Effect of high temperature VPT conditions on the development of aligned ZnO nanorod arrays grown by a three step catalyst-free method

Using Transmission Electron Microscopy-related techniques, we study the effect of the high temperature in the Vapour Phase Transport (VPT) process on the morphology and chemistry of VPT ZnO nanorod arrays deposited on a two-step Chemical Bath Deposition (CBD) buffer layers on silicon substrates. Though well-aligned and c-axis oriented arrays of ZnO nanorods are achieved, we have noticed the strong dependence of the nanorod morphology on the VPT growth conditions such as the temperature ramp rate and the placement of samples with respect to the metal source. The development of conical structures in the nanorod bases and the formation of a double intermediate layer below the base of nanorods are the main features found. The modifications of the ZnO nanostructures both in the base and in the underlying buffer layers due to the high VPT temperatures are also examined in detail

Study of morphological and chemical changes of aligned zinc oxide nanorods growth by vapour phase transport on chemical bath deposited buffer layers

c-axis aligned ZnO nanorods were deposited by vapour phase transport on textured chemical bath deposited buffer layers. In this work we examine the role of the buffer layer and how it influences the vapour phase transport deposition process using both scanning and scanning transmission electron microscopes and related techniques. Vapour phase transport deposition on chemical bath deposited buffer is a complex growth process with many simultaneously effects including; (i) substantial morphological transformation at high temperature, which influences the base of the nanorods; (ii) the formation of a mixed amorphous / crystalline ZnxSi1-xOy interface during the vapour phase transport growth on silicon substrates; (iii) the overgrowth of the ZnO seed layers, by the silica interface rendering them inactive for nanorod nucleation, suggesting there is a minimum critical thickness ZnO buffer layer necessary for vapour phase transport growth of ZnO nanorods on silicon substrates. We discuss the relative importance of these effects on the overall growth process and use this understanding to explain previous results in the literature

Étude des performances épuratoires de la technique du lagunage aéré appliquée à la station d’épuration de la ville d’Errachidia - Maroc

Dans le but d’évaluer le rendement de la nouvelle station d’épuration de la ville d’Errachidia type lagunage aéré, nous avons étudié les paramètres physico-chimiques et bactériologiques des eaux brutes et épurées de la station. Pour cela, nous avons réalisé un ensemble de mesures tels que : la température, le pH et la conductivité (paramètres sur places), la demande biochimique en oxygène DBO5, la demande chimique en oxygène DCO et les matières en suspension MES (paramètres physico-chimiques), les coliformes fécaux (CF) et les coliformes totaux (CT) (paramètres bactériologiques). Les résultats d’analyses ont montré une évolution des rendements épuratoires de la nouvelle station par rapport à l’ancienne de type lagunage naturel. Ces rendements mesurés à partir de la DBO5, DCO et MES donnent des valeurs respectivement de 82%, 83% et 88%. D’autre part la qualité bactériologique des eaux épurées est conforme à une réutilisation agricole.Mots-clés : station d’épuration, MES, DCO, DBO5, paramètres bactériologiques

ZnO micro/nanocrystals grown by Laser Assisted Flow Deposition

Laser assisted flow deposition (LAFD) is a very high yield method based on a vapor-solid mechanism, allowing the production of ZnO crystals in a very short time. The LAFD was used in the growth of different morphologies (nanoparticles, tetrapods and microrods) of ZnO micro/nanocrystals and their microstructural characterization confirms the excellent crystallinity of the wurtzite structure. The optical properties of the as-grown ZnO crystals investigated by low temperature photoluminescence (PL) evidence a well-structured near band edge emission (NBE) due to the recombination of free (FX), surface (SX) and donor bound ((DX)-X-0) excitons. Among the most representative emission lines, the 3.31 eV transition was found to occur in the stacking faults-free microrods. The luminescence behavior observed in H passivated samples suggests a closer relationship between this optical center and the presence of surface states. Besides the unintentionally doped micro/nanocrystals, ZnO/Ag and ZnO/carbon nanotubes (CNT) hybrid structures were processed by LAFD. The former aims at the incorporation of silver as a p-type dopant and the latter envisaging photovoltaic applications. Silver-related spherical particles were found to be inhomogeneously distributed at the microrods surface, accumulating at the rods tips and promoting the ZnO nanorods re-nucleation. Despite the fact that energy dispersive X-ray measurements suggest that a fraction of the silver could be incorporated in the ZnO rods, no new related luminescence lines or bands were observed when compared with the as-grown samples. For the case of the ZnO/CNT composites two main approaches were adopted: i) a direct deposition of ZnO particles on the surface of vertically aligned multi-walled carbon nanotubes (VACNTs) forests without employing any additional catalyst and ii) new ZnO/CNT hybrids were developed as bucky paper nanocomposites. The use of the LAFD technique in the first approach preserves the CNTs structure and alignment and avoids the collapse of the VACNTs array, which is a major advantage of this method. On the other hand, LAFD grown ZnO nanoparticles and tetrapods were used to produce ZnO/CNT buckypaper nanocomposites. When compared with the as-grown samples the PL spectra of the composites structures behave differently. For the case of the ZnO/VACNTs no changes on the peak position and spectral shape were observed. Only an enhancement of the overall luminescence was found to occur. On contrary, for the buckypaper nanocomposites notable changes on the spectral shape and peak position were observed, likely due to distinct surface band bending effects for the ZnO nanoparticles and tetrapods embedded in the CNTs

Imaging and Analysis by Transmission Electron Microscopy of the Spontaneous Formation of Al-Rich Shell Structure in AlxGa1-xN/GaN nanowires

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