Eric Bêche

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.

Plasma Membranes Modified by Plasma Treatment or Deposition as Solid Electrolytes for Potential Application in Solid Alkaline Fuel Cells

In the highly competitive market of fuel cells, solid alkaline fuel cells using liquid fuel (such as cheap, non-toxic and non-valorized glycerol) and not requiring noble metal as catalyst seem quite promising. One of the main hurdles for emergence of such a technology is the development of a hydroxide-conducting membrane characterized by both high conductivity and low fuel permeability. Plasma treatments can enable to positively tune the main fuel cell membrane requirements. In this work, commercial ADP-Morgane® fluorinated polymer membranes and a new brand of cross-linked poly(aryl-ether) polymer membranes, named AMELI-32®, both containing quaternary ammonium functionalities, have been modified by argon plasma treatment or triallylamine-based plasma deposit. Under the concomitant etching/cross-linking/oxidation effects inherent to the plasma modification, transport properties (ionic exchange capacity, water uptake, ionic conductivity and fuel retention) of membranes have been improved. Consequently, using plasma modified ADP-Morgane® membrane as electrolyte in a solid alkaline fuel cell operating with glycerol as fuel has allowed increasing the maximum power density by a factor 3 when compared to the untreated membrane.

FTIR and XPS investigations of a-SiOxNy thin films structure

Amorphous silicon oxynitride (a-SiOxNy) thin films with large composition variation were deposited by reactive sputtering. Their structural study was carried out by mean of FTIR and XPS analysis. The IR absorption peak maximum was found to shift towards higher wavenumbers as the oxygen content increases and the absorption peaks of Si-O and Si-N bonds also appear. The Si 2p photoelectron peak was decomposed considering five tetrahedra of SiOvN4-v (where v = 0, 1, 2, 3 and 4) following the Random Bonding Model (RBM). But the comparison between RBM theoretical and experimental predictions and the non-linear behaviour of the modified Auger parameter (α) showed that the a-SiOxNy structure can be well described only considering a mixture of SiO2, Si3N4 and SiOxNy phases.

SiH bonding environment in PECVD a-SiOxNy:H thin films

We constructed silicon oxynitride thin films of various compositions by Plasma Enhanced Chemical Vapor Deposition and studied the global structure by infrared absorption. The Si-H band frequency is related to the environment of Si atom. We considered the Si-H band as the sum of several gaussian curves corresponding to the different silicon-centered tetraedra present in the material. The frequency of Si-H bond for each tetrahedron was calculated using Lucovsky linear relations and then the tetrahedra were attributed to gaussians found by decomposition of the band. The results show the presence of tetrahedra with both N and O atoms bound to silicon. These tetrahedra cannot agree with a model of phase separation, however the Random Bonding Model envisages the existence of these environments. So we consider our silicon oxynitride films to be a homogeneous statistical mixture of the various bonds rather than a mixture of phases.

Solution Layer Deposition: A Technique for the Growth of Ultra-Pure Manganese Oxides on Silica at Room Temperature.

With the ever increasing miniaturization in microelectronic devices, new deposition techniques are required to form high-purity metal oxide layers. Herein, we report a liquid route to specifically produce thin and conformal amorphous manganese oxide layers on silicon substrate, which can be transformed into a manganese silicate layer. The undesired insertion of carbon into the functional layers is avoided through a solution metal-organic chemistry approach named Solution Layer Deposition (SLD). The growth of a pure manganese oxide film by SLD takes place through the decoordination of ligands from a metal-organic complex in mild conditions, and coordination of the resulting metal atoms on a silica surface. The mechanism of this chemical liquid route has been elucidated by solid-state (29) Si MAS NMR, XPS, SIMS, and HRTEM.

Adsorption and Incorporation of Cadmium into a Calcium Hydroxyapatite

The removal of cadmium from water by fixation into a calcium phosphate apatite Ca10(PO4)6(OH)2 (CaHA) was investigated in batch experiments. These ones were carried out using a wide range of initial Cd2+ concentration, three different temperatures, and several CaHA surface areas. The amount of immobilized cadmium was proportional to the surface area of CaHA, whatever the experimental parameters might be. It could reach 7.1 mol of Cd per mol of starting CaHA. Thermal and XPS analyses on the exchanged powders proved that a part of cadmium was quickly adsorbed at the grains surface in the form of hydrated complexes [Cd(OH2)n]2+. The latter were formed by an ionic exchange between adsorbed calcium and cadmium of the solution. Adsorption reaction was mainly limited by the number of specific sites available on the grains surface. Structural analyses showed that another part of Cd was slowly incorporated into a solid solution Ca10-xCdx(PO4)6(OH)2 (CaCdHA) onto the CaHA crystals surface. Results demonstrated unambiguously that the incorporation process was a surface precipitation and not an intracrystalline diffusion.

Controlled Growth and Grafting of High-Density Au Nanoparticles on Zinc Oxide Thin Films by Photo-Deposition

The integration of high-purity nano-objects on substrates remains a great challenge for addressing scaling-up issues in nanotechnology. For instance, grafting gold nanoparticles (NPs) on zinc oxide films, a major step process for catalysis or photovoltaic applications, still remains difficult to master. We report a modified photodeposition (P-D) approach that achieves tight control of the NPs size (7.5 ± 3 nm), shape (spherical), purity, and high areal density (3500 ± 10 NPs/μm2) on ZnO films. This deposition method is also compatible with large ZnO surface areas. Combining electronic microscopy and X-ray photoelectron spectroscopy measurements, we demonstrate that growth occurs primarily in confined spaces (between the grains of the ZnO film), resulting in gold NPs embedded within the ZnO surface grains thus establishing a unique NPs/surface arrangement. This modified P-D process offers a powerful method to control nanoparticle morphology and areal density and to achieve strong Au interaction with the metal oxide substrate. This work also highlights the key role of ZnO surface morphology to control the NPs density and their size distribution. Furthermore, we experimentally demonstrate an increase of the ZnO photocatalytic activity due to high densities of Au NPs, opening applications for the decontamination of water or the photoreduction of water for hydrogen production.