Search results for "optical"
showing 10 items of 7671 documents
The interdependence of structural and electrical properties in TiO2/TiO/Ti periodic multilayers
2013
International audience; Multilayered structures with 14-50 nm periods composed of titanium and two different titanium oxides, TiO and TiO2, were accurately produced by DC magnetron sputtering using the reactive gas pulsing process. The structure and composition of these periodic TiO2/TiO/Ti stacks were investigated by X-ray diffraction and transmission electronic microscopy techniques. Two crystalline phases, hexagonal close packed Ti and face centred cubic TiO, were identified in the metallic-rich sub-layers, whereas the oxygen-rich ones comprised a mixture of amorphous TiO2 and rutile phase. DC electrical resistivity rho measured for temperatures ranging from 300 to 500 K exhibited a meta…
Variable-charge method applied to study coupled grain boundary migration in the presence of oxygen
2009
International audience; One of the important differences between simulation and experiments in grain boundary (GB)-dominated metallic structures is the lack of impurities such as oxygen in computational samples. A modified variable-charge method [Elsener A, Politano O, Derlet PM, Van Swygenhoven H. Modell Simul Mater Sci Eng 2008;16:025006] based on the Streitz and Mintmire approach [Streitz FH, Mintmire JW. Phys Rev B 1994;50:11996] is used to study coupled GB motion in an Al bicrystal with a [1 1 2] symmetrical tilt GB in the presence of substitutional O, and compared with the stick–slip process identified by Cahn and Mishin [Cahn JW, Mishin Y, Suzuki A. Acta Mater 2006;54:4953]. It is found…
Nanoparticle dispersion in liquid metals by electromagnetically induced acoustic cavitation
2016
Abstract Aim of this study is to investigate experimentally the effect of magnetically induced cavitation applied for the purpose of nanoparticle dispersion in liquid metals. The oscillating magnetic force due to the azimuthal induction currents and the axial magnetic field excites power ultrasound in the sample. If the fields are sufficiently high then it is possible to achieve the acoustic cavitation threshold in liquid metals. Cavitation bubble collapses are known to create microscale jets with a potential to break nanoparticle agglomerates and disperse them. The samples are solidified under the contactless ultrasonic treatment and later analyzed by electron microscopy and energy-dispers…
Continuous hydrothermal synthesis in supercritical conditions as a novel process for the elaboration of Y-doped BaZrO3
2021
Abstract The present work describes a novel process for the elaboration of a ceramic material. Y-doped barium zirconate, an electrolyte material for Protonic Ceramic Fuel cell, was synthesized by a continuous hydrothermal process in supercritical conditions (410 °C/30.0 MPa) using nitrate precursors and NaOH reactants. The use of supercritical water allowed the formation of particles of about 50 nm in diameter with a narrow size distribution. X-Ray Diffraction examination revealed that a major perovskite phase with few BaCO3 and YO(OH) impurities was obtained. BaCO3 is assumed to form due to faster kinetics than Y-doped BaZrO3 resulting in a Ba-deficient perovskite phase. The Ba-deficiency …
Fabrication and characterization of low cost Cu 2 O/ZnO:Al solar cells for sustainable photovoltaics with earth abundant materials
2016
Abstract The low cost electrodeposition method was used to grow Cu2O thin films and experimentally determine the optimal absorber layer thickness. Raman scattering studies indicate the presence of solely crystalline Cu2O and SEM images show that the thin films consist of grains with a pyramidal shape. The influence of the thickness of the light absorbing Cu2O layer on the basic characteristic of the heterojunction and their properties have been investigated using reflectivity, current–voltage (J–V), capacitance–voltage (C–V) and the external quantum efficiency (EQE) measurements. The depletion layer, the charge collection length of the minority carrier, and reflectivity are the main factors…
HCl gas gettering of low-cost silicon
2013
HCl gas gettering is a cheap and simple technique to reduce transition metal concentrations in silicon. It is attractive especially for low-cost silicon materials like upgraded metallurgical grade (UMG) silicon, which usually contain 3d transition metals in high concentrations. Etching of silicon by HCl gas occurs during HCl gas gettering above a certain onset temperature. The etching rate as well as the gettering efficiency was experimentally determined as a function of the gettering temperature, using UMG silicon wafers. The activation energy of the etching reaction by HCl gas was calculated from the obtained data. The gettering efficiency was determined by analyzing Ni as a representativ…
Gel combustion synthesis and magnetic properties of CoFe2O4, ZnFe2O4, and MgFe2O4 using 6-aminohexanoic acid as a new fuel
2020
Abstract For the first time, 6-aminohexanoic acid is used as an alternative fuel in the synthesis of the spinel ferrites with compositions CoFe2O4, ZnFe2O4 and MgFe2O4 using gel combustion synthesis with different oxidizer-to-fuel (O/F) ratios. The gel precursors were studied by differential thermal analysis and thermogravimetry (DTA/TG), which showed that the ignition temperature depends on the gel precursor, being around 230 °C, 130 °C and 275 °C for CoFe2O4, ZnFe2O4, and MgFe2O4, respectively. These results showed than the 6-aminohexanoic acid has an ignition temperature lower than the urea and the citric acid when were used in the synthesis of the spinel ferrites by gel combustion. More…
Half-Heusler compounds: novel materials for energy and spintronic applications
2012
Half-Heusler compounds are an impressive class of materials with a huge potential for different applications such as future energy applications and for spintronics. The semiconducting Heusler compounds can be identified by the number of valence electrons. The band gap can be tuned between 0 and 4 eV by the electronegativity difference of the constituents. Magnetism can be introduced in these compounds by using rare-earth elements, manganese or ‘electron’ doping. Thus, there is a great interest in the fields of thermoelectrics, solar cells and diluted magnetic semiconductors. The combination of different properties such as superconductivity and topological edge states leads to new multifunct…
Correlations between density distributions, optical spectra, and ion species in a hydrogen plasma (invited)
2016
An experimental study of plasma distributions in a 2.45 GHz hydrogen discharge operated at 100 Hz repetition rate is presented. Ultrafast photography, time integrated visible light emission spectra, time resolved Balmer-alpha emission, time resolved Fulcher Band emission, ion species mass spectra, and time resolved ion species fraction measurements have been implemented as diagnostic tools in a broad range of plasma conditions. Results of plasma distributions and optical emissions correlated with H + , H + 2 , and H + 3 ion currents by using a Wien filter system with optical observation capability are reported. The magnetic field distribution and strength is found as the most critical facto…
Raman characterization of Pb2Na1−xLaxNb5−xFexO15 and Pb0.5(5−x)LaxNb5−xFexO15 (0≤x≤1) solid solutions
2011
Abstract The ferroelectric compounds Pb 2 Na 1− x La x Nb 5− x Fe x O 15 and Pb 0.5(5− x ) La x Nb 5− x Fe x O 15 (0≤ x ≤1) with the tungsten bronze type structure have been investigated using Raman spectroscopy. The evolution of the spectra as a function of composition at room temperature is reported. In the frequency range 200–1000 cm −1 three main A 1 phonons around 240 ( υ 1 ), 630 ( υ 2 ) and 816 ( υ 3 ) cm −1 were observed. The broadening of the Raman lines for high values of x originates from a significant structural disorder. This is in good agreement with the relaxor character of these compositions. The lowest-frequency part of the spectra, below 180 cm −1 , reveals a structural ch…