Pontos quânticos de carbono (C-dots) luminescentes na região do azul-verde aprisionados em matriz de sílica foram produzidos por um processo novo, baseado na pirólise de grupos contendo carbono dispersos nas bordas dos grãos de dimensões nanométricas de sílica (AEROSIL) previamente sinterizados a frio sob alta pressão, onde nenhuma técnica de passivação foi exigida. A análise de difração de elétrons de área selecionada (SAED – Selected Area Electron Diffraction) e espectroscopia de perda de energia de elétrons (EELS – Electron Energy Loss Spectroscopy) confirmaram a formação de C-dots contendo átomos de carbono com ligações do tipo sp2. Foram investigados diferentes valores de pressão (2,5, 4 e 7,7 GPa) para sinterização a frio e diferentes temperaturas de pirólise, a partir de 500 até 900°C. Resultados de análise térmica revelaram pequena perda de massa durante a pirólise das amostras, praticamente independente da pressão utilizada na sinterização. Espectroscopia na faixa do infravermelho revelou alterações nas bandas de aborção na faixa correspondente aos modos de vibração de CH2 e CH3, dependentes da temperatura e da pressão utilizadas. Os espectros de fotoluminescência (FL) foram fortemente dependentes do comprimento de onda de excitação e observou-se uma intensidade de emissão mais elevada no intervalo entre 500-550 nm para a amostra sinterizada a frio em 7,7 GPa e tratada termicamente a 800°C para excitação em 460 nm. Também foi investigado a contribuição da matriz de silica após a sinterização. / Quantum dots in the blue-green region embedded in a silica matrix were produced by a new process based on the pyrolysis of groups containing carbon dispersed on the edges of the grain of nanosized silica (AEROSIL) previously sintered under high pressure, where no passivation technique was required. The Selected Area Electron Diffraction (SAED) and Electron Energy Loss Spectroscopy (EELS) confirmed the formation of Cdots containing carbon atoms with sp2 bonds. Different pressure values (2,5, 4 and 7,7 GPa) were investigated for cold sintering and the pyrolsys was in the temperature range from 500 to 900°C. Results of thermal analysis revealed a small loss of mass during the pyrolysis of the samples, practically independent of the sintering pressure. Infrared spectroscopy revealed changes in the absorption bands in the range corresponding to the CH2 and CH3 vibration modes, depending on the temperature and pressure conditions. Photoluminescence (PL) spectra were strongly dependent on the excitation wavelength and a higher emission intensity was observed in the range 500-550 nm for the sample sintered at 7.7 GPa and pyrolysed at 800°C for excitation at 460 nm. The contribution of the silica matrix after sintering was also investigated.

"August 1999." / Thesis (Ph.D.)--Chinese University of Hong Kong, 1999. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

Atomically thin two-dimensional nanomaterials such as graphene and transition metal dichalcogenides (TMDCs) have seen a rapid growth of exploration since the isolation of monolayer graphene. These materials provide a rich field of study for physics and optoelectronics applications. Many applications seek to combine a two dimensional (2D) material with another nanomaterial, either another two dimensional material or a zero (0D) or one dimensional (1D) material. The work in this thesis explores the consequences of these interactions from 0D to 2D. We begin in Chapter 2 with a study of energy transfer at 0D-2D interfaces with quantum dots and graphene. In our work we seek to maximize the rate of energy transfer by reducing the distance between the materials. We observe an interplay with the distance-dependence and surface effects from our halogen terminated quantum dots that affect our observed energy transfer. In Chapter 3 we study supercapacitance in composite graphene oxide- carbon nanotube electrodes. At this 2D-1D interface we observe a compounding effect between graphene oxide and carbon nanotubes. Carbon nanotubes increase the accessible surface area of the supercapacitors and improve conductivity by forming a conductive pathway through electrodes. In Chapter 4 we investigate effective means of improving sample quality in TMDCs and discover the importance of the monolayer interface. We observe a drastic improvement in photoluminescence when encapsulating our TMDCs with Boron Nitride. We measure spectral linewidths approaching the intrinsic limit due to this 2D-2D interface. We also effectively reduce excess charge and thus the trion-exciton ratio in our samples through substrate surface passivation. In Chapter 5 we briefly discuss our investigations on chemical doping, heterostructures and interlayer decoupling in ReS₂. We observe an increase in intensity for p-doped MoS₂ samples. We investigated the charge transfer exciton previously identified in heterostructures. Spectral observation of this interlayer exciton remained elusive in our work but provided the motivation for our work in Chapter 4. We also discuss our preliminary results on interlayer decoupling in ReS₂.

Orientador: Leila Aparecida Chiavacci Favorin / Coorientador: Rosemeire L. Rodrigues Pietro / Banca: Sandra Helena Pulcinelli / Banca: Tais Maria Bauab / Resumo: Os óxidos metálicos, como óxido de zinco (ZnO) são utilizados como agentes antimicrobianos inorgânicos frente à grande diversidade de microrganismos. Devido ao tamanho reduzido, as nanopartículas (NP) de ZnO são promissoras para combater infecções, uma vez que a diminuição do tamanho da partícula pode resultar em melhor atividade antimicrobiana, pois por terem tamanho menor, as NP podem com maior facilidade penetrarem na membrana ou induzir a maiores produções de espécies reativas de oxigênio (ERO). O objetivo desse trabalho foi desenvolver suspensões e pós de nanopartículas de ZnO com tamanho e superfície controladas, com a finalidade de avaliar a influência do tamanho e da modificação de superfície na atividade antimicrobiana do ZnO frente às bactérias Staphylococcus aureus e Escherichia coli e levedura Cândida albicans. As NP de ZnO foram preparadas pelo processo sol-gel de acordo com a metodologia proposta por Spanhel e Anderson (1991) com modificação da razão de hidrólise para controle do tamanho das NP seguida da adição de (3-Glycidyloxypropyl)trimethoxysilane (GPTMS), como modificador de superfície. Os nanomateriais obtidos foram caracterizados por diferentes técnicas: difração de raios X (DRX); espectroscopia na região do ultravioleta-visível (UV-vis), espalhamento de raios X à baixo ângulo (SAXS); espalhamento de raios X a alto ângulo (WAXS); análise termogravimétrica (TG); microscopia eletrônica de transmissão (MET); Espectroscopia de raios X por dispersão de energi... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Metal oxides such as zinc oxide (ZnO) are used as inorganic antimicrobial agents against great diversity of microorganisms. Due the reduced size, ZnO nanoparticles (NP) are promising to combat infections, since the decrease in particle size may result in better antimicrobial activity, because of their smaller sizes, NP can more easily penetrate the membrane or induce a greater production of reactive oxygen species (ROS). The aim of this work was to develop suspensions and powders of ZnO nanoparticles with controlled size and surface, in order to evaluate the influence of size and surface modification on ZnO antimicrobial activity against bacteria Staphylococcus aureus and Escherichia coli and yeast Candida albicans. The ZnO NP were prepared by the sol-gel process according to the methodology proposed by Spanhel and Anderson (1991) with hydrolysis ratio modification for NP size control followed by the addition of (3-Glycidyloxypropyl) trimethoxysilane (GPTMS) as surface modifier. The nanomaterials obtained were characterized by different techniques: X-ray diffraction (XRD); Ultraviolet-visible spectroscopy (UV-vis); small angle light scattering (SAXS); high angle light scattering (WAXS); thermogravimetric analysis (TG); Transmission electron microscopy (TEM); energy dispersive spectroscopy (EDS) and zeta potential. With the XRD technique, we verified the obtaining of ZnO NP in the wurtizite phase and it was possible to calculate the crystallite size for the different samples ... (Complete abstract click electronic access below) / Mestre

Orientador: Américo Sheitiro Tabata / Banca: Euzi Conceição Fernandes da Silva / Banca: Ligia de Oliveira Ruggiero / Banca: Sandro Martini / Banca: José Humberto Dias da Silva / O Programa de Pós-Graduação em Ciência e Tecnologia de Materiais, PosMat, tem caráter institucional e integra as atividades de pesquisa em materiais de diversos campi da Unesp / Resumo: Neste trabalho investigamos pontos quânticos de InAs sobre um substrato de GaAs crescidos pela técnica de epitaxia por feixe molecular (MBE, Molecular Beam Epitaxy). Esses pontos quânticos emitem radiação no intervalo de 1,3 üm a 1,5 üm (0,95 eV a 0,83 eV), que corresponde à janela óptica onde ocorre a mínima atenuação do sinal em redes de transmissão por fibras ópticas. Realizamos dois tipos de estudo em dois conjuntos de amostras. No primeiro caso analisamos a influência de alguns parâmetros de crescimento nas propriedades ópticas desses pontos quânticos. No segundo caso, analisamos a influência de um tratamento térmico nas propriedades ópyicas. Resultados de fotoluminescência (PL - photoluminescence) para o primeiro estudo mostraram uma grande influência da velocidade de crescimento nos espectros de emissão que apresentaram múltiplos picos, muito provavelmente associados com o estado fundamental e seus respectivos estados excitados dos pontos quânticos. Para o segundo estudo os resultados de PL mostraram que a emissão óptica consistia de uma larga banda situada entre 1,3 a 1,5 üm. Entretanto, observou-se que, após tratamento térmico durante 3 horas a uma temperatura de 550 ºC, a intensidade da PL aumentou por um fator 3. Além disso, a larga banda observada tornou-se um conjunto de pelo menos 5 picos discretos. O efeito de tratamentos térmicos em poços quânticos é bem conhecido e foi bem explorado na literatura. Em pontos quânticos, os mesmos efeitos também existem, porém, outros de igual importância tembém se apresentam. Dentre os mais importantes podemos citar a redistribuição dos tamanhos dos pontos quânticos, que podem em alguns casos limites fazer com que o ponto quântico desapareça, e a redistribuição das tensões entre a interface ponto quântico/matriz. Neste trabalho... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: This study investigated InAs large quantum dot on GaAs substrate grown by the techique of molecular beam epitaxy (MBE). These quantum dots emit in the spectral range of 1.3 üm and 1.5 üm (0.95 eV to 0.83 eV), which corresponds to the window of minimal signal attenuation on transmission networks by optical fiber. We have performed two kinds of study into two different sets of samples. In the first case, we have analyzed the influence of some growth parameters on the optical properties of these quantum dots. In the second one, we have analyzed the influence of a thermal treatment on the optical properties. Results of photoluminescence (PL) on the first study showed a great influence of growth velocity in the PL spectra line shape. For the second study the results of PL on an as grown sample showed that the emission signal was a large optical band in the wave length range of 1.3 üm and 1.5 üm. However, it was observed that after the thermal treatment of 3 hours at a temperature of 550 ºC, the intensity of these PL emissions increased by a factor 3. Moreover, the observed large band has become a series of at least 5 discrete peaks. The effect of heat treatments in quantum wells is well known and has been well explored in literature. In quantum dot, the same effects are expected; however, other equally important effects are also present. The most important is the size redistribution of the quantum dots, which can in some limit cases, vanish these quantum dot. Our study identified the origin of these multiple peaks, and found emissions of PL at room temperature in the optical window between 1.3 and 1.5 üm. / Doutor

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No. of bitstreams: 2 Dissertação - José Antônio do Nascimento Neto - 2015.pdf: 1464228 bytes, checksum: 6ffcc85c1cb4ac729567b0a5239e3030 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2015-05-18 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Manganese-doped ZnS nanoparticles (ZnS:Mn) are attractive quantum dots (QDs) for applications in several areas of science and technology due to its high luminescence and low toxicity. In this work we describe the synthesis of ZnS:Mn nanoparticles by co-precipitation synthesis method in aqueous medium, using acetate and chloride salts as precursors of Zn and Mn ions and sodium sulfide as sulfur precursor. An investigation of the effect of the ions precursor salts was carried auto on the nanoparticles composition, crystal structure and optical properties. Atomic absorption spectroscopy, X-ray photoelectron spectroscopy, UV-visible spectroscopy and spectrofluorometry have been used to characterize the doping status, the crystal structure, and the optical properties of the obtained ZnS:Mn nanoparticles. Using 2.4 – 4.8% Mn to Zn molar ratio in the synthesis were obtained nanoparticles presenting a doped range of 0.3 – 1.2%, for both precursor investigated. It was found a synthesis strategy based on chloride salts, which allowed the preparation of nanoparticles free of chloride ions. The x ray diffraction analysis showed that the zinc blend structure is the only crystalline phase present in the nanoparticles, and the mean size estimated by Debye-Scherrer was in the range of 3 - 5 nm. The photoluminescence spectra (PL) in the range of 350 - 700 nm of the nanoparticles prepared from both precursor salts present only a intense emission at 590 nm (excitation at 335 nm) assigned to the 4T1–6A1 transition within the 3d shell of Mn2+, which indicates that the ZnS nanocrystals were successfully doped. The photoluminescence quantum yields (PL QYs) measured for the nanoparticles were in the range of 1.5 - 3%, which are in the range of that presented in the literature for ZnS:Mn QDs prepared by aqueous synthesis without further surface treatment. / As nanopartículas de sulfeto de zinco dopadas com manganês (ZnS:Mn) apresentam-se como pontos quânticos (quantum dots, QDs) bastante atraentes para aplicações em diversas áreas da ciência e tecnologia por apresentarem alta luminescência e baixa toxicidade. Nesse trabalho foi investigado o efeito dos sais precursores dos íons zinco e manganês, acetato e cloreto, na composição, nas propriedades estruturais e nas propriedades ópticas de nanopartículas de ZnS:Mn sintetizadas pelo método de coprecipitação em meio aquoso, utilizando o sulfeto de zinco como fonte de enxofre. A caracterização composicional das nanopartículas realizada por espectroscopia de dispersão de raios X (EDS) mostrou que a relação Zn:S obtida nos nanocristais foi em média 1:08 e a análise por espectroscopia da absorção atômica mostrou que a dopagem obtida (relação molar Mn/Zn 0,3 - 1,2%) é inferior à empregada na síntese (relação molar Mn/Zn 2,4 - 4,8%). Foi estabelecida uma metodologia de síntese a partir do sal de cloreto que permitiu a obtenção de nanopartículas livres de íons cloreto. As análises por difratometria de raios X mostraram a presença de uma única fase cristalina (blenda de zinco) em todas as nanopartículas. Não houve diferença significativa entre os tamanhos médios (estimados pela equação de Debye-Scherrer) das nanopartículas obtidas com os dois sais precursores, tendo sido obtidas nanopartículas com tamanhos médios de 3 a 5 nm. As análises por UV-Vis mostraram um deslocamento da banda de absorção para comprimentos menores do que o ZnS (bulk) indicando o efeito de confinamento quântico nas nanopartículas obtidas, devido a dopagem com manganês e do tamanho das nanopartículas. O espectro de emissão de todas as nanopartículas mostraram apenas um pico com o máximo de emissão em 590nm, o que confirma a dopagem do ZnS apenas com os íons Mn2+. Os valores de rendimento quânticos determinados ficaram na faixa de 1,5% – 3%, que são condizentes com os apresentados na literatura para nanopartículas de ZnS:Mn sintetizadas em meio aquoso, sem posterior funcionalização. Os resultados obtidos estimulam a realização de novas sínteses a partir dos precursores cloretos visando a obtenção de nanopartículas com maior rendimento quântico e, passíveis de serem funcionalizadas com diferentes ligantes.

Terahertz (THz) technology is still currently a rapidly developing area of research with applications already demonstrated in the fields of biology, medicine, security, chemical/materials inspection and astrophysics to name a few. The diversity of applications which require the generation and measurement of THz or sub-millimeter (sub-mm) electromagnetic (EM) signals is the result of the vast number of chemical elements and compounds which exhibit molecular transitions and vibrational behavior that occur at frequency ranges corresponding to the so-called 'THz gap', roughly defined as 0.05-10 THz. The THz gap was named as such because of the relative difficulty in generating and analysing EM waves in this frequency band. This was due to the inherent challenges in generating either electrical signals with response periods below 1 picosecond (ps), or optical signals with wavelengths in the far-infrared (FIR) range. High absorption of THz signals in atmosphere via absorption by molecules such as H2O also impeded early developments and is a key issue in THz systems even today. There is now a wide variety of THz system solutions, each of which exhibits a different set of operational advantages and limitations. Arguably, the most well-established THz technique to date is based on the use of photoconductive antennas (PCAs) driven by ultrafast pulsed or dual-wavelength laser systems. This technique is the basis for the work presented in this thesis, which is an investigation into the potential utilisation of quantum dot (QD)-based semiconductor materials and devices in THz systems. This thesis discusses the work carried out in the development of a novel class of PCA devices which were postulated to enable efficient optical-to-THz signal conversion, whilst also overcoming several major limitations normally exhibited by PCA devices such as limited optical wavelength pumping range and thermal breakdown. To summarise briefly, these issues were addressed by considering: the additional pump absorption energy ranges enabled by the inclusion of multiple bandgap-engineered semiconductor materials and quantum-confined structures; the higher thermal conductivity and hence pump tolerance exhibited by relatively high-quality (low defect) absorption layers; and by simultaneously harnessing the ultrafast charge carrier modulation exhibited by the integrated QDs. Additionally, some work was carried out using QD-based lasers as pump sources, with the initial intention to explore the feasibility of a fully QD-based THz transceiver system and draw some conclusions as to the future potential for ultra-compact or even lab-on-chip THz systems, for example.

Various colloidal delivery systems, including polymeric nanoparticles, metal colloids, liposomes, and microemulsions have been reported to enhance the delivery of therapeutic agents following intranasal administration. However, the mechanisms involved in the uptake of these nanomaterials, especially those in the ultrafine size ranges (diameter < 20 nm) through nasal mucosa and their subsequent biodistribution in the body are not well characterized. The objectives of this study address the knowledge gap regarding ultrafine nanoparticle transfer in the nasal mucosa by quantifying nanoparticle uptake and biodistibution patterns in the presence and absence of known inhibitors of endocytic processes. The uptake of ~ 10 nm fluorescent quantum dots (QDs) was investigated by measuring the concentration of QDs following exposure to bovine respiratory and olfactory mucosal explants. An inductively coupled optical emission spectroscopy method was developed to measure the amount of QDs within the tissues. The results demonstrated that carboxylate-modified QDs (COOH-QDs) show ~2.5 fold greater accumulation in the epithelial and submucosal regions of the olfactory tissues compared to the respiratory tissues. Endocytic inhibitory studies showed that in respiratory tissues clathrin-dependent, macropinocytosis and caveolae-dependent endocytosis process were all involved in the uptake of COOH-QDs. Whereas in olfactory tissues, clathrin-dependent endocytosis was the major endocytic pathway involved in uptake of COOH-QDs. Additional energy-independent pathways appeared to also be active in the transfer of COOH-QDs into the olfactory mucosa. Interestingly, PEGylated quantum dots (PEG-QDs) of similar size ~15 nm were not internalized into the bovine nasal tissues. In vivo fluorescence imaging was used to study the biodistribution of quantum dots following nasal instillation in mice. These studies showed that majority of COOH-QDs remain in the nasal tissues for relatively long periods of time (up to 24 h) whereas PEG-QDs showed no such accumulation. Biodistribution studies of gold nanoparticles (~15 nm) in mice using micro-CT showed that gold nanoparticles were transferred to the posterior turbinate region and a fraction of the administered dose distributed to regions in close proximity to the olfactory bulb. Both NIR imaging and micro-CT imaging were useful tools for visualization of in vivo nanoparticle distribution. A diazepam-containing microemulsion (dispersed phase ~40 nm) was formulated to investigate the uptake mechanisms utilized for fluid-phase colloidal dispersions in the nasal mucosa. The resulting diazepam-containing microemulsion showed enhanced transfer of the drug into the bovine nasal respiratory and olfactory tissues. It is unclear if endocytosis of the fluid-phase nanodispersions played a role in drug absorption from the microemulsions in a manner similar to the uptake of solid-phase nanoparticles, however, since there was significant loss of the epithelial cell layer following exposure to the microemulsion formulation which likely altered the barrier properties of the epithelium. These studies have increased the fundamental understanding of ultrafine nanoparticle uptake in the nasal tissues and the resulting nanoparticle biodistribution patterns. While ultrafine nanoparticles may have limited application in the development of efficient drug delivery systems, an understanding of the size-dependent and tissue-dependent processes responsible for the uptake of particulates into mucosal tissues will contribute to the rational development of nanoparticulate drug delivery strategies investigating the nasal and other routes of administration.

In this work, the algorithm used by AlphaZero is adapted for dots and boxes, a two-player game. This algorithm is explored using different numbers of convolutional filters and training loops, in order to better understand the effect these parameters have on the learning of the player. Different board sizes are also tested to compare these parameters in relation to game complexity. AlphaZero originated as a Go player using an algorithm which combines Monte Carlo tree search and convolutional neural networks. This novel approach, integrating a reinforcement learning method previously applied to Go (MCTS) with a supervised learning method (neural networks) led to a player which beat all its competitors.

The focus of this dissertation is on the interactions of compounds containing group 12 and 16 elements. This work is presented in three major parts. First, the interaction of the synthetic dithiol N,N’-bis(2-mercaptoethyl)isophthalamide), abbreviated BDTH2, with selenite. Second, the interaction of cysteine with Cd(II) and the biologically relevant Cd-Cysteine crystal structure. Third, the green synthesis of CdSe quantum dots (QDs). The interaction of BDTH2 with selenite is different from the interactions with other metals and metalloids previously studied. Under ambient conditions, BDTH2 is oxidized to the disulfide, BDT(S-S), while selenite is reduced to elemental selenium. However, under carefully controlled conditions, the reaction of BDTH2 with selenite produces a mixture of BDT(S-S) and the covalently bound Se(II) species, BDT(S-Se-S). While the mixture could not be separated, experimental 77Se NMR combined with computational analysis confirmed the presence of BDT(S-Se-S). The interaction of the amino acid cysteine with Cd(II) was studied as a means to sequester, and potentially recycle, Cd(II) from bulk CdS waste. Single crystals of Cd(Cys)Cl·H2O were grown, and the crystal structure determined. Surprisingly, this is only the second structure to be determined by X-ray crystallography of a compound containing the Cd-Cysteine unit. Not only does this structure have biological relevance, but it also corrects a structure proposed in 1965. Using the knowledge gained from studying the interaction of BDTH2 with selenite, a green synthesis of water-soluble CdSe QDs by the reaction of selenite with Cd(Cys)Cl·H2O in water at room temperature was developed. This green method for the synthesis of CdSe QDs was extended to ZnSe and HgSe QDs. The mechanism of CdSe formation was investigated using Cd(II) combined with various thiols.