Temperature dependence of the first order Raman scattering in thin films of mc-Si:H

The temperature effect on microcrystalline silicon (mc-Si:H) films produced by R.F. magnetron sputtering has been studied by Raman spectroscopy. The thermal behaviour of mc-Si:H films and crystalline silicon is compared and interpreted on the basis of anharmonic effects. We have studied the first order Raman spectra of our films for several Ar+ laser powers. Our results show a blue shift and a broadening of the Raman spectra with increasing the laser power. This effect is not due to structural changes since it is reproducible. The sample temperature has been calculated according to the well known relation between Stokes and anti-Stokes components. Our results show that the temperature effect is stronger in mc-Si:H than in crystalline silicon. This difference can be attributed to the size of the microcrystals, which are imbedded in a amorphous matrix surrounded by a third phase called grain boundary

Bio-based nanofilms/coatings for food applications

Edible packaging for food is one of the areas where developments are being made based on nanotechnological solutions, e.g. through the development of edible nanofilms and nanocoatings, in particular under the form of edible nanolaminates. Polysaccharides, proteins and/or lipids are used due their GRAS statute. Polysaccharide- and protein-based films/coatings provide good barriers to O2 and CO2, but are very permeable to water vapor; in turn, lipid-based films/coatings provide excellent barriers to water vapor but have a limited resistance to other gases and have low mechanical resistance. The use of successive nano-layers will provide better physical stability in aggressive environments, better chemical stability to active compounds which may be incorporated into these structures; and improved control of the release rates of such compounds. The application of this technology can be used for the enhancement of food safety, for the encapsulation of functional food ingredients, and in systems providing the integration of sensing, localization, reporting and remote control of food products. At the current state of knowledge, many of these applications may be difficult to adopt commercially due the difficult to be implement at an industrial scale. Moreover, the effects of nanotechnological systems in the human body are still unclear. This means that using nanotechnological applications in foods must be justified essentially by their advantages, which must be clearly perceived by the consumer. Not doing so will undermine consumers’ trust on this emerging technology, eventually hindering its success in future applications

Photoluminescence of erbium doped microcrystalline silicon thin films produced by reactive magnetron sputtering

Microcrystalline silicon thin films doped with erbium were produced by RF sputtering and their structural, chemical and optical properties were studied by X-ray diffractometry at grazing incidence, Rutherford back scattering and optical transmission spectroscopy. The samples exhibit a sharp photoluminescence (PL) spectrum from the Er centres with the strongest peak positioned at 1.536 microm with a full width at half maximum of about 8 nm. When the temperature varies between 5K and 300K the photoluminescence decreases only five fold, in contrast to the behaviour reported for monocrystalline silicon

Pesquisa-ação: fundamentos do planejamento e do diagnóstico em comunidades rurais.

O presente trabalho nasceu da necessidade de divulgar um aspecto operacional da metodologia da pesquisa-ação chamada de diagnóstico. O estudo tem sido realizado por uma equipe de pesquisadores, extensionistas e agricultores nos Estados da Bahia, Pernambuco e Paraíba através da Embrapa Mandioca e Fruticultura, EMATER-PB, EBDA, EMATER-PE. No Brasil, as comunidades, municípios e regiões apresentam-se de forma diferenciada, com menor ou maior complexidade. Logo, para se intervir em determinada área para promover um processo de mudanças e necessário compreender primeiro sua realidade.bitstream/item/81305/1/Pesquisa-Acao-Jose-Cerqueira-Documentos-93-2000.pd

Structural studies and influence of the structure on the electrical and optical properties of microcrystalline silicon thin films produced by RF sputtering

Microcrystalline silicon thin films were produced by reactive magnetron sputtering on glass substrates under several different conditions (RF power and gas mixture composition). The film structure was studied by X-ray diffractometry (XRD), transmission electron microscopy (TEM) and Raman spectroscopy, allowing the determination of crystal sizes, crystallinity and mechanical strain. These parameters were evaluated by fitting a pseudo-Voigt function to the X-ray data, and by the application of the strong phonon confinement model to the Raman spectra. The degree of crystallinity and the presence of single crystals or crystal agglomerates, which was confirmed by TEM, depends on the preparation conditions, and strongly affects the optical spectra and the electrical transport properties.Fundação para a Ciência e a Tecnologia (FCT) - PRAXIS XX