The origin of high Curie temperature ferromagnetism in dilute magnetic semiconductors and oxides has often been attributed to clustering and crystallographic phase separation of magnetic atoms, which ...may have a detrimental impact on the properties of the host material for target applications. We present Density Functional Theory calculations on the stability and magnetic interactions of embedded Fe+1 ions in diamond by considering various possible cluster configurations. We find that Fe ions have a strong tendency to form embedded clusters in diamond, with larger cluster sizes (n>3) suppressing the induced spin moment. Also, we find that the electronic structure of the stable embedded Fe+1 clusters is insulating, in contrast to homogeneous distribution, where a half metallic character with 100% spin polarisation at the Fermi level has previously been predicted. These results present important implications to the understanding of the properties of transition metal dopants in diamond, as well as in other dilute magnetic semiconductors where the effect of aggregation of dopants has generally been neglected.
Studying constitutions can do something beyond merely help us understand the 'de jure' laws in action within a country or to make predictions about how a particular state is likely to act. Studying ...constitutions also helps us appreciate the goals of the people who draft constitutions and their perception of the world in which such goals are most likely to be realized. When we study constitutions, we gain insights into the things that constitutional drafters and ratifiers think desirable and the mechanisms that they think are conducive to achieving their desired outcomes. And when we look at a range of constitutions that come from within a particular jurisdiction or a particular constitutional tradition, we can begin to grasp the full range of ways in which people who are associated with that jurisdiction and tradition could realize their shared dreams and aspirations.
Different nanocomposites silica-resin based were prepared and characterized in order to achieve a porous monolith that contains bentonite and allows the flow of aqueous systems. The bentonite used to ...prepare the nanocomposites was a good adsorbent for various molecules in aqueous media in stirred tank reactor. But the challenge was the obtention of porous bentonite composite columns for industrial applications. The primary composite, silica-resin, was prepared by the sol–gel precursor mixture of the tetraethylorthosilicate (TEOS) and a phenolic resin, made up the gel which is then dried and cured at 180 °C. Bentonite was added to the precursor mixture obtaining the, silica-resin-bentonite composite, and also other potencial adsorbent, carbon, was added obtaining the silica-resin-bentonite-carbon composite. The different composites were mineralogical and structurally evaluated by X-ray diffraction, Infrared spectroscopy with Fourier transform, Differential thermal analyses and thermogravimetric analyses. The textural characterization was performed by Adsorption of nitrogen (Sg-BET), Mercury intrusion porosimetry and Scanning electron microscopy. The comparison of the characteristics and properties between the composites evidenced that the addition of bentonite modify the sol–gel process and interferes in the composite cured process, so that, modify the mesoporosity and macroporosity of the composite. But, there is a maximum clay limit to obtain an homogeneous monolith. The addition of carbon decreases the porosity of the composite to a greater extent when the granulometry is greater.
Porous ceramic materials exhibit high permeability, specific surface, and thermal shock resistance, and therefore they may be used successfully in the production of filters, membranes, and as a ...substrate for catalytic reactions, etc. One method for preparing high material porosity is addition of a pore-forming substance. Porosity (open and closed), pore size distribution, their size and shape, depend on the nature, amount, and morphology of pore-forming substance. In this article the effect is elucidated of three different types of carbon additives on porosity of ceramic prepared from clay and chemical binder precursor. Carbon materials are studied in an x-ray diffractometer. Ceramic material properties are studied using a mercury porosimeter, the Archimedes method, scanning electron and optical microscopes, and microcomputer tomography.
We report on the chemical design of chiral molecular junctions with stress‐dependent conductance, whose helicity is maintained during the stretching of a single molecule junction due to the stapling ...of both ends of the inner helix. In the reported compounds, different conductive pathways are observed, with clearly different conductance values and plateau‐length distributions, attributed to different conformations of the helical structures. The large chiro‐optical responses and the potential use of these molecules as unimolecular spin filters have been theoretically proved using state‐of‐the‐art Density Functional Theory (DFT) calculations, including a fully ab‐initio estimation of the CISS‐originating spin polarization which is done, for the first time, for a realistic molecular system.
A stapled chiral helical single‐molecule potentiometer based on ortho‐oligophenylethynylene skeleton is described. Its stretching during STM measurements promotes different conductive pathways, attributed to different conformations of the helical scaffold, while maintaining the helicity. State of the art calculations on polarization pave the way to use these structures as unimolecular spin filters.
In the Valleys of the Negro and Neuquén Rivers (North Patagonia, Argentina), different pesticides are applied to fruits in the fields as well as in the packing plants. Thiabendazole (2-(thiazol-4-yl) ...benzimidazole, IUPAC chemical name) is widely used as post-harvest fungicide on fruits before packing and transportation. The surplus from the packing plants reaches the Limay and Neuquén Rivers, through open channels thereby contaminating the water bodies. A regional montmorillonite, selected by its physicochemical properties and high degree of tetrahedral substitution, was used to adsorb thiabendazole in order to reduce toxicity to a reference value. The adsorption was followed by UV spectrophotometry (
λ=298 nm) using batch equilibration, under various sets of conditions established by varying the following parameters: contact time, adsorbate/adsorbent ratio, pH and ionic strength. Concerning adsorption mechanism, this was elucidated based on studies by infrared spectroscopy and X-ray diffraction analysis and determinations of cation exchange mechanisms.
Montmorillonite was able to completely remove the thiabendazole concentration found in industrial effluents. Moreover, no desorption was detected within 30 days after adsorption.
The production of n-type doped diamond has proved very difficult. Since boron, a shallow acceptor, can be passivated by hydrogen, it is possible that some of the difficulties in producing ...electrically active donors could be due to passivation by hydrogen which is present during the CVD growth of diamond. We report ab initio modelling of the interaction of hydrogen with boron, phosphorus and sulfur in diamond, and show that it is energetically favourable for hydrogen to bind to these centres and passivate them. We further investigated the possibility of the trapping of a second hydrogen atom at these centres, where we found that the complexes consisting of a dopant and two hydrogen atoms are energetically favourable for sulfur, with a binding energy similar to that found for H
2* in diamond.
The shallow n-type doping of boron doped diamond with an excess of deuterium has attracted considerable attention. However, despite numerous studies, the nature of this donor is the subject of ...continued debate.
We show that BH2 possesses a substantial number of metastable states, which are likely to play a role in the properties of the BH2 defect, and that it is possible in principle for these higher energy metastable structures to be reached. The levels induced by these metastable BH2 defects are shown to be shallower than the original deep BH2 levels, but still deeper than the experimentally observed donor levels.
We also report spin density distributions of BH2 centres, which may be compared with experiment, towards establishing the nature of the new donor.
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