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In previous work, nanopowders have been obtained during the deposition of thin layers from Hexamethyldisiloxane (HMDSO) using low frequency plasma. The aim of this work is the study of the ...

International audience; The present study proposes an alternative eco-friendly method to prepare a thin composite coating based on graphene embedded in siloxane polymers which can be used as application for the corrosion protection of steel. The nanocomposite coatings were elaborated by a dielectric barrier discharge using a nebulized colloidal suspension of graphene nanosheets (GNs) dispersed in hexamethyldisiloxane (HMDSO) used as the precursor for the polymer matrix. After obtaining a stable colloidal solution, it was nebulized into the plasma reactor to form a plasma polymer (pp) coating from HMDSO (ppHMDSO) in which GNs were incorporated (GN@ppHMDSO) on the mild steel substrate. The chemical structure of the hybrid coatings was characterized by X-ray photoelectron spectroscopy and Fourier transform infrared spectrometry. Raman spectra of GNs and GN@ppHMDSO coatings suggest the existence of charge transfer between the GNs and the HMDSO matrix. Furthermore, scanning electron microscopy confirms the synthesis of micro/nanocomposite with a fairly homogeneous dispersion of the GNs in the polymer matrix. The corrosion resistance of the samples was evaluated by electrochemical impedance spectroscopy which showed that the hybrid coatings GN@ppHMDSO deposited by a one-step atmospheric pressure plasma process, presented excellent anticorrosion performance with 99.99% of protection efficiency.

International audience; Polyurethane (PUR) ester foams are found in 20th century museum collections in a variety of artworks and objects. Unfortunately PUR ester foams are prone to degradation, and present e among other plastic materials e important conservation issues. They are very sensitive to moisture, and their hy-drolysis leads to several degradation processes such as yellowing and embrittlement, drastically changing the artwork aspect and materiality. Few researches were conducted on the consolidation of PUR ester foams. In this paper, a curative treatment that should limit the hydrolysis of the degraded PUR foams, and that mechanically consolidate the foams' structure is presented. This work focuses on the innovative use of alkoxysilanes mixtures and on their application modes on foam samples. Different binary mixtures of OTMS (n-octyltriethoxysilane, hydrophobic and trifunctional) and AMDES (3-aminopropylmethyldiethoxysilane, hydrophilic and bifunctional) in various proportions were tested. The kinetic evolution of their polycondensation using spectral decomposition of FTIR spectra revealed that OTMS does not react with atmospheric water vapor and that the presence of an amine (AMDES) is required to initiate its polycondensation. This result justifies the use of a mixture of both siloxanes. The different treatments were then applied on artificially degraded PUR ester foams using concentration of 2.5% and 10% of alkoxysilanes in HMDS (hexamethyldisiloxane, solvent). The treatment was applied by pouring the solution over the samples and resulted in a homogeneous impreg-nation of the foams, whereas vaporization modes were unsuccessful regarding the penetration of the treatment in the foam cells. The hydrophilicity of the treatments was characterized using water contact angle measurements and it appears that at least 25% of hydrophobic OTMS in the mixture is needed to decrease the wettability of the samples, in order to avoid further hydrolysis. The reinforcement properties were studied using mechanical tests, and resulted in a need of a solution of 10% (in HMDS) for an acceptable reinforcement. Finally, colorimetric measurements showed that the visual aspect of the degraded samples was improved with the treatment.

Chemical sensors generally suffer from the cross sensitivity problem. For this purpose, the identification of volatile organic compounds (VOCs) using a unselective sensor requires a combination of sensors followed by pattern recognition methods. In the current study, four quartz crystal microbalances (QCMs) were coated by plasma enhanced chemical vapor deposition (PECVD) with the pure vapor of hexamethyldisiloxane (HMDSO) at monomer pressures ranging from 5 to 40 Pa. The coated QCM-based sensors were used for the detection of volatile organic molecules. The sensors responses towards different VOCs showed the possibility to tune the chemical affinity of the sensors by changing only the monomer pressure during the sensitive layer deposition process. Fourier transform infrared (FTIR) spectroscopy and atomic force microscopy (AFM) were used to investigate chemical composition and surface morphology of the coated QCM sensors, respectively. The sensor responses have been used as a database for the ident...

Cyclic formation of dust nanoparticles in hexamethyldisiloxane (HMDSO, Si2O(CH3)6)-argon RF discharge with pulsed injection of HMDSO was studied using time-resolved mass spectrometry (MS) and optical emission spectroscopy (OES). A large amount of C2H2, considered as promoter of dust nucleation in hydrocarbon plasmas, was found as a by-product of HMDSO fragmentation. Although no negative ions were detected the presence of C2H2 in the HMDSO-Ar discharge supports the hypothesis of a dust growth mechanism based on negative ions being trapped in the plasma. It was found that at the beginning of each cycle of dust formation during α–γ′ transition, the discharge sustaining process is accompanied by a strong consumption of the HMDSO main by-products: HMDSO-15, CH4 and C2H2. At the end of the cycle, corresponding to the progressive disappearance of dust, the discharge switches back to its initial conditions. The beginning of the inverse transition, i.e. γ′–α, is most likely correlated to the growing void in the dust cloud and dust disappearance. In presence of dust nanoparticles, Ar+ and ArH+ dominate the ion population and consequently the discharge maintenance. When the dust particles gradually disappear, the discharge is rather controlled by Si2O(CH3)5+ ions. Moreover, the increased amount of such heavy ions reveals clearly their important income in the dust repelling process due to the drag force on the large sized dust even at short time scale during the injection time of HMDSO. Atomic-H production increases during the transition from dusty plasma to HMDSO-rich plasma with no dust and its role is associated to a delay in the dust nucleation stage.

International audience; This work examines the growth dynamics of TiO2-SiO2 nanocomposite coatings in plane-to-plane Dielectric Barrier Discharges (DBDs) at atmospheric pressure operated in a Townsend regime using nebulized TiO2 colloidal suspension in hexamethyldisiloxane as the growth precursors. For low-frequency (LF) sinusoidal voltages applied to the DBD cell, with voltage amplitudes lower than the one required for discharge breakdown, Scanning Electron Microscopy of silicon substrates placed on the bottom DBD electrode reveals significant deposition of TiO2 nanoparticles (NPs) close to the discharge entrance. On the other hand, at higher frequencies (HF), the number of TiO2 NPs deposited strongly decreases due to their “trapping” in the oscillating voltage and their transport along the gas flow lines. Based on these findings, a combined LF-HF voltage waveform is proposed and used to achieve significant and spatially uniform deposition of TiO2 NPs across the whole substrate surface. For higher voltage amplitudes, in the presence of hexamethyldisiloxane and nitrous oxide for plasma-enhanced chemical vapor deposition of inorganic layers, it is found that TiO2 NPs become fully embedded into a silica-like matrix. Similar Raman spectra are obtained for as-prepared TiO2 NPs and for nanocomposite TiO2-SiO2 coating, suggesting that plasma exposure does not significantly alter the crystalline structure of the TiO2 NPs injected into the discharge.

International audience; Oxygen and water vapor barrier coatings were made by plasma enhanced chemical vapor deposition on a polymer multilayer substrate. Plasma deposition was realized on the external PET layer of the substrate by using a RF plasma source and two different precursors (trimethylsilane (TMS) and hexamethyldisiloxane (HMDSO)). Two types of monolayer deposits (SiOx and SiOxCzHw) were investigated for each precursor. The structure and composition of the deposited coatings were characterized by FTIR spectroscopy and XPS analysis. Their surface topography was imaged by AFM and the surface energy was determined thanks to contact angle measurements. Oxygen and water barrier properties of the coated substrate were interpreted in terms of coating structure and composition and TMS was identified as the most interesting precursor for enhanced barrier properties. The sensitivity of the coatings to thermal exposure was also investigated. A multilayer deposit approach consisting in alternating organic and inorganic deposited layers was developed. By this route, additional significant enhancement of oxygen and water barrier performances was achieved upon 3 layer deposition.

Optical emission spectroscopy was used to analyze the very-low-frequency cyclic evolution of the electron energy and density caused by repetitive formation and loss of dust nanoparticles in argon plasmas with pulsed injection of hexamethyldisiloxane (HMDSO, [CH3]6Si2O). After elaborating a Boltzmann diagram for Ar high-lying levels and a collisional-radiative model for Ar 2p (Paschen notation) states, temperatures characterizing the low- and high-energy parts of the electron population were calculated. Relative electron densities were also estimated from relative line emission intensities. Both temperatures increase when the dust occupation increases, and then decrease when dust is lost. The opposite trend was observed for the electron density. Such cyclic behaviors of the electron energy and electron density in the HMDSO-containing plasmas are in good agreement with the evolution processes in dusty plasmas, in which the formation of negative ions followed by an electron attachment on the surfaces of the nanoparticles is a critical phenomenon driving dust growth.

International audience; In the context of a universal search for alternatives to chromate-based coatings, which are toxic for both human beings and the environment, a multilayer coating for Al protection purposes is developed and investigated in the current work. The first layer is selected to be a hexamethyldisiloxane-based plasma polymer film (PPF), deposited by Plasma Enhanced Chemical Vapor Deposition (PECVD), due to a number of interesting features that are characteristic of plasma polymers. The second layer is synthesized via the polymerization of the 2-ethylhexyl acrylate monomer initiated from the free radicals trapped on the surface of the PPF during its growth. A subsequent layer of a copolymer of 2-ethylhexyl acrylate and glycidyl methacrylate, poly(EHA-co-GMA), is deposited by spin coating to increase the corrosion resistance of the coating. An improvement in the anti-corrosion properties of the multilayer coating by approximately three orders of magnitude as compared to the uncoated Al substrate is observed. Further enhancement of the adhesion and scratch resistance properties is addressed via UV-crosslinking and the incorporation of in situ generated silica nanoparticles into the final layer.

International audience; The ionization cross section of hexamethyldisiloxane (HMDSO) molecules (m/z = 162), pentamethyldisiloxane radicals (m/z = 147) and tetramethyl hydro disiloxane radicals (m/z = 133) have been measured versus electron energy up to 30 eV. The radicals are produced selectively by two different mechanisms which are the energy transfer by collision with metastable argon species and the VUV photolysis. The absolute ionization cross section values are determined and analytical functions derived from the Binary-Encounter-Bethe theory (BEB) are given to calculate the direct ionization of molecules or radicals versus electron energy lower than 30 eV.

International audience; A range of hybrid, SiOCH films were deposited on silicon substrates within a radio frequency plasma reactor using hexamethyldisiloxane (HMDSO) as a precursor. The plasma polymerized films were deposited at various HMDSO/argon/oxygen ratios. The composition and structure, at microscopic and nanoscopic levels, of the deposited films were determined by external reflection and transmission Fourier Transform Infrared (FTIR) spectroscopy as well as by X-Ray Photoelectron Spectroscopy (XPS). The content of carbon and oxygen in films were found to be inversely proportional to each other. XPS results showed that the outermost surface of the deposited films are nanoporous and coexist with microporosity which was revealed by electron microscopy. The structure of deposited coatings is anisotropic as was documented by polarized external reflection FTIR spectroscopy. Several correlations between the film chemical composition, surface structure, and macroscopic properties of the films such as: hydrophobicity and hydrophilicity were established.

Different hexamethyldisiloxane (HMDSO) dissociation processes are investigated by means of absorption spectroscopy and mass spectrometry. All of these processes are expected to occur in plasma containing Ar-HMDSO gas mixture. We successively study interactions of the HMDSO molecule with electrons (energy ranges from 15 to 70 eV), with Ar((3)P(2)) metastable species (internal energy 11.55 eV) and with VUV photon (7.3 to 10.79 eV). The studies of HMDSO interactions with Ar((3)P(2)) and VUV photon provide new results concerning the dissociation pathways and the collision cross-sections. In the case of Ar((3)P(2)), the dissociation mechanisms result mainly in Si-C or Si-O bond breaking, producing SiMe(2,1) radicals. Less efficient mechanisms involve also Si-C and Si-O bond breaking producing Me, Si(2)Me(5)O, or SiMe(3), on one hand, and, on the other hand, Si-C and C-H bond breaking producing Si(2)Me(4)OH. In the case of photon interaction, the dissociation process is more selective and mainly produces Si(2)OMe(5) pentadisiloxane and methyl radicals due to Si-C bond breaking. Si-O bond breaking produces also SiMe(3) in a lower concentration. Dissociation cross-section values of HMDSO ranging from σ = 45 × 10(-20) m(2) to 180 × 10(-20) m(2) and from σ = 0.7 × 10(-22) m(2) to 18.3 × 10(-22) m(2), correspond to a global dissociation mechanism by Ar((3)P(2)) collision and to a selective dissociation mechanism (producing Si(2)OMe(5) and Me) by VUV photon interaction, respectively. All results are compared and discussed.

SiO x H y C z micrometer thick films are deposited from an argon/hexamethyldisiloxane (HMDSO) mixture on Si (1 0 0) substrate by plasma enhanced chemical vapor deposition (PECVD) process using a Torche a Injection Axiale (TIA) at atmospheric pressure. Both main effects of deposition parameters and first-order interactions on the hardness and elastically modulus are investigated from a Rechtschaffner design of experiments (DOEs). This screening design, based on series of two and three-level saturated design, allows the reduction of the total number of experiments by a factor 1.5 in the present work, without compromising the quality of the results. First conclusions demonstrate that torch–substrate distance and HMDSO flow rates are the main influent factors affecting the mechanical behavior of the deposited films, which is basically explained by their indirect effects both on the precursor dissociation in plasma phase and on film growth mechanisms. Additionally, the use of a desirability approach enables to converge towards a multi-criteria optimum of deposition conditions for the expected mechanical properties.

Plasma-enhanced (PE)CVD is used to create, in a single step, a superhydrophobic (SH) (water contact angle over 150°) layer starting from hexamethyldisiloxane (HMDSO) vapor (i.e., without fluorine) in a low-frequency, capacitively coupled plasma reactor under low pressure. Several SH microstructures are obtained, depending on experimental parameters (gas pressures, substrate rotation, pulsed glow discharge, plasma duration) deposited on various substrate types. The presented technique can produce thin SH transparent films (below 1 µm) or thicker ones (above 10 µm) to modify the surface of a macroporous hydrophilic membrane in order to render it SH with a water transmembrane pressure close to 2 bar.

The effect of surface temperature on the deposition of silicon oxide (SiO x ) films with a non-thermal microwave axial injection torch (TIA) was investigated in an open air reactor. Argon was used as plasma gas and hexamethyldisiloxane (Si 2 O 2 C 6 H 18 ) as silicon precursor. The parametric study reported here focuses on the influence of the substrate temperature on the morphological and chemical properties of the films deposited in the interval [0 °C–130 °C]. A similar effect of low and high surface temperature on the deposition process and on the microstructure of the deposited films was highlighted. Macroscopically, particles were promptly produced in the gas phase and incorporated to the film, which generates high surface roughness. Microscopically, FTIR results have shown a high carbon contamination of the deposited films at low and high temperatures, resulting in understoichiometric SiO x films. They have also demonstrated that an optimum growth window for smooth and particle free SiO x was to keep the surface temperature between 30 and 60 °C. Simple reaction mechanisms for powder formation and continuous silicon oxide thin films growth are suggested for each temperature ranges.

In this study, Doppler broadening energy spectroscopy (DBES) combined with slow positron beam was used to discuss the effect of substrate types on the fine structure of a plasma-polymerized SiOCH layer as a function of depth. From the SEM pictures, the SiOCH films formed on different substrates showed hemispherical macrostructures, and the deposition rate was dependent on the mean pore size. It appears that the morphology of the plasma-polymerized SiOCH films was associated with the porosity-related characteristics of the substrate such as the size/shape of pores. As deposited on the MCE-022 substrate (mixed cellulose esters membrane with a mean pore size of 0.22 μm) with a nodular structure, the SiOCH films had pillar-like structures and high gas permeabilities. DBES results showed that the SiOCH films deposited on different substrates were composed of three layers: the SiOCH bulk layer, the transition layer, and the substrate. It was observed that the microstructure of the SiOCH films was affected layer by layer; a higher surface pore size in the substrates induced thicker transition layers with higher microporosities and led to thinner bulk layers having higher S parameter values during the plasma polymerization. It was also observed that the change in O 2 /N 2 selectivity was consistent with the DBES analysis results. The gas separation performance and DBES analysis results agreed with each other.

SiO x H y C z nanometric layers are deposited from hexamethyldisiloxane by atmospheric pressure microwave plasma torch on Si(100) substrates submitted to temperatures varying on the range [0 °C; 120 °C]. Atomic force microscopy (AFM) characterizations of samples grown at intermediate substrate temperatures (~30 °C) demonstrate a layer-by-layer growth (Frank van der Merwe growth) leading to smooth flat and compact films while films deposited at lower and higher substrates temperatures show an island-like growth (Volmer-Weber growth) generating a high surface roughness. Concomitantly, a detailed infrared spectroscopy analysis of the growing films evidences structural modifications due to changes in the bond types, Si-O-Si conformation and stoichiometry correlated with scanning electron microscopy and AFM characterizations. Then, deposition conditions and specific microstructure are selected with the aim of generating 3-dimensional SiO x H y C z nanostructure arrays on nanoindented Si (100) templates. The first results are discussed.

International audience; Most of polymers resulting from plasma polymerization exhibit a structure, which is very complex and different from those synthesized by conventional polymerization methods. The molecular structure of such plasma polymers is difficult to assess, but its characterization is a crucial issue. Mass spectrometry (MS) seems to be a promising analytical approach to get this molecular information. The chemical structure of a ppHMDSO (plasma polymer HexaMethylDiSiloxane) film, deposited by means of atmospheric pressure dielectric barrier discharge process, has first been characterized by means of FTIR spectroscopy. Additional insights in the polymer structure were provided by mass spectrometric techniques. MALDI-TOF-MS and ESI-Q-TOF-MS analyses were carried out to obtain information on high molecular weight oligomers and/or small polymers col lected in the THF soluble fraction of a ppHMDSO film. Although uncertainty still remains about the detected species, it could be concluded they were copolymers such as poly(dimethylsiloxane-co-methylsiloxane) or poly(dimethylsiloxane-co-SiO(2)) with a number of monomers up to 20, and some structures could be proposed for the end groups.

An atmospheric pressure dielectric barrier discharge burning in nitrogen with a small admixture of hexamethyldisiloxane (HMDSO) was used for the deposition of thin organosilicon films. The thin films were deposited on glass, silicon and polycarbonate substrates, and the substrate temperature during the deposition process was increased up to values within the range 25–150 °C in order to obtain hard SiO x -like thin films. The properties of the discharge were studied by means of optical emission spectroscopy and electrical measurements. The deposited films were characterized by the Rutherford backscattering and elastic recoil detection methods, x-ray photoelectron spectroscopy, infrared spectroscopy measurements, ellipsometry and the depth sensing indentation technique. It was found that the films' properties depend significantly on the substrate temperature at deposition. An increase in substrate temperature from 25 to 150 °C led to an increase in film hardness from 0.4 to 7 GPa and the film chemical composition changed from CH x Si y O z to SiO x H y . The films were transparent in the visible range.

International audience; Self-organization of SiO2 nanodots is obtained by chemical vapor deposition out of hexamethyldisiloxane (HMDSO) and atmospheric pressure remote Ar–O2 plasma operating at high temperature (1200–1600 K). The dewetting of the film being deposited when it is still thin enough (1 μm), droplet-shaped coatings with a Gaussian distribution in thickness over their width are deposited. The coatings are submitted to high compressive stress. When it is relaxed, “nestlike structures” made of nanoribbons are synthesized.

An SiO x C y H z /mixed cellulose ester (MCE) composite membrane was fabricated by plasma deposition of hexamethyldisiloxane (HMDSO) monomer on the surface of an MCE substrate. The purpose is to apply the membrane for the oxygen enrichment of an O 2 /N 2 mixture. The variation in the fine structure of the plasma-polymerized layers (SiO x C y H z ) prepared at different plasma conditions was identified using slow-positron beams. Although the SiO x C y H z layers displayed similar FTIR spectra, they evidently showed differences based on the data from Doppler broadening energy spectroscopy (DBES) and positron annihilation lifetime spectroscopy (PALS). These data indicated distinct differences in the physical structure despite the similarities in the chemical structure of the films. The deposited layer (mixture of HMDSO species and MCE species) had more hydrocarbon group, resulting in a looser structure of the deposited layer at the initial period of plasma deposition. However, the MCE species content of the deposited layer decreased with the deposition time, and the deposited layer became denser. From PALS, the o -Ps lifetime ( τ 3 , corresponding to the free-volume size) decreased along the plasma deposition layer growth direction. These results corresponded with those obtained from XPS very well. The plasma-deposited membrane was applied for O 2 /N 2 separation. The O 2 permeability decreased and the concentration of O 2 in the permeate increased with the deposition time and as the plasma power increased.

Low pressure Plasma Enhanced Chemical Vapour Deposition is commonly used to deposit insulators on temperature sensitive substrates. In these processes, the ion bombardment experienced by films during its growth is known to have benefits but also some disadvantages on material properties. In the present paper, we investigate the influence of this bombardment on the structure and the electrical properties of SiO 2 -like film deposited from oxygen/hexamethyldisiloxane radiofrequency plasma in continuous and pulsed modes. First, we studied the ion kinetics thanks to time-resolved measurements by Langmuir probe. After, we showed the ion bombardment in such plasma controls the OH bond content in deposited films. Finally, we highlight the impressive reduction of fixed charge and interface state densities in films obtained in pulsed mode due to a lower ion bombardment.

Wettability of polyimide (PI) and polypropylene (PP) films have been improved using SiO x -like thin layers deposited from a mixture of hexamethyldisiloxane (HMDSO) and oxygen in a microwave distributed electron cyclotron resonance plasma reactor. The films wettability evolution behaviors were evaluated through the results of contact angle measurements, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The plasma depositions of SiO x thin layers in presence of VUV radiation induce a contact angle decrease to about 7° and 35° for PI and PP films, respectively. XPS data showed that such difference in wettability is attributed to the increase of hydrophilic group's proportion at the surface of coated PI films due to VUV irradiation. AFM images showed that the PI surface topography remains relatively smooth when coated in presence of VUV radiation. However, in the case of PP films, AFM images revealed the growth of irregular structure due to a substrate etching effect supported by VUV radiation. For polymers coated without VUV irradiation, the deconvolution of the C1s peaks showed a significant decrease of C O bonds for both PI and PP substrates.

The present work deals with the study of helium microwave plasmas at atmospheric pressure generated in a resonant cavity and their applications in surface treatment. First of all, a state of art of microwave atmospheric pressure plasmas and their applications is presented. Next, a collisional-radiative model for pure helium discharge and post-discharge is described. The results of the model are compared to experimental data obtained at 2500 K and a coherent set of cross-sections and rate constants is obtained for these conditions. Emission and absorption spectroscopy diagnostics are employed to characterize the helium plasma. The gas temperature is determined by the rotational synthetic spectra method. The evolution of the gas temperature, as a function of the input power, the concentration and the nature of impurities in helium, is measured. It turns out that the plasma volume plays a significant role on the gas temperature. The He(23S) concentration is determined by laser absorption in pulsed and continuous mode. In continuous mode, the metastable concentration is divided by 3 with 360 ppm of impurity, regardless of the nature of the impurity. Nevertheless, during the post-discharge, in pulsed mode, the nature of the impurity plays an important role. These measurements support the idea that He+ and not He2+ is the main ion. Concerning the applications, only post-discharges are utilized. We demonstrate that deposition of SiOx using hexamethyldisiloxane as precursor can be efficient. We show that titanium nitriding at high temperature is possible, Les travaux présentés dans ce mémoire portent sur l'étude des plasmas d'hélium générés par micro-ondes en cavité résonnante à la pression atmosphérique et sur leurs applications en traitement de surfaces. Tout d'abord, un état de l'art sur les plasmas micro-ondes à la pression atmosphérique et leurs applications est présenté. Ensuite, un modèle collisionnel-radiatif de la décharge et de la post-décharge d'hélium pur est établi. Les résultats du modèle sont comparés aux mesures expérimentales obtenues à 2500 K et un jeu de sections efficaces et de constantes cinétiques valables pour ces conditions est proposé. Expérimentalement, des analyses par spectroscopie d'émission et d'absorption sont employées. La température du gaz est déterminée par la méthode du spectre rotationnel synthétique en fonction de la puissance, de la concentration et de la nature des impuretés introduites dans l'hélium. Il s'avère que le volume du plasma est un paramètre déterminant sur la température du gaz. La concentration du métastable He(23S), en décharge continue et pulsée, est déterminée par absorption laser. En décharge continue, la concentration du métastable est divisée par trois avec 360 ppm d'impureté, la nature de l'impureté n'ayant pas d'importance. En revanche, en post-décharge la nature de l'impureté est déterminante. Les mesures réalisées indiquent que He+ et non He2+ serait l'ion majoritaire. Concernant les applications de ce type de plasma, nous avons travaillé en post-décharge uniquement. Nous avons démontré la faisabilité du procédé de dépôt de SiOx à partir d'hexaméthyldisiloxane. Nous avons aussi montré que la nitruration du titane à haute température était possible

The present work deals with the study of helium microwave plasmas at atmospheric pressure generated in a resonant cavity and their applications in surface treatment. First of all, a state of art of microwave atmospheric pressure plasmas and their applications is presented. Next, a collisional-radiative model for pure helium discharge and post-discharge is described. The results of the model are compared to experimental data obtained at 2500 K and a coherent set of cross-sections and rate constants is obtained for these conditions. Emission and absorption spectroscopy diagnostics are employed to characterize the helium plasma. The gas temperature is determined by the rotational synthetic spectra method. The evolution of the gas temperature, as a function of the input power, the concentration and the nature of impurities in helium, is measured. It turns out that the plasma volume plays a significant role on the gas temperature. The He(23S) concentration is determined by laser absorption in pulsed and continuous mode. In continuous mode, the metastable concentration is divided by 3 with 360 ppm of impurity, regardless of the nature of the impurity. Nevertheless, during the post-discharge, in pulsed mode, the nature of the impurity plays an important role. These measurements support the idea that He+ and not He2+ is the main ion. Concerning the applications, only post-discharges are utilized. We demonstrate that deposition of SiOx using hexamethyldisiloxane as precursor can be efficient. We show that titanium nitriding at high temperature is possible, Les travaux présentés dans ce mémoire portent sur l'étude des plasmas d'hélium générés par micro-ondes en cavité résonnante à la pression atmosphérique et sur leurs applications en traitement de surfaces. Tout d'abord, un état de l'art sur les plasmas micro-ondes à la pression atmosphérique et leurs applications est présenté. Ensuite, un modèle collisionnel-radiatif de la décharge et de la post-décharge d'hélium pur est établi. Les résultats du modèle sont comparés aux mesures expérimentales obtenues à 2500 K et un jeu de sections efficaces et de constantes cinétiques valables pour ces conditions est proposé. Expérimentalement, des analyses par spectroscopie d'émission et d'absorption sont employées. La température du gaz est déterminée par la méthode du spectre rotationnel synthétique en fonction de la puissance, de la concentration et de la nature des impuretés introduites dans l'hélium. Il s'avère que le volume du plasma est un paramètre déterminant sur la température du gaz. La concentration du métastable He(23S), en décharge continue et pulsée, est déterminée par absorption laser. En décharge continue, la concentration du métastable est divisée par trois avec 360 ppm d'impureté, la nature de l'impureté n'ayant pas d'importance. En revanche, en post-décharge la nature de l'impureté est déterminante. Les mesures réalisées indiquent que He+ et non He2+ serait l'ion majoritaire. Concernant les applications de ce type de plasma, nous avons travaillé en post-décharge uniquement. Nous avons démontré la faisabilité du procédé de dépôt de SiOx à partir d'hexaméthyldisiloxane. Nous avons aussi montré que la nitruration du titane à haute température était possible

In the present paper, O-atom kinetics is investigated in low pressure (around 0.7?Pa) O2/hexamethyldisiloxane pulsed plasmas by time-resolved optical emission spectroscopy. In order to distinguish direct O-atom excitation by electron impact from dissociative excitation of O2, CO, CO2 and H2O molecules formed in O2/HMDSO plasmas, measurements were first carried out in pure O2, CO2 and H2O plasmas. From these measurements it was concluded that direct O-atom excitation by electron impact was the dominant mechanism and that actinometry could be used to monitor O-atom kinetics provided molecular oxygen dissociative excitation is taken into account. Second, the surface O-atom loss coefficient measured in oxygen pulsed plasmas is in agreement with the literature (10?1) and is five times higher than the one measured in CO2 pulsed plasma (2 ? 10?2). This latter result is attributed to competition effect at surface sites between CO and O. Finally, we point out the influence of water molecule wall adsorption on O-atom kinetics in H2O and O2/HMDSO pulsed plasmas. During the post-discharge, H2O and/or OH molecules adsorbed at the reactor walls strongly reduce the O-atom loss coefficient. During the discharge, ion bombardment enhances desorption of molecules leading to an increase in the O-atom loss coefficient.

The present work deals with the synthesis of Zn-Si-O and Ti-Si-O composite thin films by a hybrid process. The coatings are prepared by combining PECVD (Plasma Enhanced Chemical Vapour Deposition) of silicon oxide from hexamethyldisiloxane (HMDSO-Si2C6H180) and reactive sputtering of a zinc or a titanium target. Any composition of the deposited layer can be obtained from zinc oxide or titanium oxide to silicon oxide, by controlling the HMDSO flow rate in the reactor. The morphologies evolve from columnar to dense by adding silicon in the coating. Moreover, a competitive deposition process takes place between PECVD and sputtering. The critical flow rates above which the PECVD silicon oxide deposition takes place on the substrate and on the target can be described from measurements of the thin film deposition rates as a function of the HMDSO flow rate. The coating caracterisations show that they are, near the coating-substrate interface, made of a mixture of non-stoechiometric oxides whose composition is different from a ZnO+SiO2 or a TiO2+SiO2 mixing. Titanium and silicon are in excess near the coating-substrate interface, respectively in the Ti-Si-O and Zn-Si-O thin films. Then the atomic concentrations of titanium and silicon progressively decrease when reaching the surface of the thin film. These behaviours are correlated with an increase of the temperature during the first phase of deposition that increases the PECVD deposition kinetics and determines the contamination state of the target; Ce travail s'intéresse à la synthèse de films minces composites Zn-Si-O et Ti-Si-O à l'aide d'un procédé hybride combinant le dépôt de silice par PECVD (Plasma Enhanced Chemical Vapour Deposition) à partir du précurseur organométallique hexaméthyldisiloxane (HMDSO-Si2C6H180), et la pulvérisation réactive de zinc ou de titane. L'élaboration de revêtements dont la composition s'échelonne d'un oxyde métallique ZnOx ou TiOx à la silice est rendue possible en agissant sur le débit du précurseur. L'ajout de silicium dans le revêtement fait évoluer sa morphologie de colonnaire à dense. De plus un phénomène de compétition entre les composantes PECVD et pulvérisation du procédé est mis en évidence. Ainsi la mesure des vitesses de dépôt en fonction du débit d'HMDSO permet de déterminer les valeurs de débits critiques de précurseurs à partir desquelles le dépôt de silice par PECVD est initié, et pour lesquelles le recouvrement de la cible par le dépôt de silice se produit. Les caractérisations des revêtements montrent que ceux-ci sont constitués, dans une zone proche de l'interface avec l'acier d'un mélange d'oxydes non stoechiométriques qui diffère de manière importante d'un mélange ZnO+SiO2 ou TiO2+SiO2. Pour les revêtements de type Ti-Si-O le titane est en excès dans la zone proche de l'interface tandis que dans les revêtements de type Zn-Si-O le silicium est en excès. On observe alors une décroissance progressive de la concentration atomique respectivement de titane et de silicium lorsqu'on approche de la surface du revêtement. Ces évolutions peuvent être reliées à un effet de l'augmentation de la température dans la première phase de l'élaboration, qui agit sur la cinétique de dépôt par PECVD et conditionne l'état de contamination de la cible

The present work deals with the synthesis of Zn-Si-O and Ti-Si-O composite thin films by a hybrid process. The coatings are prepared by combining PECVD (Plasma Enhanced Chemical Vapour Deposition) of silicon oxide from hexamethyldisiloxane (HMDSO-Si2C6H180) and reactive sputtering of a zinc or a titanium target. Any composition of the deposited layer can be obtained from zinc oxide or titanium oxide to silicon oxide, by controlling the HMDSO flow rate in the reactor. The morphologies evolve from columnar to dense by adding silicon in the coating. Moreover, a competitive deposition process takes place between PECVD and sputtering. The critical flow rates above which the PECVD silicon oxide deposition takes place on the substrate and on the target can be described from measurements of the thin film deposition rates as a function of the HMDSO flow rate. The coating caracterisations show that they are, near the coating-substrate interface, made of a mixture of non-stoechiometric oxides whose composition is different from a ZnO+SiO2 or a TiO2+SiO2 mixing. Titanium and silicon are in excess near the coating-substrate interface, respectively in the Ti-Si-O and Zn-Si-O thin films. Then the atomic concentrations of titanium and silicon progressively decrease when reaching the surface of the thin film. These behaviours are correlated with an increase of the temperature during the first phase of deposition that increases the PECVD deposition kinetics and determines the contamination state of the target, Ce travail s'intéresse à la synthèse de films minces composites Zn-Si-O et Ti-Si-O à l'aide d'un procédé hybride combinant le dépôt de silice par PECVD (Plasma Enhanced Chemical Vapour Deposition) à partir du précurseur organométallique hexaméthyldisiloxane (HMDSO-Si2C6H180), et la pulvérisation réactive de zinc ou de titane. L'élaboration de revêtements dont la composition s'échelonne d'un oxyde métallique ZnOx ou TiOx à la silice est rendue possible en agissant sur le débit du précurseur. L'ajout de silicium dans le revêtement fait évoluer sa morphologie de colonnaire à dense. De plus un phénomène de compétition entre les composantes PECVD et pulvérisation du procédé est mis en évidence. Ainsi la mesure des vitesses de dépôt en fonction du débit d'HMDSO permet de déterminer les valeurs de débits critiques de précurseurs à partir desquelles le dépôt de silice par PECVD est initié, et pour lesquelles le recouvrement de la cible par le dépôt de silice se produit. Les caractérisations des revêtements montrent que ceux-ci sont constitués, dans une zone proche de l'interface avec l'acier d'un mélange d'oxydes non stoechiométriques qui diffère de manière importante d'un mélange ZnO+SiO2 ou TiO2+SiO2. Pour les revêtements de type Ti-Si-O le titane est en excès dans la zone proche de l'interface tandis que dans les revêtements de type Zn-Si-O le silicium est en excès. On observe alors une décroissance progressive de la concentration atomique respectivement de titane et de silicium lorsqu'on approche de la surface du revêtement. Ces évolutions peuvent être reliées à un effet de l'augmentation de la température dans la première phase de l'élaboration, qui agit sur la cinétique de dépôt par PECVD et conditionne l'état de contamination de la cible

X-ray photoelectron spectroscopy and Auger spectroscopy studies of gas-phase hexamethyldisiloxane (HMDSO) are presented. The photodissociation of this molecule is studied using various experimental coincidence techniques. We compare the fragmentation pathways observed after core ionization followed by Auger decay and after valence double photoionization of the molecule. A strongly selective production of the doubly charged tetramethyldisiloxane ion is observed in the low binding-energy regions. Theoretical calculations are carried out to tentatively explain the stability of the produced dication.

International audience; Films synthesized by plasma enhanced chemical vapor deposition from a mixture of octamethyltrisiloxane and hexamethylcyclotrisiloxane have been studied regarding to their preparation, deposition, chemical composition and membrane properties according to hydrocarbon vapor selectivities of solubility.;Composition of the plasma glow discharge in neutral species has been studied by mass spectrometry whereas structural information of the deposited membranes has been extracted from Fourier transform infra-red (FTIR) spectroscopy. In the deposition conditions presented here leading to plasma-polymerized films, heavy radicals mostly contribute to their growth and their chemical composition. Depending on the precursors ratio in the plasma, i.e. linear and cyclic clusters ratio in the deposited material, solubility of selectivity against nitrogen of the deposited material varies from 50 up to 150 for hexane vapor. (C) 2003 Elsevier B.V. All rights reserved.

International audience; Thin ppHMDSO plasma polymer films deposited in a low pressure hexamethyldisiloxane plasma have been exposed to oxygen plasmas ignited in the same reactor at different pressures. The time evolution of the ppHMDSO film during the oxygen plasma treatment (30 s to one hour) was monitored in situ bymulti-wavelength ellipsometry. The treated films were analysed ex situ by X-ray reflectometry, spectroscopic ellipsometry and infrared spectroscopy. On the other hand, the oxygen atom density aswell as the oxygen ion density and energy weremeasured by actinometry and Langmuir probe measurements, respectively. For all the investigated oxygen plasma conditions, the film thickness and extinction coefficient significantly decrease. If the O2þ ion energy is low enough (typically less than 10 eV) the 65nm ppHMDSO can even be transformed into a 45 nm-thick carbon free SiO2-like film. In contrast, if the ion energy is higher than 10 eV, the ppHMDSOis only partially oxidised. Based on the oxygen atom flux measurement, it is concluded that the number of oxygen atoms impinging on the ppHMDSO film is not the only parameter which governs the treatment. The oxygen ion energy appears to have a key role as far as energetic ions are likely to induce the formation of a dense superficial SiO2 layer which prevents the diffusion of O atoms in the film and the out diffusion of volatile oxidation products.

Thin SiO x C y H z film membranes were deposited from two different organosilicon precursors, one cyclic and one linear, in a low-frequency plasma polymerisation process. The ability of the films for effective recovery of various organic contaminants from aqueous waste was tested using the process of pervaporation. Four separate organic components, phenol, chloroform, pyridine and methylisobutylketone (MIBK), each representative of an industrially significant family of chemicals, were chosen for evaluation. Trends between the pervaporation performances of plasma polysiloxane membranes and the composite plasma parameter V / FM ( V : input voltage; F : monomer flow rate; M : monomer molecular weight) were found. Pervaporation measurements reveal that polysiloxane membranes synthesised by the plasma deposition process are sufficiently permeable for the mass transfer boundary layer above the membrane to be dominant. The permeability of plasma membranes formed from cyclic octamethylcyclotetrasiloxane were up to an order of magnitude more permeable than those formed from linear hexamethyldisiloxane. Future work should involve vapour permeation.

International audience; This paper is devoted to the optical emission spectra (OES) of low pressure (1 mTorr–1 Torr) plasmas created in tetraethoxysilane (TEOS) and hexamethyldisiloxane (HMDSO) used pure or mixed with oxygen. The UV-visible emission spectra are recorded at low resolution (0.3 nm) using a 46 cm focal length monochromator and at high resolution (0.3 cm$^{−1}$) using a Fourier transform spectrometer. Since almost all the atomic and molecular emissions have been identified, the spectra displayed here can be used as reference emission spectra for TEOS, HMDSO and O$_2$/TEOS(HMDSO) plasmas. The OES of O$_2$/TEOS and O$_2$/HMDSO plasmas are very close and are dominated by CO, OH, H$_2$ and H emissions. In contrast, the OES of TEOS and HMDSO plasmas are quite different: the emissions of excited Si, SiO and SiH are characteristics of HMDSO plasma, while those of OH, CO, CO$^+$, C$_2$O$^+$ are characteristics of TEOS plasmas. On the basis of these spectra and the data reported in the literature, it is finally concluded that the CO and OH molecules detected in TEOS plasmas are very likely created at the reactor walls by desorption from the growing film.

International audience; We present an extension of the classical axisymmetric Bretherton theory giving the thickness of the liquid film left on the walls of a drained tube, treating the case of weak inertia by a regular perturbation method. The results obtained by numerical integration fit Taylor's [J. Fluid Mech. 10, 161 (1961)] experiments, obtained with viscous fluids (glycerine and strong sucrose solutions), and Aussillous and Quere's [Phys. Fluids 12, 2367 (2000)] experiments with low viscosity liquids (hexamethyldisiloxane and water) when inertia becomes important. The discrepancies observed between the theory and high Reynolds numbers experiments (Re>1000) are commented on.