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  • Articles: DFG German National Licenses  (46)
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  • Articles: DFG German National Licenses  (46)
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  • 1
    Electronic Resource
    Electronic Resource
    Electron-stimulated desorption of positive and negative oxygen ions from YBa2Cu3O7 surfaces (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 6858-6860 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electron-stimulated desorption of positive and negative oxygen ions from YBa2Cu3O7 surfaces has been studied as a function of electron kinetic energy in the 70–600 eV range. It has been found that the threshold electron kinetic energy needed to induce positive oxygen ion desorption occurs at 260±5 eV, whereas that associated with negative oxygen ion desorption was found to be 100±5 eV. These electron kinetic energies correspond to Cu, Y, and Ba core-level binding energies. These results suggest that negative and positive oxygen ion desorption may be initiated via a primary core level ionization. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360450
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Growth of Zn δ-doped AlxGa1−xAs by low pressure metal organic vapor phase epitaxy (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 3546-3548 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A very significant Zn evaporation from nongrowing AlxGa1−xAs surface during a post-δ-doping purge step was observed in growth of Zn δ-doped AlxGa1−xAs (x〈0.65) by low pressure metal organic vapor phase epitaxy using dimethylzinc as a doping precursor. A δ-doping sequence different from the normal "purge-doping-purge'' is therefore proposed to minimize the Zn evaporation. Using this δ-doping sequence, the dopant memory effect was investigated and the best hole profile of Zn δ-doped GaAs (Al0.35Ga0.65As) was obtained, having a full width at half-maximum of 7.0 nm for a peak concentration of 1.1×1020 cm−3 (13 nm for 4.8×1018 cm−3). It was found that the growth temperature significantly influences the hole concentration of Zn δ-doped GaAs and the hole concentration decreases and the hole profile width increases with increasing Al content of Zn δ-doped AlxGa1−xAs. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359930
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  • 3
    Electronic Resource
    Electronic Resource
    Surface recession and oxidation of silicon during bombardment by low energy oxygen ions (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 3831-3834 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Vertical expansion of a silicon surface bombarded by 10 keV O+ ions is demonstrated using surface stylus profilometry. The surface expands gradually as the incorporated oxygen concentration increases, and a maximum is obtained when the bombardment dose reaches the critical one for formation of a continuous surface layer of SiO2. Through a combination of crater depth measurements and chemical etching the surface recession and the incorporation of oxygen are monitored as a function of bombardment dose. Comparison is made with calculations based on a model where simultaneous sputter erosion and surface swelling are taken into account. The surface swelling is assumed to be proportional to the retained oxygen dose. Experimentally determined sputtering yields are utilized in the calculations, and good agreement is shown with the measured data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357386
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  • 4
    Electronic Resource
    Electronic Resource
    Very high carbon δ -doping concentration in AlxGa1−xAs grown by metalorganic vapor phase epitaxy using trimethylaluminum as a doping precursor (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 3554-3559 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using trimethylaluminum (TMAl) or trimethylgallium (TMGa) as a doping precursor, carbon δ-doped AlxGa1−xAs has been grown in metalorganic vapor phase epitaxy. Compared to TMGa, TMAl exhibits very high carbon δ-doping efficiency. The best hole profile of carbon δ-doped Al0.3Ga0.7As grown at 580 °C using TMAl as a doping precursor has a peak hole density of 1.6×1019 cm−3 for a full width at half-maximum of 85 A(ring) with most of the incorporated carbon atoms being electrically active. When TMGa is used as the doping precursor, the hole density of carbon δ-doped AlxGa1−xAs significantly increases with an increase of the Al mole fraction. By comparison, the use of TMAl almost induces independence of the hole density on the Al mole fraction. The hole density of carbon δ-doped Al0.3Ga0.7As weakly increases when reducing the δ-doping temperature regardless of the doping precursors. The hole density of carbon δ-doped Al0.3Ga0.7As grown at 580 °C is proportionally associated with the moles of TMGa or TMAl totally input during a δ-doping step. Using heavily carbon δ-doped layers in Al0.3Ga0.7As, a carbon δ-doped pipi doping superlattice possessing a bulk-doped-like hole profile with an average hole density of 1.1×1019 cm−3 is therefore demonstrated as an alternative with unique advantages over other conventional carbon bulk-doping approaches. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361377
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  • 5
    Electronic Resource
    Electronic Resource
    Oxidation of silicon by low energy oxygen bombardment (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 1840-1846 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High resolution Rutherford backscattering and channeling has been used to study the formation of surface oxides during room temperature bombardment of silicon with oxygen in a secondary ion mass spectrometry system. Stoichiometric SiO2 is formed at angles of incidence (to the surface normal)≤25° and the angular dependence is adequately modeled using the profile code. A linear dependence of oxide thickness on energy is obtained in the energy range 3–40 keV (per oxygen ion) and this is consistent with trim code calculations. The suboxide damage has also been measured and studied during annealing. Our data are consistent with a simple model of oxygen build up and formation of strong Si–O bonds during room temperature bombardment. Once a buried SiO2 layer is reached and Si bonds are saturated, oxygen can migrate in SiO2 to extend the oxide towards the surface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357704
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  • 6
    Electronic Resource
    Electronic Resource
    Isotope effects for mega-electron-volt boron ions in amorphous silicon (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 4836-4840 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The depth profiles of 10B and 11B implanted into amorphous silicon have been analyzed by secondary ion mass spectrometry. Implantation energies between 0.4 and 5.0 MeV were used, and each sample was sequentially implanted with both 10B and 11B without changing the acceleration voltage but only the field in the mass analyzing magnet. A shift between the two profiles is clearly resolved and has been carefully studied as a function of ion energy. A maximum shift of 3.5% in mean projected range (Rp) is revealed at 0.6–0.8 MeV [Rp(11B)≥Rp(10B)], and for higher energies the ratio Rp(11B)/Rp(10B) decreases slowly to a value of ∼1.006 at 5.0 MeV. This reverse shift (heavier isotope penetrates deeper) is attributed to a larger electronic stopping cross section (Se) for 10B than for 11B at a given energy E where Se∼Ep and p≥0. The experimental data for Rp(11B)/Rp(10B) and Rp(11B) are compared with calculations, and it is demonstrated that the variation of Rp(11B)/Rp(10B) with ion energy hinges strongly on the Se vs E dependence. A close velocity proportional dependence (p=0.50±0.03) is found to be valid up to ∼300 keV, and then p decreases gradually with a maximum in Se (p=0) at ∼2.0 to 2.5 MeV. A semiempirical expression is presented for Se and shown to yield excellent agreement with both the relative isotope shift and the absolute range values; the deviations are less than 0.2% and 3.0%, respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353798
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  • 7
    Electronic Resource
    Electronic Resource
    High dose, heavy ion implantation into metals: The use of a sacrificial carbon surface layer for increased dose retention (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 4014-4019 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ion implantation into metals has the potential of producing metastable compounds and solutions that cannot be achieved using conventional processing methods. However, when high doses of heavy ions into metals are necessitated, the technique is often limited by sputtering effects which dictate a maximum achievable implanted ion concentration in the target. Sputtering of light materials (such as C) by heavy ions is much less significant, however. This study investigates the feasibility of "protecting'' a metal target surface from sputtering during a heavy ion implant by using a thin "sacrificial'' C layer deposited on the target surface. Uncoated and C-coated (∼1000-A(ring)-thick C) Cu targets were bombarded with 600–1000 keV I− ions to a total dose of ∼2×1017 I/cm2. Uncoated samples displayed typical saturation behavior, retaining between 17% and 42% of the dose, depending on the energy. The maximum I concentration achieved in the uncoated samples was about 6 at. %. Excellent results were achieved with the C-coated samples, with retentions of 100% and peak I concentrations between 18 and 33 at. %. Significant mixing of C was found to occur at the C/Cu interface, however as the implantation energy was increased the I concentration profile shifted more deeply into the sample and away from the mixed C/Cu region. This suggested that higher energies and careful tailoring of the implant parameters can eliminate any problems with C mixing.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352254
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  • 8
    Electronic Resource
    Electronic Resource
    Conductivity in insulators due to implantation of conducting species (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 3841-3845 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Control of the surface conductivity of insulators can be accomplished by high dose ion implantation of conductive species. The use of C+ as the implant species is particularly interesting because C can either form electrically insulating sp3 bonds or electrically conducting sp2 bonds. In the present work, fused quartz plates have been irradiated with 100 keV C+ ions to doses up to 1×1017 ions/cm2 at room temperature and at 200 °C. The ion beam induced conductivity was monitored in situ and was found to increase by up to 8 orders of magnitude for the ion dose range studied. Xe implantations over a similar range did not induce any changes in the conductivity showing that the increase in conductivity is caused by the presence of the C in the fused quartz matrix and not by damage. The conductivity, σ, is found to vary with dose D as log σ∝D−1/3 over a wide dose range, strongly supporting a hopping model for the conduction mechanism. The dependence of the conductivity on implantation temperature and on post-implantation annealing sheds light on the clustering of the C implants. The temperature dependence of the conductivity for the highest doses employed (1×1017 C+/cm2) can be described very well by ln σ∝T. This is a peculiar dependence which does not comply with any of the standard models for conduction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352893
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  • 9
    Electronic Resource
    Electronic Resource
    Simulation of ultrahigh recycling divertors for tokamaks (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 2207-2212 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The handling of power carried by the charged particles into the scrape-off layer of a tokamak reactor remains a major obstacle for its continuous and reliable operation. Ways of reducing this power through radiation have been studied numerically using fluid models for both the plasma and neutral gas. A new model for the combined plasma and neutral gas transport in two dimensions capable of simultaneously representing regions of fully ionized plasma, partially ionized plasma, and pure neutral gas has been assembled and implemented in the planet code [J. Nucl Mat. 196/198, 883 (1992)]. Divertor plasma temperatures of just below 1 eV have been achieved in a pure hydrogen plasma, resulting in an ionization-free region together with ionization and recombination fronts detached from the material walls. In this regime energy reaches the walls almost exclusively in the form of radiation which, in principle, solves the divertor heat load problems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870620
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  • 10
    Electronic Resource
    Electronic Resource
    Selectivity of nanocavities and dislocations for gettering of Cu and Fe in silicon (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 78 (2001), S. 2682-2684 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The selectivity of interstitial-based extended defects (loops) and nanocavities for the gettering of Cu and Fe in Si has been studied. Controlled amounts of Cu and Fe were introduced by ion implantation into wafers containing pre-existing nanocavities and/or dislocations. Results show that Cu has a strong preference for gettering to open volume defects, even when high concentrations of interstitial-based loops are present in close proximity. However, the gettering of Fe in samples containing both vacancy- and interstitial-type defects is more complex, with Fe accumulation at all regions in the sample which contain defects, whether they are vacancy- or interstitial-like in character. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1363689
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