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Estudo de dispositivos eletrônicos baseados em filmes de diamante dopados com boro
(Universidade Federal de São Carlos, 2018-01-29) Araujo, Luana Santos; Chiquito, Adenilson José; https://lattes.cnpq.br/7087360072774314; https://lattes.cnpq.br/8776491740006506
In this work, the main objective was the study of boron doped diamond films aiming the use of them as semiconductor material for electronic devices. Schottky diodes and a field effect transistor were the devices built with these films. We have determined the main transport properties (resistivity and carrier density) that revealed the semiconductor behavior of doped boron synthetic diamond films (p-type). We also have studied the influence of cleaning processes on the surface quality of diamond for the production of good metal-diamond electrical contacts. We have observed the increase in resistivity as well as a reduction of the surface conductivity that is associated to the removal of hydrogen terminated diamond layers in the ionic cleaning process. The changes promoted by cleaning were studied current-voltage and capacitance-voltage measurements. The analysis of the temperature dependent resistivity indicated the hopping mechanism as the dominant conduction process over a wide temperature range. In addition, we investigated the presence of deep energy levels of impurities or defects in the diamond lattice using capacitance spectroscopy. Finally, after well established the contacts properties on the diamond surface we fabricated and analyzed the characteristics of a prototype field effect transistors based on boron doped diamond with oxygen termination.
Potencial de uso de fibras de Schizolobium parahyba (Vell.) Blake na preparação de compósitos de polipropileno
(Universidade Federal de São Carlos, 2018-01-29) Silva, Juliette Pereira da; Lucas, Alessandra de Almeida; https://lattes.cnpq.br/9754332336954137; Pádua, Franciane Andrade de; https://lattes.cnpq.br/2945447364979913; https://lattes.cnpq.br/9803905934952536
The use of plant fibers as reinforcement of thermoplastic polymers in recent years has aroused great worldwide interest, since natural fibers offer economic, processing and environmental advantages. In this context, the objective of this study was to evaluate the properties of wood and fibers of Schizolobium parahyba (Vell.) Blake at early age, from experimental planting, as reinforcement of polypropylene (PP) matrix composites. The basic density, cellulose content, hemicelluloses, lignin, extractives and ashes, as well as the fiber size and microfibril angulation of the wood of four guapuruvu trees (A1, A2, A3 and A4) were determined. Then, the mechanical behavior of reinforced polypropylene matrix composites with different fiber contents was evaluated in order to establish their relation between the characteristics of the wood and the fibers. The contents of guapuruvu fibers used were 0; 20 and 30% by mass and the compatibilizing agent was 2%. The composites were prepared in a co-rotational double-threaded extruder. The extrudate compositions were granulated and then injection molded. The basic density of guapuruvu ranged from 0.237 g.cm-³ to 0.243 g.cm-³, with a clear tendency to reduce wood density with tree height. Regarding the anatomical characteristics, there were no variations in the results of fiber length, fiber width and lume diameter among the different trees studied. The wall thickness of the fibers was higher in samples A1 and A2 and the angle of microfibrils was higher in A3 and lower in A2. In addition, there was no statistical difference in the results of aspect ratio among the trees. Regarding the chemical composition, there were no variations in the results for lignin, cellulose, hemicelluloses and extractives among the studied trees. As for ash, the highest concentration was found in A1 and the lowest in A2 and A3. The results showed that the tensile strength increased with the percentage increase of fibers for all samples, except for sample A1, where tensile strength values were similar in the compositions of 20% and 30%. Similarly, the modulus of elasticity also increased with the addition of fibers in all samples, and this effect was more pronounced for the 30% percentage of guapuruvu fiber. Already the elongation at the break decreased in comparison to the pure PP and with the percentage increase of fibers. The Izod impact strength values of the composites did not change significantly in relation to the pure polymer By the results obtained it can be deduced that the guapuruvu fibers from native species, rapid growth, easy adaptation, which has a low density wood can be used as filler in PP composites, exerting a reinforcing action. Having the composite prepared with 30% by weight guapuruvu fibers and 2% Polybond 3200 presented better properties.