Search results for "alli"
showing 10 items of 10341 documents
Numerical modelling for the diameter increase of silicon crystals grown with the pedestal method
2021
Abstract The pedestal method is one of crucible-free crystal growth methods, that has been less researched than the well-known floating zone (FZ) method. However, the pedestal method may be a cost-effective alternative to FZ, if large diameter feed rods are available. The investigated system contains two electromagnetic inductors: high-frequency inductor for pedestal top surface melting and middle-frequency inductor for pedestal side heating. The present work describes recent advances in numerical modelling of heat transfer and phase boundaries in axially symmetrical approximation, neglecting the melt flow. The shape of high-frequency inductor was optimized with the algorithm of gradient de…
Static and dynamic structure of $ZnWO_4$ nanoparticles
2011
Abstract Static and dynamic structure of ZnWO 4 nanoparticles, synthesized by co-precipitation technique, has been studied by temperature dependent x-ray absorption spectroscopy at the Zn K-edge and W L 3 -edge. Complementary experimental techniques, such as x-ray powder diffraction, Raman and photoluminescence spectroscopies, have been used to understand the variation of vibrational, optical, and structural properties of nanoparticles, compared to microcrystalline ZnWO 4 . Our results indicate that the structure of nanoparticles experiences strong relaxation leading to the significant distortions of the WO 6 and ZnO 6 octahedra, being responsible for the changes in optical and vibrational …
Comparing the luminescence processes of YVO4:Eu and core-shell YVO4@YF3 nanocrystals with bulk-YVO4:Eu
2017
Abstract Comparative analysis of bulk, non-coated and core-shelled nanocrystalline YVO4:Eu was performed by means of time-resolved luminescence and VUV excitation luminescence spectroscopy techniques. Nanocrystalline YVO4:Eu samples – both as-prepared and YF3 core-shelled – have been synthesized by means of a microwave-assisted synthesis in ionic liquids, which allows to obtain 10–12 nm nanoparticles with high crystallinity. The results show noticeable differences between bulk and nanocrystalline YVO4:Eu in photoluminescence experimental data, which explains by influence of the nanocrystal surface. A YF3 core-shell layer around YVO4:Eu nanoparticles partially recovers the intensity of the E…
Optimization of physicochemical and optical properties of nanocrystalline TiO 2 deposited on porous silicon by metal-organic chemical vapor depositio…
2020
International audience; Titanium dioxide (TiO2) is very employed in solar cells due to its interesting physicochemical and optical properties allowing high device performances. Considering the extension of applications in nanotechnologies, nanocrystalline TiO2 is very promising for nanoscale components. In this work, nanocrystalline TiO2 thin films were successfully deposited on porous silicon (PSi) by metal organic chemical vapor deposition (MOCVD) technique at temperature of 550°C for different periods of times: 5, 10 and 15 min. The objective was to optimize the physicochemical and optical properties of the TiO2/PSi films dedicated for photovoltaic application. The structural, morphologi…
X-ray and dielectric characterization of Co doped tetragonal BaTiO3 ceramics
2016
ABSTRACTThe crystal structure modifications of BaTiO3 induced by cobalt doping were studied. The polycrystalline (1 − x)BaTiO3 + xCo2O3 samples, with x ≤ 10 wt.%, were prepared by high temperature sintering conventional method. According to X-ray phase and structural characterization, performed by full-profile Rietveld refinement technique, all synthesized samples showed tetragonal symmetry perovskite structure with minor amount of parasitic phases. Pure single-phase composition has been detected only in the low level of doping BaTiO3. It was indicated that substitution of Co for the Ti sites in the (1 − x)BaTiO3 + xCo2O3 series led to decrease of tetragonality (c/a) of the BaTiO3 perovskit…
Validation of mathematical model for CZ process using small-scale laboratory crystal growth furnace
2018
The present material is focused on the modelling of small-scale laboratory NaCl-RbCl crystal growth furnace. First steps towards fully transient simulations are taken in the form of stationary simulations that deal with the optimization of material properties to match the model to experimental conditions. For this purpose, simulation software primarily used for the modelling of industrial-scale silicon crystal growth process was successfully applied. Finally, transient simulations of the crystal growth are presented, giving a sufficient agreement to experimental results.
Induced crystallographic changes in Cd1−xZnxO films grown on r-sapphire by AP-MOCVD: the effects of the Zn content when x ≤ 0.5
2020
High-resolution X-ray diffraction, scanning electron microscopy and transmission electron microscopy techniques were used to investigate, as a function of the nominal Zn content in the range of 0–50%, the out-of-plane and in-plane crystallographic characteristics of Cd1−xZnxO films grown on r-plane sapphire substrates via atmospheric pressure metal–organic chemical vapor deposition. The study is conducted to search for knowledge relating to the structural details during the transition process from a rock-salt to a wurtzite structure as the Zn content increases in this CdO–ZnO system. It has been found that it is possible to obtain films exhibiting a single (001) cubic orientation with good …
3D modeling of growth ridge and edge facet formation in 〈100〉 floating zone silicon crystal growth process
2019
Abstract A 3D quasi-stationary model for crystal ridge formation in FZ crystal growth systems for silicon is presented. Heat transfer equations for the melt and crystal are solved, and an anisotropic crystal growth model together with a free surface shape solver is used to model the facet growth and ridge formation. The simulation results for 4″ and 5″ crystals are presented and compared to experimental ridge shape data.
Mathematical modelling of the feed rod shape in floating zone silicon crystal growth
2017
Abstract A three-dimensional (3D) transient multi-physical model of the feed rod melting in the floating zone (FZ) silicon single-crystal growth process is presented. Coupled temperature, electromagnetic (EM), and melt film simulations are performed for a 4 inch FZ system, and the time evolution of the open melting front is studied. The 3D model uses phase boundaries and parameters from a converged solution of a quasi-stationary axisymmetric (2D) model of the FZ system as initial conditions for the time dependent simulations. A parameter study with different feed rod rotation, crystal pull rates and widths of the inductor main slit is carried out to analyse their influence on the evolution …
Thermal stability of magnetic characteristics of Co/Ag/Fe and Co/Ag/Fe20Ni80 spin-valve structures
2017
Abstract We investigated the thermal stability of magnetic characteristics of Co/Ag/Fe and Co/Ag/Fe 20 Ni 80 spin-valve structures. Thin film systems were obtained with the help of sputtering method. For the first type of systems two particular thicknesses ( d ML = 3 and 20 nm) and different disposition of magnetic layers (ML) were used. For the second type different thickness of Ag ( d NML ) spacer layer was used. The research of the crystal structure was performed with the transmission electron microscope. The results demonstrate that every investigated as-deposited sample does not include solid solutions, intermetallic compounds or impurities. It has been found that among the spin-valve…