This work was focused on assessing the influence of the glycerol in chitosan matrices, analyzing the changes produced in the molecular mobility, mechanical, thermal, barrier and structural properties. The addition of glycerol in the matrix decreased the stress values, increasing the elasticity and water vapor permeability of the films, with a marked decrease in glass transition temperature; Detailed analyses of Fourier Transform IR Spectroscopy spectra supported the observed changes, especially in the spectral windows 1700-1500 cm −1 revealing the modifications at molecular level caused by hydrogen bond interactions between chitosan and water in the presence of glycerol. Positron annihilation spectroscopic (PALS) measurements allowed determining the free volume assuming spherical holes as well as monitoring the structural changes in chitosan films caused by the addition of both, glycerol and water molecules. It was possible to infer that for unplasticized matrices, a sustained increase of the radius between 0.06 and 0.2 of X water was observed, followed by a plateau up to 0.35. In the other case, with the addition of glycerol, there were two plateaus, the first between 0.25 and 0.37 of X water , and the second from 0.41 to 0.47. For higher glycerol concentrations, the plasticizer would be mainly bounded to the chitosan pack more efficiently and the water present in the system would be predominantly free in the matrix causing its swelling. Findings on molecular mobility contributed to the understanding of the role of water and glycerol in the structural arrangement and its influence on film properties.
The fabrication of nanostructured ZnO thin films is a critic process for a lot of applications of this semiconductor material. The final properties of this film depend fundamentally of the morphology of the sintered layer. In this paper a process is presented for the fabrication of ZnO nanostructured layers with morphology control by pulsed electrodeposition over ITO. Process optimization is achieved by pulsed electrodeposition and results are assessed after a careful characterization of both morphology and electrical properties. SEM is used for nucleation analysis on pulsed deposited samples. Optical properties like transmission spectra and Indirect Optical Band Gap are used to evaluate the quality of the obtained ZnO structures. Solar cell devices with industrial application are stratified laminar materials, with several dm 2 of exposed surface, processed by piling up several layers with different composition, each of them has a different function and complementary in the device. The performance of present commercial solar cells (that are based in semiconductors III-V, with Si poly or mono crystalline) is determined by the different fabrication process.1,2 In all of them, the production of diverse interfaces is the design factor, developed by growing different layers. The final properties of the semiconductor are defined by the type of boundary, the chemical species present, etc. . .. One of the determining factors in the final performance of the cell is its morphology, and the final product quality depends on the possibility of having a close control on the nucleation parameters.3,4 The optimization of these interfaces is a challenge for the photovoltaic industry, optimization must be based on a thorough understanding on the growth mechanisms. Likewise, the key for a successful implementation of photovoltaic energy is based on how industry attains a cheaper and more efficient process for cell fabrication. It is therefore necessary to reduce costs and production time of the cells without decreasing its performance. This requires more efficient production processes. These goals are common to all manufacturers of photovoltaic cells. Given the above scenario electrodeposition is selected as a favoured technique. This study develops the manufacture of inorganic layers of nanostructured ZnO for photovoltaic applications trough low-cost technology. In particular, Pulsed current electrodeposition (ED) is to be presented as a highly promising alternative. The aim of this study is to analyze the influence of waveform control for the electrodeposition current on the morphology as a tool to control the optical properties of the thin layer. The selected material (ZnO) has a mesoporous nanocrystalline structure optimal for the development of hybrid solar cells. These materials have been characterized using different techniques to quantify the ability of the photovoltaic material, and at the same time, to correlate morphology and optoelectronic properties. In particular, the optical, electrical and structural best suited fo...
The electric field gradient (EPPES) at Hf sites in amorphous Hf& Cu"alloys was measured for x =0. 33, 0.44, 0.50, and 0.59 with use of the time-differentia1 perturbed angular correlation technique. The results show no evidence of crystallinelike local order in these alloys, supporting a description of their local structure in terms of a dense random packing of atoms. The local and lattice contributions to the EFCx, as well as their dependence on composition, are discussed.
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