Although it is known that gold (Au) is diamagnetic in bulk form, it has been reported that Au displays magnetic properties when reduced to the nano-scale. Researchers found magnetism in Au nanoparticles (NPs) in a size range from 2 to 10 nanometers. Moreover, the Au nanoparticles are usually coated by thiol-containing organic caps, which are believed to be responsible for the magnetism. However, others suggest that organic capping is not necessary to observe magnetism in Au NPs, and magnetism may be an intrinsic property for nano-structured gold. For this investigation, we used pulsed laser deposition to prepare nano-structured gold of different sizes and concentrations to investigate the magnetic properties. Our experiment results confirmed that for the samples in which Au is in the metallic state as nanoparticles with ~5 nm diameter, as well as inthe alloy form, bonded with indium, the samples show ferromagnetism when embedded in an Al2O3 matrix without any thiol-containing organic capping. Our results suggest that ferromagnetism is an intrinsic property of Au nano-structures, which means that it is not necessary to incorporate Au-S bonds with organic coatings in order to observe this phenomenon. We believe due to the significant broken symmetry at the surface of the nanoparticles, holes are generated in d bands of the surface Au atoms. These holes are most possibly responsible for ferromagnetism in Au nanoparticles. The realization of magnetism in Au coupled with the lack of clear understanding of its origin makes the investigation of magnetism of diamagnetic metals ripe for further inquiry. / Ph. D.

La détection et la surveillance des gaz est un enjeu important tant pour la sécurité industrielle que pour la protection de l’environnement et des personnes. Le dihydrogène, prend une place de plus en plus importante en tant que combustible et vecteur énergétique mais il est extrêmement inflammable et explosif dans un large domaine de 4 à 75 % dans l’air. De même, l’ammoniac est très utilisé dans l’industrie comme gaz réfrigérant ou comme élément de base pour la production chimiques d’autres composés. Ce gaz présente des risques sur l’environnement et sur les êtres vivants et peut former des mélanges explosifs avec l’air dans les limites de 15 à 28 % en volume. Les capteurs de gaz permettant d’indiquer la présence et/ou la quantification de ces gaz prennent alors toute leur importance. Dans la continuité de nos nombreux travaux sur les capteurs résistifs à base d’assemblages discontinus de nano-objets, l’objet de ce travail de thèse a été de préparer des capteurs résistifs pour la détection de H2 et NH3. Ces capteurs sont à base d’assemblages 2D de nanoparticules de compositions complexes. Trois types de nanoparticules cœur-coquille ont été synthétisés : Au@ZnO, Au@SnO2 et Au@Ag. Différentes techniques physico-chimiques (UV-Visible/TEM / DRX etc) ont permis de caractériser les particules obtenues. L’étape suivante a consisté à les assembler en monocouches compactes. Les films ont été obtenus par la méthode d’assemblage de Langmuir-Blodgett. Après transfert à la surface d’un substrat en verre supportant des électrodes inter digitées, les performances de détection des capteurs résistifs fabriqués ont été alors évaluées. Les capteurs à base de Au@ZnO et Au@SnO2 ont été testés sous H2, tandis que les capteurs à base de Au@Ag l’ont été sous NH3. Les capteurs fabriqués ont montré des performances attractives de détection de H2 et NH3 dans des gammes de concentration étendues. Une autre contribution importante de ce travail concerne la compréhension des mécanismes de détection. Diverses techniques analytiques, tels que la TPD (Température désorption Programmed) et la TPR (Température de réduction programmée) ont été utilisés pour permettre la discussion des les mécanismes impliqués. / Gas sensing and monitoring are important issues for both industrial safety and protection of the environment and human beings. Dihydrogen, is increasingly used as fuel and energy carrier but it is extremely flammable and explosive in a wide range between 4 and 75% in air.Similarly, ammonia is widely used in industry as a cooling gas or as a reagent for the chemical production of other compounds.This gas presents risks to the environment and to living beings and can form explosive mixtures with air within 15 to 28% by volume.Gas sensors, indicating the presence and /or quantification of these gases, are very important.In continuation of our work on resistive sensors based on discontinuous assembly of nano-objects, the aim of this thesis was to prepare resistive sensors for the detection of H2 and NH3.These sensors are based on 2D assemblies of complex compositions of nanoparticles. Three types of core-shell nanoparticles were synthesized: Au@ZnO, Au@SnO2 and Au@Ag. Different physicochemical techniques (UV-Visible / TEM / DRX etc.) were used to characterize the particles. The next step was to assemble them in compact monolayers. The films were obtained by Langmuir-Blodgett assembling technique. Then, they were transferred to the surface of a glass slide supporting interdigitated electrodes. Sensing performances of the as-fabricated resistive sensor were evaluated.Sensors based on Au@ZnO and Au@SnO2 nanoparticles were tested towards H2, while Au@Ag based sensors were tested under NH3.The sensors showed attractive performances in H2 and NH3 detection within wide concentration ranges. Another important contribution of this work is the understanding of detection mechanisms. Various analytical techniques such as TPD (Temperature Programmed Desorption) and TPR (temperature programmed reduction) were used for the discussion of the mechanisms involved.

Dans une optique de développement de nouvelles membranes innovantes, ce travail de thèse a permis l'élaboration de films minces nano-structurés et nano-poreux à partir de particules de polymère (copolymères ABA, AB, et homopolymère/MOF). Ces films ont notamment pu être utilisés en tant que membranes de filtration d'eau ou de mélange de gaz. Concernant les copolymères triblocs de type ABA (PS-PNaSS-PS), cette étude a montré que des films nano-poreux présentant des structures variées (nid d'abeilles, isoporeuse et compacte) pouvaient être obtenus. Les morphologies de ces particules pouvaient être adaptées en fonction de la taille des blocs hydrophiles et hydrophobes du copolymère, de la composition en solvant et de la concentration. Pour l'élaboration de films à partir de copolymère diblocs, des nanoparticules sphériques monodisperses, constituées de PDMAEMA-PMMA, ont été préparées in situ (PISA) par polymérisation RAFT en dispersion dans l'éthanol, à partir d'un agent de transfert fonctionnalisé coumarine. Les expériences successives d'irradiation UV ont montré que les nanopaticules ainsi fonctionnalisées pouvaient être connectées de façon réversible via la dimérisation de la coumarine. Les films minces ainsi élaborés présentaient des propriétés dynamiques dues à l'établissement de la formation réversible du cyclobutane lors de l'irradiation UV de la coumarine. Ce travail de thèse a été clôturé par la préparation de « Mix Matrix Membranes (MMMs) » à partir d'un mélange de polyimide (Matrimid®) et de nanoparticules de ZIF-8 pour la réalisation de membranes à perméation gazeuse. Une nouvelle approche d'élaboration des MMMs a permis d'obtenir la formation de membranes parfaitement homogènes avec une cohésion améliorée entre les MOF et la matrice de polymère. Une meilleure séparation du mélange de gaz CH4/CO2 a ainsi pu être obtenue. / This thesis deals with the development of nano-structured thin nano-porous films from polymeric particles (ABA, AB copolymers and polymer/MOF) in perspective of developing new innovative membranes. The obtained films have been used as water filtration or gas separation membranes. Regarding the ABA triblock copolymer made of polystyrene-sodium polystyrene sulfonate-polystyrene (PS-PNaSS-PS) it was shown that nano-porous films with various structures (honeycombs, isoporous and compact), could be made. The morphologies of these nanoparticles could be tuned depending on the hydrophobic and hydrophilic block ratios, solvent composition and concentration. Concerning the study of the diblock copolymer, monodisperse spherical nanoparticles of PDMAEMA-b-PMMA were made in situ (PISA) using a coumarin functionalized RAFT chain transfer agent in ethanol. Upon UV irradiation, these particles could be connected reversibly through the dimerization of the coumarin function present on their corona. The resulting thin films had dynamic characteristic due to the establishment of the reversible formation of the cyclobutane ring under UV irradiation. This manuscript was concluded by preparation of Mix Matrix Membranes (MMMs) from mixture of polyimide (Matrimid®) and ZIF-8 nanoparticles to be used as gas permeation membrane. The employed new approach in this study led to formation of perfectly homogeneous membranes with improved cohesion between the MOF structure and the polymeric matrix. A better separation of CH4 / CO2 gas mixtures was achieved using the prepared MMM.

Typical surface preparation consists of exposure to cleaning chemical to remove contaminants followed by rinsing with ultra-pure water which is followed by drying. Large quantities of water, various chemicals, and energy are used during rinsing and drying processes. Currently there is no in-situ metrology available to determine the cleanliness of micro- and nano-structures as these processes are taking place. This is a major technology gap and leads to over use of resources and adversely affects the throughput.Surface preparation of patterned wafers by batch processing becomes a major challenge as semiconductor fabrication moves deeper in submicron technology nodes. Many fabs have already employed single wafer tools. The main roadblock for single-wafer tools is their lower throughput. This obstacle is eased by introduction of multi chamber tools. To reduce cycle time and resource utilization during rinse and dry processes without sacrificing surface cleanliness and throughput, in-situ metrology is developed and used to compare typical single wafer spinning tools with immersion tools for rinsing of patterned wafers. This novel metrology technology includes both hardware for an in-situ measurement and software for process data analysis. Successful incorporation of this metrology will eliminate dependency on external analysis techniques such as Inductively Coupled Mass Spectroscopy (ICPMS), Scanning Electron Microscope (SEM), and Tunneling Electron Microscope (TEM), and will lead to fast response time.In this study the electro-chemical residue sensor (ECRS) was incorporated in a lab scale single-wafer spinning and single- wafer immersion tool. The ECRS was used to monitor dynamics of rinsing of various cleans such as ammonium peroxide mixture (APM), hydrochloric peroxide mixture (HPM), and sulfuric peroxide mixture (SPM). It was observed that different cleaning chemicals impact the subsequent rinse not only through adsorption and desorption but also through surface charge. The results are analyzed by using a comprehensive process model which takes into account various transport mechanisms such as adsorption, desorption, diffusion, convection, and surface charge. This novel metrology can be used at very low concentration with very high accuracy. It is used to study the effect of the key process parameters such as flow rate, spin rate, temperature, and chemical concentration.

Neste trabalho estudamos o efeito SERS de moléculas adsorvidas em sistemas eletroquímicos em termos da participação do mecanismo de transferência de carga na intensificação total observada. Desenvolvemos um modelo para o mecanismo químico de transferência de carga assitido por fótons, de maneira a explicar a variação do potencial de máxima intensificação SERS (Vmax) com a energia da radiação excitante. O modelo permite também o uso da expressão para o espalhamento Raman no domínio do tempo para o cálculo de perfis de excitação SERS (intensidade SERS versus potencial aplicado) de moléculas adsorvidas em interfaces eletroquímicas. Este método de cálculo dos perfis de excitação SERS foi aplicado para os casos da piridina e do íon complexo [Fe2(CN)104,4\'-bpy]6- em eletrodo de prata. Os resultados mostram existir uma boa relação entre os perfis calculados e os obtidos experimentalmente. Como resultado dos cálculos efetuados, o modelo fornece ainda dados sobre o deslocamento das curvas de poço potencial dos estados excitados envolvidos nos processos de transferência de carga assistidos por fótons. Nos capítulos seguintes, estudamos algumas conseqüências deste modelo, e sua aplicação em diferentes sistemas químicos. Um dos sistemas estudados foi o íon complexo [Ru(bpy)2viol]+ adsorvido em eletrodo de prata. Observa-se que a intensidade relativa dos modos vibracionais de cada um dos ligantes varia com o potencial aplicado ao eletrodo. Esses resultados podem ser explicados considerando-se dois processos de transferência de carga superficie → adsorbato assistidos por fótons. O primeiro deles deve-se a uma transição envolvendo estados doadores próximos ao nível de Fermi do metal (EF) e estados receptores (orbitais π*) localizados no violurato. O segundo envolve estados doadores em EF e orbitais π* da bpy. A energia da transição de transferência de carga metal → adsorbato varia com o potencial aplicado. Existe portanto a possibilidade de se alcançar diferentes estados eletrônicos excitados do adsorbato, intensificando, seletivamente, diferentes cromóforos com um único comprimento de onda. Assim, através da variação do potencial aplicado ao eletrodo é possível modular a transição de transferência de carga Ag → complexo de modo a envolver cada um dos diferentes ligantes. Estudamos também o mecanismo envolvido no efeito SERS da molécula FePc (ftalocianina de ferro) em eletrodo de prata. Nesse sistema, foi possível apresentar uma versão mais detalhada para o efeito químico envolvido na intensificação SERS incluindo o efeito de múltiplos estados excitados e acoplamento vibrônico, enfatizando as relações de simetria e overlap de funções de onda que regem os mecanismos de intensificação Raman ressonante. A excitação dos espectros SERS em comprimentos de onda fora da condição de Raman ressonante pode intensificar modos vibracionais de simetria a2g (não permitidos no espectro Raman normal) desde que o potencial aplicado esteja próximo à condição de ressonância para uma transição de transferência de carga superficie/adsorbato. O mecanismo químico de intensificação envolvido no efeito SERS desse sistema pode ser descrito como um processo de transferência de carga modulado pelo potencial, envolvendo dois estados doadores da FePc e um estado aceptor localizado na superficie do eletrodo de prata. Enquanto os modos totalmente simétricos (a1g) são intensificados por um mecanismo de Franck-Condon, os modos a2g têm a simetria apropriada para acoplar dois estados eletrônicos de simetria A1u e A2u, sendo intensificados através do mecanismo de Herzberg- Teller. Os efeitos da natureza química do solvente, e das interações solvente-soluto nas geometrias de adsorção e nas posições dos estados eletrônicos do adsorbato, são analisados para os ciano complexos Fe(phen)2(CN)2 e [Fe2(BPE)(CN)10]6-. Os resultados obtidos demonstram a influência decisiva da natureza química de solventes e eletrólitos suporte na espectroscopia de espécies adsorvidas em interfaces eletroquímicas. De fato, a natureza das interações solvente-adsorbato ou eletrólito-adsorbato podem determinar a ligação à superficie, e, desta maneira, intensificação seletiva de modos vibracionais da molécula pode ser obtida. A partir do estudo do processo de transferência de carga entre a superficie e os complexos adsorvidos através dos perfis de excitação SERS foi possível, em alguns casos, mapear os níveis de energia do adsorbato com relação ao nível de Fermi do metal. / In this work, attention has been given to systems in which the charge transfer (CT) mechanism is contributing to the enhancement of the Raman scattering of species adsorbed on metal surfaces in order to address the participation of a resonance Raman effect on this part of the total enhancement. A model for the adsorbate-metal surface interaction and the charge transfer mechanism for surface-enhanced Raman scattering (SERS) is presented. The fundamental observation behind the currently proposed model is that ali previous theories indicate that Raman intensity should be at maximum when the incident laser frequency is resonant with a surface/adsorbate charge transfer band. This fact leads to the conclusion that this aspect of the chemical effect may be due to a resonance Raman mechanism. Therefore, for such mechanism to be valid, the chemical effect of SERS must follow the already well established principies of resonance Raman theory. In this model, the metal surface provides a source of electrons that may, upon interaction with light, flow into and out of the adsorbed species. Based on this model we have proposed a formalism derived from the time-domain description of the resonance Raman effect that describes the dependence of the SERS intensities of molecules adsorbed in electrochemical interfaces upon the applied potential. This approach accounts for the enhancement of totally symmetric modes via a Franck-Condon mechanism, and only one electronic excited state of the adsorbate/surface system is considered. The analytical expression derived to calculate the SERS intensity versus applied potential profiles and their dependence on the exciting radiation has been applied for pyridine and for the ion complex [Fe2(CN)10bpy]6- adsorbed on a silver electrode. A good agreement between calculated and experimental excitation profiles have been obtained for both investigated species. Resonance Raman spectroscopy is also an electronic spectroscopy, and, as presented in this work, the SERS effect, or part of it, is also an electronic spectroscopy. Its intensity contains, therefore, information about the structure of the excited electronic state involved in the charge transfer process. This information is provided by the calculation of the SERS excitation profiles according to the derived expression in the form of ΔK values. The remaining sections of this work are dedicated to the study of the SERS effect of coordination compounds adsorbed on silver electrodes. One of the investigated systems is the mixed ligand ion complex [Ru(bpy)2viol]+. The SERS measurements have shown that the vibrational modes of both ligands can be selectively enhanced by changing the electrochemical applied potential at a fixed laser excitation energy. This result indicates the presence of two different metal to adsorbate photon assisted charge transfer processes. The first one involves a density of donor states near the Fermi level (EF) of the metal and na acceptor state localized on the violurate ligand, while the second process involves na acceptor state localized on the bpy ligand. These results demonstrate the possibility of reaching different excited electronic states of molecules adsorbed on electrode surfaces, selectively enhancing different chromofores by changing the applied potential and of assigning electronic charge transfer transitions based on SERS results. In order to provide a more detailed description of the charge transfer mechanism of enhancement working in the SERS effect of adsorbed molecules, including the role of multiple excited electronic states, vibronic coupling and symmetry selection rules, the SERS effect of iron phthalocyanine is discussed. The charge transfer mechanism of enhancement in this system is characterized as a potential modulated charge transfer process involving two donor states at the FePc and an acceptor state at the silver electrode surface. Excitation of the SERS spectra at wavelengths off resonance with the Q-band may enhance the a2g vibrational modes (non allowed modes at normal Raman condition), via a Herzberg-Teller mechanism, providing that the applied potential is dose to the resonance condition for the adsorbate to metal charge transfer transition. The effects of the chemical nature of the solvent in the adsorption geometry and in the position of the electronic states of adsorbates is discussed for the cyano complexes Fe(phen)2(CN)2 and [Fe2(BPE)(CN)10]6-. The results obtained have demonstrated the decisive role played by the chemical nature of solvents and supporting electrolytes in the surface-enhanced spectroscopy of species adsorbed at electrochemical interfaces. In fact, the nature of solvent or electrolyte - molecule interaction can determine the bonding to the surface, and therefore, selective enhancement of vibrational modes within a molecule can be accomplished. Based on the charge transfer processes between the surface and the adsorbed molecules probed by the SERS excitation profiles, it has been possible, in some cases, to determine the position of the energy levels of the adsorbate in relation to the Fermi level of the metal electrode.

Le système des nano-colonnes auto-assemblées de GeMn, riches en Mn et entourées d'une matrice de germanium quasi pure, est un matériau prometteur pour la spintronique. Selon les paramètres de croissance, les échantillons contiennent des nano-colonnes de type cohérents sur la matrice de Ge, de type amorphe, ou/et des nano-inclusions de Ge3Mn5. Ce manuscrit présente notre étude des propriétés électroniques, magnétiques et structurales des nano-colonnes de GeMn à l'aide du rayonnement synchrotron. Les mesures de la diffusion et diffraction des rayons X en incidence rasante dans des échantillons contenant des nano-colonnes cohérentes et sans précipités de Ge3Mn5 montrent un certain désordre dans les nano-colonnes. Les cartographies de l'espace réciproque ont pu être quantitativement expliquées en considérant la déformation de la matrice de germanium due à l'inclusion des nano-colonnes dans celle-ci, ainsi que par leurs corrélations de position, sans avoir recours à d'autres phases cristallines. La spectroscopie d'absorption et le dichroïsme circulaire magnétique de rayons X ont permis de sonder spécifiquement les propriétés magnétiques des atomes de Mn dans des échantillons sans précipités de Ge3Mn5. On observe une allure des spectres XAS-XMCD des nano-colonnes très similaire à celle observée dans le cas de Ge3Mn5. Le moment magnétique local sur le manganèse possède une composante orbitale faible mais non-nulle et une amplitude totale (0.8 +/- 0.1 µB) plus faible que celle attendue pour Ge3Mn5 (~2.6 µB) ou pour des atomes de Mn substitutionnels (~3 µB). Ceci indique une origine différente de la phase des nano-colonnes. Les spectres XAS-XMCD ont été calculés pour différentes structures modèles, incluant des défauts simples ainsi de nouvelles phases cristallines, les paramètres critiques des calculs ayant été identifiés. Le meilleur accord est observé pour une nouvelle phase de type Ge2Mn.

Cette thèse a comme objectif principal la combinaison en temps réel et in-situ de deux types de spectroscopies différentes: la microscopie en champ proche et la spectroscopie avec la lumière de synchrotron. Donc cette thèse a pour but l'introduction de nouvelles techniques expérimentales qui permettent d'explorer les propriétés des matériaux à l'échelle nanométrique. Ces nouveaux instruments sont sensés permettre d'obtenir à la fois une image topographique et un contraste chimique avec une résolution latérale de 10-40 nm. Ceci repousserait les limites de chacune de ces deux familles de spectroscopies et ouvrirait la porte à de nouvelles opportunités de recherche et de défis. Pour réussir cette combinaison in situ et en temps réel, un microscope à force atomique (AFM) a spécialement été construit. Ce microscope a été développé autour d'un diapason à cristal de quartz qui était le capteur de force avec lequel des forces à l'échelle manométrique ont été mesurées. Le microscope développé ici a été utilisé dans différentes lignes de lumières au synchrotron (ESRF) avec deux objectifs essentiellement différents. Un premier objectif était de faire de la spectroscopie, comme la mesure d'un seuil d'absorption, localement au moyen de la pointe de l'AFM. Ce type de mesures a effectivement été fait, mais la résolution latérale obtenue n'était pas donnée par la géométrie de la pointe mais par la taille du faisceau X. La pointe de l'AFM a également été utilisée pour mesurer la diffraction de Bragg dans des cristaux de tailles inférieures au micromètre. Un deuxième objectif a été d'utiliser la pointe de l'AFM pour interagir mécaniquement avec des systèmes à l'échelle nanométrique et simultanément utiliser un faisceau X pour mesurer des changements du paramètre de mailles dans les systèmes en question. Ainsi, la pointe de l'AFM a été utilisée pour déformer élastiquement un cristal de SiGe pendant que le signal de diffraction été mesuré. Ceci a permis d'observer des décalages des pics de Bragg en fonction de la pression appliquée par la pointe. La combinaison in-situ de microscopie atomique avec la diffraction a, cette fois ici, permis d'obtenir le module d'Young d'un cristal à l'échelle nanométrique sans aucun paramètre ajustable.

Orientador: Marceloi Ornaghi Orlandi / Banca: José Antônio Malmonge / Banca: Neftali Lenin Villarreal Carreño / Resumo: Nanoestruturas unidimensionais (1D) é foco de intensivos estudos para possibilitar a fabricação de dispositivos nano escalares e sensores. As nanofitas de óxidos metálicos como In2O3 e SnO2 têm sido estudadas devido as suas excelentes propriedades elétricas e sensoras. A dopagem intencional desses óxidos pode modificar suas propriedades e render novas aplicações, pois nanofitas de óxido de índio dopadas de estanho (ITO) possuem alta condutividade elétrica e alta transmitância na região do espectro visível. O objetivo desse trabalho foi estudar o crescimento de nanoestruturas de In2O3 dopado com estanho (ITO) sintetizadas via fase vapor pelo processo de redução carbotérmica com a co-evaporação dos óxidos. Os materiais obtidos nas sínteses foram caracterizados por difração de raios X, espectroscopia no ultravioleta-visível, medidas elétricas e microscopia eletrônica. Para esse estudo foram variadas algumas condições de síntese objetivando obter nanofitas de ITO que apresentassem boa homogeneidade estrutural e morfológica. Na primeira etapa do estudo variou-se a razão óxido/carbono nos materiais de partida, e os resultados mostraram que as variadas proporções de óxidos e carbono influenciam nas fases de crescimento das nanoestruturas. A síntese que apresentou melhor homogeneidade teve seu tempo de patamar variado e, por fim, variou-se o fluxo de gás de arraste, sendo que esses dois parâmetros não influenciam significativamente na homogeneidade do material obtido. Desta forma, otimizou-se as condições de síntese sem que houvesse prejuízo na qualidade do material obtido, o que é importante visando aplicações tecnológicas do material. Além disso, com base nos resultados de microscopia eletrônica e nas reações químicas que ocorrem durante a síntese um mecanismo de crescimento das nanoestruturas foi proposto. / Abstract: 1D nanostructures is the main focus of many studies due to the possibility to produce devices with high performance.Nanobelts of the metallic oxides In2O3 and SnO2 have been studied because its excellent electrical and sensing properties. The intentional doping of the oxides can modify its properties and yield new applications because tin doped indium oxide nanobelts (ITO) have high electrical conductivity and high transmittance in the visible spectrum. The aim of this work was to study the growth of tin doped In2O3 (ITO) nanostructures synthesized by vapor phase using the Carbothermal reduction process with the co-evaporation of oxides. The materials obtained after the synthesis were characterized by X-ray diffraction, spectroscopy in the ultraviolet-visible, electrical measurements and electron microscopy. For this study were used different conditions of synthesis, aiming to obtain ITO nanobelts with good structural and morphological homogeneity. In the first stage of the study the parameter altered was ratio ranged oxide / carbon in the starting material, and the results showed that different proportions of oxides and carbon influenced the phases that nanostructures were obtained. The synthesis that presented the best homogeneity had his time varied and, finally, ranged up the flow of gas drag of level varied, and that these two parameters did not significantly affect the homogeneity of the material. Thus, the conditions for synthesis were optimized with no loss in quality of material, which is important for technological applications of the material. Furthermore, based on the results of electron microscopy and chemical reactions that occur during the synthesis, and a growth mechanism nanostructures was proposed. / Mestre

Ce travail de thèse est une contribution à l'étude de la dynamique de spin des porteurs dans des structures semiconductrices III-V en vue d’applications possibles dans le domaine émergent de la spintronique dans les semiconducteurs. Deux approches différentes on été envisagées afin de pouvoir obtenir une polarisation en spin des porteurs longue et robuste : i) le confinement spatial dans des nano-structures 0D (boîtes quantiques), ii) l’ingénierie des centres paramagnétiques dans des couches massives.Pour la première approche, nous avons étudié les propriétés de polarisation de spin d’excitons confinés dans des boîtes quantiques de GaN/AlN insérées dans des nano-fils. Nous avons d’abord mis en évidence un taux important de polarisation de la photoluminescence (15 %) à basse température sous excitation quasi-résonante et nous avons démontré que cette polarisation est temporellement constante pendant la durée de vie des excitons. Grâce à des mesures en température, nous avons aussi démontré que cette polarisation n’est aucunement affectée jusqu’à 300 K. Nous avons aussi développé un modèle détaillé basé sur la matrice densité pour décrire le dégré de polarisation de la photoluminescence et sa dépendance angulaire.Pour la deuxième approche, nous avons réalisé un dispositif prototype de filtrage de spin basé sur l’implantation de centres paramagnétiques dans des couches massives de InGaAs. Le principe repose sur la création de défauts interstitiels paramagnétiques comme précédemment démontré dans notre groupe pour les nitrures dilués tels que GaAsN. Le but de ce travail a été le développement d’un procédé de création de ces défauts qui puisse surmonter les inconvénients liés à l’insertion de l’azote dans les semiconducteurs de type GaAs : a) la dépendance de l’efficacité du filtrage de spin avec de l’énergie de photoluminescence, b) l’impossibilité de créer des zones actives avec des motifs spécifiques.Dans ce travail, nous démontrons que des régions actives de filtre à spin peuvent être créées par implantation ionique de défauts paramagnétiques avec une densité et des motifs spatiaux prédéfinis. Grâce à des études par photoluminescence, nous avons d’une part mis en évidence des taux de recombinaison dépendant en spin pouvant aller jusqu’à 240 % dans les zones implantées. D’autre part, nous avons déterminé la dose d’implantation la plus favorable grâce à une étude systématique sur différents échantillons implantés avec des densités ioniques étendues sur quatre ordres de grandeurs. Nous avons également observé que l’application d’un champ magnétique externe produit une augmentation significative du taux de recombinaison dépendant en spin due à la polarisation en spin des noyaux implantés / This thesis work is a contribution to the investigation by photoluminescence spectroscopy of the spin properties of III-V semiconductors with possible applications to the emerging semiconductor spintronics field. Two approaches have been explored in this work to achieve a long and robust spin polarization: i) Spatial confinement of the carriers in 0D nanostructured systems (quantum dots). ii) Defect engineering of paramagnetic centres in a bulk systems. Concerning the first approach, we have investigated the polarization properties of excitons in nanowire-embedded GaN/AlN quantum dots. We first evidence a low temperature sizeable linear polarization degree of the photoluminescence (~15 %) under quasi-resonant excitation with no temporal decay during the exciton lifetime. Moreover, we demonstrate that this stable exciton spin polarization is unaffected by the temperature up to 300 K. A detailed theoretical model based on the density matrix approach has also been developed to account for the observed polarization degree and its angular dependence.Regarding the second approach, we have demonstrated a proof-of-concept of conduction band spin-filtering device based on the implantation of paramagnetic centres in InGaAs epilayers. The principle relies on the creation of Ga interstitial defects as previously demonstrated in our group in dilute nitride GaAsN compounds. The driving force behind this work has been to overcome the limitations inherent to the introduction of N in the compounds: a) The dependence of the photoluminescence energy on the spin-filtering efficiency. b) The lack of spatial patterning of the active regions.In this work we show how the spin-filtering defects can be created by ion implantation creating a chosen density and spatial distribution of gallium paramagnetic centers in N-free epilayers. We demonstrate by photoluminescence spectroscopy that spin-dependent recombination (SDR) ratios as high as 240 % can be achieved in the implanted areas. The optimum implantation conditions for the most efficient SDR are also determined by the systematic analysis of different ion doses spanning four orders of magnitude. We finally show how the application of a weak external magnetic field leads to a sizable enhancement of the SDR ratio from the spin polarization of the implanted nuclei

Made available in DSpace on 2014-06-11T19:25:32Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-07-08Bitstream added on 2014-06-13T19:32:43Z : No. of bitstreams: 1 lucindo_ja_me_ilha.pdf: 4031068 bytes, checksum: 3eb0babe24686f1deb0c263ea98155e4 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Nanoestruturas unidimensionais (1D) é foco de intensivos estudos para possibilitar a fabricação de dispositivos nano escalares e sensores. As nanofitas de óxidos metálicos como In2O3 e SnO2 têm sido estudadas devido as suas excelentes propriedades elétricas e sensoras. A dopagem intencional desses óxidos pode modificar suas propriedades e render novas aplicações, pois nanofitas de óxido de índio dopadas de estanho (ITO) possuem alta condutividade elétrica e alta transmitância na região do espectro visível. O objetivo desse trabalho foi estudar o crescimento de nanoestruturas de In2O3 dopado com estanho (ITO) sintetizadas via fase vapor pelo processo de redução carbotérmica com a co-evaporação dos óxidos. Os materiais obtidos nas sínteses foram caracterizados por difração de raios X, espectroscopia no ultravioleta-visível, medidas elétricas e microscopia eletrônica. Para esse estudo foram variadas algumas condições de síntese objetivando obter nanofitas de ITO que apresentassem boa homogeneidade estrutural e morfológica. Na primeira etapa do estudo variou-se a razão óxido/carbono nos materiais de partida, e os resultados mostraram que as variadas proporções de óxidos e carbono influenciam nas fases de crescimento das nanoestruturas. A síntese que apresentou melhor homogeneidade teve seu tempo de patamar variado e, por fim, variou-se o fluxo de gás de arraste, sendo que esses dois parâmetros não influenciam significativamente na homogeneidade do material obtido. Desta forma, otimizou-se as condições de síntese sem que houvesse prejuízo na qualidade do material obtido, o que é importante visando aplicações tecnológicas do material. Além disso, com base nos resultados de microscopia eletrônica e nas reações químicas que ocorrem durante a síntese um mecanismo de crescimento das nanoestruturas foi proposto. / 1D nanostructures is the main focus of many studies due to the possibility to produce devices with high performance.Nanobelts of the metallic oxides In2O3 and SnO2 have been studied because its excellent electrical and sensing properties. The intentional doping of the oxides can modify its properties and yield new applications because tin doped indium oxide nanobelts (ITO) have high electrical conductivity and high transmittance in the visible spectrum. The aim of this work was to study the growth of tin doped In2O3 (ITO) nanostructures synthesized by vapor phase using the Carbothermal reduction process with the co-evaporation of oxides. The materials obtained after the synthesis were characterized by X-ray diffraction, spectroscopy in the ultraviolet-visible, electrical measurements and electron microscopy. For this study were used different conditions of synthesis, aiming to obtain ITO nanobelts with good structural and morphological homogeneity. In the first stage of the study the parameter altered was ratio ranged oxide / carbon in the starting material, and the results showed that different proportions of oxides and carbon influenced the phases that nanostructures were obtained. The synthesis that presented the best homogeneity had his time varied and, finally, ranged up the flow of gas drag of level varied, and that these two parameters did not significantly affect the homogeneity of the material. Thus, the conditions for synthesis were optimized with no loss in quality of material, which is important for technological applications of the material. Furthermore, based on the results of electron microscopy and chemical reactions that occur during the synthesis, and a growth mechanism nanostructures was proposed.