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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 2024-2032 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: It is shown that sp2 phase organization plays an important role in the field emission from nanostructured carbons. Emission is found to depend on the cluster size, anisotropy, and mesoscale bonding of the sp2 phase, and the electronic disorder. It is found by Raman spectroscopy that increasing the size of sp2 clusters in the 1–10 nm range improves emission. Anisotropy in the sp2 phase orientation can help or inhibit the emission. sp2 clusters embedded in the sp3 matrix or electronic disorder induced by localized defects oriented in the field direction can provide a local field enhancement to facilitate the emission. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 789-794 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The changes in the photoconductivity of hydrogenated tetrahedral amorphous carbon (ta-C:H) with nitrogen incorporation were studied. Low level nitrogen incorporation improves the photoconductivity, by shifting the Fermi level upwards in the band gap. Films with a photosensitivity of about 200 at room temperature under white light illumination of 35 mW/cm2 were obtained; thus is the highest value so far reported for diamond-like carbons. At high temperatures, photoconductivity is controlled by nonradiative recombination through gap states, whereas at low temperatures it occurs by energy-loss hopping in the band tails. Nitrogen addition does not create extra charge defect recombination centers. Low temperature photoconductivity allows the direct determination of the localization radius of the band tail states. This radius varies from 2–3 Å in ta-C:H to 9 Å in ta-C. This illustrates how hydrogen can increase state localization and the photoluminescence efficiency in amorphous carbons. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 6002-6010 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The work function of tetrahedral amorphous carbon (ta-C) has been measured by Kelvin probe to lie in the range 4–5 eV, irrespective of its sp3 content or nitrogen addition. This implies that the surface barrier to emission is dominant and that emission changes caused by sp3 bonding or nitrogen addition are not directly due to changes in work function. Hydrogen, oxygen, and argon plasma treatments are all found to increase the emission of a-C, but hydrogen and argon treatments are found to reduce the work function while oxygen treatment increases it. Detailed studies of the surface with varying plasma treatment conditions suggest that the changes in emission arise mainly from changes in the surface microstructure, such as the formation of sp2 regions within the sp3 bulk. The need for local field enhancement mechanisms to account for emission over the sizeable barrier is emphasized, which may arise from local chemical nonhomogeneity, or formation of nanometer-size sp2 clusters embedded in an sp3 matrix. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 84 (1998), S. 5575-5582 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The photoconductivity of tetrahedral amorphous carbon (ta-C) and hydrogenated tetrahedral amorphous carbon (ta-C:H) has been studied as a function of temperature, photon energy, and light intensity in order to understand the transport and recombination processes. ta-C and ta-C:H are found to be low mobility solids with μτ products of order 10−11–10−12 cm2/V at room temperature because of their relatively high defect densities. Deep defects tend to be the dominant recombination centers, but at high and moderate temperatures only a fraction of these centers or even tail states can act as recombination centers because the carrier demarcation levels do not always span the gap. For excitation by high energy UV photons, a peak in the photoconductivity is found at 200 K, similar to the thermal quenching effect found in a-Si:H, and attributed to competitive recombination between two classes of centers with very different capture cross sections. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 2627-2629 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electron field emission from amorphous carbon is found to depend on the clustering of the sp2 phase. The size of the sp2 phase is varied by thermal annealing and it dominates the effect of other parameters, such as chemical composition, surface termination, sp3 content, or conductivity. The optimum size of the sp2 phase is determined by Raman spectroscopy and is of the order of 1 nm. The field emission originates from the sp2 regions and is facilitated by the large field enhancement from more conductive sp2 clusters in an insulating sp3 matrix. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 2456-2458 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electronic applications of diamond-like carbon have been limited by its relatively high disorder and defect density. We find that the density of paramagnetic defects in hydrogenated tetrahedral amorphous carbon and the Urbach slope of the optical absorption edge can be reduced by annealing at 300 °C, with little effect on the optical gap. This leads to a reduction in the dark conductivity and an increase in the photosensitivity. The effect is attributed to the migration of hydrogen through the C–C network, to allow better passivation of dangling bonds and a modification of the more weakly bonded sp2 clusters with narrower local band gaps. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    International journal of biometeorology 34 (1991), S. 221-225 
    ISSN: 1432-1254
    Keywords: Phenology ; Birch ; Beech ; Oak ; Spruce
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
    Notes: Abstract The relation of first shoot emergence in various tree species (birch, beech, oak and spruce) to meteorological parameters was studied on the basis of phenological and meteorological observations at five locations in Slovenia during 1967–1986. A physical model was developed using tree branch temperature obtained by the energy balance equation. The gained linear dependence of first shoot emergence on effective tree branch temperature was compared with the results obtained by multiple regression analysis among first shoot emergence, effective temperature, global radiation, wind velocity and precipitation. A new method was developed to define the proper biological temperature threshold which was used for effective temperature calculations. Results of the physical model and of the multiple regression analysis are statistically significant and give similar correlations between first shoot emergence and meteorological parameters.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Journal of thermal analysis and calorimetry 15 (1979), S. 141-150 
    ISSN: 1572-8943
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Résumé On a étudié la décomposition thermique des copolymères binaires de l'acrylonitrile avec des quantités variables d'α-méthylstyrène (2–40%), àp=10−2−10−4 torr etT=0–600°. Les produits de décomposition (solides, liquides et gaz) ont été caractérisés par spectroscopie IR et UV, Chromatographie en phase gazeuse, osmométrie sous pression de vapeur et analyse élémentaire. Le méchanisme de décomposition a été établi à partir des résultats obtenus.
    Abstract: Zusammenfassung Die thermische Zersetzung der binären Kopolymere von Akrylnitril mit verschiedenen Mengen von α-Methylstyrol (2–40%) wurde beip=10−2−10−4 Torr undT=0–600° untersucht. Die Zersetzungsprodukte (Festkörper, Flüssigkeiten und Gase) wurden durch IR- und UV-Spektroskopie, Gaschromatographie, Dampfdruck-Osmometrie und Elementaranalyse charakterisiert. Der Zersetzungsmechanismus wurde an Hand der erhaltenen Ergebnisse bestätigt.
    Notes: Abstract The thermal decomposition of binary copolymers of acrylonitrile with variable amounts of α-methylstyrene (2–40%) has been studied atp=10−2−10−4 torr andT=0–600°. The decomposition products (solids, liquids and gases) have been characterized by IR and UV spectroscopy, gas chromatography, vapor pressure osmometry and elemental analysis. The decomposition mechanism has been ascertained on the basis of the obtained results.
    Type of Medium: Electronic Resource
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