Neste trabalho e apresentado um estudo, via teoria de massa efetiva multibanda autoconsistente de heteroestruturas de semicondutores magnéticos diluídos, generalizada para incluir parâmetros de diferentes materiais. A interacao magnética e descrita por um modelo de campo médio baseado no mecanismo de troca indireta, com a possibilidade de inclusão de diferentes íons magnéticos. As equacoes de massa efetiva são resolvidas de forma autoconsistente com o auxílio da equacao de Poisson. As interacoes de spin-órbita e de troca-correlacao, na aproximacao de densidade local, são incluídas no cálculo. O método e aplicado para o estudo das estruturas de bandas e densidades de carga com separacao por spin do portador de heteroestruturas com dopagem tipo-n e tipo-p, variando a geometria dos pocos magnéticos e também o período da super-rede, as densidades de portadores e as concentracoes de íons magnéticos. Solucoes autoconsistentes da equacao de massa efetiva são encontradas para o oxido semicondutor (Zn,Co)O. Será mostrada a separacao de portadores por spin em funcao dos parâmetros variados, simulando diversas concentracoes possíveis, utilizadas em sistemas descritos na literatura, e será analisado o comportamento dos perfis de potencial. Usando os dados obtidos, um diagrama de fases será traçado com base na polarizacao total ou parcial dos portadores, e o seu comportamento será discutido. Também serão mostradas as estruturas de bandas, os perfis de potencial e as distribuicoes de carga do semicondutor (GaMn)As, variando as densidades de portadores e a direcao do campo magnético intrínseco, gerado pela dopagem com íons magnéticos. Os resultados obtidos neste trabalho podem servir de guia para futuras experiências e para o desenvolvimento de dispositivos com semicondutores magnéticos diluídos baseados em (Zn,Co)O e (Ga,Mn)As. Os métodos aqui descritos são gerais e podem ser utilizados para outros materiais. / This work presents a self-consistent multiband effective mass theory applied to diluted magnetic semiconductor heterostructures, generalized to include parameters of different ma- terials. The magnetic interaction is described by a mean-field approximation based on indirect- exchange mecanism, with the possibility of inclusion of different magnetic ions. The effective mass equations are solved self-consistently with the help of the Poisson equation. Spin-orbit and exchange-correlation interactions are included in the simulation in the local density appro- ximation. The method is used to study band structures and charge densities separated by spin in n- and p-type heterostructures. The magnetic well\'s geometry, the superlattice period, the carrier density and the magnetic ion concentration are changed. Self-consistent solutions of the effective mass equation are found for the semiconductor oxide (Zn,Co)O. Charge separation by spin will be show in function of the variation of the simulation parameters, simulating several ion concentrations and charge densities used in systems described in literature, and the potenti- als profiles will be analised. Using the data obtained a phase diagram will be plotted, based on the carrier total or partial carrier polarization, and a model for the behavior of the phase diagram will be discussed. It will also be shown band structures, potential profiles and charge densities of the (Ga,Mn)As semiconductor, varying it carrier density and the direction of the intrinsic magnetic field, generated by the magnetic ions that doped the heterostructure. The results ob- tained in this work can be used as a guide in future experiences and development of devices with diluted magnetic semiconductors based on (Zn,Co)O and (Ga,Mn)As. The methods here described are general and can be used for other materials.

Polycrystalline Zn1-xCrxO (0.01 ≤ x ≤ 0.09) samples synthesized by solid state reaction technique were sintered at different temperatures following slow step sintering schedule. Structural, micro-structural, optical, magnetic properties and homogeneity were investigated using suitable characterisation techniques. Cr2O3 and CrO2 phases have been detected in the XRD patterns and Raman spectra of Zn1-xCrxO samples with x ≥ 0.05. Photoluminescence study has indicated improved optical property of the samples compared to undoped ZnO. While low percentage Cr doped samples showed diamagnetic behaviour, higher percentage doped samples (≥ 5%) exhibited ferromagnetic, paramagnetic and anti-ferromagnetic behaviours depending upon the sintering temperatures. The magnetic properties have been analysed through Electron Spin Resonance study. A g-value of 1.97 indicates Cr in +3 valence state in doped ZnO system. Presence of Cr3+ and Cr4+ in ZnO is understood to facilitate super exchange interactions to promote ferromagnetism at room temperature. ESR study shows improved magnetic homogeneity achieved by slow step sintering process. / Physics / M. Sc. (Physics)

O presente trabalho teve como objetivo utilizar a técnica nuclear de Correlação Angular γ-γ Perturbada (CAP) para a medida de interações hiperfinas em filmes finos e amostras em pó de óxidos semicondutores SnO2 e TiO2 puros e dopados com metais de transição para uma investigação sistemática de defeitos estruturais e do magnetismo sob o ponto de vista atômico tendo como principal motivação a candidatura à aplicação desses óxidos em spintrônica. O trabalho também teve como foco a preparação e caracterização das amostras por meio de técnicas convencionais, como difração de raios X, microscopia eletrônica de varredura, espectroscopia de energia dispersiva e medidas de magnetização. Amostras puras dos filmes foram medidas mediante a variação sistemática da temperatura de tratamento térmico e do campo magnético aplicado. Tais medidas foram realizadas no HISKP, na Universidade de Bonn (Rheinische Friedrich-Wilhelms-Universität Bonn), através de implantação de íons de 111In(111Cd) ou 181Hf(181Ta); no IPEN, por sua vez, essas medidas foram realizadas após a difusão dos mesmos núcleos de prova. Outra parte das medidas CAP foram feitas através de implantação de íons de 111mCd(111Cd) e 117Cd(117In) no Isotope Mass Separator On-Line (ISOLDE) do Centre Européen Recherche Nucléaire (CERN). As medidas foram realizadas nos intervalos de temperatura de 8 K a 1173 K. Para análise de ferromagnetismo, medidas foram feitas à temperatura ambiente com e sem aplicação de campo magnético externo. Após a comparação dos resultados das medidas macroscópicas e atômicas das amostras, foi possível concluir que há uma correlação entre os defeitos, o magnetismo e a mobilidade dos portadores de carga nos semicondutores aqui estudados. Um passo adiante na busca de semicondutores, cujo ordenamento magnético possibilite o seu uso na eletrônica baseada em spin. Alguns resultados já foram publicados, incluindo resultados obtidos na Universidade de Bonn durante o período de doutorado sanduíche [1-7]. / This study aimed the use of nuclear technique Perturbed γ-γ Angular Correlation Spectroccopy (PAC) to measure the hyperfine interactions in thin films and powder samples of SnO2 and TiO2 pure and doped with transition metals to obtain a systematic investigation of defects and magnetism from an atomic point of view with the main motivation the application in spintronics. The work also focused on the preparation and characterization of samples by conventional techniques such as X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy and magnetization measurements. Pure samples of the films were measured by the systematic variation of thermal treatment and applied magnetic field. These measurements were performed in HISKP at the University of Bonn (Rheinische Friedrich-Wilhelms-Universität Bonn) using 111In(111Cd) or 181Hf (181Ta); at IPEN, in turn, these measurements were performed after the diffusion of the same probe nuclei. Another part of PAC measurements were carried out using 111mCd(111Cd) and 117Cd (117In) in Isotope Mass Separator On-Line (ISOLDE) at Centre Européen Recherche Nucléaire (CERN). The measurements were performed from 8 K to 1173 K. After comparing results from macroscopic techniques with those from PAC, it was concluded that there is a correlation between the defects, magnetism and the mobility of charge carriers in semiconductors studied here. A step forward in the search for semiconductors, whose magnetic ordering allows its use in electronics based on spin. Some results have been published, including results obtained at the University of Bonn for the sandwich doctorate period [1-7].

O presente trabalho teve como objetivo utilizar a técnica nuclear de Correlação Angular γ-γ Perturbada (CAP) para a medida de interações hiperfinas em filmes finos e amostras em pó de óxidos semicondutores SnO2 e TiO2 puros e dopados com metais de transição para uma investigação sistemática de defeitos estruturais e do magnetismo sob o ponto de vista atômico tendo como principal motivação a candidatura à aplicação desses óxidos em spintrônica. O trabalho também teve como foco a preparação e caracterização das amostras por meio de técnicas convencionais, como difração de raios X, microscopia eletrônica de varredura, espectroscopia de energia dispersiva e medidas de magnetização. Amostras puras dos filmes foram medidas mediante a variação sistemática da temperatura de tratamento térmico e do campo magnético aplicado. Tais medidas foram realizadas no HISKP, na Universidade de Bonn (Rheinische Friedrich-Wilhelms-Universität Bonn), através de implantação de íons de 111In(111Cd) ou 181Hf(181Ta); no IPEN, por sua vez, essas medidas foram realizadas após a difusão dos mesmos núcleos de prova. Outra parte das medidas CAP foram feitas através de implantação de íons de 111mCd(111Cd) e 117Cd(117In) no Isotope Mass Separator On-Line (ISOLDE) do Centre Européen Recherche Nucléaire (CERN). As medidas foram realizadas nos intervalos de temperatura de 8 K a 1173 K. Para análise de ferromagnetismo, medidas foram feitas à temperatura ambiente com e sem aplicação de campo magnético externo. Após a comparação dos resultados das medidas macroscópicas e atômicas das amostras, foi possível concluir que há uma correlação entre os defeitos, o magnetismo e a mobilidade dos portadores de carga nos semicondutores aqui estudados. Um passo adiante na busca de semicondutores, cujo ordenamento magnético possibilite o seu uso na eletrônica baseada em spin. Alguns resultados já foram publicados, incluindo resultados obtidos na Universidade de Bonn durante o período de doutorado sanduíche [1-7]. / This study aimed the use of nuclear technique Perturbed γ-γ Angular Correlation Spectroccopy (PAC) to measure the hyperfine interactions in thin films and powder samples of SnO2 and TiO2 pure and doped with transition metals to obtain a systematic investigation of defects and magnetism from an atomic point of view with the main motivation the application in spintronics. The work also focused on the preparation and characterization of samples by conventional techniques such as X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy and magnetization measurements. Pure samples of the films were measured by the systematic variation of thermal treatment and applied magnetic field. These measurements were performed in HISKP at the University of Bonn (Rheinische Friedrich-Wilhelms-Universität Bonn) using 111In(111Cd) or 181Hf (181Ta); at IPEN, in turn, these measurements were performed after the diffusion of the same probe nuclei. Another part of PAC measurements were carried out using 111mCd(111Cd) and 117Cd (117In) in Isotope Mass Separator On-Line (ISOLDE) at Centre Européen Recherche Nucléaire (CERN). The measurements were performed from 8 K to 1173 K. After comparing results from macroscopic techniques with those from PAC, it was concluded that there is a correlation between the defects, magnetism and the mobility of charge carriers in semiconductors studied here. A step forward in the search for semiconductors, whose magnetic ordering allows its use in electronics based on spin. Some results have been published, including results obtained at the University of Bonn for the sandwich doctorate period [1-7].

Ink-jet printing offers an ideal answer to the emerging trends and demands of depositing at ambient temperatures picoliter droplets of oxide solutions into functional thin films and device components with a high degree of pixel precision. It is a direct single-step mask-free patterning technique that enables multi-layer and 3D patterning. This method is fast, simple, easily scalable, precise, inexpensive and cost effective compared to any of other methods available for the realization of the promise of flexible, and/or stretchable electronics of the future on virtually any type of substrate. Because low temperatures are used and no aggressive chemicals are required for ink preparation, ink-jet technique is compatible with a very broad range of functional materials like polymers, proteins and even live cells, which can be used to fabricate inorganic/organic/bio hybrids, bio-sensors and lab-on-chip architectures. After a discussion of the essentials of ink-jet technology, this thesis focuses particularly on the art of designing long term stable inks for fabricating thin films and devices especially oxide functional components for electronics, solar energy conversion, opto-electronics and spintronics. We have investigated three classes of inks: nanoparticle suspension based, surface modified nanoparticles based, and direct precursor solution based. Examples of the films produced using these inks and their functional properties are: 1) In order to obtain magnetite nanoparticles with high magnetic moment and narrow size distribution in suspensions for medical diagnostics, we have developed a rapid mixing technique and produced nanoparticles with moments close to theoretical values (APL 2011 and Nanotechnology 2012). The suspensions produced have been tailored to be stable over a long period of time. 2)In order to design photonic band gaps, suspensions of spherical SiO2 particles were produced by chemical hydrolysis (JAP 2010 and JNP 2011 - not discussed in the thesis). 3) Using suspension inks, (ZnO)1-x(TiO2)x composite films have been printed and used to fabricate dye sensitized solar cells (JMR 2012). The thickness and the composition of the films can be easily tailored in the inkjet printing process. Consequently, the solar cell performance is optimized. We find that adding Ag nanoparticles improves the ‘metal-bridge’ between the TiO2 grains while maintaining the desired porous structure in the films. The photoluminescence spectra show that adding Ag reduces the emission intensity by a factor of two. This indicates that Ag atoms act as traps to capture electrons and inhibit recombination of electron-hole pairs, which is desirable for photo-voltaic applications. 4) To obtain and study room temperature contamination free ferromagnetic spintronic materials, defect induced and Fe doped MgO and ZnO were synthesized ‘in-situ’ by precursor solution technique (preprints). It is found that the origin of magnetism in these materials (APL 2012 and MRS 2012) is intrinsic and probably due to charge transfer hole doping. 5) ITO thin films were fabricated via inkjet printing directly from liquid precursors. The films are highly transparent (transparency &gt;90% both in the visible and IR range, which is rather unique as compared to any other film growth technique) and conductive (resistivity can be ~0.03 Ω•cm). The films have nano-porous structure, which is an added bonus from ink jetting that makes such films applicable for a broad range of applications. One example is in implantable biomedical components and lab-on-chip architectures where high transparency of the well conductive ITO electrodes makes them easily compatible with the use of quantum dots and fluorescent dyes. In summary, the inkjet patterning technique is incredibly versatile and applicable for a multitude of metal and oxide deposition and patterning. Especially in the case of using acetate solutions as inks (a method demonstrated for the first time by our group), the oxide films can be prepared ‘in-situ’ by direct patterning on the substrate without any prior synthesis stages, and the fabricated films are stoichiometric, uniform and smooth. This technique will most certainly continue to be a versatile tool in industrial manufacturing processes for material deposition in the future, as well as a unique fabrication tool for tailorable functional components and devices. / <p>QC 20120907</p>

This work presents the development of a GaN-based dilute magnetic semiconductor (DMS) by metal organic chemical vapor deposition (MOCVD) that is ferromagnetic at room temperature (RT), electrically conductive, and possesses magnetic properties that can be tuned by n- and p-doping. The transition metal series (TM: Cr, Mn, and Fe) along with the rare earth (RE) element, Gd, was investigated in this work as the magnetic ion source for the DMS. Single- phase and strain-free GaTMN films were obtained. Optical measurements revealed that Mn is a deep acceptor in GaN, while Hall measurements showed that these GaTMN films were semi-insulating, making carrier mediated exchange unlikely. Hysteresis curves were obtained for all the GaTMN films, and by analyzing the effect of n- and p-dopants on the magnetic properties of these films it was determined that the magnetization is due to magnetic clusters. These findings are supported by the investigation of the effect of TM dopants in GaN nanostructures which reveal that TMs enhance nucleation resulting in superparamagnetic nanostructures. Additionally, this work presents the first report on the development of GaGdN by MOCVD providing an alternate route to developing a RT DMS. Room temperature magnetization results revealed that the magnetization strength increases with Gd concentration and can be enhanced by n- and p-doping, with holes being more efficient at stabilizing the ferromagnetic signal. The GaGdN films obtained in this work are single-phase, unstrained, and conductive making them suitable for the development of multifunctional devices that integrate electrical, optical, and magnetic properties.

Nanotechnology is a technology of the design and the applications of nanoscale materials with their fundamentally new properties and functions. Nanosensor devices based on nanomaterials provide very fast response, low-cost, long-life time, easy to use for unskilled users, and provide high-efficiency. 1-D ZnO nanostructures materials have great potential applications in various sensing applications. ZnO is a wide band gap (3.37 eV at room temperature) semiconductor materials having large exciton binding energy (60 meV) and excellent chemical stability, electrical, optical, piezoelectric and pyroelectric properties. By doping the transition metals (TM) into ZnO matrix, the properties of ZnO nanostructures can be tuned and its room  temperature ferromagnetic behavior can be enhanced, which provide the TM-doped ZnO nanostructures as promising candidate for optoelectronic, spintronics and high performance sensors based devices. The synthesis of ZnO and TM-doped ZnO nanostructures via the low temperature hydrothermal method is considered a promising technique due to low cost, environmental friendly, simple solution process, diverse 1-D ZnO nanostructures can be achieved, and large scale production on any type of substrate, and their properties can be controlled by the growth parameters. However, to synthesize 1-D ZnO and TM-doped ZnO nanostructures with controlled shape, structure and uniform size distribution on large area substrates with desirable properties, low cost and simple processes are of high interest and it is a big challenge at present. The main purpose of this dissertation aims to develop new techniques to synthesize 1-D ZnO and (Fe, Mn)-doped ZnO nanostructures via the hydrothermal method, to characterize and to enhance their functional properties for developing sensing devices such as biosensors for clinical diagnoses and environmental monitoring applications, piezoresistive sensors and UV photodetector. The first part of the dissertation deals with the hydrothermal synthesis of ZnO nanostructures with controlled shape, structure and uniform size distribution under different conditions and their structural characterization. The possible parameters affecting the growth which can alter the morphology, uniformity and properties of the ZnO nanostructures were investigated. Well-aligned ZnO nanorods have been fabricated for high sensitive piezoresistive sensor. The development of creatinine biosensor for clinical diagnoses purpose and the development of glucose biosensor for indirect determination of mercury ions for an inexpensive and unskilled users for environmental monitoring applications with highly sensitive, selective, stable, reproducible, interference resistant, and fast response time have been fabricated based on ZnO nanorods. The second part of the dissertation presents a new hydrothermal synthesis of (Fe, Mn)-doped-ZnO nanostructures under different preparation conditions, their properties characterization and the fabrication of piezoresistive sensors and UV photodetectors based devices were demonstrated. The solution preparation condition and growth parameters that influences on the morphology, structures and properties of the nanostructures were investigated. The fabrication of Mn-doped-ZnO NRs/PEDOT:PSS Schottky diodes used as high performance piezoresistive sensor and UV photodetector have been studied and Fe-doped ZnO NRs/FTO Schottky diode has also been fabricated for high performance of UV photodetector. Finally, a brief outlook into future challenges and relating new opportunities are presented in the last part of the dissertation.

Thesis (Ph. D.)--University of Washington, 2007. / Vita. Includes bibliographical references (leaves 114-127).

Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / O desenvolvimento de semicondutores magnÃticos tÃm despertado crescente interesse dos pesquisadores devido suas promissoras aplicaÃÃo na spintrÃnica. Estes semicondutores podem ser produzidos a partir da dopagem de semicondutor nÃo magnÃtico com Ãons de metais de transiÃÃo. Neste trabalho, difraÃÃo de raios-x e espectroscopia no infravermelho foram utilizados para estudar as caracterÃsticas estruturais de Ãxidos semicondutores magnÃticos diluÃdos nanoestruturados do tipo SnO2 dopados com Fe, Co ou Mn, produzidos pelo mÃtodo sol-gel proteico. PadrÃes nanoestruturados de SnO2 sem dopagem foram produzidos com temperaturas de calcinaÃÃo de 300, 350 e 400ÂC para servir de base de comparaÃÃo. Foram sintetizadas sÃries de amostras com fÃrmula geral Sn1&#8722;x Mx O2&#8722;&#948; , onde M Ã o elemento magnÃtico (Fe, Co ou Mn) e x a concentraÃÃo de dopante, com as mesmas temperaturas de calcinaÃÃo e com trÃs concentraÃÃes de dopante (5, 10 e 20%). A difraÃÃo de raios-x foi utilizada para identificar as fases do composto assim como calcular os parÃmetros estruturais, tamanhos de cristalito e microdeformaÃÃes residuais. A anÃlise indicou que a sÃntese resultou na obtenÃÃo de compostos com estrutura SnO2 com dimensÃes nanomÃtricas. Amostras calcinadas a 400ÂC apresentaram a presenÃa de fases espÃrias. A dopagem foi confirmada pela variaÃÃo dos parÃmetros de rede dos compostos em funÃÃo do tipo e concentraÃÃo dos dopantes. Os modos vibracionais das ligaÃÃes quÃmicas nos compostos foram identificados por espectroscopia infravermelho. Com base nesta anÃlise, foi possÃvel estudar o comportamento energÃtico das ligaÃÃes iÃnicas quando os elementos dopantes estÃo incorporados em sÃtios de Ãons Sn4+ na matriz hospedeira. / The development of magnetic semiconductors has arisen growing attention due to their promising applications in spintronics. These materials can be produced by doping of a non-magnetic semiconductor with magnetic ions of transition metals. In this work, x-ray diffraction and infrared spectroscopy were used to study the structural characteristics of nanostructured Fe, Co or Mn-doped SnO2 oxide diluted magnetic semiconductors. The material was produced by a protein based sol-gel method called proteic sol-gel. To provide a basis for comparison, nanostructured standards of undoped SnO2 were produced with calcination temperatures of 300, 350 and 400&#9702; C. Samples of Sn1&#8722;x Mx O2&#8722;&#948; , where M is the magnetic dopant (Fe, Co or Mn) and x the dopant concentration, were prepared with the same calcination temperatures and x = 5, 10 and 20%. X-ray diffraction was used to identify the crystalline phases in the samples as well as to calculate structural parameters, particle sizes and residual microstrain. The analysis indicated that the synthesis resulted in nanosized compounds with the SnO2 structure. Samples calcined at 400&#9702; C presented the presence od spurious phases. Doping was confirmed by the variation of lattice parameters of compounds as a function of type and concentration of dopants. Vibrational modes of chemical bonds were identified by infrared spectroscopy. Based on this analysis, it was possible to study the energetic behavior of ionic bonds when doping elements are incorporated in Sn4+ sites in the host matrix.

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