Miniaturisation of electronic and optoelectronic devices have enabled the realization of system-on-a-chip technology in modern image sensors, where the photo sensor arrays and the corresponding signal processing circuitry are monolithically integrated in a single chip. Apart from intrinsic advantages, the drive towards miniaturisation has been further fuelled by the exotic properties exhibited by semiconductor materials at the nano scale. As the dimension of the material is gradually reduced from the bulk, interesting physical and chemical properties begin to emerge owing to the increased confinement of charge carriers in different spatial dimensions. Solution-processed optoelectronics have revolutionised the field of device physics over recent years due to the superior performance, ease of processing, substrate flexibility, cost-effective production of large-area devices and other advantages associated with the technique. In the present work, solution-processed photo detectors have been fabricated on SiO2/Si substrate facilitating the ease of integration with conventional silicon CMOS technology. The present thesis deals with the successful exploitation of most common point defects in semiconductor nanostructures to reduce the overlap of hole wave function with the envelop wave function of the ground state electron to improve photoconduction. As a result of the investigation process, successful strategies have been devised for the improvement of photoconduction by engineering the defect states. In the first study, the intrinsic copper vacancies and the capping agent thiol have been employed to trap photo holes in photo detectors based on copper indium selenide nanoparticles, thereby allowing the photoelectrons to transit the device. In the second study, the optical excitation of charge carriers into the defect-related band originating from oxygen vacancies further raises the photoconductivity of molybdenum trioxide nanobelts based photodetectors. In the third study, the absence of photoconductivity in zinc selenide based quantum dots has been attributed to the radiative recombination of photogenerated carriers at the donor-acceptor states caused by the self-compensation of point defects in the dots. In the final study, the crucial role of the energy depth of trap states in determining the carrier relaxation dynamics (temporal response) of the photodetector based on SnO2 nanowires has been discussed in detail. .

Orientador: Leinig Antonio Perazolli / Resumo: Neste trabalho foi estudado cerâmicas densas a base de SnO2, utilizando técnicas de Difração de Raios X (DRX), Microscopia Eletrônica de Varredura (MEV) e Transmissão (MET), área de superfície pelo método B.E.T., Análise Térmica, Dilatometria e Caracterização Elétrica, com o objetivo de entender seu comportamento elétrico, para possível utilização como varistor. O primeiro passo foi estudar algumas características do SnO2 dopado com diferentes concentrações de ZnO, tais como densidade, tamanho de grão, limite de solução sólida, formação de precipitados e a concentração ideal de ZnO a ser adicionado ao SnO2 para produção de cerâmicas densas. Em seguida passou-se a estudar o sistema SnO2- ZnO-WO3, obtendo para o novo sistema os mesmos parâmetros estudados no sistema SnO2- ZnO, e também as posições dos dopantes na rede cristalina do SnO2 e as características elétricas do sistema SnO2-ZnO-WO3 para utilização como varistor. E por último pesquisou-se, dando-se ênfase aos estudos de caracterização elétrica, o sistema SnO2-ZnO-WO3 acrescido de novos dopantes, a fim de se obter um varistor de baixa tensão. Obteve-se varistores de média e alta tensão de boa qualidade, com α>50, Er≅1.300 a 19.000V/cm e If=0,08mA/cm2 e varistores de baixa tensão com pequeno comportamento varistor, apresentando α=4,6, Er≅400V/cm e If≅0,4mA/cm2. / Abstract: In this work it was studied dense ceramic of the SnO2 based, using techniques of XRay Diffraction (XRD), Scanning Electronic Microscopy (SEM) and Transmission (TEM), surface area for the B.E.T. method, Thermal Analysis, Dilatometry and Electric Characterization, with the objective of understanding your electric behavior, for possible use as varistor. The first step was to study some characteristics of SnO2 doped with different concentrations of ZnO, such as density, grain size, limit of solid solution, precipitate formation and the ideal concentration of ZnO to be added at the SnO2 to product dense ceramics. Soon after that we started the study the system SnO2-ZnO-WO3 obtaining for the new system the same parameters studied in the system SnO2-ZnO, and also the positions of the dopings in the crystalline net of SnO2 and the electric characteristics of the system SnO2- ZnO-WO3 for use as varistor. And the last thing it has researched, giving emphasis to the studies of electric characterization, the system SnO2-ZnO-WO3 added of new dopings, trying to obtain a low tension varistor. We obtained medium and high tension varistors of good quality, with α>50, Er≅1,300 to 19,000V/cm and If=0.08mA/cm2 and low tension varistors of bad quality, presenting α=4.6, Er≅400V/cm and If ≅0.4mA/cm2. / Mestre

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Chemical bath deposition (CBD) is the analog in liquid phase of the well-known chemical vapor deposition technique in the vapor phase. In CBD, deposition of thin films takes place from aqueous solutions at low temperatures by a chemical reaction between dissolved precursors, with the help of a complexing agent. Among all techniques used to grow Group II-VI semiconductors, CBD has the advantage of being a simple, low temperature, and inexpensive large-area deposition technique. So far, its contribution in thin film solar cells industry has been mainly limited to growing n-type CdS and/or ZnS window layers for CdTe-based and CIGS-based solar cells. In this work we first optimize the CBD process of CdS using nitrilotriacetic acid and hydrazine as complexing agents as an alternative to ammonia. We then study the effect of the cadmium precursor on the optical/electrical properties, as well as crystal structure, morphology, and composition of CBD-CdS films. A better understanding of the CBD process of CdS as a whole has been achieved and high quality CBD-CdS films have been obtained. Next, we investigate in-situ doping of CBD-CdS with group III elements, such as B, Al, In, and Ga. The objective is to show that CBD is capable of not only growing CdS but also of doping it to reduce its resistivity and, as a result, facilitate its use in solar cells as well as other optoelectronic device fabrication. A four orders of magnitude drop of film resistivity has been achieved without a significant change in film bandgap, structure, or morphology. Finally, we test the possibility of using CBD to grow transparent conducting oxide (TCO) films, such as Al-doped ZnO films and cadmium stannate films. First, we study CBD of ZnO and later in-situ doping of ZnO using Al. High quality ZnO thin films have been grown using CBD with the help of four different complexing agents. Post heat treatment in argon ambient helped reduce resistivity of CBD-ZnO undoped films to ~ 10-1 Ω-cm. In-situ doping of such films using Al shows promising results. Such films could be an alternative to indium tin oxide (ITO) layers that are commonly used as TCO layers for solar cells. Another approach is to use CBD to grow CdO and SnO2 thin films, with the goal of obtaining Cd2SnO4 by later annealing of these two layers. Cadmium stannate is another TCO candidate that could replace ITO in the near future. We have succeeded in growing CBD-CdO thin films using three different complexing agents. Undoped CBD-CdO films with a resistivity as low as 1.01 x10-2 Ω-cm and a carrier density as high as 2.59 x 1020 cm-3 have been obtained. SnO2 films have been successfully grown using CBD. Fabrication of Cadmium stannate thin films using CBD is investigated. In summary, our objective to expand the use of CBD beyond just growing CdS and ZnS, and to test the possibility of using it for in-situ doping of group II-VI semiconductors as well as TCO layers fabrication proved to be successful. We believe that this may have a significant impact on solar cells as well as other optoelectronic devices fabrication industry, due to the simplicity and the cost-effectiveness of CBD.

Devido à elevada razão superfície/volume dos nanomateriais, estes apresentam propriedades únicas que são consequência das propriedades de suas superfícies. Para estabilizar as nanopartículas, as quais tendem ao crescimento para reduzir o excesso de energia, uma estratégia é a introdução de aditivos que segreguem na superfície e reduzam a energia de superfície. Neste trabalho, o sistema de importância tecnológica SnO2-TiO2 foi estudado. Nanopartículas de Sn1-xTixO2 (0,00 x 1,00) foram sintetizadas pelo método dos precursores poliméricos. Difratogramas de raios X mostram que uma solução sólida com estrutura do tipo rutilo é obtida para x 0,90. A evolução dos parâmetros de rede, os espectros obtidos por perda de energia de elétrons (EELS) e os espectros no infravermelho coletados no modo de refletância difusa (DRIFT) sugerem a segregação do Ti4+ na superfície, que justifica a elevada solubilidade do Ti4+ no SnO2. Os espectros Raman são coerentes com a segregação, mostrando que, mesmo sem a formação de segunda fase, ocorrem regiões ricas em Ti. A segregação está relacionada também à redução do tamanho de cristalito e ao aumento da área de superfície específica devido à redução da energia de superfície (de 1,40 Jm-2 em x = 0,00 até 1,08 Jm-2 em x = 0,50) determinada por calorimetria de adsorção de água e coerente com os dados da calorimetria de dissolução. Para x 0,90, ocorre a formação da fase anatásio além do rutilo e os fenômenos de estabilização dos polimorfos podem ser explicados pela modificação da energia de superfície. Com base na caracterização feita, as atividades fotocatalíticas das nanopartículas foram avaliadas e foi verificado um aumento da eficiência devido à superior área de superfície das amostras aditivadas em relação às amostras puras. / Due to the high surface/volume ratio, nanomaterials have unique properties as a consequence of their surface properties. In order to stabilize the nanoparticles, which tend to grow to reduce their excess energy, one can introduce additives that are prone to segregate at the surfaces and reduce the surface energy. In this work, the technologically relevant SnO2-TiO2 system was studied. Sn1-xTixO2 (0.00 x 1.00) nanoparticles were synthesized by polymeric precursors method. X-ray diffraction patterns show that a rutile-structured solid solution is formed for x 0.90. Lattice parameters evolution, electron energy loss spectra (EELS) and diffuse reflectance infrared spectra (DRIFT) suggest a Ti4+ surface segregation, which explains the high Ti4+ solubility in SnO2. Raman spectra are in accord with the segregation, showing Ti-rich sites in the absence of a second crystalline phase. The segregation is also related to a decrease in the crystallite size and an increase in the surface area due to a decrease in the surface energy (from 1.40 Jm-2 for x = 0.00 to 1.08 Jm-2 for x = 0.50) determined by water adsorption calorimetry and consistent with drop solution calorimetry data. For x 0.90, the formation of anatase occurs in addition to rutile, and the polymorphic stability can be explained according to the surface energy modification. Based on these results, photocatalytic activity of the samples were evaluated, and an increase in the efficiency due to a higher surface area was observed for the samples containing additive compared to pure samples.

L'avènement de sources lumineuses performantes et compactes à base de silice dopée par des ions de terres rares (TR) passe par l'obtention de rendements d'émission élevés, ce qui nécessite une bonne dispersion de ces ions. Les vitrocéramiques, associant une matrice vitreuse avec des nanocristaux (NC), permettent une telle dispersion et fournissent néanmoins une transparence optique adéquate. D'autre part, les NC présentent une absorption de lumière spectralement large et peuvent transférer leur énergie vers les ions de TR pour améliorer l'efficacité d'émission. Dans ce travail, des vitrocéramiques à base de silice contenant des NC de SnO₂ ont été élaborées sous forme de couches minces et de massifs par la technique sol-gel. Les propriétés optiques et structurales des systèmes sous forme de couches minces ont été comparées à celles des systèmes massifs. Plusieurs paramètres, tels que la concentration maximale d'étain, les températures de cristallisation et de densification, diffèrent selon la morphologie des matériaux. L'influence réciproque entre la matrice de silice et les NC de SnO₂ a été étudiée par l'utilisation conjointe de plusieurs techniques d'analyses telles que les spectroscopies vibrationnelles, la DRX, la MET, la porosimétrie BET... L'ajout d'étain retarde la densification de la matrice, laissant une porosité résiduelle. La luminescence des ions Er³⁺ et Eu³⁺ (largeur de bande d'émission, durée de vie) a montré clairement l'existence de 2 types de sites hôtes, l'un cristallin et l'autre amorphe. Enfin, les NC de SnO₂ favorisent la dispersion des ions de TR, conduisant à des durées de vies encourageantes et à un transfert d'énergie entre cristal et TR.

<p>Many materials exhibit interesting and novel properties when prepared as thin films. Thin film metal oxides have had an impact on the technological progress of the microelectronics mainly due to their electrical and optical properties. Since the future goes towards the nanometre scale there is an increasing demand for thin film deposition processes that can produce high quality metal oxide films in this scale with high accuracy.</p><p>This thesis describes atomic layer deposition of Ta₂O₅, HfO₂ and SnO₂ thin films and chemical vapour deposition of SnO₂ thin films. The films have been deposited by employing metal iodides and oxygen as precursors. All these processes have been characterised with regards to important processing parameters. The films themselves have been characterised by standard thin film analysing techniques such as x-ray diffraction, scanning electron microscopy, atomic force microscopy and transmission electron microscopy. The chemical and physical properties have been coupled to critical deposition parameters. Furthermore, additional data in the form of electrical and gas sensing properties important to future applications in the field of microelectronics have been examined.</p><p>The results from the investigated processes have shown the power of the metal iodide based atomic layer deposition (ALD) and chemical vapour deposition (CVD) processes in producing high quality metal oxide thin films. Generally no precursor contaminations have been observed. In contrast to metal chloride based processes the metal iodide processes produces films with a higher degree of crystalline quality when it comes to phase purity, roughness and epitaxy. The use of oxygen as oxidising precursor allowed depositions at higher temperatures than normally employed in water based ALD processes and hence a higher growth rate for epitaxial growth was possible.</p>

<p>In this research project, nanostructured composites based on Tin dioxide (SnO2) and Titanium dioxide (TiO2) with poly-4-styrene sulfonic acid (PSSA) doped polyaniline (PANI) conducting polymer has been investigated based on their structural, electrical and electrochemical properties. The synthesis of conducting polymers and their metal oxide or composites have been carried out chemically or electrochemically according to methods modified from the literature. Layer-by-layer construction of nano-Metal Oxide/PSSA doped polyaniline composites were successfully constructed by electroanalytical methods on the surface of a glassy carbon working electrode (GCE).</p>

Many materials exhibit interesting and novel properties when prepared as thin films. Thin film metal oxides have had an impact on the technological progress of the microelectronics mainly due to their electrical and optical properties. Since the future goes towards the nanometre scale there is an increasing demand for thin film deposition processes that can produce high quality metal oxide films in this scale with high accuracy. This thesis describes atomic layer deposition of Ta2O5, HfO2 and SnO2 thin films and chemical vapour deposition of SnO2 thin films. The films have been deposited by employing metal iodides and oxygen as precursors. All these processes have been characterised with regards to important processing parameters. The films themselves have been characterised by standard thin film analysing techniques such as x-ray diffraction, scanning electron microscopy, atomic force microscopy and transmission electron microscopy. The chemical and physical properties have been coupled to critical deposition parameters. Furthermore, additional data in the form of electrical and gas sensing properties important to future applications in the field of microelectronics have been examined. The results from the investigated processes have shown the power of the metal iodide based atomic layer deposition (ALD) and chemical vapour deposition (CVD) processes in producing high quality metal oxide thin films. Generally no precursor contaminations have been observed. In contrast to metal chloride based processes the metal iodide processes produces films with a higher degree of crystalline quality when it comes to phase purity, roughness and epitaxy. The use of oxygen as oxidising precursor allowed depositions at higher temperatures than normally employed in water based ALD processes and hence a higher growth rate for epitaxial growth was possible.

ABSTRACT SYNTHESIS AND CHARACTERIZATION OF ETHANOL ELECTRO-OXIDATION CATALYSIS Demir-Kivrak, Hilal Ph.D., Department of Chemical Engineering Supervisor : Prof. Dr. Deniz &Uuml / ner Co-supervisor : Dr. Sadig Kuliyev October 2010, 196 pages In this study, the role of defects, the role of Sn in relation to defects, and the role of oxide phase of tin in ethanol electro-oxidation reaction were investigated. Firstly, adsorption calorimetry measurements were conducted on monometallic (1%Pt, 2%Pt, and 5%Pt) and bi-metallic (5% Pt-Sn) &gamma / -Al2O3 supported Pt catalysts. It was observed that while saturation coverage values decreased, intermediate heats remained same for Pt-Sn catalysts by the increasing amount of tin. The effect of particle size was investigated on Pt/C (pH=5), Pt/C (pH=11) catalysts at different scan rates. At high scan rates (quite above diffusion limitations), current per site activities were nearly the same for 20% Pt/C (E-Tek), Pt/C (pH=11), and Pt/C (pH=5) catalysts, which explained as electro-oxidation reaction takes place at the defects sites. Furthermore, the effect of support on ethanol electro-oxidation was investigated on CNT supported Pt catalyst. Results indicate that only the metal v dispersions improved ethanol electro-oxidation reaction and support did not have any effect on ethanol electro-oxidation reaction. Results on the 20% Pt-Sn/C (15:1 to 1:1 Pt: Sn atomic ratios) and 20% Pt-SnO2/C (6:1 and 1:1) catalysts indicated that ethanol electro-oxidation activity increased by increasing tin amount. For 20% Pt-Sn/C catalysts, Pt-Sn (6:1)/C indicated best activity. On the other hand, 20% Pt-SnO2 (6:1)/C catalyst was better than Pt-Sn (6:1)/C in terms of ethanol electro-oxidation activity due to the fact that there was low contact between Pt and tin oxide particles.