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OXYGEN-EXCESS RELATED DEFECTS IN SiO2-BASED MATERIALS: COUPLING THEORY AND EXPERIMENTS
Blaž Winkler, 2019, doctoral dissertation

Abstract: This work is primarily focused on application of standard first-principle computational approaches to model oxygen excess related point defects in amorphous silica. Atomic models with their respective electronic and optical properties are explored together with some conversion mechanisms between defect models. The first chapter overviews extensive literature about the already known properties of oxygen related defects. Second chapter briefly introduces main methods that have been used in this research, in particular Density Functional Theory (DFT) as energy and force engine with short description of minimal energy path (MEP) algorithm used for modeling chemical/migration reactions, GW approximation for charged electronic excitations (band structure) and Bethe-Salpeter Equation (BSE) for neutral excitations (optical absorption and excitonic structure including electron hole interaction). The third chapter is devoted to the presentation of results. Thanks to the calculation of optical properties of peroxy bridge (POL), a correlation has been found between structural disorder, specifically dihedral angle dispersion, and low coupling with light, which has been identified as main reason why no clear absorption bands have been assigned to the POL. Structure and stability of some other defects, like interstitial ozone molecule (ozonyl) and dioxasilirane (silicon analogy of dioxirane), have been studied. These defects are usually not considered as most important species, however their calculated formation energies are lower compared to some known defects, which indicates they might be present in silica. From a detailed study on possible reaction mechanisms, it has been found that ozonyl might be one of the most important intermediate steps for oxygen exchange reactions. Results also show that dioxasilirane can be spontaneously created during the interaction of oxygen with lone pair defects. By exploring different reactions between oxygen and pre-existing oxygen deficiency centers (ODCs), calculations predict two kinds of passivation behaviors: single-barrier reversible mechanisms with the formation of dioxasilirane-like groups, for which the network keeps the memory of the precursory lone pair defects, and single or multiple-barrier mechanisms, for which the network loses its memory, either because of the high reverse barrier or because of a reconstruction. Final part of this research has been devoted to experimental characterization of the response and tolerance of optical fibers loaded with oxygen under irradiation. These include experiments on commercial fiber along with canonical samples (Optical fibers developed with the intention of studying correlations between different fabrication parameters, dopant/impurity concentration and doping concentrations). Studied fibers also include rare-earth doped fibers.
Found in: ključnih besedah
Keywords: Silica, DFT, GW-approximation, Bethe-Salpeter equation, NEB, defect, oxygen, oxygen excess centers, oxygen deficiency centers, optical absorption, optical fibers, radiation induced attenuation.
Published: 07.05.2019; Views: 2542; Downloads: 131
.pdf Fulltext (13,18 MB)

3.
Overview of radiation induced point defects in silica-based optical fibers
Blaz Winkler, Imène Reghioua, Simonpietro Agnello, Marco Cannas, Philippe Paillet, Nicolas Richard, Adriana Morana, A. Boukenter, Youcef Ouerdane, Vincenzo De Michele, Antonino Alessi, Sylvain Girard, Layla Martin-Samos, Luigi Giacomazzi, Diego Di Francesca, Thierry Robin, 2019, review article

Found in: ključnih besedah
Summary of found: ...optical fibers, point defects, radiation-induced attenuation, GLPC, NBOHC, STH, ODC, P-doping, Ge-doping, Al-doping...
Keywords: optical fibers, point defects, radiation-induced attenuation, GLPC, NBOHC, STH, ODC, P-doping, Ge-doping, Al-doping
Published: 09.05.2019; Views: 2035; Downloads: 0
.pdf Fulltext (2,27 MB)

4.
Regulation and controlling the motility properties of Pseudomonas aeruginosa
Fazlurrahman Khan, Dung Thuy Nguyen Pham, Sandra Oloketuyi, Young-Mog Kim, 2020, review article

Abstract: Chronic infections caused by Pseudomonas aeruginosa have been a major concern as their spread and mortality continue to be on the rise. These infections are majorly attributed to biofilm formation via sequential steps where motility plays an essential role in initial attachment of bacterial cells onto biotic and abiotic surfaces, thereby contributing to multi-drug resistance among pathogens. Therefore, attenuating motility properties can be considered as highly potential for controlling P. aeruginosa biofilm formation. This strategy has employed the use of various natural and chemically synthesized compounds. The present review article explained the importance and regulation of different types of motilities properties. Furthermore, it also covered several important alternative approaches using anti-motility agents which could be helpful for controlling P. aeruginosa biofilm-associated infections. Further studies are required for in-depth understandings about the mechanisms of motilities controlling of these molecules at molecular levels.
Found in: ključnih besedah
Summary of found: ...Biofilm, Motility, Attenuation, Antibiofilm drugs, Pseudomonas aeruginosa...
Keywords: Biofilm, Motility, Attenuation, Antibiofilm drugs, Pseudomonas aeruginosa
Published: 12.01.2021; Views: 1256; Downloads: 0
.pdf Fulltext (4,83 MB)

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