O presente trabalho trata da obtenção de ligas de NiFe de NiFeCo sob a forma de filmes finos e também no seu uso na tentativa em se construir um sensor magnético tipo fluxgate planar. A técnica de produção utilizada foi a eletrodeposição com regime galvanostático. A solução eletrolítica utilizada era constituída por sais de níquel e ferro e alguns aditivos. Para depositar os filmes de NiFe, o eletrodo auxiliar era constituído de níquel; enquanto que para depositar os filmes de NiFeCo, o eletrodo auxiliar era constituído de cobalto. Os filmes foram depositados em substratos de cobre utilizando densidades de corrente no intervalo de 4 até 28 mA/cm2, com tempos totais de 40 e 60 minutos. A caracterização morfológica foi realizada utilizando Microscopia Eletrônica de Varredura superficial e de seção lateral e para encontrarmos a composição dos elementos presentes na amostra, realizamos a Espectroscopia de Energia Dispersiva e Difração de Raios-X. Quanto à caracterização magnética foi utilizado o Magnetômetro de Amostra Vibrante e também magnetometria utilizando o Superconducting Quantum Interference Devices (este foi utilizado somente para os filmes de NiFeCo) como o elemento detector do equipamento. Os filmes de NiFe crescem com orientações cristalinas ao longo dos planos (110) e (200); as quantidades de níquel e ferro atingem valores constantes a partir da densidade de corrente de 15 mA/cm2 (embora sempre haja mais níquel que ferro); o ponto de menor coercividade magnética (58,4 A/m) também ocorre a partir dessa densidade de corrente, onde filmes com 1 ?m de espessura são conseguidos para um tempo total de 40 minutos. Nota-se uma assimetria para os campos aplicados perpendicular e paralelamente à superfície do filme. Os filmes de NiFeCo crescem com orientações ao longo dos planos (111) e (200). Embora sempre haja mais níquel (constante em 70%), as concentrações de Fe e Co se igualam apenas para uma densidade de corrente próxima de 15mA/cm2. Abaixo desse valor há mais ferro, e acima mais Co. A partir dessa densidade de corrente, novamente observa-se um mínimo no valor da coercividade magnética do material (81 A/m). A partir dessa densidade de corrente, tal grandeza teve seu valor mantido praticamente constante. Para essa densidade de corrente filmes de 6 ?m de espessura são obtidos para um tempo de 40 minutos. Uma menor assimetria magnética é observada comparada com o caso anterior. Por esses dados, acreditamos que o filmes de NiFeCo seja um melhor candidato para a confecção do sensor planar tipo fluxgate, e testes iniciais de sua fabricação também são apresentados. / This work presents the results about the fabrication and characterization of thin films of NiFe and NiFeCo alloys. The attempts to construct the planar fluxgate are also presented. Galvanostatic electrodeposition using an electrolytic solution containing Ni and Fe was used: NiSO4 (0,7 mol/l); NiCl2 (0,02 mol/l); FeSO4 (0,03 mol/l); H3BO3 (0,4 mol/l) and C7H5O3NS.2H2O (0,016 mol/l). The auxiliary electrode was made on Ni for the NiFe films, while another one made on Co was used for the NiFeCo films. Films were deposited on copper substrates using current densities form 4 up to 28 mA/cm2, and total deposition time of 40 and 60 minutes. Structural characterization was performed using Scanning Electron Microscopy (surface and cross-section); Energy Dispersive Spectroscopy, and Xray Diffraction. Magnetic characterization was performed using two methods: the Vibrating Sample Magnetometry and magnetometry using a SQUID (Superconducting Quantum Interference Devices) sensor. NiFe films grow with crystalline planes oriented along the (110) e (200) directions; the amount of each material reach constant values for current densities above 15 mA/cm2 (even though there is always more Ni). The point of minimum magnetic coercivity (58,4 A/m) also occurs for this current density, where films 1 ?m-thick are obtained for a total deposition time of 40 minutes. An asymmetry is observed for magnetic fields applied parallel and perpendicular to the surface of the films. NiFeCo films grow with crystalline planes oriented along the (111) and (200) directions; the amount of Ni remains constant (about 70%) for the whole current density range. The amount of Fe decreases with increasing current density, while the amout of Co shows the opposite behavior. They have equal values for current densities of about 15mA/cm2, where the minimum coercivity of 81A/m is achieved. For higher current densities the coercivity remains constant. For the current density of 15mA/cm2, 6 ?m-thick films are obtained for a total deposition time of 40 minutes. The magnetic asymmetry is smaller than for the case of the NiFe films. According to the obtained data, we believe that NiFeCo is a better candidate for the fabrication of planar magnetic fluxgate sensors. Initial tests for the fabrication of a prototype are also presented.

The aim of this thesis is a systematic study of physical properties of magnetic multilayered nanostructures. Namely it include multilayered spin valves NiFe/Cu/Co with magnetic anisotropy iduced by magnetic field applied during the deposition. Induced magnetic anisotropy influences exchange interactions between magnetic layers and so it gives the possibility to control magnetic properties of nanolayers. This is important for applications in MRAM, magnetoresistive read heads and spin-transfer-torque devices. Magnetooptic spectroscopy and Kerr effect hysteresis loop measurement were used as effective probe techniques. Secondly we examinated Ar3+ rf sputtering influence on multilayer interface quality level. We found out, that Ar3+ irradiation during deposition process has a possitive effect on interface quality.

Les hydrogénases NiFe sont des métalloenzymes capables de catalyser efficacement la production et l'oxydation du dihydrogène à des potentiels proches de l'équilibre thermodynamique. Leur site actif est constitué d'un complexe hétérobimétallique comportant un atome de nickel en environnement soufré relié par deux ponts thiolates à un motif organométallique fer-cyano-carbonyle. Afin d'obtenir des catalyseurs de production d'hydrogène alternatifs au platine actuellement utilisé dans les électrolyseurs et pour approfondir la compréhension du mécanisme catalytique de l'enzyme, nous avons élaboré plusieurs modèles de faible poids moléculaire inspirés de la structure du site actif de ces enzymes : il s'agit de complexes dinucléaires possédant le motif papillon Ni(µ-S2)M (M= Ru, Mn et Fe). Les propriétés électrocatalytiques de ces composés ont été évaluées : ils s'avèrent tous actifs en production d'hydrogène. La modification de la densité électronique et de l'encombrement stérique au niveau du centre ruthénium des complexes Ni-Ru synthétisés a permis d'optimiser les performances de ces catalyseurs en termes de stabilité, de vitesse de catalyse et de surtension. Une étude mécanistique du cycle catalytique des complexes Ni-Ru a également été menée : en combinant mesures électrochimiques et calculs théoriques (DFT), elle a permis de proposer un intermédiaire catalytique hydrure de nature pontante entre les deux métaux Ni et Ru. Enfin, le complexe dinucléaire Ni-Fe synthétisé constitue l'un des premiers modèles à la fois structural et fonctionnel des hydrogénases NiFe.

The objective of the proposed research is to use MEMS technology to develop low profile power inductors with minimized eddy current losses to be used in high power density compact switching converters. Eddy currents arise in high-flux density metallic cores as increased switching frequencies of DC-DC converters cause the skin depth to be small compared with the core thickness. Laminations can reduce the eddy current losses but converters operating with switching frequencies in the MHz regime may require submicron laminations. Previous research has been done to fabricate inductors with micron-scale laminated cores for high frequency switching converters. To optimize the previous fabrication technique, an automated electroplating system was developed for the fabrication of thick magnetic cores comprising large number of submicron laminations without human intervention. Inductors with higher inductance, quality factor and power handling capacity have been realized compared to previously developed inductors. The inductors are characterized in terms of saturation behavior and power handling capability. A miniaturized DC-DC converter with power conversion capacity of 10 Watts has been demonstrated using the fabricated inductor.

The biosynthesis of [NiFe]-hydrogenase and urease in Helicobacter pylori requires several accessory proteins for proper assembly of the nickel-containing active sites. Critical to the maturation of both enzymes in H. pylori is the GTPase HypB. In this work, the metal-binding properties of H. pylori HypB (HpHypB) were investigated and a link between metal binding and the other biochemical properties of HpHypB was established. HpHypB binds stoichiometric nickel or zinc with nanomolar affinities, in partially overlapping sites located between two major GTPase motifs. Upon metal binding, the GTP hydrolysis activity and oligomeric properties of the protein are modulated. Furthermore, the stoichiometry and affinity of the nickel is altered when HpHypB is bound to nucleotide, a change not observed for zinc. Mutagenesis of the metal ligands suggest that a conserved cysteine is responsible for transducing the metal-bound state to altered GTPase activity and a conserved histidine is a required nickel ligand only in the nucleotide-bound state. Together, these results suggest that the metal-binding and GTP hydrolysis properties of HpHypB are intimately linked and may comprise a mechanism through which the [NiFe]-hydrogenase and urease maturation pathways can discriminate between Ni(II) and Zn(II). Characterization of the Escherichia coli GTPase YjiA, a member of the same GTPase family as HpHypB, demonstrated that YjiA can bind Ni(II), Zn(II), or Co(II) at a site in a similar location as in HpHypB. Metal binding also regulates the GTPase activity and oligomerization of YjiA. This finding suggests that metal-responsive GTPase activity may be a trait of this family of GTPases. Together, this work describes a unique link between the metal-binding and biochemical properties of the G3E GTPases and provides insight into the role of HpHypB in [NiFe]-hydrogenase and urease maturation.

The biosynthesis of [NiFe]-hydrogenase and urease in Helicobacter pylori requires several accessory proteins for proper assembly of the nickel-containing active sites. Critical to the maturation of both enzymes in H. pylori is the GTPase HypB. In this work, the metal-binding properties of H. pylori HypB (HpHypB) were investigated and a link between metal binding and the other biochemical properties of HpHypB was established. HpHypB binds stoichiometric nickel or zinc with nanomolar affinities, in partially overlapping sites located between two major GTPase motifs. Upon metal binding, the GTP hydrolysis activity and oligomeric properties of the protein are modulated. Furthermore, the stoichiometry and affinity of the nickel is altered when HpHypB is bound to nucleotide, a change not observed for zinc. Mutagenesis of the metal ligands suggest that a conserved cysteine is responsible for transducing the metal-bound state to altered GTPase activity and a conserved histidine is a required nickel ligand only in the nucleotide-bound state. Together, these results suggest that the metal-binding and GTP hydrolysis properties of HpHypB are intimately linked and may comprise a mechanism through which the [NiFe]-hydrogenase and urease maturation pathways can discriminate between Ni(II) and Zn(II). Characterization of the Escherichia coli GTPase YjiA, a member of the same GTPase family as HpHypB, demonstrated that YjiA can bind Ni(II), Zn(II), or Co(II) at a site in a similar location as in HpHypB. Metal binding also regulates the GTPase activity and oligomerization of YjiA. This finding suggests that metal-responsive GTPase activity may be a trait of this family of GTPases. Together, this work describes a unique link between the metal-binding and biochemical properties of the G3E GTPases and provides insight into the role of HpHypB in [NiFe]-hydrogenase and urease maturation.

Recently, the giant magneto impedance (GMI) effect has been studied extensively because of its potential applications in sensor elements. The focus of this thesis work is to explore different compositions and processing conditions for CoSiB and NiFe thin films to obtain the soft magnetic properties and to evaluate their potential use in GMI sensor applications. Prior to this study, an MH Looper was constructed, which was extremely important and provided the basic magnetic characterization of the many ferromagnetic thin films deposited during this work. The CoSiB films were co-sputter deposited in an ultra high vacuum chamber. Films with different relative compositions of Co, Si and B were deposited by varying respective target powers. Different substrate bias conditions were also studied. Also, NiFe films were studied by varying relative composition by variation of target powers and also by variation deposition pressure. The effect of annealing was also studied. The magnetic and electrical characterization of these films was done using the MH Looper, Quad-pro four-point probe resistivity measurement, and Low Frequency Impedance analyzer HP4192A. Finally, CoSiB films with soft magnetic properties were obtained with optimized set of deposition parameters. A sample for GMI measurement was prepared, consisting of a multilayer thin film structure: CoSiB 200nm/ Cu 400nm / CoSiB 200nm. A serpentine pattern was generated on this film by photolithography technique. After obtaining the pattern, GMI studies were performed using LF impedance analyzer. This instrument was capable of providing the drive frequency in the range of 5Hz to 13MHz, but the impedance mis-match of the test fixture limited useful measurements to 9MHz. The highest GMI ratio observed was 6.2% at a 21 Oe longitudinal magnetic bias field at an 8MHz drive frequency. Transverse permeability measurements were performed by the use of two magnetic field axes of the MH Looper. The permeability behavior of the device reflects the impedance behavior with the external field. Permeability measurements were also performed on NiFe GMI Device with NiFe 600nm/ Cu 1200nm / NiFe 600nm sandwich structure. This sample was not successfully patterned and hence the impedance measurements could not be performed. Correlation of the magnetic properties of the structures was studied with the impedance responses.

Zusammenfassung Das beta-Proteobakterium Ralstonia eutropha H16 besitzt zwei [NiFe]-Hydrogenasen, die dem Organismus das Wachstum mit H2 als alleiniger Energiequelle unter aeroben Bedingungen ermöglichen. Reguliert wird die Expression dieser [NiFe]-Hydrogenasen durch ein bakterielles Zweikomponentensystem. Die Signaltransduktionskette besteht aus einer H2-sensierenden, regulatorischen [NiFe]-Hydrogenase (RH), einer Histidin-Proteinkinase und einem Response-Regulator. Um Einblicke in die Struktur-Funktions-Beziehung der H2-sensierenden Komponente zu bekommen, wurden Aminosäure-Austausche in konservierten Bereichen nahe des NiFe-Zentrums der RH durchgeführt. Der Austausch des invarianten Glu13 (E13Q, E13L) resultierte im Verlust der regulatorischen, der H2-oxidierenden und der H/D-Austauschaktivitäten. Spektroskopische Daten wiesen auf ein vollständig assembliertes NiFe-Zentrum hin. Mit Hilfe der ortho-/para-Konversionsaktivität wurde gezeigt, dass dieses Zentrum nach wie vor H2 binden kann. Dies deutet darauf hin, dass eine H2-Bindung am aktiven Zentrum nicht für die regulatorische Funktion der RH ausreicht. Durch den Austausch des Asp15 in His wurde der Konsensus eines konservierten Motivs der Standard-Hydrogenasen hergestellt. Das entstandene RH-Mutantenprotein besaß nur noch eine sehr niedrige H2-oxidierende Aktivität, bei nahezu unveränderter H/D-Austauschrate sowie intakter regulatorischer Aktivität. Dies deutet darauf hin, dass der H2-Umsatz nicht entscheidend für die H2-Sensierung ist. Um Informationen über die Struktur des aktiven Zentrums der RH zu erhalten, war es notwendig, große Mengen RH zu isolieren. Hierfür wurde die Strep-tag-Technologie eingesetzt, die es ermöglichte, die RH als natives Doppeldimer und als homodimeres Protein zu reinigen. Röntgenabsorptionsspektroskopie ergab erstmals, dass sich die Koordination des Nickel-Atoms im aktiven Zentrum sowohl im oxidierten als auch im reduzierten Zustand der RH deutlich von der in Standard-Hydrogenasen unterscheidet. / The beta-proteobacterium Ralstonia eutropha H16 is capable of using H2 as a facultative energy source by means of two distinct, energy-converting [NiFe]-hydrogenases. Transcription of the hydrogenase genes is regulated in response to the availability of H2 via a histidyl-aspartyl phosphorelay comprising a heterodimeric, regulatory [NiFe]-hydrogenase (RH), a histidine protein kinase and a response regulator. In order to gain insights into the mechanism of H2-mediated signal transduction, conserved amino acid residues close to the NiFe active site of the RH were exchanged. Replacement of the strictly conserved Glu13 within the RH large subunit by glutamine and leucine resulted in the loss of the regulatory, H2-oxidizing and hydrogen/deuterium exchange activities. Infrared spectroscopic analysis revealed, that the RH E13Q and E13L derivatives contained a fully assembled NiFe active site and showed para-/ortho-H2 conversion activity. These results indicated that H2-binding at the active site is not sufficient for H2 sensing. Replacement of Asp15, a residue unique in H2 sensors, by histidine restored the consensus of energy-linked [NiFe]-hydrogenases. The resulting RH mutant protein showed only traces of H2-oxidizing activity, whereas the H/D-exchange activity and the regulatory activity were nearly unaffected. H2-dependent signal transduction in the respective mutant strain was less sensitive to O2 than in the wild type. These results suggest that the H2 sensing is independent of H2 turnover. To get insights into the structure of the RH it was necessary to isolate large amounts of RH. By establishing the Strep-tag technology, allowing a fast, mild and efficient purification, it was possible to isolate the native RH-double dimer as well as the modified monodimeric RHstop protein in sufficient amounts for spectroscopic analyses. X-ray absorption spectroscopy showed for the first time that the RH active site undergoes significant structural changes upon exposure to H2.

In der Entwicklung von Technologien für die nachhaltige Erzeugung, Speicherung und Umwandlung von Energie werden Hochleistungskatalysatoren benötigt. Im Rahmen dieser Arbeit werden verschiedene Übergangsmetall-basierte Katalysatoren, namentlich TiO2/Kohlenstoff-Komposite, anorganisch-organische Hybridsysteme auf Basis von NiFe Phosphonaten sowie Ni Phosphide, synthetisiert, charakterisiert und hinsichtlich ihrer photo- und elektrokatalytischen Eigenschaften untersucht. Es wird gezeigt, dass die Grenzflächeneigenschaften der TiO2/C-Komposite signifikant durch die Gestaltung des Heizvorgangs während der Synthese beeinflusst werden. Insbesondere der Einsatz von Mikrowellenstrahlung vermag die Synthese von Kohlenstoff-basierten Materialien positiv zu beeinflussen. Schnelles Erwärmen führt zu stärkeren Wechselwirkungen zwischen Nanopartikeln und Kohlenstoff, einheitlicheren Beschichtungen und kleineren Partikeln mit schmaleren Partikelgrößenverteilungen, wodurch die photokatalytische Aktivität verbessert wird. Schichtartige, hybride NiFe-Phenylphosphonat-Materialien werden ausgehend in Benzylalkohol dargestellt und ihre Aktivität in der OER im basischen Milieu untersucht. Die Hybridpartikel werden in-situ in NiFe-Hydroxid Nanoschichten umgewandelt. Röntgenspektroskopische Untersuchungen deuten auf eine induzierte, teilweise verzerrte Koordinationsumgebung der Metallzentren im Katalysator hin. Die Kombination der synergistischen Effekte zwischen Ni und Fe mit den strukturellen Eigenschaften des Hybridmaterials ermöglicht einen effizienten Katalysator. Weiterhin werden Nickel-Phosphide durch die thermische Behandlung der Phenyl- oder Methylphosphonate des Nickels, welche Schichtstrukturen aufweisen, in H2(5%)/Ar-Atmosphäre synthetisiert. Ni12P5, Ni12P5-Ni2P und Ni2P Nanopartikel, die mit einer dünnen Schicht aus Kohlenstoffmaterial beschichtet sind, werden erhalten. Ni12P5-Ni2P und Ni2P Nanopartikel katalysieren die Wasserstoffentwicklungsreaktion (HER) im Sauren effektiv. / High-performance catalysts play a key role in the development of technologies for sustainable production, storage, and conversion of energy. In this thesis, transition-metal-based catalysts, including TiO2/carbon composites, hybrid organic-inorganic NiFe phosphonates, and Ni phosphides are synthesized, characterized, and investigated in photocatalytic or electrocatalytic reactions. TiO2 is frequently combined with carbon materials, such as reduced graphene oxide (rGO), to produce composites with improved properties. TiO2 is more efficiently stabilized at the surface of rGO than amorphous carbon. Rapid heating of the reaction mixture results in a stronger coupling between the nanoparticles and carbon, more uniform coatings, and smaller particles with narrower size distributions. The more efficient attachment of the oxide leads to better photocatalytic performance. Layered hybrid NiFe-phenylphosphonate compounds are synthesized in benzyl alcohol, and their oxygen evolution reaction (OER) performance in alkaline medium is investigated. The hybrid particles transformed in situ into NiFe hydroxide nanosheets. X-ray absorption spectroscopy measurements suggest the metal sites in the active catalyst inherited partly the distorted coordination. The combination of the synergistic effect between Ni and Fe with the structural properties of the hybrid results in an efficient catalyst that generates a current density of 10 mA cm-2 at an overpotential of 240 mV. Moreover, nickel phosphides are synthesized through thermal treatment under H2(5%)/Ar of layered nickel phenyl- or methylphosphonates that act as single-source precursors. Ni12P5, Ni12P5-Ni2P and Ni2P nanoparticles coated with a thin shell of carbonaceous material are produced. Ni12P5-Ni2P and Ni2P NPs efficiently catalyze the hydrogen evolution reaction (HER) in acidic medium. Co2P and CoP NPs are also synthesized following this method.

Le sujet de cette thèse est l'étude des effets de taille finie sur les propriétés fondamentales de matériaux utilisés dans les dispositifs associés au stockage magnétique de l'information. Nous proposons l'approche multiniveaux comme alternative possible pour augmenter les densités de stockage des media planaires ou perpendiculaires, continus ou discrets. En fonctionnement, une couche doit être manipulée sans modifier l'état magnétique des autres couches. La première partie de ce mémoire est consacrée à l'étude des effets de taille finie sur les couplages magnétostatiques dans des systèmes composés de deux couches ferromagnétiques à base de cobalt/platine à anisotropie perpendiculaire, séparées par un métal non-magnétique. Pour des états désaimantés, nous avons mis en évidence la corrélation des configurations en domaines des couches, attribuée aux couplages inter-couches. Pour différentes impulsions de champs, la réplication des domaines nous a permis d'observer des états rémanents singuliers permettant de mieux comprendre le phénomène. Pour des réseaux de nanostructures, la réplication due aux couplages intra-nanostructure se manifeste par un décalage en champ du cycle d'hystérésis sur la couche de plus faible champ coercitif. Le seconde partie de ce mémoire traite des effets de taille finie sur les propriétés d'anisotropie d'échange pour des bicouches ferromagnétique/antiferromagnétique typiquement utilisées dans les têtes de lecture d'ordinateurs. Pour des systèmes à anisotropie planaire, nous avons montré que les nanostructures et les antiferromagnétiques minces sont plus sujets à l'activation thermique. Il en résulte une augmentation ou une réduction du champ d'échange pour les nanostructures par rapport aux couches continues en fonction des conditions d'épaisseur d'antiferromagnétique et de température. Ces résultats permettent de lever certaines contradictions apparentes de la littérature. Pour des couches continues à anisotropie perpendiculaire, l'orientation relative des spins du ferromagnétique et de l'antiferromagnétique influence de manière significative les propriétés d'anisotropie d'échange. L'impression des domaines du ferromagnétique dans l'antiferromagnétique, par traitements thermiques permet de générer des cycles d'hystérésis « doubles » et d'ajuster leurs propriétés magnétiques. Des premiers résultats prometteurs concernant les effets de taille finie sur les propriétés des systèmes à anisotropie perpendiculaire ont été obtenus.