CdSe/Se multilayer thin films were prepared using sequential thermal evaporation technique by varying the thickness of selenium sublayers. Identifying the prominent peaks observed in the XRD spectra of the top layer CdSe which corresponds to the (100) plane with wurtzite structure, the average size of the crystallites was calculated for the CdSe nanocrystals. Experimentally measured band gaps are larger than bulk band gap of CdSe. This confirms the presence of spin-orbit splitting of energy levels. Size of the crystallites was then calculated with the theoretical prediction of the effective mass approximation model (i.e., Brus model). It resulted in that the diameters of crystallites were much smaller than the Bohr exciton diameter (11.2 nm) of CdSe. Thus, the structural and optical properties of CdSe/Se multilayer thin films reveal the effect of quantum confinement of CdSe crystallites in Se matrix for various sublayer thicknesses. Confinement effect is more pronounced while sublayer thickness of selenium increases.

______________________________________________________________________________________Resumo -A degradação dos solos e a perda por erosão por manejo inadequado constituem uma séria ameaça à produtividade agrícola e contribuem para o agravamento de impactos ambientais. Práticas edáficas, vegetativas e mecânicas de conservação dos solos estão sendo desenvolvidas para auxiliarem na atenuação desses problemas. Nesse contexto, a presente pesquisa foi realizada com o objetivo de avaliar o efeito da cobertura morta na conversação de um solo argilo-arenoso no estado do Mato Grosso. O estudo foi desenvolvido em condições de campo na Universidade Federal do Mato Grosso, Campus Rondonópolis e um delineamento inteiramente casualizado com dois tratamentos, com e sem cobertura vegetal, onde se avaliou temperatura do solo, quantificação de plantas espontâneas, umidade do solo e umidade do ar na superfície do solo. Verificou-se que a cobertura morta manteve o solo com um gradiente de temperatura em torno de dois graus inferiores ao tratamento sem cobertura, além de reduzir o surgimento de plantas espontâneas em 36 vezes e elevar a umidade do solo em aproximadamente quatro graus, porém não teve efeito sobre a umidade do ar na superfície do solo. Portanto, O uso da cobertura morta é uma prática vantajosa, a qual melhora as características hidrotérmicas do solo e reduz a incidência de plantas espontâneas. Palavras-chave: Serrapilheira, Degradação do Solo, Proteção do Solo.Abstract-Soil degradation and erosion loss due to inadequate management pose a serious threat to agricultural productivity and contribute to the aggravation of environmental impacts. Soil, vegetative and mechanical practices of soil conservation are being developed to assist in the attenuation of these problems. The present research was carried out with the objective of evaluating the effect of mulching in the conversation of a sandy loam soil in the state of Mato Grosso. The study was developed under field conditions at the Federal University of Mato Grosso, Rondonópolis Campus and a completely randomized design with two treatments, with and without vegetation cover, where soil temperature, spontaneous plant quantification, soil moisture and relative humidity of the soil surface. It was verified that mulching kept the soil with a temperature gradient around two degrees lower than the uncovered treatment, besides reducing the emergence of spontaneous plants in 36 times and raising soil moisture by approximately four degrees, but not had an effect on soil surface moisture. Therefore, the use of mulch is an advantageous practice, which improves the hydrothermal characteristics of the soil and reduces the incidence of spontaneous plants

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