The oxidation behaviour of TiAlN based hard coatings with the addition of Cr and/or Y was investigated using scanning electron microscopy, scanning/transmission electron microscopy, energy dispersive X-ray analysis, thermogravimetry and X-ray diffraction. The coatings were deposited using the combined cathodic arc/unbalanced magnetron deposition technique. The main practical application of these films is dry high speed cutting in difficult to cut materials such as AISI A2 steel. Especially in the case of TiAlCrYN coating with an oxynitride and Cr-enriched overcoat, extensive research on the oxidation behaviour was performed and described here. Heat treatments in air between 600-1000°C for different duration were carried out. The Ti[0.44]Al[0.54]Cr[0.02]N coating was used as the starting point for the investigations. The effect of heat on the composition of the interface region was investigated. This region is of utmost importance for the adhesion of the film. In the case of TiAICrN the interface stability was not guaranteed because of diffusion of the substrate elements Cr and Fe to the coating surface after annealing for 1h at 900°C. In comparison, the diffusion of substrate elements Cr and Fe in a ~2.3 mum thick coating of Ti[0.43]Al[0.52]Cr[0.03]Y[0.02]N and of Ti[0.34]Al[0.62]Cr[0.03]Y[0.01]N with overcoat, reached only a distance of ~600nm into the coating. This was achieved by the diffusion of Y to the grain boundaries. Y probably reacted at the same time with inward diffusing O. The diffusion of Y to the boundaries was observed after heat treatment for 1h at 900°C or 10h at 800°C.Ti[0.26]Al[0.26]N/Cr[0.48]N was the coating with the least oxide layer growth after oxidation for 1h at 900°C. An oxide layer thickness of only ~100nm was measured. For the TiAICrYN coating with overcoat an oxide layer of 230nm and for TiAICrYN of 430nm formed after 1h at 900°C. TiAlCrN in comparison formed an oxide layer of ~800nm after 1 h at 900°C.The oxide layers formed after 1h at 900°C consisted mainly of an Al[2]O[3] and TiO[2] bi-layer in the case of TiAlCrN and TiAlCrYN. The addition of a Cr-rich oxynitride overcoat led to the formation of a mixture out of Al[2]O[3], Cr[2]O[3] and TiO[2] in the oxide layer. In the case of TiAlN/CrN, a solid solution consisting of Cr[2]O[3] and Al[2]O[3] was observed. In general a stress relief after heat treatment was observed. At the same time the formation of voids along the column boundaries was identified. This was explained with the relaxation and diffusion of defects created during the deposition process. The effect of different substrate materials on the oxidation behaviour was also investigated. It was found that the formation of substrate oxides on the coating surface is very much dependent on the onset point of oxidation of the substrate material itself. The oxidation of substrate material occurred mainly through growth defects and pinholes. In cases where cracks formed during heat treatment of the coating, the formation of oxides out of substrate elements were observed in cracks connecting the substrate with the coating surface. Changing the bias voltage altered the formation of cracks. This research emphasises the importance of Y in the oxidation mechanism of TiAlN based hard coatings. Y blocks the diffusion path along the column boundaries and thus stowed down the diffusion and oxidation process. At the same time the addition of Cr can increase the oxidation resistance considerably, which was observed in the TiAlCrYN coating with and without overcoat.

Metal-Insulator-Metal (MIM), Metal-Insulator-Insulator-Metal (MIIM), and Metal-Insulator-Insulator-Insulator-Metal (MIIIM) quantum tunneling diodes have been designed, fabricated, and characterized. The key interest of this work was to develop tunneling diodes capable of operating and detecting THz radiation up to 30THz, which is well beyond the operation ranges of other semiconductor-based diodes. Al2O3, HfO2 and TiO2 metal oxides were employed for studying the behavior of metal-insulator-metal (MIM) and metal-insulator-insulator-metal (MIIM) quantum tunneling diodes. Specifically, ultra-thin films of these oxides with varied thicknesses were deposited by atomic layer deposition (ALD) as the tunneling junction material that is sandwiched between platinum (Pt) and titanium (Ti) electrodes, with dissimilar work functions of 5.3 eV and 4.1 eV, respectively. Due to the unique and well-controlled tunneling characteristic of the ALD ultra-thin films, reproducible MIM and MIIM diode devices have been developed. The DC characteristics of MIM and MIIM tunneling junctions with different junction areas and materials were investigated in this work. The effects of the different compositions and thicknesses of the tunneling layer on the diodes were studied systematically. Through the introduction of stacked dual tunneling layers, it is demonstrated that the MIIM and MIIIM diodes exhibited a high degree of asymmetry (large ratio between forward and reverse currents) and a strong nonlinearity in their I-V characteristics. The characterization was performed on diodes with micro and nano-scale junction areas. The MIM diodes reported herein exhibited lower junction resistances than those reported by prior works. Moreover, a study was conducted to numerically extract the average barrier heights by fitting the analytical model of the tunneling current to the measured I-V responses, which were evaluated with respect to the thickness of the constituent tunneling layer. RF characterization was performed on the MIM diodes up to 65GHz, and its junction impedance was extracted. A rigorous procedure was followed to extract the diode equivalent circuit model to obtain the intrinsic lumped element model parameters of the MIM diodes.

Orientador: Carlos Alberto dos Reis Filho / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-05T12:05:57Z (GMT). No. of bitstreams: 1 Cajueiro_JoaoPauloCerquinho_D.pdf: 1564955 bytes, checksum: 6ff645ea51f6ee2dcb9e7ab8db6363aa (MD5) Previous issue date: 2005 / Resumo: Uma nova técnica de compensação de temperatura para implementar tensões de referência em circuitos CMOS é descrita, desde o seu fundamento teórico até a comprovação experimental feita com amostras de circuitos integrados protótipos que a implementam. A ténica proposta se baseia no fato de que a tensão entre gate1, e fonte, VGS, de um transistor MOS pode tanto aumentar como diminuir com o aumento da temperatura, dependendo da corrente com que opera. Com base nisto, é possível empilhar n transistores, que estejam polarizados com uma corrente adequada de tal maneira que a queda de tensão sobre esta pilha de transistores, que tem amplitude nVGS, tenha, ao mesmo tempo, a mesma taxa de variação térmica que a tensão VGS produzida por um único transistor. Em tais condições, a diferença entre estas duas tensões é constante, tornando-se uma referencia de tensão. Uma implementação alternativa à pilha de transistores para produzir a tensão nVGS consiste num único transistor de gate ?utuante no qual a tensão VGS equivalente tem amplitude ajustável em campo. Diversos circuitos que se baseiam nesta técnica foram projetados e alguns deles fabricados em tecnologia CMOS 0,35 µm.O desempenho do melhor circuito fabricado atingiu coe?ciente térmico de 100 ppm/°C na faixa térmica de -40 a 120 °C. Outras configurações foram simuladas mostrando que é possível atingir coeficientes térmicos menores que 10 ppm/°C. O estado da arte é representado por referências de tensão que têm coeficientes térmicos de 1 ppm/°C na mesma faixa térmica em que se caracterizam os circuitos desenvolvidos. Tais referências de tensão se baseiam principalmente nos circuitos chamados de bandgap. Há também, um produto recente da empresa Intersil que utiliza um transistor que opera como memória análoga fornecendo uma tensão referência memorizada com altíssima estabilidade térmica. O princípio em que este produto se baseia, entretanto, é diferente do que está sendo proposto neste trabalho apesar do uso comum de um transistor de gate ?utuante. A contribuição deste trabalho não está no desempenho que as fontes de referência que se baseiam no princípio atingiram. Sua contribuição reside na forma como pode ser implementada, utilizando somente transistores MOS e no fato de que tem amplitude ajustável em campo. 1A palavra gate está sendo usada em toda extensão do texto, em lugar da palavra ¿porta¿, para identi?car o terminal de alta resistência de um transistor MOS / Abstract: A new technique of temperature compensation to implement a voltage reference in CMOS circuits is described, from theoretical basis to experimental evidence made with samples of integrated circuits prototypes that implement it. The proposed technique is based on the fact that the voltage between gate and source, VGS, of a MOS transistor can either increase as diminish with the increase of temperature, depending on the current with that it operates. Based in this, it is possible to pile up n transistors, that are polarized with an adequate current in such way that the voltage on this stack of transistors, that has amplitude nVGS, has, at the same time, the same thermal variation than the VGS voltage produced in only one transistor. In such conditions, the difference between these two voltages is constant, becoming a voltage reference. An alternative implementation to the stack of transistors to produce the nVGS volage consists of a ?oating gate transistor in which equivalent VGS has adjustable amplitude in ?eld. Diverse circuits that are based on this technique had been projected and some of them manufactured in technology CMOS 0,35 µm. The performance of the best manufactured circuit reached 100 ppm/°C of thermal coefficient in the thermal band of -40 to 120 °C. Other con?gurations had been simulated showing that it is possible to reach thermal coe?cients lesser that 10 ppm/°C. The state of the art is represented by voltage references that have thermal coefficients of 1 ppm/°C in the same thermal band where the developed circuits had been characterized. Such voltage references are mainly based on the circuits called bandgap. There is, also, a recent product of the Intersil company who uses a transistor that operates as analogical memory supplying a voltage reference memorized with highest thermal stability. The base principle of this product is, however, different of that being considered in this work despite the use of a ?oating gate transistor. The contribution of this work is not in the performance that the reference sources that are based on the principle had reached. Its contribution inhabits in the form as it can be implemented, only using MOS transistors and in the fact that it has adjustable amplitude in ?eld / Doutorado / Eletrônica, Microeletrônica e Optoeletrônica / Doutor em Engenharia Elétrica

L'imagerie de photoluminescence synchrotron apparaît comme uneméthode particulièrement prometteuse pour l’étude de matériaux hétérogènesmêlant composés minéraux et organiques, comme ceux des sciences des matériaux anciens.Au cours de ce travail de thèse, nous avons développé le dispositif de microscopie de photoluminescence existant de la ligne DISCO du synchrotron SOLEIL afin d’identifier de nouveaux marqueurs de photoluminescence permettant de caractériser des processus physico-chimiques intervenant pendant la fabrication ou l’altération des matériaux anciens. Ces travaux ont conduit au développement d'un système de microscopie multi-spectrale optimisé. Le développement optique d'une illumination homogène, l’optimisation de la détection et la calibration radiométrique du dispositif ont mené à l’obtention d’images de photoluminescence quantitatives.Ce dispositif a été optimisé pour répondre au mieux à des problématiques archéologiques et patrimoniales avec une analyse topologique, chimique et des structures électronique et cristalline. Ces nouveaux développements ont été testés dans le cadre de systèmes d’étude réels composés de semi-conducteurs à grand gap. En étudiant des pigments d’artiste historiques composés d’oxyde de zinc (ZnO), nous montrons que les propriétés de photoluminescence du ZnO permettent de discriminer des pigments homogènes à macro-échelle, par l’hétérogénéité de photoluminescence à micro-échelle. Deux artefacts archéologiques en alliage de cuivre et un résidu en bronze ont été étudiés. L’étude en particulier du Cu2O en microscopie de photoluminescence multi-spectrale a mis en évidence l’apport de l’analyse par photoluminescence pour reconstruire la chaîne opératoire de métallurgie et apporter de nouvelles informations dans la compréhension des processus d’altération.Ces travaux ont démontré le potentiel de cette nouvelle méthodologie etl’intérêt de développer une telle approche au champ d’application desmatériaux anciens, matériaux présentant une forte hétérogénéité sur plusieurséchelles successives. / Synchrotron photoluminescence imaging has emerged as a promisingmethod to study heterogeneous materials,composed of inorganic and organic compounds as those in ancient materials sciences.During this Ph.D., we have further developed the existing photoluminescencemicroscopy set-up of the DISCO beamline at the SOLEIL synchrotron, to identify new photoluminescence markers that allow characterizing physico-chemical processes taking place during the manufacturing or alteration processes of ancient materials. This work led to the development of an optimized multi-spectral microscopy set-up. The optical development of an homogeneous illumination, the optimisation of detection and the radiometric calibration of the set-up led to quantitative photoluminescence images. This set-up has been optimized to respond at best to archaeological and cultural heritage questions with a topological, chemical, electronic and crystalline analysis. Those new instrumental developments were tested on real systems made of wide-bandgap semiconductors. By studying historical artists' pigments composed of zinc oxide (ZnO), we have shown that the photoluminescence properties allow discriminating homogeneous pigments at macro-scale from the heterogeneity oh the photoluminescence response at the grain scale. Two copperbasedarchaeological artefacts and a bronze slag were studied. Particularly, the study of cuprous oxide (Cu2O) pointed out the considerable interest of multi-spectral photoluminescence analysis to retrieve the operational sequence of metallurgy and to provide new information for a better understanding of alteration processes.This work demonstrated the potential of this new methodology and the interest to develop such a method for ancient materials, that are characterized by a strong heterogeneity at successive scales.

Durant cette thèse, des couches minces de fer, de fer-cuivre et de cuivre-zinc déposées par pulvérisation magnétron ont été oxydées par des post-décharges plasma pour synthétiser des nanostructures d’oxydes métalliques. L’oxydation par post-décharge permet un abaissement de la température par rapport à l’oxydation thermique dans la mesure où l’oxygène moléculaire est excité ou dissocié, ce qui fournit des espèces plus réactives comme l’oxygène singulet ou l’oxygène atomique. Cette oxydation à température modérée favorise une croissance anisotrope des cristaux. L’oxydation de couches minces de Fe-Cu a conduit à la croissance de nanolamelles de Fe2O3 et de nanoparois, nanotours et nanofils de CuO. La distribution surfacique de ces nanostructures dépend de la température d’oxydation, de la concentration des espèces réactives et de la composition initiale de la couche mince. L’oxydation de couches minces de Cu-Zn a conduit à la croissance de nanofils ultra-minces de ZnO dans lesquels un confinement quantique peut se produire. Les nanostructures obtenues ont été caractérisées par différentes techniques (microscopies électroniques, diffraction des rayons X et spectrométrie de masse des ions secondaires). Les mécanismes de croissance de ces nanostructures sont basés sur le rôle des contraintes, de la température, de la concentration des espèces réactives ainsi que sur l’influence de la taille des grains sous-jacents. Les nanostructures d’oxydes métalliques obtenues serviront comme photocatalyseurs pour produire de l’hydrogène par photolyse de l’eau. Par ailleurs, les nanofils ultra-minces de ZnO serviront de photocatalyseurs pour la purification de l’eau / In this manuscript, metallic oxide nanostructures were synthesized by the oxidation of iron, iron-copper and copper-zinc thin films by means of a plasma afterglow. Thin films were deposited by magnetron sputtering. The use of plasma afterglows allows a lowering of the temperature compared with the thermal oxidation conditions, given that molecular oxygen is excited or dissociated, which provides more reactive species such as singlet oxygen or atomic oxygen. This oxidation at moderate temperature promotes anisotropic crystal growth. The oxidation of iron–copper thin films leads to the synthesis of Fe2O3 nanoblades and CuO nanowalls, nanotowers and nanowires. The surface distribution of these nanostructures depends on the oxidation temperature, the concentration of the reactive species and the initial composition of the thin layers. The oxidation of copper-zinc thin films leads to the synthesis of ultra-thin ZnO nanowires in which quantum confinement could occur. As-grown nanostructures were characterized by various techniques (electron microscopy, X-ray diffraction and secondary ion mass spectrometry). The growth mechanisms described for these nanostructures relies on the role of stress, temperature, reactive species concentration and on the effect of underlying grain size. As-synthesized nanostructures will serve as photocatalysts to produce hydrogen by water splitting. In addition, ultra-thin ZnO nanowires will also serve as photocatalysts for water purification

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