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Effect of Annealed (0001) α-Al_2O_3 Surfaces on Heteroepitaxial Growth of Silver Nanoparticles

100%
Al-Mohammad A.
Acta Physica Polonica A
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2009
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vol. 115
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issue 3
679-684
EN
The effect of annealed (0001) α -Al_2O_3 surfaces on heteroepitaxial growth of silver nanoparticles were analysed by reflection high-energy electron diffraction, transmission electron microscope and selected area electron diffraction. Ag nanoparticles were deposited on 1× 1 stoichiometric and reconstructed (111)Al//(0001) α -Al_2O_3 with the Knudsen cell. The maximum cluster density method and the Lifethenz theory of Van der Waals energy were used to investigate the Ag//(0001)α -Al_2O_3 interface parameters. The growth modes, lattice parameters, nanoparticle forms and sizes are strongly dependent on the substrate surface structures. Initially, three-dimensional islands of Ag nanoparticles grow on both kinds of surfaces with partial hexagonal shapes. Ag nanoparticles on stoichiometric surface create the (111)Ag//(0001)α -Al_2O_3 interface without any preferred epitaxial direction. On this surface, Gaussian distribution is characteristic of an atom-by-atom growth mode with density of Ag nanoparticles lower than saturation density while a coalescence growth mode appears due to binary collisions between Ag nanoparticles accompanied by a liquid-like behaviour after saturation density. In case of reconstruction substrates, the epitaxial relationships between Ag nanoparticles and the surface are formed (111)Ag//(0001)α -Al_2O_3, 〈01\bar(1)〉Ag//[12\bar(3)0]α -Al_2O_3 or 〈01\bar(1)〉Ag//[1\bar(1)00]α-Al_2O_3. The Ag nanoparticles make rotation with angles between ± 6° around the epitaxial orientations 〈1\bar(1)00〉 or 〈12\bar(3)0〉. Only the atom-by-atom growth mode were found at all Ag nanoparticles growth processes.
2
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ZnO Nanopowders as Chemical Sensor to Malathion Vapor

45%
Al-Mohammad A., Darwich R., Rukiah M., Abo Shaker S., Kakhia M.
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vol. 125
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issue 1
131-134
EN
Thick films of zinc oxide (ZnO) nanopowders have been prepared by high energy ball-milling for various spans of mill time (3-18 h). The morphology and crystal structure of the prepared ZnO powder were characterized by scanning electron microscope and X-ray diffraction. The ZnO thick films were then used to construct a gas sensor for O,O-dimethyl dithiophosphate of diethyl mercaptosuccinate (malathion) at different operating temperatures. The sensor response at 100 ppm of malathion was found to reach a maximum as large as 80 at 6 h of high energy ball-milling, four times larger than that found for ethanol. Scanning electron microscope observation of the granular state and pore size distribution analyses indicated that increasing high energy ball-milling time gave rise especially to an increase in the volume of pores in the pore size range of 6-35 nm. It is suggested that such a change in nanostructure is responsible for the marked promotion of the response to malathion.
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