Thèses sur le sujet « In silico calculations »

La résistance aux antibiotiques est une menace sérieuse pour la santé publique. En effet, si on ne change pas rapidement notre consommation excessive d'antibiotiques, la situation actuelle va se dégrader jusqu'à basculer dans une ère dite "post-antibiotique", dans laquelle plus aucun antibiotique ne sera efficace contre les infections microbiennes. Bien que ce phénomène de résistance apparaît naturellement, l'utilisation abusive d'antibiotiques accélère le processus. De plus, la présence de pathogènes multi-résistants neutralise l'effet des traitements existants et dans le cas de chirurgies courantes (césariennes, transplantations d'organe...), la situation peut rapidement s'aggraver voire devenir mortelle. C'est pourquoi des directives, émanant des autorités sanitaires, doivent être mises en place afin de contrôler l'utilisation des médicaments, et ce, à tous les niveaux de la société, des individus au secteur agricole en passant par les professionnels de santé et les industries pharmaceutiques. Le monde de la recherche scientifique, quant à elle, doit trouver des nouvelles stratégies pour enrayer la propagation de la résistance. Dans ce contexte, cette thèse a pour objectif le développement d'une méthode de prédiction, par calculs d'énergie libre, des mutations de β-lactamases favorables à l'hydrolyse des β-lactames. Ces travaux méthodologiques ont donc conduit au développement : (1) de nouveaux paramètres pour les enzymes à zinc, implémentés dans le champ de force OPLS-AA et validés par des simulations de dynamique moléculaire sur un panel de métalloenzymes représentatives, (2) d'un protocole de paramétrisation de ligands covalents pour étudier le comportement de certains β-lactames dans CMY-136, une nouvelle β-lactamase caractérisée au laboratoire, et (3) d'un protocole de calcul d'énergie libre évalué au moyen de compétitions internationales de prédiction. Ce dernier a ensuite été utilisé pour tenter d'expliquer pourquoi la carbamylation de la sérine catalytique n'a pas lieu dans certaines oxacillinases. Au travers de ces travaux, nous avons pu améliorer significativement notre approche computationnelle et désormais tout est en place pour une exploration exhaustive des mutations possibles dans les β-lactamases
Antibiotic resistance is a global concern threatening worldwide health. Indeed, if we don't change our overconsumption of antibiotics, the current situation could worsen until a "post-antibiotic" era in which existing treatment would be ineffective against microbial infections. Despite the natural occurrence of antibiotic resistance, the misuse of antibiotics is speeding up the process. Furthermore, presence of multi-resistant pathogens negates the effect of modern treatments and usual surgeries (caesarean sections, organ transplantations...) might be riskier in the future, or even lethal. That's why, common guidelines have to be edicted by health authorities in order to control antibiotic use at every level of society, from individuals to healthcare industry including health professionals and agriculture sector. As for scientific research, new strategies have to be considered in order to limit the spread of antibiotic resistance. In that context, the presented thesis aimed at developing a protocol to predict, by free energy calculations, β-lactamase mutations which could promote the hydolysis of β-lactams antibiotics. In order to achieve that, we developed several methodological approaches including: (1) new parameters for zinc enzymes implemented in OPLS-AA force field and thereafter validated using molecular dynamics simulations of representative zinc-containing metalloenzymes, (2) a protocol to parameterize covalent ligands in order to analyze the dynamical behavior of some β-lactams in CMY-136, a novel β-lactamase recently characterized in our laboratory, and (3) a pmx-based free energy protocol. The latter was also assessed through several international blinded prediction challenges, and finally used to find out why carbamylation of the catalytic serine is not observed in certain OXA enzymes. Throughout this work, we made significant improvements in our protocol, and now everything is in place for an exhaustive prediction of possible mutations in β-lactamases

The design of molecular catalysts is an ambitious task implying the fundamental issue of relating the molecular structure to the reactivity, i.e., to the catalytic activity. The rationalization of the experimental data is often not straightforward and mechanistic schemes are not transferrable when the conditions of the process are changed or the catalyst is modified even slightly. Computer-aided investigations proved to be a more and more valid support in the last decade, but in most of the cases the aim is limited to investigate in detail the catalytic mechanism of a specific reaction and no general conclusions are drawn that can be used as a guide for designing novel catalysts for the same or analogous processes. In this Project, a computational approach has been set up to investigate the family of organometallic complexes displaying catalytic activity toward [2+2+2] cycloadditions of unsaturated molecules. In a recent book (Transition-metal-mediated aromatic ring construction, John Wiley & Sons, 2013, Chapter 4), Ken Tanaka describes Rhodium mediated [2+2+2] cycloadditions and writes ‘…Although mechanistic aspects of these reactions attract interest, only a few studies have been reported in specific catalysts and substrates…’. Thus this project, abbreviated with the acronym of STREGA (Filling the Structure-Reactivity Gap: in silico approaches to rationalize the design of molecular catalysts), aims at filling the gap between the goldmine of experimental data on this class of very important reactions and their mechanistic rationalization with the purpose of outlining the essential electronic and structural features of the catalyst leading to optimal performance, selectivity, and product yield. In particular, the roles of different metal, different ancillary ligands, different aromatic ligands, and substrates have been accurately investigated; existing data from the literature were also employed for this analysis. Larger polycyclic ligands can in principle host more than a metal center; for example, Cr can be coordinated to the benzene moiety of a rhodium indenyl complex. This might lead to interesting inter metal cooperative effects which might enhance or inhibit the catalytic activity; thus bimetallic catalysts have been considered. The effect of different cooperative metal nuclei was explored changing from Cr to Mo and W, which all belong to Group 6. Finally, the role of the polycyclic aromatic ligand was investigated and found that indeed it is an important factor since it influences rhodium hapticity and consequently its reactivity. All these results allowed to establish a solid structure-activity relationship which is of general validity for rhodium half-sandwich catalysts towards alkyne [2+2+2] cycloadditions and likely is transferrable to analogous Co, Ru, and Ir based fragments.

This thesis describes the calculation of exchange interactions for systems of electrons, and their potential uses for quantum information processing. The first part treats exchange between donor impurities (including especially deep donors) in silicon, while the second describes exchange in copper and manganese phthalocyanines. Part I uses the quantum defect method and a model central-cell correction to evaluate the exchange interaction between two deep donors by a Heitler-London-type approach. This part also describes calculations of the exchange in a three-donor complex, where one donor plays the role of a 'control atom' whose optical excitation switches the coupling strengths, and the other two are qubits embodying the quantum information. Variational calculations are described which give the control electron freedom to reside on different parts of the complex it is found that the exchange between two qubits is increased when the control electron be comes delocalized, and that it is possible for the exchange to become ferromagnetic. These observations are rationalised in terms of multi-centre exchange processes using Green's function perturbation theory. In Part II, exchange interactions between copper(II) phthalocyanine (Cu(II)Pc) and manganese (II) phthalocyanine dimers (Mn(II)Pc) are described these systems have both long excited-state lifetimes and tunable magnetic properties. The theoretical studies described include both a model Green's function calculation, to understand the roles of the competing exchange processes, and ab initio density functional theory calculations. The model calculations of Cu(II)Pc show that the dominant contribution comes from so-called indirect exchange, and depends strongly on the stacking angle. The magnitude of the exchange interaction from the ab initio calculations of Cu(II)Pc roughly agrees with the experiment.

Mestrado em Ciência e Engenharia de Materiais
Esta tese apresenta os resultados de um programa de investigação sobre a difusão da lacuna, bi-lacuna e tri-lacuna em silício utilizando simulações numéricas pelo método da teoria do funcional da densidade. Este método está implementado na forma de um programa informático referido como AIMPRO (Ab Initio Modelling PROgram). Para o cálculo dos pontos cela dos mecanismos de difusão foi usado o método “Nudged Elastic Band”. As condições fronteira dos problemas foram impostas recorrendo à utilização de agregados esféricos de silício com 275 atomos, cuja superfície foi saturada por ligações Si-H. As lacunas foram então introduzidas no centro destes agregados. Os valores calculados das barreiras de difusão para a lacuna simples e para a bi-lacuna são respectivamente 0.68 e 1.75 eV. Estes valores apresentam um acordo razoável com os obtidos experimentalmente e obtidos em outros cálculos anteriores. A barreira de difusão da tri-lacuna foi, de acordo com a literatura disponível, calculada pela primeira vêz. O mecanismo de difusão mais favorável apresenta uma barreira de 2.2 eV. No seguimento dos resultados para a lacuna e bi-lacuna, pensamos que este resultado sobrestima a barreira em cerca de 0.25 eV, colocando a nossa melhor estimativa em 1.9- 2.0 eV. Varias fontes de erro nos resultados são comentadas, assim como são sugeridas várias formas de as evitar. ABSTRACT: This work presents the results of a computational investigation into the diffusion of the single vacancy (V) and small vacancy clusters, divacancy (V2) and trivacancy (V3), in silicon. The calculations were performed principally using local density functional theory as implemented by the AIMPRO (Ab Initio Modelling PROgram) code. The Nudged Elastic Band Method was used for elucidating diffusion paths and obtaining the energy barriers for diffusion of the defects considered. Based on ab-initio calculations with H-terminated Si clusters with 275 host atoms, diffusion paths for neutral Vn (n = 1 to 3) defects were found. Calculated values of the activation energy for the diffusion of the Si vacancy and divacancy are 0.68 and 1.75 eV, respectively. These values are in a reasonable agreement with those derived from experimental and previous ab-initio modelling studies. The diffusion of trivacancy in Si has been modelled for the first time. The diffusion barrier of V3 along the proposed diffusion path was found to be about 2.2 eV. This result comes overestimated as the experimental data indicates that the values of diffusion barriers for divacancy and trivacancy in Si should be similar. Probable sources of the calculation errors have been considered and possible ways to surmount these difficulties are proposed.

In this thesis we apply a variety of computational methods based on density-functional theory (DFT) to the study of defect centres in bulk silicon and silicon nanostructures. Firstly, we discuss the system-size convergence of point defect properties in the supercell method for deep-level defects in bulk silicon; we consider both the vacancy and gold impurity. For the vacancy, we investigate systematically the main contributions to the finite size error that lead to the well-known slow convergence with respect to system size of defect properties, and demonstrate that different properties of interest can benefit from the use of different k-point sampling schemes. We also present a simple and accurate method for calculating the potential alignment correction to the valence band maximum of charged defect supercells by using maximally-localised Wannier functions, and show that the localised view of the electronic structure provided by them gives a clear description of the nature of the electronic bonding at the defect centre. For the gold impurity, we show that the system becomes a non-spin-polarised negative-U centre due to the effect of Jahn-Teller distortion, thus providing a simple explanation for the absent electron paramagnetic resonance signal for gold in silicon. The calculated transition levels are found to be in excellent agreement with experimental measurements. We then investigate the segregation of arsenic impurities in silicon close to an interface with amorphous silica. We employ a multiscale approach, generating a realistic disordered interface structure from Monte Carlo simulation, with a continuous random network model of the system parametrised from DFT. We calculate the segregation energy using DFT for a large number of substitutional sites encompassing all the oxidation states of silicon, and show that the results can be understood with a minimal model based only on the local strain and volume of the defect site.

Thesis (Ph. D.)--Dept. of Chemistry and School of Computing and Engineering. University of Missouri--Kansas City, 2005.
"A dissertation in chemistry and computer networking." Advisor: James R. Durig. Typescript. Vita. Description based on contents viewed Nov. 21, 2007; title from "catalog record" of the print edition. Includes bibliographical references (leaves 415-424). Online version of the print edition.

In this dissertation, a comprehensive and rigorous analysis of BER performance in the single- and multi-channel silicon optical interconnects is presented. The illustrated computational algorithms and new results can furnish one with insight of how to engineer waveguide dimensions, optical nonlinearity and dispersion, in order to facilitate the design and construction of the ultra-fast and low-cost chip-level communications for next-generation high-performance computing systems. Two types of optical links have been intensively discussed in this dissertation, namely a strip single-mode silicon photonic waveguide and a silicon photonic crystal waveguide. Different types of optical input signals are considered here, including an ON-OFF keying modulated nonreturn-to-zero continuous-wave signal, a phase-shift keying modulated continuous-wave signal, and a Gaussian pulsed signal, all in presence of white noise. The output signal is detected and analyzed using direct-detection optical receivers. To model the signal propagation in the single- and multi-channel silicon photonic waveguides, we employ both rigorous theoretical models that incorporate all relevant linear and nonlinear optical effects and the mutual interaction between the free carriers and the optical field, as well as their linearized version valid in the low-noise power regime. Particularly, the second propagation model is designed only for optical continuous-wave signals. Equally important, the bit error rate (BER) of the transmitted signal is accurately and efficiently calculated by using the Karhunen-Loeve series expansion methods, with these approaches performed via the time-domain, frequency-domain, and Fourier-series expansion, separately. Based on the theoretical models proposed in this work, a system analysis engine has been constructed numerically. This engine can not only analyze the underlying physics of silicon waveguides, but also evaluate the system performance, which is extremely valuable for the configuration and optimization of the optical networks on chip.

Dans ce manuscrit, la synthèse et la caractérisation complète de différents matériaux hybrides dédiés à des applications dans le domaine optique ou thérapeutique sont décrites. Dans un premier temps, des systèmes macroscopiquement ordonnés sont obtenus par intercalation de colorants tels que le Styryl 722 ou la pyronine-Y dans plusieurs films à base d’argile de type smectite. Les films d’argile sont élaborés par spin-coating et les colorants intercalés par immersion des films dans les solutions de ces colorants. Les effets de l’argile sur les propriétés des colorants sont analysés en détail et leur orientation préférentielle dans l’espace inter-couches est étudié grâce à la réponse anisotropique des films en lumière linéairement polarisée. Dans la deuxième partie, la synthèse par chimie sol-gel de monolithes de silice de grande dimension contenant des colorants laser présentant une forte absorption et une émission de fluorescence dans le visible est abordée. Des colorants laser à l’état solide (SSDL) avec de bonnes stabilités photochimique, thermique et chimique sont ainsi proposés. Dans le troisième chapitre, la synthèse par voie sol-gel de nanoparticules de silice (NP) d’environ 50 nm de diamètre fonctionnalisées sur leur surface externe est ensuite décrite. Grâce à l’encapsulation de molécules de colorants fluorescents dans leur cœur et le greffage de photosensibilisateurs sur leur écorce, des nanoparticules biocompatibles adaptées à la bio-imagerie et la thérapie photodynamique (PDT) ont été préparées. Pour optimiser leurs performances, les propriétés photophysiques et plus particulièrement la production d’oxygène singulet d’une nouvelle série de photosensibilisateurs basés sur les chromophores de type PODIPY ont d’abord été étudiées en détail. A partir de ces résultats, des BODIPY particulièrement efficaces ont été greffés sur les nanoparticules de silice afin de les utiliser pour la PDT. Les propriétés photophysiques de ces matériaux ont été analysées par spectroscopie d’absorption et de fluorescence (stationnaire ou résolue en temps) et les rendements quantiques de production d’oxygène singulet déterminés par des méthodes directe (émission de luminescence de l’oxygène singulet à 1270 nm) ou indirecte (utilisation de sondes chimiques spécifiques à l’oxygène singulet). Par ailleurs les matériaux hybrides ont été complètement caractérisés par plusieurs techniques (SEM, TEM, XRD, XPS, IR, DLS, BET)
Along this manuscript different hybrid materials are synthesized and extensively characterized for several uses: from optical to therapeutic applications. First, by the intercalation of different dyes, styryl 722 and pyronine-Y into several smectite clay films, macroscopically ordered system are obtained. Clay films are elaborated by spin-coating technique and the dyes are intercalated by the immersion of clay thin films into dye solutions. The effect of clay on the dye properties is deeply analyzed and its preferential orientation in the interlayer space of the clay is studied by the anisotropic response of the films to the linear polarized light. Second, large silica monoliths with embedded laser dyes with strong absorption and fluorescence bands in different region of the Visible spectrum are attained by sol-gel chemistry to obtain solid-state dye laser (SSDL) with good photo, thermal and chemical stabilities. Third, silica nanoparticles (NP) with suitable size (50 nm) and functionalized external surface are also synthesised by sol-gel chemistry. Through the encapsulation of fluorescent dye molecules in their core and by the grafting of photosensitizers on their shell, biocompatible nanoparticles for bio-imaging and Photodynamic Therapy (PDT) applications are prepared. In order to optimize their properties, a careful investigation of the photophysical properties and mainly the singlet oxygen generation of a large range of new photosensitizers based on chromophores known as BODIPYs, is previously carried out. Based on these results, some efficient BODIPYs are selected for grafting on silica nanoparticles in order to use them for PDT. The photophysical properties of all these hybrid materials are analyzed by absorption and fluorescence (steady-state and time correlated) spectroscopies, and the singlet oxygen measurements are monitored by direct method (recording the singlet oxygen luminescence at 1270 nm) and by indirect method (using selective chemical probe). Moreover, the hybrid materials are fully characterized by several techniques such as, SEM, TEM, XRD, XPS, IR, DLS, BET

Targeting protein-protein interactions is a challenging task in drug discovery process. Despite the challenges, several studies have provided evidences for the development of small molecules modulating protein-protein interactions. In Part I, it is demonstrated that how a small molecule can induce the formation of an otherwise unstable protein-protein complex. A study of the stabilization of a FKBP12-FRB complex by a small molecule rapamycin is presented. The stability of the complex is analyzed and its interactions are characterized at the atomic level by performing free energy calculations and computational alanine scanning. It is shown that rapamycin stabilizes the complex by acting as a bridge between the two proteins; and the complex is stable only in the presence of rapamycin. The reported results and the good performance of standard molecular modeling techniques in describing the model system can be interesting not only in the design and development of improved molecules acting as FKBP12–FRB protein interaction stabilizers, but also in the somehow neglected study of protein-protein interactions stabilizers in general. In Part II, studies regarding computational modeling of the application of mechanical force to biomolecules is presented. This part is further divided into two chapters since the investigations have been performed on two biological systems. In the first chapter of Part II (chapter 6), it is described that how the osmolyte molecules affect the mechanical unfolding of a peptide. The mechanical unfolding of peptide has been performed by using Steered Molecular Dynamics. In this study, the effect of four different osmolytes on the free energy difference between the folded and the denatured state have been calculated. The observed trend mirrors the expected behavior of the studied osmolytes and unfolding pathways analysis allows an insight into the mechanism of action of osmolytes. After the successful application of Steered molecular dynamics technique on the β-hairpin peptide, the same is applied on tubulin heterodimers for the in-depth study of the lateral and longitudinal interactions which are responsible for the stability and dynamics of the microtubules. In the other chapter of Part II (chapter 7), these interactions are studied with the help of mechanical dissociation of the tubulin heterodimers. These studies have allowed the identification of the critical interactions responsible for the binding of tubulin heterodimers laterally as well as longitudinally. The observations obtained could be important for the design of compounds that target these interactions and acts as microtubule inhibitors or stabilizers.

This dissertation presents studies of the synthetic processes and applications of siloxane-based materials. Kinetic investigations of bridged organoalkoxysilanes that are precursors to organic-inorganic hybrid polysilsesquioxanes are a primary focus. Quick gelation despite extensive cyclization is found during the polymerization of bridged silane precursors except for silanes with certain short bridges. This work is an attempt to characterize and understand some of the distinct features of bridged silanes using experimental characterization, kinetic modeling and simulation. In addition to this, the dissertation shows how the properties of siloxane- materials can be engineered for drug delivery and adsorption. The phase behavior of polymerizing mixtures is first investigated to identify the solutions that favor kinetic characterization. Microphase separation is found to cause gradual loss of NMR signal for certain initial compositions. Distortionless Enhancement by Polarization Transfer 29Si NMR is employed to identify the products of polymerization of some short-bridged silanes under no signal loss conditions. This technique requires knowing indirect 29Si-1H scalar coupling constants which sometimes cannot be measured due to second-order effects. However, the B3LYP density functional method with 6-31G basis set is found to predict accurate 29Si-1H coupling constants of organoalkoxysilanes and siloxanes. The scalar coupling constants thus estimated are employed to resolve non-trivial coupled NMR spectra and quantitative kinetic modeling is performed using the DEPT Si NMR transients. In order to investigate the role of the organic bridging group, the structural evolution of bridged and non-bridged silanes are compared using Monte Carlo simulations. Kinetic and simulation models suggest that cyclization plays a key role right from the onset of polymerization for bridged silanes even more than in non-bridged silanes. The simulations indicate that the carbosiloxane rings formed from short-bridged precursors slow down but do not prevent gelation. The tuning of siloxane-based materials for adsorption technologies are also discussed here. In the first example, antioxidant enzyme loading is investigated as a means to reduce oxidative stress generated by silica nanoparticle drug carriers. Materials are engineered for promising enzyme loading and protection from proteolysis. Second, the potential of copper sulfate impregnation to enhance adsorption of ammonia by silica is explored by molecular simulation.

Les simulations numériques ont négligé jusqu’ici l’influence du support de silice amorphe sur la structure des nanoparticules métalliques déposées car l’interaction métal-silice amorphe est faible. Toutefois les études expérimentales montrent un effet de troncature sur la structure des nanoparticules. L’idée de ce travail a donc été d’étudier l’influence de ce support sur la structure et la morphologie des nanoparticules d’argent au moyen de la modélisation moléculaire (Monte Carlo et dynamique moléculaire). L’objectif de ce travail a été tout d'abord de déterminer le potentiel interatomique permettant de décrire l’interaction argent-silice. Ce potentiel a été obtenu sur la base des données expérimentales d'angles de mouillages en phase liquide et en phase solide. D’autre part, l'intensité d'interaction argent-silice a été déterminée par calculs DFT sur la cristobalite qui est un polymorphe de la silice cristalline présentant la même densité que la silice amorphe. Les énergies d'adhésions obtenues ont ainsi permis d'ajuster les paramètres du potentiel argent-silice de type Lennard-Jones. L’étude de la stabilité structurale des nanoparticules d'argent supportées à température nulle a été effectuée pour trois degrés d'approximation du support. (1) : un support parfaitement lisse décrit par un puits carré dont la profondeur est reliée à l’énergie d’adhésion, (2) : un support atomique de silice amorphe de surface plane et (3) : un support atomique de silice amorphe présentant une rugosité de surface. L’influence de la température sur la structure a été étudiée par fusion et recristallisation des nanoparticules d’argent sur les deux supports de silice amorphe. Afin d’étudier la stabilité structurale des nanoparticules en température, le calcul d’énergie libre des nanoparticules a été abordé
Numerical simulations have so far neglected the influence of amorphous silica substrate on the structure of metallic nanoparticles due to its relatively weak interaction with deposited nanoparticles. However, experimental studies have often shown a truncation effect on the structure of nanoparticles. The idea of this work was to study the influence of this substrate on the structure of silver nanoparticles using molecular modeling (Monte Carlo and molecular dynamics). The objective of this work was firstly to determine silver-silica interatomic potential. This was achieved using experimental data of wetting angles in solid and liquid phase. On the other hand, silver-silica interaction intensity was determined by DFT calculations on cristobalite which is a polymorph of crystalline silica having the same density as amorphous silica. The adhesions energies obtained were used to fit the Lennard-Jones parameters for the silver-silica interaction. The study of the structural stability of silver nanoparticles supported at zero temperature was performed for three levels of approximation of the support. (1): the smooth wall approximation where the support is described by a square-well whose depth is related to the adhesion energy of the nanoparticle, (2): an atomistic model of flat amorphous silica, (3): an atomistic model of rough amorphous silica. The influence of the temperature on the structure was investigated by melting and recrystallization of the silver nanoparticles deposited on the two silica supports. In order to study the temperature stability of the nanoparticles the free energy calculation of the nanoparticles was discussed

Die vorliegende Arbeit befasst sich mit der Synthese von Alkylmethacrylat-Blockcopolymeren, der Charakterisierung ihrer chemischen Struktur und ihres Mikrophasenseparationsverhaltens sowohl im Festkörper als auch in dünnen Filmen. Grundlegendes Ziel war die Einführung funktioneller Gruppen in ein Alkylmethacrylat-Blockcopolymersystem. Eine erste Einschätzung der Effektivität von funktionalisierten Diblockcopolymeren als Template für die Darstellung geordneter Silica-Strukturen über Sol-Gel-Reaktionen von Alkoxysilanen wurde angestrebt. Es wurde das Diblockcopolymersystem Poly(pentylmetacrylat-b-methylmethacrylat) PPMA-b-PMMA untersucht. Dieses wurde nach dem Mechanismus der anionischen Polymerisation dargestellt, um eine größtmögliche Kontrolle über Molmassen, Zusammensetzungen und Polydispersitäten ausüben zu können. Als vielseitig modifizierbare und stabile funktionelle Gruppe wurde die Allylfunktion ausgewählt. Diese konnte durch Endcapping mit Allylbromid an das Kettenende der Diblockcopolymere angebunden werden. An den Kettenanfang konnte die Allylfunktion durch Initiierung mittels Allyllithium gebunden werden. Durch Kombination von funktionellem Initiator und funktionellem Endcapping wurden bifunktionelle Diblockcopolymere erzeugt. Multifunktionalisierte Blockcopolymerproben wurden ebenfalls durch anionische Polymerisation erhalten. Durch sequenzielle Polymerisation von PMA, Allylmethacrylat und schließlich MMA wurden Triblockcopolymere dargestellt. Zwei weitere Typen von multifunktionalisierten Diblockcopolymeren, in denen die funktionellen Gruppen nahezu statistisch verteilt über einen der beiden Blöcke vorliegen, wurden durch statistische Copolymerisation erhalten. Alle Klassen von mono-, di- und multiallylfunktionalisierten Blockcopolymeren konnten durch Hydroborierung mit 9-BBN und anschließende Oxidation in mono-, di- und multihydroxylfunktionalisierte Blockcopolymere überführt werden. Die polymeranaloge Umsetzung der Hydroxylfunktion in eine Triethoxysilylfunktionon konnte modellhaft an einem hydroxylfunktionalisierten PMMA durchgeführt werden. Das Mikrophasenseparationsverhalten der Blockcopolymere wurde durch eine Kombination von analytischen Methoden wie SAXS, T-SAXS, GISAXS, TEM und AFM untersucht. Der Einfluss von Anzahl und Position der funktionellen Gruppen auf die Phasenseparation wurde geprüft. Die dargestellten Blockcopolymere zeigen ein Mikrophasenseparationsverhalten, das weitgehend mit den bereits vorliegenden Ergebnissen übereinstimmt. Trotz des geringen Wechselwirkungsparamters von χPMA,MMA = 0,065 tritt Phasenseparation auf, der Übergang von nichtgeordneter zu geordneter Phase (ODT) kann an ausgewählten Proben verfolgt werden. Die Bulkmorphologien werden nicht durch die Anwesenheit von ein oder zwei funktionellen Gruppen der Allyl- oder Hydroxylfunktion beeinflusst. Sind deutlich mehr als zwei funktionelle Gruppen entlang der Blockcopolymerkette vorhanden, kann das Mikrophasenseparationsverhalten nicht mehr direkt mit dem der nichtfunktionalisierten Diblockcopolymere verglichen werden. Blockcopolymere mit funktionellen Gruppen, die statistisch verteilt über einen der Alkylmethacrylatblöcke vorliegen, verhalten sich prinzipiell wie Diblockcopolymere. Die Phasenseparation ist schlechter ausgeprägt als in reinen Diblockcopolymeren, teilweise kann keine Phasenseparation festgestellt werden. Zum Teil kann dies auf vergrößerte Polydispersitäten und nachträgliche partielle Vernetzungsreaktionen zurückgeführt werden. Durch den Einbau von deutlich mehr als zwei funktionellen Gruppen entlang der Kette wird eine Verstärkung der Tendenz zur Phasenseparation erreicht, wenn der effektive Wechselwirkungsparameter zwischen den Blöcken größer wird als im nichtfunktionalisierten Diblockcopolymeren. Sehr polare Gruppen wie Hydroxylfunktionen beeinflussen Mikrophasenseparationsverhalten und Morphologieausbildung der Alkylmethacrylat-Diblockcopolymere stärker als wenig polare Allylfunktionen. In Triblockcopolymeren mit einem multiallyl- bzw. multihydroxylfunktionalisierten Mittelblock strebt das System einem dreiphasigen Zustand entgegen. Die experimentellen Befunde zum Phasenseparationsverhalten wurden mit theoretischen Phasendiagrammen verglichen, die für nichtfunktionalisierte Diblockcopolymere und Triblockcopolymere mit einem multiallyl- oder multihydroxylfunktionalisierten Mittelblock durch Mean-Field-Kalkulation auf Basis der RPA simuliert wurden. Das experimentell ermittelte Phasenseparationsverhalten der dargestellten Proben erfolgt im Einklang mit der berechneten Spinodalbedingung. Zum besseren Verständnis des Phasenseparationsverhaltens wurde das dynamische Relaxationsverhalten des Systems betrachtet. Zu diesem Zweck wurden Untersuchungen mittels dielektrischer Breitbandspektroskopie durchgeführt. Es wurde gezeigt, dass lokale Beweglichkeiten in den untersuchten Blockcopolymeren gehemmt und kooperative Bewegungen der α-Relaxationsprozesse im PPMA-Block langsamer bzw. bei höheren Temperaturen und im glasartigen PMMA-Block schneller bzw. bei niedrigeren Temperaturen als in den jeweiligen Homopolymeren erfolgen. Nach Untersuchung der Festkörpermorphologie wurden nicht-, mono-, di- und multifunktionalisierte Blockcopolymere hinsichtlich ihrer Morphologieausbildung in dünnen Filmen untersucht. Prinzipiell finden sich in dünnen Filmen dieselben Morphologien wie in Bulk. Durch die eingeschränkte Geometrie der Filme kommt es in dicken Filmen zur Ausbildung von Strukturen, die parallel zur Siliciumwaferoberfläche ausgerichtet vorliegen, während in sehr dünnen Filmen mit Schichtdicken kleiner als die entsprechenden Bulkdomänenabstände stehende Strukturen erzwungen werden. Für zylindrische Morphologien ist der Einfluss der Filmdicke auf die Orientierung der Strukturen deutlicher als für symmetrische lamellare Morphologien. Im Hinblick auf eine spätere Anwendung von nanostrukturierten Diblockcopolymeren wurden im Rahmen des Projektes verschiedene Ansätze verfolgt, für die nicht-, mono- und difunktionalisierte Diblockcopolymerproben der vorliegenden Arbeit von Projektpartnern eingesetzt wurden. Besonders wichtig war in diesem Zusammenhang die Anwendung von Blockcopolymeren als Template zur Erzeugung geordneter Silica-Strukturen. An der Universität von Modena und Reggio Emilia wurde eine Dissertation zum Thema organisch-anorganischer Hybridmaterialien durch den Sol-Gel-Prozess angefertigt. Die in der genannten Arbeit entwickelten Methoden wurden für die vorliegende Arbeit übernommen und für multifunktionalisierte Blockcopolymersysteme weiterführend selbst untersucht. Erste Untersuchungen zur Einschätzung der Templateigenschaften von Alkylmethacrylat-Blockcopolymeren in Silica-Sol-Gel-Reaktionen wurden an einigen multihydroxylfunktionalisierten Di- und Triblockcopolymeren durchgeführt. Die ersten vorliegenden Ergebnisse geben Grund zur Annahme, dass multihydroxylfunktionalisierte Blockcopolymere in der Lage sind, die Ausbildung von Silica-Partikeln bei in-situ durchgeführten Sol-Gel-Reaktionen mit SiO2-Precursoren in eine Richtung zu lenken, eine chemische Anbindung von organischer und anorganischer Phase zu erzwingen und die Form der ausgebildeten Silica-Nanostrukturen durch die vorgegebene Diblockcopolymermorphologie zu beeinflussen. Tatsächlich ist es gelungen, Silica in geordneter Weise in die Zylindermorphologie von PPMA-b-PMMA-Diblockcopolymeren einzubinden. Versuche, die organische Matrix durch Lösungsmittel oder Pyrolyse zu entfernen und die verbleibenden Silica-Strukturen hinsichtlich Ihrer Form und Porosität zu charakterisieren, werden zukünftig zum Verständnis des Bildungsprozesses in einer bevorzugten Phase oder an deren Grenzfläche beitragen. Die Steuerung der Silica-Partikelform kann nur dann tatsächlich gezielt erfolgen, wenn Phasenverhalten und Morphologiebildung für das Composit-System mit Silica-Precursor und verschiedenen Zwischenstufen mit jeweils unterschiedlichen Wechselwirkungen zu den Blockcopolymerphasen sowohl aus theoretischer Sicht verstanden als auch experimentell über eine größere Bandbreite nachgewiesen wurden. Das in dieser Arbeit entwickelte Blockcopolymersystem ließe sich in Bezug auf seine chemische Struktur sehr leicht auf vielfältige Weise erweitern. Für multifunktionalisierte Blockcopolymere bietet sich eine große Bandbreite von Variationen hinsichtlich Zusammensetzung, Molmasse und Verteilung von funktionellen Gruppen über beliebige Positionen entlang der Polymerkette sowohl innerhalb der drei für die vorliegende Arbeit gewählten Klassen von Di- und Triblockstrukturen als auch außerhalb dieser an. Es wurde gezeigt, dass eingebaute Allylfunktionen in der Lage sind, Vernetzungsreaktionen einzugehen, die u. U. steuerbar sind und zu definierten Nanogelstrukturen umgesetzt werden könnten. Kohlenstoffdoppelbindungen bieten Angriffspunkte für eine Vielzahl von polymeranalogen Umsetzungen, so dass aus allylfunktionalisierten Blockcopolymeren ein Pool von unterschiedlich funktionalisierten Blockcopolymeren darstellbar ist. Die Resultate der vorliegenden Arbeit zeigen, dass eine Anbindung funktioneller Gruppen an das Alkylmethacrylat-Blockcopolymer unter den gewählten Bedingungen mit guter Kontrolle über Anzahl und Position der Gruppen entlang der Kette grundsätzlich möglich ist. Der Einfluss der erzeugten funktionellen Gruppen auf das Mikrophasenseparationsverhalten des Blockcopolymersystems wurde eingeschätzt und wird in künftigen Arbeiten zum Verständnis der Strukturbildung in organisch/anorganischen Hybridmaterialien beitragen
The present study deals with the synthesis of alkyl methacrylate block copolymers, the characterization of their chemical structure and the microphase separation behavior in bulk and thin films. The main objective of this work was the attachment of functional groups to an alkyl methacrylate diblock copolymer system. A first evaluation of the ability of functionalized block copolymer structures to act as a templating material regarding silica formation in sol-gel synthesis of alkoxysilanes was aspired. The diblock copolymer system of poly(pentyl metacrylate-b-methyl methacrylate) (PPMA-b-PMMA) was chosen. It was synthesized following the mechanism of anionic polymerization to achieve effective control over molar mass, composition and polydispersity. The allyl functionality was chosen for a versatilely modifiable and stable functional group and attached to the terminal chain end by endcapping the living polymer chain ends with allyl bromide. The head of the chain was functionalized by initiation with allyl lithium. By combining functional initiation and endcapping, bifunctional diblock copolymers were synthesized. Furthermore multifunctionalized block copolymers were produced by anionic polymerization. By sequential anionic polymerization of PMA, allyl methacrylate and finally MMA, triblock copolymers were obtained. Two more classes of multifunctionalized block copolymers with functional groups randomly distributed in one of the two blocks were synthesized by random copolymerization. All types of mono-, di- and multiallylfunctionalized block copolymers were transformed into mono-, di- and multihydroxylfunctionalized block copolymers by hydroboration and subsequent oxidation. The polymer-analogue reaction of hydroxyl groups to triethoxysilane functions was carried out exemplarily for hydroxy terminated PMMA. The microphase separation behavior of the block copolymers was investigated by a combination of methods such as SAXS, T-SAXS, GISAXS, TEM and AFM. The influence of number and position of functional groups along the chain was examined. The block copolymers synthesized show a microphase separation behavior in accordance to previous results. Despite the low value of the Flory-Huggins interaction parameter χPMA,MMA = 0,065 phase separation occurred and the transition from the ordered to the disordered state (ODT) was followed for selected samples. Bulk morphologies are not influenced by the presence of one or two allyl or hydroxyl groups. In case of considerably more than two functional groups attached to the block copolymer chain the microphase separation behavior of nonfunctionalized and functionalized block copolymers cannot be compared directly. Block copolymers having functional groups randomly distributed along the chain of one of the two methacrylic blocks generally show the typical behavior of diblock copolymers. Their phase separation becomes less pronounced than in pure diblock copolymers, sometimes cannot be detected. To some extent this observation may be referred to increased polydispersities and partial crosslinking. If considerably more than two groups were attached to the block copolymer chain, the tendency towards phase separation increased in case of an increasing value of the effective interaction parameter compared to nonfunctionalized diblock copolymers. Microphase separation behavior and morphology formation are more affected by highly polar groups such as the hydroxyl function than by less polar groups like the allyl function. In triblock copolymers with a middle block of successive allyl or hydroxyl functions the systems tends to form a three phase system which offers much more possibilities regarding the formation of ordered structures. Experimental results of phase separation were compared to theoretical phase diagrams, which were calculated by a Mean Field approach for nonfunctionalized diblock and triblock copolymers with multiallyl- or multihydroxylfunctionalized middle block based on RPA. The experimental results are in good accordance with the simulated spinodal condition. To increase the understanding of microphase separation processes, the dynamic relaxation behavior of the system was investigated. Therefore samples were examined by broadband dielectric spectroscopy. It was shown that local movements of the block copolymer system were decelerated in general, cooperative dynamics of the α processes were slowed down for the fluent PPMA block while they were accelerated for the glassy PMMA block. After bulk morphology investigation thin films of non-, mono-, di- and multifunctionalized block copolymers were prepared. Generally thin films develope the same morphologies as in the bulk state. Due to the confined geometry of a thin film thick films tend to form structures oriented parallel to the wafer surface, while in thin films with thicknesses lower than the respective bulk domain spacing standing structures are constraint. For cylindrical morphologies the impact of film thickness is more obvious than in symmetric lamellar structures. With respect to a possible application of nanostructured diblock copolymers different approaches were taken by project partners using non-, mono- and difunctionalized block copolymers of the present study. Remarkable in this context was the application of block copolymers as template for the creation of ordered silica structures. A doctoral dissertation on organic/inorganic hybrid materials by sol-gel process was prepared in Modena. Methods developed in this thesis were adopted to the present study and further investigated on multifunctionalized block copolymer systems. First investigations aiming at the evaluation of the templating abilities of alkyl methacrylate block copolymers in silica sol-gel reactions were carried out with multihydroxyfunctionalized di- and triblock copolymers. Preliminary results give reason to the expectation of multihydroxyfunctionalized di- and triblock copolymers being able to direct the formation of silica nanoparticles in sol-gel reactions carried out in situ with silica precursors, enforcing the chemical bonding between organic and inorganic phases and influencing the shape of silica nanostructures by the default block copolymer nanostructure. Indeed silica was incorporated successfully into the cylindrical structure of PPMA-b-PMMA diblock copolymers. Future experiments on removing the organic matrix by solvent or pyrolysis to investigate shape and porosity of the remaining silica structures will increase the understanding of the silica formation process inside a preferential phase or at the interface of the block copolymers. Nevertheless, the silica particle shape can be taylored deliberately only if phase separation behavior and morphology evolution in the composite system containing silica precursor and several derivatives thereof with nonuniform interactions towards block copolymer phases are well understood from the theoretical point of view as well as experimental proof needs to be given over a broader range. The block copolymer system developed in the present study easily can be extended manifoldly regarding the chemical structure of the polymer. In the case of multifunctionalized block copolymers a tremendous variety of different products can be obtained by modulation of composition, molar mass and especially distribution of functional groups to any position along the polymer chain far beyond the limits of the three classes of multifunctionalized di- and triblockstructures chosen for this thesis. It was shown that allyl functions incorporated inherently are able to undergo crosslinking reactions, which may be controlled similarly to network formations by inorganic crosslinkers and may result in defined nanogel structures. Furthermore carbon doublebonds are open to attacks for various polymer-analogue reactions hence offering the possibility of creating a pool of differently functionalized block copolymers from a single sample of allylfunctionalized block copolymer. The results of the present study basically prove a feasibility of the binding of functional groups to alkyl methacrylate block copolymer chains with high control over number and position of functional groups along the polymeric chain. The impact of functional groups on the microphase separation behavior of the block copolymer system was evaluated and will increase the understanding of structure formation in organic/inorganic hybrid materials of future work

The main objective of this work is to research and obtain surface protected topological states in nano-ribbons created from the leaves of Germanene and Silicene. These sheets belong to the class of Topological Insulators and correspond to monolayers of germanium and silicon atoms in a hexagonal arrangement that is similar to the graphene sheet. For this investigation, we conducted a study of the electronic and structural properties of these sheets, as well as their respective nano-ribbons through first-principles calculations based on density functional theory (DFT). In this methodology we use the generalized gradient approximation (GGA) for estimating the exchange and correlation term, and the PAW method for the effective potential and the expansion of plane waves of the Kohn-Sham. We conducted a computer simulation with the aid of the package VASP (Vienna ab-initio Simulation Package). As a starting point for our research, we used the methodology of solid state physics in order to describe the crystalline structure of the leaves as well as their mutual space. Subsequently we analyze the band structure, from which many of its properties can be visualized. For this task, we initially proceeded to investigate the stability of these systems via total energy calculations, in turn obtaining the network parameters that minimizes the energy of the system. We also obtained the energy cutoff, ECUT used in our calculations, or in other words, determining the number of plane waves needed to expand the electronic wave functions on the DFT formalism. We continued our study, with the creation and analysis of two different configurations of nano-ribbons, one that corresponds to a straightforward cut of the sheet with the armchair termination pattern, and the other based on a reconstruction of those edges, which provide an energetically more stable system. Subsequently we obtained electronic structures, and conducted a study of its variation due to the change of the width of the nano-ribbon and ionic relaxation of its edges. In a way, we modified the above parameters in order to obtain a system that would give us a zero gap, or at least insignificant, as well as a specific configuration for the spin texture, in order to verify the evidence of surface protected topological states in these nano-ribbons.
O objetivo principal deste trabalho é a investigação e obtenção dos estados topologicamente protegidos de superfície em nano-fitas criadas a partir das folhas de Germaneno e Siliceno. Estas folhas pertencem a classe dos Isolantes Topológicos e correspondem a monocamadas de átomos de Germânio e Silício, em um arranjo hexagonal que se assemelha a folha do Grafeno. Para esta investigação, realizamos um estudo das propriedades eletrônicas e estruturais destas folhas, bem como de suas respectivas nano-fitas, através de cálculos de primeiros princípios fundamentados na teoria do funcional da densidade (DFT). Nesta metodologia utilizamos a aproximação do gradiente generalizado (GGA) para a estimativa do termo de troca e correlação, e o método PAW para o potencial efetivo e a expansão em ondas planas dos orbitais de Kohn-Sham. Realizamos a simulação computacional com o auxílio do pacote VASP (Vienna ab-initio Simulation Package). Como ponto de partida para nossa pesquisa, utilizamos a metodologia da física do estado sólido com o intuito de descrever a estrutura cristalina das folhas, bem como seu espaço recíproco. Posteriormente analisamos as estruturas de bandas, a partir das quais muitas de suas propriedades podem ser visualizadas. Para esta tarefa, inicialmente procedemos à investigação da estabilidade destes sistemas via cálculos de energia total, obtendo o parâmetro de rede a que minimiza a energia do sistema. Obtivemos também a energia de corte ECUT utilizada em nossos cálculos, ou em outras palavras, a determinação do número de ondas planas necessárias para expandir as funções de onda eletrônicas no formalismo da DFT. Prosseguimos nosso estudo, com a criação e análise de duas distintas configurações de nano-fitas, uma que corresponde a um corte simples e direto da folha com terminação no padrão armchair, e a outra baseada em uma reconstrução destas bordas, que acaba por fornecer um sistema mais estável energeticamente. Posteriormente obtivemos as estruturas eletrônicas, e realizamos um estudo de sua variação em função da alteração da largura da nano-fita e a relaxação iônica de suas bordas. De certa maneira, modificamos os parâmetros acima, de forma a obter um sistema que nos fornecesse um gap nulo, ou pelo menos desprezível, bem como uma determinada configuração para a textura de spin, de modo a verificarmos a evidência de uma proteção topológica nos estados de superfície nestas nano-fitas.
Mestre em Física

Les ressources fossiles que sont le gaz ou le pétrole permettent non seulement de couvrir la majeure partie des besoins énergétiques mondiaux, mais fournissent également les briques élémentaires carbonées utiles à des pans entiers de l’industrie chimique. L’utilisation massive de ces combustibles fossiles pose toutefois un problème écologique majeur, le réchauffement climatique, qui se doublera à terme d’un problème de disponibilité de ces ressources. Pour pallier ces difficultés, une des solutions envisagées consiste à abandonner progressivement les hydrocarbures fossiles au profit de ressources carbonées renouvelables telles que le CO₂ ou la biomasse lignocellulosique pour le stockage de l’énergie et/ou comme sources de produits chimiques. Cette entreprise, qui se propose de transformer des substrats fortement oxygénés contenant des liaisons C=O et C–O, requiert fondamentalement un apport d’énergie sous la forme de transferts d’électrons dans des réactions de réduction pour former des liaisons C–H qui préexistent dans les produits dérivés du pétrole. Dans ce contexte, le présent travail doctoral se propose en premier lieu de définir les attributs d’un réducteur renouvelable, c’est-à-dire d’une espèce chimique adaptée à la réduction – limitée à des transferts d’hydrure – de ressources renouvelables oxygénées tel que le CO₂. Les avantages et inconvénients de différentes sources d’hydrure (H₂, acide formique, hydroboranes et hydrosilanes) seront ainsi analysés à la lueur de considérations thermodynamiques et cinétiques et la renouvelabilité de ces réducteurs sera discutée. Dans un second temps, les propriétés réductrices de nouveaux réducteurs renouvelables que sont les formiates de bore et de silicium seront étudiées. Ces composés combinent une source d’hydrure renouvelable, l’acide formique, avec un élément oxophile du groupe principal dont les propriétés stéréoéléctroniques sont modulables. Par un dialogue entre expérience et théorie, il sera démontré que ces composés peuvent avantageusement remplacer les hydroboranes ou hydrosilanes, non renouvelables, dans différents processus réducteurs qui seront unifiés derrière le concept plus général d’hydroélémentations par transfert
The utilization of cheap and abundant sustainable resources such as carbon dioxide or biomass derivatives as source of fuel and chemicals imposes the development of efficient reduction methods, able to promote the conversion of C-O bonds (π and σ) into C-H bonds in an energy and atom efficient manner. Within the realm of C-O reduction methods, the utilization of main group element-based hydrides (e.g. LiAlH₄ or NaBH₄) has proven highly beneficial in terms of selectivity and versatility in the reduction of various functional groups, including poorly electrophilic CO₂. This behavior not only stems from the positive kinetic attributes of these reductants in hydride transfer reactions but also from the oxophilicity of the main group elements that ensures the reductions are downhill processes. Yet, the latter appealing features comes at an energetic price, and the preparation of main group hydrides mainly relies on energy-demanding processes, which in turn limit the recyclability of these reductants. With the goal in mind to circumvent these limitations while preserving the beneficial properties of the main-group element during reduction, one of the major objectives of the research project presented therein was to study the unknown reductive chemistry of boryl formate and silyl formates. The latter indeed combine a renewable hydride source (formic acid can be obtained by 2e electroreduction of CO₂) linked directly to the main group element by the oxygen atom of the formate, which hints at the recyclability of this class of main group element-based reductants. Through a joint experimental and theoretical study, it will be demonstrated that these compounds can advantageously replace non-renewable hydroboranes or hydrosilanes in various reducing processes, which will be unified behind the more general concept of transfer hydroelementation

Cette thèse est consacrée à l'étude des effets isotopiques dans les atomes neutres et ions négatifs. En particulier, nous ciblons notre recherche sur le calcul ab initio des déplacements isotopiques (DI) sur les électroaffinités des éléments des blocs p des deuxième et troisième périodes (B à F et Al à Cl). Ces derniers sont les systèmes les plus susceptibles d'être l'objet d'études expérimentales de haute précision.

Le premier chapitre se concentre sur une étude didactique du problème atomique et des effets isotopiques. Nous concluons par une description détaillée des motivations de notre thèse.

Le second chapitre présente le modèle Hartree-Fock (HF) et son extension multi-configurationelle (MCHF). Nous y énonçons le théorème de Brillouin et sa généralisation à un ansatz MCHF. Pour ce faire, nous formulons de manière originale le principe d'invariance d'une fonction d'onde CAS (Complete Active Set) par rapport aux rotations d'états d'orbitales. De cette formulation, nous caractérisons la famille des solutions CAS n'interagissant pas avec une fonction d'état de configuration (CSF) particulière et démontrons sa multiplicité. Finalement, nous appliquons notre technique d'analyse à l'étude de modèles concrets et prédisons l'apparition de minima locaux correspondant à chacune de ces solutions GBT. Introduisant le concept de quasi-symétrie de la fonctionnelle d'énergie, nous expliquons l'origine de fortes perturbations du "coeur" atomique dans des modèles particuliers.

Les troisième et quatrième chapitres fournissent les outils méthodologiques de base utilisés dans la deuxième partie de notre thèse qui présente des résultats quantitatifs originaux.

Le cinquième chapitre traite des DI et structures hyperfines des termes les plus bas de S, S-, Cl, Cl-, Si et Si-.

Dans le sixième chapitre, nous rapportons un profond désaccord entre théorie et expérience au sujet de la structure hyperfine de transitions de l'azote dans le infrarouge lointain. Nous montrons que les simulations basées sur nos valeurs de constantes isotopiques sont compatibles avec les spectres enregistrés moyennant une réassignation des raies faibles à des signaux de "cross-overs". Sur cette base, nous déduisons un nouvel ensemble de constantes hyperfines pour les états considérés, en bon accord avec nos valeurs théoriques, en nous basant uniquement sur les données expérimentales.

Le septième chapitre est une étude globale des configurations de plus basse énergie du C et C- (i.e. tous les états liés de ce dernier). Par une étude détaillée de nos incertitudes, nous obtenons des estimations très fiables et de grande précision pour un ensemble de propriétés. En particulier, nous présentons les valeurs de structure fine et hyperfine du C-, ainsi que les probabilités de transitions intra-configurationelles fournissant une base solide pour l'étude spectroscopique de ce système.

Dans le huitième chapitre, nous étudions la périodicité du déplacement spécifique de masse sur l'électroaffinité dans le Tableau Périodique des Eléments. Nous avançons les contributions dominantes qui interviennent dans cette grandeur et analysons les principales limitations des techniques de calcul actuelles dans ce contexte.

Nous présentons nos conclusions générales et les perspectives de notre travail dans le neuvième chapitre.

Doctorat en Sciences
info:eu-repo/semantics/nonPublished

Elektronik för extrema miljöer, som kan användas vid hög temperatur, hög strålning och omgivning med frätande gaser, har varit starkt önskvärd vid utforskning av rymden och övervakning av kärnreaktorer. Kiselkarbid (SiC) är en av kandidaterna inom material för extrema miljöer på grund av sin höga temperatur- och höga strålnings-tolerans. Syftet med denna avhandling är att karakterisera 4H-SiC MOSFETar vid hög temperatur och att konstruera SPICE modeller för 4H-SiC MOSFETar. MOSFET-transistorer karakteriserades till 500°C. Med användande av karaktäristik för en 4H-SiC NMOSFET med L/W = 10 µm / 50 µm, anpassades en SPICE LEVEL 2 kretsmodell. Modellen beskriver DC karakteristiska av 4H- SiC MOSFETar mellan 25ºC och 450ºC. Baserat på SPICE-kretsmodellen simulerades egenskaper för operationsförstärkare och digitala inverterar. Därutöver analyserades driften av pseudo-CMOS vid hög temperatur och principen för konstruktion av pseudo-CMOS föreslogs. Arean och utbytet (s.k. yield) av pseudo-CMOS integrerade kretsar uppskattades och det visar sig att SiC pseudo-CMOS integrerade kretsar kan använda mindre area än SiC CMOS integrerade kretsar.
Harsh environment electronics, which can be operated at high-temperature, high-radiation, and corrosive gas environment, has been strongly desired in space exploration and monitoring of nuclear reactors. Silicon Carbide (SiC) is one of the candidates of materials for harsh environment electronics because of its high-temperature and high-radiation tolerance.‌ The objective of this thesis is to characterize 4H-SiC MOSFETs at high- temperature and to construct SPICE models of the 4H-SiC MOSFETs. The MOSFET devices were characterized up to 500ºC. Using the characteristic of a 4H-SiC NMOSFET with L/W = 10 µm/50 µm, a SPICE LEVEL 2 circuit model was constructed. This model describes the DC characteristic of the 4H-SiC MOSFETs in the range of 25 – 450ºC. Based on the SPICE circuit model, the characteristics of operational amplifiers and digital inverters were simulated. Furthermore, the operation of pseudo-CMOS at high-temperature was analyzed and the operation principle of pseudo-CMOS was suggested. The device area and yield of pseudo-CMOS integrated circuits were estimated and it is shown that SiC pseudo-CMOS integrated circuits can use less area than SiC CMOS integrated circuits.

Im Rahmen dieser Arbeit wurden Siliciumkomplexe mit dianionischen Pyrrol-2-carbaldimin-funktionalisierten N,N,O- und N,N,N,N-Chelatliganden synthetisiert und kristallografisch, NMR- und UV/Vis-spektroskopisch und mittels quantenchemischer Berechnungen charakterisiert. Die pentakoordinierten Si-Komplexe mit N,N,O-Ligandrückgraten wiesen in Abhängigkeit von den weiteren Si-gebundenen Substituenten unterschiedlich konfigurierte verzerrt trigonal-bipyramidale Si-Koordinationssphären auf. Die Ursache der Farbigkeit dieser Verbindungen konnte mittels quantenchemischer Berechnungen detailliert erklärt werden. – Die Si-Komplexe mit N,N,N,N-Ligandrückgraten liegen in Abhängigkeit von den weiteren Si-gebundenen Substituenten als 5-fach koordinierte kationische oder neutrale 6-fach koordinierte Si-Komplexe vor. Deren Farbigkeit wurde mittels UV/VIS-Spektroskopie untersucht. Von ausgewählten Komplexen wurden die Tensoren der 29Si-NMR-Verschiebung rechnerisch und CP/MAS-NMR-spektroskopisch bestimmt.

Les compositions isotopiques du fer et du silicium au sein des différents réservoirs géologiques de haute température montrent des variations isotopiques significatives. Cependant, les mécanismes à l'origine de ces fractionnements ne sont pas clairement identifiés. La connaissance de ces mécanismes et des coefficients de fractionnement à l'équilibre est essentielle à l'interprétation des mesures faites sur les roches magmatiques naturelles. Cette étude multidimensionnelle est basée sur le calcul théorique des propriétés isotopiques du fer et du silicium dans les minéraux et les liquides silicatés, l'analyse des isotopes du fer dans les laves des Iles Kerguelen ainsi que le développement d'une méthode d'analyse in situ des isotopes du fer dans les verres silicatés et les olivines grâce à un laser femtoseconde couplé à un spectromètre de masse MC-ICP-MS. Nous présentons les propriétés isotopiques du fer et du silicium d'une variété de minéraux présents dans la croûte et le manteau, ainsi que pour la première fois, de liquides silicatés de diverses compositions. Nos résultats montrent que le fractionnement du fer et du silicium entre les minéraux contenant du Fe2+ est significatif même à haute température. Nous suggérons ici qu'après la température et le redox, les seconds voisins du silicium et du fer influent grandement le fractionnement isotopique. A partir des coefficients de fractionnement entre minéraux et liquides silicatés, nous proposons que la cristallisation fractionnée puisse être le processus majeur impliqué dans l'évolution isotopique du fer et du silicium lors de la différentiation magmatique. L'étude de la composition isotopique en fer des laves de Kerguelen souligne la complexité de l'évolution du point chaud au cours du temps, impliquant potentiellement une hétérogénéité du manteau. Enfin, le développement d'une méthode d'analyse couplant un MC-ICP-MS à un laser femtoseconde, a permis d'effectuer des mesures isotopiques du fer in situ d'olivines et de verres silicatés avec des incertitudes inférieures à 0.2 ‰
Iron and silicon isotope measurements in high-temperature geological reservoirs display significant isotopic fractionations, especially within the Earth's crust. However, the mechanisms involved in these fractionations are not fully understood. Their knowledge and that of the fractionation factors in equilibrium conditions is central to interpret the measurements carried on natural rocks. To address this issue, this work is a multidimensional approach based on first principles calculation of Fe and Si isotope fractionations in minerals and silicate melts, on Fe isotope measurements of lavas from Kerguelen Archipelago and on analytical developments of in situ Fe isotope measurements of glasses and olivines using a femtosecond laser coupled to MC-ICP-MS. We provide the theoretical Fe and Si isotope properties of various minerals relevant to Earth crust formation and, for the first time, of silicate melts. Results suggest that significant Fe and Si isotope fractionations are expected between Fe2+-bearing minerals at high temperature. We also show that, besides temperature and redox changes, iron and silicon second neighbors have a major impact on isotopic fractionations. From our set of equilibrium fractionation factors between minerals and melts, we suggest that fractional crystallization could be the main process involved in Fe and Si isotope evolution during magmatic differentiation. In addition, iron isotope composition of Kerguelen oceanic basalts underlines the complexity of the hotspot evolution, with potential source heterogeneity. Finally, the analytical developments performed on MC-ICP-MS with femtosecond laser, allow in situ Fe isotope measurements of silicate glasses and minerals with an uncertainty better than 0.2‰

Dissertation (Ph.D.)--Worcester Polytechnic Institute.
Keywords: laser beam characteristics; heat transfer; hole profile; MEMS; hole formation; laser micromachining; laser microdrilling; plasma effects; silicon; 304 stainless steel; Fourier theory; lattice-phonon vibration. Includes bibliographical references. (p.379-390)

Aufgrund ihrer Eigenschaften und möglicher Anwendungen werden Siliciumkomplexe mit O,N,O´-Ligandsystemen in der Literatur beschrieben. Jedoch fehlen bisher Untersuchungen zur Strukturaufklärung. Im Rahmen dieser Arbeit wurden zahlreiche Silicium-, Germanium- und Zinnkomplexe mit chiralen O,N,O´-Liganden synthetisiert und strukturanalytisch charakterisiert. Dazu wurden die Liganden durch Kondensationsreaktionen von enantiomerenreinen Aminosäuren mit aromatischen ortho-Hydroxyaldehyden bzw. Acetylaceton hergestellt. Die weitere Umsetzung der Liganden mit Elementhalogeniden der Gruppe 14 führte zu den angestrebten Komplexverbindungen. Alle hergestellten Verbindungen wurden umfassend charakterisiert (NMR-, UV/Vis-, IR-Spektroskopie, Elementaranalyse, Einkristallstrukturanalyse, Drehwert). Quantenchemische Berechnungen an einfachen Modellverbindungen sowie an hergestellten Silicium- und Zinnkomplexen führten zu einem grundlegenden Verständnis der Festkörper-NMR-Parameter dieser Verbindungsklasse.

This thesis "Silicone damper of a six-cylinder in-line diesel engine " is focused on the proposal of alternative using of silicone damper for the a six-cylinder in-line diesel engine, which is made for tractors and other industrial aplications. The aim of this thesis is to count the oscilation of crankshaft by the help of appropriate dynamic model, then to propose such a basic parameters of silicone damper, which absorbes torsion blip crankshaft to acceptable value. The next part of my thesis is proposal of the constructive implementation of fixation the silicone damper on the free part of crankshaft. The last part of my thesis is comparing and evaluating the oscilation of crankshaft without a dumper and with a new propsal of the silicone damper.

Le graphène est un cristal bidimensionnel composé d'atomes de carbone arrangés sur un réseau en nids d'abeille. Ce matériau présente des propriétés électroniques intéressantes tant au niveau fondamental qu'en vue d'applications avec notamment une structure de bande exotique en " cône de Dirac " et de grandes mobilités de porteurs. Sa fabrication par graphitisation du SiC est particulièrement adaptée aux applications électroniques. Nous avons étudié ce système par microscopie à effet tunnel (STM) et simulations numériques ab initio avec comme objectif la caractérisation au niveau atomique de l'interface graphène - SiC(000-1) (face carbone) et l'étude de l'impact du substrat sur la structure électronique du graphène. Après un chapitre introductif à la thématique du graphène, suivi d'un chapitre présentant les deux techniques utilisées au cours de ce travail, nous présentons nos échantillons faiblement graphitisés obtenus sous ultra-vide. Nous avons identifié deux types d'interfaces, les reconstructions natives de la surface du SiC(000-1) appelées (2x2)C et (3x3), sur lesquelles reposent les ilots monoplan de graphène, avec un fort désordre rotationnel donnant lieu à des figures de moiré sur les images STM. Nous montrons par imagerie STM et spectroscopie tunnel que l'interaction graphène/(3x3) est très faible. Nous étudions ensuite le cas d'interaction plus forte graphène/(2x2) successivement du point de vue des états du graphène et des états de la reconstruction, dans l'espace direct et réciproque, de façon expérimentale et théorique. Enfin, nous considérons l'effet de défauts observés par STM à l'interface des ilots sur (2x2), modélisés par des adatomes d'hydrogène, sur le dopage et la structure de bande électronique du graphène.

The objective of this theses is arch bridge design over the expressway. Bridge is consist of bridge deck, which has three pillars and composite arc. The Bridge deck is on the edges fixed into the foundations and in the middle adherent on overhead cables. The bridge is carried by combination of strands and aerial cables mounted on reinforced concrete arch. Overhead cables are slant due to the transverse direction of the bridge in the longitudinal direction is in the direction of the arc. Model of the construction was made in a calculated program SCIA ENGINEER 2011. The designe is in accordance with applicable standards.

Im Fokus dieser Arbeit standen zwei Ziele. Zum einem war es Forschungsgegenstand, dass Konzept der Zwillingspolymerisation auf germaniumhaltige, molekulare Vorstufen wie zum Beispiel Germylene, spirozyklische Germaniumverbindungen und molekulare Germanate zu erweitern und somit organisch-anorganische Komposite beziehungsweise Hybridmaterialien darzustellen. Dazu wurden neuartige Germaniumalkoxide auf der Basis von Benzylalkoholaten, Salicylalkoholaten sowie Benzylthiolaten synthetisiert, charakterisiert und auf ihre Fähigkeit Komposite beziehungsweise Hybridmaterialien über den Prozess der Zwillingspolymerisation zu erhalten studiert. Ein zweites Ziel dieser Arbeit war es, Beziehungen zwischen der Struktur und der Reaktivität dieser molekularen Vorstufen sowie deren Einfluss auf die Eigenschaften der erhaltenen Polymerisationsprodukte zu identifizieren und systematisch zu untersuchen. Hierfür wurden zum einen verschiedene Substituenten, welche unterschiedliche elektronische sowie sterische Eigenschaften aufweisen, an den aromatischen Einheiten der molekularen Vorstufen eingeführt. Die Effekte der Substituenten auf den Prozess der Zwillingspolymerisation und auf die Eigenschaften der Komposite beziehungsweise Hybridmaterialien wurden für die Verbindungsklasse der Germanium(II)salicylalkoholate, der molekularen Germanate sowie der spiro-zyklischen Siliziumsalicylalkoholate untersucht. Spirozyklische Siliziumsalicylalkoholate, wie zum Beispiel 4H,4’H-2,2‘-Spirobi[benzo[d][1,3,2]dioxasilin], wurden im Rahmen dieser Arbeit mit einbezogen, da sie aufgrund ihres nahezu idealen Zwillingspolymerisationsprozesses geeignete Modelverbindungen für Reaktivitätsstudien darstellen. Zudem wurde der Einfluss der Substituenten auf die Charakteristika der aus den Kompositen beziehungsweise Hybridmaterialien erhaltenen Folgeprodukte (poröse Kohlenstoffmaterialien und oxydische Materialien) studiert. Des Weiteren wurde eine Serie von spirozyklischen Germaniumthiolaten, welche isostrukturell zu 4H,4’H-2,2‘-Spirobi[benzo[d][1,3,2]dioxasilin] sind, synthetisiert, um systematisch den Einfluss der Chalkogenide, Sauerstoff und Schwefel, in benzylständiger sowie phenylständiger Position auf deren Reaktionsvermögen im Polymerisationsprozess zu untersuchen. Die experimentellen Ergebnisse zu den Struktur-Reaktivitätsbeziehungsstudien wurden, soweit es jeweils durchführbar war, mittels quantenchemische Rechnungen validiert und die daraus gezogenen Schlüsse in die Diskussion zur Interpretation der experimentellen Ergebnisse mit einbezogen.

Дисертація спрямована на вирішення важливої науково-технічної проблеми розвитку науково-технологічних основ високотемпературних (600 –3000 °С) хімічних процесів у електротермічному псевдозрідженому шарі (ЕТПШ) з одержанням чистого графіту, високотемпературного воденьвмісного газу, піровуглецевого покриття, пірографіту та чистого карбіду кремнію. Поставлені задачі вирішені шляхом теоретичних та експериментальних методів вивчення високотемпературних процесів у ЕТПШ. Для аналізу ефективності теплових процесів і режимів роботи використовуються термодинамічні методи, методи теорії тепло- та масообміну, методи теорії подібності. Серед вагомих наукових результатів можна виділити: теоретично та експериментально доведена можливість високотемпературного очищення природного графіту Заваліївського родовища у ЕТПШ; на основі термодинамічних розрахунків визначені основні теплотехнічні характеристики високотемпературних процесів, які доцільно проводити у ЕТПШ; на основі термодинамічних та теплотехнічних розрахунків встановлені основні параметри, необхідні для створення та конструювання нового обладнання з ЕТПШ; створено парк експериментального обладнання з ЕТПШ з різними характеристиками та способом нагрівання для дослідження високотемпературних термохімічних процесів; на основі експериментальних даних та з застосуванням сучасного мікроскопічного обладнання визначена залежність між структурою піровуглецю та теплотехнічними параметрами процесу піролізу вуглеводневих газів; розроблено методику визначення густини піровуглецевого покриття на дисперсному матеріалі; проведенням серії експериментів на різних установках з ЕТПШ визначено оптимальну температуру (1500 °С) та конструкцію реактору з ЕТПШ для виходу 98 % об. водню під час реакції піролізу метану; удосконалено конструкцію реактора з ЕТПШ для обробки діелектричного матеріалу шляхом застосування комбінованого способу нагрівання; вперше експериментально досягнута температура ЕТПШ 3070 °С; вперше експериментально доведено утворення карбіду кремнію з капсульованого піровуглецем кварцового піску при високотемпературній обробці у реакторі з ЕТПШ; експериментально доведена принципова можливість нанесення піровуглецевого покриття у ЕТПШ на моделі мікротвелу, які за своїми фізико-хімічними властивостями наближені до дисперсного ядерного палива (Dy2O3, Gd2O3, Sm2O3); удосконалено методику розрахунку теплового балансу для проведення термохімічних процесів у типовому реакторі з ЕТПШ, під час проведення експериментальних досліджень підтверджено адекватність даної методики; при випробуваннях дослідних зразків пресованих прокладок з терморозширеного графіту (в основу якого закладений графіт очищений у ЕТПШ) було визначено, що їх механічна міцність відповідає показникам раніш використовуваних прокладок фірми «Гідропресс» (РФ). Результати досліджень відкривають перспективи для створення енергоефективної та екологічно чистої технології очищення природного та штучного графіту; можуть бути використані при створенні виробництва водню як для хімічної промисловості, так і для металургії (високотемпературний водневмісний газ); відкривають перспективу створення енергоефективної технології одержання високочистого дрібнодисперсного карбіду кремнію. Одержані експериментальні дані щодо залежності структури піровуглецевого покриття від теплофізичних параметрів процесу та проведені дослідження його матеріалознавчих характеристик, які відкривають широку перспективу застосування одержаних піровуглецевих покриттів у хімічній технлології, енергетиці та різних високотехнологічних галузях. Одержані результати з нанесення піровуглецевого покриття на дисперсні матеріали з високою густиною мають перспективу застосування у спецметалургії. Результати досліджень з виготовлення ущільнюючих прокладок з ТРГ передані ВП «Атоменергомаш» ДП НАЕК «Енергоатом» для створення виробничої дільниці. Повне освоєння всього циклу виробництва ущільнень з ТРГ дозволить ліквідувати імпортозалежність країни в цій сфері та підвищити безпеку експлуатації вітчизняних АЕС. The dissertation is aimed at solving an important scientific and technical problem of development of scientific and technological bases of high – temperature (600… 3000 ° C) chemical processes in an electrothermal fluidized bed (ETFB). These processes include the production of pure graphite, a high-temperature hydrogencontaining gas, pyrocarbon coating, pyrographite, and pure silicon carbide. These problems are solved by theoretical and experimental methods of studying high-temperature processes in the ETFB. To analyze the efficiency of thermal processes and modes of operation, thermodynamic methods, methods of heat and mass transfer theory, methods of similarity theory are used. The important scientific results are: on the basis of thermodynamic calculations the basic thermotechnical characteristics of high-temperature processes which it is expedient to carry out in the ETFB are defined; on the basis of thermodynamic and thermotechnical calculations the basic parameters necessary for creation and design of the new equipment from ETFB are established; the possibility of high-temperature purification of natural graphite of the «Zavaliyevskoye deposit» in the ETFB is theoretically and experimentally proven; a park of experimental equipment with ETFB with different characteristics and method of heating for the study of high-temperature thermochemical processes is created; on the basis of experimental data and with the use of modern microscopic equipment the dependence between the structure of pyrocarbon and thermal parameters of the process of pyrolysis of hydrocarbon gases is proposed; a method for determining the density of the pyrocarbon coating on the dispersed material is developed; conducting a series of experiments on different installations with ETFB the optimal temperature (1500 °C) and the design of the reactor with ETFB for the yield of 98 % vol. hydrogen during the methane pyrolysis reaction are determined; the design of the reactor with ETFB for processing dielectric material by using a combined method of heating is improved; for the first time the temperature of ETFB 3070 °C is experimentally reached; for the first time the formation of silicon carbide from enriched pyrocarbon quartz sand during hightemperature treatment in a reactor with ETFB is experimentally proved; the fundamental possibility of applying a pyrocarbon coating in ETFB on the model of microspherical nuclear fuel, which in their physicochemical properties are close to dispersed nuclear fuel (Dy2O3, Gd2O3, Sm2O3) is experimentally proved; the method of calculating the heat balance for thermochemical processes in a typical reactor with ETFB is improved, during the experimental studies the adequacy of this technique was confirmed; When testing prototypes of extruded gaskets made of thermally expanded graphite (based on graphite purified in ETFB), it was determined that their mechanical strength corresponds to the previously used gaskets of the company "Hydropress" (RF). The research results open up prospects for the creation of energy-efficient and environmentally friendly technology for cleaning natural and artificial graphite; can be used in the creation of hydrogen production for both the chemical industry and metallurgy (high-temperature hydrogen-containing gas); open the prospect of creating an energy-efficient technology for obtaining high-purity fine silicon carbide. The obtained experimental dependences of the structure of pyrocarbon coating on the thermal parameters of the process and the study of its material characteristics open a wide prospect of application of the obtained pyrocarbon coatings in chemical technology, energy, and various high-tech industries. The obtained results on the application of pyrocarbon coating on dispersed materials with high density have the prospect of application in special metallurgy. The results of research on the manufacture of sealing gaskets from thermally expanded graphite were transferred to the Separate subdivision "Atomenergomash" of the State Enterprise "National Energy Company "Energoatom" for the creation of a production site. Full development of the entire cycle of production of thermally expanded graphite seals will eliminate the country's import dependence in this area and increase the safety of domestic nuclear power plants. Die Dissertation ist auf die Lösung des wichtigen issenschaftstechnischen Problems der Ausarbeitung der wissenschaftstechnologischen Grundlagen von Hochtemperaturprozessen (600 – 3000 °C) in der elektrothermischen Wirbelschicht (ETWS) mit Erzeugung des Reingraphits, des wasserstoffhaltigen Hochtemperaturgases, der pyrolytischen Kohlenstoffschicht, des pyrolytischen Graphits und des reinen Siliziumcarbids gerichtet. Die gestellten Aufgaben wurden durch theoretische und experimentale Verfahren zur Untersuchung der Hochtemperaturprozesse in der ETWS gelöst. Zur Analyse der Effektivität von Wärmeprozessen und Betriebsweisen werden die thermodynamischen Verfahren, Verfahren der Theorie des Wärme- und Massenaustausches, Verfahren der Ähnlichkeitstheorie verwendet. Unter den wichtigen wissenschaftlichen Ergebnissen ist es hervorzuheben: es wurde eine Möglichkeit der Hochtemperaturreinigung des Naturgraphits der Lagerstätte Zavaliye in der ETWS theoretische und experimental nachgewiesen; aufgrund der thermodynamischen Berechnungen sind wärmetechnische Haupteigenschaften der Hochtemperaturprozesse bestimmt, die zweckmäßig ist in der ETWS durchzuführen; aufgrund der thermodynamischen und wärmetechnischen Berechnungen wurden Grundparameter festgestellt, die zur Ausarbeitung und Konstruierung neuer Ausrüstung mit der ETWS notwendig sind; es wurde den Park der experimentalen Ausrüstung zur Untersuchung der thermochemischen Hochtemperaturprozesse aufgrund der experimentalen Daten geschaffen und unter Verwendung der modernen mikroskopischen Ausrüstung wurde die Abhängigkeit zwischen der Struktur des pyrolytischen Kohlenstoffs und den wärmetechnischen Parametern des Pyrolyseprozesses von Kohlenwasserstoffgasen bestimmt; es wurde das Verfahren zur Bestimmung der Dichte der pyrolytischen Kohlenstoffschicht auf einem Dispersionsstoff ausarbeitet; durch die Serie der Experimente auf verschiedenen technologischen Anlagen mit der ETWS wurden die optimale Temperatur (1500 °C) und der Aufbau des Reaktors mit der ETWS zur Erzeugung des 98 %-reinen Wasserstoff bei der Pyrolyse des Methans bestimmt; es wurde der Aufbau des Reaktors mit der ETWS zur Bearbeitung eines dielektrischen Stoffs durch Verwendung des kombinierten Erwärmungsverfahrens verbessert; zum ersten Mal wurde die Temperatur der ETWS 3070 °C erreicht; zum ersten Mal wurde die Bildung des Siliziumcarbids aus dem verkapselten mit dem pyrolytischen Kohlenstoff Quarzsands bei der Hochtemperaturbearbeitung im Reaktor mit der ETWS experimental nachgewiesen; es wurde eine prinzipielle Möglichkeit des Auftragens der pyrolytischen Kohlenstoffs in der ETWS auf Modelle des Mikrowärmeentwicklungselements, die nach ihren physikalisch-chemischen Eigenschaften einem Dispersionskernbrennstoff (Dy2O3, Cd2O3, Sm2O3) ähnlich sind, experimental nachgewiesen; es wurde die Methodik der Berechnung der Wärmebilanz zur Durchführung von thermochemischen Prozessen im Wärmereaktor mit der ETWS verbessert, die Angemessenheit dieser Methodik wurde während der experimentalen Untersuchungen bestätigt; beim Test der Versuchmuster der gepressten Dichtungen aus dem thermoerweiterten Graphits (erzeugt aus dem gereinigten in der ETWS Graphit) wurde es festegestellt, dass ihre mechanische Festigkeit den Kennziffern der früher verwendeten Dichtungen der Firma „Hydropress― (RF) entspricht. Die Ergebnisse der Untersuchungen eröffnen Perspektiven zum Schaffen der energieeffektiven Technologie der Reinigung des Natur- und Kunstgraphits; sie können bei der Bildung der Wasserstofferzeugung wie für die Chemieindustrie, als auch für die Metallurgie (das wasserstoffhaltige Hochtemperaturgas) verwendet werden; sie eröffnen auch die Perspektive einer Bildung der energieeffektiven Technologie der Erzeugung des hochreinen Kleindispersionssiliziumcarbids. Die erhaltenen experimentalen Daten in Bezug auf die Abhängigkeit der der Struktur des pyrolytischen Kohlenstoffs von den wärmephysikalischen Prozessparametern und die durchgeführten Untersuchungen dessen Eigenschaften aus dem Gesichtspunkt der Werkstoffkunde, die eine breite Perspektive zur Verwendung der erhaltenen pyropytischen Kohlenstoffschichten in der chemischen Technologie, Energetik und anderen hochtechnologischen Zweigen eröffnen. Die erhaltenen Ergebnisse nach dem Auftragen einer pyrolytischen Schicht auf Dispersionsstoffe mit hoher Dichte haben eine Verwendungsperspektive in der Metallurgie. Die Ergebnissen der Untersuchungen zur Herstellung von Dichtungen aus dem TEG wurden dem BU „Atomenergomash―des SU NAEG „Energoatom― zur Bildung einer Produktionsabschnitts übergeben. Eine vollständige Nutzbarmachung des gesamten Herstellungszyklus von Dichtungen aus dem TEG wird ermöglichen die Importanhängigkeit des Landes in diesem Bereich zu liquidieren und die Betriebssicherheit der einheimischen KKW zu erhöhen.

碩士
國立交通大學
電子研究所
106
The tremendous advances of modern semiconductor technology has brought forth extraordinarily scaling down of transistors, while in the meantime it is approaching the bottleneck caused by the short-channel effect. One possible solution in overcoming this is to increase the gate-to-channel control or suppress the drain-side-voltage effect, such as the Fin Field-Effect Transistor. Another way to suppress the short-channel effect is to eliminate the region dominated by the drain-side electric field (v.s that from the gate), e.g. to fabricate a thinner channel, and the thinnest that can possibly be made is a single layer of atoms, the so-called two-dimensional materials. Silicene, compared to the first two-dimensional material graphene, not only has a potential advantage of being highly compatible with traditional silicon-based transistor, but also preserve the super high mobility as graphene. In fact, in 2015, a prototype of the first silicene transistor has been demonstrated to be feasible We perform density-functional calculations of both a stand-alone silicene and the interface with the silicon dioxide. Since a strain less silicene has a gapless Dirac cone, we first calculate the electronic structures of the stand-alone strained silicene, and observe its band gap opened as a function of the applied strains. We perform such calculations using a wide range of exchange-correlation functionals, including not only the standard local-density and generalized-gradient approximations but also hybrid functionals HSE06, PBE0, and B3LYP, and further go beyond density-functional theory using the GW approximation to justify which of the above exchange-correlation functionals outperforms the rest in determining the band gap. Then we place the silicene on a silicon dioxide substrate, expecting the mismatch strain to open a band gap. To avoid chemical bonding at the interface so that the silicene π-bonds and in turn the Dirac-cone high mobility are preserved, we need to carefully choose an appropriate termination atomic layer of the silicon dioxide and introduce additional passivation atoms at the interface. We find the Si-terminated silicon dioxide surface passivated by the hydrogen atoms serves as the optimal substrate to obtain a high-mobility semiconducting silicene on top of it, among all the cases in this study. Further investigation into the interface bonding reveals that the optimal property of the above surface likely results from one bond per passviated atom. This suggest that further experiments in fabricating silicene on a silicon dioxide surface may consider passivation treatments using hydrogen, halogens, or single-dangling-bond functional groups like hydroxides. Direct calculations of the mobility of the strain-free, strained but stand-alone, and on-substrate silicenes show that the strained one preserves the same order of magnitude for the mobility, and that of the on-substrate is estimated to be lowered by one order. All our computational findings can provide helpful preliminary guidance in developing transistor based on two-dimensional materials that is feasible in the industrial product lines.

碩士
國立中山大學
物理學系
85
The large specific surface area of the orous silicon (PS) enables us to distinguish surface vibrational modes from the bulk vibrational modes observed in recent Fourier transformation infrared spectroscopy (FTIR) measurements. In a first step to understand these observations, we have performed ab initio molecular-dynamics (MD) calculations for the vibrational frequencies for the Si (001) surface by the Fourier transformation of the auto correlation functions of velocities of the Si atoms. Our MD method isbased on the real-space Norm-conserving pseudopotential method implemented with the Ceperley-Alder exchange-correlation potential. We have identified that, the vibrational frequency at 180.4 cm-1 can be attributed to dimers on the Si(001) surface. The vibrational frequencies, 48.1 cm-1, 66.1 cm-1, and 518 cm-1 found in this study are near-surface Si vibrational modes. The vibrational frequency at 502 cm-1, is identified to be due to the vibrational motion of inner-layer silicon atoms, which agrees with the Raman measurements.

The evolution of the solar cell market has motivated significant advances in the search of cheaper and more efficient materials. Crystalline silicon is one of the most dominant materials for photovoltaic (PV) applications, with one of the best cost-efficiency relations available. However, there is room for improvement with the elimination or passivation of many defects that can trap positive and negative charge carriers (holes and electrons) followed by their recombination. Transition metal (TM) impurities are among the most dangerous recombination centers contributing severely to the loss of the efficiency of the solar cells. While some of them can be driven to form large precipitates in the grain boundaries of the crystals, opening some "impurity-free"paths, others, due to their low diffusivity, will stay isolated or in the form of small aggregates. Hydrogen passivation is considered to be an important solution for the mitigation of the electrical activity associated to these defects. The main goal of this thesis is to study the interaction between hydrogen and several defects originating either from transition metals or other common impurities in solar silicon by means of first-principles calculations based on the density functional theory. These calculations were done with the application of the generalized gradient approximation (GGA) for the exchange and correlation potentials, employing 216 and 512-Si supercells. The issues addressed here can be divided in three parts: the calculation of the electronic structure of isolated transition metal impurities in silicon (chapter 3), the interaction between hydrogen and these metallic impurities (chapters 4 and 5), and the interaction between hydrogen and defects originating from common impurities such as Carbon and Oxygen (chapter 6). The main results of this thesis can be summarized as follows: (i) in agreement with previous models and with the available experimental data, slow-diffusing transition metals from groups IV, V and VI are stable at the tetrahedral interstitial sites, producing significant electronic activity, with multiple deep donor levels, and, in some cases, acceptor levels; (ii) the effectiveness of hydrogen passivation of the electronic activity arising from transition metal impurities is limited by the doping type of the material: while in n-type silicon the formation of metallic-hydrogen complexes is likely, in p-type this is not possible to observe due the long range electrostatic repulsion between positively charged hydrogen and metallic impurities; (iii) these metallic-hydrogen complexes display appreciably less electronic activity than the isolated metallic impurities and, in some cases, full passivation is achieved; (iv) the interaction between hydrogen and typically inert impurities such as carbon and oxygen leads to the formation of a defect with multiple stable configurations that can work both as an electron or a hole trap, leading to the recombination.
A evolução do mercado de células solares tem motivado avanços significativos na busca de materiais mais baratos e eficientes. O silício cristalino é um dos materiais mais dominantes para aplicações fotovoltaicas (PV), com uma das melhores relações custo-eficiência disponíveis. No entanto, há espaço para melhorias com a eliminação ou passivação de muitos defeitos capazes de capturar portadores de carga positivos e negativos (lacunas e eletrões), seguindo-se a sua recombinação. Impurezas como os metais de transição são alguns dos centros de recombinação mais eficazes que contribuem drasticamente para a perda da eficiência das células solares. Enquanto alguns deles podem ser levados a formar precipitados nos limites de grão dos cristais, abrindo assim alguns caminhos "livres de impurezas", outros, devido à sua baixa difusividade, permanecem isolados ou na forma de pequenos agregados. A passivação com hidrogénio é considerada uma solução importante para mitigar a atividade elétrica associada a esses defeitos. O objetivo principal desta tese é o estudo da interação do hidrogénio com múltiplos defeitos que têm a sua origem tanto em impurezas de metais de transição como em outras impurezas comuns em silício para aplicações fotovoltaicas através de cálculos de primeiros princípios baseados na teoria do funcional da densidade. Estes cálculos foram realizados com a aplicação da aproximação do gradiente generalizado (GGA) para os potenciais de correlação e troca utilizando super-células de silício de 216 ou 512 átomos. Os assuntos aqui abordados podem-se dividir em três partes: O cálculo da estrutura electrónica de impurezas de metais de transição isoladas em silício (capítulo 3), a interação entre o hidrogénio e essas impurezas (capítulos 4 e 5) e a interação entre hidrogénio e defeitos que têm a sua origem em impurezas comuns tais como o carbono e o oxigénio. Os resultados principais obtidos nesta tese podem ser resumidos do seguinte modo: De acordo com os modelos existentes e os resultados experimentais disponíveis, metais de transição dos grupos IV, V e VI são estáveis em posições intersticiais com simetria tetraédrica, produzindo atividade electrónica significativa, com múltiplos níveis dadores profundos e, em alguns casos, níveis aceitadores; a eficácia da passivação por hidrogénio da atividade electrónica produzida por impurezas de metais de transição é limitada pelo tipo de dopagem do material: enquanto que em silício tipo n a formação de complexos de metal-hidrogénio é possível, no caso de silício tipo p isto não se observa devido à repulsão eletrostática a longa distância entre o hidrogénio e as impurezas metálicas, uma vez que, para este tipo de dopagem, em equilíbrio termodinâmico, ambos se encontram no estado de carga positivo. Estes complexos de metal-hidrogénio apresentam significativamente menos atividade electrónica do que metais isolados, e, em alguns casos, existe uma passivação completa do defeito; a interação entre o hidrogénio e impurezas tipicamente inertes como o carbono e oxigénio resulta na formação de um defeito com múltiplas configurações estáveis e que é capaz de funcionar como um centro de captura tanto para eletrões como lacunas, resultando na sua recombinação.
Programa Doutoral em Engenharia Física

碩士
國立中興大學
物理學系所
101
Advanced MOSFET device formed from novel Si-based materials, such as silicon-germanium (SiGe) alloys, are simple and low cost to manufacture. In this thesis we focus on hole mobility in the inversion layer of the MOSFETs using novel silicon-germanium alloy channel materials. The primary topic of this work is the theoretical calculation of hole mobility in the SiGe alloy PMOSFET inversion layer. Hole mobility in the SiGe alloy inversion layer is calculated using a k.p band structure method and the Kubo-Greenwood mobility formula. The model parameters used in the calculations are calibrated by matching the measured low-field mobility of Si and Ge. We study alloy-limited, phonon-limited, and total mobilities in the inversion layers of relaxed and biaxial strained SiGe on (100), (110), and (111) substrates, respectively.

碩士
國立中興大學
物理學系所
102
With the advantage of being easily integrated into silicon process, silicon-germanium alloy has been applied to Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) components under 28 nm. This study is divided into two parts, including (1) valence band structure of silicon-germanium alloy and (2) hole mobility. In regard to band structure, linear combination of atomic orbits (LCAO) is applied to calculating the band structure of valence band. It is discovered that the splitting energy of Heavy hole and Split of hole at Γ point appears linear with Ge content. The density of states (DOS) and the velocity squared (V2) are calculated by k．p method (6x6 Luttinger-Kohn matrix) and is fitted with polynomial analytical model. The result is close to the numerical computation result. In terms of mobility, Kubo-Greenwood mobility equation is utilized for the calculation. In consideration of phonon scattering and alloy scattering, alloy deformation potential about 0.8-1.0 eV presents more consistent with the experimental measurement.

碩士
國立臺灣大學
光電工程學研究所
105
For several decades, the semiconductor device theory was basically based on semi-classical model, where Poisson, drift-diffusion, and Schrodinger equation with effective mass or k.p method are solved to obtain the solution. The materials were often treated as perfect crystals, then the E-k relation and factors like density of state, effective mass and carrier density can all be written as analytical terms. However, as the dimensions of metal-oxide field effect transistors reach a few atomic scale, a model considering many-body physics with a reasonable time consumption is necessary. The new method needs to include the atomic potential into the Schrodinger Hamiltonian, then choose a suitable basis to solve the eigenvalue problem. Among all these approaches, the Tight Binding method (TBM) is the most popular. TBM directly uses the atomic orbital as the basis, and assumes that the potential is bonded tightly at the central atom. In this paper, we applied the tight binding method to silicon nanowires, and calculated the bandgap, effective mass and density of states. We studied the quantum confinement effect on the nanowires with different width, and compared to the infinite quantum well and the perfect crystal models. The results show that the quantum confinement effect will enlarge the bandgap and the carrier effective mass, and also rearrange the conduction band edge position in the k-space due to the effective mass difference between the lateral and perpendicular directions. Then we further applied our model to the novel 2D material. Molybdenum disulfide (MoS2) is a 2D material with good mechanical and chemical properties. It can endure a large strain (12%), and its nanoribbon structure has interesting edge properties. So we applied TBM to MoS2 and its nanoribbon to study the strain effects and edge states properties. The results show that the tensile strain can make the bandgap and the carrier effective mass smaller; however, the K-to-Gamma valley transition at the valence band edge gives it a larger hole effective mass.

With the continued scaling down of MOSFET dimensions has come the introduction of high-κ gate insulators, high mobility substrates, and new device geometries. The purpose of this work is to model the low-field electron mobility to evaluate the performance of the various options to continue Moore's Law. We model the electron mobility in Si, Ge, and III-V inversion layers and quantum wells, including scattering with surface optical phonons associated with high-kappa gate insulators, bulk phonons, and surface roughness scattering. We compare the low-field mobility results with Monte Carlo simulations to understand the role of mobility in predicting device performance in short-channel devices. For the first time, the theory describing surface optical phonon scattering is extended to the symmetric double-gate structure with a Si body - accounting for the coupling of the two interfaces and screening via the substrate plasmon.

碩士
中國文化大學
應用化學研究所
95
We investigated bonding and optimized geometries of 2Li+Be、2Be+Li adsorbed on the Si(111) surfaces at the B3LYP/6-31G* level. In the case of Si(100), the Si9H12 cluster was used to represent the surface unit with one Si=Si surface dimmer, while in the case of Si(111),different sizes of Si-H clusters were used, depending on the extent of marginal distortion of the unit cell. General speaking, the bond lengths in 2Li+Be and 2Be+Li adsorbates are greatly reduced due to the flowing of charge density from metal antibonding orbitals into the surface dangling bonds.

Electronic band structure of various crystal orientations of relaxed and strained bulk, 1D and 2D confined semiconductors are investigated using nonlocal empirical pseudopotential method with spin-orbit interaction. For the bulk semiconductors, local and nonlocal pseudopotential parameters are obtained by fitting transport-relevant quantities, such as band gap, effective masses and deformation potentials, to available experimental data. A cubic-spline interpolation is used to extend local form factors to arbitrary q and the resulting transferable local pseudopotential V(q) with correct work function is used to investigate the 1D and 2D confined systems with supercell method. Quantum confinement, uniaxial and biaxial strain and crystal orientation effects of the band structure are investigated. Regarding the transport relavant quantities, we have found that the largest ballistic electron conductance occurs for compressively-strained large-diameter [001] wires while the smallest transport electron effective mass is found for larger-diameter [110] wires under tensile stress.

博士
國立清華大學
物理學系
96
Abstract This dissertation aims at developing a theoretical approach to treat the 24-wave diffraction occurred in a Fabry-Perot type of resonant cavity of silicon by solving an eigenvalue-eigenvector equation, derived by Stetsko and Chang, deduced from the X-ray multiple-wave dynamical diffraction equation. We anticipate the calculations can offer a crystal clear physical picture for the experimental resonance pattern of the 24-wave diffraction in the X-ray Fabry-Perot cavity, and aid us design an appropriate resonant cavity to fulfill the experimental purposes. The resonance pattern accompanied by nine coplanar diffractions occurred in an X-ray Fabry-Perot cavity of silicon at photon energy of 14.4388 keV at which 24 beams are simultaneously excited has been realized by employing the back diffraction of (12 4 0) by Chang et al.. The calculation is in a good agreement with the observed one. The interference fringes of the concentric rings accompanied by nine diffraction lines passing through the center of rings distinctly show up in the calculated pattern. Meanwhile, the dispersion surface and the linear absorption coefficient have been mapped out from the solved eigenvalues. The excitation of mode and the phases of the diffracted waves have also been calculated from the solved eigenvalues and eigenvectors and from boundary conditions. According to the calculated dispersion surface and linear absorption coefficient, we find that in the total reflection region, most of energy is reflected off the crystal, and the absorption reaches the maximum value, and the phase of the diffracted waves changes drastically. In the exact 24-wave region, the phase of the diffracted wave changes further by doubling the values. The effect of the crystal thickness and the gap width on the reflectivity and transmissivity are also surveyed. The larger the reflectivity and the lower the transmissivity, the thicker is the crystal plate. The more the number of the resonance peaks, the wider is the gap width between the two plates. The time response curves of the cavity show a periodic structure of time due to the interference among the resonance peaks. In brief, we have established a theoretical approach to treat the multiple-wave diffraction in the Fabry-Perot type of resonant cavity. The calculation is in a good agreement with the observed one. The procedures for the dynamical calculations are also offered in this dissertation.

Since materials properties are determined by the interactions between the constituent atoms, an accurate description of the inter-atomic interactions is crucial to characterize and control material properties. Particularly, a quantitative understanding of the formation and nature of defects and impurities becomes increasingly important in the era of nanotechnology, as the imperfections largely influence many properties of nanoscale materials. Indeed, due to its technological importance and scientific interest, there have been significant efforts to better understand their behavior in semiconductors and oxides, and their interfaces, yet many fundamental aspects are still ambiguous due largely to the difficulty of direct characterization. Hence, our study has focused on developing a better understanding of atomic-scale defects and impurities using first principles quantum mechanical calculations. In addition, based on the improved understanding, we have attempted to address some engineering problems encountered in the current technology. The first part of this thesis focuses on mechanisms underlying the transient enhanced diffusion of arsenic (As) during post-implantation annealing by examining the interaction of As with vacancies in silicon. In the second part, we address some fundamental features related to plasma-assisted nitridation of silicon dioxide; this study shows that oxygen vacancy related defects play an important role in (experimentally observed) peculiar nitridation at the Si/SiO2 interface during post O2 annealing. In the third part, we examine the interaction between vacancies and dopants in sp2–bonded carbon such as graphene and nanotube, specifically the formation and dynamics of boron-vacancy complexes and their influence on the electrical properties of host materials. In the fourth part, we study the interfacial interaction between amorphous silica (a-SiO2) and graphene in the presence of surface defects in a-SiO2; this study shows possible modifications in the electronic structure of graphene upon the surface defect assisted chemical binding onto the a-SiO2 surface. In the last part, we examine the structural and electronic properties of bismuth vanadate (BiVO4) which is a promising photocatalyst for water splitting to produce hydrogen; this study successfully explains the underlying mechanism of the interesting photocatalytic performance of BiVO4 that has been experimentally found to strongly depend on structural phase and doping.
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博士
國立臺灣大學
電子工程學研究所
100
In this dissertation, two important topics are investigated and discussed for MOSFET (metal-oxide-semiconductor field-effect transistor) and photovoltaic technologies, respectively. One is the electron mobility calculation in the strained silicon or strained germanium inversion layers. The other is the performance improvement together with material and device characterization of amorphous silicon based solar cells. Part I: It is the goal for the CMOS (complementary metal-oxide-semiconductor) industry enabling large-scale decrease in chip area and improving transistor performance by scaling down the devices to give higher drive current and higher circuit speed. However, the device scaling down requires a complicated process improvement and high cost, especially when the approaching of the physical limits. Both the higher gate capacitance Cg and the higher carrier mobility μ can improve the drive current Id since Id ~ Cg∙μ. Thus, mobility enhancement offers an alternative way to further improve the drive current. Several various techniques such as substrate strain, process strain, and mechanical/package strain have been proposed to give strain into the silicon channel. In order to find out the optimal strain condition which gives highest electron mobility for silicon channels, the electron mobility in the silicon inversion layer is comprehensively studied for various substrate orientations, various channel directions, and various stress conditions. Furthermore, it was well known that bulk germanium (Ge) substrate offer 2x higher mobility for electrons and 4x higher mobility for holes as compared to Si. Thus, the strain induced electron mobility change in Ge channel inversion layer is also comprehensively studied. Part II: In recent years, the air pollution and global warming issues resulting from the mass consumption of fossil fuels have attracted more and more attention due to the aim for sustainability of the ecosystem on earth. The development of clean energy resources is thus an important challenge in these years. Among the wide variety of renewable energy, solar cells (also called photovoltaics, PV), which is pollution free in use and almost available everywhere in the world, is the most promising candidate. Although conventional crystalline silicon solar cells have higher efficiency, higher energy consumption during process and smaller substrate area give bottlenecks for this technique in the future from the ecological and economical point of view. Amorphous silicon based thin film solar cells, which can give large-scale applications and shorter energy pay-back time (EPBT), are the most commercially available thin film PV technology with abundant and non-toxic absorber material. However, the still limited stable efficiency has to be improved to compete with other PV technologies. In this dissertation, some material property and device structure are investigated to improve the initial and stable efficiency of a-Si based thin film solar cells.

Non-canonical DNA structures are involved in fundamental biological processes as replication, transcription and repair. Their dysregulation is indeed connected to the development of several human diseases, including cancer. As more and more information about their existence and function in living cells are documented, such DNA structures have emerged as promising therapeutic targets. In the last decades, the G-quadruplex folding has caught the attention of scientists because of its implication in the origin and growth of various cancer forms. The stabilization of G-quadruplex structures at human telomeres is thought to be particularly attractive as it might lead to the identification of potential drug candidates with wide-spectrum anticancer activity and reduced side effects in comparison to classical chemotherapies. The research project underlying this thesis concerns the structural investigation on the interaction of non-canonical DNA foldings, especially of the human telomeric G-quadruplex, with natural and synthetic compounds in order to select potential anticancer drugs. The characterization of ligand-DNA adducts has been carried out primarily by X-ray crystallography which provides detailed structural information. In addition, alternative techniques, as CD spectroscopy and in silico calculations, have supplied complementary data with particular reference to the formation of adducts in solution.