Search results for "stoichiometry"
showing 10 items of 270 documents
Deposition Kinetics and Compositional Control of Vacuum-Processed CH3NH3PbI3 Perovskite
2020
Halide perovskites have generated considerable research interest due to their excellent optoelectronic properties in the past decade. To ensure the formation of high-quality semiconductors, the deposition process for the perovskite film is a critical issue. Vacuum-based processing is considered to be a promising method, allowing, in principle, for uniform deposition on a large area. One of the benefits of vacuum processing is the control over the film composition through the use of quartz crystal microbalances (QCMs) that monitor the rates of the components in situ. In metal halide perovskites, however, one frequently employed component or precursor, CH3NH3I, exhibits nonstandard sublimatio…
Scanning electron microscopy study of twins in ZnSe single crystals grown by solid-phase recrystallization
2001
ZnSe single crystals were grown from n-type microcrystalline boules by a solid phase recrystallization (SPR) method. During SPR, twinned regions appear with different electronic recombination properties. The recrystallizations were performed under different atmospheres, Ar or Se, and pressures to investigate the influence of growth conditions on these structural features. Recombination properties were studied by means of cathodoluminescence (CL) and remote-electron beam induced current (REBIC). Wavelength dispersive X-ray (WDX) mappings were also performed to analyze possible differences in stoichiometry related to the presence of extended defects.
Grain growth in Na 0.5 Bi 0.5 TiO 3 -based solid solutions
2019
This paper discusses effects of different dopants, sintering technique and parameters on microstructure and properties of pure and Yb, Er-doped Na0.5Bi0.5TiO3 (NBT). All stoichiometric compositions follow the abnormal grain growth mechanism (AGG) and exhibit a bimodal grain size distribution. Bi over-stoichiometry, two step sintering and hot pressing are effective inhibitors of AGG. Microstructure of sintered NBT greatly influences such properties as dielectric permittivity and depolarization temperature.
The scent of Mare Nostrum : medicinal and aromatic plants in Mediterranean soils
2012
In the Mediterranean area, the simultaneous occurrence of pedological, climatic and economic constraints often sets a limit on the profitability of agriculture, and farmers are forced to grow a reduced number of species, dealing with a secure—albeit low—market income. The introduction of medicinal and aromatic plants (MAPs) inside the current farming systems could represent a useful means to meet the multifunctional role of agriculture: producing safe food, in respect of the environment, and contributing to the development of rural areas. The study of the relationships between MAPs and the soils in which they may be grown may have two approaches: (1) the evaluation of yield and qualitative …
Kinetics of proton release and uptake by channelrhodopsin-2
2012
Electrophysiological experiments showed that the light-activated cation channel channelrhodopsin-2 (ChR2) pumps protons in the absence of a membrane potential. We determined here the kinetics of transient pH change using a water-soluble pH-indicator. It is shown that ChR2 released protons prior to uptake with a stoichiometry of 0.3 protons per ChR2. Comparison to the photocycle kinetics revealed that proton release and uptake match rise and decay of the View the MathML sourceP3520 intermediate. As the View the MathML sourceP3520 state also represents the conductive state of cation channeling, the concurrence of proton pumping and channel gating implies an intimate mechanistic link of the tw…
Structural and physicochemical characterization of the inclusion complexes of cyclomaltooligosaccharides (cyclodextrins) with melatonin
2002
The stoichiometry, geometry, stability, and solubility of the inclusion complexes of melatonin (MLT) with native cyclomaltooligosaccharides (α-, β- or γ-cyclodextrins, CDs) are determined experimentally by high-resolution NMR spectroscopy, calorimetric and solubility measurements, and mass spectrometry. The observed differences are discussed in terms of molecular recognition expression of the host-guest (h-g) interactions within the hydrophobic CDs cavities of different size. The 1:1 h-g stoichiometry in water solution prevails at low CD concentrations; the trend to form higher order associations is observed at increasing CD concentrations. The stability order β-CD>γ-CD>α-CD for the c…
Pentameric Circular Iron(II) Double Helicates and a Molecular Pentafoil Knot
2012
We report on the synthesis of 11 pentameric cyclic helicates formed by imine condensation of alkyl monoamines with a common bis(formylpyridine)bipyridyl-derived building block and iron(II) and chloride ions. The cyclic double-stranded helicates were characterized by NMR spectroscopy, mass spectrometry, and in the case of a 2,4-dimethoxybenzylamine-derived pentameric cyclic helicate, X-ray crystallography. The factors influencing the assembly process (reactant stoichiometry, concentration, solvent, nature and amount of anion) were studied in detail: the role of chloride in the assembly process appears not to be limited to that of a simple template, and larger circular helicates observed with…
[99mTc]Ca-Phytate: Some colloidal characteristics related to the optimal preparation conditions
1983
Abstract Some physico-chemical characteristics of the colloidal radiopharmaceutical [ 99 m Tc]Ca-phytate related to optimal preparation conditions have been studied. (1,2) It is demonstrated that the Ca 2+ -phytate stoichiometry is 6:1. Two different Ca-phytate colloids seem to be formed, mainly depending on the Ca 2+ :phytate molar ratio-one of low mycelar size for a 1:1 Ca 2+ :phytate molar ratio ( cmc ∗ = 5.10 −5 M ) , and another one, with a higher mycelar size for a 6:1 molar ratio (cmc = 8.10 −5 M). This last one it probably better for providing a good quality splenic uptake.
Mechanochemical synthesis of inorganic halide perovskites: evolution of phase-purity, morphology, and photoluminescence
2019
Dry mechanochemical ball-milling of halide precursor salts is a promising route for the synthesis of high-purity halide perovskites in a fast and solvent-free manner. However, there is a lack of information on the process mechanisms, kinetics, and possible side-effects. Here, we investigated in detail the mechanochemical synthesis of fully-inorganic CsPbBr3 by ball-milling of stoichiometric CsBr and PbBr2. Detailed structural, morphological and optical analyses reveal several beneficial and detrimental effects of milling as a function of time. Three stages are identified during the process: (i) at short milling times (t < 5 min) different ternary compounds are formed, including stoichiometr…
Anodic layers formed on steel in phosphate buffer solution
1986
In-situ gamma scattering and ex-situ conversion electron Mossbauer, and Auger spectroscopy were applied to investigate anodic layers on steel. Samples treated in the active potential range in phosphate buffer solution show a Fe(II)-phosphate deposit on the surface. After treatment in the passive potential region, only Fe3+was found to exist in the oxide layer. The passive layer does not consist of stoichiometric oxidic phases.