Tesi sul tema "Pt"
Segui questo link per vedere altri tipi di pubblicazioni sul tema: Pt.
Cita una fonte nei formati APA, MLA, Chicago, Harvard e in molti altri stili
Vedi i top-50 saggi (tesi di laurea o di dottorato) per l'attività di ricerca sul tema "Pt".
Accanto a ogni fonte nell'elenco di riferimenti c'è un pulsante "Aggiungi alla bibliografia". Premilo e genereremo automaticamente la citazione bibliografica dell'opera scelta nello stile citazionale di cui hai bisogno: APA, MLA, Harvard, Chicago, Vancouver ecc.
Puoi anche scaricare il testo completo della pubblicazione scientifica nel formato .pdf e leggere online l'abstract (il sommario) dell'opera se è presente nei metadati.
Vedi le tesi di molte aree scientifiche e compila una bibliografia corretta.
1
Paulino, Marcia Elizangela. "\"Estudo da reação de eletro-oxidação de metanol sobre eletrodos monocristalinos de platina modificados com eletrodepósitos de cobre e estanho\"". Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/75/75131/tde-12042007-094545/.
Testo completoAbstract (sommario):
A eletro-oxidação de metanol foi estudada em eletrodos de platina monocristalina de índices de Miller (100) e (111) modificados superficialmente com metais cobre e estanho nas condições de UPD (Underpotential Deposition) e OPD (Overpotential Deposition). Os experimentos foram conduzidos em EDRMP (Eletrodo de Disco Rotatório com Menisco Pendente) em conjunto com as técnicas eletroquímicas. Os depósitos de cobre foram realizados em condições de UPD e OPD enquanto que estanho em OPD, dada as limitações de rearranjo estrutural da superfície cristalográfica do eletrodo. As análises dos resultados indicaram que o grau de recobrimento dos metais sobre o suporte é menor que uma monocamada, cerca de 10% desta. Tais resultados comparados com a literatura indicam a formação de aglomerados, ilhas, em estruturas bi e tridimensionais no caso do cobre. Em estanho foi atingido maior grau de recobrimento. No entanto, comparando os resultados para estanho com o da literatura, este não se depositou na forma de adátomos, mas como hidróxido ou sulfato. Esta forma de interação do estanho com a platina é a responsável pela diminuição do potencial de oxidação do metanol sobre o substrato. Na eletro-oxidação do metanol os melhores resultados foram obtidos na presença de estanho, no entanto ressalta-se que neste caso a influência da rotação não foi significante e as medidas de cronoamperometria indicaram melhor atividade nesta situação com o eletrodo modificado.Methanol oxidation reaction was studied with copper and tin modified single-crystal electrodes. This study was carried out using UPD and OPD techniques using the EDRMP configurations the results showed that the coverage degree of copper and tin on platinum single-crystal as less than one monolayer (_ 10% monolayer) and possible with the formation of islands in bi and tridimenision. The deposition of copper was not good to the methanol oxidation reaction, possible due to a higher solvatation by anions at the Cu sites, conducting to a blocking effect on the Pt neighboring atoms. The tin deposition have shown a higher activity for methanol oxidation reaction. This ascribed to the hydroxides formation at tin sites, which increase the kinetics of CO oxidation following the bifunctional mechanism.
2
Макаренко, К. В. "Високочутливий газовий сенсор на основі тришарової плівки Pt/TiO2/Pt". Master's thesis, Сумський державний університет, 2020. https://essuir.sumdu.edu.ua/handle/123456789/82015.
Testo completoAbstract (sommario):
Мета роботи полягає у аналізі особливостей при розробці конструкції
високочутливого напівпровідникового газового сенсору на основі тришарової
плівки Pt/TiO2/Pt, у тому числі і на підкладці із гнучкого матеріалу, а також у
вивченні його технічних характеристик, в тому числі при дії різних факторів.
У роботі описані та проаналізовані особливості конструкції чутливого
елементу напівпровідникового газового сенсора на основі тришарової плівки
Pt/TiO2/Pt. Дана багатошарова плівкова система була отримана методом
реактивного магнетронного розпилення на постійному струмі. Також при
виготовленні сенсору виготовлявся метод фотолітографії. При вимірюванні
електрофізичних властивостей сенсору (реакція зміни електроопору на
концентрацію газу) використовувався автоматизований комплекс, що
складається з газової камери, системи керування та реєстрації сигналу. Потік та
концентрація газу були керовані двома контролерами, які керуються через
програмне забезпечення.
3
Nxumalo, Silethelwe. "The Pt₈V ordering transformation in Pt 11 at. % V". Doctoral thesis, University of Cape Town, 2006. http://hdl.handle.net/11427/4958.
Testo completoAbstract (sommario):
Includes bibliographical references (leaves 121-125).The Pt₈V ordering transformation in Pt 11 qt.% V alloys has been studied. The study included determining the thermodynamic stability of Pt₈V, the kinetics of Pt₈V ordering transformation and the strengthening due to the presence of the ordered phase. Transmission electron microscopy, using election diffraction and dark and bright field imaging, and X-ray diffraction were used for structural characterisation. Electrical resistivty was used to investigate the kinetics of Pt₈V ordered phase. Microhardness measurements were used to investigate the Pt₈V ordered phase and its effects on hardness.
4
Rufino, Élen Cristina Gonçalves. "Estudo da estabilidade de eletrocatalisadores Pt/C e Pt-RuOx/C". Universidade de São Paulo, 2011. http://www.teses.usp.br/teses/disponiveis/59/59138/tde-08082011-134145/.
Testo completoAbstract (sommario):
Neste trabalho, foram investigadas as modificações na estrutura e a estabilidade de eletrocatalisadores Pt/C e Pt-RuOx/C, preparados pela decomposição térmica de precursores poliméricos. Experimentos de varredura de potencial e experimentos com potencial fixo foram realizados com o objetivo de acelerar os mecanismos de degradação dos catalisadores. Para identificar e compreender os fatores que levaram a degradação dos catalisadores, foram realizados experimentos para determinação da área superficial eletroquimicamente ativa dos catalisadores, através da adsorção/oxidação de CO, análises dos catalisadores por difração de raios X (DRX) e análises das soluções por espectrometria de massa com fonte de plasma indutivamente acoplado (ICP-MS).Foram avaliadas as modificações na estrutura e a estabilidade dos eletrocatalisadores Pt/C e Pt-RuOx/C quando submetidos a 2000 varreduras de potencial em diferentes intervalos (i) 0,05-0,5 V; (ii) 0,05-0,7 V e (iii) 0,05-0,9 V na presença e na ausência de metanol e também quando submetidos a um potencial fixo por várias horas. Foi observado, de maneira geral, um aumento no tamanho dos cristalitos, dissolução dos componentes metálicos e uma redução da área superficial eletroquimicamente ativa. Os resultados obtidos na primeira parte do trabalho também mostraram que a degradação dos catalisadores foi maior na presença de metanol e que condições de potencial cíclico aceleram os mecanismos de degradação quando comparadas a condições de potencial fixo. Após uma melhor compreensão dos mecanismos de degradação, a segunda parte do trabalho foi voltada para investigação da influência de modificações no método Pechini durante a síntese dos eletrocatalisadores Pt-RuOx/C na estrutura e estabilidade destes catalisadores. Para isto, os catalisadores foram submetidos a varreduras de potencial entre 0,05-0,6 V e experimentos com potencial fixo em 0,6 V na presença de metanol. Para avaliar a influência das modificações no método de preparo na eletroatividade dos catalisadores, foram realizados testes em uma DMFC utilizando uma MEA (Membrane Electrode Assemblies) formada por ânodo Pt-RuOx/C / membrana de Nafion® 117 / cátodo Pt/C comercial (E-TEK). O estudo da estabilidade mostrou que o catalisador cuja mistura composta pelas resinas e suporte de carbono foi submetida à rotação em um moinho de bolas antes do tratamento térmico se mostrou bem mais estável que os demais catalisadores (submetidos ao ultrassom). Já os catalisadores preparados com uma única resina contendo Pt e Ru e submetidos ao ultrassom antes do tratamento térmico, mostraram os melhores resultados nos experimentos em condições operacionais em célula a combustível unitária. A terceira e última parte deste trabalho teve por objetivo investigar os efeitos da utilização do carbono Black Pearls 2000 como suporte na estabilidade e eletroatividade de eletrocatalisadores Pt-RuOx/C. Testes em uma DMFC e varreduras de potencial na presença de metanol foram realizados e os resultados comparados com os obtidos para os catalisadores sintetizados com carbono Vulcan XC-72. Os catalisadores sintetizados com carbono Black Pearls 2000 apresentaram maior área superficial eletroquimicamente ativa que os catalisadores preparados com carbono Vulcan XC-72 pelo mesmo procedimento, indicando uma melhor dispersão das partículas metálicas sobre o suporte, uma vez que a quantidade de Pt nos catalisadores foi mantida constante. Esta melhor dispersão das nanopartículas metálicas sobre o suporte resultou em maiores valores de densidade de potência e densidade de corrente em célula a combustível unitária operando com metanol na fase líquida. Para dois dos três catalisadores, o desempenho foi superior ao catalisador comercial da E-TEK. A dissolução dos componentes metálicos e a redução da área superficial eletroquimicamente ativa foi menor para os catalisadores preparados com carbono Black Pearls 2000 e o tamanho de cristalito não variou após 2000 varreduras de potencial. Todos estes resultados mostram uma maior estabilidade dos catalisadores preparados com este suporte.In this work, changes in the structure and stability of the Pt/C and Pt-RuOx/C catalysts, prepared by the thermal decomposition of polymeric precursors, were investigated. Potential scans and constant potential experiments were carried out, to accelerate catalyst degradation mechanisms. To comprehend the catalyst degradation, determination of the electrochemical active surface area by means of the method based on the CO-stripping voltammetry curve, catalysts analyses by X-ray diffraction (XRD), and solution analyses by inductively coupled plasma mass spectrometry (ICP-MS) were accomplished.The changes in the structure and stability of Pt/C and Pt-RuOx/C electrocatalysts subjected to 2000 potential scans at different potential ranges (0.05-0.5, 0.05-0.7, and 0.05-0.9 V) were monitored in sulfuric acid solution, in the absence and in the presence of methanol. The influence of application of a constant potential for a prolonged time period was also investigated. As a general behavior, there was increase in particle size, dissolution of catalyst components, and reduction in the electrochemically active surface area. Catalyst degradation was more pronounced in the presence of methanol, and the cyclic potential conditions revealed higher degradation rate compared to the rate observed in constant potential conditions. After a better comprehension of the degradation mechanisms, the second part of this work focused on monitoring the influence of modifications made to the Pechini method during the synthesis of Pt-RuOx/C electrocatalysts on the structure and stability of these catalysts after they were subjected to a large number of potential scans between 0.05 and 0.6 V and at constant potential of 0.6V vs. RHE for a prolonged time period in sulfuric acid 0.5 mol L-1 and in methanol 0.1 mol L-1 solution. DMFC tests were accomplished using membrane electrode assemblies (MEAs) prepared by hot-pressing a pretreated Nafion® 117 membrane together with the Pt-RuOx anode and an E-TEK cathode, in order to compare the catalytic activity of catalysts prepared by different methods. The stability study demonstrated that the catalyst whose resin/carbon support mixture was agitated in a balls mill before being subjected to heat-treatment was more stable than the other prepared catalysts (subjected to ultrasound). The catalysts prepared with the single resin consisting of Pt and Ru, subjected to ultrasound before heat-treatment, furnished the highest power density in the single fuel cell. The third and last part of this work aimed to investigate the effects of the use of Black Pearls 2000 carbon support on the stability and electroactivity of the Pt-RuOx/C catalysts. DMFC tests and potential scans in the presence of methanol were performed, and results were compared with those obtained for the catalysts synthesized with Vulcan XC-72 carbon. Catalysts synthesized with Black Pearls 2000 carbon presented larger electrochemically active surface area compared to catalysts prepared with Vulcan XC-72 carbon using the same procedure. This indicates better metallic particles dispersion on the support, since the amount of Pt was kept constant in the catalysts. This better dispersion of metallic particles on the carbon support resulted in higher power density and current density in the single fuel cell operating with methanol in the liquid phase. The performance of two of the three prepared catalysts was better than that of E-TEK commercial catalyst. The dissolution of the metallic components and the reduction in the electrochemically active surface area was smaller for catalysts prepared with Black Pearls 2000 carbon, and the crystallite size did not change after 2000 potential scans. All these results demonstrate the superior stability of the catalysts prepared with this support.
5
Saouabe, Mohammed. "Influence du mode de préparation sur les propriétés de catalyseurs bimétalliques supportés : Pt-Ir, Pt-Re, Pt-Sn". Poitiers, 1992. http://www.theses.fr/1992POIT2320.
Testo completoAbstract (sommario):
Au cours de cette etude, nous avons compare les proprietes de catalyseurs bimetalliques de type reformage, prepares par des methodes classiques telles que la coimpregnation ou les impregnations successives, et une technique plus originale faisant appel a la formation d'un complexe ionique bimetallique a l'interieur de la porosite de l'alumine. L'ensemble des resultats obtenus sur les couples platine-iridium, platine-rhenium et platine-etain montrent que cette derniere methode de preparation conduit a une meilleure interaction entre les deux metaux sur une alumine de reformage. Cependant cette interaction depend de differents parametres lors de l'impregnation et de l'activation des precurseurs metalliques. Elle est optimale lorsque le catalyseur seche est active par reduction en presence d'hydrogene dilue en montee lente de temperature. En revanche, une calcination prealable a 400c entraine une segregation des metaux. En consequence la formation de l'alliage est inhibee lors de la reduction; neanmoins le degre de reduction du second metal, lorsque celui-ci est difficilement reductible comme dans le cas du rhenium ou de l'etain, est augmente en presence de platine. Ce phenomene peut s'expliquer par une reduction partielle des oxydes de second metal par spillover d'hydrogene en presence de platine. Le chlore ajoute sous forme d'acide chlorhydrique inhibe fortement les interactions platine-rhenium alors que la formation de l'alliage platine-etain n'est pas sensible a cet element. Enfin la nature du complexe mixte et la teneur globale en metaux jouent egalement un role sur l'interaction entre le platine et le second metal
6
Fonfé, Benjamin. "Hydrogenation of tetralin over oxide supported Pt and Pt-Pd catalysts". kostenfrei, 2008. http://mediatum2.ub.tum.de/doc/669041/669041.pdf.
Testo completo
7
Benlaharche, Tewfik. "Étude et modélisation thermodynamique du système Mo-Pt-Si". Thesis, Nancy 1, 2008. http://www.theses.fr/2008NAN10036/document.
Testo completoAbstract (sommario):
L’étude menée sur le système Mo-Pt-Si vise à contribuer à la connaissance d’alliages métalliques complexes destinés à des applications à hautes températures rencontrées dans les industries aéronautiques ou verrières. Sa description d’un point de vue thermodynamique est rendu difficile par son caractère réfractaire lié à la présence du molybdène d’une part et à sa complexité due au nombre élevé de ses constituants (3 éléments) d’autre part. Seule une approche du problème par une modélisation thermodynamique de type CALPHAD permet d’aboutir à un résultat significatif. Comme l’impose l’établissement d’une modélisation d’un système ternaire, à savoir l’étude préalable des trois bordures binaires, le premier volet de ce travail a été consacré à l’étude des systèmes Pt-Si, Mo-Pt et Mo-Si. Parallèlement au travail d’optimisation, des mesures expérimentales réalisées dans le cadre de cette étude (radiocristallographie, analyse thermique, microsonde,….) ont permis de déterminer les équilibres entre phases, les enthalpies de formation des différents composés intermétalliques ainsi que les mécanismes structuraux responsables des grands domaines de stabilité observés pour certaines phases. La première approche du système ternaire Mo-Pt-Si, obtenue à partir de la banque de données intégrant les optimisations binaires, a permis de cibler et interpréter des expériences de contrôles des équilibres entre phases en condition isotherme et anisotherme. Un nouveau siliciure ternaire a ainsi été découvert et pris en compte dans le calcul. Enfin, à travers de nombreux exemples nous montrons la cohérence de la modélisation avec l’ensemble des données expérimentalesThe study on the Mo-Pt-Si system contributes to the knowledge of complex metal alloy, which are intended for applications at high temperatures in the aerospace or glass industries. Its thermodynamic description is difficult because its refractory character related to the presence of the molybdenum and to its complexity due to the high number of the constituents (3 elements). Only an approach of problem by a modelling thermodynamics of CALPHAD type gives to a significant result. As imposes the establishment of a modelling of a ternary system by the study of three binary borders, the first part of this work was devoted to the study of Pt-Si, Mo-Pt and Mo-Si systems. Along with the optimization, an experimental measurements used in this study (X-ray, thermal analysis, microprobe,….) allowed to determine the equilibria phases, the enthalpies of formation of the various intermetallic compounds as well as the structural mechanisms responsible for large domains of stability observed for some phases. The first approach of the Mo-Pt-Si ternary system obtained from the database including the binary optimisations, allowed to interpret the experiments of controls of equilibria phases in isotherm and anisotherm conditions. A new ternary silicide was discovered and took into account in calculation. Finally, through many examples we show the agreement of the modelling with all experimental data
8
Nascimento, José Henrique do. "Sistemas fotônicos PT-simétricos". Universidade Federal de Alagoas, 2018. http://www.repositorio.ufal.br/handle/riufal/3512.
Testo completoAbstract (sommario):
The spatial evolution of a pair of resonant Bragg modes through a medium characterized by a complex one-dimensional PT -symmetric periodic relative electric permittivity is thoroughly investigated. By using the two wave model, analytic solutions of Maxwell’s equations are derived in the nonparaxial regime in order to investigate the periodic energy exchange between the Bragg modes for the Hermitian optical lattices as well as for complex lattices and also to investigate the spatial evolution of the real part of the electric field that propagates through this medium. Three regimes defined by the symmetry breaking point are discussed: below it, above it and at it. These regimes are determined by the existence of four complex eigenvalues below the symmetry breaking point, which collide and coalesce into a pair of complex doubly degenerate eigenvalues at the breaking point. Above the critical value each member of the pair bifurcates into a pair of complex values and now they have a nonzero real part. In the Hermitian case, it is demonstrated that a complete reciprocal energy transfer between the pair of Bragg modes, in a manner similiar to the Pendellösung effect known from X-ray diffraction by a crystal, takes place. When the optical lattice is complex, the dynamics of the energy transfer is completely different from the Hermitian case: below the symmetry breaking point there exist a very nonreciprocal beating-like oscillatory behavior of the energy transfer between the Bragg modes; above the symmetry breaking point the spatial evolution of the energy transfer grows unlimited but an oscillatory evolution still takes place; and at the symmetry breaking point the phenomenon of mode trapping does not occur in this nonparaxial regime (previously seen in PT -symmetric optical lattices in the paraxial regime). For the complex lattice, all these regimes share the common features: existence of a preferable mode for which the energy is transferred and a spatial evolution of this transfer in a nonreciprocal fashion, some of the characteristics very well known of PT -symmetric optical systems.CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
A evolução espacial de um par de modos de Bragg ressonantes através de um meio descrito por uma permissividade elétrica relativa PT -simétrica é completamente investigada. Usando o modelo de duas ondas, soluções analíticas para as equações de Maxwell são derivadas no regime não-paraxial a fim de investigar a transferência de energia entre esses modos de Bragg para uma rede ótica Hermitiana bem como para uma rede ótica complexa e também estudar a evolução espacial da parte real do campo elétrico que se propaga através desse meio. Três regimes definidos pela quebra de simetria são discutidos: abaixo, acima e no ponto de quebra de simetria. Estes regimes são determinados pela existência de quatro autovalores complexos distintos abaixo da quebra de simetria, que colidem e coalescem num par de autovalores valores complexos duplamente degenerados no ponto de quebra de simetria. Acima do ponto de quebra, quatro autovalores complexos distintos voltam a existir e agora cada um possui uma parte real não-nula. No caso Hermitiano, é demonstrado que uma transferência de energia completamente recíproca entre o par de modos de Bragg, numa maneira similiar ao efeito Pendellösung conhecido da difração de raios X por cristais, ocorre. Quando a rede ótica é complexa, a dinâmica da transferência de energia é completamente diferente do caso Hermitiano: abaixo do ponto de quebra de simetria existe um comportamento oscilatório do tipo batimento muito não-recíproco para a transferência de energia entre os modos de Bragg; acima do ponto de quebra de simetria a evolução espacial da transferência de energia cresce ilimitadamente mas um evolução oscilatória ainda ocorre; no ponto de quebra o fenômeno do aprisionamento de modo não ocorre nesse regime não-paraxial (anteriormente visto em redes óticas PT -simétricas no regime paraxial). Para a rede ótica complexa, todos estes regimes compartilham características em comum: existência de um modo preferencial para o qual a energia é transferida e uma evolução espacial dessa transferência de maneira não-recíproca, algumas das características muito bem conhecidas de sistemas óticos PT simétricos.
9
Darlington, Michael James David. "The stability of single crystal Pt and Pt₃Ni surfaces during electro-oxidation". Thesis, University of Liverpool, 2014. http://livrepository.liverpool.ac.uk/2005579/.
Testo completoAbstract (sommario):
In an e�ort to gain a fundamental understanding of the link between catalyst surface structure, reactivity and stability, experiments have been performed on Pt(111), Pt3Ni(111) and Pt(100) single crystal electrode surfaces via a combina- tion of in-situ structural probes and electrochemical (cyclic voltammetry) mea- surements. Pt(111), which is the least active of the low index surface for the Oxygen Reduction Reaction (ORR), showed morphological changes after oxida- tion reduction cycles, with the formation of stable platinum adislands. The more active Pt(100) surface undergoes a drastic roughening of the surface during ox- idation/reduction cycles, which is due to the fact that the surface is unlikely to recrystallise into the more open (100) surface structure. In essence, although the Pt surfaces with a more open atomic geometry, e.g. (100) and (110), are more reactive than the close-packed (111) surface, they are intrinsically less stable. The bimetallic alloy Pt3Ni(111) surface has been shown to be over 10 times more ac- tive for the ORR than pure Pt(111) and exhibits a compositional oscillation at the surface which is formed of Pure Pt. Upon repetitive cycling the Pt3Ni(111) surface undergoes a similar morphological change to that of Pt(111), where the formation of adislands was seen in STM measurements. These adislands retain some of the active segregated surface structure, preserving the electronic modi�cation due to the Ni-rich subsurface. This leads to a stable surface that remains more active than the pure Pt(111) electrode after prolonged cycling of the potential into the region of oxidation/reduction. Perhaps the key insight that can be obtained from these experiments is that electrode activity towards the ORR is intrinsically linked to surface stability, i.e. the more active the surface, the less stable it is. This, in fact, may be a general e�ect in electrocatalysis.
10
Silva, Pedro Gustavo de Sousa. "Dilemas de um Partido de Governo: Conflitos entre PT e Governo Lula (2003-2006)". Universidade Federal do CearÃ, 2011. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=6081.
Testo completoAbstract (sommario):
CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel SuperiorA vitÃria de Lula nas eleiÃÃes 2002 inaugurou um quadro completamente novo no cenÃrio polÃtico nacional. O PT e os tradicionais aliados (PC do B, PSB, CUT, UNE, MST, etc.) assumem pela primeira vez a tarefa de âser governoâ no Ãmbito federal. Embora o Partido fosse a principal forÃa polÃtica da gestÃo no Poder Executivo e no Congresso Nacional, a sigla despontou como um dos agentes que mais divergiram do governo Lula. De um lado, setores do PT cumprem o papel de protagonistas nas tensÃes com o governo. De outro lado, uma parte majoritÃria do Partido faz a defesa da gestÃo e segue as orientaÃÃes do Poder Executivo para as votaÃÃes no Congresso Nacional. Essa dinÃmica de conflitos entre PT e governo Lula (2003-2006) constitui meu objeto de estudo. Busco entender as razÃes dos conflitos entre esses agentes. A investigaÃÃo percorreu diversas fontes, dentre as quais se destacam: notÃcias veiculadas na imprensa (Folha de SÃo Paulo impresso e on-line), periÃdicos do PT e de suas tendÃncias, sites vinculados aos personagens e instituiÃÃes da pesquisa (PT e suas tendÃncias, parlamentares), documentos partidÃrios (resoluÃÃes, notas, manifestos), textos acadÃmicos referentes ao assunto, revistas, etc. No que diz respeito ao arcabouÃo teÃrico, conceitos como trade-off eleitoral, âlinha polÃticaâ e âcoalizÃo dominanteâ foram tomados como essenciais para a anÃlise do material empÃrico e elaboraÃÃo dos argumentos. Para alÃm da disputa entre projetos e perspectivas ideolÃgicas, os conflitos entre petistas e governo expressavam tambÃm os distintos parÃmetros de aÃÃo que orientavam os agentes polÃticos. A esquerda petista e o grupo dominante no PT pautaram a relaÃÃo com os dirigentes governamentais atravÃs de distintos parÃmetros.
11
Antunes, Ettore Paredes. "Estudo da atividade eletrocatalítica de multicamadas metálicas de Ir/Pt e Cu/Pt eletrodepositadas sobre Pt(policristalina) para eletrooxidação de moléculas orgânicas pequenas". Universidade Federal de São Carlos, 2013. https://repositorio.ufscar.br/handle/ufscar/6575.
Testo completoAbstract (sommario):
Made available in DSpace on 2016-06-02T20:36:49Z (GMT). No. of bitstreams: 1
5680.pdf: 7847035 bytes, checksum: 99b6945abbfe45fb028cce964b60c302 (MD5)
Previous issue date: 2013-09-26Financiadora de Estudos e Projetos
The search for alternative energy sources stead fossil fuel has driven the development of new energy generating devices. Among these, the Direct Alcohol Fuel Cells are a kind of device that directly convert chemical energy into electricity from short chain alcohols. However, it is necessary to develop electrodes with high catalytic activity. Several materials composed by Pt have been proposed in the literature in different metallic binary and tertiary compositions Metallic Multilayer (MM) systems. In this dissertation, were fabricated MM electrodes containing deposits of thin alternating layers of Ir/Pt, PtIr/Pt and Cu/Pt, all above Pt polycrystalline by chronoamperometry. We have used the technique of Factorial Design for screening the following variables: intermediate and external layers thickness and composition of the intermediate layers. For the electrooxidation of ethylene glycol, the structure that showed the highest electrocatalytic effect was Pt/Ir3.0/Pt3.0 (3.0 is the thickness of each layer in monolayers) that shows an increase of peak current density of 175% and lower activation energy about 26.2 kJ mol-1. Electrooxidation was monitored by FTIR in situ and was observed an increase of 255% on CO production of species during electrooxidation and anticipation in the process of formation of CO2 by 100 mV. The proposed structures for Cu/Pt MM were not formed, which was confirmed by AFM images, but clustered in grain, and the electrode Pt/Cu1,5/Pt9,0 grew by 78% in the peak current density in the electrooxidation methanol and also shift 200 mV to cathodic potentials in CO electrooxidation. Although these studies have not reached a definitive explanation, though the results were added to the dissertation.
A necessidade de buscar fontes energéticas alternativas ao consumo de combustíveis fósseis tem impulsionado o desenvolvimento de novos dispositivos geradores de energia. Dentre estes, as células à combustível direto é um dispositivo que converte diretamente a energia química em elétrica a partir de álcoois de cadeias curtas. Entretanto, faz-se necessário desenvolver eletrodos com alto poder catalítico e muitos deles, compostos por Pt, têm sido propostos na literatura em diferentes composições metálicas binárias, terciárias e sistemas de Multicamadas Metálicas (MM). Nesta dissertação, foram confeccionados eletrodos de MM contendo depósitos de finas camadas alternadas de Ir/Pt, PtIr/Pt e Cu/Pt, todos sobre Pt policristalina, por cronoamperometria. Foi utilizada a técnica de Planejamento Fatorial para triagem das variáveis, que foram: espessura das camadas intermediárias e externas e a composição da camada intermediária. Para a eletrooxidação de etileno glicol, a estrutura que apresentou o maior efeito eletrocatalítico foi Pt/Ir3,0/Pt3.0 (3,0 é a espessura de cada camada em monocamadas) com incrementos na densidade de corrente de pico de 175% e menor energia de ativação, 26,2kJ mol-1. Também foi acompanhada a eletrooxidação por FTIR in situ, onde se observou um incremento de 255% na produção de espécies CO durante a eletrooxidação e a antecipação no processo de formação de CO2 foi de 100 mV. As estruturas de Cu/Pt não formaram MM, que foi confirmado por imagens de AFM, mas se aglomeraram em grãos e o eletrodo de Pt/Cu1,5/Pt9,0 apresentou incremento de 78% na densidade de corrente de pico na eletrooxidação de metanol e também deslocamento de 200 mV para potenciais mais catódicos no início da eletrooxidação de CO. Apesar de não termos chegado a uma explicação definitiva, os resultados foram acrescentados à dissertação.
12
Zulke, Alana Aragon. "Desenvolvimento de multicamadas metálicas do tipo Pt/Ir/Pt eletrodepositadas em titânio para eletrocatálise". Universidade Federal de São Carlos, 2012. https://repositorio.ufscar.br/handle/ufscar/6527.
Testo completoAbstract (sommario):
Made available in DSpace on 2016-06-02T20:36:38Z (GMT). No. of bitstreams: 1
4377.pdf: 4163228 bytes, checksum: c226cdaadadec6b48a2334a2446ba4e3 (MD5)
Previous issue date: 2012-04-19Universidade Federal de Sao Carlos
Regarding to the search for new energy sources, of renewable character, fuel cells fall into one of the most studied proposals on Electrochemistry. More specifically, the direct fuel cells (DAFCs) using short-chain alcohols as fuel, have attracted the attention of researchers over the past two decades. Problems related to the energy efficiency of Pt-based catalysts for use in fuel cells, drive several studies in the literature concerning to the modification of these catalytic systems. Thus, have been proposed in the literature, other materials than pure Pt, such as alloys in binary and ternary composition, and more recently, metallic multilayered structures(MM), the latter being the study object of this work. Platinized titanium electrodes were prepared by potentiostatic electrodeposition technique (0.05 V vs RHE), and times of 1000 sec were necessary to obtain an identical polycrystalline platinum voltammetric profile, with guaranteed reproducibility. On these substrates, Ir/Pt bilayered systems were electrodeposited controlling films thickness through the deposition charge. Calculations revealed mass loading of platinum between13.4 and 26.3 μg and maximum film thickness of 43.2 nm. AFM images confirmed the homogeneity of the coatings as well as the total covering of the substrate. A screening of variables with the aid of a 22 factorial design with central point showed better intrinsic catalytic activity (current density normalized by the electroactive area) for the Ti/Pt25mC/Ir6mC/Pt system, which answers were around 270% higher than those obtained for Ti/Pt systems. In addition to the methanol oxidation voltammetry, chronoamperometric tests of methanol oxidation and CO stripping voltammetry suggest the MM-like systems are less susceptible to the catalyst poisoning phenomenon compared to the Ti/Pt systems. Assuming that there are no area effects due the current normalization through the electroactive area, nor the possibility of a bifunctional mechanism occurring,considering that are just Pt catalytic centers exposed, an explanation for the purposes of promoting catalytic activity may be based on electronic effects due to the possible compressive stress generated by the bilayer Ir/Pt causing an energy enlargement of the d band, lowering the adsorbates energy of adsorption. EIS data indicated a lower resistance to charge transfer in the reactions performed on MM systems, which strengthens the argument regarding the positive electronic effects associated with MM-like structures.
No que diz respeito à busca por novas fontes energéticas, de caráter renovável, as células combustíveis se enquadram em uma das propostas mais estudadas na Eletroquímica. Mais especificamente, as células à combustível direto (DAFCs) que utilizam alcoóis de cadeia curta como combustível, vêm atraindo a atenção dos pesquisadores nas últimas duas décadas. Problemas relativos à eficiência energética dos catalisadores baseados em Pt para aplicação em células combustíveis, impulsionam diversos estudos na literatura concernentes à modificação desses sistemas catalíticos. Desta forma, têm sido propostos na literatura, diferentes materiais além da Pt pura, como ligas de composição binária e ternária, e mais recentemente, as multicamadas metálicas(MM), tendo sido esta última proposta objeto de estudo do presente trabalho. Eletrodos de titânio platinizados foram confeccionados através da técnica de eletrodeposição potenciostática a 0,05V vs ERH, sendo que tempos de 1000s foram necessários para se obter um perfil voltamétrico idêntico ao da platina policristalina, com reprodutibilidade garantida. Sobre estes substratos, sistemas de bicamadas Ir/Pt foram eletrodepositados controlando-se a espessura através da carga de deposição. Os cálculos de massa revelaram cargas de platina entre 13,4 e 26,3μg e espessuras máximas de filme de 43,2nm. Imagens de AFM confirmaram a homogeneidade dos eletrodepósitos bem como o recobrimento total do substrato. Uma triagem de variáveis com o auxílio de um planejamento fatorial 22 com ponto central apontou melhores atividades catalíticas intrínsecas (densidade de corrente normalizada pela área eletroativa) para o sistema Ti/Pt25mC/Ir6mC/Pt, cujas respostas foram em torno de 270% maiores que em relação ao Ti/Pt. Além das voltametrias de oxidação do metanol, ensaios de cronoamperometrias de oxidação do metanol e voltametria do stripping de CO sugerem que os sistemas tipo-multicamada sejam menos suscetíveis ao fenômeno de envenenamento catalítico, em relação aos sistemas Ti/Pt somente. Partindo do pressuposto que não existam efeitos de área, devido a normalização das correntes obtidas pelas áreas eletroativas, e nem a possibilidade de um mecanismo bifuncional, assumindo que apenas Pt está exposta no sistema catalítico, uma explicação para os efeitos promotores da atividade catalítica pode estar baseado em efeitos eletrônicos devido a um possível estresse compressivo gerado pela bicamada Ir/Pt, causando alargamento em energia da banda d e logo, menores energias de adsorção de adsorbatos. Dados de EIS indicaram uma menor resistência à transferência de carga nas reações realizadas sobre as MM, o que fortalece a argumentação em relação aos efeitos eletrônicos positivos associados às estruturas tipo MM.
13
Великодний, Дмитро Володимирович, Дмитрий Владимирович Великодный, Dmytro Volodymyrovych Velykodnyi, Ірина Володимирівна Чешко, Ирина Владимировна Чешко, Iryna Volodymyrivna Cheshko, Зінаїда Миколаївна Макуха, Зинаида Николаевна Макуха, Zinaida Mykolaivna Makukha e М. О. Шумакова. "Тензоефект у магнітооптичних властивостях плівкових систем Fe/Pt/П та [Fe/Pt][8]/П". Thesis, Сумський державний університет, 2013. http://essuir.sumdu.edu.ua/handle/123456789/43923.
Testo completo
14
Murrugarra, Tomairo David Manuel. "Anillo de cobordismo MU*(pt)". Bachelor's thesis, Universidad Nacional Mayor de San Marcos, 2005. https://hdl.handle.net/20.500.12672/1254.
Testo completoAbstract (sommario):
El objetivo principal de la presente tesis es estudiar la estructura del anillo de Cobordismo Complejo MU*(pt). Milnor y Novikov fueron los primeros en mostrar que este es un anillo polinomial sobre generadores de grado par sobre Z. Este cálculo se realiza utilizando la sucesión espectral de Adams sobre una teoría de homología generalizada. La exposición de este teorema ocupa la parte final de este trabajo. En la primera parte se presenta el teorema de Adams sobre la convergencia de su sucesión espectral. En la segunda parte, se describe el espectro de Thom y la teoría de homología generalizada asociada a este espectro, que en este caso viene a ser el Cobordismo Complejo. También se describe de manera breve la estructura del Álgebra de Steenrod y su dual, que se utilizará al momento de calcular la estructura del anillo de homología H* (MU; Zp). Al final se adjunta un apéndice sobre álgebras y algebroides de Hopf, que incluye algunos isomorfismos de cambio de anillos.-- The main objective of the present thesis is to study the structure of the Complex Cobordism Ring MU*(pt). Milnor y Novikov first accomplished this, and they(independently) showed that it is a polynomial ring over Z on generator of every even degree. It is achieved by using the Adams Spectral Sequence over a generalized theory. This theorem is expounded at the end of this work. In the first part, I present the theorem about the convergence of the Adams spectral sequence. In the second, I describe the Thom Spectrum and the generalized homology theory associated to this spectrum, in this case it is the Complex Cobordism. I also describe quickly the Steenrod Algebra and its dual, which will be used when we determine the structure of singular homology ring H * (MU; Zp). Finally, I attach an appendix about Hopf algebroides and Hopf algebras, which contains some change of ring isomorphism.
Tesis
15
Curnick, Oliver J. "Ionomer-stabilised Pt and Pt-Ti bimetallic electrocatalysts for the proton exchange membrane fuel cell". Thesis, University of Birmingham, 2012. http://etheses.bham.ac.uk//id/eprint/3732/.
Testo completoAbstract (sommario):
This work aims to address the need for more durable electrocatalysts with lower precious metal content for proton exchange membrane fuel cells (PEMFCs), through the development of novel electrocatalyst materials and preparation routes. In this work, 'Nafion-Pt/C' electrocatalysts have been derived from ionomer-stabilised Pt nanoparticles synthesised via a novel, wet-chemical route that offers unprecedented control over the formation of the Pt-ionomer interface, with a view towards maximising the utilisation of the electrocatalyst. Nafion-Pt/C electrocatalysts have been characterised using ex-situ electrochemical techniques, and single-cell PEMFC testing to determine their activity and selectivity towards the oxygen reduction reaction (ORR), and to compare their utilisation and durability with commercially-available electrocatalysts. Nafion-Pt/C catalysts with agglomerated Pt particles exhibited a twofold improvement in durability vs. commercial catalysts, whilst offering similar ORR activities. Their enhanced durability was attributed to inhibition of Pt particle growth mechanisms by a passivating layer of Nafion introduced during the synthesis of Nafion-stabilised colloidal Pt. The second part of this work investigated methods for the synthesis of bimetallic nanoparticles consisting of an early transition-metal core (Ti) enclosed in a Pt shell, expected to offer higher intrinsic activity towards oxygen reduction than Pt alone, whilst being less prone to degradation than other alloys of Pt such as Pt-Ni, Pt-Co and Pt-Fe.
16
Scholes, Fiona Helen. "Far-infrared emission spectroscopy of C₆D₆ and CO on pt(111) and pt(110)". Thesis, University of Cambridge, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.621412.
Testo completo
17
Matsutsu, Molefi. "Pt and Pt-Pd cluster interaction with graphene and TiO₂ based supports: A DFT study". Doctoral thesis, University of Cape Town, 2016. http://hdl.handle.net/11427/22922.
Testo completoAbstract (sommario):
Density functional theory (DFT) calculations have been performed to gain insight into the role of defects present on the surface of graphene and TiO₂ based supports on supported metal clusters. The clusters considered are a Pt₃₈ cluster and a bimetallic Pt₃₂Pd₆ alloy. The defects considered on graphene based supports are monovacancy defective graphene, OH and COOH functionalised graphene. The defects considered on TiO₂ based supports are a partially reduced TiO₂(110) surface with a surface oxygen bridge vacancy and hydroxylated TiO₂(110) surface with surface OH groups. The defect free graphene and TiO₂ surfaces were also considered. For both the Pt₃₈ and Pt₃₂Pd₆ cluster, and on both defect containing graphene and TiO₂ (except on hydroxylated TiO₂(110) surface) the binding of the clusters is enhanced relative to binding on the defect free supports. Enhanced binding at the defects imply that the clusters are bound strongly to the support and thus less likely to detach from the support material relative to binding on the defect free supports. Therefore, the defects may improve the durability of the catalyst by limiting particle detachment. The electronic properties of the cluster are modified differently depending on the identity of the defect present on the support. On the graphene based supports, OH functionalisation is expected to result in weaker binding energy of adsorbate molecules, whereas COOH functionalisation is expected to result in stronger binding energy of adsorbates for the supported Pt₃₈ cluster. This is due to different shifts in d-band centre of the facets on the cluster supported on these supports. Therefore, it can be expected that the Pt₃₈ cluster supported on OH functionalised graphene will be more tolerant to poison molecules. This is due to reduced binding strength of adsorbates on OH functionalised graphene compared to adsorption on COOH functionalised graphene. For the Pt₃₂Pd₆ cluster the OH and COOH functional groups do not appreciably modify the d-band centre of the facets available to reactants, and thus is expected not to significantly modify the binding strength of adsorbate molecules relative to binding on the free unsupported Pt₃₂Pd₆ cluster. The binding energy of adsorbate molecules on the Pt₃₈ cluster supported on defect containing TiO₂ is expected to be stronger than on the Pt₃₈ cluster supported on defective graphene based supports, due to higher extent of upward shift of the d-band centre of the exposed facets. The enhanced binding energy of adsorbates on the Pt₃₈ cluster supported on TiO₂ supports may be detrimental to catalyst durability and activity. This can be due to strong binding of poison molecules and reaction intermediates which maybe too strongly bound on the surface such that they cannot participate in further reaction steps. Overall it might turn out that the functionalised graphene based supports are better support materials over the TiO₂ based materials for particular reactions. The Nb-doped partially reduced TiO₂(110) surface attaches the Pt₃₂Pd₆ cluster strongly to the support compared to the functionalised graphene supports. Furthermore, the binding energy of adsorbate molecules is expected to be weaker on the Pt₃₂Pd₆ cluster supported on the Nbdoped partially reduced TiO₂(110) surface compared to the functionalised graphene supports. This might be beneficial as poison molecules may be weakly bound to the cluster resulting in high resistance to poisoning which can also have a positive effect on catalyst activity. In addition to enhancing binding of the cluster to the support and affecting the binding energy of adsorbates on the supported clusters, some of the defects can also alter the ordering pattern of Pd and Pt atoms within the Pt₃₂Pd₆ cluster. OH functionalised graphene and Nbdoped partially reduced TiO₂(110) surface result in segregation of Pd towards the clustersupport interface, thereby exposing more Pt atoms at the surface facets of the cluster. The modified arrangement of Pt and Pd atoms may result in modification of the reactivity of the Pt₃₂Pd₆ cluster. The results of this study indicate that the defects can play a vital role in determining the activity and durability of the catalyst. By having the right combination of defects on the support material, the durability and catalytic activity of the catalyst can be fine-tuned simultaneously. This can lead to better design of catalysts.
18
Atli, Halil Atilla. "Réactivité de surfaces d'alliages monocristallins Pt-Ni et Pt-Fe vis-à-vis de l'hydrogène". Lyon 1, 1992. http://www.theses.fr/1992LYO10104.
Testo completoAbstract (sommario):
La reactivite de surface d'alliages monocristallins -pt#5#0ni#5#0(111), pt#5#0ni#5#0(110) et pt#8#0fe#2#0(111)- vis-a-vis de l'hydrogene a ete etudiee sous basses pressions essentiellement par thermodesorption (tds) et mesure de variation de travail de sortie des electrons. Les travaux anterieurs ont montre que la premiere couche de surface se caracterise par une forte segregation de pt sur les faces denses (111), de ni sur la face ouverte (110). La composition et la structure de ces surfaces ont ete controlees par spectroscopie auger (aes) et diffraction d'electrons lents (leed). L'adsorption d'hydrogene n'induit ni structure ordonnee, ni reconstruction de surface. Les mesures ont montre que la cinetique d'adsorption, le recouvrement et l'energie d'activation de desorption de l'hydrogene sont nettement attenues par comparaison aux metaux purs de references: pt(111) et ni(110), en accord avec l'intervention d'un effet electronique confirme par les mesures de la variation de travail de sortie. Cet effet a ete precise sur ptfe(111) grace a des mesures de photoemission d'electrons. Des mesures complementaires sous pression relativement elevee (470 torr) ont montre que la vitesse d'echange h2-d2 est comparable sur ces trois surfaces d'alliages. L'ensemble des resultats a ete discute en relation avec les proprietes catalytiques de ces alliages de facon a tenter d'expliquer l'exaltation d'activite hydrogenante par rapport aux metaux purs correspondants
19
Roca, Lizarazu Maria. "Finding the Holocaust in metaphor : renegotiations of trauma in contemporary German- and Austrian-Jewish literature". Thesis, University of Warwick, 2017. http://wrap.warwick.ac.uk/95167/.
Testo completoAbstract (sommario):
This thesis investigates representations of the Holocaust and the Second World War across a range of German- and Austrian-Jewish writers who belong to the second or third generation born after the Holocaust. These writers relate to the events from the position of the “nonwitness” (Weissman 2004), and in the face of major shifts in Holocaust memory since the millennium: the disappearance of the survivor and eyewitness generation entails a transition from first-hand memories of the war period to an increasingly ritualised cultural memory of the events. This transformation intersects with larger changes in Holocaust memory in the last 15 years, such as the re- and hypermediation of Holocaust memory and the emergence of a globalised Erinnerungskultur. The Holocaust has therefore emerged as a highly discursivised “floating signifier” (Huyssen 2003), which travels transgenerationally, transmedially and transnationally. Engaging with these shifts, I argue that Marianne Hirsch’s concept of “postmemory” (Hirsch 1997) and recent trauma theory remain embedded in a biologising framework of analysis that views cultural transmission in terms of contagious inheritance. Drawing on cultural and literary theories and transnational memory studies, I develop a new approach that focuses on the Holocaust as a form of “travelling trauma” (Tomsky 2011), tracing its remediation and recycling across geographical, cultural, medial, and representational boundaries. My readings of texts by Benjamin Stein, Maxim Biller, Vladimir Vertlib, and Eva Menasse explore how these authors (re-)negotiate the various travels of Holocaust memory in the age of remediation. By initiating a dialogue between the realms of theory and contemporary fiction, this thesis engages with a broad body of recent German- and Austrian-Jewish Holocaust fiction, while at the same time critically investigating key paradigms in the field of memory and trauma studies.
20
Haberlah, Gesine. "Zwischen Autobiographie und Fiktion : neue literarische Schreibweisen bei Felicitas Hoppe, Charlotte Roche, Stephan Wackwitz und David Wagner". Thesis, University of Nottingham, 2016. http://eprints.nottingham.ac.uk/33440/.
Testo completoAbstract (sommario):
This thesis examines forms of autobiographical writing in the 21st century which are located at the intersection of autobiography and fiction. The literary sources selected question established genre boundaries, while also reflecting contemporary cultural discourses and creating particular images of their authors. My analysis investigates the new literary strategies emerging in Charlotte Roche’s Schoßgebete (2011), Stephan Wackwitz’s Ein unsichtbares Land (2003), Felicitas Hoppe’s Hoppe (2012) and David Wagner’s Leben (2012) in order to identify how texts such as these combine autobiography and fiction. Using a range of literary theories my textual analysis shows that autobiographical writing in the 21st century is more extensive than critical approaches such as ‘autofiction’ and ‘life writing’ suggest. The thesis demonstrates how genre hybridisations, intertextual combinations and inter-discursive conjunctions in the texts also move beyond Philippe Lejeune’s differentiation between autobiography and the novel. By combining characteristics of fictional narratives with features of factual texts such as the essay, the parody of academic biography or specifically context-related factual, in this case medical texts, these life stories reflect our understanding of identity in significantly new ways. Moreover, my investigation proves that the new forms of autobiographical writing engage with contemporary issues such as the role of the media and celebrity culture, national history and memory discourses, transculturalism and the significance of writing in the 21st century, medical developments and their consequences. The texts’ contribution to these discourses also constructs the authors’ self-presentation. Strategies and techniques identified range from provocative self-staging through positioning within a framework of national and family history, to outlining autobiographical poetics, or presenting different private and public facets of the author’s persona. My thesis addresses not only the effects of the increasing (public) interest in the private life of authors in contemporary autobiographical writing but also contributes to wider research on autobiography, genre and intertextuality.
21
Becker, Renate. "Die literarische Darstellung weiblicher Subjektivität in der westdeutschen Frauenliteratur der siebziger und achtziger Jahre". Thesis, University of Warwick, 1988. http://wrap.warwick.ac.uk/110021/.
Testo completoAbstract (sommario):
Although the emphasis of this thesis is on the literary representation of female subjectivity in contemporary women's writing in West Germany, the first chapter looks back on the history of women's emancipation in Germany from the early 19th century until today. Selected examples of women's writing will show how women - in their writing and often their lives - attempted to break out of the restrictions which existing male images of women and society as a whole had set up for them. Included in this chapter are the beginnings of women's movements and the struggle for political and social rights. A comparison between those early beginnings and today allows the identification of differences and similarities. The pursuit of the question of how women break out of existing images or how they subvert them in their writing is not only of interest in Chapter I, but is followed up in the whole thesis. This has to lead to another question, namely that of female subjectivity. As women in a patriarchal society are enclosed by a set of images in whose production they did not actively partake, and as the exclusion of women from history perpetuated itself in the absence of women from the history of ideas and from language as the representative of the symbolic order (Lacan), the original question has to be modified to include the assumption that exclusion and absence cannot be overcome by the rational decision to be present. The emphasis in HButungen by Verena Stefan (Chapter II) is therefore on the possibilities of a feminist subject to express subjectivity, focussing also on the relationship between ideology and subjectivity. In Chapter III, which analyses the autobiography by Inga Buhmann Ich habe mir elite Geechlchte geechrleben, the focus is on the conflict between subjectivity and truth, as a self-imposed rule to "confess". Chapter IV is divided into two parts and includes an analysis of the po6tstructuralist theories of subjectivity of Jacques Lacan and Julia Kristeva, with emphasis on the role and function of language. The focus of the analysis of Rahschnitt by Ursula Krechel and Altweibereommer? by Pola Veseken (Chapter V) is on the subversion of language and the deconstruction of the unified, coherent subject as the producer of meaning, and the portrayal of female subjectivity as the réintroduction of the imaginary into the symbolic. Through these analyses the question of female subjectivity and the related one as to how women break out of existing images or subvert them in their writing are constantly addressed. The thesis is written in German.
22
Graves, S., S. Goel, F. Chen, H. Valdovinos, T. Barnhart, W. Cai e R. Nickles. "Production and novel radiochemical separation of 194Au from Pt for use in multi-modality nanoparticles". Helmholtz-Zentrum Dresden - Rossendorf, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-166428.
Testo completoAbstract (sommario):
Introduction
Gold nanoparticles (AuNPs) have demonstrated their incredible versatility in applications such as in vitro and in vivo imaging, cancer therapy, and drug delivery.[1-3] These AuNPs come in many shapes including nanospheres, nanorods, nanoshells, and nanocages. Their versatility stems from the ability to construct or label a single AuNP with many functions. Many types of AuNPs are inherently flourescent, allowing for ex vivo utilization as well as small animal fluorescence imaging.[4] High atomic number and physical density allow for the possibility of using AuNPs as computed tomography (CT) contrast agents, especially in dual energy applications.[5]
Some attempts have been made to bring AuNPs into the realm of nuclear medicine, mostly involving the extrinsic labeling of chelated radio-metals. Although these strategies have brought some success, an intrinsic labeling strategy could reduce concerns of in vivo instability, and changes in pharmacokinetic behavior.[6] Intrinsic radiolabeling strategies involve synthesizing the nanoparticles in the presence of a gold radioisotope, which is thereby structurally incorporated. The isotope of choice for this technique has typically been 198Au (t½ = 2.7 d, Eγ = 411.8 keV) as it is reactor produced and commercially available. However with such a high energy gamma ray, SPECT aquisition is far from optimal.
Motivated by the shortcomings of previous intrinsic labeling techniques, we have sought to develop 194Au (t½ = 1.48 d, β+ = 1.73 %) as a potential PET isotope for labeling AuNPs. Although this nuclide has a weak positron branching ratio, it also has prominent gamma ray energies of 328 and 294 keV which are closer to the optimal SPECT energy window, allowing for the ability to image with both PET and SPECT.
Material and Methods
194Au was produced by natPt(p,x) using 16 MeV protons. Target construction consisted of a water jet cooled platinum disc.
Following irradiation, targets were etched by fresh concentrated aqua regia at 80 °C for four hours. The resulting solution was diluted by a factor of four and loaded onto a 50 mg UTEVA (Eichrom extraction resin) column equilibrated by 1 M HNO3. The column was rinsed with 10 mL 1 M HNO3, and the product was eluted using concentrated HNO3 in less than 1 mL.
Results and Conclusion
End of bombardment (EOB) yield for 194Au was measured to be 0.134 mCi/μAh by high purity germanium analysis. The half life was measured to be 38.5 ± 2.8 hours, which agrees well with the true half life of 37.92 hours. In addition to the production of 194Au, the production of 190–193Au and 196Au was observed. Most notably, the EOB yield for 193Au (t½ = 17.7 h) was 0.189 mCi/μAh.
Target dissolution was slow and incomplete after four hours of etching. Alternative dissolution strategies i.e. electrolytic dissolution may be needed moving forward. The separation of 194Au from bulk Pt via the UTEVA extraction resin was robust and efficient, with an average separation efficiency of 96 %. An extensive literature review revealed no other Au/Pt separation from solutions containing aqua regia. Future goals include synthesis of ultrasmall 194Au incorporated AuNPs using a facile thermal reduction method.PET, CT and fluorescence imaging will also be carried out in vivo to establish the multimodal capabilities of the intrinsically radio-labeled nanoplatforms.
To conclude, a novel separation technique has been developed to separate 194Au from Pt for use in intrinsically radiolabeled multi-modal AuNPs.
23
Zignani, Sabrina Campagna. "Estudo da estabilidade de catalisadores catódicos em célula eletroquímica". Universidade de São Paulo, 2009. http://www.teses.usp.br/teses/disponiveis/75/75131/tde-25082009-100339/.
Testo completoAbstract (sommario):
O objetivo do presente trabalho foi avaliar a estabilidade de eletrocatalisadores de Pt/C e ligas binárias de Pt-Co/C e Pt-Ni/C contendo 20% em massa de metal sobre carbono frente à reação de redução de oxigênio em células eletroquímicas. O trabalho experimental desenvolvido compreende várias etapas como preparação de catalisadores, tratamento térmico e preparação de eletrodos. O catalisador foi preparado pela redução de precursores com borohidreto de sódio, e suportado em carbono de alta área superficial (Vulcan XC-72, Cabot, 240m2g-1). O eletrodo da célula é um eletrodo de difusão de gás (EDG) de alta área superficial. Os catalisadores foram tratados termicamente em atmosfera de H2 a 550°C por uma hora. Os testes de estabilidade foram 30h de cronoamperometria ou ciclagem de potencial totalizando 1000 ciclos. Absorção Atômica, DRX (difração de raios-x) e EDX (energia dispersiva de raios-x) foram feitos antes e após os experimentos. Em geral observou-se que os catalisadores de Pt-Co/C e Pt-Ni/C apresentaram maior atividade para a RRO comparados a Pt/C, mas em contrapartida estes materiais sofrem corrosão e após algumas horas de operação há dissolução de metal e a atividade decresce muito. Os testes de cronoamperometria revelaram maior estabilidade de corrente para os materiais bimetálicos, o que não ocorre na ciclagem. Pt/C destaca-se após a ciclagem de potencial apresentando maior atividade comparado aos experimentos iniciais. A perda de atividade das ligas devese a dissolução do metal menos nobre diminuindo a área ativa e favorecendo a formação de aglomerados de Pt/C na superfície. Desta forma Pt/C ganha destaque após a dissolução de Co e Ni que inicialmente apresentaram bons resultados. Com relação aos materiais tratados termicamente o tamanho de cristalito para todos aumenta, decrescendo muito a atividade catalítica, mas em contrapartida torna-os mais estáveis em relação a perdas por dissolução dos metais.The aim of the present work was to evaluate the stability of Pt/C and bi-metallic Pt- Co/C and Pt-Ni/C electrocatalysts, containing 20 mass % of metal on carbon, for the oxygen reduction reaction (ORR) in fuel cells. The experimental work encompassed several steps such as catalyst syntheses, heat treatments, and electrode preparation. The catalysts were synthesized by reducing precursors with sodium borohydride on high surface area carbon (Vulcan XC-72, Cabot, 240 m2g-1). The working electrode is a high surface area gas diffusion electrode (GDE). The catalysts were heat treated in a hydrogen atmosphere for 1 hour at 550oC. The stability tests performed were 30h of cronoamperometry and potential cycling up to 1000 cycles. The catalysts were characterized by atomic absorption, x-ray diffraction (XRD), and energy dispersive x-ray spectrometry (EDX), performed before and after the electrochemical tests. The Pt-Co/C and Pt-Ni/C catalysts presented higher activity for the ORR when compared with that of the Pt/C catalyst. Conversely, these bi-metallic catalysts underwent a corrosion process, resulting in metal dissolution and activity decrease after a few hours of operation. The cronoamperometry tests revealed higher current stability for the bi-metallic catalysts, which was not the case during cycling. Pt/C stands out after potential cycling showing greater activity in initial experiments. The decrease of activity observed for the bi-metallic catalysts was ascribed to the dissolution of the less noble metal, decreasing the active area and favoring the formation of Pt/C agglomerates on the surface. Thus, Pt/C presents better performance than the bi-metallic catalysts after the dissolution of Co and Ni. Concerning the heat treated materials, an increase of the crystallite size was observed for all the catalysts, resulting in a large drop of the catalytic activity but, on the other hand, an increase of the stability of the bi-metallic catalysts against metal dissolution.
24
More-Chevalier, Joris. "Etude de l’effet magnétoélectrique dans les hétérostructures de Pt/TbXDy1-XFe2/Pt/PbZrXTi1-XO3/Pt en couches minces déposées sur des substrats de siliciumsubstrats de silicium". Caen, 2015. http://www.theses.fr/2015CAEN2029.
Testo completoAbstract (sommario):
Ce travail de thèse porte sur l’étude de l’effet magnétoélectrique (ME) dans les matériaux composites TbxDy1-xFe2 (Terfenol-D)/Pt/Pb(ZrxTi1-x)O3 (PZT) en couches minces déposées sur substrats Pt/SiO2/Si. L’objectif est d’obtenir de bons coefficients de couplage magnétoélectrique permettant l’exploitation de ces composites dans des dispositifs microélectroniques. La première partie de ce travail porte sur l’étude des relations entre les propriétés structurales et les propriétés magnétiques des films de Terfenol-D. Il a notamment été montré qu’il est possible d’obtenir, dans différentes conditions, des films de Terfenol-D possédant des propriétés magnétiques intéressantes (bonne aimantation et faible champ coercitif), ouvrant la voie à l’assemblage de ces films avec un matériau piézoélectrique. La seconde partie porte sur la mise au point et l’étude de dispositifs Terfenol-D/Pt/PZT. Un travail important a été réalisé afin de développer une technique de mesure de l’effet ME qui puisse permettre de soustraire les effets électromagnétiques parasites induits dans le circuit de mesure. Des modèles électriques ont été conçus, permettant d’obtenir des valeurs plus réalistes du coefficient de couplage ME. Deux paramètres clés, la température de recuit de la couche de Terfenol-D et l’influence de l’épaisseur de la couche de platine intermédiaire, ont été étudiés dans le but d’obtenir le meilleur couplage ME possible. Finalement, un très bon coefficient de couplage de 15,5 V/cm. Oe a été obtenu sur l’un des dispositifs ME. Ces résultats ouvrent la perspective de développer des dispositifs ME en couches minces exploitables dans l’industrie de la microélectroniqueThis work focuses on the ME effect in Terfenol-D/Pt/PZT thin film composites deposited on Pt/SiO2/Si substrates. The goal of this work is to obtain good ME coefficients that could allow applying these omposites in microelectronic devices. The first section concerns the study of the interdependence between structural and magnetic properties in Terfenol-D thin films. It has been shown that it is possible to obtain Terfenol-D thin films with good magnetic properties (high magnetization and low coercive field) allowing the use of these films with piezoelectric materials. The second part is about Terfenol-D/Pt/PZT multiferroïc thin films processing. A significant work has been performed to finalize a ME measurement system without induced electromagnetic noises. Electrical models have been developed to give more realistic values of the ME coefficient. Two key points, the annealing temperature and the intermediate platinum layer thickness, were studied to get large ME coupling. Finally, an important ME coefficient of 15. 5 V/cm. Oe has been obtained on one of the ME devices. Consequently, these results in ME thin films could be used to develop microelectronic devices
25
Hilgers, Karsten. "Kernchemische Studien zur Entwicklung neuerer Produktionsverfahren für die therapierelevanten Radionuklide ¹⁴°Nd, ¹⁹¹Ir, ¹⁹¹Pt, ¹⁹³mPt und ¹⁹⁵Pt". Jülich : Forschungszentrum Jülich in der Helmholz-Gemeinschaft, 2005. http://deposit.ddb.de/cgi-bin/dokserv?idn=97844213X.
Testo completo
26
Eckardt, Markus [Verfasser]. "ORR activity and stability of Pt-based and Pt-free catalysts for PEMFC applications / Markus Eckardt". Ulm : Universität Ulm, 2020. http://d-nb.info/1203716257/34.
Testo completo
27
Breitwieser, Matthias, Matthias Klingele, Benjamin Britton, Steven Holdcroft, Roland Zengerle e Simon Thiele. "Improved Pt-utilization efficiency of low Pt-loading PEM fuel cell electrodes using direct membrane deposition". Elsevier, 2015. https://publish.fid-move.qucosa.de/id/qucosa%3A72517.
Testo completoAbstract (sommario):
Direct membrane deposition was used to produce record platinum catalyst utilization efficiency polymer electrolyte membrane fuel cells. The novel membrane fabrication technique was applied to gas diffusion electrodes with low Pt-loadings of 0.102 and 0.029 mg/cm2. Under oxygen atmosphere and 300 kPaabs total pressure, 88 kW/gPt cathodic catalyst utilization efficiency with a symmetrical Pt-loading of 0.029 mg/cm2 on the anode and cathode side was achieved. This is 2.3 times higher than the Pt-utilization efficiency of a reference fuel cell prepared using a commercial Nafion N-211 membrane and identical catalyst layers, emphasizing that the improvement is purely attributable to the novel membrane fabrication technique. This value represents the highest Pt-utilization efficiency reported in literature. The results strongly motivate the application of employing direct membrane deposition techniques to prepare low resistance polymer electrolyte thin films in order to compensate for kinetic losses introduced when using low catalyst loadings.
28
Karima, Alilat. "Matériaux piézoélectriques pour applications transducteurs acoustiques de puissance : PIN-PT nanocéramiques et PMN-PT céramique texturées". Châtenay-Malabry, Ecole centrale de Paris, 2008. http://www.theses.fr/2008ECAP1097.
Testo completoAbstract (sommario):
Le cœur des transducteurs électro-acoustiques en détection sous-marine est une céramique piézoélectrique de structure Pérovskite ABO3. Dans le cas des dispositifs d’émission, le matériau piézoélectrique est soumis d’une part à un fort champ électrique alternatif et à des déformations élastiques élevées entraînant un échauffement qui peut induire une diminution irréversible de ces propriétés. L’objectif de cette thèse est de développer des matériaux piézoélectriques stables en température et sous fort champ électrique alternatif. Nous avons, dans un premier temps, étudié les propriétés non-linéaire des céramiques de 0. 63Pb(In1/2Nb1/2)O3-0. 37PbTiO3 dopés (Mn, PbO, PMN) et non-dopés. Nous avons montré que le manganèse entraîne une diminution des pertes diélectriques et mécaniques et contribue au durcissement du matériau qui lui confère une bonne stabilité sous fort champ. L’effet de taille des grains sur les propriétés non-linéaires des céramiques de PIN-37PT a été ensuite étudié. La densification sous pression unaxiale a permis d’obtenir des nanocéramiques denses (~98% de la densité théorique) présentant des tailles de grain comprises entre 300 nm et 100 nm. De plus, les mesures diélectriques ont montré que plus la taille des grains diminue, meilleure est la stabilité sous fort champ électrique. Enfin, des céramiques texturées suivant la direction [001] de composition 65Pb(Mn1/3Nb2/3)O3-0. 35PbTiO3 ont été élaborées par la méthode de croissance interfaciale. Le traitement thermique sous un environnement scellé et une atmosphère saturée en PbO a permis d’obtenir de façon reproductible des céramiques texturées denses (>96% de la densité théorique)The heart of the electroacoustic transducers in underwater detection is a piezoelectric ceramics of Pérovskite ABO3 structure. In the emission devices case, the piezoelectric material is subjected on the one hand to a strong alternate electric field and high elastic strain involving a heating which can induce an irreversible reduction in these properties. The objective of this thesis is to develop stable piezoelectric materials in temperature and under strong alternate electric field. We, initially, studied the non-linear properties of 0. 63Pb(In1/2Nb1/2)O3-0. 37PbTiO3 ceramics doped (Mn, PbO, PMN) and not-doped. We showed that manganese involves a reduction in the dielectric and mechanical losses and contributes to the hardening material which confers a good stability under strong field to him. The grains size effect on the PIN-37PT ceramics non-linear properties was then studied. The thickening under unaxiale pressure made it possible to obtain the nanoceramic dense ones (~98% of the theoretical density) having grain sizes ranging between 300 nm and 100 nm. Moreover, dielectric measurements showed that more the grains size decreases, better is stability under strong electric field. Finally, textured ceramics according to the direction [001] of 65Pb (Mn1/3Nb2/3) O3-0. 35PbTiO3 composition were worked out by the interfacial growth method. The heat treatment under a sealed environment and an saturated atmosphere with PbO made it possible to obtain dense textured ceramics (> 96% of the theoretical density) in a reproducible way
29
Junior, Flávio Colmati. "Estudo de catalisadores de Pt-Sn para o ânodo da célula a combustível de membrana trocadora de prótons alimentada com etanol direto". Universidade de São Paulo, 2007. http://www.teses.usp.br/teses/disponiveis/75/75131/tde-27032008-084800/.
Testo completoAbstract (sommario):
Eletrocatalisadores de Pt-Sn suportados em carbono de elevada área superficial foram preparados por redução química de precursores metálicosm em solução usando como agente redutor o ácido fórmico. Esse método mostrou-se muito eficiente sendo possível obter tanto catalisadores com baixos teores de Sn (razão atômica Pt:Sn de 9:1) como com altos teores de Sn (razão atômica Pt:Sn de 1:3). Entretanto, apesar de ser o Sn reduzido e ancorado sobre o substrato de carbono apenas parte deste Sn é inserido na rede cristalina da Pt sendo necessário um tratamento térmico em atmosfera redutora para aumentar o grau de liga. Foram realizados tratamentos térmicos entre 100 e 500 ºC e o melhor desempenho na célula a combustível foi obtido com o material Pt3Sn tratado a 200 ºC. O tratamento térmico a 200ºC permitiu um incremento no grau de liga dos metais Pt e Sn sem modificar a estrutura cúbica de face centrada da Pt e sem promover a coalescência das nanopartículas ancoradas no suporte de carbono. Os materiais de Pt-Sn foram caracterizados através de difração de raios-X, absorção de raios-X e microscopia eletrônica de transmissão. A atividade para a eletro-oxidação de etanol foi avaliada através de técnicas eletroquímicas e experimentos em células a combustível unitárias. Para complementar o estudo da eletro-oxidação de etanol foram realizados estudos fundamentais usando monocristais de Pt com baixos e altos índices de Miller.Carbon supported Pt-Sn catalysts were prepared by reduction of Pt and Sn precursors with formic acid. The method allowed the efficient preparation of catalysts with low Sn contents (Pt:Sn ratio 9:1) and with high Sn contents (Pt:Sn ratio 1:3. In spite of the fact that Sn was anchored in the material, only part of the Sn is inserted in the fcc structure of Pt. Therefore, a thermal treatment in a reducing atmosphere was necessary to increase the degree of alloy. Thermal treatments were done between 100 and 500 oC and the Pt3Sn material treated at 200 oC showed the best performance in a direct ethanol fuel cell. The thermal treatment at 200 oC allowed an increase of the degree of alloy without modifying the face centered cubic Pt structure and without promoting the coalescence of the nanoparticles anchored on the carbon support. The Pt-Sn catalysts were characterized by X-ray diffraction, X-ray absorption and transmission electron microscopy. The activity for the electro-oxidation of ethanol was evaluated with electrochemical techniques and experiments in a single direct ethanol fuel cell. Studies with Pt single crystals with low and high Miller indices were done to complement the study of the ethanol electro-oxidation.
30
Millican-Slater, Adam. "Aspects of PT-symmetric quantum mechanics". Thesis, Durham University, 2004. http://etheses.dur.ac.uk/3125/.
Testo completoAbstract (sommario):
PT-symmetric quantum mechanics is an alternative to the usual hermitian quantum mechanics. We will start this thesis by taking an overview of the subject, seeing some of the elementary consequences of this different approach. The main part of the work will be an depth study of a specific Hamiltonian(diagram) This is a generalisation of the well understood harmonic oscillator with angular momentum. By making this generalisation we break the hermiticity of the problem. This leads to some intriguing results. We will be particularly interested in the merging of eigenvalues for M <1.We study the problem using a number of techniques. First the Hamiltonian is studied at the classical level and the behaviour of a particle moving in the corresponding potential is studied. Having seen the consequences at the classical level we return to the quantum case. The Hamiltonian is first solved perturbativly. This method is shown to be valid for PT-symmetric quantum mechanics. It is shown that asymptotic limits of the matrix do not capture the full behaviour of the energy levels. We then move on to study the problem considering techniques arising from the ODE/IM correspondence. Using this approach we are able to give an analytic description of the phenomena and explain the merging of eigenvalues.
31
Tanjung, Michael. "PT. Telekomunikasi Indonesia: challenging year ahead". Master's thesis, NSBE - UNL, 2014. http://hdl.handle.net/10362/11714.
Testo completo
32
Peräntie, J. (Jani). "Electric-field-induced dielectric and caloric effects in relaxor ferroelectrics". Doctoral thesis, Oulun yliopisto, 2014. http://urn.fi/urn:isbn:9789526204406.
Testo completoAbstract (sommario):
Abstract In this thesis, dielectric and thermal behaviours due to the application of an electric field were studied in relaxor ferroelectric (1−x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT) and (1−x)Pb(Zn1/3Nb2/3)O3-xPbTiO3 (PZN-PT) systems of great technological importance. Special attention was given to the behaviour of the electric-field-induced phase transitions and electrocaloric effect, which are closely related to the existing and potential applications. Reactive sintering or columbite methods were used to fabricate polycrystalline PMN-PT ceramics with various compositions (x=0−0.3). In addition, commercial PMN-PT single crystals with composition close to the morphotropic phase boundary region were used. A studied PZN-PT crystal composition was grown by solution gradient cooling technique. Materials were mainly studied by means of dielectric and direct temperature measurements. The electrocaloric effect observed in a ceramic PMN-PT system was found to show distinct maximum values close to the thermal depolarization temperatures with low electric fields. The temperature range and magnitude of the electrocaloric effect was significantly expanded to high temperatures with increasing electric fields due to the contribution of polar nanoregions. The maximum electrocaloric temperature change was in the range of 0.77−1.55 °C under an electric field of 50 kV/cm. In addition, temperature change measurements on depoled PMN-0.13PT ceramics demonstrated that the electrocaloric effect is accompanied with an irreversible part below its depolarization temperature due to hysteresis loss and a possible phase transition type response related to the evolution of the macroscopic polarization. An electric field application to the <001> and <011> directions in PMN-PT crystals was found to cause distinct anomalies in the dielectric and temperature change responses. These anomalies were attributed to the complex polarization rotation routes and different phase stability regions in the electric-field-temperature phase diagrams of PMN-PT. Furthermore, measurements on PMN-PT crystals provided the first direct indications of a temporarily reversed electrocaloric effect with an increasing electric field. In addition, the measured electrocaloric trends in PZN-PT crystal were reproduced by a simple lattice model and mean-field approximation around the transition temperature. This demonstrated that the electrocaloric effect is driven mainly by the dipolar entropy loweringTiivistelmä Tässä työssä tutkittiin dielektristen ominaisuuksien ja lämpötilan käyttäytymistä teknologisesti merkittävissä (1−x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT) ja (1−x)Pb(Zn1/3Nb2/3)O3-xPbTiO3 (PZN-PT) ferrosähköisissä relaksorimateriaaleissa sähkökentän vaikutuksen alaisena. Tutkimuksen erityishuomion kohteena olivat sähköisesti indusoidut faasimuutokset sekä sähkökalorinen ilmiö, jotka liittyvät läheisesti nykyisiin sekä tulevaisuuden sovellutuksiin. Monikiteisiä PMN-PT keraamikoostumuksia (x=0−0,3) valmistettiin sekä reaktiivisella sintrauksella että kolumbiittimenetelmällä. Lisäksi tutkimuksessa käytettiin kaupallisia PMN-PT erilliskiteitä, joiden koostumus on lähellä morfotrooppista faasirajaa. Työssä käytetty PZN-PT erilliskide kasvatettiin jäähdyttämällä korkean lämpötilan liuoksesta. Materiaaleja tutkittiin pääosin lämpötilan ja dielektristen ominaisuuksien mittauksilla. Kun PMN-PT keraamisysteemiin kohdistettiin alhainen sähkökenttä, sähkökalorisen ilmiön selkeä maksimiarvo havaittiin lähellä materiaalin termistä depolarisaatiolämpötilaa. Suuremmilla sähkökentän arvoilla sähkökalorinen ilmiö voimistui ja sen lämpötila-alue laajeni korkeampiin lämpötiloihin polaaristen nanoalueiden kytkeytymisen vuoksi. Sähkökalorisen lämpötilamuutoksen maksimi vaihteli välillä 0,77−1,55 °C sähkökentän arvolla 50 kV/cm. Lisäksi lämpötilamittaukset depoolatulle PMN-0,13PT koostumukselle osoittivat, että sähkökalorisen ilmiön ohella materiaalissa esiintyy makroskooppisen polarisaation muodostumiseen liittyvä palautumaton lämpöenergia depolarisaatiolämpötilaa pienemmissä lämpötiloissa hystereesihäviön ja mahdollisen faasimuutoksen vaikutuksesta. PMN-PT erilliskiteiden dielektrisyys- ja lämpötilavasteessa havaittiin selkeitä muutoksia sähkökentän vaikuttaessa <001> ja <011> kidesuuntiin. Nämä muutokset ovat selitettävissä PMN-PT:n polarisaation kompleksisten rotaatiosuuntien ja erityyppisten sähkökenttä-lämpötila -faasidiagrammien stabiilisuusalueiden avulla. PMN-PT kiteiden mittauksissa havaittiin myös ensimmäinen suora osoitus väliaikaisesti käänteisestä sähkökalorisesta ilmiöstä sähkökentän kasvaessa. Lisäksi mitatut PZN-PT erilliskiteen sähkökaloriset ominaisuudet transitiolämpötilan läheisyydessä pystyttiin pääpiirteittäin mallintamaan käyttämällä yksinkertaista hilamallia ja keskimääräisen kentän approksimaatiota. Mallinnuksen mukaan sähkökalorinen ilmiö aiheutuu pääasiassa sähköisesti indusoidusta dipolientropian alenemisesta
33
Schimpf, Sabine. "Partielle Gasphasen-Hydrierung von 2-Butenal zu 2-Butenol an Pt/TiO2- und Pt-Sn/TiO2-Katalysatoren". Doctoral thesis, [S.l. : s.n.], 1999. http://deposit.ddb.de/cgi-bin/dokserv?idn=967371872.
Testo completo
34
Klewe, Christoph [Verfasser]. "Static and non-equilibrium magnetic proximity effects in Pt/NiFe2O4 and Pt/Ni1 – xFex heterostructures / Christoph Klewe". Bielefeld : Universitätsbibliothek Bielefeld, 2016. http://d-nb.info/1084887142/34.
Testo completo
35
Heße, Simon [Verfasser], e Hans Peter [Akademischer Betreuer] Oepen. "Magnetotransport in Co/Pt-Schichtsystemen und Charakterisierung einzelner Co/Pt-Nanoteilchen / Simon Heße. Betreuer: Hans Peter Oepen". Hamburg : Staats- und Universitätsbibliothek Hamburg, 2014. http://d-nb.info/1054421684/34.
Testo completo
36
Gorchon, Jon. "Current and field induced magnetization reversal in Pt/Co/Pt and (Ga, Mn)(As, P) ferromagnetic films". Thesis, Paris 11, 2014. http://www.theses.fr/2014PA112143.
Testo completoAbstract (sommario):
La manipulation de l’état magnétique d’un système ferromagnétique présente un grand intérêt en raison de possibles applications technologiques. Comprendre les mécanismes fondamentaux qui contrôlent l’aimantation est donc particulièrement important. La compréhension de certains mécanismes peut également avoir un impact dans d’autres domaines de la physique. C’est le cas par exemple de la dynamique de déplacement de parois de domaines sous champ magnétique dans le régime de reptation (creep) qui peut être assimilé à celui d’une interface élastique et qui présente un caractère universel. Cette thèse présente tout d’abord, à travers un travail expérimental sur des couches ultra-minces de Pt/Co/Pt, une description complète de la dynamique de déplacement de parois de domaines sous champ magnétique. Une analyse auto-cohérente permet d’extraire tous les paramètres de contrôle, des exposants universels sont confirmés et un nouveau régime dynamique (le TAFF) est identifié. Une deuxième étude porte sur le déplacement de parois sous courant électrique en géométrie étendue dans un film de (Ga,Mn)(As,P). Cette étude met en évidence des instabilités de forme des parois de domaines soumises à un gradient de courant électrique. Les limites de stabilités sont analytiquement prédites et présentent un bon accord avec les expériences. Un troisième travail porte sur le renversement de l’aimantation à l’interface entre un film de (Ga,Mn)(As,P) et une électrode non ferromagnétique. Un renversement stochastique de l’aimantation sous courant continu est mis en évidence. Son origine réside dans l’accumulation de spin à l’interface qui diminue fortement l’aimantation locale. Un modèle simplifié permet de décrire la probabilité de retournement de l’aimantation et d’extraire les temps caractéristiques associésEffectively manipulating the magnetic state of a ferromagnet has a great interest for possible technological applications. Understanding the underlying fundamental mechanisms is thus particularly important. In some cases, the understanding of some mechanisms may even importantly impact other areas of physics. This is the case for example with field induced magnetic domain walls motion in the creep regime, where the wall can be assimilated to an elastic interface and follows an universal behavior. This thesis presents through an experimental work on Pt/Co/Pt ultra-thin samples, a complete description of the temperature and field dependent domain wall dynamics. A self-consistent analysis allows the extraction of all control parameters, identifying the new Thermally Activated Flux Flow regime, and confirming universal thermal scaling exponents. A second study focuses on current induced domain wall motion in an extended geometry of a (Ga,Mn)(As,P) ferromagnetic film. This study unveils domain wall shape instabilities under a gradient of current. The instability limits are analytically predicted in agreement with the experimental observations. A third work concerns the magnetization reversal mechanism evidenced at the interface between a (Ga,Mn)(As,P) film and a non-ferromagnetic electrode under a current flow. The reversal is shown to be stochastic and mainly governed by the spin accumulation at the interface, which reduces importantly the local magnetization. A simplified model allows the description of the reversal probability and the time scales involved in the mechanism of reversal are accessed and discussed
37
Souza, Nyccolas Emanuel de. "Catalisadores 'PT' e 'PT"SN' modificados com 'SN''O IND.2' para a oxidação eletroquímica de etanol /". Araraquara [s.n.], 2011. http://hdl.handle.net/11449/92048.
Testo completoAbstract (sommario):
Orientador: Hebe de Las Mercedes VillullasBanca: Antônio Carlos Dias Ângelo
Banca: Lucia Helena Mascaro
Resumo: Com o intuito de avaliar a influência da presença de óxido na resposta eletrocatalítica para a oxidação de etanol, foram preparados quatro materiais constituídos de partículas metálicas de Pt ou liga PtSn, suportados sobre SnO2 e carbono, ou diretamente sobre carbono (Pt-SnO2/C, Pt/C, PtSn/C e PtSn-SnO2/C). As nanopartículas metálicas e as nanopartículas de SnO2 foram preparadas inicialmente em estado coloidal, em processos de síntese realizados separadamente para garantir bom controle das propriedades dos materiais. Os catalisadores foram caracterizados por difratometria de raios-X, espectroscopia de fotoelétrons induzidos por raios-X e espectroscopia de absorção de raios-X dispersivos. Os resultados mostraram que houve formação de liga PtSn nos catalisadores PtSn/C e PtSn-SnO2/C e a formação de SnO2 em todos os catalisadores modificados com estanho. Os catalisadores com liga PtSn apresentaram um preenchimento da banda 5d da platina, enquanto que a modificação com SnO2 ocasionou um esvaziamento da banda. Experimentos de oxidação de CO adsorvido mostraram que os materiais possuem diferentes características superficiais, e que os catalisadores contendo liga PtSn têm menores areas de Pt eletroquimicamente ativa. A atividade catalítica para a oxidação de etanol foi avaliada por voltametria cíclica e cronoamperometria, que evidenciaram um melhor desempenho para os materiais PtSn/C e PtSn-SnO2/C. Os resultados obtidos indicam que a liga PtSn é fundamental para a promoção da atividade catalítica de oxidação de etanol em sistemas PtSn.
Abstract: Aiming to evaluate the influence of oxides on the electrocatalytic activity for ethanol oxidation, four catalysts containing metallic Pt or PtSn nanoparticles supported either on SnO2 and carbon; or directely on carbon (Pt-SnO2/C, Pt/C, PtSn/C, and PtSn-SnO2/C) were prepared. Metallic nanoparticles and SnO2 nanoparticles were obtained, initially in colloidal state, in separate synthesis procedures to ensure adequate control of their properties. All catalysts were characterized by X-ray diffraction, X-ray photoelectron spectroscopy and dispersive X-ray absorption spectroscopy. The results showed that a PtSn alloyed phase was formed on the PtSn/C and PtSn-SnO2/C catalysts and the presence of SnO2 in all materials containing tin. The two catalysts containing PtSn alloy showed a more filled Pt 5d band, while the addition of SnO2 produced a vacancy increase of the d band. Experiments of adsorbed CO oxidation showed that the catalyts have different surface characteristics, and that materials containg a PtSn alloyed phase have lower Pt electrochemically active areas. The catalytic activity for ethanol oxidation was evaluated by cyclic voltammetry and chronoamperometry, evidencing a better performance for PtSn/C and PtSn-SnO2/C. The results obtained indicate that the presence of PtSn alloy is necessary to enhance the catalytic activity for ethanol oxidation on PtSn systems
Mestre
38
Mateus, João Henrique do Carmo. "PT Multimedia: spinning off PT Multimedia". Master's thesis, 2016. http://hdl.handle.net/10362/17267.
Testo completoAbstract (sommario):
The purpose of the present case – and accompanying Teaching Notes – is to better understand the spin-off of PT Multimédia, by Portugal Telecom, after receiving a Public Takeover Offer from Sonaecom, in 2006. The Government and the Competition Authority had never looked in a serious way at PT’s dominant position and the lack of room for competition in the TMT sector – PT was the owner of both the cable and copper networks, having access to privileged information from its competitors with control over the wholesale and retail businesses. In 2006, the company received a takeover offer from Sonaecom, the TMT subsidiary from the Portuguese conglomerate Sonae. The offer was voted and rejected by a majority of PT shareholders, but the whole process triggered several recommendations from the regulatory bodies. As a result, PT divested its cable business with the spin-off of PT Multimédia, giving birth to a new competitor and a totally different landscape in the telecommunications sector in Portugal.
39
Nowak, Lukáš. "Kontrola magnetické anizotropie v multivrstvách Pt/Co/Pt". Master's thesis, 2021. http://www.nusl.cz/ntk/nusl-448241.
Testo completoAbstract (sommario):
This thesis aims to explore the effect of in situ ion gun etching on magnetic proper- ties, such as perpendicular magnetic anisotropy, of Pt/Co/Pt multilayers. Perpendicular magnetic anisotropy is of interest due to its importance in spintronic application. Calibration spectroscopic ellipsometry measurements of Pt and Co layers to obtain sputter yields of respective magnetron targets were performed as a first step. After that, ten Pt/Co/Pt multilayers with different Co and top Pt layer thicknesses were prepared. Five of these samples were etched by the ion gun, mounted inside of the magnetron chamber, during different stages of the deposition. To characterize the prepared samples, experimental and modeled Kerr rotation spectra were confronted. This provided an insight into the cross-sections of the investigated samples. Magnetic hysteresis loops measured by vibrating sample magnetometer and Kerr rotation setup demonstrated higher coercive field and change of the slope of the loop induced by ion etching. When compared to the obtained cross-sections, a correlation between the change of magnetic loops and intermixing of Pt and Co at the interface was visible. This intermixing was higher in samples treated by the ion gun. 1
40
Yang, Jin-Cherng, e 楊金成. "Electrochemical Sensor Based on Pt/Nafion and Pt/Nafion/Pt Membrane Electrrodes for NO Sensing". Thesis, 1997. http://ndltd.ncl.edu.tw/handle/02235195409838274068.
Testo completoAbstract (sommario):
碩士國立臺灣大學
化學工程學系
85
The oxidation of nitric oxide(NO) at platinum membrane electrodes is discussed. The Pt/Nafion and Pt/Nafion/Pt membrane electrodes were prepared by the impregnation-reduction procedure. The electrochemical behaviors during the oxidation of nitric oxide at the platinum/solid polymer electrolyte interface, including the limiting current density, sensitivity, response time, aging, and redox characteristics, were studied. The NO oxidation limiting current is observed when the Pt/ Nafion membrane electrodes is operated beyond 1.0V (vs. Ag/ AgCl). An I-E relation has been derived which takes into account the polarization behaviors in both kinetic and mass transfer controlled regimes. Experimental analysis yields various parameters in the steady-state model. Kinetic and surface parameters, such as the apparent rate constant, transfer coefficient, and reaction order have been extracted from the experimental results. In addition, Up to the upper limit of 500ppm NO employed in this study, there is a linear relationship between the limiting current and the concentration of nitric oxide. At a gas flow rate of 200mL/ min, the maximum sensitivity of the electrochemical sensor is found to be 1.422mA/cm2ppm. Sensitivity decreased 11.2% after the first sensing; sensitivity also decreased when the electrode is operated continuously for 20 hrs, presumably due to the partial oxidation of Pt. However, sensitivity is recovered when the electrode In the case of the Pt/Nafion/Pt electrode, similar electrochemical behaviors were observed as compared to that of the Pt/Nafion* electrode. However, the sensitivity is lower for the Pt/Nafion*/Pt electrode. Moreover, the polarization behavior of the Pt/Nafion/Pt electrode does not show an ideal mass transfer control regime, which eventually may limit the application in NO sensing.
41
Li, Yang-Shyun, e 李仰薰. "The Perpendicular Anisotropy and Antiparallel Coupling in [Co/Pt], [Co0.3Fe0.7/Pt], and [Fe/Pt] Multilayers". Thesis, 2010. http://ndltd.ncl.edu.tw/handle/96947657629245299344.
Testo completoAbstract (sommario):
碩士國立中正大學
物理所
98
Ferromagnetic materials with perpendicular anisotropy, such as CoPt and FePt, which may have high thermal stability and the characteristic of reduction of the switching current in spin-transfer-torque devices, has become the most prosing candidate for the further application on random access memory. In this thesis, we fabricated [Co/Pt],[Co0.3Fe0.7/Pt],and [Fe/Pt] multilayered structure by DC and RF sputtering techniques and carried out detailed magnetic characterizations. The major results include:
42
Wang, Yu-Fang, e 王毓芳. "Carbon Supported Pt and Pt-Ru Catalyst: Preparation and Catalysis". Thesis, 1997. http://ndltd.ncl.edu.tw/handle/73764385535697823038.
Testo completoAbstract (sommario):
碩士國立中正大學
化學工程研究所
85
Abstract The goals of this research were to prepare cabon supported Pt and Pt- Ru catalysts for methanol fuel cell and for oxidation of acetaldehyde. The oxidation reaction of acetaldehyde were carried out with a continous fix bed reactor at 40℃and 520psig. Both fresh and the reacted catalysts were characterized by CO chemisorption , fast Fourier transform infrared (FFT-IR) spectroscopy, temperature programmed reduction (TPR), atomic absorption spectroscopy (AA), and extended X-ray absorption fine structure (EXAFS). Together with the reaction and characterization results, the following conclusions were obtained regarding the structure and catalytic performance of the catalysts： (1) The despersion of the catalyst was increased with decreasing the amount of water used for the preparation because of the hydrophorbic properties of carbon supports. (2) The catalysts with the highest metal dispersion have the metal particles with morphology characterizing three dimension. (3) For the fresh carbon-supported Pt catalysts, the highest Pt dispersion is the catalyst reduced at 200℃, the 300℃ in the middle, the lowest is the catalyst reduced at 450℃. However, the catalyst reduced at 300℃ presents the best performance. The results is the compromise between Pt metal dissoluted, metal migration and oxidation of metal particles. (4)During the oxidation reaction, only surface has been oxidized. (5)The main difference of the catalytic performance between the Pt-Ru/C catalyst with and without bimetallic interactions is over-oxidation reaction ; the catalysts without bimetalic interactions has more water yield. (6) The addition of Ru to the Pt catalysts has no improvement in metal dissoluted problem.
43
Kim, Seok koo 1973. "Platinum catalysts degradation by oxide-mediated platinum dissolution in PEMFCs (Proton Exchange Membrane Fuel Cells)". Thesis, 2011. http://hdl.handle.net/2152/28723.
Testo completoAbstract (sommario):
Proton exchange membrane fuel cells (PEMFCs) have attracted great attention due to their high power density, low-temperature operation and high energy conversion efficiency. However, the high cost of Pt catalysts and durability problems hinder their commercialization. So their cost must be lowered drastically and their durability must be extended. In an effort to overcome these problems, there have been intensive efforts to enhance the activity, durability and to lower the price of catalysts by alloying with other less expensive metals. In particular, the sluggish kinetics of ORR caused by Pt oxide at cathode and Pt catalyst degradation by electrochemical surface area (ECSA) loss have been a huge research area where a lot of researchers have paid lots of attention to solve. In this regard, the objective of this dissertation is to evaluate a series of Pt catalyst electrode surface electrochemical reactions on PEMFC electrode in order to help searching new catalysts and enhancing system design, assist in the search for new catalysts and improved system design by suggesting the developed mechanism of electrocatalyst activity and stability (durability). We have been focused on understanding the oxide-mediated dissolution of Pt by using electrochemical experiment methods such as RRDE, EQCN, SECM with a combination of ICP-MS and computational simulation with COMSOL Multiphysics. Firstly, in chapter 3, we showed the oxide-mediated Pt dissolution rate and the influence of hydrogen and cation underpotential deposition on Pt dissolution. In chapter 4, we revealed oxygen reduction reaction (ORR) plays a significant role in Pt oxide formation and reduction that influences the Pt catalyst dissolution, resulting in accelerated Pt dissolution rate at specific potential range. Finally, we found out the nature of mobile species generated during PtO₂ reduction process which have been disputed as Pt ion or other mobile species and fulfilled computational simulation for evaluation of SECM experiment in chapter 5. Based on these experiments and simulation, we were able to explain some mechanism of literature results that already were reported but have not been clearly explained so far. In terms of the purpose of this dissertation, the mechanism of oxide-mediated Pt dissolution, influence of ORR to Pt oxide formation/reduction and Pt dissolution, the nature of mobile species generated during PtO₂ reduction process, are sure to be very helpful in developing new catalysts and enhancing system design and suggested operating conditions.text
44
Buntrock, Valerie. "Understanding Pt•••Pt and Pt•••Au metallophilic interactions in single salt and double salt complexes using photophysical tools". Thesis, 2013. https://hdl.handle.net/2144/15251.
Testo completoAbstract (sommario):
Seven [Pt(tpy)X]Y (X=Cl, Y=Cl•2H2O, X=Cl, Y=Cl•DMSO, X=Cl, Y=PF6, X=Cl, Y=SbF6, X=Cl, Y=SbF6•CH3CN, X=Br, Y= Br•2H2O, and X=Br, Y=PF6) complexes were prepared and characterized. Structural analysis shows consistent patterns in Pt^...Pt interactions that vary slightly depending on the coordinating halogen, X, counteranion, Y, and lattice solvent. Diffuse reflectance was used to identify solid-state ^1MMLCT absorption bands, and the relationship between Pt-Pt distance and ^1MMLCT absorption energy will be discussed.
Metallophilic Pt^...Au interactions in [Pt(tpy)X][AuX'2] (X=X'=CN, X=Cl, X'=C6F5, X=Br, X'=C6F5, X=I, X'=C6F5) double salts were investigated. Structural characterization showed Pt^...Au metallophilic interactions were only observed in X=X'=CN, while Pt^...Pt interactions were observed in X=I, X'=C6F5. The closest contacts in X=Cl, X'=C6F5 and X=Br, X'=C6F5 were between the Lewis acidic Pt center of the cation and a Lewis basic ortho carbon of the pentafluorophenyl group on the anion. Photophysical characterization showed MMLCT features in the solid-state but only monomeric MLCT features localized on the [Pt]+ and [Au]- units in solution.
The chromophore [Pt(tpy)(CCPh)]^+ was studied in [Pt][Au(C6F5)2] and [Pt][Pt(C^N)(CN)2] (C^N = ppy, F2ppy, or bzq) double salts. Structural characterization showed formation of a channel of [Pt(tpy)(CCPh)]+ moieties supported by metallophilic interactions in [Pt][Au(C6F5)2] and [Pt][Pt(F2ppy)(CN)2]. Solution electronic absorption spectra showed MLCT features centered on the cation and anion units for all four complexes. An additional ^1MMLCT band near 520 nm is present in the solid-state arising from Pt^...Pt interactions formed between cation units.
Three [Pt(tpy)Cl][Pt(C^N)(CN)2] (C^N = ppy, F2ppy, and bzq) double salts were prepared and characterized. A new solution MMLCT feature was identified for all three double salts using UV-vis and fluorescence spectroscopy. Support of solution cation and anion association using solution conductivity and dynamic light scattering measurements will be discussed.
45
Vineeth, Mohanan P. "Spin Hall Effect Mediated Current Induced Magnetization Reversal in Perpendicularly Magnetized Pt/Co/Pt Based Systems". Thesis, 2016. http://etd.iisc.ac.in/handle/2005/3078.
Testo completoAbstract (sommario):
In the present thesis, magnetization reversal in both out-of-plane and in-plane magnetized thin lms and in devices fabricated out of those lms are explored. Pt/Co/Pt stacks with ultrathin Co layer were in-estimated initially for understanding their magnetic properties in this thesis. These perpendicular magnetized systems are good candidates for magnetic hard disc drives due to their large anisotropy, which may allow miniaturization of magnetic data storage devices. The spin Hall e ect mediated current-induced magnetization reversal in patterned Pt/Co/Pt devices were extensively investigated. Investigation of the magnetization reversal by means of a current instead of a magnetic eld is necessary to explore the possibilities of solid state magnetic memory devices. This is the primary motivation behind the investigation of current-induced magnetization reversal in Pt/Co/Pt system, in this thesis. Another important proposal for magnetic data storage is the race track memory, where the domain walls separating magnetic domains (in in-plane or out-of-plane magnetized materials) are moved by using a current. This involves a great deal of understanding of the domain wall motion in Nano-conduits under applied magnetics ends, and currents and also its interaction with engineered geometrical features. In this thesis work, magnetic led-driven domain wall pinning and deepening experiments on in-plane magnetized nanowires of perm alloy were performed to un-distend this interaction and the e act of domain wall chirality.
In chapter 1, a general introduction to di errant data storage technologies and the current progress in the leg of spintronic is presented. This will highlight a perspective of this thesis work with respect to the present day research in spintronic and magnetization reversal studies.
In chapter 2, a basic background of magnetism using the micromag-netic framework is illustrated. A brief introduction to magnetic domain walls is also presented. The Landau-Lifshitz-Gilbert dynamical equation is discussed and some case studies applied to a single domain particle with uniaxial anisotropy under the effect of spin-orbit torque are illu trated. The basics of spin-orbit coupling leading to spin Hall e ect is also explain
In chapter 3, most of the essential experimental tools along with their basic working principles are described. Extensive e orts have been in-vested in designing and building the experimental tools. These include custom designs of a sputter deposition system, an ultra-high vacuum chamber for pulsed laser ablation, a magneto-optic Kerr e ect magne-tometer, a Kerr imaging system and a magneto-transport setup. All of these experimental setups have been automated, details of which are brie y discussed in this chapter. The Kerr imaging system was designed to measure hysteresis loops, observe domain wall motion and to measure domain wall velocity under applied magnetic elds and electric current. The magneto-transport setup was used for studying the domain wall pinning and depinning experiments in permalloy nanowires.
In chapter 4, the optimization process for obtaining perpendicular mag-netic anisotropy in Pt/Co/Pt lms is described. The spin reorientation transition with varying thickness of Co (from 1.5 nm down to 0.35 nm) was studied. The magnetization easy axis direction changes from in-plane to out-of-plane as the thickness of Co is reduced. The dependence of Curie temperatures of ultrathin Co lms, with thickness as low as 0.35 nm, on the underlayer Pt thickness and its crystallinity was studied in detail. The e act of Ta but err layer on the texture of the Pt lm, and on the Curie temperature of the Pt/Co/Pt system was evaluated. To gain further insight of the role of the bottom Pt/Co and the top Co/Pt interfaces, ultrathin Cu lbs were inserted at the respective interfaces, and the anisotropy and magnetization reversal behaviour of these lbs were investigated.
In chapter 5, studies on current-induced magnetization reversal in mi-corn sized wires of Pt/Co/Pt trilete is presented. The spin Hall e act assisted spin-orbit torque was used to reversibly switch the magnetization of these devices with and without the help of an external magnetic led. Since both the top and bottom layers are Pt, any contribution from Rashia e act towards spin-orbit torque could be ignored. By preparing devices with unequal top and bottom Pt thicknesses, a net spin-orbit torque could be applied to the magnetization of the Co layer. The thickness gradient/induced anisotropy in the Co layer was utilized to experimentally investigate current-induced deterministic switching. Sin-gel domain simulations with spin-orbit torque were also carried out to understand the mechanism of deterministic switching of magnetization in Pt/Co/Pt devices. This study is expected to have made sign cant contributions and to open up the possibilities of further investigation in the studies of spin-orbit torque in Pt/Co/Pt systems for solid state magnetic memory devices.
In chapter 6, magnetic led-induced reversal in systems with in-plane magnetic anisotropy is presented. Here the e act of the width of a Nanos-trip on the anisotropy of a soft magnetic material like perm alloy was in-estimated. By introducing a nucleation pad to one end of the perm alloy nanowire, a single domain wall was generated at the junction with apple-cation of a proper magnetic led sequence. This domain wall could be in-jested into the nanowire by a magnetic led and pinned at a geometrical constriction inside the nanowire. The statistics of domain wall pinning and deepening processes indicated two di errant types of domain walls involved in the reversal process. With the assistance of micro magnetic simulations the domain walls were ident end as vortex walls of di errant chirality’s. Thus the interaction of domain walls with a Nano constriction and its dependence on the chirality of domain walls are understood.
In chapter 7, a brief summary of the results obtained during the course of investigations is presented. An outlook presented at the end will help the readers of this thesis to understand the important research problems in this area and their potential future aspects.
46
Vineeth, Mohanan P. "Spin Hall Effect Mediated Current Induced Magnetization Reversal in Perpendicularly Magnetized Pt/Co/Pt Based Systems". Thesis, 2016. http://hdl.handle.net/2005/3078.
Testo completoAbstract (sommario):
In the present thesis, magnetization reversal in both out-of-plane and in-plane magnetized thin lms and in devices fabricated out of those lms are explored. Pt/Co/Pt stacks with ultrathin Co layer were in-estimated initially for understanding their magnetic properties in this thesis. These perpendicular magnetized systems are good candidates for magnetic hard disc drives due to their large anisotropy, which may allow miniaturization of magnetic data storage devices. The spin Hall e ect mediated current-induced magnetization reversal in patterned Pt/Co/Pt devices were extensively investigated. Investigation of the magnetization reversal by means of a current instead of a magnetic eld is necessary to explore the possibilities of solid state magnetic memory devices. This is the primary motivation behind the investigation of current-induced magnetization reversal in Pt/Co/Pt system, in this thesis. Another important proposal for magnetic data storage is the race track memory, where the domain walls separating magnetic domains (in in-plane or out-of-plane magnetized materials) are moved by using a current. This involves a great deal of understanding of the domain wall motion in Nano-conduits under applied magnetics ends, and currents and also its interaction with engineered geometrical features. In this thesis work, magnetic led-driven domain wall pinning and deepening experiments on in-plane magnetized nanowires of perm alloy were performed to un-distend this interaction and the e act of domain wall chirality.
In chapter 1, a general introduction to di errant data storage technologies and the current progress in the leg of spintronic is presented. This will highlight a perspective of this thesis work with respect to the present day research in spintronic and magnetization reversal studies.
In chapter 2, a basic background of magnetism using the micromag-netic framework is illustrated. A brief introduction to magnetic domain walls is also presented. The Landau-Lifshitz-Gilbert dynamical equation is discussed and some case studies applied to a single domain particle with uniaxial anisotropy under the effect of spin-orbit torque are illu trated. The basics of spin-orbit coupling leading to spin Hall e ect is also explain
In chapter 3, most of the essential experimental tools along with their basic working principles are described. Extensive e orts have been in-vested in designing and building the experimental tools. These include custom designs of a sputter deposition system, an ultra-high vacuum chamber for pulsed laser ablation, a magneto-optic Kerr e ect magne-tometer, a Kerr imaging system and a magneto-transport setup. All of these experimental setups have been automated, details of which are brie y discussed in this chapter. The Kerr imaging system was designed to measure hysteresis loops, observe domain wall motion and to measure domain wall velocity under applied magnetic elds and electric current. The magneto-transport setup was used for studying the domain wall pinning and depinning experiments in permalloy nanowires.
In chapter 4, the optimization process for obtaining perpendicular mag-netic anisotropy in Pt/Co/Pt lms is described. The spin reorientation transition with varying thickness of Co (from 1.5 nm down to 0.35 nm) was studied. The magnetization easy axis direction changes from in-plane to out-of-plane as the thickness of Co is reduced. The dependence of Curie temperatures of ultrathin Co lms, with thickness as low as 0.35 nm, on the underlayer Pt thickness and its crystallinity was studied in detail. The e act of Ta but err layer on the texture of the Pt lm, and on the Curie temperature of the Pt/Co/Pt system was evaluated. To gain further insight of the role of the bottom Pt/Co and the top Co/Pt interfaces, ultrathin Cu lbs were inserted at the respective interfaces, and the anisotropy and magnetization reversal behaviour of these lbs were investigated.
In chapter 5, studies on current-induced magnetization reversal in mi-corn sized wires of Pt/Co/Pt trilete is presented. The spin Hall e act assisted spin-orbit torque was used to reversibly switch the magnetization of these devices with and without the help of an external magnetic led. Since both the top and bottom layers are Pt, any contribution from Rashia e act towards spin-orbit torque could be ignored. By preparing devices with unequal top and bottom Pt thicknesses, a net spin-orbit torque could be applied to the magnetization of the Co layer. The thickness gradient/induced anisotropy in the Co layer was utilized to experimentally investigate current-induced deterministic switching. Sin-gel domain simulations with spin-orbit torque were also carried out to understand the mechanism of deterministic switching of magnetization in Pt/Co/Pt devices. This study is expected to have made sign cant contributions and to open up the possibilities of further investigation in the studies of spin-orbit torque in Pt/Co/Pt systems for solid state magnetic memory devices.
In chapter 6, magnetic led-induced reversal in systems with in-plane magnetic anisotropy is presented. Here the e act of the width of a Nanos-trip on the anisotropy of a soft magnetic material like perm alloy was in-estimated. By introducing a nucleation pad to one end of the perm alloy nanowire, a single domain wall was generated at the junction with apple-cation of a proper magnetic led sequence. This domain wall could be in-jested into the nanowire by a magnetic led and pinned at a geometrical constriction inside the nanowire. The statistics of domain wall pinning and deepening processes indicated two di errant types of domain walls involved in the reversal process. With the assistance of micro magnetic simulations the domain walls were ident end as vortex walls of di errant chirality’s. Thus the interaction of domain walls with a Nano constriction and its dependence on the chirality of domain walls are understood.
In chapter 7, a brief summary of the results obtained during the course of investigations is presented. An outlook presented at the end will help the readers of this thesis to understand the important research problems in this area and their potential future aspects.
47
Jeong, Doo Seok [Verfasser]. "Resistive switching in Pt/TiO2/Pt / submitted by Doo Seok Jeong". 2008. http://d-nb.info/990714357/34.
Testo completo
48
Lin, Jia-Horng, e 林嘉宏. "Hydroisomerization of n-heptane on Pt/BEA and Pt/MOR Catalysts". Thesis, 1998. http://ndltd.ncl.edu.tw/handle/64477700152214965929.
Testo completo
49
Glaner, Lizelle. "A study of the Ni-Pt-Ru and Co-Pt-Ru systems". Thesis, 2011. http://hdl.handle.net/10539/10537.
Testo completoAbstract (sommario):
The solidification projections and 1000°C isothermal sections of the Ni-Pt-Ru and Co-Pt-Ru systems were determined by characterising alloys of different using SEM and XRD on arc-melted as-cast and annealed samples. Hardness measurements were undertaken and the hardness indentations were also used to determine the preliminary toughness of the samples.
The solidification projection of the Ni-Pt-Ru system showed that the (Ni,Pt) solvus retreats to the Pt corner in the ternary wherever (Ru) formed where it was not expected and a third phase appeared after heat treatment on a locus from ~Ni20: Pt30: Ru50 to ~Ni10: Pt50: Ru40. A possible miscibility gap in the (Ni,Pt) phase was found in Alloy LG 10. Alloys LG 1 underwent the ordering after heat treatment. The other alloys softened after annealing. Reasonable toughness was exhibited by all the alloys because of the fcc phase that occur in all of them. The Co-Pt-Ru system showed that the α→ε transformation that took place in two of the component binaries was stabilised in the ternary system, in both the as-cast and annealed alloys. The L + (Ru) → fcc (Co,Pt) peritectic reaction was demonstrated by many of the annealed alloys. During heat treatment (Ru) precipitates formed and this indicated that the fcc (Co,Pt) solvus was sloping and retreating towards lower Ru contents at lower temperatures. The hardnesses of the alloys did not change very much after heat treatment, with the exception of Alloys LG 11 and LG 15. Alloy LG 11 showed ordering and Alloy LG 15 showed a significant decrease in hardness due to the coarsening of the microstructure. The toughness remained reasonable for al the alloys as a result of the presence of the fcc phase in all of them.
50
Jan, Kao Yu, e 高玉娟. "Study of Pt or Ir atoms and custers diffusion on Pt surfaces". Thesis, 2008. http://ndltd.ncl.edu.tw/handle/98703201464765918748.
Testo completoAbstract (sommario):
碩士國立臺灣師範大學
物理學系
96
study of Pt or Ir atoms and clusters diffusion on Pt surfaces Using the field ion microscope in ultra high vacuum, we observe directly the diffusion behavior of Pt or Ir atoms on Pt surfaces. After annealing at 135K, single Pt occupies at FCC site exclusively on Pt(111). This phenomenon is decided by the apex of the image triangle. By site mapping, we analyze how many steps Pt diffuses, and then put the mean square displacements into the Boltzmann distribution. The diffusion activation energy of Pt on Pt(111) is 0.33±0.01 eV. According to the frequency of Pt occupation at FCC (HCP) site, the binding energy of Pt at FCC site is 0.04 eV greater than HCP site at least. The probability of Ir7 on Pt(111) as close-packed hexagon is 35/40. During 40 diffusion events, we get the diffusion activation energy of Ir7 on Pt(111) is 1.41±0.03 eV. Comparing Ir7/Pt(111) with Pt7/Pt(111)[3], Ir7 on Pt(111) has greater diffusion energy than Pt7 on the same substrate. Comparing Ir7/Pt(111) with Ir7/Ir(111)[6], Ir7 on Ir(111) has greater diffusion activation energy than on Pt(111). Finally, We discuss the factors of the diffusion activation energy, including the binding energy of the adsorbed clusters, and the interaction between the adsorbed clusters and the substrate.