Vincent Rouessac

Surface investigation of plasma HMDSO membranes post-treated by CF4/Ar plasma

Abstract Fluorination treatment has been performed on polysiloxane membranes using a plasma glow discharge of a gases mixture CF4 and argon (plasma enhanced chemical vapor deposition). Atomic force microscopy, XPS analyses and contact angle measurements have been undertaken to explain the surface transformation and behavior, which strongly depend on the morphology, the composition and the hydrophilic/hydrophobic character of the plasma-polymerized initial membranes. Main result is that fluorination, which leads to hydrophobic membranes, has a more relevant effect on amorphous silica-like membranes than on polymer-like ones, according to their chemical composition whereas the plasma surface reaction induces a substantial microstructural modification of the polymer-like membrane, i.e. the grains and aggregates size and distribution.

Microporous Silica Membrane: Basic Principles and Recent Advances

Publisher Summary This chapter discusses the basic principles and the recent advancement of microporous silica membrane. It discusses several inorganic membranes are available, focusing on the synthesis and applications of microporous amorphous silica membranes. Microporous amorphous silica exhibits a weak stability in aqueous solutions or wet streams, which limits its use as separative membranes to specific applications. The main current developments deal with gas separation applications—in particular hydrogen separation. The thermal stability of silica membranes compared with organic and hybrid layers and their interconnected porosity inside a stiff oxide skeleton enable to reach very good permeability–selectivity balances. The chapter discusses different synthesis methods used to prepare supported amorphous silica membranes. The designing of silica membrane and associated separative properties are also explained.

Gas permeation of PECVD membranes inside alumina substrate tubes

The purpose of this work is the gas permeation study of silicon carbide membranes inside asymmetric porous alumina tube. Membranes have been synthesized by the Plasma Enhanced Chemical Vapor Deposition (PECVD). The reactor we have set up allows the deposition of amorphous hydrogenated inorganic thin films on the inner surface of tubular substrates and involves the reaction between an organosilicon vapor (Diethylsilane: SiH2(C2H5)2) and a transported glow discharge of argon. In a previous study, the composition and morphology of a:SixCyHz layers have been investigated as a function of different plasma conditions (electric power applied to the plasma, gases flow rates, substrate temperature). It appears that the well controlled homogeneity and composition of the layers result in a good control of the substrate temperature induced by the glow discharge heating during the deposition. The good mechanical properties and thermal stability of the amorphous hydrogenated silicon carbide layers, and the alumina substrate allow an important heating without any damage. In this work the permeation and separation experiments are performed using a laboratory made gas permeation cell by testing H2, CO2, and N2 gases through thin films synthesized with different conditions on two kind of alumina tubes whose average pore size is 5 or 200 nm. The nitrogen permeance at room temperature is in the range of 10−6–10−7 mol m−2 s−1 Pa−1 for membranes with a thickness above 1 μm. This permeability remains quite constant regardless pressure, which means that our membranes permeate gases principally according the Knudsen diffusion mechanism.

Synthesis and characterization of porous ferrimagnetic membranes

Abstract Nanoporous ferrimagnetic membranes based on maghemite (γ-Fe2O3) and cobalt ferrite (Fe2CoO4) were prepared by the sol–gel route using colloidal ferrofluids. These membranes were used for the separation of paramagnetic and diamagnetic gaseous species at room temperature. Their magnetic properties were analyzed using a SQUID magnetometer, and their structures and porous textures were studied by X-ray diffraction, scanning electron microscopy and nitrogen adsorption–desorption analysis. O2–N2 adsorption and air separation experiments were carried out in order to study the magnetic interactions in static and dynamic conditions, respectively. A slight effect of the magnetic field on the selectivity of these membranes was observed. However, the measured selectivity values αN2/O2 were always close to 1. Although an optimization of the membranes remains possible, it seems difficult to reach the high selectivity values required for technological applications.

Dynamic constitutional electrodes toward functional fullerene wires

Constitutional mesoporous thin-layer electrodes have been used to generate confined fullerene wires allowing a capacitive diffusion of electrons.

In-Situ Mass Spectrometry Analyses of the Fragmentation of Linear and Cyclic Siloxanes in a Glow Discharge Compared with Ex-Situ FTIR Analyses of the Deposits

Mass Spectrometry (MS) analyses, up to 300 amu, were performed on linear hexamethyldisiloxane (HMDSO) and cyclic octamethylcyclotetrasiloxane (OMCTSO) vapors in low frequency plasmas (40 kHz). The fragmentation rates of the precursors, and possible oligomerization in the gas phase, depend on the plasma power. Two extreme plasma power conditions were compared: a high plasma power density and a low plasma power density, corresponding to silica-like and polymer-like film deposition conditions, respectively. The results of ex-situ Fourier transform infrared spectroscopy (FTIR) analyses can be explained by the plasma composition analyzed by MS.

Sorption and permeation characteristics of hybrid organosilicon thin films deposited by PECVD

Abstract Thin a-SiO x C y H z film membranes were deposited from hexamethyldisiloxane precursor on ester of cellulose porous substrates at low-frequency plasma conditions. The sorption properties of the films were measured for CH 4 , C 2 H 6 , C 3 H 8 , n -C 4 H 10 and i -C 4 H 10 by using a gravimetric method with a quartz microbalance. The gas permeability coefficients were determined by using the constant-volume pressure-increase method. Correlations were established between the physical parameters of the penetrants and the corresponding sorption, permeation and diffusion coefficients observed.

Depth-resolved impact of integration process on porosity and solvent diffusion in a SiOCH low-k material

The impact of plasma etching and chemical wet cleaning on solvent diffusion in porous network of a SiOCH low-k dielectric material is studied. Characterization of porosity and pore size distribution by means of ellipso-porosimetry and positron annihilation lifetime spectroscopy are presented. The results are compared with solvent diffusion kinetics, measured using probe molecules of different polarity, surface energies and molecular sizes. Infrared spectroscopy, Doppler broadening of annihilation radiation and time-of-flight secondary ion mass spectrometry measurements are also performed to investigate material modifications causing variations of diffusion kinetics.

Effects of surface properties of different substrates on fine structure of plasma-polymerized SiOCH films prepared from hexamethyldisiloxane (HMDSO)

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.

Efficient Sensing of Explosives by Using Fluorescent Nonporous Films of Oligophenyleneethynylene Derivatives Thanks to Optimal Structure Orientation and Exciton Migration

The fluorescence of thin films of a diimine-substituted phenyleneethynylene compound can be efficiently quenched by nitroaromatic vapors, which is not the case for the unsubstituted parent compound. Thin-film porosity is usually considered to be an essential factor for efficient quenching, but in the present case the origin of the quenching is completely different, as both films are nonporous and hermetic to 2,4-dinitrotoluene (DNT) molecules. The molecular organization in the two crystallized thin films offers a low level of π stacking for both compounds, but the orientation of the phenylenethynylene fluorophore differs markedly with respect to the surface of the films. For the substituted compound, the fluorophore is almost parallel to the surface, thus making it readily available to molecules of a nitroaromatic quencher. This rationale is also observed in the case of a related compound bearing methoxy side chains instead of the long octyloxy moieties. Fluorescence-lifetime experiments show that the efficient quenching process in the nonporous crystallized films of the substituted compound is due to a fast (<70 ps) diffusion of excitons from the bulk of the film toward the surface where they are quenched, thus providing evidence of antenna effects.