Cold spray has seen rapid advancement since its inception and has shown significant potential as a method of additive manufacturing. However, the large plastic deformation and repeated heating/cooling cycles that the material undergoes during the cold spray process can result in gradients in material structure and large residual stresses. The purpose of this study is to extend the existing EMMI material model to include anisotropic material response through the use of orientation distribution functions to predict residual stresses and anisotropy resulting from cold spray and similar additive manufacturing processes. Through the use of a finite element simulation, yield surfaces for a two-step tension problem were generated and analyzed to capture the effects of the four coaxiality parameters that govern the model.

Copper-based multi-level metallization systems in today’s ultralarge-scale integrated electronic circuits require the fabrication of diffusion barriers and conductive seed layers for the electrochemical metal deposition. Such films of only several nanometers in thickness have to be deposited void-free and conformal in patterned dielectrics. The envisaged further reduction of the geometric dimensions of the interconnect system calls for coating techniques that circumvent the drawbacks of the well-established physical vapor deposition. The atomic layer deposition method (ALD) allows depositing films on the nanometer scale conformally both on three-dimensional objects as well as on large-area substrates. The present work therefore is concerned with the development of an ALD process to grow copper oxide films based on the metal-organic precursor bis(tri-n-butylphosphane)copper(I)acetylacetonate [(nBu3P)2Cu(acac)]. This liquid, non-fluorinated β-diketonate is brought to react with a mixture of water vapor and oxygen at temperatures from 100 to 160°C. Typical ALD-like growth behavior arises between 100 and 130°C, depending on the respective substrate used. On tantalum nitride and silicon dioxide substrates, smooth films and self-saturating film growth, typical for ALD, are obtained. On ruthenium substrates, positive deposition results are obtained as well. However, a considerable intermixing of the ALD copper oxide with the underlying films takes place. Tantalum substrates lead to a fast self-decomposition of the copper precursor. As a consequence, isolated nuclei or larger particles are always obtained together with continuous films. The copper oxide films grown by ALD can be reduced to copper by vapor-phase processes. If formic acid is used as the reducing agent, these processes can already be carried out at similar temperatures as the ALD, so that agglomeration of the films is largely avoided. Also for an integration with subsequent electrochemical copper deposition, the combination of ALD copper and ruthenium proves advantageous, especially with respect to the quality of the electroplated films and their filling behavior in interconnect structures. Furthermore, the ALD process developed also bears potential for an integration with carbon nanotubes. / Kupferbasierte Mehrlagenmetallisierungssysteme in heutigen hochintegrierten elektronischen Schaltkreisen erfordern die Herstellung von Diffusionsbarrieren und leitfähigen Keimschichten für die galvanische Metallabscheidung. Diese Schichten von nur wenigen Nanometern Dicke müssen konform und fehlerfrei in strukturierten Dielektrika abgeschieden werden. Die sich abzeichnende weitere Verkleinerung der geometrischen Dimensionen des Leitbahnsystems erfordert Beschichtungstechnologien, die vorhandene Nachteile der bisher etablierten Physikalischen Dampfphasenabscheidung beheben. Die Methode der Atomlagenabscheidung (ALD) ermöglicht es, Schichten im Nanometerbereich sowohl auf dreidimensional strukturierten Objekten als auch auf großflächigen Substraten gleichmäßig herzustellen. Die vorliegende Arbeit befasst sich daher mit der Entwicklung eines ALD-Prozesses zur Abscheidung von Kupferoxidschichten, ausgehend von der metallorganischen Vorstufe Bis(tri-n-butylphosphan)kupfer(I)acetylacetonat [(nBu3P)2Cu(acac)]. Dieses flüssige, nichtfluorierte β-Diketonat wird bei Temperaturen zwischen 100 und 160°C mit einer Mischung aus Wasserdampf und Sauerstoff zur Reaktion gebracht. ALD-typisches Schichtwachstum stellt sich in Abhängigkeit des gewählten Substrats zwischen 100 und 130°C ein. Auf Tantalnitrid- und Siliziumdioxidsubstraten werden dabei sehr glatte Schichten bei gesättigtem Wachstumsverhalten erhalten. Auch auf Rutheniumsubstraten werden gute Abscheideergebnisse erzielt, jedoch kommt es hier zu einer merklichen Durchmischung des ALD-Kupferoxids mit dem Untergrund. Tantalsubstrate führen zu einer schnellen Selbstzersetzung des Kupferprecursors, in dessen Folge neben geschlossenen Schichten während der ALD auch immer isolierte Keime oder größere Partikel erhalten werden. Die mittels ALD gewachsenen Kupferoxidschichten können in Gasphasenprozessen zu Kupfer reduziert werden. Wird Ameisensäure als Reduktionsmittel genutzt, können diese Prozesse bereits bei ähnlichen Temperaturen wie die ALD durchgeführt werden, so dass Agglomeration der Schichten weitgehend verhindert wird. Als besonders vorteilhaft für die Ameisensäure-Reduktion erweisen sich Rutheniumsubstrate. Auch für eine Integration mit nachfolgenden Galvanikprozessen zur Abscheidung von Kupfer zeigen sich Vorteile der Kombination ALD-Kupfer/Ruthenium, insbesondere hinsichtlich der Qualität der erhaltenen galvanischen Schichten und deren Füllverhalten in Leitbahnstrukturen. Der entwickelte ALD-Prozess besitzt darüber hinaus Potential zur Integration mit Kohlenstoffnanoröhren.

Copper-based multi-level metallization systems in today’s ultralarge-scale integrated electronic circuits require the fabrication of diffusion barriers and conductive seed layers for the electrochemical metal deposition. Such films of only several nanometers in thickness have to be deposited void-free and conformal in patterned dielectrics. The envisaged further reduction of the geometric dimensions of the interconnect system calls for coating techniques that circumvent the drawbacks of the well-established physical vapor deposition. The atomic layer deposition method (ALD) allows depositing films on the nanometer scale conformally both on three-dimensional objects as well as on large-area substrates. The present work therefore is concerned with the development of an ALD process to grow copper oxide films based on the metal-organic precursor bis(tri-n-butylphosphane)copper(I)acetylacetonate [(nBu3P)2Cu(acac)]. This liquid, non-fluorinated β-diketonate is brought to react with a mixture of water vapor and oxygen at temperatures from 100 to 160°C. Typical ALD-like growth behavior arises between 100 and 130°C, depending on the respective substrate used. On tantalum nitride and silicon dioxide substrates, smooth films and self-saturating film growth, typical for ALD, are obtained. On ruthenium substrates, positive deposition results are obtained as well. However, a considerable intermixing of the ALD copper oxide with the underlying films takes place. Tantalum substrates lead to a fast self-decomposition of the copper precursor. As a consequence, isolated nuclei or larger particles are always obtained together with continuous films. The copper oxide films grown by ALD can be reduced to copper by vapor-phase processes. If formic acid is used as the reducing agent, these processes can already be carried out at similar temperatures as the ALD, so that agglomeration of the films is largely avoided. Also for an integration with subsequent electrochemical copper deposition, the combination of ALD copper and ruthenium proves advantageous, especially with respect to the quality of the electroplated films and their filling behavior in interconnect structures. Furthermore, the ALD process developed also bears potential for an integration with carbon nanotubes. / Kupferbasierte Mehrlagenmetallisierungssysteme in heutigen hochintegrierten elektronischen Schaltkreisen erfordern die Herstellung von Diffusionsbarrieren und leitfähigen Keimschichten für die galvanische Metallabscheidung. Diese Schichten von nur wenigen Nanometern Dicke müssen konform und fehlerfrei in strukturierten Dielektrika abgeschieden werden. Die sich abzeichnende weitere Verkleinerung der geometrischen Dimensionen des Leitbahnsystems erfordert Beschichtungstechnologien, die vorhandene Nachteile der bisher etablierten Physikalischen Dampfphasenabscheidung beheben. Die Methode der Atomlagenabscheidung (ALD) ermöglicht es, Schichten im Nanometerbereich sowohl auf dreidimensional strukturierten Objekten als auch auf großflächigen Substraten gleichmäßig herzustellen. Die vorliegende Arbeit befasst sich daher mit der Entwicklung eines ALD-Prozesses zur Abscheidung von Kupferoxidschichten, ausgehend von der metallorganischen Vorstufe Bis(tri-n-butylphosphan)kupfer(I)acetylacetonat [(nBu3P)2Cu(acac)]. Dieses flüssige, nichtfluorierte β-Diketonat wird bei Temperaturen zwischen 100 und 160°C mit einer Mischung aus Wasserdampf und Sauerstoff zur Reaktion gebracht. ALD-typisches Schichtwachstum stellt sich in Abhängigkeit des gewählten Substrats zwischen 100 und 130°C ein. Auf Tantalnitrid- und Siliziumdioxidsubstraten werden dabei sehr glatte Schichten bei gesättigtem Wachstumsverhalten erhalten. Auch auf Rutheniumsubstraten werden gute Abscheideergebnisse erzielt, jedoch kommt es hier zu einer merklichen Durchmischung des ALD-Kupferoxids mit dem Untergrund. Tantalsubstrate führen zu einer schnellen Selbstzersetzung des Kupferprecursors, in dessen Folge neben geschlossenen Schichten während der ALD auch immer isolierte Keime oder größere Partikel erhalten werden. Die mittels ALD gewachsenen Kupferoxidschichten können in Gasphasenprozessen zu Kupfer reduziert werden. Wird Ameisensäure als Reduktionsmittel genutzt, können diese Prozesse bereits bei ähnlichen Temperaturen wie die ALD durchgeführt werden, so dass Agglomeration der Schichten weitgehend verhindert wird. Als besonders vorteilhaft für die Ameisensäure-Reduktion erweisen sich Rutheniumsubstrate. Auch für eine Integration mit nachfolgenden Galvanikprozessen zur Abscheidung von Kupfer zeigen sich Vorteile der Kombination ALD-Kupfer/Ruthenium, insbesondere hinsichtlich der Qualität der erhaltenen galvanischen Schichten und deren Füllverhalten in Leitbahnstrukturen. Der entwickelte ALD-Prozess besitzt darüber hinaus Potential zur Integration mit Kohlenstoffnanoröhren.

Im Fokus der vorliegenden Arbeit lag die Untersuchung polykristalliner TiO2:Ta-Schichten, hergestellt mittels Gleichstrom-Magnetron-Sputtern durch Verwendung reduzierter keramischer Targets und anschließender thermischer Nachbehandlung im Vakuum der zunächst nichtleitfähigen amorphen Precursorschichten. Es wurden die physikalischen Zusammenhänge, welche die strukturellen, elektrischen und optischen Eigenschaften der kristallinen TiO2:Ta-Schichten beeinflussen analysiert und dabei eine empfindliche Abhängigkeit vom Sauerstofffluss während der Abscheidung festgestellt. Es zeigte sich, dass die Verringerung der kinetischen Energie der Plasmateilchen beim Magnetron-Sputtern durch die Erhöhung des Gesamtdruckes vorteilhaft ist, um das Wachstum des gegenüber Rutil besser leitfähigen Anatas in Verbindung mit dem für niedrige Widerstände notwendigen Sauerstoffdefizit zu realisieren. Bei einem Gesamtdruck von 2 Pa abgeschiedene polykristalline TiO2:Ta-Schichten haben einen spezifischen Widerstand von 1,5·10-3 Ωcm, eine hohe Ladungsträgermobilität (≈8 cm2V-1s-1) und einen geringen Extinktionskoeffizienten von 0,006. Die Abhängigkeit des elektrischen Widerstandes vom Sauerstoffdefizit in der TiO2:Ta-Schicht wurde unter dem Gesichtspunkt der Ladungsträgeraktivierung sowie der Bildung von Ti-Fehlstellen diskutiert, welche vermutlich zur Kompensation und Lokalisierung von freien Elektronen beitragen. Darüber hinaus wurde zur effizienteren Gestaltung der thermischen Nachbehandlung die konventionelle Vakuumtemperung erstmalig erfolgreich durch die Blitzlampentemperung ersetzt. / The work is focused on understanding the physical processes responsible for the modification of the structural, electrical and optical properties of polycrystalline TiO2:Ta films formed by vacuum annealing of initially not conductive amorphous films deposited by direct current magnetron sputtering. It is shown that the oxygen deficiency of amorphous and annealed TiO2:Ta films, respectively, is critical to achieve low resistivity and high optical transmittance of the crystalline films. Increasing the total pressure during magnetron sputter deposition is shown to be beneficial to achieve the desired oxygen deficient anatase growth, which is discussed in terms of energetic particle bombardment. Polycrystalline anatase TiO2:Ta films of low electrical resistivity (1,5·10-3 Ωcm), high free electron mobility (≈8 cm2V-1s-1), and low extinction (0,006) are obtained in this way at a total pressure of 2 Pa. The dependence of the polycrystalline film electrical properties on the oxygen content is discussed in terms of Ta dopant electrical activation as well as transport limiting processes taking into account the formation of Ti-vacancies. In addition, the conventional vacuum annealing has been successfully substituted by the flash lamp annealing in the millisecond range.

Due to mining activities, the natural vegetation cover in Gatumba area was removed and replaced either by crops or bare wasteland with reduced available arable land. The main aim of the study was to assess the impact of the mining activities on the plant mineral uptake and the dynamics of the vegetation. The vegetation in this area under investigation was diversified and heterogeneous. Trace element concentrations in soils were similar to those in plant parts but some elements were highly concentrated in soils than in plants. According to the bioaccumulation factors of the analyzed trace elements in plant parts, two categories of plants were identified, and these are excluders and accumulators. No toxic levels of the evaluated trace elements were found in the analyzed plant samples. As a recommendation for the adaptation of plants to Gatumba mining environment, the most useful plant species for the revegetation/restitution of the technosols should be Sesbania sesban, Crotalaria dewildemaniana and Tithonia diversifolia subject to further experiments on trace elements bioaccumulation and organic matter production / Environmental Sciences / M.A. Science (Environmental Sciences)

O uso do peróxido de hidrogênio eletrogerado in situ em Processos Oxidativos Avançados (POAs) é um promissor método para o tratamento de efluentes orgânicos. Neste contexto, o desenvolvimento de materiais mais eficientes para viabilizar a reação de redução do oxigênio (RRO) pelo mecanismo envolvendo a transferência de dois elétrons ainda é de grande importância. O presente estudo objetiva a obtenção e a avaliação da atividade catalítica de nanopartículas de óxidos metálicos, Ta2O5, MoO3, Nb2O5 ou ZrO2, incorporadas em carbono Printex 6L e em grafeno no estudo da redução do oxigênio visando a eletrogeração de peróxido de hidrogênio. A caracterização morfológica e microestrutural desses materiais foi investigada por difração de raios X, microscopia eletrônica de transmissão e espectroscopia de fotoelétrons excitados por raios X. O mecanismo da RRO foi analisado pela técnica do eletrodo de disco-anel rotatório. O carbono Printex 6L apresentou uma eficiência de corrente para a eletrogeração de H2O2 (I(H2O2)%) igual a 65,3% em K2SO4 0,1 mol L-1 (pH =2). Após o tratamento térmico desse substrato pelo método dos precursores poliméricos, a eficiência de corrente aumentou 17,1%, ou seja, I(H2O2)% igual a 76,5%. A modificação do carbono Printex 6L com nanopartículas cristalinas de Ta2O5, MoO3, Nb2O5 ou ZrO2 deslocou o potencial de meia-onda para a RRO para valores menos negativos e aumentou a I(H2O2)%. O Nb2O5/C apresentou a maior I(H2O2)%, 87,1%, enquanto o ZrO2/C deslocou o potencial em 137 mV. O estudo comparativo entre três substratos de carbono para a redução do oxigênio, revelou que o óxido de grafeno reduzido apresentou maior atividade para a RRO comparado ao óxido de grafeno e ao carbono Printex 6L, tanto em eletrólito ácido quanto em eletrólito alcalino. A modificação do rGO com Nb2O5 ou ZrO2 pelo método hidrotermal aumentou a atividade catalítica desse substrato para a RRO. A maior eletrogeração de H2O2 foi observada na presença do ZrO2. De fato, um aumento de 73,7% para 88,5% em K2SO4 0,1 mol L-1 (pH =2), e de 72,9% para 83,1% em NaOH 0,1 mol L-1, foi observado em rGO e ZrO2-rGO, respectivamente. Além disso, o ZrO2-rGO apresentou menor sobrepotencial para a RRO comparado ao rGO sem modificador. Portanto, a presença das nanopartículas de óxidos metálicos na matriz condutora de carbono amorfo intensificou a atividade catalítica para a eletrogeração do H2O2, tanto em carbono Printex 6L quanto em óxido de grafeno reduzido, indicando o efeito sinérgico entre as nanopartículas e o subtrato de carbono. Consequentemente, os catalisadores avaliados neste trabalho são promissores para a eletrogeração de espécies oxidantes in situ e sua aplicaçao em POAs. / In situ electrogeneration of hydrogen peroxide has been greatly application in Advanced Oxidation Processes (AOPs) as an effective water treatment technology. In this context, the development of electrode materials that enable the oxygen reduction reaction (ORR) mechanism through a two-electron pathway with high selectivity at low overpotential has a pronounced importance. In the present study, we investigate the properties of Ta2O5, MoO3, Nb2O5 or ZrO2 nanoparticles supported on Printex 6L carbon and reduced graphene oxide for the electrocatalysis of oxygen reduction to H2O2. The structures and morphologies of these materials were characterized by X-ray diffraction analysis, transmission electron microscopy and X-ray photoelectron spectroscopy. Electrochemical activities toward the ORR were evaluated using a rotating ring-disk electrode system. Printex 6L carbon showed a current efficiency for H2O2 production (I(H2O2)%) of 65.3% in K2SO4 0.1 mol L-1 (pH =2) whereas the carbon heat-treated by the polymeric precursor method displayed 76.5% yield of H2O2 electrogeneration. Carbon Printex 6L modified with Ta2O5, MoO3, Nb2O5 or ZrO2 nanoparticles shifted the half-wave potential for the ORR to less negative potential and increased the I(H2O2)%. The Nb2O5/C showed the highest I(H2O2)%, 87,1%, and the ZrO2/C shifted the potential 137 mV. The comparative study of ORR in acid and alkaline media for the three different conductive carbon pigment showed that the reduced graphene oxide displayed higher activity to oxygen reduction than graphene oxide and Printex 6L carbon. Reduced graphene oxide modified with Nb2O5 or ZrO2 nanoparticles by hydrothermal method increased the catalytic activity of this substrate for ORR which the highest H2O2 electrogeneration was observed for ZrO2-rGO. Indeed, an increase from 73.7% to 88.5% in K2SO4 0.1 mol L-1 (pH =2) and from 72.9% to 83.1% in NaOH 0.1 mol L-1 was obtained for rGO and ZrO2-rGO, respectively. Additionally, the ZrO2-rGO electrocatalyst exhibited overpotential lower than that of rGO unmodified. Therefore, the metallic oxides nanoparticles in both carbon Printex 6L and reduced graphene oxide enhanced the catalytic activity for H2O2 electrogeneration indicating the synergistic effect between the nanoparticles and the amorphous carbon. The catalysts evaluated in this study are promising for in situ electrogeneration of oxidizing agents to be used in the degradation of organic pollutants.

O uso do peróxido de hidrogênio eletrogerado in situ em Processos Oxidativos Avançados (POAs) é um promissor método para o tratamento de efluentes orgânicos. Neste contexto, o desenvolvimento de materiais mais eficientes para viabilizar a reação de redução do oxigênio (RRO) pelo mecanismo envolvendo a transferência de dois elétrons ainda é de grande importância. O presente estudo objetiva a obtenção e a avaliação da atividade catalítica de nanopartículas de óxidos metálicos, Ta2O5, MoO3, Nb2O5 ou ZrO2, incorporadas em carbono Printex 6L e em grafeno no estudo da redução do oxigênio visando a eletrogeração de peróxido de hidrogênio. A caracterização morfológica e microestrutural desses materiais foi investigada por difração de raios X, microscopia eletrônica de transmissão e espectroscopia de fotoelétrons excitados por raios X. O mecanismo da RRO foi analisado pela técnica do eletrodo de disco-anel rotatório. O carbono Printex 6L apresentou uma eficiência de corrente para a eletrogeração de H2O2 (I(H2O2)%) igual a 65,3% em K2SO4 0,1 mol L-1 (pH =2). Após o tratamento térmico desse substrato pelo método dos precursores poliméricos, a eficiência de corrente aumentou 17,1%, ou seja, I(H2O2)% igual a 76,5%. A modificação do carbono Printex 6L com nanopartículas cristalinas de Ta2O5, MoO3, Nb2O5 ou ZrO2 deslocou o potencial de meia-onda para a RRO para valores menos negativos e aumentou a I(H2O2)%. O Nb2O5/C apresentou a maior I(H2O2)%, 87,1%, enquanto o ZrO2/C deslocou o potencial em 137 mV. O estudo comparativo entre três substratos de carbono para a redução do oxigênio, revelou que o óxido de grafeno reduzido apresentou maior atividade para a RRO comparado ao óxido de grafeno e ao carbono Printex 6L, tanto em eletrólito ácido quanto em eletrólito alcalino. A modificação do rGO com Nb2O5 ou ZrO2 pelo método hidrotermal aumentou a atividade catalítica desse substrato para a RRO. A maior eletrogeração de H2O2 foi observada na presença do ZrO2. De fato, um aumento de 73,7% para 88,5% em K2SO4 0,1 mol L-1 (pH =2), e de 72,9% para 83,1% em NaOH 0,1 mol L-1, foi observado em rGO e ZrO2-rGO, respectivamente. Além disso, o ZrO2-rGO apresentou menor sobrepotencial para a RRO comparado ao rGO sem modificador. Portanto, a presença das nanopartículas de óxidos metálicos na matriz condutora de carbono amorfo intensificou a atividade catalítica para a eletrogeração do H2O2, tanto em carbono Printex 6L quanto em óxido de grafeno reduzido, indicando o efeito sinérgico entre as nanopartículas e o subtrato de carbono. Consequentemente, os catalisadores avaliados neste trabalho são promissores para a eletrogeração de espécies oxidantes in situ e sua aplicaçao em POAs. / In situ electrogeneration of hydrogen peroxide has been greatly application in Advanced Oxidation Processes (AOPs) as an effective water treatment technology. In this context, the development of electrode materials that enable the oxygen reduction reaction (ORR) mechanism through a two-electron pathway with high selectivity at low overpotential has a pronounced importance. In the present study, we investigate the properties of Ta2O5, MoO3, Nb2O5 or ZrO2 nanoparticles supported on Printex 6L carbon and reduced graphene oxide for the electrocatalysis of oxygen reduction to H2O2. The structures and morphologies of these materials were characterized by X-ray diffraction analysis, transmission electron microscopy and X-ray photoelectron spectroscopy. Electrochemical activities toward the ORR were evaluated using a rotating ring-disk electrode system. Printex 6L carbon showed a current efficiency for H2O2 production (I(H2O2)%) of 65.3% in K2SO4 0.1 mol L-1 (pH =2) whereas the carbon heat-treated by the polymeric precursor method displayed 76.5% yield of H2O2 electrogeneration. Carbon Printex 6L modified with Ta2O5, MoO3, Nb2O5 or ZrO2 nanoparticles shifted the half-wave potential for the ORR to less negative potential and increased the I(H2O2)%. The Nb2O5/C showed the highest I(H2O2)%, 87,1%, and the ZrO2/C shifted the potential 137 mV. The comparative study of ORR in acid and alkaline media for the three different conductive carbon pigment showed that the reduced graphene oxide displayed higher activity to oxygen reduction than graphene oxide and Printex 6L carbon. Reduced graphene oxide modified with Nb2O5 or ZrO2 nanoparticles by hydrothermal method increased the catalytic activity of this substrate for ORR which the highest H2O2 electrogeneration was observed for ZrO2-rGO. Indeed, an increase from 73.7% to 88.5% in K2SO4 0.1 mol L-1 (pH =2) and from 72.9% to 83.1% in NaOH 0.1 mol L-1 was obtained for rGO and ZrO2-rGO, respectively. Additionally, the ZrO2-rGO electrocatalyst exhibited overpotential lower than that of rGO unmodified. Therefore, the metallic oxides nanoparticles in both carbon Printex 6L and reduced graphene oxide enhanced the catalytic activity for H2O2 electrogeneration indicating the synergistic effect between the nanoparticles and the amorphous carbon. The catalysts evaluated in this study are promising for in situ electrogeneration of oxidizing agents to be used in the degradation of organic pollutants.

A new approach to the discovery of high absorbing semiconductors for solar cells was taken by working under a set of design principles and taking a systemic methodology. Three transition metal chalcogenides at varying states of development were evaluated within this framework. Iron pyrite (FeS���) is well known to demonstrate excellent absorption, but the coexistence with metallic iron sulfides was found to disrupt its semiconducting properties. Manganese diselenide (MnSe���), a material heavily researched for its magnetic properties, is proposed as a high absorbing alternative to iron pyrite that lacks destructive impurity phases. For the first time, a MnSe��� thin film was synthesized and the optical properties were characterized. Finally, CuTaS���, a known but never characterized material, is also proposed as a high absorbing semiconductor based on the design principles and experimental results. / Graduation date: 2013

The objective of this work is to evaluate the reaction initiation characteristics of quasi-statically compressed intermetallic-forming aluminum-based reactive materials upon impact initiation, consisting of equi-volumetric tantalum-aluminum, tungsten-aluminum, nickel-aluminum, and pure aluminum. A modified Taylor rod-on-anvil setup was employed to determine the reaction initiation threshold kinetic energy and actual energy for plastic deformation and subsequent reaction. Experimental sample remnants were recovered and examined through X-ray diffraction to determine reaction products.The overall results indicate that of the various intermetallic-forming systems investigated, Ta+Al was the most reactive and was the only system where any reaction products were retrieved. While all of the intermetallic systems reacted in air, only Ta+Al and W+Al reacted in vacuum environment suggesting differences in reaction mechanisms influencing the reactivity of intermetallic mixtures. Based on the threshold energy for onset of reaction it appears that the Ta-Al compacts show reaction conditions below those required for reaction of Al in air. This combined with the fact that Ta+Al compacts also react in vacuum implies that the Ta+Al undergoes anaerobic intermetallic reaction while the other systems react with the oxidation of Al. The effect of compact packing density on the kinetic energy threshold for reaction initiation were also evaluated. It was observed more densely packed Ta+Al and Ni+Al powder compacts react more easily than less densely packed samples. While the effect of packing density is not as obvious in the case of pure Al and W+Al powder compacts. Finally, a particle size effect is seen on Ni+Al on samples of < 92% density where coarser (+325 -200 mesh) equal-volumetric powder mixtures were observed to be more reactive than finer Ni+Al (-325 mesh).

Made available in DSpace on 2014-12-17T14:07:22Z (GMT). No. of bitstreams: 1 AntonioCPS.pdf: 2085220 bytes, checksum: 8e64ae2c2f5ffe8a64dd3420c9c87327 (MD5) Previous issue date: 2007-03-23 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico / In this work was used a plasma torch of non transferred arc with argon as work gas, using a power supply with maximum DC current of 250 A and voltage of 30 V to activate the plasma and keep it switched on. The flame temperature was characterized by optical emission spectroscopy, through Boltzmann-plot-method. The torch has been used like igniter in the aluminothermic reduction of the mixture tantalum oxide and aluminum, seeking to obtain metallic tantalum. In heating of the reagents only one particle will be considered to study interactions between plasma-particle, seeking to determinate its fusion and residence time. The early powders were characterized by laser granulometry, scanning electron microscopy (SEM) and X-ray diffraction analysis. The final product of this reaction was characterized by SEM and X-ray diffraction. Crystallite size was calculated by the Scherrer equation and microdeformation was determined using Willamsom-Hall graph. With Rietveld method was possible to quantify the percentile in weight of the products obtained in the aluminothermic reaction. Semi-quantitative chemical analysis (EDS) confirmed the presence of metallic tantalum and Al2O3 as products of the reduction. As was waited the particle size of the metallic tantalum produced, presents values in nanometric scale due the short cooling time of those particles during the process / Neste trabalho foi utilizada uma tocha de plasma de arco n?o transferido com arg?nio como g?s de trabalho, utilizando uma fonte de pot?ncia com corrente m?xima de 250 A e tens?o m?xima de sa?da de 30 V fornecida pelo fabricante. A temperatura da tocha foi caracterizada atrav?s da espectroscopia de emiss?o ?ptica, utilizando a curva de Boltzmann. A tocha foi usada como ignitor para a rea??o de redu??o aluminot?rmica do ?xido de t?ntalo mais alum?nio para a produ??o de t?ntalo met?lico. No aquecimento dos reagentes apenas uma part?cula ser? considerada para o estudo da intera??o tocha-part?cula, com o objetivo de determinar seu tempo de fus?o e resid?ncia. Os p?s de partida foram caracterizados atrav?s da granulometria a laser, microscopa eletr?nica de varredura (MEV) e difra??o de raios X. O produto final desta rea??o foi caracterizado por MEV e difra??o de raios X. O tamanho de cristalito foi calculado atrav?s da equa??o de Scherrer e a microdeforma??o foi determinada utilizando o gr?fico de Willamsom-Hall. Com o m?todo de Rietveld foi poss?vel quantificar o percentual em peso do produto da rea??o aluminot?rmica. An?lise qu?mica semiquantitativa (EDS) confirmou a presen?a do Ta met?lico e Al2O3 como produtos da redu??o. Como era de se esperar, o tamanho das part?culas do t?ntalo met?lico produzida apresenta valores na faixa de nan?metro devido pequeno tempo de resfriamento durante o processo