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  • 1
    Electronic Resource
    Electronic Resource
    Single-walled carbon nanotubes formation with a continuous CO2-laser: experiments and theory (2000)
    Springer
    Applied physics 70 (2000), S. 161-168 
    Details
    ISSN: 1432-0630
    Keywords: PACS: 81.05.Tp; 51.10.+y; 34.10.+x
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract. It has been proved [1] that the use of a CO2-laser system operating in continuous wave mode (cw) can be efficiently used for the production of carbon single-walled nanotubes (SWNTs). In this article we first describe in detail the variable experimental conditions (different ambient gases, static gas pressure, and gas flow) for SWNT formation and summarize the results of the characterization studies of the synthesized materials. Second, we analyze the influence of the different experimental conditions on the SWNTs formation process. We show that the heat transport, kinetic, and diffusion processes allow us to explain seemingly different formation conditions in a qualitative and semi-quantitative agreement with the experimental results. The presented self-consistent scenario for nanotube formation in a gas phase allowed us to propose future experiments on testing the mechanism of nanotube formation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003390050028
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  • 2
    Electronic Resource
    Electronic Resource
    Sulphydryl groups in intrinsic polypeptides of Micrococcus lysodeikticus membranes: Their role in protein transconformation during membrane solubilization (1979)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 6 (1979), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.1979.tb03711.x
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  • 3
    Electronic Resource
    Electronic Resource
    Analysis and modeling of AlxGa1−xN-based Schottky barrier photodiodes (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 2081-2091 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Schottky barrier photovoltaic detectors have been fabricated on n-AlxGa1−xN(0≤x≤0.35) and p-GaN epitaxial layers grown on sapphire. Their characteristics have been analyzed and modeled, in order to determine the physical mechanisms that limit their performance. The influence of material properties on device parameters is discussed. Our analysis considers front and back illumination and distinguishes between devices fabricated on ideal high-quality material and state-of-the-art heteroepitaxial AlxGa1−xN. In the former case, low doping levels are advisable to achieve high responsivity and a sharp spectral cutoff. The epitaxial layer should be thin (〈0.5 μm) to optimize the ultraviolet/visible contrast. In present devices fabricated on heteroepitaxial AlxGa1−xN, the responsivity is limited by the diffusion length. In this case, thick AlxGa1−xN layers are advisable, because the reduction in the dislocation density results in lower leakage currents, larger diffusion length, and higher responsivity. In order to improve bandwidth and responsivity, and to achieve good ohmic contacts, a moderate n-type doping level (∼1018 cm−3) is recommended. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1305838
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  • 4
    Electronic Resource
    Electronic Resource
    Ultraviolet electroluminescence in GaN/AlGaN single-heterojunction light-emitting diodes grown on Si(111) (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 1569-1571 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: GaN:Mg/AlGaN single-heterojunction light-emitting diodes were grown on Si(111) substrates by plasma-assisted molecular-beam epitaxy. High-quality Mg-doped GaN layers with hole concentrations up to 1.2×1017 holes/cm3 and intense low-temperature photoluminescence, which increases in annealed samples, were obtained. Smooth AlGaN layers, with surface roughness below 5 nm, were used as buffer layers. Continuous-wave room-temperature ultraviolet electroluminescence was observed at 365 nm with a full width at half maximum of 8 nm. An estimated optical power output of 1.5 μW was achieved under 15 V/35 mA operation. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.372052
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  • 5
    Electronic Resource
    Electronic Resource
    Effect of indium content on the normal-incident photoresponse of InGaAs/GaAs quantum-well infrared photodetectors (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 78 (2001), S. 2390-2392 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Longwavelength InGaAs/GaAs quantum-well infrared photodetectors with indium contents ranging from 25% to 40% have been grown and characterized. Material quality has been assessed by photoluminescence and transmission electron microscopy. Intersubband photocurrent, excited by polarized (TE or TM) infrared light, has been analyzed in order to determine the responsivity for normal-incident radiation. It is found that the TE to TM responsivity ratio is lower than 10% in all the samples studied. By changing the indium content from 25% to 40%, the increase in the TE to TM photoresponse ratio is as low as 3%. Our results are opposite to previous reports of experimental observation of significant TE-polarized light absorption. However, the low efficiency for normal-incident radiation agrees with various theoretical predictions. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1365951
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  • 6
    Electronic Resource
    Electronic Resource
    High visible rejection AlGaN photodetectors on Si(111) substrates (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 2785-2787 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on the fabrication and characterization of Schottky barrier photodetectors based on Si-doped Al0.35Ga0.65N layers grown on Si(111) substrates, for solar UV-band monitoring (λ〈320 nm). The epilayers have been obtained by plasma-assisted molecular-beam epitaxy, showing a full width at half maximum of 15 arcmin in x-ray diffraction measurements. A very high visible rejection (〉104) and a responsivity of 5 mA/W at 257 nm are reached. The detector time response is limited by the resistance×capacitance product, with a minimum time constant of 20 ns in the zero-load-resistance limit. After photodiode voltage breakdown, the effect on the detector response is discussed. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.126475
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  • 7
    Electronic Resource
    Electronic Resource
    Diameter distribution of single wall carbon nanotubes in nanobundles (2000)
    Springer
    The European physical journal 18 (2000), S. 201-205 
    Details
    ISSN: 1434-6036
    Keywords: PACS. 78.30.Na Fullerenes and related materials - 63.22.+m Phonons in low-dimensional structures and small particles
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: The frequency of the Raman active A1g radial breathing mode has been widely used as a tool to estimate the distribution of diameters of single wall carbon nanotubes (SWNT). However, the relation between frequency and diameter is not straightforward and results are model-dependent. Because most of the experiments are performed on bundles and not on isolated tubes, the model should especially take into account the van der Waals intertube interactions. Here, we use a pair-potential approach to account for such interactions and we derive a nonlinear relation between the SWNT diameter and the frequency of the A1g radial breathing modes. We demonstrate a good agreement between calculations and the diameters derived from diffraction experiments on the same samples.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100510070049
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  • 8
    Electronic Resource
    Electronic Resource
    Single-walled carbon nanotubes produced by cw CO2-laser ablation: study of parameters important for their formation (2000)
    Springer
    Applied physics 70 (2000), S. 145-151 
    Details
    ISSN: 1432-0630
    Keywords: PACS: 81.05.Tp; 81.10.Bk; 61.48.+c
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract. The production of single-walled carbon nanotubes (SWNTs) using the cw CO2-laser ablation technique is reported. Different metals and metal concentrations in the carbon targets as well as different buffer gases and gas pressures have been used in order to study their influence on the formation of SWNTs. It is shown that the conditions near the evaporation zone, i.e. especially the local temperature environment induced by the laser radiation as well as the used metals play a key role in the formation process of SWNTs. Employing a very simple experimental setup the cw CO2-laser ablation technique easily provides the environment favorable for the growth of high quality SWNT material under a wide range of experimental conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003390050026
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  • 9
    Electronic Resource
    Electronic Resource
    Coke formation on an industrial reforming Pt–Sn/γ‐Al2O3 catalyst (2000)
    Springer
    Catalysis letters 65 (2000), S. 209-216 
    Details
    ISSN: 1572-879X
    Keywords: coke formation ; industrial reforming catalyst ; Pt–Sn/γ‐Al2O3 ; coke characterization ; coke burning off
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The characterization of the coke deposited on an industrial Pt–Sn/γ‐Al2O3 catalyst, used in a continuous reforming process, was performed with AFM, XRD, FTIR, EPR, NMR, TG‐DTG and DTA techniques. Composition, structure and location of the coke on the catalyst were investigated. The coke was predominantly deposited on the catalyst surface and in the interstices between the catalyst particles. Its content increased along the reactor from top to bottom. Coke was deposited in the form of uniform films and clusters of three‐dimensional disks with diameters between 0.12 and 0.18 μm. It had a pseudo‐graphite structure produced by the dehydrogenation and polymerization of the aromatic precursor compounds. The coked catalyst showed a good combustion behavior; it was regenerated below 550°C. These results are important to elucidate the coke formation mechanism, to generate new continuous reforming catalysts, and to optimize the reactor operation parameters.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1019042027077
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  • 10
    Electronic Resource
    Electronic Resource
    Fitness effect analysis of a heterochromatic supernumerary segment in the grasshopper Eyprepocnemis plorans (2000)
    Springer
    Chromosome research 8 (2000), S. 425-433 
    Details
    ISSN: 1573-6849
    Keywords: Eyprepocnemis plorans ; fitness ; heterochromatin ; population dynamic ; supernumerary chromosome segment
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Several components of fitness were analysed in relation to the presence of a supernumerary chromosome segment (SCS) in two natural populations of the grasshopper Eyprepocnemis plorans, including clutch size, egg fertility, egg and embryo productivity and survivability from embryo to adult, and SCS transmission through males. The results have shown the absence of a significant relationship between SCS presence and these fitness components, with the single exception of egg fertility which decreases significantly in SCS females with mating shortage. This fertility decrease is thus expected to be relevant for the population dynamics of the SCS only in low-density populations, those in which it is difficult for females to find a male to copulate with before each egg-batch is ready to be laid. The analysis of the SCS transmission through males showed no significant differences between expected and observed SCS frequencies. The SCS polymorphism seems to be at a status close to neutrality in respect to fitness, but its slight disadvantage in transmission through females carrying B chromosomes predicts that the polymorphism should tend to disappear, unless SCS recurrent amplification, or another undiscovered force, counteracts this tendency.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009214904031
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