor used in the Atomic Layer Deposition (ALD) TaN process has been studied from 343 to 723 K using a specific reactor coupled with a Knudsen cell mass spectrometer. This reactor is built as tandem cells: an evaporation cell and a cracking cell. This reactor tries to simulate the conditions found in the bubbler of the ALD system by the evaporation cell and in the hot reaction zone of ALD by the cracking cell. Experiments showed that the saturated gaseous phase (originated from PDMAT evaporation) is composed of Ta(N(CH3)2)4(g), and in smaller amounts of Ta(N(CH3)2)5(g) and OTaN4C8H24(g). Cracking experiments, performed at different temperatures, showed that PDMAT is a minor component of the gaseous phase, meanwhile Ta(N(CH3)2)4(g), and HN(CH3)2(g), are the major gaseous species that decompose at higher temperatures. Oxygen containing molecules are also observed in all temperature range.

The developments of NMR spectroscopy at high temperature now allow us to study in situ a great number of molten materials. This technique is sensitive to local environment around the nucleus, and gives selective and quantitative information not limited by the disorder existing in liquids. NMR can thus provide a microscopic approach of the structure and dynamics of molten compounds by means of knowledge of different species existing in the melt, the average coordination, or nature of the first neighbors. We present high temperature NMR approach of molten fluoride systems of nuclear interest and description of the local structure around each nucleus, and its evolution with the composition. To cite this article: C. Bessada et al., C. R. Chimie 9 (2006).

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La purification du silicium à un certain degré est requis pour l'industrie photovoltaïque. Par voie métallurgique, le phosphore est éliminé du silicium fondu dans un four à induction sous vide.Cette étude présente la simulation du processus de déphosphoration du silicium en prenant en compte un facteur jusqu'alors négligé, à savoir la présence d'oxygène résiduel.Un travail d'optimisation thermodynamique du système Si - P est effectué, où la solubilité du phosphore dans le silicium est notamment déterminée. Les coefficients d'activité qui découlent de celle-ci sont incorporés dans un algorithme créé pour simuler ce phénomène. En s'appuyant également sur des données issues de la littérature, ce programme prédit le temps de distillation d'un échantillon de silicium de type n ainsi que sa perte de masse en fonction de la pression d'oxygène dans l'enceinte.La validation expérimentale de ces résultats est envisagée en utilisant un dispositif de lévitation électromagnétique. Il permet de faire fondre un échantillon de silicium sans creuset contaminant et avec une atmosphère contrôlée., Purifying silicon to a certain degree is needed in the photovoltaic industry. In the metallurgical route, phosphorus is removed from molten silicon in an induction vacuum refining furnace.This study presents the simulation of the silicon dephosphorization process that takes into account a neglected factor thus far, namely the residual oxygen amount.A thermodynamic assessment is performed for the Si - P system, and the phosphorus solubility in silicon is determined. Resulting activity coefficients are incorporated in an algorithm created to simulate this phenomenon. By also using other literature data, this program predicts the distillation time of a n-type silicon sample as well as its weight loss as a function of the oxygen pressure in the enclosure.The experimental validation of those results is intended with an electromagnetic levitation device. It enables to melt a silicon sample without any contaminant crucible and under a controlled atmosphere.

Hydrides for solid-state hydrogen storage are one of the future solutions - pollutant free - for the storage and the transport of energy. Among the candidates, LiBH4 was selected considering its high gravimetric hydrogen capacity (up to 13.6 wt.% H2). This material has thermodynamic and kinetic properties insufficiently established to be included in future applications. Its decomposition can be facilitated within the presence of the hydride MgH2. Thus, the composite MgH2-xLiBH4 (0< x< 3.5) reactivated by high energy ball-milling, was studied regarding its microstructural properties and stability of the phases. The desorption reaction of hydrogen, with or without additives, shows the appearance of additional phases accompanying the principal reaction. Heat capacity measurements of LiBH4 revealed the presence of an abnormal behaviour before the polymorphous transition (Ttrs = 386 K), attributed to the increase of crystal defects in agreement with the existence of a hypo-stoichiometric domaine LiBH4- observed at higher temperatures. The stability of the three-phase system LiBH4-LiH-B was studied resulting to the principal reaction of decomposition: LiBH4(s,l) LiH(s) + B(s) + 1,5H2(g). Vapour pressure measurements of LiBH4 showed that H2 is the major component of decomposition with minor species such as B2H6 and BH3. The thermodynamic properties of LiBH4 were critically assessed, gathering the new data with those existing in the literature, in the aim of modelling of reactions occurring in hydride mixtures., Le stockage d'hydrogène en phase solide sous forme d'hydrures, est l'une des solutions nonpolluantes futures pour le stockage et le transport de l'énergie. Parmi les matériaux candidats, LiBH4 a été sélectionné vu sa capacité gravimétrique élevée en hydrogène (jusqu'à 13,6 % H2 en masse). Ce matériaux possède des propriétés thermodynamiques et cinétiques insuffisamment établies pour comprendre son comportement dans les applications futures. Sa décomposition peut être facilitée en présence de l'hydrure MgH2. Ainsi, le composite MgH2-xLiBH4 (0