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  • 1
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    Alternative view of Serengeti road (2010)
    Nature Publishing Group (NPG)
    Details
    Publication Date: 2010-10-15
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Homewood, Katherine -- Brockington, Daniel -- Sullivan, Sian -- England -- Nature. 2010 Oct 14;467(7317):788-9. doi: 10.1038/467788e.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/20944723" target="_blank"〉PubMed〈/a〉
    Keywords: Animal Migration ; Animals ; *Ecosystem ; *Environmental Policy ; Tanzania ; *Transportation
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 2
    Electronic Resource
    Electronic Resource
    Evaluation of silicon-on-insulator substrates using photoconductive frequency resolved spectroscopy (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 6754-6758 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We describe here the application of photoconductive frequency resolved spectroscopy to determine excess carrier lifetime distributions and carrier kinetics in SIMOX (separation by implanting oxygen) material. In order to evaluate the influence of the implant and anneal processes on the quality of the silicon overlayer we have also analyzed unprocessed bulk silicon, high temperature annealed bulk silicon and as-implanted SIMOX material. Our photoconductive frequency resolved spectroscopy results reveal that the SIMOX layers have a higher density of defects than standard device quality silicon substrates. Characteristic parameters of the dominant traps in these materials have been obtained from Arrhenius plots of the lifetime distributions. The defects found in these SIMOX layers are shown to be formed during the high temperature anneal stage of the material production.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355073
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  • 3
    Electronic Resource
    Electronic Resource
    The analysis of the temperature dependence of photoconductive frequency-resolved spectroscopy in the presence of carrier trapping: Application to polycrystalline silicon (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 2958-2964 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The analysis of photoconductive frequency-resolved spectroscopy is developed for variable temperature measurements. It is shown that when the excess carrier kinetics is dominated by carrier trapping the technique can be used to obtain the major trap parameters. This analysis is applied as an example to polycrystalline silicon on insulator on silicon films and a dominant trap with an activation energy of 70 meV is identified.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.354055
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  • 4
    Electronic Resource
    Electronic Resource
    Raman scattering and photoluminescence analysis of silicon on insulator structures obtained by single and multiple oxygen implants (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 1678-1683 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An analysis of silicon on insulator structures obtained by single and multiple implants by means of Raman scattering and photoluminescence spectroscopy is reported. The Raman spectra obtained with different excitation powers and wavelengths indicate the presence of a tensile strain in the top silicon layer of the structures. The comparison between the spectra measured in both kinds of samples points out the existence in the multiple implant material of a lower strain for a penetration depth about 300 nm and a higher strain for higher penetration depths. These results have been correlated with transmission electron microscopy observations, which have allowed to associate the higher strain to the presence of SiO2 precipitates in the top silicon layer, close to the buried oxide. The found lower strain is in agreement with the better quality expected for this material, which is corroborated by the photoluminescence data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349536
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  • 5
    Electronic Resource
    Electronic Resource
    Optical characterization of thermal mixing in quantum wells and heterostructures using a Green's function model (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 7581-7584 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We describe a simple Green's function model of interface mixing in quantum wells that provides exact quantitative solutions for real structures. Examples are given of several important low-dimensional heterostructures. The model enables the energy of the band-edge optical transition to be predicted as mixing proceeds, so that optical characterization techniques such as photoluminescence or absorption provide a powerful tool for studying mixing and obtaining interdiffusion constants.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347526
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  • 6
    Electronic Resource
    Electronic Resource
    The effects of ion implantation on the interdiffusion coefficients in InxGa1−xAs/GaAs quantum well structures (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 1686-1692 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Photoluminescence coupled with repetitive thermal annealing has been used to determine the diffusion coefficients for intermixing in InxGa1−xAs/GaAs quantum wells and to study the subsequent effects of ion implantation on the intermixing. It is shown that following ion implantation there is a very fast interdiffusion process, which is independent of the implanted ion and that is thought to be due to the rapid diffusion of interstitials created during the implantation. Following this rapid process, it was found that neither gallium nor krypton ions had any effect on the subsequent interdiffusion coefficient. Following arsenic implantation in addition to the initial damage related process, an enhanced region of interdiffusion was observed with a diffusion coefficient that was an order of magnitude greater than that of an unimplanted control wafer. This enhanced process is thought to be due to the creation of group III vacancies by the arsenic atoms moving onto group V lattice sites. This fast process was present until the structure had broadened by about 75 A(ring) when the diffusion coefficient returned to the unimplanted control value. The activation energy for the interdiffusion was measured over the temperature range 1050–750°C and a value of 3.7±0.1 eV was measured. This was found to be independent of the implanted ion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353204
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  • 7
    Electronic Resource
    Electronic Resource
    Interdiffusion in InGaAs/GaAs quantum well structures as a function of depth (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 3782-3786 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Interdiffusion in InGaAs/GaAs quantum wells has been studied using photoluminescence to follow the development of the diffusion with time in a single sample. Two distinct regimes are seen; a fast initial diffusion and a second steady-state diffusion. The steady-state diffusion was found to be dependent on the depth of the quantum well from the surface and to correlate with published data on the indiffusion of gallium vacancies into gallium arsenide.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352884
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  • 8
    Electronic Resource
    Electronic Resource
    The effects of silicon and beryllium on the interdiffusion of GaAs/ AlxGa1−xAs and InxGa1−xAs/GaAs quantum well structures (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 7715-7719 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effects of silicon and beryllium at doping levels of up to 1019 cm−3 on the interdiffusion of GaAs/AlxGa1−xAs and InxGa1−xAs/GaAs quantum wells after annealing have been studied using photoluminescence. It was found that for beryllium concentrations up to 2.5 ×1019 cm−3 and for silicon doping concentrations up to 1018 cm−3, no change in the interdiffusion coefficients could be measured. For a silicon doping concentration of 6×1018 cm−3 a dramatic degradation of the material quality was observed following annealing at 750 °C for 15 s. This resulted in the luminescence from the well disappearing and the appearance of deep level luminescence related to donor-gallium vacancy complexes and arsenic antisite defects. From these results we suggest that the position of the Fermi level plays no role in the intermixing of III-V heterostructures and that most of the enhanced intermixing observed in silicon-doped GaAs/AlxGa1−xAs structures is related to silicon relocation at very high doping levels.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353969
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  • 9
    Electronic Resource
    Electronic Resource
    Laminated gaskets for absorption and electrical measurements in the diamond anvil cell (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 5760-5763 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We have developed gaskets laminated from two layers of steel both for optical absorption and for electrical measurements in the diamond anvil cell. For absorption, these gaskets provide masking around the sample, avoiding the need for imaging of the gasket hole. For electrical measurements, laminated gaskets avoid the need for specially prepared diamonds as the feedthrough wires are not in contact with the anvils. Using argon as a pressure medium, both techniques have been used up to about 50 kbar at 300 and at 10 K.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143359
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  • 10
    Electronic Resource
    Electronic Resource
    Low temperature annealing of 4H–SiC Schottky diode edge terminations formed by 30 keV Ar+ implantation (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 3973-3977 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Edge termination of Schottky barrier diodes has been achieved using 30 keV Ar+ ions implanted at a dose of 1×1015 cm−2. The reverse-bias leakage current is reduced by 2 orders of magnitude following postimplant annealing at a temperature of 600 °C. The thermal evolution of the implantation induced defects was monitored using positron annihilation spectroscopy and deep-level transient spectroscopy. Two distinct defect regions are observed using the positron technique. The depth of the first is consistent with the range of the implanted Ar+ ions and consists of clustered vacancies. The second extends to ∼250 nm, well beyond the range of the incident ions, and is dominated by point defects, similar in structure to Si–C divacancies. An implant damage related deep level, well defined at Ec−Et=0.9 eV, is observed for both the as-implanted and the 600 °C annealed sample. The effect of annealing is a reduction in the concentration of active carrier trapping centers. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.372443
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