Thesis (Ph. D.)--University of Nevada, Reno, 2008. / "December 2008." Includes bibliographical references (leaves 161-173). Online version available on the World Wide Web.

Thesis (Ph. D.) --Memorial University of Newfoundland, 1997. / Restricted until November 1998. Bibliography: leaves 264-281.

Thesis (M.S.)--University of Texas at El Paso, 2008. / Title from title screen. Vita. CD-ROM. Includes bibliographical references. Also available online.

Made available in DSpace on 2014-06-11T19:23:29Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-07-06Bitstream added on 2014-06-13T19:50:18Z : No. of bitstreams: 1 pineiz_tf_me_bauru.pdf: 2151623 bytes, checksum: a3aa74574b72ca684cf6ef1a0dc34297 (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Dióxido de estanho (Sn'X IND. 2') é um semicondutor de bandgap largo com condutividade do tipo-n na forma não dopada, sendo aplicado em dispositivos diversos. Neste trabalho, filmes finos e géis secos de Sn'X IND. 2' dopados com os íons terras-raras 'Ce POT. 3+' e Eu POT 3+' foram sintetizados através do processo sol-gel. Por outro lado, filmes finos de GaAs têm também sido amplamente utilizados, devido a alta mobilidade eletrônica e transição direta. Neste trabalho, também foram produzidos filmes finos de GaAs através da técnica de evaporação resistiva. Serão mostrados e discutidos aqui resultados referentes a filmes finos de Sn'X IND. 2' dopado com íons terras-raras, filmes finos de GaAs e resultados referentes ao crescimento de filmes finos de GaAs sobre filmes finos de SnO2 dopados com terras-raras. Medidas de absorção óptica permitiram avaliar a qualidade óptica dos filmes e estimar a energia do bandgap. Dados de difração de raios-X mostraram estrutura do tipo rutilo e fase cassiterita dos filmes de Sn'X IND. 2' e também as direções principais dos filmes de GaAs. A microscopia eletrônica de varredura permitiu a espessura e a qualidade morfológica da heterojunção, tanto com relação à interface Sn'X IND. 2'/GaAs como da superfície. A investigação das propriedades elétricas em Sn'X IND. 2' mostra a alta resistividade do material devido ao caráter aceitador de íons terras-raras na matriz. Foi investigada também a captura de elétrons fotoexcitados por centros de 'Ce POT 3+' termicamente ativados. Do modelo proposto, foram obtidos parâmetros importantes, como a barreira de captura devido aos defeitos dominantes. Resistividade em função da temperatura na heterojunção Sn'X IND. 2'/GaAs mostrou a diminuição da resistência do conjunto. / Tin dioxide (Sn'X IND. 2') is a wide bandgap semiconductor material whith n-type conductivity the undoped form. This compound has been applied for several kinds of devices. In this work, thin films and xeogels of Sn'X IND. 2' doped with the rare-earth ions 'Ce POT. 3+' and Eu POT 3+' have been produced by the sol-gel process. On the other band, GaAs thin films have also been widely used, due to high electronic mobility and direct bandgap transition. In this work, GaAs thin films have been deposited by the resistive evaporation technique. It is shown and discussed here results concerning rare-earth doped Sn'X IND. 2' thin films. GaAs thin films and the growing of GaAs on the top of rare-earth doped Sn'X IND. 2'. Through the optical absorption spectra it has been possible to evaluate the films optical quality and to estimate the optical bandgap. X-ray diffraction data show the rutile like structure and cassiterie phase of Sn'X IND. 2' thin films and also show the main directions of GaAs films. Scanning electron microscopy allowed evaluating the thickness and morphological quality of the heterojunction, concerning the infarce as well as the surface. Investigation of electrical properties of Sn'X IND. 2' shows high resistivity of this material due to the acceptor-lide character of rare-earth ions in the matrix. It has also been investigated the trapping of photo-induced electrons by the thermally activated Ce centers. From a proposed model, it has been obtained some relevant parameters, such as the capture barrier due to the dominant defects. Data of resistivity as function of temperature for the Sn'X IND. 2'/GaAs heterojunction show the decrease of overall resistance.

Made available in DSpace on 2014-12-17T14:07:17Z (GMT). No. of bitstreams: 1 LauraXL_DISSERT.pdf: 3047950 bytes, checksum: 570af1df35d3161d6677ac6ec832e390 (MD5) Previous issue date: 2013-12-16 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / Recent studies are investigating a new class of inorganic materials which arise as a promising option for high performance applications in the field of photoluminescence. Highlight for rare earth (TR +3 ) doped, which have a high luminous efficiency, long decay time and being able to emit radiation in the visible range, specific to each element. In this study, we synthesized ZrO2: Tb +3 , Eu +3 , Tm +3 nanoparticles complex polymerization method (CPM). We investigated the influences caused by the heat treatment temperature and the content of dopants in zirconia photoluminescent behavior. The particles were calcined at temperature of 400, 500 and 600 ? C for two hours and ranged in concentration of dopants 1, 2, 4 and 8 mol% TR +3 . The samples were characterized by thermal analysis, X-ray diffraction, photoluminescence of measurements and uv-visible of spectroscopies. The results of X-ray diffraction confirmed the formation of the tetragonal and cubic phases in accordance with the content of dopants. The photoluminescence spectra show emission in the region corresponding simultaneous to blue (450 nm), green (550 nm) and red (615 nm). According to the results, ZrO2 particles co-doped with rare earth ions is a promising material white emission with a potential application in the field of photoluminescence / Estudos recentes investigam uma nova classe de materiais inorg?nicos que surgem como uma op??o promissora em aplica??es de alto desempenho no campo da fotoluminesc?ncia. Destaque para f?sforos dopados com ?ons de terras raras (TR +3 ), que possuem uma alta efici?ncia luminosa, um longo tempo de decaimento e por serem capazes de emitir radia??es na faixa do vis?vel, espec?ficas de cada elemento. Neste trabalho, foram sintetizadas nanopart?culas de ZrO2:Tb +3 , Eu +3 , Tm +3 pelo m?todo de polimeriza??o dos complexos (MPC). Foram investigadas as influ?ncias causadas pela temperatura de tratamento t?rmico e pelo teor dos dopantes no comportamento fotoluminescente da zirc?nia. As part?culas foram calcinadas nas temperaturas de 400, 500 e 600?C durante duas horas e a concentra??o dos dopantes variou em 1, 2, 4 e 8% mol TR +3 . As amostras foram caracterizadas por an?lises t?rmicas (TG/ DSC), difra??o de raios X (DRX), medidas de fotoluminesc?ncia (FL) e espectroscopia na regi?o do UV-Vis?vel (UV-vis). Os resultados de difra??o de raios X confirmaram a forma??o das fases tetragonal e c?bica de acordo com o teor de dopantes. Os espectros de fotoluminesc?ncia apresentam emiss?es simult?neas correspondentes na regi?o do azul (450 nm), do verde (550 nm) e do vermelho (615 nm). De acordo com os resultados obtidos, as part?culas de ZrO2 codopadas com ?ons de terras raras apresentam-se como um material promissor para emiss?o no branco com um potencial de aplica??o no campo da fotoluminesc?ncia

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Les terres rares (TR) sont aujourd’hui les « vitamines » des nouvelles technologies, elles se retrouvent dans tous les objets technologiques du quotidien et contribuent notablement au développement d’énergies vertes principalement par l’intermédiaire d’aimants permanents à base de terres rares (APTR). Ces derniers, de type NdFeB ou SmCo, représentent actuellement plus de 50 % du marché des TR et offrent un fort potentiel de recyclage. La présente étude se concentre sur le recyclage et la valorisation des APTR, principalement grâce au développement de l’électrochimie en milieu liquide ionique (LI) qui permet d’atteindre les potentiels de réduction des TR (< -2 V vs. ENH). Samarium, néodyme, dysprosium, praséodyme et cobalt ont effectivement été électrodéposés dans [C1C4Pyrr][Tf2N] suivant une méthode potentiométrique à 25 °C et sur une électrode de carbone vitreux.Deux méthodes globales de recyclage sont finalement proposées et ont été appliquées à des APTR industriels. La première est entièrement électrochimique. Elle est basée sur une phase d’électrodissolution de l’APTR dans le LI puis d’une électrodéposition sélective permettant de récupérer les métaux de transition. Une électrodéposition des TR est ensuite envisageable. La deuxième méthode s’appuie sur une lixiviation acide afin de séparer efficacement les métaux de transition des TR grâce à la formation de sels phosphatés. Une dissolution des sels obtenus dans un LI permettrait ensuite d’électrodéposer les ions métalliques. / Rare earth elements (REE) are currently essential for new technologies development; from everyday life objects to green energies devices, they are especially used in permanent magnets. NdFeB and SmCo permanent magnets represent more than 50% of the REE market and offer a high recycling opportunity. The present study focuses on their recycling, mainly via electrochemistry in ionic liquid medium (IL), which enables to reach the reduction potentials of REE (< -2 V vs. ENH).Samarium, neodymium, dysprosium, praseodymium and cobalt were successfully electrodeposited in [C1C4Pyrr] [Tf2N] according to a potentiometric method at 25 ° C and on a glassy carbon electrode.Two general recycling methods are finally proposed and have been applied to industrial permanent magnets. The first uses only electrochemistry and is based on a first magnet electrodissolution step in the IL followed by a selective electroplating to recover the transition metals. Electrodeposition of REE could then be possible. The second method starts by an acid leaching of the magnet in order to efficiently separate the transition metals from REE via the formation of phosphate salts. Dissolution of the salts obtained in LI would then enable to electrodeposit the metal ions.

Orientadora: Sandra Regina Pombeiro Sponchiado / Banca: Mauricio Cesar Palmieri / Banca: Gustavo Rocha de Castro / Banca: Luis Augusto Martins Ruotolo / Banca: Elma Neide Vasconcelos Martins Carrilho / Resumo: A biossorção é considerada uma tecnologia eficiente, economicamente viável e ecologicamente sustentável comparada aos métodos convencionais para a remoção e recuperação de metais de alto valor agregado, como as terras-raras (TRs), presentes em efluentes industriais. No entanto, o grande desafio para o sucesso deste processo é selecionar um biossorvente com alto desempenho, seletividade, disponibilidade em grande quantidade e baixo custo. Neste contexto, o presente estudo avaliou a capacidade de biossorção dos elementos cério e lantânio pela biomassa pigmentada produzida pelos fungos Aspergillus nidulans (mutante MEL1) e Cladosporium sp. como também o efeito dos pré-tratamentos físicos e químicos. Dentre os biossorventes estudados, a biomassa de A. nidulans (mutante MEL1) foi selecionada por apresentar uma maior taxa de crescimento (37,5 mg L-1 h-1) como também uma capacidade de remoção para íons Ce3+ (27%) e La3+ (21%) superior ao Cladosporium sp. Os resultados referentes ao efeito dos pré-tratamentos mostraram que a biomassa pré-tratada com CaCl2 (0,5 mol L-1 à temperatura ambiente) exibiu uma maior capacidade biossortiva para Ce3+ (qmax = 76,92 mg g-1), enquanto que a biomassa pré-tratada com NaOH (0,2 mol L-1 à temperatura ambiente) apresentou maior biossorção para La3+ (qmax = 96,15 mg g-1). Em relação a manutenção do pH em 5,1 durante o processo de biossorção foi observado um aumento de 33% e 20% na capacidade biossortiva de Ce3+ e La3+ respectivamente, em comparação ao ... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Biosorption is considered to be an efficient, economically viable and ecologically sustainable technology compared to conventional methods for the removal and recovery of high value - added metals, such as rare earths (TRs), present in industrial effluents. However, the major challenge for the success of this process is to select a biosorbent with high performance, selectivity, availability in large quantity and low cost. In this context, the present study evaluated the biosorption capacity of the cerium and lanthanum elements by the pigmented biomass produced by the fungi Aspergillus nidulans (MEL1 mutant) and Cladosporium sp . as well as the effect of physical and chemical pre - treatments. Among the biosorbents studied, A. nidulans biomass (MEL1 mutant) was select ed because it presented a high growth rate (37.5 mg L - 1 h - 1 ) as well as a higher removal capacity for Ce 3+ (27%) and La 3+ (21%) than Cladosporium sp . The results sh owed that the free biomass pretreated with CaCl 2 (0.5 mol L - 1 at environment temperature) showed higher biosortive capacity for Ce 3+ (q max = 76.92 mg g - 1 ), while the biomass pretreated with NaOH (0.2 mol L - 1 at environment temperature) presented higher biosorption for La 3+ (qmax = 96.15 mg g - 1 ). In relation to the maintenance of pH in 5.1 during the biosorption process, a 33% and 20% increase in the bioso rtive capacity of Ce 3+ and La 3+, respectively, was obse rved, compared to the process without pH adjustment. With the chara... (Complete abstract click electronic access below) / Mestre

The scientific relevance and potential for technological applications of complex materials have made them the focus of active investigation in order to fully charac- terize the competition and interactions between their electronic, structural, orbital, and spin degrees of freedom. Optical and terahertz (THz) spectroscopy provide ac- cess to electronic and low frequency quasiparticle responses, and therefore play a key role in understanding the fundamental mechanisms which dictate the macroscopic properties of complex materials. Time-resolved experiments, in turn, have the po- tential to disentangle the various coexisting energy scales through a careful selection of the pump and probe characteristics. This work investigates the role played by the electronic, structural and magnetic excitations in the insulator-to-metal transi- tions (IMT) of VO2, V2O3 and NdNiO3, through studies under different conditions of temperature, strain, doping and photoexcitation. Our work shows that a complete understanding of the IMT in VO2 requires sev- eral length scales and time scales to be considered. Indeed, epitaxial strain leads to anisotropy in the IMT characteristics of thin films of (100) and (110) VO2/TiO2, measured using THz spectroscopy, which can be explained by strain induced modi- fications both in the (microscopic) V3d orbitals and in the geometry of mesoscopic metallic domains. On the other hand, ultrafast studies which track, with femtosecond resolution, the electronic and structural dynamics of VO2 thin films following THz excitation reveal a delay in the onset of the structural response with respect to the electronic one, lending support to the correlation rather than Peierls driven picture of the IMT in this material. As for V2O3, the IMT is seen to occur via nucleation and growth of metallic domains, as previously reported in VO2. However, a scaling of the photoinduced conductivity dynamics rise time is further identified, which reveals the temperature and fluence dependence of the nucleation and growth process. Finally, strained NdNiO3 films exhibit a two step dynamical conductivity response following optical excitation, different from that of the vanadates with which they share a complex, albeit more tunable, phase diagram. This hints at a significant role being played by the magnetic structure during the IMT in NdNiO3.