ZnO nanostructures were synthesized by a proteic sol-gel method, using zinc nitrate hexahydrate and gelatin as precursors. Size and shape evolution of ZnO nanostructures were achieved by annealing temperature in the range 250-1000 ºC. The crystalline structure, morphology and optical properties of the ZnO nanoparticles were characterized by X-Ray Diffraction (XRD), Raman Spectroscopy (RS), Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), and room temperature Photoluminescence (PL). The result of structural characterization shows the formation of platelets and nanorods in the micro-scale and ZnO nanostructures with high quality hexagonal wurtzite crystal. Sharp peaks in RS after annealing temperature, related to wurtzite structure, were observed corroborating with XRD and TEM measurements. Room temperature PL spectra showed two contribution bands which peaked at ~380 nm, originating from the recombination of free excitons, and ~520 nm corresponding to the impurities and structural defects, like oxygen vacancies and zinc interstitial. The effects of annealing temperature in the structural and optical properties are detailed and the results compared among the experimental techniques. The high quality of the samples obtained by an alternative organic precursor method opens a low-cost route to technological applications of zinc oxide.
Utilizamos vídeos disponíveis na web que mostram testes de colisões de automóveis para investigar as propriedades do impulso de uma força. Este tema, pouco abordado em sala de aula, possui, em colisões de automóveis, uma possibilidade de aplicação em problemas reais e importantes para a compreensão de fenômenos presentes em nosso cotidiano. Segundo os PCN+, o dispositivo de airbag seria um excelente exemplo para ilustrar as propriedades do impulso. Para a investigação deste problema através de vídeos, utilizamos o software livre Tracker, onde determinamos propriedades físicas, tais como de posição, velocidade e aceleração, relacionadas ao movimento dos carros e manequins utilizados nos testes.
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