Grâce à leur propriétés uniques, les nanofils d'InAs et de Bi1-xSbx sont important pour les domaines de la nanoélectronique et de l'informatique quantique. Alors que la mobilité électronique de l'InAs est intéressante pour les nanoélectroniques; l'aspect isolant topologique du Bi1-xSbx peut être utilisé pour la réalisation de Qubits basés sur les fermions de Majorana. Dans les deux cas, l'amélioration de la qualité du matériau est obligatoire et ceci est l'objectif principal cette thèse ou` nous étudions l'intégration des nanofils InAs sur silicium (compatibles CMOS) et où nous développons un nouvel isolant topologique nanométrique: le Bi1-xSbx. Pour une compatibilité CMOS complète, la croissance d'InAs sur Silicium nécessite d'être auto- catalysée, entièrement verticale et uniforme sans dépasser la limite thermique de 450 ° C. Ces normes CMOS, combineés à la différence de paramètre de maille entre l'InAs et le silicium, ont empêché l'intégration de nanofils InAs pour les dispositifs nanoélectroniques. Dans cette thèse, deux nouvelles préparations de surface du Si ont été étudiées impliquant des traitements Hydrogène in situ et conduisant à la croissance verticale et auto-catalysée de nanofils InAs compatible avec les limitations CMOS. Les différents mécanismes de croissance résultant de ces préparations de surface sont discutés en détail et un passage du mécanisme Vapor-Solid (VS) au mécanisme Vapor- Liquid-Solid (VLS) est rapporté. Les rapports d'aspect très élevé des nanofils d'InAs sont obtenus en condition VLS: jusqu'à 50 nm de diamètre et 3 microns de longueur. D'autre part, le Bi1-xSbx est le premier isolant topologique 3D confirmé expérimentalement. Dans ces nouveaux matériaux, la présence d'états surfacique conducteurs, entourant le coeur isolant, peut héberger les fermions de Majorana utilisés comme Qubits. Cependant, la composition du Bi1-xSbx doit être comprise entre 0,08 et 0,24 pour que le matériau se comporte comme un isolant topologique. Nous rapportons pour la première fois la croissance de nanofils Bi1-xSbx sans défaut et à composition contrôlée sur Si. Différentes morphologies sont obtenues, y compris des nanofils, des nanorubans et des nanoflakes. Leur diamètre peut être de 20 nm pour plus de 10 microns de long, ce qui en fait des candidats idéaux pour des dispositifs quantiques. Le rôle clé du flux Bi, du flux de Sb et de la température de croissance sur la densité, la composition et la géométrie des structures à l'échelle nanométrique est étudié et discuté en détail. / InAs and Bi1-xSbx nanowires with their distinct material properites hold promises for nanoelec- tronics and quantum computing. While the high electron mobility of InAs is interesting for na- noelectronics applications, the 3D topological insulator behaviour of Bi1-xSbx can be used for the realization of Majorana Fermions based qubit devices. In both the cases improving the quality of the nanoscale material is mandatory and is the primary goal of the thesis, where we study CMOS compatible InAs nanowire integration on Silicon and where we develop a new nanoscale topological insulator. For a full CMOS compatiblity, the growth of InAs on Silicon requires to be self-catalyzed, fully vertical and uniform without crossing the thermal budge of 450 °C. These CMOS standards, combined with the high lattice mismatch of InAs with Silicon, prevented the integration of InAs nanowires for nanoelectronics devices. In this thesis, two new surface preparations of the Silicon were studied involving in-situ Hydrogen gas and in-situ Hydrogen plasma treatments and leading to the growth of fully vertical and self-catalyzed InAs nanowires compatible with the CMOS limitations. The different growth mechanisms resulting from these surface preparations are discussed in detail and a switch from Vapor-Solid (VS) to Vapor- Liquid-Solid (VLS) mechanism is reported. Very high aspect ratio InAs nanowires are obtained in VLS condition: upto 50 nm in diameter and 3 microns in length. On the other hand, Bi1-xSbx is the first experimentally confirmed 3D topololgical insulator. In this new material, the presence of robust 2D conducting states, surrounding the 3D insulating bulk can be engineered to host Majorana fermions used as Qubits. However, the compostion of Bi1-xSbx should be in the range of 0.08 to 0.24 for the material to behave as a topological insula- tor. We report growth of defect free and composition controlled Bi1-xSbx nanowires on Si for the first time. Different nanoscale morphologies are obtained including nanowires, nanoribbons and nanoflakes. Their diameter can be 20 nm thick for more than 10 microns in length, making them ideal candidates for quantum devices. The key role of the Bi flux, the Sb flux and the growth tem- perature on the density, the composition and the geometry of nanoscale structures is investigated and discussed in detail.

Near-field optical microscopy has attracted remarkable attention, as it is the only technique that allows the investigation of local optical properties with a resolution far below the diffraction limit. Especially, the scattering-type near-field optical microscopy allows the nondestructive examination of surfaces without restrictions to the applicable wavelengths. However, its usability is limited by the availability of appropriate light sources. In the context of this work, this limit was overcome by the development of a scattering-type near-field microscope that uses a widely tunable free-electron laser as primary light source. In the theoretical part, it is shown that an optical near-field contrast can be expected when materials with different dielectric functions are combined. It is derived that these differences yield different scattering cross-sections for the coupled system of the probe and the sample. Those cross-sections define the strength of the near-field signal that can be measured for different materials. Hence, an optical contrast can be expected, when different scattering cross-sections are probed. This principle also applies to vertically stacked or even buried materials, as shown in this thesis experimentally for two sample systems. In the first example, the different dielectric functions were obtained by locally changing the carrier concentration in silicon by the implantation of boron. It is shown that the concentration of free charge-carriers can be deduced from the near-field contrast between implanted and pure silicon. For this purpose, two different experimental approaches were used, a non-interferometric one by using variable wavelengths and an interferometric one with a fixed wavelength. As those techniques yield complementary information, they can be used to quantitatively determine the effective carrier concentration. Both approaches yield consistent results for the carrier concentration, which excellently agrees with predictions from literature. While the structures of the first system were in the micrometer regime, the capability to probe buried nanostructures is demonstrated at a sample of indium arsenide quantum dots. Those dots are covered by a thick layer of gallium arsenide. For the first time ever, it is shown experimentally that transitions between electron states in single quantum dots can be investigated by near-field microscopy. By monitoring the near-field response of these quantum dots while scanning the wavelength of the incident light beam, it was possible to obtain characteristic near-field signatures of single dots. Near-field contrasts up to 30 % could be measured for resonant excitation of electrons in the conduction band of the indium arsenide dots. / Die optische Nahfeldmikroskopie hat viel Beachtung auf sich gezogen, da sie die einzige Technologie ist, welche die Untersuchung lokaler optischer Eigenschaften mit Auflösungen unterhalb der Beugungsgrenze ermöglicht. Speziell die streuende Nahfeldmikroskopie erlaubt die zerstörungsfreie Untersuchung von Oberflächen ohne Einschränkung der verwendbaren Wellenlängen. Die Nutzung ist jedoch durch das Vorhandensein entsprechender Lichtquellen beschränkt. Im Rahmen dieser Arbeit wurde diese Beschränkung durch Entwicklung eines streuenden Nahfeldmikroskops überwunden, das einen weit stimmbaren Freie-Elektronen-Laser als primäre Lichtquelle benutzt. Im theoretischen Teil wird gezeigt, dass ein optischer Kontrast erwartet werden kann, wenn Materialien mit unterschiedlichen Dielektrizitätskonstanten kombiniert werden. Es wird hergeleitet, dass diese Unterschiede in unterschiedlichen Streuquerschnitten für das gekoppelte System aus Messkopf und Probe resultieren. Diese Streuquerschnitte definieren die Stärke des Nahfeldsignals, welches auf unterschiedlichen Materialien gemessen werden kann. Ein optischer Kontrast kann also erwartet werden, wenn unterschiedliche Streuquerschnitte untersucht werden. Dass dieses Prinzip auch auf übereinander geschichtete oder sogar verborgene Strukturen angewendet werden kann, wird in dieser Doktorarbeit an zwei Probensystemen experimentell gezeigt. Im ersten Beispiel wurden die unterschiedlichen Dielektrizitätskonstanten durch örtliches Ändern der Ladungsträgerdichte in Silizium durch Bor-Implantation erreicht. Es wird gezeigt, dass die Dichte der freien Ladungsträger an Hand des optischen Kontrastes zwischen implantiertem und reinem Silizium ermittelt werden kann. Zu diesem Zweck wurden zwei unterschiedliche Ansätze verwendet, ein nicht-interferometrischer mittels variabler Wellenlängen und ein interferometrischer mit einer konstanten Wellenlänge. Weil diese Techniken gegensätzliche Informationen liefern, können sie genutzt werden, um die effektive Ladungsträgerdichte quantitativ zu bestimmen. Beide Ansätze lieferten konsistente Resultate für die Trägerdichte, welche sehr gut mit den Vorhersagen der Literatur übereinstimmt. Während die Strukturen im ersten Beispiel im Mikrometer-Bereich lagen, wird die Möglichkeit, verborgene Nanostrukturen zu untersuchen, an Hand einer Probe mit Indiumarsenid Quantenpunkten demonstriert. Diese sind von einer dicken Schicht Galliumarsenid bedeckt. Zum ersten Mal wird experimentell gezeigt, dass Übergänge zwischen Elektronenzuständen in einzelnen Quantenpunkten mit Nahfeldmikroskopie untersucht werden können. Durch die Messung der Nahfeld-Antwort der Quantenpunkte unter Änderung der Wellenlänge des eingestrahlten Lichtes war es möglich, charakteristische Nahfeld-Signaturen der einzelnen Quantenpunkte zu erhalten. Nahfeld-Kontraste bis zu 30 Prozent konnten für die resonante Anregung der Elektronen im Leitungsband der Indiumarsenid Punkte beobachtet werden.

Ce travail porte sur la croissance épitaxiale et la caractérisation optique de boîtes quantiques d’InAs/InP(001) en faible densité en vue de la réalisation de nouveaux composants nanophotoniques émettant à 1,55 µm. Les propriétés structurales et optiques des îlots ont été corrélés pour différents paramètres de croissance d’un système d’épitaxie par jet moléculaire à sources solides. Nos résultats soulignent l’influence des reconstructions de surface d’InAs sur la forme des îlots. Des boîtes, plutôt que des bâtonnets allongés généralement observés,peuvent être directement formées dans des conditions de croissance adéquates. Une transition de forme de bâtonnets vers des boîtes est également démontrée par des traitements postcroissance sous arsenic. Les faibles densités de boîtes sont obtenues pour des faibles épaisseurs d’InAs déposées. Leur émission est facilement contrôlée à 1,55 µm par une procédure d’encapsulation spécifique appelé « double cap ». Quelques propriétés des boîtes individuelles d’InAs/InP sont ensuite évaluées. Les études de micro-photoluminescence révèlent des pics d’émission très fins et distincts autour de 1,55 µm confirmant les propriétés« quasi-atomiques » de ces boîtes uniques. Enfin, nous proposons pour la première fois une méthode à haute résolution spatiale qui permet d’étudier le transport de charges autour d’une boîte unique grâce à une technique de cathodoluminescence à basse tension d’accélération.Une mesure directe de la longueur de diffusion des porteurs avant capture dans une boîte a été obtenue. Ces résultats ouvrent de nouvelles perspectives quant à l’intégration de ces boîtes uniques dans des microcavités optiques pour la réalisation de sources de lumières quantiques à 1,55 µm. / This thesis focus on the epitaxial growth and optical characterization of diluted InAs/InP(001) quantum dots for the realisation of new nanophotonic devices emitting at 1.55μm. The structural and optical properties of the quantum islands are correlated to different growth parameters of a solid source molecular beam epitaxy system. Our results highlight the influence of InAs surface reconstructions on the island shape. Dots rather than elongated dashes usually observed can be directly formed by adequate growth conditions. Dash to dot shape transition is also demonstrated by post-growth treatments. Low dot densities are obtained for small InAs deposited thickness. Their emission wavelength is easily tuned to1.55 µm using the “double cap” procedure for the growth of the InP capping layer. Optical properties of such single InAs/InP quantum dots are then evaluated. Microphotoluminescence studies reveal sharp and well separated emission lines near 1.55 µm from single dots confirming their atom-like properties. Last, we propose for the first time a highspatial resolution method to study the carrier transport in the vicinity of a single quantum dotusing a low-voltage cathodoluminescence technique. A direct measurement of the carrier diffusion length before capture into one dot has been obtained. These results open the way to the integration of these single dots into optical micro-cavities for the realisation of quantumlight sources at 1.55 µm.

Neste trabalho apresentamos um estudo sistemático das propriedades ópticas e estruturais de super-redes de pontos quânticos auto-organizados de lnAs. As superredes foram crescidas por epitaxia de feixes moleculares sobre substratos de GaAs orientados na direção (100) com diferentes números de camadas de pontos quânticos e diferentes valores do espaçamento entre elas. As propriedades estruturais das super-redes foram observadas em seção transversal por microscopia eletrônica de transmissão convencional e de alta resolução. Os resultados permitem determinar a evolução da altura, do diâmetro e da densidade dos pontos quânticos em função da modificação da espessura da camada de espaçamento. Também observamos que pontos quânticos empilhados muito próximos tendem a relaxar através da formação de defeitos estruturais identificados como micromaclas. As propriedades ópticas foram investigadas por meio de fotoluminescência a baixa temperatura, bem como variando-se a potência de excitação e a temperatura da amostra. Reportamos um novo comportamento da posição do pico de fotoluminescência com a redução da espessura da camada de espaçamento. Interpretamos este comportamento em termos de modificação do tamanho dos pontos quânticos, acoplamento eletrônico, relaxamento parcial da tensão e formação de centros de recombinação não-radiativa. Usando essas interpretações, calculamos os espectros de fotoluminescência das super-redes, que ajustam muito bem os dados experimentais. As interpretações propostas são também sustentadas pela influência da espessura da camada de espaçamento na intensidade integrada de fotoluminescência e nas energias de ativação / In this work we present a comprehensive and systematic study of the optical and structural properties of self-organized InAs quantum dots superlattices. The superlattices were grown by molecular beam epitaxy on GaAs (100) substrates with different number of quantum dot layers and different thicknesses between these layers. Their structural properties have been observed by conventional and highresolution cross-sectional transmission electron microscopy. The results allow us to sketch the evolution of the dot height, diameter and density when the spacer layer thickness is modified in a wide range. We also observe that closely stacked quantum dots tend to relax through the formation of structural defects identified as microtwins. The optical properties have been investigated by means of conventional, power dependent- and temperature dependent photoluminescence. We report for the first time on an unusual behavior of the photoluminescence peak position when the spacer layer thickness is reduced. We interpret this behavior in terms of quantum dot size modification, electronic coupling, partial strain relaxation and non-radiative recombination centers formation. Using these interpretations, we then produce simulated photoluminescence spectra that fit very well the experimental data. These interpretations are further supported by the spacer layer thickness influence upon photoluminescence integrated intensity and activation energies.

Estudamos a adsorção de Te em superfícies de GaAs(001) e InAs(001) com periodicidades 1x1, 1x2, 2x1 e 2x2, para as concentrações de telúrio Tc= 0, 1/4, 1/2, 3/4 e 1. Realizamos cálculos dentro do formalismo do funcional da densidade empregando pseudopotenciais de norma conservada. Para a relaxação das estruturas empregamos a dinâmica molecular de Car e Parrinello. Nossos resultados apontam para uma redução na estabilidade das superfícies na proporçã em que aumenta a concentração de Te na uperfície. A cobertura de As (Tc = 0) é energeticamente mais favorável que as recobertas com qualquer concentração de Te, tanto na superfície de GaAs(001) quanto na de InAs(001). Observouse ainda nas superfícies com Tc = 0 Tc = 1, que a dimerização dos átomos de As e da ordem de 30% mais intensa que dos átomos e Te. Comparando as dimerizações do Te nas superfícies com concentrações Tc 1/2, observamos que elas são maiores sobre o InAs(001) (célula terminada em In) que sobre o GaAs(001) terminada em Ga). Outra tendência verificada e a \"flutuação\" do Te sobre as superfícies. Para uma mesma concentração verificamos a \"preferência de adsorção\" em sítios fora da cadeia de dímeros indicando uma adsorção monoatômica. Para concentração Tc = 1 na superfície GaAs(001):Te2x2 observamos duas geometrias possíveis: uma com cadeias de dímeros seguindo o modelo \"dimerrowmissing\" e outra com dois tipos de dímeros em posições alternadas ao longo da dir~ao (110). Analisando as energias de adsorção nas duas superfícies verificamos que a adsorção sobre o InAs é mais favorável que sobre o GAs. Analisamos ainda a estrutura eletrônica das superfícies em todas as reconstruções e concentrações consideradas e verificamos anda o caráter semicondutor das superfícies com concentração Tc = 1/2. / We have carried out ab initio density functional calculations to investigate the adsorption of Te on GaAs(001) and lnAs(001) surfaces as a function of Te surface coverage: Tc = 0, 1/4, 1/2, 3/4, 1. In order to determine the equilibrium atomic positions, the geometry was relaxed according he calculated total energy and forces following the Car Parrinello approach for molecular dynamics. Our calculations indicate that a full monolayer of As (Tc = 0) is energetically more favourable than any of the studied coverage of Te (Tc = 1/4, 1/2, 3/4, 1), where the stability is educed with increasing Te coverage. The dimerization of surface As atoms is about 30% more intense than surface Te atoms. Comparing the Te dimerization on InAs(001), In terminated, and aAs(OOI), Ga terminated, we observed that the Te atoms dimerize more over lnAs than GaAs surface. Another observation is the tendency of the Te atoms to \'l1oat\" from the surface with increasing coverage. For the same concentrations of Te the atoms \"prefer\" to be adsorbed on the offchain sites indicating a monoatomic adsorption. The adsorption energy of Te on InAs(001) is more favorable than GaAs(001). We also determined the surface band structure for all reconstructions and Te concentrations, veryfying the semiconductor nature for Tc = 1/2.

Estudamos a adsorção de Te em superfícies de GaAs(001) e InAs(001) com periodicidades 1x1, 1x2, 2x1 e 2x2, para as concentrações de telúrio Tc= 0, 1/4, 1/2, 3/4 e 1. Realizamos cálculos dentro do formalismo do funcional da densidade empregando pseudopotenciais de norma conservada. Para a relaxação das estruturas empregamos a dinâmica molecular de Car e Parrinello. Nossos resultados apontam para uma redução na estabilidade das superfícies na proporçã em que aumenta a concentração de Te na uperfície. A cobertura de As (Tc = 0) é energeticamente mais favorável que as recobertas com qualquer concentração de Te, tanto na superfície de GaAs(001) quanto na de InAs(001). Observouse ainda nas superfícies com Tc = 0 Tc = 1, que a dimerização dos átomos de As e da ordem de 30% mais intensa que dos átomos e Te. Comparando as dimerizações do Te nas superfícies com concentrações Tc 1/2, observamos que elas são maiores sobre o InAs(001) (célula terminada em In) que sobre o GaAs(001) terminada em Ga). Outra tendência verificada e a \"flutuação\" do Te sobre as superfícies. Para uma mesma concentração verificamos a \"preferência de adsorção\" em sítios fora da cadeia de dímeros indicando uma adsorção monoatômica. Para concentração Tc = 1 na superfície GaAs(001):Te2x2 observamos duas geometrias possíveis: uma com cadeias de dímeros seguindo o modelo \"dimerrowmissing\" e outra com dois tipos de dímeros em posições alternadas ao longo da dir~ao (110). Analisando as energias de adsorção nas duas superfícies verificamos que a adsorção sobre o InAs é mais favorável que sobre o GAs. Analisamos ainda a estrutura eletrônica das superfícies em todas as reconstruções e concentrações consideradas e verificamos anda o caráter semicondutor das superfícies com concentração Tc = 1/2. / We have carried out ab initio density functional calculations to investigate the adsorption of Te on GaAs(001) and lnAs(001) surfaces as a function of Te surface coverage: Tc = 0, 1/4, 1/2, 3/4, 1. In order to determine the equilibrium atomic positions, the geometry was relaxed according he calculated total energy and forces following the Car Parrinello approach for molecular dynamics. Our calculations indicate that a full monolayer of As (Tc = 0) is energetically more favourable than any of the studied coverage of Te (Tc = 1/4, 1/2, 3/4, 1), where the stability is educed with increasing Te coverage. The dimerization of surface As atoms is about 30% more intense than surface Te atoms. Comparing the Te dimerization on InAs(001), In terminated, and aAs(OOI), Ga terminated, we observed that the Te atoms dimerize more over lnAs than GaAs surface. Another observation is the tendency of the Te atoms to \'l1oat\" from the surface with increasing coverage. For the same concentrations of Te the atoms \"prefer\" to be adsorbed on the offchain sites indicating a monoatomic adsorption. The adsorption energy of Te on InAs(001) is more favorable than GaAs(001). We also determined the surface band structure for all reconstructions and Te concentrations, veryfying the semiconductor nature for Tc = 1/2.

InAs/GaSb superlattices are an attractive material system for infrared light emitting diodes, due to the ability to tune the band gap throughout most of the infrared regime. A key consideration in the epitaxial growth of these heterostructures is crystalline material quality. In developing thick layers of epitaxially grown material, there are moderate amounts of elastic strain that can be incorporated into a heterostructure, beyond which deformations will form that will alleviate the lattice mismatch. This thesis investigates the optical and electronic properties of lattice-mismatched and strained materials through the study of thick dual-color light emitting diodes, broadband light emitting diodes, and InAs/GaSb superlattice devices developed on GaAs substrates and GaAs integrated circuits. A dual-color infrared light emitting diode is demonstrated emitting in the mid-wave infrared band at 3.81 μm and 4.72 μm. The design of the device stacks two independently operable InAs/GaSb superlattices structures on top of one another, so that 10 μm of material is grown with molecular beam epitaxy. Each layer is lattice-matched to a GaSb substrate. At quasi-continuous operation, radiances of 5.48 W/cm2-sr and 2.67 W/cm2-sr are obtained. A broadband light emitting diode spanning the mid-wave infrared is demonstrated with eight stages of InAs/GaSb superlattices individually tuned to a different color. The performance of the device is compared with an identical eight stage device emitting in the middle of the mid-wave infrared. The emission of the fabricated broadband device spans from 3.2 μm to 6 μm with peak radiance of 137.1 mW/cm2-sr. Growth of antimonide-based devices on GaAs is desirable to the relative transparency of semi-insulating substrates throughout the infrared, and as semi-insulating GaSb substrates are not available. The growth of bulk GaSb on GaAs is explored through different techniques in order to confine relaxation due to lattice mismatch strain to the GaSb/GaAs interface. A low temperature nucleation technique with a thin GaSb wetting layer is found to have the best overall surface morphology, although screw dislocations are a prominent feature on all samples. The dislocations and overall surface roughness are not found to destructively impact the overall device quality, as four stage InAs/GaSb superlattice devices grown on GaAs substrates are found to have superior electroluminescent emission and external quantum efficiency compared to an identical device grown on a GaSb substrate due to the higher substrate transparency and superior thermal properties. Epitaxy on electronics growth techniques on GaAs integrated circuits are developed to bypass the hybridization process in light emitting diode development. Chips obtained from Quorvo, Inc. are found to endure ultra-high vacuum molecular beam epitaxy environment at higher temperatures with silicon nitride encapsulation, and a low temperature oxide removal technique is developed using an atomic hydrogen source. Chemical-mechanical polishing techniques are developed to create an “epi-ready” substrate surface. Ultimately, no photoluminescent emission is observed from InAs/GaSb superlattices grown on GaAs integrated circuits, although electroluminescent emission is still possible.

This dissertation involves the study of epitaxial behavior of one-dimensional nanomaterials like single-walled carbon nanotubes and Indium Arsenide nanowires grown on metallic catalyst surfaces. It has been previously observed in our novel microplasma based CVD growth of SWCNTs on Ni-Fe bimetallic nanoparticles that changes in the metal catalyst composition was accompanied by variations in the average metal-metal bond lengths of the nanoparticle and that in turn, affected nanotube chirality distributions. In this dissertation, we have developed a very simplistic model of the metal catalyst in order to explain the nanotube growth of specific nanotube chiralities on various Ni-Fe catalyst surfaces. The metal catalyst model is a two-dimensional flat surface with varying metal-metal bond lengths and comprising of constituent metal atoms. The effect of the composition change was modeled as a change in the bond length of the model catalyst surface and density functional theory based calculations were used to study specific nanotube caps. Our results indicated that nanotube caps like (8,4) and (6,5) show enhanced binding with increased metal-metal bond lengths in the nanoparticle in excellent agreement with the experimental observations. Later, we used this epitaxial nucleation model and combined with a previously proposed chirality-dependent growth rate model to explore better catalysts that will preferentially grow an enhanced chirality distribution of metallic nanotubes. From our DFT calculations and other geometrical considerations for nanotube growth, we demonstrated that the pure Ni0.5Cu0.5 metal nanoparticles and its lattice-strained surfaces can serve as a promising catalyst for enhanced growth of metallic nanotubes. Finally, we extended this model of epitaxial growth to study the growth of,andoriented nanowires on gold metal nanoparticles where a faster growth rate ofnanowires was previously observed in experiments on shaped nanoparticles than that on spherical nanoparticles. The DFT calculations indicated an enhanced growth selectivity of theoriented nanowires on the Au(111) surfaces. However, the DFT results also show that theandNWs will preferentially grow on the Au(100) surface than on the Au(100) surface. The epitaxial model based DFT calculations of nanotube and nanowire growth on metal catalyst surfaces presented in this dissertation, provide a deep insight into their epitaxial growth mechansims and, can be easily exploited to layout better design principles of synthesizing catalysts that helps in growing these one-dimensional nanomaterials with desired material properties.

Nous étudions, par spectroscopie optique à l'échelle de la boîte quantique unique InAs/GaAs,la décohérence de l'exciton neutre dans une boîte, sa structure fine et la relaxation de sonspin.Nous montrons que la cohérence est limitée intrinsèquement par un couplage non-perturbatifaux phonons acoustiques, et extrinsèquement par l'existence d'un environnementélectrostatique fluctuant autour des boîtes.Nous observons que la structure fine dépend de la densité locale de boîtes, qui affecte leurgéométrie et leur état de contrainte, et mettons à jour des boîtes originales émettant une lumière très polarisée.Nous étudions la relaxation du spin excitonique en mesurant le taux de polarisation del'émission. Sur un ensemble de boîtes, nous observons un temps de relaxation d'une dizainede ns à 10 K et montrons que la dynamique de cette relaxation est sensible à l'environnementdes boîtes. Sur boîte unique, nous montrons que le spin peut relaxer très rapidement (en 100ps), même à 10 K.

Les structurations de la matière à l'échelle nanométrique ont ouvert de larges champs d'étude. L'analyse des propriétés structurales des nanostructures, de leur degré d'organisation ainsi que leur influence sur les propriétés électroniques représentent actuellement un défi de première importance. Pour accéder à ces informations, il est souvent nécessaire de faire appel à un ensemble de techniques expérimentales et numériques souvent complexes dans leur mise en oeuvre. Dans cette contribution, nous étudions l'organisation et le confinement électronique dans des multiplans de boîtes quantiques, en nous appuyant à la fois sur une étude expérimentale et un travail de modélisation. Les interférences Raman, observées dans la gamme des phonons acoustiques, résultent de l'interaction entre ces derniers et les états électroniques localisés dans les nanostructures. Parce qu'ils explorent une gamme allant de quelques nanomètres à plusieurs centaines de nanomètres, les phonons acoustiques représentent une sonde particulièrement efficace pour l'étude des nanosystèmes. Les interférences Raman utilisent leur sensibilité pour la mesure des propriétés structurales et électroniques. Elles permettent de mesurer les effets de corrélation verticale et latérale dans les multiplans de boîtes quantiques. Nous avons développé un modèle général dont le domaine d'application s'étend des systèmes contenant quelques plans au super-réseaux. En utilisant l'analyse de Fourier des interférences, on détermine la fonction d'auto-corrélation de la densité de probabilité électronique selon l'axe de croissance. Sensible à la taille et à la forme de la densité électronique, les interférences Raman ouvrent la voie à une imagerie optique de la densité électronique.