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  • 1
    ISSN: 1432-0630
    Keywords: PACS: 68.55.Jk; 68.55.Nq; 81.60.Bn
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: At 300 K, an amorphous Al-oxide film is formed on NiAl(001) upon oxygen adsorption. Annealing of the oxygen-saturated NiAl(001) surface to 1200 K leads to the formation of thin well-ordered θ-Al2O3 films. At 300 K, and low-exposure oxygen atoms are chemisorbed on CoGa(001) on defects and on step edges of the terraces. For higher exposure up to saturation, the adsorption of oxygen leads to the formation of an amorphous Ga-oxide film. The EEL spectrum of the amorphous film exhibits two losses at ≈400 and 690 cm-1. After annealing the amorphous Ga-oxide films to 550 K thin, well-ordered β-Ga2O3 films are formed on top of the CoGa(001) surface. The EEL spectrum of the β-Ga2O3 films show strong Fuchs-Kliewer (FK) modes at 305, 455, 645, and 785 cm-1. The β-Ga2O3 films are well ordered and show (2×1) LEED pattern with two domains, oriented perpendicular to each other. The STM study confirms the two domains structure and allows the determination of the two-dimensional lattice parameters of β-Ga2O3. The vibrational properties and the structure of β-Ga2O3 on CoGa(001) and θ-Al2O3 on NiAl(001) are very similar. Ammonia adsorption at 80 K on NiAl(111) and NiAl(001) and subsequent thermal decomposition at elevated temperatures leads to the formation of AlN. Well-ordered and homogeneous AlN thin films can be prepared by several cycles of ammonia adsorption and annealing to 1250 K. The films render a distinct LEED pattern with hexagonal [AlN/NiAl(111)] or pseudo-twelve-fold [AlN/NiAl(001)] symmetry. The lattice constant of the grown AlN film is determined to be aAlN= 3.11 Å. EEL spectra of AlN films show a FK phonon at 865 cm-1. The electronic gap is determined to be Eg= 6.1±0.2 eV. GaN films are prepared by using the same procedure on the (001) and (111) surfaces of CoGa. The films are characterized by a FK phonon at 695 cm-1 and an electronic band gap Eg= 3.5±0.2 eV. NO adsorption at 75 K on NiAl(001) and subsequent annealing to 1200 K leads to the formation of aluminium oxynitride (AlON). An oxygen to nitrogen atomic ratio of ≈2:1 was estimated from the analysis of AES spectra. The AlON films shows a distinct (2×1) LEED pattern and the EEL spectrum exhibits characteristic Fuchs-Kliewer modes. The energy gap is determined to be Eg= 6.6±0.2 eV. The structure of the AlON film is derived from that of θ-Al2O3 formed on NiAl(001).
    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 108 (1998), S. 2251-2260 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The growth and structure of solid nitrogen films on Ag(110) at 15 K was investigated by means of high resolution electron energy loss spectroscopy (EELS), thermal desorption spectroscopy (TDS), and low energy electron diffraction (LEED). The N2 film exhibits a parallelogram structure in the monolayer. For the bilayer and multilayers an incoherent hexagonal structure has been found. The dynamics of the resonant vibrational excitation of the N2 molecule via the 2Σu resonance is studied in detail both by the EELS method (as a function of the surface coverage) and theoretically. This allows a discussion of the effect of the adsorption on the vibrational excitation process and, in particular, on the overtone excitation. The 2Σu resonance excitation process is found to be almost not influenced by the adsorption in strong contrast with the case of the low energy (2Πg) N2 resonance. The differences between these two processes are discussed. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 7459-7466 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The adsorption and reactions of NO on NiAl(111) at 75 K were studied by high resolution electron energy loss spectroscopy, temperature programmed desorption, Auger electron spectroscopy, and low energy electron diffraction. At low exposure (≤1 L), NO mainly adsorbs molecularly on top in an upright geometry on Ni atoms. Simultaneously, a small amount of NO dissociates. Higher exposures (≥2 L up to saturation) lead to the formation of a thin amorphous Al-oxynitride (am-ALON) film. In the presence of am-ALON, a molecular adsorption of NO on am-ALON sites and/or in the neighborhood of ALON islands is observed. Besides the upright geometry, NO molecules are adsorbed in disarranged (bent or tilted) configurations. The growing am-ALON film acts as a catalyst for the reduction of NO to N2O. Substantial amounts of N2O are formed for NO exposures higher than 5 L, and are coadsorbed molecularly. The main thermal desorption products are N2O, N2, and NO. For an exposure of 20 L NO, the ratios of the amounts of desorbing molecules are: N2O:N2:NO=1:0.43:0.36. It could be shown that the N2 signal is due to a recombinative desorption of adsorbed nitrogen atoms. © 1997 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 77 (1995), S. 5718-5724 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The formation of thin AlN films on NiAl(001) has been studied by means of high resolution electron energy loss spectroscopy (HREELS), low-energy electron diffraction (LEED), and Auger electron spectroscopy. The AlN films were grown by the adsorption of NH3 on NiAl(001) at T=80 K and subsequent thermal decomposition at elevated temperatures. After annealing to T=1250 K, a distinct LEED pattern appears which exhibits pseudo-twelvefold symmetry. This indicates the formation of two hexagonal domains of AlN which are rotated by 90° with respect to each other. HREEL spectra of the ordered AlN film show a Fuchs–Kliewer phonon mode at 865 cm−1 in good agreement with theoretical spectra calculated on the base of the dielectric theory. The electronic energy gap of the thin AlN films is determined to be Eg(approximately-equal-to)6.1 eV. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 6467-6473 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We deal with the formation of thin aluminum oxynitride (AlON) layers after adsorption of nitric oxide (or coadsorption of oxygen and ammonia) on NiAl(001) at 75 K and subsequent annealing at 1200 K. The adsorption of NO and formation of the AlON films are investigated by means of high-resolution electron energy loss spectroscopy (HREELS), low-energy electron diffraction (LEED), and Auger electron spectroscopy (AES). The AlON film shows a distinct (2×1) LEED pattern and the HREEL spectrum exhibits five loss peaks. An oxygen to nitrogen atomic ratio of (approximately-equal-to)2 has been estimated from the AES analysis. The energy gap is determined to be Eg=6.6±0.2 eV. The structure of θ-AlON is derived from that of θ-Al2O3. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Nuclear Instruments and Methods in Physics Research Section A: 350 (1994), S. 327-337 
    ISSN: 0168-9002
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1434-601X
    Keywords: 25.55.−e
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Cross section measurements of thed(3He,p)4He reaction have been extended to an energy as low asE cm =5.4 keV. The data have an improved accuracy compared with previous work and confirm the existence of electron screening. The combined analysis of the present and previous data leads to an electron screening potential ofU e =123 ± 9 eV. A similar analysis of previous data for3He(d, p)4He leads toU e =186 ± 9 eV. Both screening potentials differ due to the molecular and atomic aggregate state of the targets involved in these investigations and are significantly larger than expected from available atomic physics models, supporting the general trend in studies of electron screening.
    Type of Medium: Electronic Resource
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