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  • 1
    ISSN: 1432-0630
    Keywords: PACS: 72.20; 72.80; 78.65
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract  Fine-grained (d≈0.1 μm), polycrystalline SiC films were prepared on top of insulating and optically transparent sapphire substrates by means of a thermal crystallization technique. Optical absorption measurements indicate that the individual SiC grains consist of relatively defect-free β-SiC surrounded by high-defect density grain-boundary material. Nominally undoped material exhibits a low dc conductivity (σ≈10-8Ω-1 cm-1) in the dark and an efficient photoconductivity upon illumination with short-wavelength UV light. The temperature dependence of the dc transport exhibits a quasi-Arrhenius-type behaviour with average activation energies of the order to 0.6 eV. A characteristic feature of this kind of transport is a continuous increase in activation energy with increasing film temperature. Upon doping with N, P and Al ions, the average activation energy is decreased and room temperature conductivities of the order of 0.1 Ω-1 cm-1 are reached. Doping with B ions, on the other hand, only leads to high-resistivity material. It is shown that the electronic transport in doped SiC-On-Sapphire (SiCOS) films can be successfully modelled in terms of a grain-boundary-dominated conduction process. In this process thermal activation across potential barriers at the grain-boundary surfaces competes with tunneling through these same barriers.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-0495
    Keywords: Key words Heavy metals ; Sediment India
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  The concentrations of various metals (Cr, Cu, Co, Fe, Mn, Ni, Pb, Zn, and Cd) were determined in recently deposited surface sediments of the Gomati River in the Lucknow urban area. Markedly elevated concentrations (milligrams per kilogram) of some of the metals, Cd (0.26–3.62), Cu (33–147), Ni (45–86), Pb (25–77), and Zn (90–389) were observed. Profiles of these metals across the Lucknow urban stretch show a progressive downstream increase due to additions from 4 major drainage networks discharging the urban effluents into the river. The degree of metal contamination is compared with the local background and global standards. The geoaccumulation index order for the river sediments is Cd〉Zn〉Cu〉Cr〉Pb. Significant correlations were observed between Cr and Zn, Cr and Cu, Cu and Zn and total sediment carbon with Cr and Zn. This study reveals that the urbanization process is associated with higher concentrations of heavy metals such as Cd, Cu, Cr, Pb, and Zn in the Gomati River sediments. To keep the river clean for the future, it is strongly recommended that urban effluents should not be overlooked before their discharge into the river.
    Type of Medium: Electronic Resource
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