Two-dimensional (2D) materials show novel electronic, optical and chemical properties and have great potential in devices such as field-effect transistors (FET), photodetectors and gas sensors. This thesis focuses on scanning tunneling microscopy and spectroscopy (STM/STS) investigation of interfaces and defects 2D transition metal dichalcogenides (TMDCs). The first part of the thesis focuses on the synthesis of 2D TiSe2 with chemical vapor transport (CVT). By properly choosing the growth condition, Sub-10 nm TiSe2 flakes were successfully obtained. A 2 × 2 charge density wave (CDW) was clearly observed on these ultrathin flakes by scanning tunneling microscopy (STM). Accurate CDW phase transition temperature was measured by transport measurements. This work opens up a new approach to synthesize TMDCs. The second part of the thesis focuses on monolayer vacancy islands growing on TiSe2 surface under electrical stressing. We have observed nonlinear area evolution and growth from triangular to hexagonal driven by STM subjected electrical stressing. Our simulations of monolayer island evolution using phase-field modeling and first-principles calculations are in good agreement with our experimental observations. The results could be potentially important for device reliability in systems containing ultrathin TMDCs and related 2D materials subject to electrical stressing. The third part of the thesis focuses on point defects in 2D PtSe2. We observed five types of distinct defects from STM topography images and measured the local density of states (LDOS) of those defects from scanning tunneling spectroscopy (STS). We identified the types and characteristics of these defects with the first-principles calculations. Our findings would provide critical insight into tuning of carrier mobility, charge carrier relaxation, and electron-hole recombination rates by defect engineering or varying growth condition in few-layer 1T-PtSe2 and other related 2D materials. / Doctor of Philosophy / Since the discovery of graphene in 2004, two-dimensional (2D) materials have attracted more and more attentions. When the thickness of a layered material thinned to one or few atoms, it shows interesting properties different from its bulk phase. Due to the reduced dimensionality, interfaces and defects in 2D materials will significantly affect the electronic property and chemical activity. However, such nanometer scale features are several orders of magnitude smaller than the wavelength of visible light, which is the limit of resolution for optical microscope. Scanning tunneling microscope (STM) is widely used in study of 2D materials not only because it can provide the topography and local electronic information at atomic scale, but also because of the possibility of directly fabricate atomic scale structure on the surface. The first part of the thesis focuses on the synthesis of 2D TiSe2 with chemical vapor transport (CVT). TiSe2 belongs to the transition metal dichalcogenides (TMDCs) family, showing a sandwiched layered structure. When the temperature goes down to 200K, a 2 × 2 superlattice called charge density wave (CDW) will show up, which is clearly observed in our STM images. The second part of the thesis focuses on monolayer vacancy islands growing on TiSe2 surface controlled by electrical stressing. During continuous STM scanning, we have observed nonlinear area growth of the vacancy islands. The shape of those islands transfers from triangular to hexagonal. We successfully simulated such growth using phase-field modeling and first-principles calculations. The results could be potentially important for device reliability in systems containing ultrathin TMDCs and related 2D materials subject to electrical stressing. The third part of the thesis focuses on defects in 2D PtSe2. We observed five types of distinct defects in our STM topography images. By comparing them with DFT-calculated simulation images, we identified the types and characteristics of these defects. Our findings would provide critical insight into tuning of carrier mobility, charge carrier relaxation, and electron-hole recombination rates by defect engineering in few-layer 1T-PtSe2 and other related 2D materials.

Die Sammlung der zwei-dimensionalen (2D) Materialien ist begrenzt, da sehr wenige Verbindungen stabil bleiben, sobald sie nur aus Oberflächen bestehen. Aufgrund ihrer außergewöhnlichen Eigenschaften sind 2D Materialien jedoch nach wie vor überaus begehrt. Vor kurzem wurden atomar definierte, chemisch gesättigte SiO2 Bilagen auf verschiedenen Metalloberflächen präpariert. Eine solche ultradünne Silika-Lage wäre eine vielversprechende Ergänzung zur Familie der 2D Materialien, wenn sie unter Strukturerhalt vom Wachstumssubstrat isoliert werden kann. In dieser Arbeit untersuchen wir die Eigenschaften einer Silika-Bilage im Zusammenhang mit Anwendungen von 2D Materialien. Die Bilage besitzt kristalline und amorphe Regionen, die beide atomar glatt sind. Die kristalline Region besitzt ein hexagonales Gitter mit gleichmäßiger Porengröße, während die amorphe Region einer komplexeren Beschreibung bedarf. In einer Studie von Baublöcken zeigen wir, dass mittelreichweitige Struktureinheiten in Korrelation mit einem Parameter für die Bindungswinkelfrustration auftreten. Das Netzwerk verschiedener Nanoporen stellt eine größenselektive Membran dar, wie wir in einer Adsorptionsstudie zeigen. Pd- und Au-Atome durchdringen den Silikafilm abhängig von der Größe der zur Verfügung stehenden Nanoporen. Der ultradünne Film hält der Einwirkung verschiedener Lösungsmittel stand und die Beständigkeit der Struktur in Wasser wird analysiert. Diese Studien deuten die außergewöhnliche Stabilität dieser Struktur an. Wir entwickeln eine polymerbasierte mechanische Exfoliation, um den Film von seinem Wachstumssubstrat zu entfernen, und zeigen, dass der Film als intakte Einheit vom Substrat abgelöst wird. Wir präsentieren anschließend den Transfer des Silikafilms auf ein TEM-Gitter, wo er schraubenartig gewundene Formen annimmt. Weiterhin wurde der Film auf ein Pt(111)-Substrat transferiert. In diesem Fall wird unter Erhalt der Struktur ein Transfer in der Größenordnung von Millimetern erreicht. / The library of two-dimensional (2D) materials is limited, since only very few compounds remain stable when they consist of only surfaces. Yet, due to their extraordinary properties, the hunt for new 2D materials continues. Recently, an atomically defined, self-saturated SiO2 bilayer has been prepared on several metal surfaces. This ultrathin silica sheet would be a promising addition to the family of 2D materials, if it can be isolated from its growth substrate without compromising its structure. In this work, we explore the properties of a silica bilayer grown on Ru(0001) in the context of 2D technology applications. The bilayer sheet exhibits crystalline and amorphous regions, both being atomically flat. The crystalline region possesses a hexagonal lattice with uniform pore size, while the amorphous region requires a more complex description. In a building block study of the amorphous region, we find that medium range structural patterns correlate with a parameter describing the bond angle frustration. The resulting network of different nanopores represents a size-selective membrane, as illustrated in an adsorption study. Pd and Au atoms are shown to penetrate the silica film selectively, depending on the presence of appropriately sized nanopores. The ultrathin silica film is shown to withstand exposure to different solvents and the stability of the structure in water is analyzed. These studies indicate extraordinary stability of this nanostructure. We develop a polymer assisted mechanical exfoliation method for removing the film from the growth substrate, providing evidence that the film is removed as an intact sheet from the growth substrate. We subsequently present the transfer of the silica bilayer to a TEM grid, where it forms micro-ribbons. Further, the film is transferred to a Pt(111) substrate, where mm-scale transfer under retention of the structure is achieved.

Cette thèse porte sur la modélisation des phénomènes de dissolution lors de la phase précoce d'un accident grave de réacteur nucléaire. L'étude s'intéresse à la dissolution de céramiques solides (ZrO2 et UO2) par un métal liquide (Zr). En cas d'hypothétique accident grave dans un Réacteur à Eau Pressurisée, les phénomènes de dissolution jouent un rôle primordial dans l'aggravation de la dégradation et la fusion des oxydes à des températures parfois largement inférieures à leur température de fusion normale. Cela concerne en particulier les principaux constituants des crayons combustibles : les pastilles d'UO2 ainsi que la couche de ZrO2 formée sur la surface externe de la gaine qui vont subir une dissolution par le zircaloy des gaines à partir de 2100 K (la température de fusion de ces oxydes étant supérieure à 2800 K). Dans l'état actuel des connaissances, on peut supposer que les phénomènes de dissolution sont responsables, d'une part, de l'effondrement prématuré des crayons combustibles dans le cœur et, d'autre part, de la formation rapide d'un bain liquide en fond de cuve si des oxydes de fer sont présents. De nombreuses études expérimentales ont été menées sur ce sujet mais la modélisation n'est pas encore satisfaisante à ce jour. Les modèles actuels sont essentiellement des modèles 1D qui ne prennent pas en compte de façon explicite la convection naturelle ni la présence d'une zone de transition diphasique au niveau de l'interface métal / céramique. Un modèle 2D, décrivant les transferts de quantité de mouvement, de chaleur et de masse, établi par prise de moyenne volumique des équations microscopiques de transport a été développé. Ce modèle est basé sur des hypothèses d'équilibre thermique local et de non-équilibre massique local et s'inspire d'un modèle de solidification de mélanges binaires (P. Bousquet-Mélou, 2000). Sur le plan théorique, l'approche est identique. Cependant, la dissolution introduit des contraintes physico-numériques supplémentaires qu'il a fallu prendre en compte. La prise en compte des deux aspects mentionnés (convection et zone diphasique) constitue une nouveauté significative par rapport aux modèles existants. Le modèle a été ensuite étendu au cas ternaire grâce à des développements nouveaux permettant de résoudre certaines difficultés supplémentaires (ajout d'une équation d'espèce, relations d'équilibre non bijectives, plusieurs coefficients de diffusion à déterminer, indétermination sur les flux à l'interface, densité du solide non constante...) afin d'étudier la dissolution UO2 / Zr. Une validation des modèles obtenus est faite à partir de résultats expérimentaux de dissolution de creusets en ZrO2 et UO2 par le zircaloy liquide et montrent la bonne qualité prédictive de notre modèle. / This thesis focuses on the modeling of dissolution phenomena during the early phase of a serious accident of nuclear reactor. The study focuses on the dissolution of solid ceramic (ZrO2 and UO2) by a liquid metal (Zr). In case of hypothetical severe accident in a pressurized water reactor, the phenomena of dissolution play a role in the further decay and melting oxides at temperatures sometimes significantly below the normal melting temperature. This concerns in particular the main constituents of fuel rods : pellets of UO2 and ZrO2 layer formed on the outer surface of the sheath that will suffer by the dissolution of zircaloy sheaths from 2100 K (the melting temperature of these oxides being greater than 2800 K). In the present state of knowledge, we can assume that dissolution phenomena are responsible for, on the one hand, the premature collapse of the fuel rods in the heart and, on the other hand, the rapid formation of a liquid bath in the bottom of the tank where iron oxides are present. Many experimental studies have been conducted on this subject but modeling is not yet satisfactory today. Current models are essentially 1D models that do not explicitly account for natural convection nore the presence of a biphasic transition zone at the interface metal / ceramic. A 2D model describing the transfer of momentum, heat and mass, determined by taking average density of microscopic transport equations has been developed. This model is based on assumptions of local thermal equilibrium and non-local mass balance and it is based on a model of solidification of binary mixtures (P. Bousquet-Mélou, 2000). In theory, the approach is identical. However, the dissolution introduced physico-digital extra constraint that had to be taken into account. Taking into account the two aspects mentioned (convection and two-phase zone) is a novelty in comparison to existing models. The model was then extended to the ternary case with new developments to resolve certain difficulties (addition of an equation of this case, non-bijective equilibrium relations, several diffusion coefficients to be determined, uncertainty on flows in interface, density of the solid non-constant ...) to study the dissolution UO2 / Zr. Validation of models is obtained from experimental results of dissolution of crucibles of UO2 and ZrO2 by liquid zircaloy and show the quality of our predictive model.

Orientador: Lucia Helena Deliesposte Cescato / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-08T11:13:35Z (GMT). No. of bitstreams: 1 Menezes_JacsonWeberde_M.pdf: 5177344 bytes, checksum: 63bfde864e58f6813890fced4db8f389 (MD5) Previous issue date: 2006 / Resumo: Nesta dissertação foi desenvolvido um novo método de gravação de estruturas bidimensionais em fotorresina, baseado na superposição de três exposições holográficas. Utilizando esta técnica, foi possível gravar estruturas de seção transversal circular. Isso resolve o problema da redução da área do gap fotonico que ocorre com as estruturas cilíndricas de seção transversal elíptica, obtida quando são utilizadas apenas duas exposições. Controlando-se a fase entre a terceira exposição e as duas anteriores é possível também gerar padrões hexagonais com diferentes formas de cilindros, que correspondem aos "átomos" do cristal fotonico, que podem apresentar novas propriedades fotonicas. Para projetar cristais fotonicos que apresentam gap fotonico na região de interesse do espectro eletromagnético, foi utilizado um programa baseado no método dos elementos finitos. Nestes projetos foram consideradas as dimensões e formas que podem ser fabricadas utilizando a técnica de dupla exposição holográfica assim como foi utilizada a aproximação de índice de refração equivalente para levar em conta a espessura da camada fotonica. Utilizando a superposição de duas exposições holográficas, associadas à litografia por corrosão por íon reativo, foram feitas tentativas de fabricação das camadas fotonicas projetadas em três materiais diferentes: silício policristalino, silício amorfo hidrogenado e silício cristalino / Abstract: In this work, it was developed a new recording method of the 2D structures in photoresist, based on the superimposition of three holographic expositions. This technique solves the problem of asymmetry of hexagonal structures, arising from the superimposition of only two expositions, which causes a strong reduction of the photonic band gap area. By controlling the phase-shift between the third exposition and the former two exposures, it is possible to generate new hexagonal patterns that can present different properties. In the design of the 2D photonic layers that present Photonic Band Gaps in the near infra-red region of the electromagnetic spectrum, it was used a software based on finite elements method. To consider the thickness of the photonic layer it was used the approach of equivalent refractive index. In the design we take into account the dimensions and shapes that can be fabricated using the technique of holographic lithography associated with RIE (Reactive Ion Etching). For fabrication of the structures we used double holographic exposures followed by RIE lithography in three different materials: poly-silicon, amorphous silicon and crystalline silicon / Mestrado / Física da Matéria Condensada / Mestre em Física

En cardiologie interventionnelle, le clinicien pourrait bénéficier d'une fusion de deux informations complémentaires provenant d'un scanner CT préopératoire et du flux d'images radiographiques servant au guidage des outils manipulés dans les vaisseaux du patient. Une telle fusion nécessite d'aligner les deux modalités et de construire des correspondances pertinentes. Nous proposons une approche basée sur la préservation de la topologie des structures mises en correspondance par le biais d'un cadre général visant à recaler des courbes ainsi qu'une méthode d'appariement d'arbre. / In interventional cardiology, the clinician can benefit from a fused visualization of a diagnostic pre-operative CT scan and the live X-ray projective images used for the guidance of dedicated tools inside the patient's vasculature. This necessitates to align both modalities and build relevant pairings between them. We have developed a general framework combining a method to register curves with a tree pairing procedure, which is able to preserve the topology of the structures.

L’angioplastie coronarienne est une intervention guidée par rayons X et réalisée par voie endovasculaire qui restaure le diamètre des vaisseaux coronaires réduit par accumulation de corps gras au sein de leurs parois. Lors de cette procédure, un guide est introduit à partir d’une artère qui peut être située au poignet ou au niveau de l’aine. La technique consiste alors à amener dans le vaisseau pathologique un ballonnet gonflable dans la zone rétrécie, localisée grâce à l’injection préalable d’un produit de contraste. Le gonflement du ballonnet élargit l’artère et s’accompagne en général de la pose d’un stent, structure métallique capable de renforcer la paroi. Le geste clinique peut être facilité en intégrant aux images le détail de la nature de la paroi, information disponible avec un scanner 3D. Le but de cette thèse est de proposer une méthode de recalage déformable pour superposer cette information 3D à des images angiographiques 2D per-opératoire en déformant le modèle 3D afin qu’il suive la dynamique cardiaque capturée dans les images angiographiques. Nous introduisons un algorithme de segmentation capable de segmenter automatiquement les vaisseaux principaux dans ces images angiographiques. Ensuite, nous présentons une approche de suivi du vaisseau 3D pathologique dans une séquence 2D+t combinant appariements et déformation d’une courbe spline. Enfin, nous décrivons l’extension au suivi d'un arbre vasculaire 3D, représenté par un arbre dont les arcs sont des courbes splines, dans une séquence 2D+t. Nous avons privilégié les approches applicables avec une seule projection angiographique, bien adapté au déroulement usuel des procédures cliniques. La performance des algorithmes a fait l’objet d’évaluations quantitatives sur des données réelles incluant 30 images pour la segmentation et 23 séquences pour le recalage. / Coronary angioplasty is an X-ray guided intervention, which aims at recovering the diameter of coronary vessels when the accumulation of fat in the vessel wall reduced it. During this procedure, a guide-wire is inserted in the blood vessel located at the wrist or groin. This guide-wire brings into the pathologic vessel a balloon at the level of the fat accumulation, thanks to a previous contrast injection which highlights the lesion. The balloon is inflated and very frequently a thin mesh tube of metallic wires (stent), which is wrapped around the balloon, is then expanded during the balloon inflation. The procedure could benefit from additional information on the nature of the inner wall, available on 3D CT scan. The aim of the thesis is to propose a dynamic registration to superimpose this 3D information onto the intraoperative 2D angiographic sequence, by deforming the 3D model so that it can follow the cardiac motion captured thanks to the angiographic images. We introduce a segmentation algorithm able to automatically segment the main vessels of the angiographic images. Then, we present a tracking approach of the 3D pathologic vessel in a 2D+t sequence combining pairings and the deformation of a spline curve. Finally, we describe the extension to the 3D vascular tree tracking represented by a tree, whose edges are spline curves, in a 2D+t sequence. We favored approaches that are applicable to a single angiographic projection, which is well adapted to the usual process of clinical procedures. All the proposed methods have been tested on real data, consisting of 30 angiographic images for the segmentation algorithm and 23 angiographic sequences for the registration algorithms.

Group III-nitride materials have attracted great attention for applications in high efficiency electronic and optoelectronics devices such as high electron mobility transistors, light emitting diodes, and laser diodes. On the other hand, group VI transition metal dichalcogenides (TMDs) in the form of MX2 has recently emerged as a novel atomic layered material system with excellent thermoelectric, electronic and optoelectronic properties. Also, the recent investigations reveal that the dissimilar heterojunctions formed by TMDs and III-nitrides provide the route for novel devices in the area of optoelectronic, electronics, and water splitting applications. In addition, integration of III-nitrides and TMDs will enable high density integrated optoelectronic circuits and the development of hybrid integration technologies. In this work, we have demonstrated kinetically controlled growth processes in plasma assisted molecular beam epitaxy (PAMBE) for the III-nitrides and their engineered heterostructures. Techniques such as Ga irradiation and nitrogen plasma exposure has been utilized to implement bulk GaN, InGaN and their heterostructures in PAMBE. For the growth of III-nitride based heterostructures, the in-situ surface stoichiometry monitoring (i-SSM) technique was developed and used for implementing stepped and compositionally graded InGaN-based multiple quantum wells (MQWs). Their optical and microstrain analysis in conjunction with theoretical studies confirmed improvement in the radiative recombination rate of the graded-MQWs as compared to that of stepped-MQWs, owing to the reduced strain in graded-MQWs. Our achievement also includes the realization of the p-type MoS2 by engineering pristine MoS2 layers in PAMBE. Mainly, Ga and nitrogen plasma irradiation on the pristine MoS2 in PAMBE has resulted in the realization of the p-type MoS2. Also, GaN epitaxial thin layers were deposited on MoS2/c-sapphire, WSe2/c-sapphire substrates by PAMBE to study the band discontinuity at GaN/TMDs heterointerface. The determination of band offset parameters for both GaN/MoS2 and GaN/WSe2 heterostructures revealed realization of type-II band alignment. Also, heterojunctions such as AlGaN/MoS2 is implemented to achieve type-I heterojunction. This work may open up a new avenue towards photonic quantum devices based on the integration of III-nitrides with 2D TMDs.

Master thesis is focused on retrieval of multimedia information based on location of mobile device. Paper describes mobile platforms technology and technology behind location sensing and two-dimensional barcode recognition. There is also included design of client-server architecture for information retrieval of location based multimedia data. Master thesis includes report of system testing and some ideas about new features for implemented location based information distribution system.

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Detta arbete undersöker hur form påverkar människors perception av en monsterkaraktär som introducerats med textbeskrivning och bild. För att undersöka detta skapades två baskaraktärer i bild och textbeskrivning. Den ena baskaraktären beskrivs som ofarlig, lugn och vänlig den andre som farlig, aggressiv och hotfull. Utifrån dessa två baskaraktärer skapades åtta nya varianter, två med mjukare former och två med kantigare former.Den teoretiska grunden för arbetet innefattar beprövade metoder inom karaktärsdesign samt teorier kring formlära och kategorisering, t ex, ”pattern-matching” vilket syftar på att människor från födseln kopplar vissa former som runt och slätt som säkra medan taggigt och vasst kopplas till fara.Dessa bilder som skapats används sedan i kvalitativa semistrukturerade intervjuer där informanterna ska placera dem på rad från mest säker att närma sig som en karaktär i ett rollspel till mest farlig. Därefter kommer frågor som går in på varför de placerat bilderna i den ordningen.