Search results for "Crystalline"
showing 10 items of 558 documents
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…
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.
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 …
Reduced temperature sensitivity of multicrystalline silicon solar cells with low ingot resistivity
2016
This study presents experimental data on the reduction of temperature sensitivity of multicrystalline silicon solar cells made from low resistivity ingot. The temperature coefficients of solar cells produced from different ingot resistivities are compared, and the advantages of increasing the net doping are explained.
Application of enthalpy model for floating zone silicon crystal growth
2017
Abstract A 2D simplified crystal growth model based on the enthalpy method and coupled with a low-frequency harmonic electromagnetic model is developed to simulate the silicon crystal growth near the external triple point (ETP) and crystal melting on the open melting front of a polycrystalline feed rod in FZ crystal growth systems. Simulations of the crystal growth near the ETP show significant influence of the inhomogeneities of the EM power distribution on the crystal growth rate for a 4 in floating zone (FZ) system. The generated growth rate fluctuations are shown to be larger in the system with higher crystal pull rate. Simulations of crystal melting on the open melting front of the pol…
Experimental and numerical investigation of laboratory crystal growth furnace for the development of model-based control of CZ process
2019
Abstract The presented study is focused on laboratory Czochralski crystal growth experiments and their mathematical modelling. The developed small-scale CZ crystal growth furnace is described as well as the involved automation systems: crystal radius detection by image recognition, temperature sensors, adjustable heater power and crystal pull rate. The CZ-Trans program is used to model the experimental results – transient, 2D axisymmetric simulation software primarily used for modelling of the industrial-scale silicon crystal growth process. Poor agreement with the experimental results is reached; however, the proven ability to perform affordable, small-scale experiments and successfully mo…
Comparative study of the luminescence properties of macro- and nanocrystalline MgO using synchrotron radiation
2013
MgO nano-powder with an average crystallite size of nanoparticles ranging 10-15 nm was synthesized using the extractive-pyrolytic method and was studied by room temperature VUV spectroscopy under synchrotron radiation excitation. Comparative analysis of their luminescent properties with that of mac- rocrystalline powder analogues and an MgO single crystal, grown by the arc-fusion method, has been per- formed under excitation by pulsed VUV synchrotron radiation. Special attention was paid to VUV spectral range, which is not reachable with commonly used lamp and laser sources. A considerable blue shift of about 0.3 eV in the excitation spectra of 2.95 eV emission band, was revealed in nanocry…
Unusual domain-wall motion in ferromagnetic semiconductor films with tetragonal anisotropy
2009
International audience; Magnetic field-driven domain-wall propagation in the flow regime is investigated in (Ga, Mn) As ferromagnetic semiconductor layers. Square-shape magnetic domains with an unexpected orientation of their edges, at pi/8 with respect to the anisotropy axes, are found. This is shown to arise from the effect of tetragonal magnetic anisotropy on domain-wall dynamics. Using a one-dimensional model for domain-wall motion and modeling domain growth by contour dynamics the shape and orientation of domains and their field range for existence are well reproduced. These results point to the key role of the vectorial nature of the order parameter in the dynamics of ferromagnetic do…