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  • 1
    ISSN: 1432-0630
    Keywords: PACS: 61.48.+c; 81.70.Pg
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: 60 and produced by low-energy ion bombardment. The desorption properties of the films were studied as a function of the film thickness, ion energy, and ion dose. The results provide strong corroborative evidence for the endohedral nature of the Li-containing species and also clearly indicate the prescence of Li2@C60 in the films. The binding energy in these films is significantly larger than in pure C60 films and evidence of degradation of the fullerenes is seen at high ion energies and/or large ion doses.
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  • 2
    ISSN: 1434-6036
    Keywords: PACS. 79.60.Dp Adsorbed layers and thin films - 73.20.At Surface states, band structure, electron density of states - 73.61.Ph Polymers; organic compounds
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: Synchrotron radiation (SR) pulses are used to eject electrons from a gold substrate covered with organized organic thin films (OOTF) in order to investigate their transmission probability through the OOTF as a function of the electron initial kinetic energy. By variation of the SR photon energy within a few eV above the Au-4f binding energy levels we controlled the initial kinetic energy of the substrate electrons. The observed oscillations in the transmission probability for porphyrin-based films as a function of the kinetic energy is argued to be due to effects of band structure above the vacuum level in the well-ordered molecular adsorbate. We also present valence photoemission spectra (PES) of different type OOTF and demonstrate how their coverage of the substrate affects the PES.
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  • 3
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Photoemission from C60 chemisorbed on Ni(110) has been studied by one-photon photoelectron spectroscopy (1ppe) and two-photon photoelectron spectroscopy (2ppe) with synchrotron radiation (SR) and with synchronized SR and laser radiation. The 1ppe photoelectron spectra are studied as a function of C60 coverage. Significant peak broadening relative to the thick film features is observed for the three leading valence bands. The large peak width of the valence levels obtained for the monolayer system is consistent with changes of the physical structure of C60 due to the strong chemical interactions with the nickel substrate. The 2ppe experiment demonstrates transient excitation of the (t2u,hg) level of C60. © 1998 American Institute of Physics.
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  • 4
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Several monolayers thick hydrogenated carbon films, C:H, were prepared by ion beam deposition from hydrocarbon process gases onto Pt and monolayer C covered Pt single crystal surfaces and investigated with Auger electron and thermal desorption spectroscopies in an UHV environment. Efficient deposition was achieved at ion energies in the 160–300 eV range. The deposited thickness and H/C ratio of the films depend on both, target temperature and H/C ratio of the process gas. It is shown that the C monolayer is crucial for efficient on-top deposition. Irrespective of the process gas used for deposition, the films grow as a C network and assume a constant H/C ratio at thicknesses greater than ∼ 3 monolayers. The H/C ratio of the films scale with the H content of the hydrocarbon process gas, a H/C ratio of 0.4 was obtained for ethane at 350 K substrate temperature. Upon thermally activated decomposition the films release molecular hydrogen as the major gaseous species and various hydrocarbons as minority species. The latter products signal chemical erosion of the film. It is shown that the rate determining step towards erosion via methane is a C–C bond breaking event which releases methyl radicals from the C network in the film. The activation energies for this step are determined as a 10 kcal/mol wide Gaussian distribution centered at 56 kcal/mol. Transport through the film is found to be so fast that it does not contribute to the observed gas release rates. © 1995 American Institute of Physics.
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  • 5
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Few monolayers thick hydrogenated carbon films doped with boron (C/B:H) were prepared and investigated in an ultrahigh-vacuum environment by high-resolution electron energy loss, Auger electron, electron energy loss, and thermal desorption/decomposition spectroscopies with specific emphasis on their chemical erosion behavior as compared to their undoped C:H counterparts. Films of thicknesses ranging from 1 to about 10 monolayers, with a maximum B/C ratio of 0.5, were grown by ion-beam deposition at room temperature on a carrier consisting of a Pt(100) single-crystal surface covered with a graphite monolayer. The process gas used was a mixture of ethane and trimethylboron of varied compositions. While at zero boron concentration the films exhibit a graphiticlike structure with about equal amounts of carbon atoms in the sp2 and sp3 hybridization state, with increasing boron concentration the film structure becomes increasingly sp3 dominated. This is evidenced by decreasing HREELS loss intensities of the vibrational modes related to graphitic hydrogenated carbon, i.e., C=C, sp2 CH stretches, and aromatic CH deformations, but enhanced C–C and sp3 CHn stretch mode intensities. No BH vibrational modes have been observed at any doping level. In accordance with these observations, the C-272 eV Auger peak line shape underwent a change characteristic for a sp3-dominated network upon B doping. The π-plasmon energy was found to shift toward lower energies at C/B:H films which also is in line with a decrease of the carbon sp2 concentration, giving further support for a change to a less graphitic structure. The observed enhanced capacity for hydrogen in the films was found to correlate in a linear fashion with the increase of the fraction of carbon atoms in the sp3 configuration. The relative hydrogen content of the films, H/C, starting at 0.4 at zero boron content, was observed to increase, saturating at 0.75 for boron concentrations greater than 10%.This in turn coincides with a substantial growth of the film hydrogen capacity, as judged from the amount of H2 desorbing from the films between 500 and 1100 K upon thermal decomposition of the films. Although hydrogen originating from sp3 CH groups increased significantly, the amount of chemically eroded species, monitored by CnHm production in the thermal decomposition spectra, was unaffected by boron doping. However, the desorption maxima for either species, hydrogen and hydrocarbons, shift to lower temperatures at boron doped films. As reasons for the effect of B doping on the chemical constitution of C/B:H films and the resulting chemical erosion behavior, the capability of B to block the formation of aromatic structures is proposed. © 1995 American Institute of Physics.
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  • 6
    ISSN: 1573-7616
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract This report summarises and builds on the results of the “Directions and Methodologies for Empirical Software Engineering Research” group discussion. In particular, we considered the strengths, weaknesses, opportunities and threats to empirical software engineering research in light of the discussions and presentations during the workshop. The following sections describe each of these aspects of our discussion in turn. In addition, to finalise our discussion we agreed on a three-point plan for future work.
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  • 7
    Electronic Resource
    Electronic Resource
    Oxford : Blackwell Science Ltd
    Anaesthesia 53 (1998), S. 0 
    ISSN: 1365-2044
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Extravascular placement of a pulmonary artery catheter occurred when it was passed down an in situ sheath, the side arm of which had already been used for administration of fluids without any problems. The case emphasises that complications occur with the use of invasive monitoring and a correctly placed line may become extravascular even in a short time.
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  • 8
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 9179-9190 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The mechanism of thin film C60 laser desorption has been investigated using nanosecond and picosecond UV laser pulses. The desorption experiments were performed under ultrahigh-vacuum conditions using reflectron time-of-flight mass spectroscopy from which the velocity distributions of the desorbed ions and the dependence of the ion yield on the laser fluence were obtained. A strong nonlinear dependence of the desorption yield on laser fluence in the threshold region, indicative of a thermal mechanism, was found for both ns and ps pulses. Typically, the C+60 velocity distributions were bimodal and could be fitted by modified Maxwell–Boltzmann distributions. The fits to the slow contributions gave translational temperatures consistent with surface temperatures due to laser heating with ns pulses as estimated by solving the one-dimensional heat equation. In contrast, translational temperatures which are much too high to be consistent with purely thermal processes were obtained for the fast contributions. These fast contributions originate from different desorption mechanisms for the two different laser pulse lengths. © 1996 American Institute of Physics.
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