4,278 research outputs found

    Ferromagnetic Ga₁ˍₓ Mnₓ As produced by ion implantation and pulsed-laser melting

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    We demonstrate the formation of ferromagneticGa₁ˍₓMnₓAsfilms by Mn ion implantation into GaAs followed by pulsed-laser melting. Irradiation with a single excimer laser pulse results in the epitaxial regrowth of the implanted layer with Mn substitutional fraction up to 80% and effective Curie temperature up to 29 K for samples with a maximum Mn concentration of x≈0.03. A remanent magnetization persisting above 85 K has been observed for samples with x≈0.10, in which 40% of the Mn resides on substitutional lattice sites. We find that the ferromagnetism in Ga₁ˍₓMnₓAs is rather robust to the presence of structural defects.The work at the Lawrence Berkeley National Laboratory was supported by the Director, Office of Science, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, of the U.S. Department of Energy under Contract No. DE-AC03-76SF00098. The work at Harvard was supported by NASA Grant No. NAG8-1680. One of the authors ~M.A.S.! acknowledges support from an NSF Graduate Research Fellowship

    Synthesis and properties of Co-doped titanate nanotubes and their optical sensitization with methylene blue

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    Here we report on a novel chemical route to synthesize homogenous cobalt doped titanate nanotubes (CoTNT), using an amorphous Co-doped precursor. The influence of the synthesis temperature, autoclave dwell time and metal doping on the structural and microstructural as well as on the optical properties of the synthesized titanate nanotubes is studied and discussed. The optical band gaps of the CoTNT samples are red shifted in comparison with the values determined for the undoped samples, such red shifts bringing the absorption edge of the CoTNT samples into the visible region. CoTNT materials also demonstrate particular high adsorption ability for methylene blue, the amount of the adsorbed dye being higher than the one predictable for a monolayer formation. This suggests the possibility of intercalation of the dye molecule between the TiO6 layers of the TNT structure. It is also shown that the methylene blue sensitized Co-doped nanostructures are highly stable under UV radiation and present a strong and broad absorption in the visible region.Comment: 31 pages, 3 tables, 7 figure

    Hora da colheita: hora de cuidar do seu produto e de você. Estação de trabalho.

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    Na presente publicação, são apresentados um conjunto de equipamentos que facilitam e aumentam o rendimento das operações de colheita e beneficiamento de hortaliças. O conjunto é adequado para pequenas propriedades rurais onde não seja viável economicamente a construção de uma casa de embalagem de alvenaria, ou em propriedades maiores que precisem de uma infraestrutura de apoio junto à lavoura, para posterior remoção dos produtos colhidos para a casa de embalagem onde são executadas operações mais complexas de beneficiamento, embalagem e armazenamento.bitstream/item/120472/1/COT-101-X2-INTERNET.pd

    Synthesis of sub-5 nm Co-doped SnO2_2 nanoparticles and their structural, microstructural, optical and photocatalytic properties

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    A swift chemical route to synthesize Co-doped SnO2_2 nanopowders is described. Pure and highly stable Sn1x_{1-x}Cox_xO2δ_{2-\delta} (0 \le x \le 0.15) crystalline nanoparticles were synthesized, with mean grain sizes < 5 nm and the dopant element homogeneously distributed in substitutional sites of the SnO2_2 matrix. The UV-visible diffuse reflectance spectra of the Sn1x_{1-x}Cox_xO2δ_{2-\delta} samples reveal red shifts, the optical bandgap energies decreasing with increasing Co concentration. The Urbach energies of the samples were calculated and correlated with their bandgap energies. The photocatalytic activity of the Sn1x_{1-x}Cox_xO2δ_{2-\delta} samples was investigated for the 4-hydroxylbenzoic acid (4-HBA) degradation process. A complete photodegradation of a 10 ppm 4-HBA solution was achieved using 0.02% (w/w) of Sn0.95_{0.95}Co0.05_{0.05}O2δ_{2-\delta} nanoparticles in 60 min of irradiation.Comment: 29 pages, 2 tables, 10 figure
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