>Magister Scientiae - MSc / Nanotechnology is spreading rapidly across the world as an extremely powerful technology. Nanoscience and nanotechnology are innovative scientific advancements that have been introduced only in this century. Nanotechnology has developed as the scientific advancement to grow and transform the entire agri-food area, with the potential to elevate global food production, in addition to the nutritional value, quality, and safety of food and food products. It has gained recognition due to its variability in shape, size, and dimension and how it correlates to its possibilities. One of those functions is nanoparticles’ (NPs) ability to have antimicrobial activity, more specifically its antifungal activity. One particular pathway of synthesising NPs is through phytonanotechnology which is the use of biomaterial to synthesis the NPs. / 2024

The acidic, non-oxidative dissolution of galena nanocrystals has been studied using both microscopic and wet-chemical methods. The effects of particle size, shape, aggregation state, and grain proximity on dissolution rates were investigated. Nearly monodisperse galena nanocrystals with an average diameter of 14.4 nm and a truncated cubic shape were synthesized. In the dissolution experiments of dispersed nanocrystals, galena nanocrystals attached on the surface of a TEM grid were exposed to deoxygenated HCl solutions (pH 3) at 25 °C. Capping groups on nanocrystals were removed via a washing process, and chemistry of nanocrystals was examined using X-ray photoelectron spectroscopy (XPS). The evolution of the size and shape of the pre- and post-dissolution nanocrystals were studied using transmission electron microscopy (TEM), and the dissolution rate was calculated directly according to the size shrinking of galena nanocrystals. To assess the size effect, galena microcrystals (~ 3 μm) were synthesized and dissolved under similar conditions to the dispersed nanocrystals. The results showed that the nanocrystals dissolved at a surface area normalized rate of one order of magnitude faster than the microcrystals. In addition, dissolution rate is orientationdependent on a single nanocrystal. High-resolution TEM (HRTEM) images indicated the {111} and {110} faces dissolve faster than {100} faces on galena nanocrystals, rationalized by the average coordination number of ions on each of these faces. To assess the aggregation effect, dissolution experiments of aggregated galena nanocrystals were conducted using a wet-chemical method, and the results were compared with the rates of microcrystals and dispersed nanocrystals. These experiments showed that the rate of aggregated nanocrystals is in the same order of magnitude as the rate of microcrystals, but one order of magnitude smaller than that of dispersed nanocrystals. Finally, the effect of the close proximity between nanocrystals on dissolution was observed by HRTEM. Dissolution was greatly inhibited on nanocrystal surfaces that were closely adjacent (1-2nm, or less) to other nanocrystals, which is probably relevant to the slow dissolution of aggregated nanocrystals. The dissolution phenomena of galena nanocrystals observed in this study is likely important for understanding the environmental fate and behavior of nanoparticles in aquatic systems. / Ph. D.

>Magister Scientiae - MSc / Combating antimicrobial resistant infections caused by nosocomial pathogens poses a major public health problem globally. The widespread use of broad-spectrum antibiotics for the treatment of wound infections has led to the appearance of multidrug-resistant (MDR) microbes which further exacerbates the growth of microbes amongst patients. It may result in prolonged debility of the patient and an increase in healthcare costs due to prolonged hospital stays and expensive treatment regimens to avoid patient-patient transmission. Therefore, it is imperative that alternative sources of treatment to antimicrobial use in wound infections needs to be developed in order to inhibit or kill resistant microbes and to provide point of care medical treatment to the less fortunate at an affordable cost. / 2021-08-30

This thesis explores theoretical aspects of scanning transmission electron microscopy (STEM) and the comparison of simulation with experiment. / The long standing contrast mismatch problem between theory and experiment in conventional high resolution transmission electron microscopy (HRTEM) is examined using the principle of reciprocity and bright field scanning transmission electron microscopy (BFSTEM). It is found that quantitative agreement between theoretical and experimental images is possible provided that theory suitably accounts for the spatial incoherence of the source, and that experimental images are placed on an absolute scale with respect to the incident beam current. Agreement between theory and experimental image contrast is found to be independent of specimen thickness and probe defocus. / Core-loss electron energy-loss spectroscopy (EELS) is a powerful experimental tool with the potential to provide atomic-resolution information about the electronic structure at defects and interfaces in materials and nanostructures. Interpretation, however, is nonintuitive due to the nonlocal ionization potential. Novel improvements in microscope design and operating environment have enabled two dimensional chemical maps. This has permitted a more thorough theoretical analysis. This thesis compares experimental STEM EELS images of LaMnO3, BiSrMnO3 and Si samples to the relevant theoretical simulations. Image features which at first appear counter intuitive are discussed and explained with the accompanying theoretical simulations. It is demonstrated, using a sample of SrTiO3, that more direct interpretation of atomic resolution chemical maps is possible when using energy dispersive x-ray spectroscopy (EDS) in STEM. / This thesis considers extending chemical mapping in STEM EELS to three dimensions using depth sectioning. It explores, theoretically, the feasibility to depth section zone-axis aligned crystals that contain embedded impurities. In STEM EELS this is found to be possible for point defects but not for larger extended objects such as nanoparticles. / The theory describing the mechanism by which contrast is obtained in elastic scanning confocal electron microscopy (SCEM) is developed. It is shown that there is no first order phase contrast in SCEM and thus low image contrast. Finally, energy filtered scanning transmission electron microscopy (EFSCEM) is developed theoretically. The fundamental equation describing image formation is derived and an efficient computation method is developed to allow the rapid calculation of EFSCEM images.

Orientador: Daniel Mario Ugarte / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-16T08:26:46Z (GMT). No. of bitstreams: 1 LagosParedes_MaureenJoel_D.pdf: 15612188 bytes, checksum: 76b816022716e5ae1bb5de0ff150c8ca (MD5) Previous issue date: 2010 / Resumo: Fios metálicos de tamanho atômico (NF's) apresentam novos efeitos químicos e físicos devido ao seu tamanho reduzido, onde pode-se destacar a condutância quântica. NF's são usualmente gerados através de um procedimento simples: duas superfícies metálicas são colocadas em contato e depois afastadas. Nos últimos estágios do estiramento antes da ruptura, um fio de alguns átomos de diâmetro é gerado enquanto a condutância é medida. Este tipo de abordagem apresenta um cenário que permite o estudo da condutância e do processo de deformação mecânica do NF. O objetivo desta tese consiste no estudo dos efeitos do arranjo atômico na condutância quântica e deformação mecânica de NF's gerados por alongamento. O arranjo atômico dos NF's foi estudado por microscopia eletrônica de transmissão de alta resolução resolvida no tempo. A condutância foi medida utilizando um sistema de quebra controlada de junções operado em ultra alto vácuo. Os experimentos foram realizados a ~ 150 K e 300 K. Neste trabalho de tese NF's de diversos tipos de morfologia, tamanho e composição química foram estudados. O estudo do efeito do arranjo atômico no processo de deformação mecânica foi realizado, principalmente, em nanotarugos (NR's) de ouro de ~ 1 nm de diâmetro. Foi verificado que a temperatura modifica drasticamente o comportamento mecânico dos NR's. Também, foi mostrado que o tamanho e a forma do NR sob deformação têm um papel determinante no processo de deformação mecânica. Além disso, foi realizado o estudo detalhado da formação de uma estrutura anômala que consiste em um nanotubo de seção transversal quadrada. Isto mostra a importância de considerar os efeitos de superfície no arranjo atômico de NF's sob deformação. O estudo da influência do arranjo atômico na deformação mecânica de NF's de ligas de ouro e cobre também foi realizada, onde foram observados eventos de segregação na escala atômica, devido a efeitos de superfície, e variações significativas no comportamento mecânico em relação a NF's puros. A origem na formação de distâncias anômalas em cadeias suspensas de ouro também foi analisada. Os resultados obtidos indicam que o carbono é o agente contaminante que induz a formação de distancias 3.2 Å. Finalmente, estudos dos efeitos do arranjo atômico na condutância de NF's de ouro e prata em função da temperatura foram realizados. Os resultados experimentais mostraram que a temperatura modifica significativamente o comportamento estrutural dos NF's formando defeitos estruturais a baixas temperaturas. As medidas de condutância a ~ 150 K também mostraram variações significativas. A partir da informação estrutural de microscopia, modelos geométricos foram estabelecidos para correlacionar a informação de condutância com o arranjo atômico através de cálculos teóricos de condutância / Abstract: Atomic-size metallic nanowires (NWs) display new physical and chemical effects, for example the quantum conductance. NWs can be usually generated by means of a simple experimental procedure: two metallic surfaces are put into contact and then they are retracted in a controlled way. During the last stages before the rupture, a wire containing a few atoms is created and its conductance can be measured simultaneously during the elongation process. This approach represents a scenario which allows us to study its conductance and mechanical properties. This thesis aims to study the thermal energy effects on NW's atomic arrangement and the corresponding influence on quantum conductance and mechanical deformation. The atomic arrangement was studied using time-resolved high resolution transmission electron microscopy. The conductance was measured using an experimental technique called mechanically controllable break junctions. Experiments were performed at ~ 150 K and 300 K. In this work were studied NW's that exhibit different morphologies, sizes and chemical composition. Firstly, the study of the atomic arrangement influence on the mechanical deformation was developed on one-nm wide gold nanorods (NRs). It was found that temperature induces drastic changes in the NR mechanical behavior. Moreover, it was shown that the NR size and shape play an essential role during the process of mechanical deformation. Second, the detailed study of the formation of anomalous silver square-cross section nanotube was performed. This revealed the strong influence of surface effects on atomic arrangement. Third, the study of atomistic aspects associated with mechanical deformation of gold-copper alloy NWs was also developed. Segregation events at atomic scale, induced by surface effects, and significant variations of the nanoalloy mechanical behavior were observed. Fourth, the analysis of the origin of formation of anomalous interatomic distances in suspended gold atom chains was performed. Our results indicate that carbon represents the most probable contaminant which induces the generation of anomalous distances (3.2 Å). Finally, the study of the atomic arrangement effects on conductance of gold and silver NWs as function of temperature was developed. Our experimental results revealed that thermal energy induces drastic changes of structural behavior, generating planar defects at low temperatures. Conductance measurements obtained at ~150 K also display significant variations. Considering structural information derived from microscopy observations, simple geometric models were defined and the conductance was calculated theoretically in order to correlate the gold and silver NW conductance and structural information / Doutorado / Física da Matéria Condensada / Doutor em Ciências

Orientador: Daniel Mario Ugarte / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-08T07:13:58Z (GMT). No. of bitstreams: 1 LagosParedes_MaureenJoel_M.pdf: 3881181 bytes, checksum: 517e8507ccdf35f0fa7a7f9fcb4b3b84 (MD5) Previous issue date: 2007 / Resumo: O estudo de fios metálicos de tamanho atômico (NF's) tem atraído grande interesse devido aos novos efeitos químicos e físicos neles observados. Entre esses novos fenômenos podemos destacar a quantização da condutância, efeito que deve ser fundamental no desenho dos novos nanodispositivos eletrônicos. NF's são usualmente gerados através de um procedimento simples de deformação mecânica: duas superfícies metálicas são colocadas em contato e depois afastadas. Nos últimos estágios do estiramento antes da ruptura, um fio de alguns átomos de diâmetro é gerado enquanto a condutância é medida. Os NF's têm sido estudados por diferentes grupos e, em diversas condições de temperatura (4 - 300 K) e pressão (de ambiente a UHV). Os resultados apresentam importantes variações e, têm gerado interpretações muito controversas. Devemos enfatizar que muitas interpretações têm sido feitas sem considerar que a deformação estrutural dos NF's deve depender fortemente da temperatura. Nesta tese estudamos as propriedades estruturais e eletrônicas NF's e, em particular analisamos a influência de efeitos térmicos no arranjo atômico, e sua manifestação na condutância. A estrutura dos NF's foi estudada por microscopia eletrônica de transmissão de alta resolução resolvidas no tempo. A condutância foi medida utilizando um sistema de quebra controlada de junções operado em ultra-alto-vácuo. Os experimentos foram realizados a ~150 e 300 K. Nossos resultados mostraram que, à temperatura ambiente os NF's são sempre cristalinos e livre de defeitos nas regiões mais finas; e deformam unicamente ao longo dos eixos cristalográficos [111], [100] e [110]. A baixa temperatura duas importantes diferenças foram observadas: (i) NF's de ouro apresentam defeitos, principalmente falhas de empilhamento e maclas. (ii) NF's alongados na direção [110] evoluem em cadeias atômicas, de comportamento mecânico muito diferente da temperatura ambiente, onde quebram abruptamente. Segundo as imagens de microscopia eletrônica, discordâncias parciais (Shockley) geram falhas de empilhamento; e cadeias de átomos suspensos são observados a ~150 e 300 K. Histogramas globais de condutância adquiridos a baixa temperatura revelaram: (i) aumento da intensidade do pico ~1 Go; (ii) leve diminuição da condutância devido ao aumento de defeitos; e (iii) a existência de uma sub-estrutura no pico ~2 Go, indicando a formação de dois arranjos atômicos estáveis. Resumidamente, nossos resultados mostram que a formação de defeitos é um evento freqüente a ~150 K. Provavelmente, mais defeitos na estrutura devem acontecer para temperaturas menores (4 - 10 K). Portanto, uma importante mudança na evolução da condutância durante a elongação de NF's deve ser esperado a baixa temperatura. Assim, a comparação direta de medidas de transporte de NF's realizadas a diferentes temperaturas pode levar a sérias discrepâncias. Esperamos ter contribuído a melhorar a compreensão e interpretação de experimentos de transporte realizados em diferentes condições, de modo tal, a gerar um modelo único e coerente que explique as propriedades físicas de NF's metálicos / Abstract: The study of atomic-size metal nanowires (NW's) is attracting a great interest due to occurrence a novel physical and chemical phenomena. Among these new phenomena, we can mention conductance quantization that will certainly influence the design of nanodevices. NW's are usually generated by means of a simple procedure: two metallic surfaces are put into contact and, then retracted. Just before rupture atomic-size NW's are formed, and the conductance is measured during the wire elongation. The interpretation of the results is troublesome, because conductance is measured during the modification of the atomic structure. This kind of experimental study has been performed by many research groups and, a quite wide range of temperatures (4 - 300 K) and vacuum condition have been used (from ambient to UHV). In fact, the results display significant variation, what has generated several controversial interpretations. It must be emphasized that many models have been derived without taking into account that the NW structural deformation should be significantly dependent on temperature. In this Thesis research work, we have studied the structural and electronic properties of gold NW's, in particular addressing how thermal effects influence the atomistic aspects of the NW deformation and how this influences the quantum conductance behavior. The structure of NW's has been studied by means of time-resolved high resolution transmission electron microscopy; the NWs transport measurements were based on a mechanically controlled break junction operated in ultra-high-vacuum. The experiments were performed at ~150 and 300 K. Our results have shown that at room temperature the atomic-size NW's. are always crystalline and free of defects, and the atomic structure is spontaneously deformed such that one of the [111]/[100]/[110] crystallographic axis becomes approximately parallel to the stretching direction. Low temperature observations revealed two important differences: i) Au NWs show extended defects, mainly stacking faults and, twinning; ii) NWs elongated along the [110] axis evolve to suspended atomic chains, while at room temperature they break abruptly. Partial Schockley dislocations generate the staking faults; suspended atoms chains are both observed at ~150 and 300 K. The global histograms of conductance at ~150 K showed that: i) a increase of the 1 Go peak intensity; ii) slight reduction of the NWs conductance due to scattering at defects and; iii) the peak at ~2 Go shows a sub structure, what is due to the occurrence of two different atomic arrangements with similar conductance. Briefly, our results revealed that the formation of defects is very frequent in NWs generated at ~150 K; the occurrence of more defects should be expected when NWs are studied at cryogenic temperatures. Then, a significant modification of the NW conductance behavior should be expected at low temperature. In these terms, the direct comparison of conductance measurements realized at different temperature regimes can lead to serious discrepancies. We hope that this work contribute to improve the interpretation and understanding of NW transport studies in order to develop a coherent and complete model that explain the physical properties of atomic-size metal NWs / Mestrado / Física da Matéria Condensada / Mestre em Física

Orientador: Daniel Mario Ugarte / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-08T07:13:40Z (GMT). No. of bitstreams: 1 LagosParedes_MaureenJoel_M.pdf: 10524108 bytes, checksum: 4c8c3fb76ef4ed87845ad6eb88cf42e9 (MD5) Previous issue date: 2007 / Resumo: O estudo de fios metálicos de tamanho atômico (NF's) tem atraído grande interesse devido aos novos efeitos químicos e físicos neles observados. Entre esses novos fenômenos podemos destacar a quantização da condutância, efeito que deve ser fundamental no desenho dos novos nanodispositivos eletrônicos. NF's são usualmente gerados através de um procedimento simples de deformação mecânica: duas superfícies metálicas são colocadas em contato e depois afastadas. Nos últimos estágios do estiramento antes da ruptura, um fio de alguns átomos de diâmetro é gerado enquanto a condutância é medida. Os NF's têm sido estudados por diferentes grupos e, em diversas condições de temperatura (4 - 300 K) e pressão (de ambiente a UHV). Os resultados apresentam importantes variações e, têm gerado interpretações muito controversas. Devemos enfatizar que muitas interpretações têm sido feitas sem considerar que a deformação estrutural dos NF's deve depender fortemente da temperatura. Nesta tese estudamos as propriedades estruturais e eletrônicas NF's e, em particular analisamos a influência de efeitos térmicos no arranjo atômico, e sua manifestação na condutância. A estrutura dos NF's foi estudada por microscopia eletrônica de transmissão de alta resolução resolvidas no tempo. A condutância foi medida utilizando um sistema de quebra controlada de junções operado em ultra-alto-vácuo. Os experimentos foram realizados a ~150 e 300 K. Nossos resultados mostraram que, à temperatura ambiente os NF's são sempre cristalinos e livre de defeitos nas regiões mais finas; e deformam unicamente ao longo dos eixos cristalográficos [111], [100] e [110]. A baixa temperatura duas importantes diferenças foram observadas: (i) NF's de ouro apresentam defeitos, principalmente falhas de empilhamento e maclas. (ii) NF's alongados na direção [110] evoluem em cadeias atômicas, de comportamento mecânico muito diferente da temperatura ambiente, onde quebram abruptamente. Segundo as imagens de microscopia eletrônica, discordâncias parciais (Shockley) geram falhas de empilhamento; e cadeias de átomos suspensos são observados a ~150 e 300 K. Histogramas globais de condutância adquiridos a baixa temperatura revelaram: (i) aumento da intensidade do pico ~1 Go; (ii) leve diminuição da condutância devido ao aumento de defeitos; e (iii) a existência de uma sub-estrutura no pico ~2 Go, indicando a formação de dois arranjos atômicos estáveis. Resumidamente, nossos resultados mostram que a formação de defeitos é um evento freqüente a ~150 K. Provavelmente, mais defeitos na estrutura devem acontecer para temperaturas menores (4 - 10 K). Portanto, uma importante mudança na evolução da condutância durante a elongação de NF's deve ser esperado a baixa temperatura. Assim, a comparação direta de medidas de transporte de NF's realizadas a diferentes temperaturas pode levar a sérias discrepâncias. Esperamos ter contribuído a melhorar a compreensão e interpretação de experimentos de transporte realizados em diferentes condições, de modo tal, a gerar um modelo único e coerente que explique as propriedades físicas de NF's metálicos / Abstract: The study of atomic-size metal nanowires (NW's) is attracting a great interest due to occurrence a novel physical and chemical phenomena. Among these new phenomena, we can mention conductance quantization that will certainly influence the design of nanodevices. NW's are usually generated by means of a simple procedure: two metallic surfaces are put into contact and, then retracted. Just before rupture atomic-size NW's are formed, and the conductance is measured during the wire elongation. The interpretation of the results is troublesome, because conductance is measured during the modification of the atomic structure. This kind of experimental study has been performed by many research groups and, a quite wide range of temperatures (4 - 300 K) and vacuum condition have been used (from ambient to UHV). In fact, the results display significant variation, what has generated several controversial interpretations. It must be emphasized that many models have been derived without taking into account that the NW structural deformation should be significantly dependent on temperature. In this Thesis research work, we have studied the structural and electronic properties of gold NW's, in particular addressing how thermal effects influence the atomistic aspects of the NW deformation and how this influences the quantum conductance behavior. The structure of NW's has been studied by means of time-resolved high resolution transmission electron microscopy; the NWs transport measurements were based on a mechanically controlled break junction operated in ultra-high-vacuum. The experiments were performed at ~150 and 300 K. Our results have shown that at room temperature the atomic-size NW's. are always crystalline and free of defects, and the atomic structure is spontaneously deformed such that one of the [111]/[100]/[110] crystallographic axis becomes approximately parallel to the stretching direction. Low temperature observations revealed two important differences: i) Au NWs show extended defects, mainly stacking faults and, twinning; ii) NWs elongated along the [110] axis evolve to suspended atomic chains, while at room temperature they break abruptly. Partial Schockley dislocations generate the staking faults; suspended atoms chains are both observed at ~150 and 300 K. The global histograms of conductance at ~150 K showed that: i) a increase of the 1 Go peak intensity; ii) slight reduction of the NWs conductance due to scattering at defects and; iii) the peak at ~2 Go shows a sub structure, what is due to the occurrence of two different atomic arrangements with similar conductance. Briefly, our results revealed that the formation of defects is very frequent in NWs generated at ~150 K; the occurrence of more defects should be expected when NWs are studied at cryogenic temperatures. Then, a significant modification of the NW conductance behavior should be expected at low temperature. In these terms, the direct comparison of conductance measurements realized at different temperature regimes can lead to serious discrepancies. We hope that this work contribute to improve the interpretation and understanding of NW transport studies in order to develop a coherent and complete model that explain the physical properties of atomic-size metal NWs / Mestrado / Física da Matéria Condensada / Mestre em Física

Orientador: Daniel Mario Ugarte / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-10T20:45:53Z (GMT). No. of bitstreams: 1 Tizei_LuizHenriqueGalvao_M.pdf: 14343917 bytes, checksum: 2e436bc0147e26276c682a3c9af78ce9 (MD5) Previous issue date: 2008 / Resumo: A completa caracterização de novos fenômenos físicos e químicos em sistemas com dimensões nanométricas requer conhecimento detalhado: a) do arranjo atômico; b) de como os diferentes elementos químicos dos materiais se redistribuem nas interfaces/superfícies (rugosidade, interdifusão, etc.); e finalmente c) como os dois primeiros fatores modificam as propriedades eletrônicas do sistema. Neste contexto, o desenvolvimento de novas ferramentas com capacidades específicas e bem adaptadas à análise de nanossistemas é imprescindível; assim técnicas de caracterização e visualização com resolução espacial nanométrica devem ser consideradas uma simples necessidade rotineira. No trabalho de mestrado que apresentamos buscamos implementar técnicas que permitam caracterizar sistemas com resolução espacial atômica. Neste sentido, implementamos um método de análise quantitativa de imagens de microscopia eletrônica de transmissão de alta resolução, que permite uma medida objetiva de variações da composição química. Esta medida é feita com base nas variações da distribuição de intensidades em uma imagem e fornece um mapa da composição química na imagem. Este procedimento de interpretação quantitativa foi aplicado ao estudo da morfologia de interfaces de poços quânticos de InGaP/GaAs crescidos por CBE (Chemical Beam Epitaxy). Estimamos que o limite de detecção de variações de composição química para este sistema seja 15%. Nesta análise, medimos parâmetros estruturais microscópicos que permitem a comparação da morfologia de diferentes poços. Com isso, concluímos que a interface InGaP/GaAs é mais rugosa que a GaAs/InGaP. Além disso, através da caracterização de poços quânticos com diferentes camadas interfaciais, concluímos que a adição de GaP na interface InGaP/GaAs reduz a rugosidade. Os resultados de rugosidade foram comparados com medidas de fotoluminescência a 6K buscando estabelecer uma correlação direta entre a qualidade da interface e a largura de linha de emissão do poço quântico. Esta correlação não foi estabelecida. Mostramos que modelos estruturais simples são ineficazes e que modelos mais elaborados são necessários para interpretação da largura de linha de emissão de um poço quântico / Abstract: The complete characterization of new physical and chemical phenomena in systems of nanometric scale requires the detailed knowledge of: a) atomic structure; b) how chemical composition distribution is redefined by interfaces and surfaces (rougheness, interdiffusion, etc.); and c) how are the electronic properties of the system influenced by those two factors. In this sense, the development of new tools with specific capabilities and well adapted to the analysis of nanosystems is essential. Therefore, characterization and imaging techniques with nanometric spatial resolution must be considered routine necessities. In this graduate work we present, we sought to implement techniques which allow the characterization of small systems with atomic spatial resolution. In this sense, we implemented a method for the qualitative analysis of high resolutions transmission electron microscopy images, which makes possible the objective measurement of chemical composition changes. This measurement is based on changes of the distribution of intensities of an image and results in a map of the chemical composition of the image. This procedure for the quantitative interpretation was used in the study of the morphology of the interfaces of InGaP/GaAs quantum wells (QW) grown by Chemical Beam Epitaxy (CBE). We estimate that our detection limit for chemical variations in this system is 15 %. In this analysis, we measured microscopic structural parameters which allow the comparison of the morphology of different QW. With this data, we concluded that the InGaP/GaAs interface is rougher that the GaAs/InGaP one. Moreover, through the characterization of QWs with different interfacial layers we concluded that the addition of a thin GaP layer reduces roughness. Morphologial results were compared with 6 K photoluminescence experiments, seeking to establish a direct correlation between interface quality and quantum well emission line width. This correlation was not established. We showed that simple structural models are inefficient and that more elaborated models are need for the quantitative interpretation of quantum wells¿ emission line width / Mestrado / Física da Matéria Condensada / Mestre em Física

Three-dimensional porous single crystals (PSCs) are a recent development in the growing world of mesoporous material. The mesoporosity allows for the material to retain their nanoproperties whilst being bulk in size. The current work concentrates on chromium oxide and cobalt oxide PSCs formed in the templates SBA-15 and KIT-6. HRTEM is the main technique used in this investigation, looking at the morphology and single crystallinity of these materials. A growth mechanism for the PSC material is proposed based on HRTEM observations. XRD studies revealed that the confinement effect, caused by the mesopores, reduces the temperature for both cobalt and chromium oxide crystallisation, as well as a different intermediate route from the metal nitrates. The properties of chromium oxide PSC are also investigated magnetically and catalytically. Some metal oxides in different templates are also presented, despite no PSC forming. HRTEM work on other nanomaterials, based on collaboration, is also presented.

Ma thèse consiste en l'étude du greffage des molécules de colorant sur des nanoparticules de ZnO, de leurs propriétés optiques et morphologiques, ainsi que les interactions électroniques entre le ZnO inorganique et le colorant organique. Nous avons créé des nanohybrides à base de nanosphères et nanobâtonnets de ZnO par deux voies: Ablation laser femtoseconde en phase liquide et Procédés chimiques. Des particules sphériques de quelques nanomètres sont générées par ablation laser révélant par la photoluminescence l'effet de confinement quantique due à la réduction de taille. Transfert d'excitation des ZnO synthétisées par ablation laser vers les molécules de colorant greffées est détecté par les excitations à un- et deux-photons. La croissance des bâtonnets de ZnO synthétisés chimiquement s'effectue par mûrissement d'Oswald et par attachement orienté. Ces modes de croissance sont étudiées en fonction du temps de synthèse et de la nature des réactants par le Microscope Electronique de Transmission à Haute Résolution. Les propriétés optiques des hybrides dépendent fortement de la forme de ZnO ainsi que du type et concentration du colorant greffé. Nous avons parvenu à remodeler l'énergie de la bande interdite des nanosphères de ZnO dans le système hybride par simple variation de la concentration du colorant. Nous avons ainsi montré l'effet de confinement quantique dû à la création de couches de charges dans le ZnO induites par la porphyrine adsorbée via ses groupes d'attachement COOH.