The spectra of tin have been photographed in the region between 350Å and 9000Å using as sources an electrodeless discharge and a condensed spark in helium. Exposure were taken by using a 3 meter normal incidence vacuum grating spectrograph and a Hilger E-478 large interchangeable quartz and glass prism spectrograph. Among thirty four hundred and four lines which were measured, two hundred and thirty five lines were classified in the spectra Sn I and Sn II on the basis of square arrays constructed by using the energy levels from Mrs. Sitterly's "Atomic Energy Levels", Volume III (1957). Five hundred and eleven lines are herein classified in the spectra Sn III, Sn IV and Sn V. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

A systematic study of the Knight shift parameters has been carried out on single crystal specimens of tin and cadmium over a range from 1⁰ K to just below the melting points. The line widths observed in cadmium are approximately half the widths quoted by other workers, enabling more precise measurements to be made. These measurements show that the anisotropy of the Knight shift in cadmium changes sign between 4⁰ K and 77⁰ K. Pronounced changes in the Knight shift parameters are observed upon alloying cadmium with mercury. The temperature dependence of the isotropic Knight shift in tin can be explained by the volume effects and the phonon contributions when the temperature exceeds the Debye temperature. Comparing the temperature dependence data with pressure dependence results of other workers the explicit temperature dependence is extracted. It appears that the variation in the anisotropy of the Knight shift above the Debye temperature is largely caused by a change in lattice parameters, specifically a change in c/a ratio. Measurements of the line width at helium temperature in isotopically pure Sn¹¹⁹ and the same isotope in natural tin as a function of crystal orientation are reported. Second moments for the different crystal orientations have been computed. Analysis of the isotopically pure tin data leads to an evaluation of relative contributions, from the various shells, to the pseudo-dipolar interaction. For the isotopically pure tin, the measurements at the helium and room temperatures enable an evaluation of the spin-lattice relaxation time, T₁. T₁T is constant over the temperature range and closely isotropic. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

No description available.

In developing photovoltaic technology for commercial use, it is essential to prioritize low cost, high efficiency, and long-term stability, along with low toxicity and quick energy payback time. Organic-inorganic metal halide perovskites are among the most promising photovoltaic materials due to their exceptional efficiency and cost-effectiveness. However, their practical significance remains unclear due to their notoriously short device operation duration. Mixed-metal tin-lead perovskites are a class of perovskites that have captured researchers' attention due to their unique optoelectronic features, including a small bandgap, making them useful for various applications (tandems, NIR light detection, and imaging e.g.). Still, the low ambient stability of tin-lead perovskites obstructs their commercialization, necessitating extensive research into their underlying breakdown mechanisms. This study aims to better understand these mechanisms and the involvement of halide chemistry, specifically emphasizing the significant role of iodine in perovskite deterioration. Our findings reveal that tin-lead-based perovskites experience cyclic degradation, with iodine and SnI4 as key degradation products that harm the stability of the perovskite. Investigating the impact of iodine is critical because it is a common component of the perovskite material, and its presence has been shown to play a crucial role in the optoelectronic properties of the perovskite. However, the presence of iodine can also lead to the degradation of the perovskite material over time, reducing the efficiency and lifespan of the perovskite solar cells. Therefore, understanding the role of iodine in perovskite deterioration is essential to improve the stability and durability of tin-lead perovskites and bring them closer to commercialization. By gaining insight into the degradation mechanisms of tin-lead perovskites, we can develop effective strategies to mitigate their degradation, enhance their stability and lifespan, and unlock their full potential for use in various photovoltaic applications, contributing to a more sustainable and environmentally conscious future.

No description available.

A nanociência emergiu nos últimos anos como uma das áreas mais importantes para os futuros desenvolvimentos tecnológicos, especialmente na área de dispositivos eletrônicos. A nanotecnologia tem um caráter primordialmente interdisciplinar, que engloba conhecimentos de física, química, engenharias e biologia. Essa tecnologia está sendo usada da fabricação de microprocessadores, bombas dosadoras de fármacos e revestimentos em materiais, entre outras aplicações. Revestimentos nanocristalinos vêm sendo obtidos por meio da técnica MOCVD (deposição química de organometálicos em fase vapor), e tem proporcionado a obtenção de filmes de melhor qualidade que os obtidos por CVD convencional ou por métodos físicos. Além disso, a técnica MOCVD apresenta-se como uma alternativa competitiva porque é relativamente barata e mais fácil de ser implantada, em relação aos métodos de deposição física. Neste trabalho foram obtidos revestimentos compostos por multicamadas de TiO2/TiN. Durante o experimento, a abertura e o fechamento das válvulas de admissão dos gases exige do operador habilidade manual para acionar a válvula e controlar o tempo de deposição, o que gera possibilidade de erros, implicando diretamente na espessura de cada camada. Assim, a necessidade de diminuir a influência do operador e poder utilizar intervalos de tempo menores que um minuto para os crescimentos, gerou a oportunidade de criar um programa de computador para gerenciar todo o sistema. Tal programa foi desenvolvido utilizando-se o conceito de Máquina de Estados para o controle de processo e simulação Hardware in the loop. / Nanoscience has emerged in recent years as one of the most important areas for future technological developments, especially in the area of electronic devices. Nanotechnology has an interdisciplinary character wich includes knowledge from physics, chemistry, engineering, and biology. This technology is being used in the manufacture of microprocessors, pumps for dose of medicine, and coating materials, among others. The MOCVD technique has been used recently to obtain nanocristalline coatings, and provide films of better quality than those obtained by conventional CVD or physical methods. Furthermore, the MOCVD technique presents itself as a competitive alternative because it is relatively inexpensive and easy to deploy compared to physical deposition methods. In this work multilayer coatings of TiO2/TiN were produced. During the experiment, the opening and closing of the valves of gases admission, requires from the operator manual ability to trigger the valve and controlling the deposition time, which creates the possibility of errors, leading directly into the thickness of each layer. Thus, the need of reducing the influence of the operator, and the possibility of using time intervals of less than a minute in the growths, created the opportunity to develop a computer program to manage the whole system. The software was developed using the State machine concept for the process control and Hardware in the loop simulation.

A nanociência emergiu nos últimos anos como uma das áreas mais importantes para os futuros desenvolvimentos tecnológicos, especialmente na área de dispositivos eletrônicos. A nanotecnologia tem um caráter primordialmente interdisciplinar, que engloba conhecimentos de física, química, engenharias e biologia. Essa tecnologia está sendo usada da fabricação de microprocessadores, bombas dosadoras de fármacos e revestimentos em materiais, entre outras aplicações. Revestimentos nanocristalinos vêm sendo obtidos por meio da técnica MOCVD (deposição química de organometálicos em fase vapor), e tem proporcionado a obtenção de filmes de melhor qualidade que os obtidos por CVD convencional ou por métodos físicos. Além disso, a técnica MOCVD apresenta-se como uma alternativa competitiva porque é relativamente barata e mais fácil de ser implantada, em relação aos métodos de deposição física. Neste trabalho foram obtidos revestimentos compostos por multicamadas de TiO2/TiN. Durante o experimento, a abertura e o fechamento das válvulas de admissão dos gases exige do operador habilidade manual para acionar a válvula e controlar o tempo de deposição, o que gera possibilidade de erros, implicando diretamente na espessura de cada camada. Assim, a necessidade de diminuir a influência do operador e poder utilizar intervalos de tempo menores que um minuto para os crescimentos, gerou a oportunidade de criar um programa de computador para gerenciar todo o sistema. Tal programa foi desenvolvido utilizando-se o conceito de Máquina de Estados para o controle de processo e simulação Hardware in the loop. / Nanoscience has emerged in recent years as one of the most important areas for future technological developments, especially in the area of electronic devices. Nanotechnology has an interdisciplinary character wich includes knowledge from physics, chemistry, engineering, and biology. This technology is being used in the manufacture of microprocessors, pumps for dose of medicine, and coating materials, among others. The MOCVD technique has been used recently to obtain nanocristalline coatings, and provide films of better quality than those obtained by conventional CVD or physical methods. Furthermore, the MOCVD technique presents itself as a competitive alternative because it is relatively inexpensive and easy to deploy compared to physical deposition methods. In this work multilayer coatings of TiO2/TiN were produced. During the experiment, the opening and closing of the valves of gases admission, requires from the operator manual ability to trigger the valve and controlling the deposition time, which creates the possibility of errors, leading directly into the thickness of each layer. Thus, the need of reducing the influence of the operator, and the possibility of using time intervals of less than a minute in the growths, created the opportunity to develop a computer program to manage the whole system. The software was developed using the State machine concept for the process control and Hardware in the loop simulation.

There are very few studies that have investigated directly the effect of an oxide film on tin whisker growth, since the cracked oxide theory was proposed by Tu in 1994. The current work has investigated the effect of using an electrochemically formed oxide and both a molybdate conversion coating and a tungstate conversion coating on tin whisker growth from Sn-Cu electrodeposits on Cu, and compared it with that from a native air-formed oxide. X-ray photoelectron spectroscopy (XPS) has been used to investigate the effect of coating parameters on the thickness and composition of the oxide film. The XPS studies show that the oxide film formed using either of the conversion coating baths was significantly thicker than that produced from the potassium bicarbonate-potassium carbonate bath. Initial observations suggest that both the tungstate-based conversion coatings and the molybdate-based conversion coatings significantly reduced whisker growth by over 80 %, compared with a native air-formed oxide, and provide improved whisker mitigation compared with the electrochemically formed oxides. The current work has also investigated the potential of using a dual-layer system, comprised of both an electrochemically formed oxide bottom layer and an acrylic conformal coating top layer, for the mitigation of tin whisker growth. The electrochemically formed oxide used in the dual-layer system was produced at 2 V vs. Ag/AgCl while passing a charge of 60 mC cm-2 and the thickness of the conformal coating was aimed to be between ~5 μm to ~6 μm. This thickness was chosen to enable the study of whisker growth on a shorter time scale and to study the effect the electrochemically formed oxide had when used in conjunction. Initial observations showed that the dual-layer system provided improved whisker mitigation compared with both the electrochemically formed oxides and acrylic conformal coatings when used singularly. As part of the self-healing work, nanocapsules filled with the reactive agent were needed to be synthesised and the compatibility of them with different solvents needed to be studied. Capsules filled with the reactive agent were successfully synthesised, however, it was found that the capsules agglomerated and the size of the capsules, in some instances, were too large to be incorporated into a thin conformal coating. Regardless, the capsules were still analysed to check the compatibility with different solvents, to identify a suitable conformal coating mixture that would not dissolve the polymer shell of the capsules. It was observed that the capsules were stable in three out of the five solvents that were analysed, them being isopropanol (IPA), butanone and methylcyclohexane.

Thesis (M.Sc. (Physics)) -- University of Limpopo, 2015 / Nanocrystalline materials of defect free anatase and rutile SnO2 together with Ti and Y in anatase SnO2 have been modelled successfully using classical molecular dynamics simulations together with Buckingham potential. The structural properties of these SnO2 phases were analysed using radial distribution functions (RDFs). The effect of increasing temperature in pure SnO2 and doped SnO2 were studied. In both pure and doped materials, RDFs suggest phase transition at higher temperature, where anatase SnO2 transforms to rutile SnO2. Rutile SnO2 was found to be more stable than anatase SnO2. The results showed that the dopants have different effects on the SnO2 material. Ti defect is found to lower the transformation temperature of anatase to rutile SnO2. Y defect is found not to have any effect on the anatase to rutile SnO2 transformation. Thermodynamic properties such as volume thermal expansion coefficient and specific heat capacity were also calculated from above Debye temperature. Volume thermal expansion coefficient was obtained from volume versus temperature curves. Volume thermal expansion coefficient for rutile and Ti-anatase SnO2 were found to be not of the same order with the calculated results. Specific heat capacity calculated from energy versus temperature curves was found to be in agreement with the Dulong and Petit law of solids. Nanocrystalline Al/Y co-doped SnO2 powders were successfully synthesized using the sol-gel method. The samples were subjected to different temperatures 100 (as prepared) 200, 400, 600, 800 and 1000 oC. The effects of co-doping and temperature on the structural and optical properties of Al/Y co-doped SnO2 nanoparticles as well as morphology were investigated. The characterization techniques used were X-ray powder diffraction (XRD), Raman spectroscopy, Scanning electron microscopy (SEM) and UV-visible spectroscopy (UV-vis). The average particle sizes were found to be in the range between 2.5–8 nm and the strains were calculated to be 2.76–0.53 with increasing temperature for as prepared and the sample sintered at different tempe-ratures. The Raman bands were found to correspond with the literature. At a higher temperature of about 800 oC the materials were found to contain the second phase which is yttrium stannate. However no information about aluminium was found. The optical band gap were found to be between 3.3–3.99 eV in the temperature range 200–1000 oC.

Thesis (M. Sc.)--University of Hong Kong, 1992.