Carbon nanostructures have been extensively used in different applications; ranging from electronic and optoelectronic devices to energy conversion. The interest stems from the fact that covalently bonded carbon atoms can form a wide variety of structures with zero-, one- and two-dimensional configuration with different physical properties. For instance, while fullerene molecules (zero-dimensional carbon structures) realize semiconductor behavior, two-dimensional graphene shows metallic behavior with exceptional electron mobility. Moreover the possibility to even further tune these fascinating properties by means of doping, chemical modification and combining carbon based sub-classes into new hybrid structures make the carbon nanostructure even more interesting for practical application.  This thesis focuses on synthesizing SWCNT and different C60 one-dimensional structures as well as tuning their properties by means of different chemical and structural modification. The purpose of the study is to have better understanding of the synthesis and modification techniques, which opens for better control over the properties of the product for desired applications. In this thesis carbon nanotubes (CNTs) are grown by chemical vapor deposition (CVD) on iron/cobalt catalyst particles. The effect of catalyst particle size on the diameter of the grown CNTs is systematically studied and in the case of SWCNTs it is shown that the chirality distribution of the grown SWCNTs can be tuned by altering the catalyst particle composition. In further experiments, incorporation of the nitrogen atoms in SWCNTs structures is examined. A correlation between experimental characterization techniques and theoretical calculation enable for precise analysis of different types of nitrogen configuration in SWCNTs structure and in particular their effect on growth termination and electronic properties of SWCNTs are studied. C60 one-dimensional structures are grown through a solution based method known as Liquid-liquid interfacial precipitation (LLIP). By controlling the crystal seed formation at the early stage of the growth the morphology and size of the grown C60 one-dimensional structures where tuned from nanorods to large diameter rods and tubes. We further introduce a facile solution-based method to photo-polymerize the as-grown C60 nanorods, and show that such a method crates a polymeric C60 shell around the nanorods. The polymeric C60 shell exhibits high stability against common hydrophobic C60 solvents, which makes the photo-polymerized nanorods ideal for further solution-based processing. This is practically shown by decoration of both as grown and photo-polymerized nanorods by palladium nanoparticles and comparison between their electrochemical activities. The electrical properties of the C60 nanorods are also examined by utilizing a field effect transistor geometry comprising different C60 nanorods. In the last part of the study a variant of CNT is synthesized in which large diameter, few-walled CNTs spontaneously transform to a collapsed ribbon shape structure, the so called collapsed carbon nanotube (CCNT). By inserting C60 molecules into the duct edges of CCNT a new hybrid structure comprising C60 molecules and CCNT is synthesized and characterized. A further C60 insertion lead to reinflation of CCNTs, which eventually form few-walled CNT completely filled with C60 molecules.

Les nanotubes de carbone (CNTs), intégrant à la fois la structure parfaite, la géométrie unique, et des propriétés exceptionnelles, sont d'une grande importance dans le domaine des nanotechnologies. Leur association avec d'autres matériaux produit de nouvelles propriétés remarquables, et étend par conséquent leurs domaines d'applications comme charges multifonctionnelles. Cette thèse vise à développer un nouveau matériau hybride avec une structure multi-échelle à base de CNTs et de particules micrométriques d'alumine (mAl2O3) par une méthode de dépôt chimique en phase vapeur (CVD). Nos études démontrent que les structures CNTs-mAl2O3 ont une propriété exceptionnelle en matière de transport thermique dans les composites polymères. Celle-ci nous a amenée à explorer plus en profondeur les mécanismes de l’organisation des CNTs sur mAl2O3, et d’étudier la cinétique de réactions chimiques dans l’espace gazeux du réacteur CVD. Dans le premier chapitre, nous faisons une revue de l'état de l'art sur la structure, les propriétés et les applications des CNTs, ainsi que les mécanismes de croissance de CNTs par CVD. Une attention particulière est également accordée aux structures hybrides nano-micrometriques qui sont synthétisées par greffage in-situ des CNTs sur des substrats micrométriques. Dans le deuxième chapitre, nous présentons trois types de structures hybrides, qui sont classifiées selon différents modes d'organisation des CNTs sur les microsphères d'alumine. L'évolution des structures hybrides est démontrée en faisant varier le diamètre, la longueur et la densité numérique des CNTs sur mAl2O3. L’organisation specifique et la dispersion homogène des CNTs permettent de diminuer considérablement leurs résistances de contacts thermiques lorsque les matériaux hybrides CNTs-mAl2O3 sont utilisés comme charges dans les composites polymères. Une amélioration importante de la conductivité thermique des composites Epoxy/CNTs-mAl2O3, par rapport à celle des composites constitués de CNTs et de résine époxy, est obtenue à une fraction massique ultra-faible en CNTs. Dans le troisième chapitre, nous avons étudié en détail les rôles joués par les paramètres CVD et les microparticules sphériques d’alumine dans la construction de structures hybrides multiformes. En particulier, les fortes corrélations entre la température, les sources de carbone et les ratios d'hydrogène ont été discutées. Le lien entre les CNTs et les microparticules est mis en évidence, ainsi que la dynamique de croissance des CNTs. L’auto-organisation des CNTs sur mAl2O3 est expliquée par les deux mécanismes suivants. Dans un premier temps, la structure hétérogène de la surface des particules entraîne une distribution différente des particules du catalyseur, et leur arrangement cristallin spécifique détermine potentiellement l’orientation des CNTs. Dans un deuxième temps, l'auto-assemblage des CNTs est dû à l’interaction des forces faibles de Van der Waals entre CNTs voisins. Le calcul basé sur le modèle du nano-cantilever montre que l’auto-assemblage des CNTs dépend fortement de leur diamètre, de leur longueur et de leur densité numérique sur mAl2O3. Dans le quatrième chapitre, la cinétique chimique des réactions dans l’espace gazeux du réacteur CVD est numériquement analysée. Le processus non-équilibré de CVD qui contient plusieurs phénomènes physico-chimiques est simulé avec succès en combinant la cinétique des réactions chimiques avec les phénomènes de transport physique. Les champs des concentrations de chaque espèce est révélée aux températures utilisées par simulation des réactions chimiques. Les sources effectives de carbone et de fer pour la croissance des CNTs ont été éclaircies en comparant les résultats de simulation avec les observations expérimentales, y compris les mesures de spectrométrie de masse. Ces analyses sont nécessaires pour améliorer la production des hybrides avec des structures homogènes. / Carbon nanotubes (CNTs), integrating perfect structure, unique geometry, and exceptional properties, are of great significance in nanotechnology. Their hybridization with a variety of other materials generates huge amounts of attractive properties, and thus expands largely their application fields as multifunctional fillers. This thesis aims to develop a novel multi-scale hybrid material based on carbon nanotubes and micrometer alumina particles (mAl2O3) by an in-situ floating chemical vapor deposition (CVD) method. Our studies demonstrate that the CNTs-mAl2O3 structures have outstanding thermal transport properties in polymer composites. This greatly motivates us to further explore the organization mechanisms of CNTs on microparticles, and to investigate gas phase chemical reaction kinetics in CVD reactor. In the first chapter, we review the state of the art of research in CNT structure, properties and applications, as well as CNT growth mechanisms in CVD. Special attention is also paid to the nano-micro hybrid structures which are synthesized by in-situ grafting CNTs on micrometer substrates. In the second chapter, we present three types of hybrid structures which are classified according to distinct CNT organization patterns on alumina microspheres. The evolution of the hybrid structures is demonstrated by varying CNT diameter, length and number density on mAl2O3. The specific organization and homogeneous dispersion of CNTs could significantly reduce their thermal contact resistances when the CNTs-mAl2O3 hybrid materials are used as fillers in polymer composites. Enhanced thermal conductivities of the Epoxy/CNTs-mAl2O3 composites are obtained at ultra-low CNT weight fractions compared with that of the composites constituted of pristine CNTs and epoxy. In the third chapter, we investigate in detail the roles played by CVD parameters and alumina spherical microparticles in the construction of multiform hybrid structures. In particular, the strong correlations among the temperature, carbon sources and hydrogen ratios are discussed. The connection between the CNTs and the microparticles are demonstrated, along with the CNT growth dynamics on mAl2O3. The self-organization behavior of CNTs on mAl2O3 is explained by the following two mechanisms: first, heterogeneous surface structures of mAl2O3 generate varied nucleation of catalyst particles, and their specific crystal arrangement potentially determines CNT growth orientations; second, the self assembly of CNTs is due to weak Van der Waals interaction forces between neighboring nanotubes. The calculation based on the nano-cantilever model shows that the CNT self assembly is greatly dependent on their diameter, length and number density on mAl2O3. In the forth chapter, gas phase chemical reaction kinetics in CVD reactor is numerically analyzed. The non-equilibrium CVD processes which involve multi physical-chemical phenomena are successfully simulated by combining the chemical reaction kinetics with the physical transport phenomena. The space-dependent concentration distribution of each species is revealed by simulating the reacting fluid at the used temperatures. The effective carbon and iron precursors for CNT growth are illuminated by comparing simulation results with experimental observations including mass spectrometry measurements. These analyses of chemical reactions in CVD system are helpful to improve the production of the hybrids with homogeneous structures.

La photonique sur silicium est envisagée comme une solution technologique très prometteuse pour le remplacement des interconnexions électriques par des interconnexions optiques devant se produire dans les prochaines années. Des dispositifs optoélectroniques comme des sources lasers, des modulateurs et des détecteurs, ont été développés pour la réalisation de circuits intégrant des émetteurs/récepteurs. Parmi les défis devant être relevés pour faire avancé la photonique sur silicium, la réduction de la consommation électrique du modulateur est un point crucial. L’intégration des composants passifs et actifs en utilisant une seule et même technologie est également un enjeu majeur pour les futurs systèmes de communication optique. Grâce au développement de l'intégration hybride de semi-conducteurs III-V sur silicium pour la réalisation de sources laser sur silicium, de nouvelles voies peuvent être envisagée pour réaliser des modulateurs optiques et des photodétecteurs efficaces et compacts. De plus, les cristaux photoniques 2D (PhC) et spécifiquement les structures à ondes lentes, qui sont connues pour renforcer les interactions entre la lumière et la matière peuvent apporter des solutions intéressantes pour diminuer de manière ultime la puissance consommée.Dans ce contexte, les travaux menés durant ma thèse ont porté plus spécifiquement sur la conception, la fabrication et la caractérisation de modulateurs à électro-absorption à onde lente en semiconducteur III-V sur silicium. Dans une première partie consacrée à la modélisation, une attention particulière est portée à la conception du cristal photonique et au couplage de la lumière du guide silicium vers l’onde lente. Les performances de la structure optimisée sont aussi analysées, donnant un modulateur de seulement 18.75 µm de longueur fonctionnant à 15 GHz avec un taux d’extinction supérieure à 5 dB sur une gamme spectrale supérieure à 10 nm. Par la suite, l’ensemble des procédés de nanotechnologies durant la thèse pour la fabrication des dispositifs sont présentés. Enfin, les résultats expérimentaux obtenus au cours de cette thèse démontrent l’effet Stark Confiné Quantiquement et l’effet de photodétection obtenu sur les structures intégrées.Les perspectives de ce travail de thèse concernent la réalisation de circuits intégrés photoniques complets, incluant sources lasers, modulateurs à électroabsorption et photodétecteurs en utilisant une seule et même technologie. / Silicon photonics is considered as a promising solution to replace electrical interconnections in the next years. Among the remaining challenges, the driving power of the active devices has to be minimized. Furthermore the use of a common technological platform for the realization of Silicon (Si) photonics passive and active devices would present a great interest in term of fabrication complexity and cost. III-V on Si is a good candidate for such a common technological platform as the physical properties of III-V semiconductors allow for active functionalities such as III-V on Si laser which have already been successfully demonstrated. In this perspective, 2D photonic crystals (PhCs) and slow light structures, which are known to intrinsically reinforce light/matter interactioncan alsobring interesting opportunities.In this context, the work is focused on the design, fabrication and characterization of slow-light III-V- on-silicon electroabsorption modulators. In a first part, the photonic crystal structure and light coupling from silicon waveguide to slowlight III-V waveguide are designed and modeled. The performance of the optimized structure is analyzed, showing a modulator operating at 15 GHz and exhibiting an extinction ratio of more than 5 dB over a spectral range of more than 10 nm, using a 18.75 µ;m-long modulator. Subsequently, the masks and fabrication steps for a hybrid III-V photonic crystalon Si modulators are presented. Finally, the experimental results obtained during this thesis are presented, showing Quantum Confined Stark Effect and photodetection in the waveguide integrated structures.The reported works open perspective towards the integrating of optical modulators with III-V on silicon nanolasers and photodetectors using a single technology.

This work presents a detailed predictive modeling methodology for comprehensive crashworthiness analysis of advanced jet engine forward sections, containing hybrid and composite structures, when subjected to soft impact. Bird strike onto the fan assembly is chosen as the impact event to be studied. The aim is to develop a numerical methodology capable of accurately capturing the full range of multifaceted damage in hybrid and composite structures as they evolve throughout the forward section of a propulsion system. Effective strategies are developed within an explicit finite element framework for modeling a bird, an engine forward section, intra-ply and inter-ply composite damage, and hybrid structural failure. The accuracy of each approach and their numerical modeling considerations are thoroughly investigated. These techniques are then combined to form the full crashworthiness methodology. It is demonstrated that the complete methodology effectively captures progressive hybrid fan blade fracture, leading edge de-bonding, composite casing delamination, and other significant progressive damage effects caused by direct impact and subsequent engine component interactions. The full damage prognosis capabilities demonstrated by this approach encompass aspects which have remained mainly unaddressed in soft impact analysis. A methodology for assessing the complete extent of impact damage for advanced structural engine designs represents a breakthrough that can contribute greatly to the rapid development of these systems in the future. / Master of Science

In the light of today’s effort to achieve sustainable future of the planet, timber as building material makes a comeback on the construction market. Since the requirements on the buildings and the internal comfort increase, there is a need for finding new solutions and products; one of them is cross-laminated timber (CLT), which has the potential to be used for high-rise buildings due to its mechanical properties. The aim of this work was to study the vibration performance of CLT floors as it is often the governing factor in design of CLT structures unlike for other common building materials. The orthotropic mechanical properties of CLT were determined by the shear analogy method and verified with a finite element (FE) model of a simply supported beam compared to hand calculations of shear forces, bending moments and deflections. The properties based on Timoshenko’s approach were evaluated as less precise regarding the deflection. The non-composite structural behaviour of a steel-CLT hybrid floor structure was predicted for FE dynamic analysis based on a comparison between modelling exercise and hand calculations. Two different methods, the Concrete Society (SC) and Steel Construction Institution (SCI) methods, both seemed to be applicable for determination of the response factor first since the mechanical properties are not used as input in the calculations. These two methods differ in certain aspects, and based on FE analysis of simply supported slab even the resulting response factor for the CLT differs significantly. Moreover, the hand calculation results were similar to those of the FE analysis for the CS method, but in less agreement for the SCI method. Nevertheless, it is not recommended to reject the latter method based on this study and further studies should be performed on real structures with response factor known from on-site measurements. A part of the first floor of Canary Wharf College was modelled and analysed, and previous measurements of the frequency and response factors enabled a validation of some assumptions. The SCI approach showed to be inadequate for this type of structure and therefore only the CS method was applied further. Analysis of the floor structures supported by walls demonstrated similar results from both the measurements and the dynamic analysis. However, if the floor slab was supported by beams, the response factor was significantly overestimated although on the conservative side. This difference suggests that the modelling of such conditions are not satisfactory. The CS method appears to assess correctly the magnitude of the response factor for CLT floors supported by walls but overestimates it in case of beam supports. The first finding shall be confirmed through analysis of other structures and a more extensive research should focus on the latter one to determine more exact behaviour of the model under different conditions.

Programa AlÃan de bolsas de estudo de alto nÃvel destinado à AmÃrica Latina / Este trabalho tem como objetivo a aplicaÃÃo da anÃlise tensorial para o tratamento de sinais no domÃnio de comunicaÃÃes sem fio. Utilizando a decomposiÃÃo tensorial conhecida como PARAFAC (decomposiÃÃo por fatores paralelos), um receptor à modelado para um sistema de comunicaÃÃo sem fio que utiliza uma estrutura MIMO na qual cada antena transmissora possui um cÃdigo de espalhamento particular, baseado na tÃcnica de mÃltiplo acesso por divisÃo de cÃdigo (CDMA). Nesse trabalho sÃo analisadas duas estruturas receptoras baseadas na decomposiÃÃo PARAFAC. A primeira à baseada no conhecimento da matriz de cÃdigos de espalhamento e a segunda à baseada no conhecimento da matriz de seqÃÃncia de treinamento. Duas famÃlias de cÃdigos sÃo consideradas: cÃdigos de Hadamard-Walsh e cÃdigos de Hadamard-Walsh truncados. Como resultado, foi observado que os receptores propostos apresentaram rÃpida convergÃncia e foram capazes de eliminar todas as ambigÃidades, inclusive aquelas que sÃo intrÃnsecas à decomposiÃÃo PARAFAC, que foram observadas em outros trabalhos. Resultados de simulaÃÃo sÃo apresentados para comparar o desempenho das duas estruturas receptoras em diversas configuraÃÃes do sistema de comunicaÃÃo, revelando o impacto dos parÃmetros do sistema (nÃmero de antenas transmissoras, nÃmero de antenas receptoras, tamanho do cÃdigo e relaÃÃo sinal-ruÃdo). / This work deals with the application of multi-way analysis to the context of signal processing for wireless communications. A tensor decomposition known as PARAFAC (PARAllel FACtors) is considered in the design of multiple-input multiple-output (MIMO) receiver for a wireless communication system with Spread Spectrum codes. We propose two supervised PARAFAC-based receiver structures for joint symbol and channel estimation. The first one is based on the knowledge of the spreading codes and the second on the knowledge of a training sequence per transmit antenna. Two code structures are considered, which are Hadamard-Wash (HW) and Truncated Hadamard-Walsh (THW). The main advantages of the proposed PARAFAC receivers is on the fact that they exhibit fast convergence and eliminate all ambiguities inherent to the PARAFAC model. Simulation results are provided to compare the performances of the two receivers for several systems configurations, revealing the impact of the number of transmit antennas, number of receiver antennas, code length and signal to noise ratio in their performances.

Neste trabalho, ligações entre vigas pré-moldadas de concreto e pilares mistos preenchidos foram propostas com a finalidade de transferir momento de flexão e força cortante das vigas para os pilares mobilizando os núcleos de concreto. Foi realizado um estudo numérico-experimental das ligações onde foi avaliada a viabilidade e a eficiência destas na transferência dos esforços. Em uma primeira fase, modelos compostos por pilar misto e consolo metálico (modelos 1 e 2) foram confeccionados, testados experimentalmente e modelados numericamente (método dos elementos finitos) para avaliar a eficiência do consolo na transferência da força cortante. Observou-se que a transferência da força cortante do consolo para o tubo metálico foi eficaz. O consolo se comportou de maneira previsível e suportou cargas elevadas. O uso de conectores de cisalhamento internos aos pilares aumentou a capacidade de carga e o desempenho dos mesmos. Na etapa seguinte da pesquisa foram confeccionados dois modelos, compostos por: pilar, viga pré-moldada, laje e consolo formando pórticos. Em um destes modelos (modelo 4) uma caixa metálica foi incorporada à viga pré-moldada e parafusado ao consolo metálico com a finalidade de transferir os momentos positivos, enquanto que outro modelo foi confeccionado e estudado sem este elemento (modelo 3). Nestes modelos foi avaliada a capacidade de transferência do momento de flexão (positivo e negativo) e forças cortantes com a ligação submetida a ciclos de carga. No modelo 3, a ligação transferiu de forma eficiente o momento negativo, porém o desempenho para o momento positivo não foi satisfatório, com baixa resistência e rigidez ao longo dos ciclos de carga. No modelo 4 foi observado considerável aumento da resistência e rigidez se comparado com o modelo anterior. Entretanto, a caixa metálica incorporada à viga pré-moldada não foi capaz de fazer com que a ligação resistisse aos momentos positivos como a mesma eficiência que resistiu aos negativos e houve degradação de suas características estruturais ao longo dos ciclos de carga. / In this work, connections of precast concrete beam to concrete-filled steel tube column were proposed to transfer the bending moment and shear forces from the beam to the composite column, mobilizing the concrete core. Was performed a numerical and experimental study of the proposed connections to evaluate the feasibility and effectiveness of them in the transfer of bending and shear forces from the beam to the column. In a first stage, models composed by column and steel corbel (models 1 e 2) were numerically and experimentally tested aiming the efficiency of the connection in shear transfer. It was observed that the transfer of shear to the steel tube was guaranteed. The corbel behaved in a predictable way and supported high loads. The use of shear connectors in the column increased the load capacity and improved the connection performance. In next stage of the research work, two models were prepared, composed by: column, precast concrete beam, steel corbel and slabs constituting frames. In one of these models (model 4) a steel box was incorporated into the precast beam and bolted to the steel corbel in order to transfer the positive moments, whereas another model was built and studied without this device (model 3). In this models were evaluated the efficiency in the transfer of bending moments (positive and negative) and shear forces with the models subjected to a cyclic loads. In the model 3, the connection transferred efficiently the negative bending, but the performance for the positive bending was not satisfactory, with reduced strength and stiffness over the load cycles. In model 4 was observed considerable increase in strength and stiffness compared with the previous model. However, the device incorporated in the precast beam was unable to make the connection resist to the positive moments with the same efficiency observed when subjected to the negative moments and a degradation of their structural characteristics was observed during the loading cycles.

Modification of the properties of solid state structures, used for gas sensing is important task in making detection and measurement systems of volatile chemical compounds. These properties depend on material, inner structure and interaction with gas atmosphere. In hybrid materials (solid-biomolecular) biochemical recognition plays important role in gas sensing mechanism. In this work the methodologies of the SPM was applied for characterization of the local point and local area properties in the gas sensitive MO films with the nanoscaled thickness that can be used for nanosystems and hybrid materials in novel types of chemical detectors. In this dissertation morphology and physical properties of metal oxide films with thickness from a few to about 50 nm was investigated and described a relationship between the gas response and film thickness. It was experimentally shown that effects of external influence on the properties of the surface nanostructures can be described by the specific characteristics of the scanning probe spectroscopy displaying the dependences of the probe contact electric current on both the probe potential and the probe pressing force. An original method based on the SPM probe controlled electrical current was proposed for the formation of nanosystems with various electrical properties on the surfaces of thin MO films. / Kryptingas kietojo kūno darinių, naudojamų išorinio dujų poveikio detekcijai, savybių keitimas yra vienas iš aktualiausių uždavinių, sprendžiamų kuriant lakiųjų cheminių junginių poveikio atpažinimo ir matavimo sistemas. Šias savybes lemia darinių medžiaga, jų struktūra bei sąveikos su dujine aplinka ypatumai, kurie hibridiniuose dariniuose iš kietojo kūno ir biomolekulių gali būti lemiami dar ir biocheminiu atpažinimu. Šiame darbe tiriami dujoms jautrūs hibridiniai dariniai ir nanosistemos, integruotos metalo oksido plėvelėse, Skenuojančio zondo mikroskopijos (SZM) metodais. Disertacijoje susieti itin plonų (<30-50 nm) SnOx sluoksnių varžos atsako į dujas bei elektrinių savybių ypatumai su sluoksnių morfologija, priklausančia nuo auginimo sąlygų ir trukmės. Eksperimentiškai įrodyta, jog SZM lokalinių srovių tyrimai, priklausomai nuo matavimo parametrų, leidžia atskirai aprašyti technologiškai keičiamas dujoms jautrių darinių charakteristikas ir tik nanosistemose vykstančius procesus, kurie, kai kuriais atvejais, gali būti stebimi ir tipiškuose dujoms jautrių darinių taikymuose. Sukurtas originalus metodas, tinkantis nanostruktūroms metalo oksidų paviršiuje formuoti bei tų struktūrų elektrinėms savybėms keisti. Skirtingai nuo literatūroje žinomo paviršiaus nanooksidinimo, pritaikyto formuoti cheminiam poveikiui atsparias dangas, mūsų metodas leidžia formuoti įvairaus elektrinio laidumo nanostruktūras metalo oksidų paviršiuje.

Kryptingas kietojo kūno darinių, naudojamų išorinio dujų poveikio detekcijai, savybių keitimas yra vienas iš aktualiausių uždavinių, sprendžiamų kuriant lakiųjų cheminių junginių poveikio atpažinimo ir matavimo sistemas. Šias savybes lemia darinių medžiaga, jų struktūra bei sąveikos su dujine aplinka ypatumai, kurie hibridiniuose dariniuose iš kietojo kūno ir biomolekulių gali būti lemiami dar ir biocheminiu atpažinimu. Šiame darbe tiriami dujoms jautrūs hibridiniai dariniai ir nanosistemos, integruotos metalo oksido plėvelėse, Skenuojančio zondo mikroskopijos (SZM) metodais. Disertacijoje susieti itin plonų (< 30-50 nm) SnOx sluoksnių varžos atsako į dujas bei elektrinių savybių ypatumai su sluoksnių morfologija, priklausančia nuo auginimo sąlygų ir trukmės. Eksperimentiškai įrodyta, jog SZM lokalinių srovių tyrimai, priklausomai nuo matavimo parametrų, leidžia atskirai aprašyti technologiškai keičiamas dujoms jautrių darinių charakteristikas ir tik nanosistemose vykstančius procesus, kurie, kai kuriais atvejais, gali būti stebimi ir tipiškuose dujoms jautrių darinių taikymuose. Sukurtas originalus metodas, tinkantis nanostruktūroms metalo oksidų paviršiuje formuoti bei tų struktūrų elektrinėms savybėms keisti. Skirtingai nuo literatūroje žinomo paviršiaus nanooksidinimo, pritaikyto formuoti cheminiam poveikiui atsparias dangas, mūsų metodas leidžia formuoti įvairaus elektrinio laidumo nanostruktūras metalo oksidų paviršiuje. / Modification of the properties of solid state structures, used for gas sensing is important task in making detection and measurement systems of volatile chemical compounds. These properties depend on material, inner structure and interaction with gas atmosphere. In hybrid materials (solid-biomolecular) biochemical recognition plays important role in gas sensing mechanism. In this work the methodologies of the SPM was applied for characterization of the local point and local area properties in the gas sensitive MO films with the nanoscaled thickness that can be used for nanosystems and hybrid materials in novel types of chemical detectors. In this dissertation morphology and physical properties of metal oxide films with thickness from a few to about 50 nm was investigated and described a relationship between the gas response and film thickness. It was experimentally shown that effects of external influence on the properties of the surface nanostructures can be described by the specific characteristics of the scanning probe spectroscopy displaying the dependences of the probe contact electric current on both the probe potential and the probe pressing force. An original method based on the SPM probe controlled electrical current was proposed for the formation of nanosystems with various electrical properties on the surfaces of thin MO films.

Cette thèse est constituée de deux parties indépendantes. La première partie traite du transport dans des gaz d'électrons bidimensionnels dans le régime de l'effet Hall quantique. Dans la deuxième partie, le courant et les corrélations croisées en courant sont étudiées pour des structures hybrides conducteur normal- supraconducteur- conducteur normal (NSN). Dans le régime de haute température de l'effet Hall quantique, la conductance longitudinale est calculée par un formalisme diagrammatique basé sur une approche de conductivité locale. Ce calcul prend en compte l'effet de dérive des électrons sur les lignes équipotentielles du potentiel de désordre et permet la dérivation microscopique de l'exposant critique de transport qui était auparavant seulement conjecturé à partir d'arguments géométriques qualitatifs. Des expressions microscopiques pour la dépendance en température et en champ magnétique de la conductance longitudinale sont dérivées et comparées avec des expériences récentes. Dans le régime de basse température de l'effet Hall quantique, le passage du courant par effet tunnel sur des points selles est étudié à partir de la diffusion de paquets d'onde d'états semi-cohérents. Nous dérivons analytiquement le coefficient de transmission d'un point selle pour le potentiel scalaire dans le graphène et trouvons que les points selles asymétriques brisent la symétrie particule-trou de la conductance. Dans des structures hybrides NSN, nous étudions l'influence de barrières additionnelles sur la conductance (non-locale) et sur les corrélations croisées en courant avec la théorie de diffusion. Dans les systèmes métalliques, où la phase est moyennée, des barrières additionnelles augmentent les processus locaux par réflexion Andreev résonante (reflectionless tunneling), mais ont peu d'influence sur les processus non-locaux et sur les corrélations croisées en courant. Dans les systèmes balistiques, des barrières additionnelles causent des oscillations Fabry-Pérot et permettent de distinguer les différents processus contribuant à la conductance et aux corrélations croisées en courant. / This thesis consists of two independent parts. The first one deals with transport in two dimensional electron gases in the regime of the quantum Hall effect. In the second part, current and current cross-correlations are studied in normal conductor-superconductor-normal conductor (NSN) hybrid structures. In the high temperature regime of the quantum Hall effect, the longitudinal conductance is calculated in a diagrammatic formalism based on a local conductivity approach. It takes the interplay between electron-phonon scattering and the drift motion along equipotential lines of the disorder potential into account and provides a microscopic derivation of the universal transport critical exponent that was up to now only conjectured from qualitative geometrical arguments. Microscopic expressions for the dependence in temperature and magnetic field of the longitudinal conductance are derived and compared to recent experiments. In the low temperature regime of the quantum Hall effect, tunneling over saddle points is studied from the scattering of semi-coherent state wave packets. We derive analytically the transmission coefficient of saddle-points in the scalar potential in graphene and find that asymmetric saddle-points break particle-hole symmetry in the conductance. In three-terminal NSN hybrid structures the influence of additional barriers on the (non-local) conductance and on current cross-correlations is studied with scattering theory. In metallic, phase averaged systems additional barriers lead to an enhancement of local processes by reflectionless tunneling but have little influence on non-local processes and on current cross-correlations. In ballistic systems, additional barriers lead to Fabry-Perot oscillations and allow to distinguish the different contributions to the conductance and to the current cross-correlations.