Microstructural characteristics and corrosion resistance of atmospheric pressure chemical vapor deposited SiO2 films from TEOS and O2

Chemical vapor deposited SiO2 films from tetraethyl orthosilicate (TEOS) is a key enabling material in numerous applications. Among the several pathways for the CVD of SiO2 films from TEOS, the poorly investigated medium temperature process involving oxygen ensures a compromise between the high thermal load of the surface reaction of the TEOS pyrolysis process, and the strong activation of gas phase reactions in the ozone assisted decomposition of TEOS. It is a promising route towards conformal coverage of complex-in-shape structures, growth rate control, and appropriate physical & chemical properties of the coating. SiOx films are obtained from TEOS+O2 in a horizontal CVD reactor operating at atmospheric pressure between 350 and 500°C. FTIR operating under normal and 55° incidence angle is used for the investigation of the structure, namely density, strain, oxygen content and stoichiometry of the films, by probing vibrational modes in the 900-1300 cm-1 region with well-resolved TO-LO phonon splitting. Complementary density values obtained by ellipsometry allow estimating the porosity of the films. Their corrosion resistance is investigated by the P-Etch test through thickness loss and is correlated with their composition, porosity and density

Silice amorphe, élaborée par CVD à partir de TEOS et O2 : Composition, stœchiométrie, structure et résistance à l’abrasion chimique

Depuis les années 80, l’élaboration de couches minces de silice, SiO2 à partir d’orthosilicate de tétraéthyle ((Si(OC2H5)4, TEOS) par dépôt chimique en phase vapeur (CVD) a été largement étudiée pour répondre aux problématiques de la microélectronique. Récemment, l’élargissement de l’éventail d’applications pour les revêtements à base de SiO2 pour l’optique, l’agroalimentaire, le biomédical, l’emballage ou la séparation des gaz, induit une modification des cahiers des charges tant pour les matériaux que les procédés. Il est souvent mis en avant les besoins de : (a) réduire le budget thermique lors de l’élaboration, (b) éliminer la formation de poudres, induites par exemple par une réactivité élevée en présence d’ozone, (c) revêtir des structures complexes, ce qui diminue l’intérêt des procédés plasma. En réponse à ces besoins, cette étude s’intéresse à la structure de couches de SiO2 amorphe élaborées à partir de TEOS et oxygène à pression atmosphérique à des températures Td comprises entre 400°C et 550°C, et corrèle ces caractéristiques à leur résistance à l’abrasion chimique

Investigation of the densification mechanisms and corrosion resistance of amorphous silica films

The barrier properties of the technologically attractive amorphous silica films depend on their structural characteristics at the atomic level, which, in turn are strongly influenced by the deposition conditions. In this paper, we propose an investigation of the poorly investigated densification mechanism of amorphous SiO2 films processed by CVD from TEOS and O2 between 400 and 550 °C. Based on literature survey and our original experimental results, we show that the densification process of these films, occurring with increasing the deposition temperature, is highlighted by a decrease of the water and silanol content, probed by transmission FTIR. We discuss the evolution of Si-O-Si related vibration signatures and we use the central force model to correlate the LO2 and LO3 shifts with the decrease of the Si-O-Si bond force constant, when the deposition temperature increases. Nuclear analysis reveals that films processed below 525 °C present hydrogen content between 5 ± 0.3 and 7 ± 0.3%at. Ellipsometry measurements attest that films processed at 550 °C are close to O/Si silica stoichiometry and hydrogen free. We show that application of the P-etch test results in particularly low erosion rate of 10 Å.s−1 for dense films processed at 550 °C

Clumpiness enhancement of charged cosmic rays from dark matter annihilation with Sommerfeld effect

Boost factors of dark matter annihilation into antiprotons and electrons/positrons due to the clumpiness of dark matter distribution are studied in detail in this work, taking the Sommerfeld effect into account. It has been thought that the Sommerfeld effect, if exists, will be more remarkable in substructures because they are colder than the host halo, and may result in a larger boost factor. We give a full calculation of the boost factors based on the recent N-body simulations. Three typical cases of Sommerfeld effects, the non-resonant, moderately resonant and strongly resonant cases are considered. We find that for the non-resonant and moderately resonant cases the enhancement effects of substructures due to the Sommerfeld effect are very small ($\sim \mathcal{O}(1)$) because of the saturation behavior of the Sommerfeld effect. For the strongly resonant case the boost factor is typically smaller than $\sim \mathcal{O}(10)$. However, it is possible in some very extreme cases that DM distribution is adopted to give the maximal annihilation the boost factor can reach up to $\sim 1000$. The variances of the boost factors due to different realizations of substructures distribution are also discussed in the work.Comment: 28 pages, 8 figures, 2 table. The detailed fomula of the propagation and boost factor are moved to the Appendix. Accepted by JCA

A collaboratively derived environmental research agenda for Galapagos

Galápagos is one of the most pristine archipelagos in the world and its conservation relies upon research and sensible management. In recent decades both the interest in, and the needs of, the islands have increased, yet the funds and capacity for necessary research have remained limited. It has become, therefore, increasingly important to identify areas of priority research to assist decision-making in Galápagos conservation. This study identified 50 questions considered priorities for future research and management. The exercise involved the collaboration of policy makers, practitioners and researchers from more than 30 different organisations. Initially, 360 people were consulted to generate 781 questions. An established process of preworkshop voting and three rounds to reduce and reword the questions, followed by a two-day workshop, was used to produce the final 50 questions. The most common issues raised by this list of questions were human population growth, climate change and the impact of invasive alien species. These results have already been used by a range of organisations and politicians and are expected to provide the basis for future research on the islands so that its sustainability may be enhanced. </jats:p

Chemical vapor deposition of amorphous silica as barrier coatings for pharmaceutical vials

L’élaboration de nouvelles solutions médicamenteuses par les laboratoires pharmaceutiques est intimement liée à la maitrise de leurs interactions avec la surface des emballages primaires en verre, afin d’assurer la préservation du principe actif. Sans cet effort, les instances de santé américaine (FDA) et européenne (EMA) ont révélé dès 2007, des altérations irréversibles du médicament et du contenant. Les conséquences sont catastrophiques, les molécules contenues dans le flacon sont dénaturées et deviennent inefficaces, et la surface du verre se délamine en générant des particules insolubles de taille micrométrique en solution. Cette thèse concerne l’étude de revêtements de silice amorphe susceptibles d’être appliqués sur la surface interne de flacons pharmaceutiques pour limiter leur réactivité avec le contenu. Les revêtements ont été élaborés par dépôt chimique en phase gazeuse (CVD), à partir de tétraethylorthosilicate (TEOS) et dioxygène à pression subatmosphérique, entre 350 et 570 °C. Le procédé permet le contrôle des vitesses de dépôt dans la géométrie 3D du flacon, tout en offrant une fenêtre de températures de traitement compatible avec sa tenue mécanique. Une approche pluridisciplinaire qui combine science des matériaux et génie des procédés est mise en œuvre, dans le but de maîtriser les propriétés physico-chimiques et fonctionnelles du revêtement et du procédé d’élaboration. Des dépôts sur substrats plans ont permis d’effectuer une étude croisée de la structure, de la composition et de la densité du film, mettant en œuvre les spectrométries FTIR et ellipsométrique et des techniques d’analyse par faisceau d’ions. Des revêtements peu hydratés, peu poreux et légèrement sous-stœchiométriques en oxygène sont élaborés à 550 °C. Leur valeur de P-etch est 10 Å.s-1 traduisant une bonne résistance à l’érosion. Un modèle cinétique apparent est développé pour la simulation du procédé de dépôt. Il considère deux espèces intermédiaires, impliqués dans deux réactions homogènes et deux hétérogènes. Il reproduit la vitesse de dépôt et sa répartition sur la surface des substrats. Des revêtements de silice amorphe sont déposés dans des flacons en verre et le procédé est simulé numériquement. La prise de masse prédite par la simulation correspond à celle mesurée expérimentalement. Les flacons revêtus sont soumis à un essai de vieillissement hydrothermal lors d’un cycle de stérilisation pendant une heure à 121 °C et 1220 hPa en contact avec de l’eau ultra-pure, suivant la préconisation USP . Ils présentent une excellente résistance hydrolytique, le revêtement empêché le relargage de substances minérales du verre au contact de l’eau. Ce travail ouvre la voie à l’élaboration, par un procédé industrialisable, de revêtements plus denses, susceptibles de remplir les exigences sévères de résistance à l’altération des solutions USP .The development of new pharmaceutical solutions is intimately linked to the control of theirinteractions with the surface of the primary glass packaging, with the aim to ensure thepreservation of the active agent. Already in 2007, the American (FDA) and European (EMA) healthauthorities revealed irreversible alterations between the contained solution and the container. Theconsequences are catastrophic, since the contained active molecules are denatured and becomeineffective, and the surface of the glass delaminates and results in suspension of micrometricsized insoluble particles in the pharmaceutical solution. This thesis focuses on the development ofamorphous silica coatings likely to be applied on the inner surface of pharmaceutical vials to limittheir reactivity with the contained solution. The coatings were processed by chemical vapordeposition (CVD) from tetraethylorthosilicate (TEOS) and dioxygen at subatmospheric pressure,between 350 and 570 °C. The process allows control of the deposition rates in the 3D geometry ofthe vials and at the same time, it operates in a temperature window that is compatible with themechanical integrity of the vial. A multidisciplinary approach, combining materials science andprocess engineering is applied, in order to control the physicochemical and functional properties ofthe coating and its deposition process. Deposition on flat substrates allowed performing a crosslinked investigation of the structure, the composition and the density of the films by FTIR andellipsometric spectroscopies and ion beam analysis techniques. Poorly hydrated, non-porous andslightly lower than SiO2 stoichiometry coatings were processed at 550 °C. Their P-etch value is 10Å.s-1, indicating a good erosion resistance. An apparent kinetic model is developed for thesimulation of the deposition process. It considers two intermediate species, involved in twohomogeneous and two heterogeneous reactions. It reproduces the deposition rate and itsdistribution over the substrates surface. Amorphous silica coatings are deposited on the internalsurface of glass vials and the deposition process is numerically simulated. The simulation predictsa mass gain that corresponds to the one experimentally determined. The coated vials are filledwith ultra-pure water and are subjected to a hydrothermal aging test with a sterilization cycleduring one hour at 121°C and 1220 hPa according to the USP recommendation. Theypresent an excellent hydrolytic resistance, corresponding to the resistance of the glass to therelease of soluble mineral substances into water. This work paves the way towards theprocessing, through an industrial transferrable process, of denser coatings which are expected tomeet severe specifications compatible with the USP recommendation

Automatic auditory processing of English words as indexed by the mismatch negativity, using a multiple deviant paradigm

Objective: The aim of this study was to investigate mismatch negativity (NEHN) responses to a variety of speech stimuli (/de:/, /ge:/, /deI/ "day", and /geI/ "gay") in a multiple deviant paradigm. It was hypothesized that all speech stimulus contrasts in the multiple deviant paradigm, including the fine acoustic speech contrast [d/g], would elicit robust MMN responses and that consonant vowel (CV) real word deviants (e.g., "day" and "gay") would elicit larger MMN responses than CV nonword deviants (e.g., "de" and "ge") within and across experimental contrasts