Optical and mechanical properties of amorphous Mg-Si-O-N thin films deposited by reactive magnetron sputtering

In this work, amorphous thin films in Mg-Si-O-N system were prepared in order to investigate the dependence of optical and mechanical properties on Mg composition. Reactive RF magnetron co-sputtering from magnesium and silicon targets were used for the deposition of Mg-Si-O-N thin films. Films were deposited on float glass, silica wafers and sapphire substrates in an Ar, N2 and O2 gas mixture. X-ray photoelectron spectroscopy, atomic force microscopy, scanning electron microscopy, spectroscopic ellipsometry, and nanoindentation were employed to characterize the composition, surface morphology, and properties of the films

Evolution structurale des céramiques (Si)-B-C sous sollicitations thermomécaniques

Self-healing matrices are composed of SiC, B-C and Si-B-C multilayers deposited by chemical vapour deposition (CVD). The boron-rich layers (Si)-B-C are amorphous in their as-deposited state but crystallize at high temperature (T ≥ 1000 °C). Various analyses (XRD, Raman spectroscopy, NMR, neutron diffraction, XANES) were used to characterize the local structure of the as-processed and heat-treated ceramics. The local structure of heat-treated ceramics was also confirmed by molecular dynamic ab initio simulations. The structure consists of icosahedral units as in B4C but faulted and connected with each other through tetrahedral CB4-XCX and trigonal BC3 sites. In Si-B-C ceramics, the same amorphous phase forms a continuum embedding SiC clusters. The structural evolution of the ceramics in inert atmosphere were studied as a function of temperature (1100°C ≤ T ≤ 1400 °C) and time (t ≤ 1 h). The metastability of the materials leads to fast kinetics of reorganization. When T and t increase, one observes successively the formation free-sp2 carbon, the crystallization of B4C and, in Si-B-C ceramics, the coarsening of the SiC nanocrystallites. The high temperature mechanical properties have also been assessed by tensile tests on Cf/(Si)-B-Cm microcomposites. The materials undergo a complex transient behaviour which is strongly temperature dependent due to the structural changes.Les matrices céramiques autocicatrisantes sont constituées d’une alternance de couches de SiC, B-C et Si-B-C, déposées par voie gazeuse (CVD). Les couches borées (Si)-B-C sont amorphes après élaboration et leur structure évolue à haute température (T ≥ 1000 °C). Diverses caractérisations (XRD, spectroscopie Raman, NMR, diffusion des neutrons, XANES) ont permis de préciser la structure locale des céramiques brutes d'élaboration. Celle-ci a par la suite été validée par des simulations par dynamique moléculaire ab initio. Elle est constituée de motifs icosaédriques, similaires à ceux de B4C, mais fautés et reliés entre eux par des environnements tétravalents CB4-xCx et trivalents BC3. Dans le cas des matériaux Si-B-C, cette même phase amorphe forme un continuum incluant des clusters de SiC. L’évolution structurale de ces céramiques sous atmosphère inerte a été étudiée en fonction de la température (1100°C ≤ T ≤ 1400 °C) et du temps (t ≤ 1 h). Le caractère métastable des matériaux induit une cinétique de réorganisation rapide. L'évolution structurale se traduit successivement, à T et t croissants, par l’apparition de carbone libre sp2, la cristallisation de B4C, ainsi que la croissance de nanocristallites de SiC dans les matériaux Si-B-C. Les propriétés mécaniques ont également été caractérisées à haute température à l’aide d’essais sur microcomposites Cf/(Si)-B-Cm. Les matériaux font preuve d’un comportement transitoire complexe et fortement dépendant de la température du fait de leur évolution structurale

Evolution structurale des céramiques (Si)-B-C sous sollicitations thermomécaniques

Self-healing matrices are composed of SiC, B-C and Si-B-C multilayers deposited by chemical vapour deposition (CVD). The boron-rich layers (Si)-B-C are amorphous in their as-deposited state but crystallize at high temperature (T ≥ 1000 °C). Various analyses (XRD, Raman spectroscopy, NMR, neutron diffraction, XANES) were used to characterize the local structure of the as-processed and heat-treated ceramics. The local structure of heat-treated ceramics was also confirmed by molecular dynamic ab initio simulations. The structure consists of icosahedral units as in B4C but faulted and connected with each other through tetrahedral CB4-XCX and trigonal BC3 sites. In Si-B-C ceramics, the same amorphous phase forms a continuum embedding SiC clusters. The structural evolution of the ceramics in inert atmosphere were studied as a function of temperature (1100°C ≤ T ≤ 1400 °C) and time (t ≤ 1 h). The metastability of the materials leads to fast kinetics of reorganization. When T and t increase, one observes successively the formation free-sp2 carbon, the crystallization of B4C and, in Si-B-C ceramics, the coarsening of the SiC nanocrystallites. The high temperature mechanical properties have also been assessed by tensile tests on Cf/(Si)-B-Cm microcomposites. The materials undergo a complex transient behaviour which is strongly temperature dependent due to the structural changes.Les matrices céramiques autocicatrisantes sont constituées d’une alternance de couches de SiC, B-C et Si-B-C, déposées par voie gazeuse (CVD). Les couches borées (Si)-B-C sont amorphes après élaboration et leur structure évolue à haute température (T ≥ 1000 °C). Diverses caractérisations (XRD, spectroscopie Raman, NMR, diffusion des neutrons, XANES) ont permis de préciser la structure locale des céramiques brutes d'élaboration. Celle-ci a par la suite été validée par des simulations par dynamique moléculaire ab initio. Elle est constituée de motifs icosaédriques, similaires à ceux de B4C, mais fautés et reliés entre eux par des environnements tétravalents CB4-xCx et trivalents BC3. Dans le cas des matériaux Si-B-C, cette même phase amorphe forme un continuum incluant des clusters de SiC. L’évolution structurale de ces céramiques sous atmosphère inerte a été étudiée en fonction de la température (1100°C ≤ T ≤ 1400 °C) et du temps (t ≤ 1 h). Le caractère métastable des matériaux induit une cinétique de réorganisation rapide. L'évolution structurale se traduit successivement, à T et t croissants, par l’apparition de carbone libre sp2, la cristallisation de B4C, ainsi que la croissance de nanocristallites de SiC dans les matériaux Si-B-C. Les propriétés mécaniques ont également été caractérisées à haute température à l’aide d’essais sur microcomposites Cf/(Si)-B-Cm. Les matériaux font preuve d’un comportement transitoire complexe et fortement dépendant de la température du fait de leur évolution structurale

Structural changes of CVD (Si)-B-C ceramics under thermomechanical treatments

Les matrices céramiques autocicatrisantes sont constituées d’une alternance de couches de SiC, B-C et Si-B-C, déposées par voie gazeuse (CVD). Les couches borées (Si)-B-C sont amorphes après élaboration et leur structure évolue à haute température (T ≥ 1000 °C). Diverses caractérisations (XRD, spectroscopie Raman, NMR, diffusion des neutrons, XANES) ont permis de préciser la structure locale des céramiques brutes d'élaboration. Celle-ci a par la suite été validée par des simulations par dynamique moléculaire ab initio. Elle est constituée de motifs icosaédriques, similaires à ceux de B4C, mais fautés et reliés entre eux par des environnements tétravalents CB4-xCx et trivalents BC3. Dans le cas des matériaux Si-B-C, cette même phase amorphe forme un continuum incluant des clusters de SiC. L’évolution structurale de ces céramiques sous atmosphère inerte a été étudiée en fonction de la température (1100°C ≤ T ≤ 1400 °C) et du temps (t ≤ 1 h). Le caractère métastable des matériaux induit une cinétique de réorganisation rapide. L'évolution structurale se traduit successivement, à T et t croissants, par l’apparition de carbone libre sp2, la cristallisation de B4C, ainsi que la croissance de nanocristallites de SiC dans les matériaux Si-B-C. Les propriétés mécaniques ont également été caractérisées à haute température à l’aide d’essais sur microcomposites Cf/(Si)-B-Cm. Les matériaux font preuve d’un comportement transitoire complexe et fortement dépendant de la température du fait de leur évolution structurale.Self-healing matrices are composed of SiC, B-C and Si-B-C multilayers deposited by chemical vapour deposition (CVD). The boron-rich layers (Si)-B-C are amorphous in their as-deposited state but crystallize at high temperature (T ≥ 1000 °C). Various analyses (XRD, Raman spectroscopy, NMR, neutron diffraction, XANES) were used to characterize the local structure of the as-processed and heat-treated ceramics. The local structure of heat-treated ceramics was also confirmed by molecular dynamic ab initio simulations. The structure consists of icosahedral units as in B4C but faulted and connected with each other through tetrahedral CB4-XCX and trigonal BC3 sites. In Si-B-C ceramics, the same amorphous phase forms a continuum embedding SiC clusters. The structural evolution of the ceramics in inert atmosphere were studied as a function of temperature (1100°C ≤ T ≤ 1400 °C) and time (t ≤ 1 h). The metastability of the materials leads to fast kinetics of reorganization. When T and t increase, one observes successively the formation free-sp2 carbon, the crystallization of B4C and, in Si-B-C ceramics, the coarsening of the SiC nanocrystallites. The high temperature mechanical properties have also been assessed by tensile tests on Cf/(Si)-B-Cm microcomposites. The materials undergo a complex transient behaviour which is strongly temperature dependent due to the structural changes

Structural changes of CVD (Si)-B-C ceramics under thermomechanical treatments

Les matrices céramiques autocicatrisantes sont constituées d’une alternance de couches de SiC, B-C et Si-B-C, déposées par voie gazeuse (CVD). Les couches borées (Si)-B-C sont amorphes après élaboration et leur structure évolue à haute température (T ≥ 1000 °C). Diverses caractérisations (XRD, spectroscopie Raman, NMR, diffusion des neutrons, XANES) ont permis de préciser la structure locale des céramiques brutes d'élaboration. Celle-ci a par la suite été validée par des simulations par dynamique moléculaire ab initio. Elle est constituée de motifs icosaédriques, similaires à ceux de B4C, mais fautés et reliés entre eux par des environnements tétravalents CB4-xCx et trivalents BC3. Dans le cas des matériaux Si-B-C, cette même phase amorphe forme un continuum incluant des clusters de SiC. L’évolution structurale de ces céramiques sous atmosphère inerte a été étudiée en fonction de la température (1100°C ≤ T ≤ 1400 °C) et du temps (t ≤ 1 h). Le caractère métastable des matériaux induit une cinétique de réorganisation rapide. L'évolution structurale se traduit successivement, à T et t croissants, par l’apparition de carbone libre sp2, la cristallisation de B4C, ainsi que la croissance de nanocristallites de SiC dans les matériaux Si-B-C. Les propriétés mécaniques ont également été caractérisées à haute température à l’aide d’essais sur microcomposites Cf/(Si)-B-Cm. Les matériaux font preuve d’un comportement transitoire complexe et fortement dépendant de la température du fait de leur évolution structurale.Self-healing matrices are composed of SiC, B-C and Si-B-C multilayers deposited by chemical vapour deposition (CVD). The boron-rich layers (Si)-B-C are amorphous in their as-deposited state but crystallize at high temperature (T ≥ 1000 °C). Various analyses (XRD, Raman spectroscopy, NMR, neutron diffraction, XANES) were used to characterize the local structure of the as-processed and heat-treated ceramics. The local structure of heat-treated ceramics was also confirmed by molecular dynamic ab initio simulations. The structure consists of icosahedral units as in B4C but faulted and connected with each other through tetrahedral CB4-XCX and trigonal BC3 sites. In Si-B-C ceramics, the same amorphous phase forms a continuum embedding SiC clusters. The structural evolution of the ceramics in inert atmosphere were studied as a function of temperature (1100°C ≤ T ≤ 1400 °C) and time (t ≤ 1 h). The metastability of the materials leads to fast kinetics of reorganization. When T and t increase, one observes successively the formation free-sp2 carbon, the crystallization of B4C and, in Si-B-C ceramics, the coarsening of the SiC nanocrystallites. The high temperature mechanical properties have also been assessed by tensile tests on Cf/(Si)-B-Cm microcomposites. The materials undergo a complex transient behaviour which is strongly temperature dependent due to the structural changes

Structural changes of CVD Si-B-C coating under thermal annealing

International audienceSi B C coatings were prepared by chemical vapor deposition (CVD) from CH3SiCl3/BCl3/H-2 gas mixtures at 900-1000 degrees C and under low total pressure (5 kPa). A selection of coatings was synthesized at different deposition temperatures and initial compositions of the gas phase. They were characterized in terms of morphology, elemental composition and structure, both at the atomic scale (by nuclear magnetic resonance and X-ray absorption) and long range (by X-ray diffraction and transmission electron microscopy). The as-deposited materials consist of an amorphous boron carbide phase (a-BxC) including icosahedron-like units and enclosing SiC nanocrystals. The SiC grain size increases with the silicon concentration in the solid, i.e. with the initial CH3SiCl3 concentration in the gas phase. The amorphous structure and the excess carbon are partly accommodated by unusual BC3 environments in boron carbides. Thermal annealing in inert atmosphere at increasing temperature and time gradually modifies their structure at short and long range. A disordered polycyclic carbon phase appears first, while the SiC grain size increases progressively, and rhombohedral boron carbide (B4C) finally crystallizes around 1300 degrees C. The organization of the SiC4 sites is improved and the BC3 sites are partially transformed into more usual intra and intericosahedrat environments. Whereas the temperature has a strong influence on the structural changes, the annealing time has only a limited effect, the structure being rapidly "frozen" in a metastable state. (C) 2012 Elsevier B.V. All rights reserved

Coloriages spéculaires

Ce texte est la présentation de la solution de l'équipe France 1 à un problème de recherche posé à l'ITYM (rédigée par G. Pallier et C. Freppel). Le problème initial concerne une condition de coloriage d'un damier. Les membres de cette équipe ont traduit ce problème en termes de graphes, puis ont mis en place une approche algorithmique qui permet d'obtenir le comportement asymptotique à partir du cas d'un damier réduit à une ligne

Phosphors based on NaZr2(PO4)3-type calcium and strontium phosphates activated with Eu2+ and Sm3+

Ca0.5Zr2(PO4)3:Eu2+, Sr0.5Zr2(PO4)3:Eu2+, and Ca0.5Zr2(PO4)3:Eu2+, Sm3+ orthophosphates prepared through precipitation using sol-gel processes are analogs of NaZr2(PO4)3 (NZP) and crystallize in space group R Their crystallographic parameters determined by X ray diffraction are consistent with the interatomic distances extracted from EXAFS data. Their luminescence spectra obtained under excitation in the range 300-400 nm contain emission bands between 425 and 525 nm. Substitution of the larger sized cat ions Eu2+ and Sm3+ for Ca2+ shifts the emission bands to shorter wavelengths and reduces their width because of the decrease in the effect of the crystal field. Analysis of the spectra indicates that Eu2+ occupies two types of crystallographic sites (independent interstitial sites of different sizes and shapes in the NZP framework structure). Codoping with Eu and Sm has ensured luminescence with chromaticity coordinates approaching those of white light: (x = 0.27, y = 0.34)

Optical and mechanical properties of amorphous Mg-Si-O-N thin films deposited by reactive magnetron sputtering

In this work, amorphous thin films in Mg-Si-O-N system typically containing amp;gt; 15 at.% Mg and 35 at.% N were prepared in order to investigate especially the dependence of optical and mechanical properties on Mg composition. Reactive RF magnetron co-sputtering from magnesium and silicon targets were used for the deposition of Mg-Si-O-N thin films. Films were deposited on float glass, silica wafers and sapphire substrates in an Ar, N-2 and O-2 gas mixture. X-ray photoelectron spectroscopy, atomic force microscopy, scanning electron microscopy, spectroscopic ellipsometry, and nanoindentation were employed to characterize the composition, surface morphology, and properties of the films. The films consist of N and Mg contents up to 40 at.% and 28 at.%, respectively and have good adhesion to substrates and are chemically inert. The thickness and roughness of the films increased with increasing content of Mg. Both hardness (16-21 GPa) and reduced elastic modulus (120-176 GPa) are strongly correlated with the amount of Mg content. The refractive index up to 2.01 and extinction coefficient up to 0.18 were found to increase with Mg content. The optical band gap (3.1-4.3) decreases with increasing the Mg content. Thin film deposited at substrate temperature of 100 degrees C shows a lower value of hardness (10 GPa), refractive index (1.75), and higher values of reduced elastic modulus (124 GPa) as compared to the thin film deposited at 310 degrees C and 510 degrees C respectively, under identical synthesis parameters.Funding Agencies|VINNOVA [2015-04809]; AForsk Foundation [14-457]; European Research Council under the European Community/ERC [335383]; Swedish Foundation for Strategic Research (SSF); Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009 00971]</p

Thermal, electrical, and mechanical properties of hard nitrogen-alloyed Cr thin films deposited by magnetron sputtering

Cr-N based materials, including stoichiometric CrN and Cr:N with a wide range of nitrogen contents, are commonly used as hard and corrosion-resistant coatings. Cr-rich films in this materials system can retain the bcc structure of metallic Cr with few percent of dissolved nitrogen, which can be used for tailoring the mechanical, thermal, and electrical properties. Here, we investigated low nitrogen containing Cr thin films deposited by high ion assisted magnetron sputtering with a substrate temperature of 200 degrees C. With the gas flow ratio maintained at f(N2/Ar) = 0.02, the substrate bias and the target power allows for control of the film composition (0.03 &amp;lt; N/Cr &amp;lt; 0.34). The films comprise a mixture of bcc-Cr and hexagonal Cr2N1-delta phases. The mechanical properties studied by nanoindentation and Brillouin inelastic light scattering revealed a hardening effect due to the multiphase nanostructure. The mechanical properties of the Cr:N films depend on the residual stress, on the amount of h-Cr2N1-delta phase and on the nanostructuring nature of the coatings. A maximum hardness of 37 GPa was achieved for a dense film with a Youngs modulus of 340 GPa, a shear modulus of 118 GPa, and a relatively low thermal conductivity of 7 W/mK.Funding Agencies|VINNOVA Competence Centre FunMat-II [2016-05156]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009 00971]; Knut and Alice Wallenberg Foundation [KAW-2020.0196]; Swedish Research Council (VR) [2016-03365, 2021-03826]</p