Blends of chitosan (from Cuban lobster) and clay micro/nanoparticles were prepared by dispersion of the clay particles in the film matrix and the films obtained were characterized in terms of water solubility, water vapor, oxygen and carbon dioxide permeability, optical, mechanical and thermal properties using an Instron universal testing machine, differential scanning calorimetry, thermogravimetric analyses and scanning electron microscopy (SEM). The water vapor barrier properties of the films were significantly improved by incorporation of clay in their composition, while the water solubility decreased as the clay concentration increased (for a constant chitosan concentration). The tensile strength of chitosan/clay films increased significantly with increasing chitosan and clay concentrations, while the values of elongation decreased slightly for high values of chitosan concentration. T m increased with the increase of chitosan concentration, but the changes in T m with the addition of clay were not significant. Polynomial models were fitted to the experimental data in order to facilitate future design of chitosan/ clay film systems.

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International audienceMetal oxide (SnO₂, TiO₂, In₂O₃, ZnO) sols are prepared by various sol-gel processes in such a way as to hinder the condensation reactions. The obtained sols are injected at 160 °C into a solution of tetradecene and dodecylamine, and kept under heating for different periods of time. Depending on the starting sol, variously crystallized oxide nanoparticles are obtained, whose phase compositions and chemical structure have been studied by X-ray diffraction (XRD) and Fourier transform IR spectroscopy. The elimination of the organic residuals has been carried out by thermal treatment, and the thermal evolution of the nanoparticles has been studied by thermal analyses and Raman spectroscopy. High-resolution transmission electron microscopy studies coupled with XRD measurements show that the thermal treatment does not markedly affect the particle size, which remains in the nanometer-sized regime (from 3.5 to 8.5 nm, depending on the system), except in the case of ZnO. The thermally purified and stabilized powders, drop-coated onto alumina substrates with pre-deposited electrical contacts, have been tested as gas-sensing devices, displaying outstanding sensing properties even at room temperature

Electrochemical deposition of metals has been used to obtain high quality Schottky diodes on compound semiconductors like GaAs 1 and InP, 2 but less attention has been dedicated to silicon despite its wider use in microelectronics. A few studies have been published recently about Pt, Au, Fe, Ni, and Cu deposition, 3-8 some of them including in situ scanning tunneling microscopy (STM) imaging, as in the case of Zn 5 and Pb. 6 Others focused on the fundamentals of nucleation and growth modes as well as the chargetransfer mechanism during electrochemical deposition. 7-9 The application of an external potential to a sample immersed in an electrolyte somehow diminishes the main advantage of the wet chemical methods for industrial purpose. Regarding metal deposition, it is both desirable and convenient for some applications to have a method that produces deposition on the sample without the need for an electrical contact, thus allowing deposition by simple immersion of the sample in a solution containing the appropriate metallic ions. This paper reports on the electrochemical study of nickel deposition at the open-circuit potential (OCP) on silicon from fluoride solutions of pH 1.2 and 8.0. The charge-transfer processes involved in the deposition mechanism and the role of surface states are also discussed, using a complete study under potentiostatic control. It is shown that this approach provides first-hand information for the analysis of the deposition mechanism.Hydrofluoric acid solutions are known to etch the insulating oxide that may form on the silicon surface under certain conditions. The presence of relatively high fluoride concentrations thus guarantees the cleanness of the substrate and its intimate contact with the solution, and simplifies the analysis of charge-exchange processes with the species in solution. Beyond this justification, a posteriori for basic research purposes, the interest in the study of metal deposition from fluoride solutions arises from several fields in the microelectronics industry, to evaluate the damaging effects of metal trace contaminants in the cleaning solutions 9,10 and to delineate p-n junctions 11,12 and reveal defects in semiconductor wafers. 13,14 In the metal coatings industry, these solutions are also employed to predeposit the samples to be subsequently coated by other electrochemical methods. 15Charge transfer at semiconductor electrodes.-In order to be reduced and deposited as metal on the surface, the metal ions in solution must draw electrons from the silicon substrate. The corresponding electrons can in principle be obtained in different ways, namely, by accumulating them at the surface of an n-type electrode under negative bias or by photogenerating them at the surface of a depleted p-type electrode. Another possibility is extracting them from the bonding levels of the substrate atoms (i.e., by oxidizing the silicon atoms). In the formalism of semiconductor electrochemistry, the first two processes involve free electrons in the silicon conduction band (CB), and the...

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We report for the first time the nonhydrolytic synthesis of soluble SnO 2 nanocrystals, by the decomposition at temperatures between 230 and 250 °C of tin(II) 2-ethylhexanoate in diphenyl ether and in the presence of amines as surface capping agents. X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) studies showed that highly crystalline nanoparticles were obtained with a mean size ranging from about 3 to about 3.5 nm, depending on the length of the alkyl chain of the amine. The use of metal 2-ethylhexanoate in the synthesis of oxide nanocrystals was generalized by preparing ZnO nanocrystals from the decomposition under similar conditions of zinc(II) 2-ethylhexanoate. In this case, soluble nanocrystals with a size ranging from about 5 to 8 nm were obtained. It is shown that the decomposition path of the precursor depends on the specific metal, and may result in the sudden formation of pyrolized products instead of soluble nanocrystals. The optical properties of capped SnO 2 nanocrystals are reported for the first time and are characterized by only a blue luminescence, while for the ZnO colloids the photoluminescence spectra are characterized by the typical band-edge and surface defects emission bands, but in these samples the latter band is unusually much weaker than the former.

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