The Drosophila mutant fumble has a defect in mitochondrially targeted pantothenate kinase (PANK) and exhibits a movement disorder in the females. The human disease pantothenate kinase associated neurodegeneration (PKAN) has the same genetic defect and a neurodegenerative phenotype as well as iron accumulation in the brain. We have found that fumble females accumulate almost 2 fold more iron in the heads than wildtype. Dietary iron supplementation increases the iron accumulation in the heads further. The small isoform of malvolio (MVL), a homologue of mammalian NRAMP iron transporters, is expressed in the heads of flies. Its expression is upregulated in the fumble females, as well as in dietary iron supplemented wildtype flies. Unlike in the wildtype, dietary iron supplementation leads to a downregulation of MVL in the fumble flies. Although iron levels were elevated in fumble, ferritin expression was relatively unchanged and remained unchanged in the heads of fumble and wildtype with dietary iron supplementation. <p>The Drosophila mutant malvolio was used to determine how iron metabolism is affected when the MVL gene is defective. Iron levels were unchanged in malvolio relative to its parental strain (w1118) with or without dietary iron supplementation. Despite similar iron levels, a small decrease in ferritin expression was found in malvolio relative to w1118, and dietary iron increased ferritin expression in malvolio. However ferritin expression decreased in the parental strain of malvolio after iron supplementation. <p>Most of the iron in the Drosophila heads was in the form of goethite and ferrihydrite. The presence of iron oxides implies that this iron is in a mineralized storage form, likely ferritin. Dietary iron supplementation induced the appearance of ferric phosphates in fumble, malvolio, and wildtype. The subcellular location of this iron is unknown. It may be non-transferrin bound iron in the hemolymph, or a cytosolic intermediate in the labile iron pool. Also of note was the presence of transferrin-bound iron in wildtype heads on normal diet that was not seen after iron supplementation or in the heads of the fumble mutant. The presence in fumble of the kind of ferrihydrite characteristic of the mitochondrial protein frataxin may indicate that iron is accumulating in mitochondria.<p>The upregulation of MVL in the fumble mutant is of significant interest because it is the first protein involved in iron metabolism found to be altered with mitochondrial PANK deficiency. A disruption in MVL could be relevant to the brain iron accumulation in fumble and could be a treatment target for human PKAN.

Alginate is an exopolysaccharide secreted by Pseudomonas aeruginosa and is a major component of biofilms that infect the lungs of cystic fibrosis patients. Ten proteins have been implicated in alginate polymerization, modification and export, and are believed to assemble into a multi-protein complex that spans the cell envelope and coordinates the synthesis and secretion of alginate. AlgK is a protein encoded in the alginate biosynthetic operon, which is required for the secretion of high-molecular weight alginate. This study describes structural and functional studies of AlgK to improve our understanding of AlgK’s role in alginate biosynthesis. To shed light on the function of AlgK, C14-palmitic acid labeling and sucrose gradient fractionation studies confirmed that AlgK is an outer membrane lipoprotein. Cellular fractionation experiments also found that AlgK is involved in the proper localization of AlgE, the alginate secretion pore in the outer membrane. The structure of AlgK was determined to 2.5 Å resolution by X-ray crystallography and revealed that the protein folds into 22 alpha-helices that pack into a flexible right-handed solenoid. Closer examination of the amino acid sequence revealed that AlgK carries 9.5 tetratricopeptide repeat (TPR)-like elements. Given the role that TPR motifs generally play in protein-protein interaction and the assembly of multi-protein complexes, the presence of these motifs in AlgK suggests that it can bind to one or more proteins. Based on the results presented in this study, we propose that AlgK acts as a scaffold for the assembly of the alginate secretion complex. By mapping highly conserved residues onto the surface of our model, three putative sites of protein-protein interaction were identified. We hypothesize that the N-terminus of AlgK binds to AlgE in the outer membrane, and the C-terminus of AlgK binds to periplasmic and/or inner membrane Alg proteins, thereby acting as a linker between the inner and outer membrane components of the alginate biosynthetic complex. We further hypothesize that together AlgE and AlgK constitute a novel exopolysaccharide secretin. The alginate biosynthetic complex appears to be distinct from the canonical capsular polysaccharide systems currently described.

The Canadian Penning Trap (CPT) mass spectrometer at the Argonne National Laboratory makes precise mass measurements of both stable and unstable nuclides. To date, more than 60 radioactive isotopes having half-lives as short as one second have been measured with the CPT with a mass precision approaching 10 ppb. This thesis will present measurements made of nuclides along the rp-process path, which describes a process resulting from a series of rapid proton-capture reactions in an astrophysical environment. One possible site for the rp-process mechanism is an x-ray burst which results from the rapid accretion of hydrogen and helium from one star onto the surface of its neutron star binary companion. Mass measurements are required as key inputs to network calculations used to describe the rp-process in terms of the abundances of the nuclides produced, the light-curve profile of the x-ray bursts, and the energy produced. This thesis will describe the CPT apparatus, explain the method used to make precise mass measurements, and present the masses of the "waiting-point" nuclides ⁶⁸Se and ⁶⁴Ge. The mass measurement results, when used in x-ray burst models, confirm both ⁶⁸Se and ⁶⁴Ge as waiting-point nuclides which delay the rp-process by approximately 30 s and 7 s respectively. / October 2005

La toxicitat del mercuri depèn de la seva probabilitat d'exposició, factors geoquímics i ecològics, i en particular de l'espècie química en què es troba. No obstant això, el nombre i veracitat de tècniques analítiques d'especiació segueix sent molt limitat. En conseqüència, les tècniques espectroscòpiques d'absorció de raig-X (XAS) basades amb la radiació sincrotró, han esdevingut eines interessants i fàcilment disponibles per a superar la manca existent en aquest camp. Entre altres, les tècniques més comuns són XANES (X-ray Absorption Near Edge Spectroscopy) i EXAFS (Extended X-ray Absorption Fine Structure). Altres progressos en aquest camp es basen en la unió de les tècniques d'absorció amb a una alta resolució espacial a nivell de microescala, usant les tècniques µ-XRF (microscopic X-ray Fluorescence) o µ-XAS. La comprensió del perill per al medi ambient plantejat pel metilmercuri (CH3HgCl i CH3HgOH) adsorbit sobre típics components del sòl ha estat assolida per la combinació de les tècniques XAS i bacteris sensors luminiscents (Escherichia coli MC1061, pmerBRBSluc). La quantitat de Hg adsorbit ha resultat ser depenent del pH, mentre que el caràcter de l'enllaç independent del pH. En comparar la interacció entre el metilmercuri i les argiles o materials húmics, els primers han donat lloc a un caràcter iònic més alt i per tant a una possibilitat de mobilització del mercuri més gran. A més, aquesta interacció ha resultat ser més estable pel CH3HgOH que pel CH3HgCl.El districte d'Almadén a Ciudad Real ha donat lloc a un dels ambient més impactats pel Hg arreu del món. En aquest context, les tècniques XAS (juntament amb SES, XRD i SEM-EDS) s'han utilitzat per a estudiar el comportament del mercuri en aquesta regió. El cinabri s'ha trobat que és l'espècie principal en minerals i sòls, mentre que el metacinabri és l'espècie principal en les escòries. En totes les mostres, també s'han trobat sals més solubles de mercuri (HgCl2, HgSO4 i schuetteite). Les tècniques de microsonda també han revelat correlacions elementals entre el Hg i el Pb, Ni i S, indicant un possible acoblament geoquímic d'aquests elements. Les correlacions també s'han identificat entre el Hg i Fe/Mn, el qual s'ha atribuït a l'absorció del mercuri sobre els oxihidròxids de Fe i Mn. D'altra banda, les indústries clor-àlcali amb càtode de mercuri han estat un dels usos industrials més importants del mercuri a Europa occidental. El gravamen del comportament del mercuri en aquests ambients ha estat conduït per les tècniques XAS acoblades a SES. La informació d'especiació ha demostrat que els compostos inorgànics de mercuri dominen en totes les mostres de sòl considerades, sent cinabri i corderoite les principals espècies. No obstant això, també s'han identificat fases lleument solubles (HgO i HgSO4) en proporcions de menor importància. Per altra banda, l'anàlisi de µ-XRF ha demostrat una correlació geoquímica de Hg, Cu i Ni, que suggereixen la formació de possibles solucions sòlides d'aquests elements dintre de la mateixa estructura cristal·lina. Finalment, les tècniques de microsonda amb radiació sincrotró s'han proposat per a l'observació directa del mercuri i altres elements presents en dents humanes restaurades amb amalgames de mercuri. Les anàlisis han demostrat una difusió mínima del Hg a través de la dent, amb la identificació d'una correlació lineal entre el Hg i el Cu. Per altra banda, s'ha identificat una difusió significativa del Cu i el Zn de l'amalgama a la regió de la dentina, suggerint un possible intercanvi del Ca2+ amb el Cu2+/Zn2+ en els cristalls d'hidroxiapatita (Ca10(PO4)6(OH)2). Per altra banda, µ-EXAFS ha determinat que l'ambient molecular inicial del Hg en la regió de l'amalgama està limitat per la fase ?-Ag2Hg3 formada durant el procés d'amalgamació / Toxicity of mercury is determined by the likelihood of exposure, geochemical and ecological factors, and in particular by the chemical species in which it is found. Chemical speciation become of an utmost importance when assessing the risk associated to mercury impacted environments. Despite this, the number and reliability of analytical techniques able to recognise different mercury species is still very limited, even more when dealing with solid samples. Hence, synchrotron-based x-ray absorption spectroscopic (XAS) techniques have risen as an interesting and readily available tool to overcome the existing speciation gap. Among others, the most common techniques dealing with speciation are XANES (X-ray Absorption Near Edge Spectroscopy) and EXAFS (Extended X-ray Absorption Fine Structure). Further developments in this field focus on the coupling of x-ray absorption techniques to a spatial resolution at a micro-scale level, by using µ-XRF (microscopic X-ray Fluorescence) or µ-XAS techniques.The understanding of the environmental hazard posed by methylmercury (CH3HgCl and CH3HgOH) adsorbed onto a number of key soil materials has been accomplished by the combination of XAS techniques and luminisent sensor bacteria (Escherichia coli MC1061, pmerBRBSluc). The amount of Hg adsorbed was observed to be pH-dependent, whereas the bond character was found to be pH-independent. When comparing interaction between methylmercury and clays or humic materials, the former resulted in a higher ionic character and consequently in a larger possibility of mercury mobilisation. Additionally, this interaction was observed to be more stable for CH3HgOH than for CH3HgCl, due to the higher reactivity of the hydroxyl group. The Almadén district in Ciudad Real has lead to one of the most Hg-impacted environments found around the world. In this context, XAS techniques (complemented with SES, XRD and SEM-EDS analyses) have been utilised to study the mercury behaviour in this region. Cinnabar has been found to be the main species in ores and soils, whereas metacinnabar was the main species in slag. In all samples, slightly soluble mercury salts (HgCl2, HgSO4 and schuetteite) have been also found. Microprobe techniques have also revealed elemental correlations between Hg and Pb, Ni and S, indicating a possible geochemical linkage of these elements. Correlations were also identified between Hg and Fe/Mn, which have been attributed to sorption of mercury onto oxy-hydroxides of Fe and Mn. Chlor-alkali industries with mercury cathode remain as one of the most important industrial applications of mercury in Western Europe, which become one of the most important point-sources for mercury contamination. The assessment of mercury behaviour in these environments has been conducted by XAS techniques coupled to SES. Speciation information showed that inorganic mercury compounds dominate in all soil samples considered, being cinnabar and corderoite the main species. However, slightly soluble phases (HgO and HgSO4) have been also identified in minor proportions. On the other hand, µ-XRF analysis has shown a geochemical correlation of Hg, Cu and Ni, which suggest the possible formation of solid solutions of these elements within the same crystalline structure.Finally, synchrotron X-ray microprobe techniques have been proposed for the direct observation of mercury and other elements present in human teeth restored with dental amalgams. Microprobe analyses showed a minimum diffusion of Hg throughout the tooth, with the identification of a linear correlation between Hg and Cu. On the other hand, a significant diffusion of Cu and Zn from the amalgam to the dentine region was identified, which suggested the possible exchange of Ca2+ by Cu2+/Zn2+ in hydroxiapatite crystals (Ca10(PO4)6(OH)2). On the other hand, µ-EXAFS has determined that the initial molecular environment of Hg in the amalgam region is limited to the ?-Ag2Hg3 phase formed during the amalgamation process.

Durante las últimas décadas, la construcción de anillos de almacenamiento de electrones exclusivamente dedicados a la producción de radiación sincrotrón ha sido la clave para justificar el gran desarrollo de los componentes ópticos para rayos X. Se requieren nuevos elementos ópticos para una explotación óptima de las propiedades de esta luz, que puede usarse para descubrir los secretos de la materia y para revelar el mundo microscópico. El uso de radiación sincrotrón como sonda ha hecho posible una gran cantidad de experimentos para expandir el conocimiento de muchas áreas científicas. Paulatinamente, la radiación sincrotrón se ha convertido en un instrumento indispensable para muchos científicos, que trabajan en disciplinas muy diferentes como la biología, la química, la ciencia de materiales o incluso la arqueología. La microscopía de rayos X ha emergido como técnica para observar estructuras que no son accesibles con microscopia óptica convencional, y que tiene ventajas respeto a la microscopía electrónica debido a la mayor longitud de penetración y a la sensibilidad química de la radiación X. La óptica de los microscopios de rayos X incluye componentes como las lentes zonales de Fresnel que se producen con técnicas de microfabricación. En este trabajo, se han fabricado lentes zonales de Fresnel utilizando distintas técnicas y se han testado en diversas Fuentes de Luz Sincrotrón. Describiremos en detalle las técnicas de micro- y nanofabricación que son necesarias para la producción de estos elementes, des de la litografía por haz de electrones a la transferencia del patrón a distintos materiales. En particular, presentamos lentes para rayos X blandos hechas de silicio. Mostraremos que éstas funcionan bien en las fuentes de luz existentes y que debido a su robustez serán también apropiadas para las fuentes de rayos X de 4a generación. También preparamos un elemento óptico difractivo que produce una mancha iluminación cuadrada y llana, y que puede usarse como lente condensadora en microscopía de rayos X de transmisión. Finalmente, también demostramos un nuevo método de fabricación que puede mejorar la resolución espacial última de las lentes difractivas para rayos X. Se fabricaron lentes zonales de Fresnel con una última zona de 20 nm y líneas de 15 nm han sido claramente resueltas en microscopía de rayos X de rastreo. Este trabajo se ha realizado en el Laboratorio de Luz Sincrotrón en Barcelona, con la participación del Centro Nacional de Microelectrónica de Barcelona (CSIC-CNM) y del Grupo de Óptica del Departamento de Física de la Universidad Autónoma de Barcelona. Al mismo tiempo, partes esenciales de este trabajo se han realizado con la colaboración del Dr. C. David y el Dr. K. Jefimovs del Labor fur Mikro- und Nanotechnologie al Paul Scherrer Institut en Villigen (Suiza). / During the last decades, the construction of electron storage rings exclusively dedicated to the production of synchrotron radiation has been a key reason to explain the large development of x-ray optics. New optical elements are required for an optimal exploitation of the properties of this light, which can be used to find out the secrets of matter and to reveal the microscopic world. The use of synchrotron light as a probe has made possible a large quantity of experiments to expand the knowledge in many scientific areas. Little by little, synchrotron radiation sources have become an indispensable tool for the research of lots of scientists, who work in very different disciplines such as biology, chemistry, physics, material science or even archaeology. X-ray microscopy has emerged as a technique to observe structures which are not accessible with conventional optical microscopy, and that has advantages in respect to electron microscopy due to the longer penetration depth and chemical sensitivity of the x-ray radiation. The optics of the x-ray microscopes includes components such as the Fresnel zone plate lenses which are made by means of microfabrication techniques. Within this work, Fresnel zone plate lenses were produced using different approaches and they have been tested in several Synchrotron Light Sources. We will describe in detail the micro- and nanofabrication techniques that are necessary for the production of such elements, from the electron beam lithography to the pattern transfer into different materials. In particular, we will present lenses for soft x-rays made of silicon. We show that they perform well at the current light sources and we think that due to their robustness they will also be suitable for the 4th generation x-ray sources. We also prepared a diffractive optical element which produces a square flat top illumination spot, and that can be used as a condenser lens in full-field transmission x-ray microscopy. Finally, we will also demonstrate a novel fabrication method which can push the ultimate spatial resolution of x-ray diffractive lenses. Fresnel zone plates with an outermost zone width of 20 nm have been fabricated and 15 nm lines have been clearly resolved in scanning transmission x-ray microscopy. This work has been carried out in the Laboratori de Llum Sincrotró in Barcelona, with the participation of the Centro Nacional de Microelectrònica de Barcelona (CSIC - CNM) and the Grup d'Òptica del Departament de Física de la Universitat Autònoma de Barcelona. At the same time, essential parts of this work have been done in close collaboration with Dr. C. David and Dr. K. Jefimovs from the Labor für Mikro- und Nanotechnologie at the Paul Scherrer Institut in Villigen (Switzerland).

No description available.

Dual energy imaging has made it possible to enhance contrast in medical images using images containing different energy information, by combining low and high energy images. Dual energy data can either be acquired using double exposures or splitting the energy spectrum into two images using one exposure. This thesis presents investigations of dual energy imaging using a detector solution developed by XCounter which provides dual energy images in a single exposure with a threshold separating low and high energy images. Phantom experiments with phantoms of aluminum and plexiglas were performed using weighted logarithmic subtraction and basis material decomposition to produce dual energy images. Methods were validated and images were evaluated in terms of signal difference in noise ratio to find the threshold and tube voltage combination for optimum energy spectrum separation. The methods were also tested on biological materials using bone, soft tissue and iodine solution as contrast enhancer, to investigate K-edge imaging.  Optimal separation of plexiglas and aluminum were found at 70 kVp and the threshold parameter set within a range of 8 to 9, which corresponds to approximately 30 to 34 keV. For K-edge imaging, the optimum separation were found close to K-edge energy of iodine. The results found in the phantom study correlated with results from the biological material study.

The main subject of this thesis is the study of electronic and magnetic properties of materials containing 3d transition metal atoms. Our motivation stems mainly from the modern fields of spintronic computing and solar energy conversion. The two primary goals of this work are to determine (i) why certain transition metal impurities in certain semiconductors can induce magnetic properties suitable for spintronic computing applications, and (ii) how transition metal impurities can be used to modify the electronic band gaps of semiconductors and insulators in ways useful for harnessing solar energy and for other applications. To accomplish these goals, we have applied both experimental and theoretical tools. We studied high quality materials prepared by advanced synthesis techniques using x-ray spectroscopy methods at synchrotron light sources. The results of these experiments were interpreted using a variety of theoretical techniques, primarily using computational software developed as part of this thesis and discussed herein. Regarding the study of introducing transition metal impurities into semiconductors to induce magnetic properties, we first developed and demonstrated a method to determine the location of impurity atoms within the host semiconductor lattice. This allowed to us explain the presence and absence of ferromagnetism in samples prepared under only slightly different synthesis conditions, which helped to address some long--standing issues in the spintronics field. We then studied an advanced and promising material -- indium (III) oxide with iron impurities -- to determine how magnetic ordering was maintained up to room temperatures. Our techniques unveiled that a portion of the iron atoms were coupled to oxygen vacancies in the material to create conditions which propelled the observed magnetism. This finding confirmed some earlier theoretical predictions by others in the field. For the study of electronic band gap modifications in semiconductors and insulators via the incorporation of transition metal atoms, we investigated a wide range of materials synthesized using different techniques. Again, we used experimental techniques to determine the location of impurity atoms within the materials, and used this to understand how band gaps were modified upon the introduction of the impurities. For Ti implantation into SiO2, Ni substitution into ZnO, and a new material, MnNCN, we have determined the electronic band gaps and used our techniques to explain how the values for the gaps arise. Finally, an additional outcome of this thesis work is a software program capable of simulating x-ray spectra using various advanced quantum models. We rewrote and built upon powerful existing programs and applied the result to the above studies. Our software was further applied in a collaborative effort with other researchers at the Canadian Light Source to study the differences in two experimental techniques for measuring x-ray absorption: partial and inverse partial fluorescence yields. By using the proper absorption and scattering formalisms to simulate each technique, we were able to explain the differences between the experimental spectra obtained from each. We explain fluorescence yield deviations using an analysis based on the spin configuration of different states, suggesting that the technique can be further extended as a quantitative spin state probe. These results could have significant implications for the field of soft x-ray absorption spectroscopy.

Las mol eculas metal-org anicas en la intercara con sustratos met alicos son sistemas interesantes para aplicaciones futuras en la grabaci on magn etica y dispositivos de espintr onica, ya que prometen sustituir algunos de los com- ponentes magn eticos basados en metales en uso hoy en d a. Las mol eculas que llevan esp n son materiales muy atractivos, tanto como capas nas bi- dimensionales en estructuras de multi-capas o como unidades magn eticas individuales, debido a sus reducidas dimensiones y propiedades funcionales. Entre esta clase de mol eculas, los imanes moleculares (SMMs) son los m as prometedores, ya que combinan propiedades magn eticas de bulk y dimensio- nes a escala molecular. Varios problemas limitan su aplicaci on en dispositivos reales: la principal es la baja temperatura de bloqueo TB, t picamente alrede- dor de la temperatura de liquefacci on de helio, por debajo del cu al los SMMs se comportan como nanoimanes; adem as, controlar el momento magn etico de una sola mol ecula no es una tarea f acil. Para superar estos obst aculos se est an investigando muchas estrategias y la m as prometedora parece ser la deposici on sobre sustratos magn eticos. Para el estudio de estos materiales, las espectroscop as de radiaci on sin- crotr on representan t ecnicas muy poderosas: la espectroscop a de absorci on de rayos X (XAS) y el dicro smo magn etico circular de rayos X (XMCD), en particular, permiten medir selectivamente diferentes elementos y medi- ciones independientes de los momentos at omicos orbitales y de esp n, can- tidades fundamentales para la comprensi on de las propiedades magn eticas macrosc opicas de la materia. En este estudio se ha investigado la interacci on del SMM TbPc2 con su- per cies ferromagn eticas (FM) de Ni. Usando la magnetometr a XMCD, se ha demostrado que TbPc2 se acopla antiferromagneticamente a la capa de Ni a trav es de la interacci on de supercanje mediada por el ligando. La ma- gnitud, pero no el signo, de la energ a de acoplamiento de canje puede ser ajustado mediante la reducci on o la oxidaci on del sustrato. Contrariamente a las mol eculas paramagn eticas, encontramos que el momento magn etico de los SMMs no sigue la magnetizaci on de la capa FM subyacente en cualquier con- dici on, sino que depende de la orientaci on relativa de los ejes de anisotrop a magn etica de la mol ecula y del sustrato, de la interacci on de supercanje y de la interacci on Zeeman. Las mol eculas de TbPc2, acopladas al Ni, conser- van sus propiedades intr nsecas de SMM, pero tambi en presentan una mejor estabilidad t ermica respecto a la mol ecula aislada, lo que demuestra una estrategia efectiva para incluir SMM en dispositivos de espintr onica. Se puede dar un paso m as hacia el control de un SMM estudiando el acoplamiento con sustratos antiferromagn eticos (AFM). Esto permitir a la inversi on de la magnetizaci on de capas moleculares con respecto al sustrato que bloquea el esp n. El fen omeno clave para demostrar este acoplamiento es el exchange bias, la anisotrop a magn etica unidireccional en la intercara entre capas FM y AFM, usada en espintr onica para estabilizar y controlar la magnetizaci on de estructuras multicapas. Aqu se investiga la posibilidad de inducir exchange bias entre SMM y capas AFM met alicas o de oxido. Las medidas de XMCD muestran que las mol eculas de TbPc2 depositadas sobre una capa na AFM de Mn tienen, despu es del enfriamiento con un campo magnetico externo aplicado, una curva de magnetizaci on abierta y despla- zada horizontalmente. Esta evidencia de exchange bias es coherente con la observaci on de esp nes bloqueados en la capa de Mn que se acoplan paralela- mente al momento magn etico del Tb, durante el enfriamiento en campo. Al contrario, las mol eculas depositadas sobre sustratos de CoO presentan ciclos de magnetizaci on paramagn eticos sin indicaci on alguna de exchange bias. Estos experimentos demuestran la capacidad de los SMMs para polarizar los esp nes bloqueados no compensados de un antiferromagneto y para formar heteroestructuras metal-org anicas que presentan exchange bias. Por ultimo, se ha puesto atenci on en la mol ecula paramagn etica MnPc. Se ha depositado esta mol ecula en varios sustratos, tanto magn eticos como no magn eticos, y se ha llevado a cabo un estudio sistem atico de la modi- caci on de la con guraci on electr onica en las diferentes muestras. Lo que observamos es que la con guraci on electr onica del MnPc se ve muy afecta- da por el sustrato y que el mecanismo principal que induce los cambios es probablemente la transferencia de carga. El MnPc en sustratos FM de Ni se comporta previsiblemente como las otras mol eculas paramagn eticas en capas FM, siguiendo la magnetizaci on del sustrato, mientras que, en capas AFM de oxido, no se observa exchange bias, como en el caso de SMM TbPc2. Tambi en hemos tratado de calcular el momento magn etico de cada muestra, descubriendo resultados inesperados que necesitan ser aclarados. Este estu- dio se encuentra todav a en una primera etapa, y necesita el apoyo de otras mediciones y c alculos teoric os para con rmar nuestras suposiciones. / Metal-organic molecules at the interface with metallic substrates are intere- sting systems for future applications in electronic and spintronic devices, as they hold promise for replacing some of the metal-based magnetic compo- nents in use today. Spin carrying molecules are highly attractive materials, both as ordered two-dimensional lms in multilayer structures and as single magnetic units, because of their reduced dimensions and functional proper- ties. Among this class of molecules, single molecule magnets (SMMs) are the most promising materials, because they combine bulk magnetic properties and molecular scale dimensions. Several problems limit their application in real devices; however the main one is the low blocking temperature (TB), tipically in the helium liquid range, under which SMMs behave like nanoma- gnets; furthermore, it is not an easy task to control the magnetic moment of a single molecule. To overcome these obstacles, many strategies are under investigation, including single molecules in break junctions, molecules depo- sition on magnetic substrates, change of the organic ligand to modify the ligand eld, etc.. To study these materials, synchrotron radiation spectroscopy represents a powerful technique: X-ray absorption spectroscopy (XAS) and x-ray magne- tic circular dichroism (XMCD), in particular, allow element selectivity and independent measurements of the atomic orbital and spin moments, funda- mentals quantities for understanding the macroscopic magnetic properties of the matter. We investigate the interaction of TbPc2 SMMs with ferromagnetic (FM) Ni surfaces. Using XMCD magnetometry, we show that TbPc2 couple anti- ferromagnetically to Ni lms through ligand-mediated superexchange. The magnitude, but not the sign of the exchange coupling energy, can be tailored by reducing or oxidizing the substrate. Contrary to paramagnetic molecules, we nd that the SMM magnetic moment does not follow the magnetization of the underlying FM layer, depending on the relative orientation of the mo- lecule and substrate magnetic anisotropy axes, superexchange, and Zeeman interaction. Coupled to Ni, TbPc2 retain their intrinsic SMM properties, but they exhibit enhanced thermal stability relative to isolated molecules, demonstrating an e ective approach to include SMM in spintronic devices. A further step towards the control of SMMs is to induce coupling with an antiferromagnetic (AFM) substrate. This nding may enable independent magnetization reversal of molecular layers with respect to the pinning sub- strate. The key phenomenon in this case is exchange bias, the unidirectional magnetic anisotropy at the interface between FM and AFM layers, used in spintronics to stabilize and control the magnetization of multilayer structures. Here we investigate the possibility to induce exchange bias between SMMs and metallic or oxide AFM layers. Element-resolved XMCD measure- ments show that TbPc2 molecules deposited on an AFM Mn thin lm present magnetic hysteresis and a negative horizontal shift of the Tb magnetization loop after eld cooling. This evidence of exchange bias is consistent with the observation of pinned spins in the Mn layer that couple parallel to the Tb magnetic moment during eld cooling. Conversely, molecules deposited on CoO substrates present paramagnetic magnetization loops with no indica- tion of exchange bias. These experiments demonstrate the ability of SMM to polarize the uncompensated pinned spins of an antiferromagnet and realize metal-organic exchange biased heterostructures. Finally, we draw attention to the behaviour of paramagnetic molecules, such as MnPc. We deposited MnPc on several substrates, both magnetic and non magnetic, and performed a systematic study of how the electronic con guration of the Mn ions and their magnetic moment are modi ed. What we observe is that the MnPc electronic con guration is highly a ected by the substrate and that the main mechanism inducing changes is likely charge transfer. MnPc on FM Ni behaves, as expected, like a normal paramagnetic molecule on FM layers, mimicking the substrate magnetization, while no exchange bias is observed on AFM oxides layers, as for TbPc2 SMM. We also tried to estimate the magnetic moment for each sample, nding unexpected results that need to be clari ed. This study is still at a rst stage, and needs the support of further measurements and calculations to con rm our assumptions.

Rapid progress over the last decade on large area thin film transistor (TFT) arrays led to the emergence of high-performance, low-power, low-cost active matrix flat panel imagers. Despite the shortcomings associated with the instability and low mobility of TFTs, the amorphous silicon TFT technology still remains the primary solution for the backplane of flat panel imagers. The use of a-Si:H TFTs as the building block of the large area integrated circuit becomes challenging particularly when the role of the TFT is extended from traditional switching applications to on-pixel signal amplifier for large area digital imaging. This is the idea behind active pixel sensor (APS) architectures in which under each pixel an amplifier circuit consisting of one or two switching TFTs integrated with one amplifying TFT is fabricated. To take advantage of the full potential of these amplifiers, it is crucial to develop APS architectures to compensate for the limitations of the TFTs. In this thesis several APS architectures are designed, simulated, fabricated, and tested addressing these challenges using the mask sets presented in Appendix A. The proposed APS architectures can compensate for inherent stabilities of the comprising TFTs. Therefore, the sensitivity of their output data to the transistor variations is significantly suppressed. This is achieved by using a well defined external current source instead of the traditional voltage source to reset the APS architectures during the reset cycle of their periodic operation. The performance of these circuits is analyzed in terms of their stability, settling time, noise, and temperature-dependence. For appropriate readout of the current mode APS architectures, high gain transresistance amplifiers with correlated double sampling capability is designed, simulated and fabricated in CMOS technology. Measurement and measurement based calculation results reveal that the proposed APS architectures can meet even the stringent requirements of low noise, real-time digital fluoroscopy.