Le traitement par laser femtoseconde dans des matériaux transparents est prometteur du fait de la possibilité de contrôler le dépôt d'énergie dans le temps et dans l'espace. Il ouvre ainsi des possibilités fantastiques pour la fabrication de nouveaux matériaux composites multifonctionnels en manipulant la taille, la forme et l'orientation des cristaux non linéaires dans les verres. Cette thèse contribue principalement à la maîtrise de la nano ou micro cristallisation dans des verres à base de silice pour le développement de nouveaux matériaux électro-optiques multi-fonctionnels par l’irradiation au laser femtoseconde. On démontre la faisabilité du traitement des matériaux par le laser femtoseconde pour remodeler les propriétés optiques linéaires et non linéaires ou de la fabrication de micro / nano agrégats, ainsi que les formes et les orientations (en particulier agrégats asymétriques), les tailles et les distributions (à l'échelle sub-micrométrique). Le mémoire débute par un chapitre introductif sur l’investigation de l’écriture par laser impulsionnel ultra-bref dans la silice pure, ainsi que dans le verre à base de silice, afin de bien maîtriser l’inscription avec ce nouveau type de laser. Nous discutons les effets des paramètres du laser sur l’écriture, telle que la vitesse de déplacement du faisceau et la polarisation du laser, sur les propriétés optiques et les structures atomiques, par exemple, la biréfringence, les champs de contraintes et le changement d’arrangement atomique. Il est mis en évidence des effets orientationnels et directionnels spécifiques de l’interaction de ce type de laser avec les verres. Le mécanisme associé fait probablement intervenir l'inclinaison du front de la phase du champ de l’impulsion par rapport au déplacement du faisceau dans le solide. La précipitation des cristaux LiNbO3 orientés dans le verre avec l’irradiation laser femtoseconde est réalisée dans le cas d’une fréquence de répétition élevée (typ. 300 kHz) permettant l’accumulation de chaleur. Des cristaux orientés avec leur axe polaire aligné dans la direction d’inscription du laser ont été fabriqués en manipulant le gradient de température par le réglage des paramètres du laser. L’imagerie microscopique de génération de seconde harmonique (GSH) montre le caractère cristallin asymétrique et fournit des informations sur les orientations dominantes favorisées lors des processus de cristallisation. Les résultats de diffraction d’électrons rétrodiffusés (EBSD) fournissent des informations détaillées sur l’orientation des cristaux et révèlent la structure des lignes écrites notamment tailles et dispersion des orientations. En outre, des débuts de modélisation ont été réalisés pour se diriger vers une maîtrise de l’écriture de structures linéaires cristallines. Une autre section du mémoire rapporte l’étude de reformation par l’irradiation avec le laser femtoseconde de nanoparticules d'or quasi-sphériques ou quasi-tige dans le verre à base de silice. Les nanoparticules d'or de la taille de 3-4 nm ont été précipitées par traitement thermique. Après l’irradiation par le laser, des mesures optiques d'absorption, de biréfringence et de dichroïsme ont été effectuées pour étudier la modification de la forme de nanoparticules d'or dans le verre. Les simulations théoriques ont été menées pour interpréter les résultats expérimentaux basés sur la théorie de Gans et le modèle de Drude avec les constantes diélectriques connus de l'or. Enfin, des stratégies de conception efficaces sont aussi suggérées pour le futur pour des applications possibles utilisant la précipitation, la forme et l'orientation des micro/nanoparticules en 3D. / Femtosecond laser processing in transparent materials is promising owing to the accessible control of energy deposition in time and in space. In this regime, it opens fantastic opportunities to manufacture novel multifunctional composite materials by manipulating the size, shape and orientation of nonlinear crystals with intrinsic symmetry embedded in glasses. This dissertation mainly contributes to the control of nano or micro crystallization inside silica-based glasses for the development of novel multifunctional electro-optical materials by femtosecond laser irradiation. We demonstrate the feasibilities of femtosecond laser materials processing for re-shaping linear and non-linear optical properties in silica-based glass by inducing or fabricating different micro/nanoclusters as well as their shapes and orientation (especially asymmetric clusters), sizes, and distributions (at the sub-micrometer scale). In this thesis, it firstly covers a chapter for the investigation on ultrafast asymmetric orientational writing in pure silica as well as in silica-based glass in order to well master the laser writing. We discuss the effects of the laser parameters on asymmetric writing such as writing speed and the laser polarization by the femtosecond-laser generated optical properties and structures, e.g., birefringence, phase change and surface topography of the cross section of laser tracks. The mechanism of orientational dependent writing is likely due to the oblique pulse front tilt affected by the polarization orientation plane leading to different anisotropic photosensitivity. 3D photo-precipitation of oriented LiNbO3-like crystals in glass with femtosecond laser irradiation is also achieved at high repetition rate (typ. 300 kHz). Oriented crystals with their polar axis mostly aligned with the laser scanning direction have been fabricated by manipulation of the temperature gradient in adjusting the laser parameters. Second harmonic generation (SHG) microscopy demonstrates optical activity of crystalline features and provides some orientation information suggestive of certain dominant or favored orientations. Electron back-scattering diffraction (EBSD) results provide more detailed local crystal orientation information and illustrate interesting features of the structure of the lines, with regions of distinctly different grain sizes and orientations. Furthermore, modeling the temperature gradient was proposed for better understanding the formation mechanism of the orientation of femtosecond laser-induced crystallization when the laser is moved (not only in the static mode). Quasi-spherical or quasi-rod gold nanoparticles in silica-based glass can be re-shaped by femtosecond laser irradiation studying through their properties, and their orientation appears to be parallel to the written lines. Gold nanoparticles in the size range of 3-4 nm were precipitated by post heat-treatment. After ultrafast laser irradiation, optical absorption, birefringence and dichroism measurements are performed to investigate the modification of gold nanoparticle shape in glass. Theoretical simulations have been carried out to interpret the experimental results based on the Gans' theory and Drude model together with the known dielectric constants of gold. Furthermore, feasible applications and efficient design strategies are also referred for future devices based on micro/nanoclusters 3D precipitation, shaping and orientation mastering.

Solutions to trajectory optimization problems are carried out by the direct and indirect methods. Under broad heading of these methods, numerous algorithms such as collocation, direct, indirect and multiple shooting methods have been developed and reported in the literature. Each of these algorithms has certain advantages and limitations. For example, direct shooting technique is not suitable when the number of nonlinear programming variables is large. Indirect shooting method requires analytical derivatives of the control and co-states function and a poorly guessed initial condition can result in numerical unstable values of the adjoint variable. Multiple shooting techniques can alleviate some of these difficulties by breaking down the trajectory into several segments that help in reducing the non-linearity effects of early control on later parts of the trajectory. However, multiple shooting methods then have to handle more number of variables and constraints to satisfy the defects at the segment joints. The sie of the nonlinear programming problem in the collocation method is also large and proper locations of grid points are necessary to satisfy all the path constraints. Stochastic methods such as Genetic algorithms, on the other hand, also require large number of function evaluations before convergence. To overcome some of the limitations of the conventional methods, improved solution techniques are developed. Three improved methods are proposed for the solution of trajectory optimization problems. They are • a genetic algorithm employing dominance and diploidy concept. • a collocation method using chebyshev polynomials , and • a hybrid method that combines collocation and direct shooting technique A conventional binary-coded genetic algorithm uses a haploid chromosome, where a single string contains all the variable information in the coded from. A diploid, as the name suggests, uses pair of chromosomes to store the same characteristic feature. The diploid genetic algorithm uses a dominant map for decoding genotype into a stable, consistent phenotype. In dominance, one allele takes precedence over another. Diploidy and dominance helps in retaining the previous best solution discovered and shields them from harmful selection in a changing environment. Hence, diploid and dominance affect a king of long-term memory in the genetic algorithm. They allow alternate solutions to co-exist. One solution is expressed and the other is held in abeyance. In the improved diploid genetic algorithm, dominant and recessive genes are defined based on the fitness evaluation of each string. The genotype of fittest string is declared as the dominant map. The dominant map is dynamic in nature as it is replaced with a better individual in future generations. The concept of diploidy and dominance in the improved method mimics closer to the principles used in human genetics as compared to any such algorithms reported in the literature. It is observed that the improved diploid genetic algorithm is able to locate the optima for a given trajectory optimization problem with 10% lower computational time as compared to the haploid genetic algorithm. A parameter optimization problem arising from an optimal control problem where states and control are approximated by piecewise Chebyshev polynomials is well known. These polynomials are more accurate than the interpolating segments involving equal spaced data. In the collocation method involving Chebyshev polynomials, derivatives of two neighboring polynomials are matched with the dynamics at the nodal points. This leads to a large number of equality constraints in the optimization problem. In the improved method, derivative of the polynomial is also matched with the dynamics at the center of segments. Though is appears the problem size is merely increased, the additional computations improve the accuracy of the polynomial for a larger segment. The implicit integration step size is enhanced and overall size of the problem is brought down to one-fourth of the problem size defined with a conventional collocation method using Chebyshev polynomials. Hybrid method uses both collocation and direct shooting techniques. Advantages of both the methods are combined to give more synergy. Collocation method is used in the starting phase of the hybrid method. The disadvantage of standalone collocation method is that tuning of grid points is required to satisfy the path constraints. Nevertheless, collocation method does give a good guess required for the terminal phase of the hybrid method, which uses a direct shooting approach. Results show nearly 30% reduction in computation time for the hybrid approach as compared to a method in which direct shooting alone is used, for the same initial guess of control. The solutions obtained from the three improved methods are compared with an indirect method. The indirect method requires derivations of the control and adjoint equations, which are difficult and problem specific. Due to sensitivity of the costate variables, it is often difficult to find a solution through the indirect method. Nevertheless, these methods do provide an accurate result, which defines a benchmark for comparing the solutions obtained through the improved methods. Trajectory design and optimization of a RLV(Reusable Launch Vehicle) Demonstrator mission is considered as a test problem for evaluating the performance of the improved methods. The optimization problem is difficult than a conventional launch vehicle trajectory optimization problem because of the following two reasons. • aerodynamic lift forces in the RLV add one more dimension to the already complex launch vehicle optimization problem. • as RLV performs a sub orbital flight, the ascent phase trajectory influences the re-entry trajectory. Both the ascent and re-entry optimization problem of the RLV mission is addressed. It is observed that the hybrid method gives accurate results with least computational effort, as compared with other improved techniques for the trajectory optimization problem of RLV during its ascent flight. Hybrid method is then successfully used during the re-entry phase and in designing the feasible optimal trajectories under the dispersion conditions. Analytical solutions obtained from literature are used to compare the optimized trajectory during the re-entry phase. Trajectory optimization studies are also carried out for the off-nominal performances. Being a thrusting phase, the ascent trajectory is subjected to significant deviations, mainly arising out of solid booster performance dispersions. The performance index during rhe ascent phase is modified in a novel way for handling dispersions. It minimizes the state errors in a least square sense, defined at the burnout conditions ensure possibilities of safe re-entry trajectories. The optimal trajectories under dispersion conditions serve as a benchmark for validating the closed-loop guidance algorithm that is developed for the ascent phase flight. Finally, an on-line trajectory command-reshaping algorithm is developed which meets the flight objectives under the dispersion conditions. The guidance algorithm uses a pre-computed trajectory database along with some real-time measured parameters in generating the optimal steering profiles. The flight objectives are met under the dispersion conditions and the guidance generated steering profiles matches closely with the optimal trajectories.

In this study, an examination of the everyday experiences of the contract migrant Filipina domestic helpers exposes a culture of indifference which pervades the Hong Kong society on all levels--individual, community, and judiciary. At the centre of the abuses inflicted upon the Helpers is the employment contract with extraordinarily restrictive terms which promotes abuse by many employers. This study also looks at the transnational informal social infrastructure which has been organized by the Filipino community to mediate the hostile working environment engendered by the indifference of the global economic and political climate upon their lives. Faced with the task of implementing new policies for controlling labour migration into Hong Kong, the legislators have focused on the end result and finding the means with which to accomplish their goal. Embedded within this process are unexamined cultural mores and practices. Although the starting point is to benefit the community, by providing domestic helpers to serve the middle and upper class households, too often the abusive consequences to individual migrants are ignored as the women become the means to an end. Migration has often been viewed as an aberration to the notion of the sedentary community. Treated as an anomaly, it is the migrant who problematizes simple theoretical positions of social organization and structure. The migrant is always treated as the one who does not conform to the ideal community and is conveniently merged into existing social categories, such as the lower status of women in Hong Kong, and the lower status of domestic workers -- relegated thereby to the periphery of the society's consciousness.

Les politiques urbaines de « reconstruction » post-apartheid de ces dernières décennies n’ont pas permis de réduire les injustices spatiales du Gauteng et de Johannesburg en particulier. Sous l’impulsion des acteurs privés, les résidences fermées d’entrée de gamme, symbole de l’ascension sociale des classes moyennes, diffusent de nouvelles formes de relégation et de fragmentation qui questionnent fortement le lien social, l’étalement et la mobilité croissante. Le peu d’investigations menées sur cette ville « moyenne », qui se veut synonyme de progrès et de modernité, offre l’opportunité de mobiliser une réflexion nouvelle sur les interrelations qui existent entre production de la ville, pratiques et territoires. Loin d’être monolithique, le logement d’entrée de gamme s’est développé à travers maints arrangements institutionnels particuliers et géographiquement situés. Le rôle des acteurs privés impliqués dans la gouvernance urbaine, souvent méconnu et rarement étudié, est devenu la clé de voûte des transformations contemporaines de la ville. L’originalité de ce travail a été de révéler les principes de constitution de savoirs spécialisés et spatialisés, qui éclairent le processus de codification des pratiques et donc la naissance de l’urbanisme sécuritaire institutionnalisé au sein de la métropole.Le détour comparatif avec Delhi a été l’occasion de valider que ces résultats avaient une portée générale cumulable, tout en délocalisant le regard. / The post-apartheid urban policies of the last decades aiming at “rebuilding” the nation, have not led to reducing spatial injustice in Gauteng, and Johannesburg in particular. Spurred on by private actors, bottom-of-the-range closed residences, which symbolise the upward social mobility of the middle class, spread new forms of relegation and fragmentation, thereby challenging social links, urban sprawl and growing mobility. The little research carried out on this “average” city, which is meant to be synonymous with progress and modernity, is an opportunity to develop new thoughts on existing interrelations between urban production, practices and territories.Far from being monolithic, bottom-of-the-range housing is being developed through many specific and geographically located institutional arrangements. The role played by private actors involved in urban governance, which is often largely unknown and rarely being studied, has become the keystone of the city’s contemporary transformations. The novelty behind this research work is that it reveals the principles of what constitutes specialised and spatialized expertise, thereby shedding light on the codification process of practices and, as such, the birth of institutionalised security town planning within the metropolis.Comparing Johannesburg with Delhi was an opportunity to validate the fact that these results could be significantly drawn concurrently, while studying two different sites

Dans le cadre de la recherche, nous nous intéressons à la pratique du projet urbain dans les villes en décroissance (ou ville rétrécissante), plus connues sous le terme anglophone de shrinking cities. Cet intérêt est né d’un questionnement plus large sur la pratique de l’architecte-urbaniste et la fabrique de la ville en ce début du XXIe siècle, où les débats se multiplient sur la ville résiliante, économe, autosuffisante face aux crises écologiques, socio- économiques et politiques actuelles. La ville en décroissance offre ainsi un cadre intéressant pour nous confronter à cette problématique où l’architecte-urbaniste se retrouve à devoir s’adapter et se réinventer face à de multiples contraintes. Par ailleurs, le programme allemand Shrinking Cities et les réflexions portées par l’architecte-chercheur allemand Philipp Oswalt ont été un élément déclencheur. Ce dernier revendiquait l’idée que la ville en décroissance était le nouveau terrain de jeu pour explorer de nouvelles pensées architecturales et urbanistiques. Il le démontre à partir d’un travail de collecte d’expériences à travers le monde. Aujourd’hui, nous proposons de poursuivre cette réflexion et de nous poser la question suivante: quels enseignements pouvons-nous tirer de ces expériences pour notre pratique et imaginer la ville de demain ? À partir de ce questionnement, nous faisons l’hypothèse que ces nouvelles pensées architecturales et urbaines (concepts, langages architecturaux, formes urbaines, etc.) participeraient à la formulation de nouvelles formes d’habiter les territoires (usages, modèles urbains, paysage, modes de vie, etc.), permettant d’envisager différemment la fabrique urbaine en ce début du XXIe. Ces démarches seraient par ailleurs actrices dans la reconnaissance de terrains favorables pour une gestion urbaine raisonnée et dans le développement de nouveaux outils et protocoles d’action imaginés par les architecte-urbanistes.Pour répondre à notre hypothèse de recherche, nous nous intéressons plus spécifiquement aux projets impulsant une mutation profonde du tissu urbain, dans sa forme comme dans ses usages que nous nommons ici par remodelage urbain. Notre analyse se base sur six démarches dites « innovantes », théoriques et réalisées, dont un cas est mis en œuvre par des habitants. Elles illustrent cette pratique dans différentes villes en décroissance depuis ces vingt dernières années.Ces cas d’étude sont situés dans des tissus urbains différents (habitat dense en centre-ville et dans les bourgs ruraux, grands ensembles, habitat pavillonnaire) pour montrer la diversité des terrains auxquels l’architecte-urbaniste peut être confronté. Parallèlement aux deux cas français (Saint-Étienne, Livradois-Forez), nous observerons d’autres expériences dans deux contextes étrangers, précurseurs en termes d’initiatives locales et de politiques urbaines : l’Allemagne (Halle- Neustadt, Dessau) et les États-Unis (Detroit). La diversité des approches et des échelles de réflexion de ces projets ne permet pas de conduire une étude comparative. Plus adaptée à notre démarche, nous proposons leur mise en discussion pour comprendre l’impact du cadre politique, socio-économique et de l’environnement urbain sur le processus de projet ainsi que la capacité de ces projets à amorcer une transformation du tissu urbain et de la ville.Notre objectif sera ainsi de comprendre l’originalité et les spécificités de ces démarches, mais aussi leurs apports potentiels dans les débats actuels sur la ville et ses évolutions. Cette démarche cherche à apporter une dimension prospective sur le sujet de la ville en décroissance. / Within the methodological framework of the academic research, this study focuses on the urban development specific to shrinking cities. This interest raised from a broader interrogation on the professional practice of urban architects and the making of the city ongoing in this early XXIth century, with regards to contemporary debates about cities that are resilient, economical, self sufficient toward ecological, socio-economical and political crises. The shrinking city offers thus an interesting framework to study architects-urban planners reactions to such contexts and constraints adaptation. Furthermore the German programm Shrinking Cities and the reflexions raised by the German architect and researcher Philipp Oswalt have been a trigger component. He claims that the shrinking city was a new playground to explore new architectural and planning thoughts. He demonstrates it from a gathering of experiences around the world. Today, we suggest to follow this reflexion and raise the following issue: which lessons are to be learned from those experiences for today’s professional practice and imagine the city of tomorrow ?From this initial questioning, we took for granted that those new ways of seeing architecture and urban project (concepts, architectural languages, urban shape, etc.) lead to new leaving standards territories (uses, urban patterns, landscape, leaving conditions, etc.), changing thus the making of the city in this beginning of XXIth century. Indeed, those processes would be influential in the identification of favourable lands for a reasoned gestion of the city and the development of new tools and acting processes imagined by architects and urban planners.To answer to our hypothesis, we focus more specifically on projects initiating a deep mutation of the urban fabric, on its form and its uses that we would call here urban reshaping. Our analysis is based on six processes meant to be “innovative”, realized or no, one of them being built by inhabitants. They illustrate this practice in different shrinking cities since the 20 past years. Those case studies are located in different urban fabrics contexts to illustrate the diversity of situations that one can be facing. In parallel of two French case studies (Saint-Etienne, Livradois-Forez), we will observe other experiences in two foreign contexts, pioneers in terms of local initiatives and urban policy: Germany (Halle-Neustadt, Dessau) and the United states (Detroit). The diversity of projects, in terms of approach and scale does not constitute a comparative study. We suggest instead a more relevant approach consisting in questioning them to understand the political, socioeconomic and environment consequences on the process of project making and the capacity of those projects to initiate a transformation of urban fabric and of the city.Our goal will be to understand the originality and specifies of those initiatives, but also potential contributions to the contemporary debates on the city and its evolutions. This approach seeks bringing a prospective dimension about the shrinking city.

La France et l’Espagne connaissent depuis plus de vingt ans des processus de recompositions territoriales, dont l’un des enjeux est la création de nouveaux territoires intermédiaires à l’échelle locale (structures intercommunales, “Pays” en France, comarcas en Espagne). Entre commune/municipio et département/provincia, ces derniers sont censés favoriser une refonte de l’organisation territoriale, mais aussi le développement de nouveaux modes de gestion territoriale, plus intégrés et plus horizontaux. À partir des exemples des régions Rhône-Alpes et Catalogne, parmi les premières à développer ces nouveaux espaces locaux, cette thèse interroge leur caractère intermédiaire et le type d’intermédiarité qui les caractérisent. L’analyse révèle la fragilité des mailles intermédiaires en construction, liée à l’échec de leurs potentielles fonctions d’intermédiarité et à la faiblesse née de leur caractère intermédiaire : elles connaissent une neutralisation interne et externe, et peinent donc à trouver leur légitimité par rapport aux niveaux existants et à d’autres nouveaux découpages locaux. La multiplication de ces derniers, qui révèle autant qu’elle explique l’échec des mailles étudiées, montre cependant que c’est moins l’échelle ou le niveau intermédiaire qui sont en cause que les modalités de leur construction. En s’appuyant sur un vaste corpus législatif et sur des enquêtes de terrain (Pays Roannais, comarques du Bages et d’Osona), en croisant de multiples échelles spatio-temporelles dans l’analyse de ces découpages locaux, ce travail invite à systématiser, dans le cadre d’une possible convergence européenne, les études géographiques des systèmes d’administration territoriale. / For more than twenty years, France and Spain have undergone various processes of territorial reshaping, among which the creation of new intermediate authorities at the local scale (inter-city structures, Pays in France, comarcas in Spain). Halfway between commune/municipio and département/provincia, these government units are intended to favor the reform of the territorial organization as well as the design of better integrated and more horizontal territorial management policies. Based on the case studies of pioneer regions Rhône-Alpes and Catalunya, among the first to develop these new local spaces, this work questions the level of intermediateness that characterizes these local units under construction. It shows that the failure of their potential intermediate functions is due to their intermediate nature which itself makes them very fragile. They are subject to both internal and external neutralization and struggle to assert their legitimacy vis à vis existing government levels and other new local territories. The dramatic increase of the latter shows that it is the way the intermediate local units under study are built rather than their mere intermediate scale that explains their failure. Based on a large corpus of legislative material, on field studies (Pays Roannais, comarques of Bages and Osona) and on a multi-level cross-analysis in both space and time, this work aims to systematise the geographical approach of local government systems, a methodology particularly relevant in the perspective of converging local policies at the European level.

With the advent of microelectronics and micromechanical systems, the benefits of miniaturized technology became evident. With the discovery of carbon nanotubes by Iijima in 1991, a material has been found that offers superior porperties such as high tensile strength, excellent electrical and heat conductivity while being lightweight, flexible and tunable by the specific atomic arrangement in its structure. The first part of this thesis deals with a new synthesis approach, which combines the known routes of chemical vapour deposition and laser ablation. The results concerning diameter and yield fit well within an established model for the nucleation and growth of carbon nanotubes and extend it by considering a larger parameter space. Furthermore, conventional laser ablation has been used to synthesize C-13 augmented carbon nanotubes, whose diameters depend among the usual synthesis parameters also on the C-13 content, an influence which is in line with the changed thermal conductivities of isotope mixtures. Manipulation of carbon nanotubes inside a transmission electron microscope forms the second part of this thesis. With the help of an in-situ nanomanipulator, several experiments involving the mechanical and electrical properties of carbon nanotubes have been performed. Two-probe resistances of individual nanotubes have been measured and the observation of individual shell failures allowed for the determination of current limits per carbon shell. With the help of electrical current, a nanotube was modified in its electrical characteristics by reshaping its structure. By application of DC-currents or square current pulses, the filling of iron- or cementite-filled multi-wall carbon nanotubes has been found to move in a polarity-defined direction guided by the nanotube walls. Depending on the current, nanotube shape, and composition of the filling different regimes of material transport have been identified, including the reworking of the inner nanotube shells. The application of a high driving current leads to a complete reworking of the host nanotube and the current-induced growth of carbonaceous nanostructures of changed morphology. Utilizing the obtained results, a transport mechanism involving momentum transfer from the electron wind to the filling atoms and a solid filling core during transport is developed and discussed. Finally, measurements of mechanical properties using electrically induced resonant or non-resonant vibrations inside the transmission electron microscope have been observed and important mechanical parameters have been determined with the help of a modified Euler-Bernoulli-beam approach. / Mit dem Aufkommen von Mikroelektronik und mikromechanischen Systemen wurden die Vorteile miniaturisierter Geräte augenscheinlich. Mit der Entdeckung von Kohlenstoff-Nanoröhren durch Iijima 1991 wurde ein Material gefunden, welches überlegene Eigenschaften wie hohe Festigkeit, exzellente elektrische und Wärmeleitfähigkeit zeigt, während es zeitgleich leicht und flexibel ist. Diese Eigentschaften können durch eine Änderung der spezifischen atomaren Anordnung in der Nanoröhrenhülle beeinflusst werden. Der erste Teil dieser Dissertationsschrift behandelt einen neuartigen Syntheseansatz, welche die bekannten Syntheserouten der chemischen Gasphasenabscheidung und Laserablation kombiniert. Die Ergebnisse bezüglich des Durchmessers und der Ausbeute lassen sich gut mit einem etablierten Modell der Nukleation und des Wachstums von Kohlenstoff-Nanoröhren beschreiben - sie erweitern es, indem sie einen größeren Parameterraum berücksichtigen. Des Weiteren wurde konventionelle Laserablation benutzt, um C-13 angereicherte Kohlenstoff-Nanoröhren herzustellen, deren Durchmesser nicht nur von den üblichen Parametern, sondern auch vom C-13 Anteil abhängt. Diese Abhängigkeit geht mit der veränderten thermischen Leitfähigkeit von Isotopenmischungen einher. Die Manipulation von Kohlenstoff-Nanoröhren in einem Transmission-Elektronenmikroskop formt den zweiten Teil der Dissertationschrift. Mit Hilfe eines in-situ Manipulators wurden vielfältige Experimente durchgeführt, um die mechanischen und elektrischen Eigenschaften der Kohlenstoff-Nanoröhren zu bestimmen. Zweipunktmessungen des Widerstands einzelner Nanoröhren und die Beobachtung des Versagens einzelner Kohlenstoffschichten erlaubte die Bestimmung der Stromtragfähigkeit einzelner Hüllen. Mit Hilfe eines elektrischen Stromes konnte eine Nanoröhre durch die veränderung der Struktur in ihren elektrischen Eigenschaften verändert werden. Unter Verwendung dauerhaften oder gepulsten Gleichstroms konnte die Eisen- oder Zementit-Füllung der Kohlenstoff-Nanoröhren in eine polaritätsabhängige Richtung bewegt werden. Die Füllung wurde dabei durch die Wände der Nanoröhre geführt. Abhängig von Strom, Form der Nanoröhre und Zusammensetzung der Füllung ließen sich verschiedene Bereiche des Materialtransports identifizieren, u.a. das Umarbeiten einiger innerer Kohlenstoffschichten. Ein hoher Strom hingegen bewirkt eine Umarbeitung der kompletten Nanoröhre und strominduziertes Wachstum von Kohlenstoff-Nanostrukturen mit veränderter Morphologie. Mit Hilfe der gewonnenen Resultate wurde ein Transportmodell entwickelt, welches den Impulstransfer von Elektronen an Füllungsatome sowie einen festen Füllungskern während des Transports diskutiert. Messungen der mechanischen Eigenschaften, welche mit Hilfe von resonanter oder nicht-resonanter elektrischer Anregung von Schwingungen im Transmissions-Elektronenmikroskop durchgeführt wurden bilden den Abschluss der Arbeit. Durch die Beobachtungen konnten mit einem modifizierten Euler-Bernoulli-Balkenmodell wichtige mechanische Eigenschaften bestimmt werden.

With the advent of microelectronics and micromechanical systems, the benefits of miniaturized technology became evident. With the discovery of carbon nanotubes by Iijima in 1991, a material has been found that offers superior porperties such as high tensile strength, excellent electrical and heat conductivity while being lightweight, flexible and tunable by the specific atomic arrangement in its structure. The first part of this thesis deals with a new synthesis approach, which combines the known routes of chemical vapour deposition and laser ablation. The results concerning diameter and yield fit well within an established model for the nucleation and growth of carbon nanotubes and extend it by considering a larger parameter space. Furthermore, conventional laser ablation has been used to synthesize C-13 augmented carbon nanotubes, whose diameters depend among the usual synthesis parameters also on the C-13 content, an influence which is in line with the changed thermal conductivities of isotope mixtures. Manipulation of carbon nanotubes inside a transmission electron microscope forms the second part of this thesis. With the help of an in-situ nanomanipulator, several experiments involving the mechanical and electrical properties of carbon nanotubes have been performed. Two-probe resistances of individual nanotubes have been measured and the observation of individual shell failures allowed for the determination of current limits per carbon shell. With the help of electrical current, a nanotube was modified in its electrical characteristics by reshaping its structure. By application of DC-currents or square current pulses, the filling of iron- or cementite-filled multi-wall carbon nanotubes has been found to move in a polarity-defined direction guided by the nanotube walls. Depending on the current, nanotube shape, and composition of the filling different regimes of material transport have been identified, including the reworking of the inner nanotube shells. The application of a high driving current leads to a complete reworking of the host nanotube and the current-induced growth of carbonaceous nanostructures of changed morphology. Utilizing the obtained results, a transport mechanism involving momentum transfer from the electron wind to the filling atoms and a solid filling core during transport is developed and discussed. Finally, measurements of mechanical properties using electrically induced resonant or non-resonant vibrations inside the transmission electron microscope have been observed and important mechanical parameters have been determined with the help of a modified Euler-Bernoulli-beam approach. / Mit dem Aufkommen von Mikroelektronik und mikromechanischen Systemen wurden die Vorteile miniaturisierter Geräte augenscheinlich. Mit der Entdeckung von Kohlenstoff-Nanoröhren durch Iijima 1991 wurde ein Material gefunden, welches überlegene Eigenschaften wie hohe Festigkeit, exzellente elektrische und Wärmeleitfähigkeit zeigt, während es zeitgleich leicht und flexibel ist. Diese Eigentschaften können durch eine Änderung der spezifischen atomaren Anordnung in der Nanoröhrenhülle beeinflusst werden. Der erste Teil dieser Dissertationsschrift behandelt einen neuartigen Syntheseansatz, welche die bekannten Syntheserouten der chemischen Gasphasenabscheidung und Laserablation kombiniert. Die Ergebnisse bezüglich des Durchmessers und der Ausbeute lassen sich gut mit einem etablierten Modell der Nukleation und des Wachstums von Kohlenstoff-Nanoröhren beschreiben - sie erweitern es, indem sie einen größeren Parameterraum berücksichtigen. Des Weiteren wurde konventionelle Laserablation benutzt, um C-13 angereicherte Kohlenstoff-Nanoröhren herzustellen, deren Durchmesser nicht nur von den üblichen Parametern, sondern auch vom C-13 Anteil abhängt. Diese Abhängigkeit geht mit der veränderten thermischen Leitfähigkeit von Isotopenmischungen einher. Die Manipulation von Kohlenstoff-Nanoröhren in einem Transmission-Elektronenmikroskop formt den zweiten Teil der Dissertationschrift. Mit Hilfe eines in-situ Manipulators wurden vielfältige Experimente durchgeführt, um die mechanischen und elektrischen Eigenschaften der Kohlenstoff-Nanoröhren zu bestimmen. Zweipunktmessungen des Widerstands einzelner Nanoröhren und die Beobachtung des Versagens einzelner Kohlenstoffschichten erlaubte die Bestimmung der Stromtragfähigkeit einzelner Hüllen. Mit Hilfe eines elektrischen Stromes konnte eine Nanoröhre durch die veränderung der Struktur in ihren elektrischen Eigenschaften verändert werden. Unter Verwendung dauerhaften oder gepulsten Gleichstroms konnte die Eisen- oder Zementit-Füllung der Kohlenstoff-Nanoröhren in eine polaritätsabhängige Richtung bewegt werden. Die Füllung wurde dabei durch die Wände der Nanoröhre geführt. Abhängig von Strom, Form der Nanoröhre und Zusammensetzung der Füllung ließen sich verschiedene Bereiche des Materialtransports identifizieren, u.a. das Umarbeiten einiger innerer Kohlenstoffschichten. Ein hoher Strom hingegen bewirkt eine Umarbeitung der kompletten Nanoröhre und strominduziertes Wachstum von Kohlenstoff-Nanostrukturen mit veränderter Morphologie. Mit Hilfe der gewonnenen Resultate wurde ein Transportmodell entwickelt, welches den Impulstransfer von Elektronen an Füllungsatome sowie einen festen Füllungskern während des Transports diskutiert. Messungen der mechanischen Eigenschaften, welche mit Hilfe von resonanter oder nicht-resonanter elektrischer Anregung von Schwingungen im Transmissions-Elektronenmikroskop durchgeführt wurden bilden den Abschluss der Arbeit. Durch die Beobachtungen konnten mit einem modifizierten Euler-Bernoulli-Balkenmodell wichtige mechanische Eigenschaften bestimmt werden.