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  • 1
    Electronic Resource
    Electronic Resource
    High-speed, low-noise metal–semiconductor–metal ultraviolet photodetectors based on GaN (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 762-764 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present the fabrication and characterization of nonintentionally doped GaN and GaN:Mg Schottky metal–semiconductor–metal (MSM) photodetectors, grown on sapphire by metalorganic chemical vapor deposition. Low-leakage, Schottky contacts were made with Pt/Au. The devices are visible blind, with an ultraviolet/green contrast of about five orders of magnitude. The response times of the MSM devices were 〈10 ns and about 200 ns for GaN and GaN:Mg, respectively. The noise power spectral density remains below the background level of the system (10−24 A2/Hz) up to 5 V, for the undoped GaN MSM detector. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.123303
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  • 2
    Electronic Resource
    Electronic Resource
    Band-gap narrowing and potential fluctuation in Si-doped GaN (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 102-104 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We investigate the optical properties of two sets of Si-doped GaN epitaxial layers with different degree of compensation. The electron concentration dependence of the band-gap energy measured by photoluminescence is interpreted as band-gap narrowing effect and evaluated by a simple relation. The photoluminescence peak positions of heavily compensated samples are shifted downward with respect to those of moderately compensated samples, and the down shift becomes larger at higher electron density. Based on analysis of photoluminescence spectra, these prominent behaviors are accounted for by band-edge potential fluctuation associated with inhomogeneous residual impurities. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.122964
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  • 3
    Electronic Resource
    Electronic Resource
    High-quality visible-blind AlGaN p-i-n photodiodes (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 1171-1173 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the fabrication and characterization of AlxGa1−xN p-i-n photodiodes (0≤x≤0.15) grown on sapphire by low-pressure metalorganic chemical vapor deposition. The devices present a visible rejection of six orders of magnitude with a cutoff wavelength that shifts from 365 to 338 nm. Photocurrent decays are exponential for high load resistances, with a time constant that corresponds to the RC product of the system. For low load resistances, the transient response becomes non-exponential, with a decay time longer than the RC constant. This behavior is justified by the strong frequency dependence of the device capacitance. By an admittance analysis, we conclude that speed is not limited by deep levels, but by substitutional Mg capture and emission time. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.123960
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  • 4
    Electronic Resource
    Electronic Resource
    Characterization of the progressive growth of columns by excimer laser irradiation of silicon (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 3303-3305 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The growth mechanism of columns produced by excimer laser irradiation of a silicon target is investigated. The micrometric columns are formed by a cumulative process with well-defined steps. The first steps lead to silicon hillocks, which evolve to columns through a little-understood mechanism. To investigate it, we irradiated a Si(100) single crystal in air with the necessary pulses of an excimer laser beam to obtain two samples, one with a partially and one with a fully developed column structure. Then we alternated scanning electron microscopy observations with irradiation pulses on the same target area. The progressive evolution of the laser-generated structures is presented. Columns grow at notably high rates, from around 0.5 μm/pulse during the early stages to 0.2 μm/pulse on average for 10–20 μm tall columns. The experimental results lead us to suggest a hydrodynamic growth mechanism. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.125332
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  • 5
    Electronic Resource
    Electronic Resource
    Kinetic aspects of the solid hydrogenation– disproportionation–desorption–recombination process in Nd13.67Co15.74Al0.77Ga0.27Zr0.03Fe62.2B7.33 alloys (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 84 (1998), S. 3786-3791 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The hydrogenation–disproportionation–desorption–recombination process is known as a novel method for producing permanent magnets. The hydrogen driven reactions involved in this process are carefully studied here using Mössbauer effect, x-ray diffraction and scanning microscopy, in the Nd13.67Co15.74Al0.77Ga0.27Zr0.03Fe62.2B7.33 alloy. The temperature dependence of the hydrogenation disproportionation in the 119 kPa isochore line was obtained. Hydrogen absorption seems to occur in two steps: absorption from Nd at the grain boundaries followed by absorption from the Nd2Fe14B type phase. In order to determine the recombination kinetics, a typical mass of the alloy was submitted to disproportionation reaction at 800 °C under a hydrogen pressure of 119 kPa, followed by recombination, which was achieved by vacuum desorption at 800 °C and subsequent quenching to room temperature after various time intervals. It was found that the relative fraction of the Nd2(Fe,Co)14B phase, as obtained from the Mössbauer effect, increases as f=1−exp(−ktn) with n=0.99±0.05. From this growing law it is inferred that recombination occurs without long range diffusion and starts at the grain boundaries with zero nucleation rate. An activation energy of 0.64±0.13 eV/atom was obtained for this process. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.368589
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  • 6
    Electronic Resource
    Electronic Resource
    The trophic role of lutjanid fish and impacts of their fisheries in two ecosystems in the Gulf of Mexico (1998)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 53 (1998), S. 0 
    Details
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The trophic role of snappers was evaluated on the continental shelves of the south-western Gulf of Mexico and the Yucatan in the south-eastern Gulf of Mexico. Mass-balanced, steady-state trophic models of the two ecosystems were constructed with Ecopath and perturbations were simulated in the ecosystems with Ecosim by increasing fishing mortality. Impacts were measured by changes in biomass of snappers and other groups, and in some indices of stability: persistence, recovery time and resilience. The snapper populations differed between ecosystems. The western Gulf of Mexico system appeared more complex and more stable than the Continental Shelf of Yucatan. Although overall stability indices between ecosystem suggested a similar structure and function, there were clear differences at a group level. Correlation of stability attributes between groups suggested differences in the role of snappers between the ecosystems suggesting that each stock should be managed individually.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1095-8649.1998.tb01024.x
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  • 7
    Electronic Resource
    Electronic Resource
    Energy flow and network analysis of Terminos Lagoon, SW Gulf of Mexico (1998)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 53 (1998), S. 0 
    Details
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The food web in Terminos Lagoon, south-western Gulf of Mexico was dominated by the detrital pathway, with benthic invertebrates playing a significant role in transferring energy from detritus to higher trophic levels. The fish yield per unit of net primary production was only 0.04%. Fractional trophic levels ranged from 1.0 to 3.31, with fish occupying the highest trophic levels. Using network analysis, the system network was mapped into a linear food chain and five discrete trophic levels were found with a mean trophic transfer efficiency of 7%. Analysis of mixed trophic impacts showed that fish had very little impact on the other compartments, due to their relatively low biomass and consumption, with exception of the Engraulidae. Detritus and lower trophic levels had significant positive impacts on other groups in the system, suggesting ‘bottom-up’ control of the food web. A high detritivory: herbivory ratio (4.6: 1) indicated that most of the primary production was recycled through the detritus-based food web. A Finn cycling index of 7% and average path length of 10 were obtained.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1095-8649.1998.tb01026.x
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  • 8
    Electronic Resource
    Electronic Resource
    Evaluation of the internalization process of the fish pathogen Renibacterium salmoninarum in cultured fish cells (1999)
    Oxford, UK : Blackwell Science Ltd
    Journal of fish diseases 22 (1999), S. 0 
    Details
    ISSN: 1365-2761
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2761.1999.00160.x
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  • 9
    Electronic Resource
    Electronic Resource
    The GTC: An Advanced 10m Telescope for the ORM (1998)
    Springer
    Astrophysics and space science 263 (1998), S. 355-360 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The Gran Telescopio CANARIAS (GTC) is a high performance 10-m class telescope whose construction has been promoted by the IAC (Instituto de Astrofísica de Canarias). It will be installed at the Roque de los Muchachos Observatory (ORM), in the island of La Palma. First light is planned for end-2002. The key science drivers for the project are image quality, operational efficiency and reliability, as emphasized in the Conceptual Design Document which was finished in mid-97. The Preliminary Design is now proceeding on all aspects of the project. The GTC Project is presently funded at the 70% level by Spain. The scientific drives behind the GTC project are described here, as well as the current technical, managerial, and operational baseline.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1002116107527
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  • 10
    Electronic Resource
    Electronic Resource
    Abundance of arbuscular mycorrhizal fungi spores in different environments in a tropical rain forest, Veracruz, Mexico (1999)
    Springer
    Mycorrhiza 8 (1999), S. 267-270 
    Details
    ISSN: 1432-1890
    Keywords: Key words Arbuscular mycorrhizae ; Tropical rain forest ; Gaps ; Mexico
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  The aim of this study was to compare mycorrhizal abundance and diversity in sites with different regimes of disturbance in a tropical rain forest at Los Tuxtlas, Veracruz, Mexico. Arbuscular mycorrhizal spores were quantified at two sites: closed canopy and gaps in the forest. Data were recorded during dry, rainy, and windy ("nortes") seasons. Spores of eight Glomus species, sporocarps of three Sclerocystis species, three species of Acaulospora and two of Gigaspora were found. Significant differences in the number of species and spores were found among seasons. The highest numbers of species and spores were observed during the dry season, with a marked decrease during the rainy season. Our results show that disturbance does not but seasonality does affect abundance and richness of mycorrhizal spores in this tropical wet forest.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s005720050244
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