J. Durand

Inorganic membranes and solid state sciences

Abstract The latest developments in inorganic membranes are closely related to recent advances in solid state science. Sol–gel processing, plasma-enhanced chemical vapor deposition and hydrothermal synthesis are methods that can be used for inorganic membrane preparation. Innovative concepts from material science (templating effect, nanophase materials, growing of continuous zeolite layers, hybrid organic–inorganic materials) have been applied by our group to the preparation of inorganic membrane materials. Sol–gel-derived nanophase ceramic membranes are presented with current applications in nanofiltration and catalytic membrane reactors. Silica membranes with an ordered porosity, due to liquid crystal phase templating effect, are described with potential application in pervaporation. Defect-free and thermally stable zeolite membranes can be obtained through an original synthesis method, in which zeolite crystals are grown inside the pores of a support. Hybrid organic–inorganic materials with permselective properties for gas separation and facilitated transport of solutes in liquid media, have been successfully adapted to membrane applications. Potential membrane developments offered by CVD deposition techniques are also illustrated through several examples related to the preparation of purely inorganic and hybrid organic–inorganic membrane materials.

Chemical bonding analysis of a-SiC : H films by Raman spectroscopy

Abstract The local structure of hydrogenated amorphous silicon-carbon films is investigated by Raman spectroscopy. The data are analyzed over a wide frequency range including Stokes and anti-Stokes scattering, for different alloy compositions. Their interpretation is based on a lineshape analysis of the spectra by using the density of vibrational states of the different crystalline materials, and taking into account multiple-order processes. The tendency to chemical ordering into a sp3 connected network prevails in Si-rich films. The higher the carbon amount, the less ordered are the films, due to the presence of a mixed sp2-sp3 polymeric phase. The results are compared with those deduced from various other techniques and theoretical predictions.

Plasma sputtering deposition of platinum into porous fuel cell electrodes

Platinum is deposited into porous carbon materials relevant for fuel cell electrodes using plasma sputtering techniques. The resulting platinum concentration profile extends up to 2 µm into the porous carbon and is well fitted by a generalized stretched Gaussian function, which displays the non-thermal nature of the penetration process. Platinum deposits are observed to grow as clusters. On the outermost carbon particles, platinum nano-cluster sizes of 3.5 nm have been measured. In tests using actual PEM fuel cells, current densities as high as 1000 mA cm−2 have been obtained at 400 mV with 25 cm2 plasma electrodes. This compares favourably with commercially available electrodes but the present electrodes have a platinum density 4.5 times lower and hence can be considered to be significantly more efficient.

Morphological properties of chemical vapour deposited AlN films

Abstract In this paper we analyse some results on AIN CVD film deposition, published in the literature, from a morphological point of view, and we propose a model to explain the observed preferential orientations based on the reactivity of the AIN crystal faces of the equilibrium form.

Interface studies and electrical properties of plasma sulfide layers on n‐type InP

The growing conditions and the basic interface properties of InP‐sulfide‐metal structures formed by direct and indirect plasma‐enhanced sulfidation were investigated. The grown‐in sulfide layer is an admixture of InPS4 and In2S3. The relative concentration of the low‐gap indium sulfide is responsible for the high leakage currents (10−3 A cm−2) in the direct plasma layers. In the indirect plasma case the leakage currents are reduced to 10−6 A cm−2 with breakdown voltages about 7×106 V cm−1. The current transport and the frequency dependence of the capacitance of these diodes are consistently attributed to traps located in the sulfide near the semiconductor (SC) surface with a concentration in the 1011 cm−2 range. Detailed measurements of the capacitance‐voltage characteristics reveal that the Fermi level in InP is swept through the upper half portion of the band gap and that accumulation and strong depletion regimes are reached. These measurements also reveal that the room‐temperature hysteresis‐free C‐V p...

Inorganic to organic crossover in thin films deposited from O2/TEOS plasmas

The structure of thin films prepared from O2/TEOS plasmas in an rf helicon reactor has been investigated using in situ UV-visible spectroscopic ellipsometry and ex situ X-ray, reflectivity, Fourier transform infrared, photoelectron and Rutherford backscattering spectroscopy. It is shown how the structure of the films evolves from an inorganic silica-like structure towards an organic SiOxCyHz framework when the relative proportion of TEOS in the plasma increases. On the one hand, the structure and properties of the silica-like films are shown to be very close to those of a thermal oxide. On the other hand, the organic films have larger refractive index and extinction coeAcient but are less dense than the SiO2-like films. It is shown that the increase in the refractive index and extinction coeAcient is correlated to the carbon incorporation into the film. It is further established that the O/Si content ratio is enhanced from about 2 to 2.5 with increasing TEOS volume fraction. This evolution is explained by the increasing number of Si‐O‐H and Si‐O‐CxHy bonds in the material at the cost of the number of ‐Si‐O‐Si‐ bonds. It is furthermore shown that the abrupt character of the transition between silica-like and organic films is likely to be correlated to the depletion in oxygen atoms in the plasma. ” 2000 Elsevier Science B.V. All rights reserved.

Gas diffusion and sorption properties of polysiloxane membranes prepared by PECVD

Abstract Thin a-SiO x C y H z film membranes were deposited from two different cyclic and linear organosilicon precursors in a low-frequency plasma polymerization process. The qualification of the films for effective gas permeation membranes was tested on the ester of cellulose substrates using N 2 , H 2 , CO 2 and CH 4 . The gas permeability and diffusion coefficients were determined by using the constant-volume pressure-increase method. The solubility coefficients ( S ) were obtained by using a gravimetric method with a quartz microbalance. Correlations between the composite plasma parameter ( V / FM ) ( V : input voltage, F : monomer flow rate and M : monomer molecular weight), which describes the energetic character of the plasma and the permeation performances of plasma polysiloxane membranes were established. Permeation measurements reveal that a wide range of gas transport properties can be obtained according to the applied plasma energy. The global mass transfer could be controlled by diffusion or sorption mechanism according to the relative influence of the different structural factors (chain packing density, chain flexibility and chemical composition) of plasma polysiloxane films directly related to deposition parameters.

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.

Oxidation stages of aluminium nitride thin films obtained by plasma-enhanced chemical vapour deposition (PECVD)

Abstract Oriented (100) aluminium nitride thin films grown on silicon wafers (100) and other substrates, were deposited at 330°C by the metal-organic PECVD process. The oxidation behaviour in air of these films was studied at temperatures from 500°C to 1300°C by X-ray diffraction, scanning electron microscopy and Auger electron spectroscopy. Two textural changes occur: granular and porous textures at 900°C and 1100°C, respectively. These correspond to the amorphous Al 2 O 3 and the crystalline α-alumina formation. Infra-red absorption spectroscopy shows that the oxidation effectively starts at 600°C and reveals an oxynitride phase between the amorphous Al 2 O 3 coating which is formed, and the AlN remaining.

XPS and FTIR study of silicon oxynitride thin films

SiN x , SiO x and SiO x H y deposits containing various hydrogen concentrations were prepared in a plasma enhanced chemical vapour deposition (PECVD) reactor using SiH 4 , NH 3 and N 2 O as precursor gases. These deposits were made for anti-reflection coatings on polymer substracts. In this work, we present a study of the compositions and the chemical environments of silicon, oxygen and nitrogen in these films by using XPS, XAES and FTIR characterization methods. It is shown that the Sio x N y deposits are constituted by various silicon environments which can be described by the presence of Si(O x N y H z ) tetrahedra with x + y + z = 4. The amount of Si-H bonds increases in the deposits when the nitrogen concentration increases. Si-OH chemical bonds were detected for low nitrogen concentration.