Search results for "Stoichiometry"
showing 10 items of 270 documents
Light-Induced Sublimation of Cadmium Sulphide
1984
It has recently been shown that single crystal CdS, illuminated by light whose photon energy exceeds the bandgap, can eject particles from its surface while the temperature is well below the value required for vacuum sublimation. This phenomenon has obvious applications to the fabrication of surface structures as well as to the production of thin films that can show good CdS stoichiometry. This work will present several data on the morphology of the etched surface and its dependance on crystal orientation; results of an analysis of the recondensed thin film phase from the ejected material will also be shown. Emphasis will be devoted to examples of high resolution surface structures fabricat…
Synthesis of a New Copper-Azobenzene Dicarboxylate Framework in the Form of Hierarchical Bulk Solids and Thin Films without and with Patterning
2011
Reaction of copper(II) acetate with azobenzene-4,4′-dicarboxylic acid results in the formation of a metal–organic framework with the unexpected stoichiometry of Cu(II):ligand of 2:1. The bulk synthesis results in microspheres assembled from either nanobricks or nanoflakes, depending on the ratio of the reactants in solution. While the former behaves like a bulk solid with clear reflections in the X-ray and electron diffraction experiments, the latter obviously is dominated by surface effects, with a significant fraction of slightly expanded elemental cells and a significantly increased outer surface area. The material could also be deposited on a variety of surfaces using a stepwise layer-b…
Oxidation of pentan-2-ol -Part II: Experimental and modeling study
2021
International audience; The oxidation of pentan-2-ol was investigated at high-pressure in a jet-stirred reactor and in a shock tube. Experiments in the JSR were carried out at 10 atm, between 500-1180 K, for five different equivalence ratios of = 0.35, 0.5, 1, 2, 4 and 1000 ppm of fuel, at a constant residence time of 0.7 s. Reactant, product and intermediate species mole fractions were quantified using Fourier transform infrared spectrometry (FTIR) and gas chromatography (GC). Ignition delay times were measured for pentan-2-ol/O 2 mixtures in argon in a shock tube at 20 and 40 bar, in a temperature range of 1070-1460 K and for equivalence ratios of = 0.5, 1 and 2. Ignition delay times of a…
Series of charge transfer complexes obtained as crystals in a confined environment
2021
A series of charge transfer complexes (CTCs) were successfully formed by solvent free processing techniques, using the 1,2,4,5-tetracyano benzene (TCNB) as πA molecule and a series of p-dihydroquinones (H2Qs) as πD counterparts. Additionally to the classical co-evaporation techniques, we obtained CTCs in less than an hour, in a very simple confined environment, between two 100 μm – spaced glass plates. A systematical study by Raman spectroscopy on crystals highlighted the CTCs formation. Moreover, three new crystalline structures were obtained, namely TCNB-H2Q that crystallizes in columns connected to each other by H-bonds, while with the methoxy- and dimethoxy-H2Qs the CTC forms crystals w…
Organometal Halide Perovskites: Bulk Low-Dimension Materials and Nanoparticles
2015
Organometal halide perovskites (hybrid perovskites) contain an anionic metal–halogen-semiconducting framework and charge-compensating organic cations. As hybrid materials, they combine useful properties of both organic and inorganic materials, such as plastic mechanical properties and good electronic mobility related to organic and inorganic material, respectively. They are prepared from abundant and low cost starting compounds. The perovskite stoichiometry is associated with the dimensionality of its inorganic framework, which can vary from three to zero, 3D consisting of corner-sharing MX6 octahedra, and 0D consisting of isolated octahedra. Small-sized organic cations can fit into the MX6…
Compaction of tungsten oxide films by ion-beam irradiation
1993
Abstract Evaporated amorphous tungsten oxide films with low densities, deposited on different substrates, have been irradiated with various types of ions of different energies up to 30 MeV, and with fluences up to 10 18 cm −2 . Compaction of the films up to nearly the bulk density was observed. No changes of the stoichiometry as determined by various ion-beam analysis techniques were detectable. Raman measurements showed that ion-beam-modified films are also amorphous, but have a different microstructure from as-deposited films. The irradiated films have a higher refractive index than the as-deposited films. A low threshold for the compaction effect of a few times 10 12 ions cm −2 was found…
Transient absorption and luminescence of LiNbO3 and KNbO3
2001
Abstract The results of time-resolved optical absorption spectra in congruent and stoichiometric LiNbO3 as well as KNbO3 crystals are reported. The role of different polaron types in transient absoiption and luminescence spectra and decay kinetics are discussed.
The Cation Sublattice Ordering in the Ferroelectric LiNbO3:Zn Single Crystals
2014
It has been revealed for the first time by Raman spectroscopy that in LiNbO3:Zn crystal with Zn2+ concentration range 0.03–0.94 mol.% the ordering of the main doping cations and vacant octahedrons along the polar axis is better than in the undoped crystal of congruent composition. Thus, the configuration of oxygen octahedrons is closer to ideal. The line widths of the Raman spectra in this concentration range are narrower than in congruent LiNbO3 crystals and closer to the line width in stoichiometric crystals with the best known cation ordering. As far as Zn2+ concentration is small, the growth technique changes very slightly compared to the growth of the pure LiNbO3 crystals.
Near-field scanning optical microscopy to study nanometric structural details of LiNbO3 Zn-diffused channel waveguides
2008
A near-field scanning optical microscope (NSOM) is used to perform structural and optical characterization of the surface layer after Zn diffusion in a channel waveguide fabricated on lithium niobate. A theoretical approach has been developed in order to extract refractive index contrast from NSOM optical transmission measurements (illumination configuration). As a result, different solid phases present on the sample surface can be identified, such as ZnO and ZnNb2O6. They appear like submicrometric crystallites aligned along the domain wall direction, whose origin can be ascribed to some strain relaxation mechanism during the annealing process after Zn diffusion. Jose.Canet-Ferrer@uv.es
The Effect of Technological Factors on the Synthesis of PbMg 1/3 Nb 2/3 O 3
2003
Conventional technique of solid phase reactions allows one to obtain PbMg 1/3 Nb 2/3 O 3 material with about 20 vol.% of the pyrochlore phase. The latter can be reduced to 5 vol.% by Swartz-Shrout two-stage solid state reaction via MgNb 2 O 6 having the columbite structure. A single-phase perovskite product can be obtained by by the two-stage columbite method from mixtures containing 0.2 mol. parts of overstoichiometric MgO. The best results are obtained by using magnesium carbonate hydroxide pentahydrate (MgCO 3 ) 4 ·Mg(OH) 2 ·5H 2 O as the magnesium source. The modified route yields stoichiometric single-phase PMN.