Fundação de Amparo a Pesquisa do Estado de Minas Gerais / Upon the current need for research with TiO2 nanocrystals (TiO2 NCs) properly characterized in order to evaluate their biological effects, this work was done aiming to synthesize and characterize TiO2 NCs, and evaluate their biocompatibility. The nanoparticles were synthesized by the precipitation in aqueous solution technique, and characterized by the techniques of X-ray diffraction, micro-Raman and spectrophotometry. To evaluate the biocompatibility, TiO2 NCs were tested in vivo using subcutaneous implants using Balb/c mice at a dose of 1g/kg for 15, 30 and 90 days for later histological analysis of the groups of 15 and 90 days and transmission electron microscopy of the group 30 days. In vitro evaluation consisted of cell viability assays, detection and measurement of nitric oxide metabolites and measurement of cytokine production in situ and in cultured macrophages challenged with different concentrations of TiO2 NCs. Cell viability was assessed after 72 hours by the MTT colorimetric assay, using five different concentrations of a solution of 10μg/ml, 20μg/ml, 40μg/ml, 100μg/ml and 200μg/ml in culture challenge of peritoneal macrophages Balb/c mice with 2, 12, 24 and 72 hours. From the supernatant of cultures of peritoneal macrophages was evaluated the production of nitrite by the Griess method and dosage levels of TNF-α, IL-1β, IL-12, IFN- and IL-4 by ELISA. The same technique was used for the determination of cytokine levels obtained from subcutaneous tissues underwent implantation of TiO2 NCs. After analysis of the data distribution by Kolmogorov-Smirnov test, we proceeded to their analysis by the Kruskal-Wallis test with Bonferroni post-test. The experiments of synthesis and characterization resulted in TiO2 nanocrystals of 8.5 nm on average, mixed phase, high purity level and quantum confinement effects. Histological analysis of the 15 days group showed a intense granulomatous nonspefic type inflammatory response with signs of necrosis and hemorrhage, which progressed with a slight reduction in its intensity, observed especially at 90 days of observation. Presence of clusters of nanocrystals with macroscopic dimensions, surrounded by macrophages and multinucled giant cells forming granulomas with fibrous capsules, which could be regarded as a typical reaction of granulomatous foreign body type and more intense fibrosis formation at 90 days within the material deployed. Nanocrystals were identified in lymph nodes in the different periods of study, suggesting that these particles might be transposed. Electron microscopy confirmed the evidence of apoptosis and vacuolar degeneration. The MTT test resulted in 40% viable cells in only 10 and 20μg/ml. The in vitro cytokine assay showed that there was not a tendency dose or time-dependent samples, presenting different behavior of TNF-α, IL-1β, IL-12 and increased production of IFN- probably due to low production of IL -4. The nitrite production was higher in the samples of 10μg/ml. The production of all cytokines in vivo experiment by the 15 days group was enhanced, decreasing in a time-dependent fashion, collaborating with the findings in vivo. We conclude that the TiO2 nanocrystals present in the tested concentrations presented inflammatory effects in vivo, cytotoxic and inflammatory conditions in vitro. These findings show that the experimental conditions studied NCs are not biocompatible. / Mediante a atual necessidade de pesquisas com nanocristais de TiO2 (NCs TiO2) devidamente caracterizados a fim de se avaliar seus efeitos biológicos, realizou-se este trabalho que teve como objetivos a síntese e caracterização dos NCs TiO2, e a avaliação de sua biocompatibilidade. As nanopartículas foram sintetizadas pela técnica da precipitação via solução aquosa, e caracterizadas por meio das técnicas de difração de raios-X, micro-Raman e espectrofotometria. Para a avaliação da biocompatibilidade, os NCs TiO2 foram submetidos a testes in vivo por meio de implantes subcutâneos utilizando camundongos Balb/c na dose de 1g/kg, por 15, 30 e 90 dias para posterior análise histológica dos grupos de 15 e 90 dias e microscopia eletrônica de transmissão do grupo de 30 dias. Avaliação in vitro consistiu de ensaios de viabilidade celular, detecção e mensuração de metabólitos do óxido nítrico e mensuração da produção de citocinas in loco e em cultura de macrófagos desafiados por diferentes concentrações de NCs TiO2. A viabilidade celular foi avaliada após 72 horas pelo teste colorimétrico MTT, utilizando-se cinco concentrações diferentes de solução de 10μg/ml, 20μg/ml, 40μg/ml, 100μg/ml e 200μg/ml, em desafio de cultura de macrófagos peritoneais de camundongos Balb/c por 2, 12, 24 e 72 horas. Do sobrenadante de culturas de macrófagos peritoneais avaliou-se a produção de nitrito pelo método de Griess e dosagem dos níveis das citocinas TNF-α, IL-1β, IL-12, INF- e IL-4 por ELISA. A mesma técnica foi utilizada para a dosagem dos níveis de citocinas obtida dos tecidos subcutâneo submetido ao implante de NCs TiO2. Após a análise da distribuição dos dados pelo teste Kolmogorov-Smirnov, procedeu-se a sua análise por meio do teste de Kruskal-Wallis com pós-teste de Bonferroni. Os experimentos de síntese e caracterização resultaram nanocristais de TiO2 de 8,5nm em média, fase mista, alto grau de pureza e efeitos de confinamento quântico. As análises histológicas do grupo de 15 dias evidenciaram uma resposta inflamatória do tipo granulomatosa inespecífica intensa com sinais de necrose e hemorragia, que evoluiu com discreta redução em sua intensidade, constatada em especial aos 90 dias de observação. Presença de aglomerados de nanocristais de dimensões macroscópicas, rodeados de macrófagos e células gigantes multinucleadas formando granulomas, com cápsulas fibrosas, que poderiam ser consideradas como uma reação típica do tipo granulomatosa de corpo estranho e formação de fibrose mais intensa aos 90 dias no interior do material implantado. Houve a identificação dos nanocristais nos linfonodos nos diferentes períodos de estudo, sugerindo que estas partículas possam ser carreadas a distância. A microscopia eletrônica confirmou a evidência de apoptose e degeneração vacuolar. O teste MTT resultou em 40% de células viáveis somente em 10 e 20μg/ml. A dosagem de citocinas in vitro demonstrou que não houve uma tendência dose ou tempo dependente das amostras, apresentando comportamentos distintos de produção de TNF-α, IL-1β, IL-12 e maior produção de INF- devido provavelmente à baixa produção de IL-4. A produção de nitrito foi maior nas amostras de 10μg/ml. A produção de todas as citocinas do experimento in vivo pelo grupo de 15 dias foi acentuada, decrescendo de forma tempo dependente, colaborando com os achados in vivo. Conclui-se que os nanocristais de TiO2 nas concentrações testadas apresentaram efeitos inflamatórios in vivo, citotóxicos e inflamatórios in vitro. Estes achados atestam que nas condições experimentais utilizadas os NCs estudados não são biocompatíveis. / Mestre em Odontologia

Orientador: Oswaldo Luiz Alves / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Quimica / Made available in DSpace on 2018-08-08T20:29:31Z (GMT). No. of bitstreams: 1 Romano_Ricardo_D.pdf: 7756171 bytes, checksum: bd3a8af5af06fb7ec50b3cd881d41bfd (MD5) Previous issue date: 2007 / Resumo: O desenvolvimento das nanoestruturas e suas aplicações compõem uma das áreas científicas em mais dinâmica ascensão. Grande parte dos estudos na área concentra-se nos métodos de preparação e, de uma forma geral, podem ser divididos em métodos físicos ou químicos. Os primeiros reúnem processos baseados em sistemas de feixes moleculares ou litografia, enquanto os últimos envolvem reações químicas em meios onde o crescimento dos cristais possa ser controlado e estabilizado. Nesta Tese foram preparadas nano(micro)estruturas de semicondutores II-VI e IV-VI a partir de três abordagens químicas distintas. Na primeira, foram obtidos nanocompósitos pelo encapsulamento de nanocristais de CdS e PbS no ambiente microporoso de um vidro transparente, comercialmente conhecido por Vycor®. A técnica envolvida foi a impregnação de peças do vidro com precursor single-source seguida por tratamento térmico visando a pirólise in situ do precursor. Efeitos de confinamento quântico no espectro óptico e micrografias eletrônicas de transmissão confirmaram a natureza nanométrica da fase ocluída. Na segunda, foram obtidos cristais nano e micrométricos de CdS, PbS e ZnS através da técnica conhecida por moldagem molecular por solvente coordenante, na qual precursores single-source foram tratados solvotermicamente em solventes coordenantes e levaram à formação de bastões de CdS, microestrelas de PbS e intercalatos de ZnS com etilenodiamina. Na última abordagem, nanocristais coloidais de CdSe com diferentes faixas de tamanho (2 a 7 nm) foram preparados com a finalidade de se estudar o comportamento da estrutura local e dinâmica vibracional do CdSe em função da redução no tamanho e substituição do agente de recobrimento usado na síntese / Abstract: The development of nanostructures and their applications constitute one of the most exciting scientific areas. A great number of studies in this area concern the preparation methods. Generally, they are classified in physical and chemical methods. The former class is based on molecular beam and lithography techniques, while the latter involves chemical reactions where crystal growth can be controlled and stabilized. In this Thesis, II-VI and IV-VI semiconductor nano(micro)structures were prepared according to three different approaches. In the first one, nanocomposites were obtained through the encapsulation of CdS and PbS nanocrystals into a porous and transparent commercial glass, named Vycor®. Glass pieces were impregnated with single-source precursors and, then, thermally treated in order to achieve in situ pyrolysis, making use of the porous environment as the stabilizer for the crystal growth. Quantum confinement effects in the optical spectrum and transmission electron micrographs characterized the nanometric dimensions of the occluded phase. In the second approach, a technique known as molecular templating by coordenant solvents was employed in order to obtaining CdS, PbS and ZnS nano(micro)crystals showing unusual morphologies. Single-source precursors were solvothermically treated in such solvents leading to CdS nanowires, PbS microstars and ZnS-ethylenediamine intercalates. In the last approach, colloidal CdSe nanocrystals with different size ranges (2 up to 7 nm) were prepared and employed in the study of the local structure and vibrational dynamics of CdSe as a function of crystal size reduction and substitution of the covering agent used in the synthetic procedure / Doutorado / Quimica Inorganica / Doutor em Ciências

A malária é uma doença infecciosa aguda ou crônica causada por parasitas do gênero Plasmodium. Estima-se a ocorrência de 110 milhões de novos casos ao ano e cerca de um a dois milhões de óbitos em todo o mundo como decorrência da infecção. O ácido orótico ou vitamina B13 possui baixa solubilidade em praticamente todos os solventes, tal característica limita seu uso em preparações farmacêuticas. Quanto ao seu mecanismo de ação, o composto demonstrou atividade na inibição da diidroorotase e da diidroorotato desidrogenase, enzimas utilizadas no ciclo de replicação da malária, e também em outras enzimas da síntese das pirimidinas. Considerando seu potencial na terapêutica antimalárica, a baixa solubilidade do ácido orótico constitui limitação para o desenvolvimento de medicamento. Devido a sua simplicidade e vantagem em relação às outras estratégias existentes, a obtenção de nanocristais têm revelado elevado potencial para solucionar problemas associados à baixa velocidade de dissolução de fármacos, em especial aqueles com baixa solubilidade. O objetivo do presente trabalho foi a obtenção de nanocristais de ácido orótico empregando moagem à alta energia, bem como sua caracterização físico-química. Foram obtidos nanocristais de ácido orótico com redução de até 350 vezes no tamanho de partícula em relação a matéria-prima utilizada. Os ensaios para a caracterização físico-química evidenciaram comportamentos térmico e estrutural diferenciado do ácido orótico nanonizado. A solubilidade de saturação dos nanocristais de ácido orótico foi aumentada em até 13 vezes. A utilização do Povacoat® na produção dos nanocristais permitiu a obtenção de formulações mais estáveis, com melhor aspecto e com características físico químicas desejáveis à uma formulação contendo nanocristais. Adicionalmente, as formulações preparadas com o Povacoat® contendo até 13% de ácido orótico apresentaram toxicidade suave. Desse modo, os nanocristais de ácido orótico demonstram potencial como fármaco inovador para o tratamento da malária. / Malaria is an acute or chronic infection caused by parasites of the genus Plasmodium. It is estimated to occur than 110 million new cases per year and about one to two million deaths worldwide as a consequence of infection. The vitamin B13 or orotic acid has low solubility in almost all solvents, this characteristic limits their use in pharmaceutical preparations. Regarding its mechanism of action, the compound has demonstrated activity in inhibiting dihydroorotate dehydrogenase and diidroorotase, enzymes used in the replication cycle of malaria, and also other enzymes of the synthesis of pyrimidines. Considering their potential in antimalarial therapy, the low solubility of orotic acid constitutes a limitation for the development of medicine. Due to its simplicity and advantage over other existing approaches, obtaining nanocrystals have revealed high potential to solve problems associated with low dissolution rate of drugs, especially those with low solubility. The objective of this study was to obtain orotic acid nanocrystals using the high energy ball milling as well its physical chemical characterization. There were obtained nanocrystals orotic acid with reduction of 350 times in particle size in relation to the original material used. The tests for the physicochemical characterization showed thermal behavior and different structural nanonizado orotic acid. The saturation solubility of the nanocrystals orotic acid was increased to 13 times. The use of Povacoat® in the production of nanocrystals allowed obtaining more stable compositions with improved appearance and desirable physicochemical characteristics to a formulation containing nanocrystals. Additionally, the formulations prepared with the Povacoat® containing up to 13% of orotic acid showed mild toxicity. Thus, orotic acid nanocrystals demonstrate potential as a novel drug for the treatment of malaria.

CdTe QDs capped with mercaptopropionic acid (MPA) and thioglycolic acid (TGA) were covalently linked to zinc and indium tetraaminophthalocyanines (TAPcs) using N-ethyl-N(3-dimethylaminopropyl) carbodiimide (EDC) and N-hydroxy succinimide (NHS) as the coupling agents. The results presented give evidence in favour of formation of an amide bond between the MTAPc and CdTe QDs. Both the linked ZnTAPc–QD complexes and the mixture of QDs and ZnTAPc (without chemical linking) showed Förster resonance energy transfer (FRET), though the linked showed less FRET, whereas the QD interactions with InTAPc yielded no evidence of FRET. Both MTAPcs quenched the QDs emission, with quenching constants of the order of 103–104M−1, binding constants of the order of 108-1010M-1 and the number of binding sites for the MTAPc upon the QD being 2. High energy transfer efficiencies were obtained (in some cases as high as 93%), due to the low donor to acceptor distances. Lastly, both MTAPc were shown to be poor optical limiters because their imaginary third-order susceptibility (Im[χ(3)]) was of the order of 10-17-10-16 (optimal range is 10-9-10-11), the hyperpolarizability (γ) of the order of 10-37-10-36 (optimal range is 10-29-10-34) and the k values were above one but below ten.

Semiconductor devices are commonplace in every household. One application of semiconductors in particular, namely solid state lighting technology, is destined for a bright future. To this end, ZnO nanostructures have gained substantial interest in the research community, in part because of its requisite large direct band gap. Furthermore, the stability of the exciton (binding energy 60 meV) in this material, can lead to lasing action based on exciton recombination and possibly exciton interaction, even above room temperature. Therefore, it is very important to realize controllable growth of ZnO nanostructures and investigate their properties. The main motivation for this thesis is not only to successfully realize the controllable growth of ZnO nanorods, but also to investigate the structure, optical and electrical properties in detail by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), photoluminescence (PL) spectroscopy (steady state and time resolved) and X-ray diffraction (XRD). Furthermore, strong rectification in the ZnO/p-Si heterojunction is demonstrated. Nanorods have been successfully synthesized on silicon by a two-step process, involving the pre-coating of the substrate by a seed layer, followed by the chemical bath deposition of the nanorods. ZnO seed layers with particle sizes of about 5 nm are achieved by the thermal decomposition of zinc acetate dihydrate dissolved in ethanol. The effects of the seed layer density on the distribution, alignment and uniformity of subsequently grown nanorods were studied. The aspect ratio, orientation and distribution of nanorods are shown to be well controlled through adjusting the density of the ZnO nanoparticles pre-coated onto the substrates. It is shown that the seed layer is a prerequisite for the growth of well aligned ZnO nanorods on lattice mismatched Si substrate. The influence of various nanorod growth parameters on the morphology, optical and electrical properties of the nanorods were also systematically studied. These include the oxygen to zinc molar ratio, the pH of the growth solution, the concentration of the reactants, the growth temperature and growth time, different hydroxide precursors and the addition of surface passivating agents to the growth solution. By controlling these xii parameters different architectures of nanostructures, like spherical particles, well aligned nanorods, nanoflowers and thin films of different thicknesses are demonstrated. A possible growth mechanism for ZnO nanostructures in solution is proposed. XRD indicated that all the as-grown nanostructures produced above 45 C crystallize in the wurtzite structure and post growth annealing does not significantly enhance the crystalline quality of the material. In material grown at lower temperature, traces of zinc hydroxide were observed. The optical quality of the nanostructures was investigated using both steady-state PL and time-resolved (TR) PL from 4 K to room temperature. In the case of as-grown samples, both UV and defect related emissions have been observed for all nanostructures. The effect of post-growth annealing on the optical quality of the nanostructures was carefully examined. The effect of annealing in different atmospheres was also investigated. Regardless of the annealing environment annealing at a temperature as low as 300 C enhances the UV emission and suppresses defect related deep level emission. However, annealing above 500 C is required to out-diffuse hydrogen, the presence of which is deduced from the I4 line in the low temperature PL spectra of ZnO. TRPL was utilized to investigate lifetime decay profiles of nanorods upon different post growth treatments. The bound exciton lifetime strongly depends on the post-growth annealing temperature: the PL decay time is much faster for as grown rods, confirming the domination of surface assisted recombination. In general, the PL analysis showed that the PL of nanorods have the same characteristics as that of bulk ZnO, except for the stronger contribution from surface related bound excitons in the former case. Surface adsorbed impurities causing depletion and band bending in the near surface region is implied from both time resolved and steady state PL. Finally, although strong rectification in the ZnO/p-Si heterojunction is illustrated, no electroluminescence has been achieved. This is explained in terms of the band offset between ZnO and Si and interfacial states. Different schemes are proposed to improve the performance of ZnO/Si heterojunction light emitting devices.

This thesis presents the development of a selective-etch fabrication process to create sub-10 nanometre metallic gaps and the subsequent use of the gaps to study the electronics of nanocrystals and molecules. A complete picture of the success of the process required both examination by scanning electron microscopy as well as probing the current response to an applied bias at low temperature. The empty gaps were fully characterised before self-assembling 7 nm CdSe nanocrystals onto the metal with the help of linker molecules. The I-V characteristics of the empty gaps showed a reduction of the tunnelling barrier height from the expected value (~5.1 eV, the work function of Au) when the results were fitted to the Simmons tunnelling model for a metal-insulator-metal system. Results indicate that after the barrier height is surpassed, a transition from direct to field-effect (Fowler-Nordheim) tunnelling occurs. After CdSe assembly, the collected I-V characteristics of the system at 77 K showed varied results. Many devices displayed conductance peaks at low voltages comparable to the results of the shadow evaporation process for 4.2 nm nanocrystals (also documented in this thesis). Several devices revealed switching between multiples of fundamental curves, suggesting conduction through multiples of nanocrystals.

This dissertation explores the effect of nanometer-scale changes in structure on the energetics of photocatalytic and photovoltaic materials. Of particular interest are semiconductor nanocrystals (NCs), which have interesting chemical properties that lead to novel structures and applications. Chief among these properties are quantum confinement and the high surface area-to-volume ratio, which allow for chemical tuning of the energetics and structure of NCs. This tunable energetic landscape has led to increasing application of NCs in various areas of research, including solar energy conversion, light-emitting diode technologies, and photocatalysis. However, spectroscopic methods to determine the energetics of NCs have not been well developed, due to chemical complexities of relevant NCs such as polydispersity, capping ligand effects, core-shell structures, and other chemical modifications. In this work, we demonstrate and expand the utility of photoelectron spectroscopy (PES) to probe the energetics of NCs by considering the physical processes that lead to background and secondary photoemission to enhance photoemission from the sample of interest. A new methodology for the interpretation of UP spectra was devised in order to emphasize the minute changes to the UP spectra line shape that arise from nanoscopic changes to the NCs. We applied various established subtractions that correct for photon source satellites, secondary photoelectrons, and substrate photoemission. We then investigated the effect of ligand surface coverage on the surface chemistry and density of states at the top of valence band (VB). We systematically removed ligands by increasing numbers of purification steps for two diameters of NCs and found that doing so increased photoemission density at the top of the VB, which is due to undercoordinated surface atoms. Deeper VB structure was also altered, possibly due to reorganization of the atoms in the NC. Using the new UPS interpretation methodology, we examined the evolution of the valence band energy (EVB) of CdSe NCs as it was modified from spherical NC to rod to Au-NP tipped nanorod (NR). We also employed potential-modulated attenuated total reflectance spectroscopy (PM-ATR) to probe the conduction band energy (ECB) of the series. The EVB decreased with each modification, which is predicted with a band-bending model. This trend was also observed in the ECB, as revealed by spectroelectrochemistry, along with the appearance of new metal-semiconductor states in the band gap. UPS was finally used to investigate the even more complex Pt-NP tipped CdSe@CdS core@shell NR heterostructure. The addition of the CdS shell decreases the EVB relative to CdSe, as expected from common cation II-VI compounds. The Pt-NC increases the EVB, which, like the Au-CdSe NR, is predicted by employing a band-bending model. XPS revealed that PtSx-like chemical states were formed near the CdS-Pt interface. These experiments, along with the improved UP spectra interpretation methodology, demonstrate the wealth of information regarding surface chemistry and energetics that can be obtained with PES which can be applied to not only NCs, but also to metal oxide or molecular thin films.

Nanoindentation is a widely used technique to measure the mechanical properties of films with thickness ranging from nanometers to micrometers. A much better understanding of the contact mechanics is obtained mostly through finite element modeling. The experiments were modeled using the software package Nano SP1 that is based on COSMOSM™ (Structural Research & Analysis Corp, www.cosmosm.com), a finite element code. The fundamental material properties affecting pile-up are the ratio of the effective modulus to yield stress Eeff/σ and the work hardening behavior. Two separate cases of work hardening rates were considered; one with no work hardening rate and other with a linear work hardening rate. Specifically, it is observed that pile up is large only when hf/hmax is close to one and degree of work hardening rate is small. It should also be noted that when hf/hmax < 0.7 very little pile-up is observed no matter what the work-hardening behavior of the material. When pile-up occurs the contact area is greater than that predicted by the experimental methods and both the hardness and modulus are overestimated. In this report the amount by which these properties are overestimated are studied and got to be around 22% approx. Bluntness of the tip often leads to the misinterpretation of the load-displacement data. Further analysis was done in order to find out the amount of deviation from the ideal tip due to tip bluntness. Radius of the tips were also calculated for cubecorner (41.35 nm) and conical indenter (986.05 nm).

Orientador: Ioshiaki Doi / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-08T01:34:23Z (GMT). No. of bitstreams: 1 Pinto_EmilioSergioMarinsVieira_M.pdf: 2911838 bytes, checksum: d0f5e53a1aaa54372eda0b11016226b6 (MD5) Previous issue date: 2006 / Resumo: Nesta dissertação estudamos a obtenção de nanocristais (NCs) de Ge pela técnica de LPCVD (Low Pressure Chemical Vapor Deposition), buscando otimizar as condições de processo que resultassem em NCs com características de tamanho, densidade por unidade de área e uniformidade de tamanhos, que são necessárias para aplicação em dispositivos de memórias de porta flutuante. Os NCs foram fabricados por processo de dois passos: 1) formação de núcleos de Si na superfície do SiO2, a partir de silana (SiH4); 2) crescimento de Ge sobre os núcleos de Si através de deposição de germana (GeH4). Realizamos ciclos de deposição e caracterização das amostras, e os parâmetros de processo: temperatura, pressão total, fluxos de silana e germana e tempo de deposição, foram alterados convenientemente, com base na literatura e nos resultados obtidos a cada ciclo de fabricação. As amostras foram caracterizadas quanto à morfologia, por microscopia de força atômica (AFM) e a estrutura dos NCs foi analisada por microscopia eletrônica de transmissão de alta resolução (HRTEM). Estudamos a influência dos parâmetros de processo nas características dos NCs e observamos tendências de aumento da densidade de NCs com a elevação da temperatura, pressão total e fluxo de SiH4 do passo 1. E, o tamanho dos NCs tendem a diminuir com a redução da temperatura, pressão total e tempo de deposição do passo 2. Os resultados mostram que com os parâmetros: 600 ºC / 5 Torr / 20 sccm de SiH4 / 20 seg. para a nucleação de Si e 550 ºC / 2 Torr / 5 sccm / 30 seg. para a deposição de Ge, é possível obter alta densidade de NCs por unidade área de 4x1010 NCs/cm2 com diâmetro médio de 19 nm e altura média de 4,5 nm / Abstract: In this thesis we studied the synthesis of Ge nanocrystals (NCs) by the LPCVD technique (Low Pressure Chemical Vapor Deposition). We looked for NCs with characteristics of sizes, density and uniformity of sizes that are necessary for applications in floating gate memory devices. To reach those characteristics we have optimized the process conditions. The NCs were fabricated by a process of two steps: 1) formation of Si nuclei on SiO2 surface, through the silane (SiH4) decomposition; 2) Ge growth on Si nuclei through germane (GeH4) deposition. We accomplished deposition cycles and characterization of the samples. The process parameters: temperature, total pressure, silana and germana flow and deposition time, were altered conveniently based on the literature and results obtained at each production cycle. The morphology of the samples was analyzed by atomic force microscopy (AFM) and the NCs structures were analyzed by high resolution transmission electron microscopy (HRTEM). We studied the influence of the process parameters in the NCs characteristics and we have observed tendencies of NCs density increase with rise of the temperature, total pressure and SiH4 flow of step 1. The NCs size tends to decrease with the reduction of temperature, total pressure and deposition time of step 2. The results show that with the parameters: 600 ºC / 5 Torr / 20 sccm de SiH4 / 20 sec. for the Si nucleation and 550 ºC / 2 Torr / 5 sccm / 30 sec. for the Ge deposition, it¿s possible to reach a high density of NCs (4x1010 NCs/cm2) with diameter of 19 nm and average height of 4,5 nm / Mestrado / Eletrônica, Microeletrônica e Optoeletrônica / Mestre em Engenharia Elétrica

Orientador: Marcelo Knobel / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-04T01:56:42Z (GMT). No. of bitstreams: 1 Brandl_AnaLucia_D.pdf: 5290468 bytes, checksum: 32290a7675f89cf9c2a2ea53be70c6fb (MD5) Previous issue date: 2004 / Resumo: Sistemas magnéticos granulares são constituídos de pequenas partículas magnéticas imersas numa matriz não magnética. Essas partículas têm formas e tamanhos variados, eixos de anisotropia variados e orientados aleatoriamente e, dependendo do tipo de matriz (isolante ou condutora) e da concentração do material magnético, diferentes tipos de interações magnéticas podem estar presentes. Esses materiais apresentam diversas propriedades físicas interessantes, como magneto-resistência gigante e efeito Hall gigante. Devido à complexidade desses sistemas, a sua magnetização só pode ser calculada analiticamente em dois casos limites: quando a temperatura é zero (modelo Stoner-Wohlfarth) ou quando a temperatura é alta (modelo de Langevin). Embora o modelo de Langevin seja aplicado com bastante sucesso para temperaturas acima da temperatura de bloqueio média (TB) do sistema, mostramos nesse trabalho que os resultados podem ser enganosos, fornecendo parâmetros estruturais muito diferentes dos reais. Essas discrepâncias podem ser atribuídas a efeitos de interações magnéticas e a efeitos de anisotropia, ambos desconsiderados no formalismo de Langevin. Os principais resultados experimentais apresentados nesta dissertação foram obtidos de um conjunto de filmes granulares do tipo metal-isolante, com partículas nanocristalinas de Co imersas numa matriz amorfa de SiO2, fabricados por evaporação catódica. A caracterização magnética foi realizada através de medidas de magnetização em função do campo, susceptibilidade resfriada com e sem campo magnético aplicado e magnetização termo-remanente. A caracterizção estrutural foi realizada através de medidas de microscopia de transmissão de elétrons, difração de raio-x e espalhamento de raio-x a baixo ângulo / Abstract: Granular magnetic systems are formed by magnetic grains whose size is of the order of a few nanometers, embedded in a non-magnetic (insulating or metallic) matrix. These ultrafine particle systems present size, shape, and anisotropy distributions, besides randomly orientated easy directions. Magnetic interactions always exist, being stronger or weaker according to the volume concentration and the matrix type. These systems have shown interesting magnetotransport properties, as giant magnetoresistance and giant Hall effect. Owing to the inherent complexity of the nanostructure, the magnetization can be analytically calculated only in two limiting cases: when T = 0 (Stoner-Wohlfarth model) or for high temperatures (Langevin model). The Langevin model presents very good results when applied at temperatures higher than the mean blocking temperature (TB) of the system. However this adequacy can be just apparent: the obtained structural parameters are very different from the real ones, as we show in this work. These discrepancies can be attributed to magnetic interactions andanisotropy effects, both unconsidered in the Langevin formalism. The main results presented in this thesis were obtained from a set of metal-insulator granular films, composed of Co nanoparticles immersed in an amorphous SiO2 matrix. The films were produced by magnetron co-sputtering. The magnetic characterization was perfomed with magnetization loops, zero-field cooled and field cooled susceptibilities, and thermoremanent magnetization. The microstructural characterization was done by transmission electron microscopy, x-ray diffraction, and small angle x-ray scattering / Doutorado / Física / Doutor em Ciências