The aim of the present work is to produce silver‐containing SiCxOyHz thin films by using simultaneous sputtering of silver and plasma polymerization in an HMDSO plasma. The ratio of plasma polymerization to sputtering was adjusted by using a pulsed flow rate of the hexamethyldisiloxane precursor, which permitted an accurate control of the co‐deposition process. The presence of silver in the gas phase was detected by optical emission spectroscopy. The silver volume fraction was controlled over a wide range by superimposing physical sputtering onto the polymerization process taking place simultaneously within a very low and narrow range of HMDSO plasma pressure. The polymer matrix structures were analyzed by several techniques. FTIR spectra revealed the presence of SiOSi, SiCSi, SiCH3 and CC groups whose amount varied with the silver content. TEM analysis showed Ag nanoparticles with sizes varying from 4 to 70 nm depending on the silver volume fraction.magnified image

Summary: In this paper, the gas phase composition of hexamethyldisiloxane (HMDSO) microwave plasma at 4 × 10−3 mbar and of the corresponding films were studied by FTIR spectroscopy under different power conditions. At low powers, species with a chemical structure very similar to that of HMDSO were observed in the gas phase, whereas the film essentially contained short [(CH3)2SiO]n‐like chains with a low branching rate and the end group Si(CH3)3. At higher powers, the chemical entities present in the gas phase contained several (SiO)x bonds, whereas the branching rate in the film increased with the amount of SiH, SiC and SiO bonds. The interpretation of these observations led to a proposal involving a chemical mechanism. In this mechanism, the increasing decomposition of HMDSO into by‐products, which themselves increasingly decompose as the power is raised, plays a determining role.

In situ diagnostic measurements and reactor modelling are used to study the N2O dissociation by radio frequency (RF) discharges. Measurements are undertaken at 0.5 and 1 Torr gas pressure with a RF power density varying from 4.2 to 35.7 mW cm-2. The reactor modelling involves an electrical discharge model coupled to hydrodynamic and mass transfer models. Only an electrical discharge model accounting for the negative ion conversion from O- to NO- and the subsequent electron detachment allow a good coherence between the measured and predicted power densities. The electron-N2O dissociation cross sections are first fitted in the present work and then the corresponding dissociation rates, obtained from the electrical model, are used in the mass transfer model which includes eight species (N2O, N2, O2, NO, NO2, N, O(3P) and O(1D)). The corresponding results are in good agreement with the experimental ones related to the production of N2 and O2 and the consumption of N2O. Furthermore, the reactor model results show that N2 and O2 are the most abundant products (>1014 molecules/cm3) at 1 Torr.

Given the growing use of nanotechnology in many common consumer products, including foods, evaluation of the consequences of chronic exposure to nanoparticles in humans has become a major public health issue. The oral route of exposure has been poorly explored, despite the presence of a fraction of nanosized particles in certain food additives/supplements and the incorporation of such particles into packaging in contact with foods. After their ingestion, these nanoparticles pass through the digestive tract, where they may undergo physicochemical transformations, with consequences for the luminal environment, before crossing the epithelial barrier to reach the systemic compartment. In this review, we consider two examples, nanosilver and nanotitanium dioxide. Despite the specific features of these particles and the differences between them, both display a close relationship between physicochemical reactivity and bioavailability/biopersistence in the gastrointestinal tract. Few studies have focused on the interactions of nanoparticles of silver or titanium dioxide with the microbiota and mucus. However, the microbiota and mucus play key roles in intestinal homeostasis and host health and are undoubtedly involved in controlling the distribution of nanoparticles in the systemic compartment.