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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 2942-2950 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present a detailed study of the effects of ion bombardment on the optoelectronic properties of a-Si:H films. Two series of samples were deposited from a rf glow discharge at 30 and 100 mTorr of silane pressure, corresponding to two different deposition conditions. The energy of the ions impinging on the substrate was increased by applying a negative dc bias in steps of 25 V to the substrate holder. The increase of the substrate bias from 0 to −100 V had no effect on the deposition rate of a-Si:H at 30 mTorr, whereas a factor of 2 decrease was observed for deposition at 100 mTorr. The density of states of the a-Si:H films, determined by photothermal deflection spectroscopy and by the constant-photocurrent method, decreased as the substrate bias was increased up to −50 V, especially for the series deposited at 100 mTorr. At the same time the valence-band tail became sharper. These observations are consistent with the improvement of the electron drift-mobility deep-trapping-lifetime (μdτd)e product, determined by time-of-flight, and of the hole-mobility recombination-lifetime (μτr)h product determined from the voltage dependence of the photocurrent collection efficiency. For both series of samples, the films with the best electronic properties were obtained at a negative substrate bias of 50 V. No correlation was found between the substrate bias and the light-induced degradation behavior of these films. The saturated density of light-induced defects shows a direct correlation with the optical gap.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 7071-7077 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The photoelectron and Auger spectra of SiF4 have been measured, using synchrotron radiation in the 100 to 125 eV photon energy range in the vicinity of the Si2p ionization threshold. Partial photoionization cross sections have been obtained for outer, inner valence states and satellite states in the same energy range, together with the threshold photoelectron spectrum. At the energies of the discrete resonances observed below 112 eV, the core excited molecule is found to decay mostly by resonant Auger and to a small extent by autoionization. Among the resonant Auger pathways, those in which two electrons (rather than one) are ejected are found to play a dominant role. Above threshold, especially around the energy of the first continuum resonance, normal Auger processes are observed. Also, we offer a new interpretation of the Auger spectrum based on large configuration interaction in the final state and on the screening of the Si2p hole by the lone-pair electrons of the fluorine atoms. We also find some evidence of cascade Auger processes which explain the formation of triply ionized molecules.
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 7078-7086 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Partial ion yields from photoionization of SiF4 have been measured with time-of-flight mass spectrometry, photoion–photoion coincidence and triple photoion coincidence techniques using synchrotron radiation from 100 to 136 eV, in the region of the silicon 2p edge where strong resonances are found. From the photon energy dependence of positive ion pairs and of doubly charged fragment intensities, with a suitable normalization procedure, we have estimated the total double photoionization cross section. Below the Si2p edge, the double to single dissociative ionization branching ratio follows the resonance behavior, and is consistent with the photoelectron results of de Souza et al. (Paper I) and discussed in terms of multibond breaking dissociation pathways of residual excited ions (singly and doubly charged) produced by resonant Auger decay processes. Above the Si2p edge, the fragmentation is found to originate from dissociative double ionization occurring after normal Auger processes. The small additional contribution of triple dissociative ionization is consistent with a second order Auger process. In contrast, the underlying valence ionization continuum is responsible for all parent intensity and most of the SiF+3 fragment expected from the normal dissociative ionization channels. The measurement of appearance energies of fragment ion pairs by the photoion–photoion coincidence method, offers a direct measurement of the first direct double ionization onset in SiF4 and new values for other dissociative SiF2+4 states which complement those found by Auger spectroscopy.
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 2534-2540 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Fragmentation of N2O after selective core excitation of terminal and central nitrogen, has been studied by a multicoincidence technique (PEPIPICO) using synchrotron radiation. We show that dissociation dynamics is dependent upon the excited site, especially in the case of the "atomization'' of the molecule. The central nitrogen is always found with very little kinetic energy, except after Nt→Π* transition. A bent intermediate geometry is proposed to explain this observation.
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 317-320 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The metastability of the electronic properties of hydrogenated amorphous silicon (a-Si:H) films deposited at high rates by the rf glow discharge decomposition of mixtures containing 40% silane in helium is compared with that of device quality a-Si:H material deposited at 250 °C under standard low deposition rate conditions. The density of states above the Fermi level of the films obtained under helium dilution decreases for deposition temperatures increasing from 250 to 350 °C, both after annealing and after light soaking. At 350 °C, the density of states becomes comparable in both states to that of device quality low deposition rate a-Si:H. We observe a correlation between these results and the degradation of the photoconductivity and the below-Fermi-level defect density measured in situ during light soaking. © 1995 American Institute of Physics.
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  • 6
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: New experimental developments for high-resolution spectroscopy and dynamics studies of complex multi-ionized molecules are presented. Using photoion-photoion coincidence measurements in the doubly ionized C6F6 (hexafluorobenzene) molecule obtained with a conventional time-of-flight spectrometer and the ACO storage ring as an example, we demonstrate the importance of improving (i) the light source by using the new storage ring Super-ACO, (ii) the detection mode by using the photoelectron-photoion-photoion coincidence method, and (iii) the mass resolution of the spectrometer by constructing a reflectron time-of-flight mass spectrometer.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 3728-3737 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: In this article we describe the design and the operation of an original, high transmission, electrostatic "double toroidal" electron energy analyzer. The double toroidal analyzer allows the high resolution and high luminosity simultaneous measurement of the kinetic energy, and angular distribution of electrons, using a two-dimensional position sensitive detector. The exact shape of the electrodes is deduced from both analytical and numerical electron trajectory calculations. The electron detector is based on a charge analysis and optimized to attain a 100 kHz counting rate. The actual performances of the analyzer are illustrated with spectra obtained after resonant Auger decay of N2O excited around the nitrogen K shell (hν=401 eV), and of Kr after 3d5/2→5p excitation at hν=91.2 eV. A "étendue" of 15% of the pass energy, as well as a resolving power (Ep/δE) of 100were measured. © 1997 American Institute of Physics.
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 1554-1557 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An experimental setup is presented to measure coincidence spectra between a fluorescence photon (260 nm≤λph≤600 nm) and one or two photoions after core excitation providing information about the dissociation channels leading to excited, fluorescing states. The dissociation of ICN molecules excited in the iodine 4d shell is discussed. Upon resonant excitation the intensity due to the parent ion is found to be negligibly small and the atomic fragments comprise the most important part of the fluorescence intensity. For the first time coincidences between one photon and two photoions have been measured. In general, the observed mean slopes of the double coincidence peaks are consistent with photoelectron-photoion-photoion) measurements on ICN. In the I+/CN+ channel the singly charged iodine atom is found with relatively high percentage in a different excited state than in the I+/C+ or I+/N+ channels. © 1995 American Institute of Physics.
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  • 9
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 62 (1993), S. 2063-2065 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The results of a study of the kinetics of the light-induced annealing of defects in hydrogenated amorphous silicon (a-Si:H) are presented. Our results show that at temperatures between 92 and 152 °C illumination increases the rate of annealing compared to annealing in the dark. The rates of annealing in the dark and under illumination exhibit the same functional dependence on the defect density. This observation suggests that the mechanisms for "dark'' and "light'' annealing are identical.
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  • 10
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 998-1005 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Deexcitation electron spectra of core-excited NO have been measured at several excitation energies in the N 1s→2π and O 1s→2π resonances. The nitrogen spectra exhibit significant variation with excitation energy; the oxygen spectra vary only slightly. Sensitivity to excitation energy occurs because each resonance represents the overlap of three transitions to 2Σ+, 2Δ, and 2Σ− states, and each of these excited states decays to a unique set of levels in the final-state ion. We have analyzed all spectra by taking into account excitation energy, lifetime-vibrational interference, and the ordering and splitting of the core-excited levels. Good agreement between calculated line shapes and experiment occurs if it assumed that the level ordering is 2Δ, 2Σ−, 2Σ+ for core-excited nitrogen and 2Σ−, 2Δ, 2Σ+ for core-excited oxygen. Photoexcitation data for oxygen have been analyzed to determine the energies of these states 531.7, 532.7, and 533.7 eV. The deexcitation spectrum from the 2Δ state of nitrogen core-excited NO to the ground state of NO+ has been analyzed using the theory of lifetime-vibrational interference to give a lifetime width for the core-excited state of 146 meV. A similar analysis for the deexcitation of the oxygen core-excited state is less conclusive, but is consistent with a lifetime width of 180 meV.
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