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  • 1
    ISSN: 1432-0630
    Keywords: 61.10.-i ; 78.55.-m ; 72.80.Ey
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract ZnSe films were grown by chemical vapour deposition on GaAs substrates. The influence of the source temperature (between 820 and 900° C) and the substrate temperature (between 620 and 790° C) on the film properties were investigated by Hall measurements, X-ray diffraction, and photoluminescence. With respect to blue luminescent devices the ratio of excitonic to deep level transitions was found to be optimum at low growth rates when the source temperatures were kept below 840° C. P-type conduction up to a net carrier concentration of 8×1018 cm−3 could be obtained by substrate temperatures above 700° C. Lattice contraction versus substrate temperature pointed to a reduced incorporation of donors at higher growth temperatures.
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  • 2
    ISSN: 1432-0630
    Keywords: 07.60.Pb ; 07.65.Eh ; 78.65-s
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Opaque samples are imaged by Scanning Nearfield Optical Microscopy (SNOM) in reflection mode: A quartz glass fiber tip is used both to illuminate the sample and to collect light locally reflected from or emitted by the surface. The collected light is coupled out by a 2×2 fiber coupler and fed into a grating spectrometer for spectral analysis at each sampled point. The tip-sample distance is controlled by a shear-force feedback system. The simultaneous measurement of topography and optical signals allows an assessment of imaging artifacts, notably topography-induced intensity changes. It is demonstrated that an optical reflectance contrast not induced by topographic interference can be found on suitable samples. Local spectral analysis is shown in images of a photoluminescent layer.
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  • 3
    ISSN: 1432-0630
    Keywords: 68.65 ; 79.60
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract In this work we present a systematic study of the local photovoltaic properties of ReS2, using a scanning tunneling microscope (STM). The tunneling junction of the STM was optically illuminated during the tunneling process. The phase sensitive detected photo-induced tunneling current (PITC) was studied as a function of wavelength and surface topography. In order to improve the performance of ReS2 solar cells, the samples were treated with NaI/I2 and EDTA solutions. Relative to the untreated sample, the EDTA-treated samples show an increase in the photo-induced tunneling current by a factor of 8–10 in the whole spectral range, the NaI/I-treated samples by 2–3. Two dimensional mapping of the PITC was performed on an atomic scale and compared to the surface topography.
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  • 4
    ISSN: 1434-601X
    Keywords: 21.10.−k ; 27.20.+n ; 25.70.Np ; 21.10.Re
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Total charge-changing cross sections have been measured for8Li on C and Pb targets, for9Li on C, Al, Cu, Sn and Pb targets, as well as for11Li on C, Sn and Pb targets at about 80 MeV/nucleon. These data are compared to measured total reaction cross sections and Glauber-type calculations using Hartree-Fock density distributions. These comparisons allow to draw conclusions on the proton density distribution of the neutronrich lithium isotopes. The results show that even for the most exotic nucleus11Li the proton distribution is only very weakly influenced by the long tail in the neutron density distribution already established in several experiments.
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  • 5
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In CSFeBr3 the Fe2+ ion with effective spin one has locally a singlet ground state (m=0). The antiferromagnetic interactions between neighbouring Fe-ions are too weak as compared with the anisotropy constant to introduce long range order in the absence of an external field. By inelastic neutron scattering we studied the magnetic excitations in an external magnetic field up to 5 Tesla applied along thec-axis. A linear Zeeman splitting was observed with a Landé factorg=2.4. The field renormalizes the dispersion curves in such a way that the exchange interaction has decreasing influence with increasing field. Theoretical calculations according to the excitonic model of Lindgård describe the experimental results very well. At 4.1 Tesla a phase transition appears to a commensurate long range order with a 120° arrangement of the spins in the hexagonal plane. Within the limits of experimental observation this phase transition has no influence on the dynamical behaviour. No critical phenomena could be observed. The dynamical structure factor |G j(ℚ)|2 of the lower Zeeman split modes decreases with increasing field.
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  • 6
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The spin hamiltonian for nuclear magnetic order in copper is investigated with respect to magnetoelastic couplings to the lattice. These arise due to the dipolar, Ruderman Kittel and the quadrupolar interaction. While the latter is quenched for the ideal fcc-lattice, it is found that for copper it will dominate the magnetoelastic terms of the nuclear spin hamiltonian. The absolute size of the quadrupole contribution is determined by the effective charge and (anti-) shielding effects. This interaction can give rise to an effective anisotropy in the fcc-system which can be quite large compared to the small stabilisation energies for nuclear order in copper. Consequences for the nuclear ordering in copper are briefly discussed and compared to the available experimental and theoretical data.
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  • 7
    ISSN: 1434-6036
    Keywords: 75.10.Dg ; 75.25.+z ; 75.30.Et
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In CsFeCl3 the Fe2+-ion with effective spin one has locally a singlet ground state (m s =0). The ferromagnetic interactions along thec-direction and the anti-ferromagnetic interactions perpendicular to it are too week as compared to the anisotropy to introduce longrange order in the absence of an external field. By inelastic neutron scattering we have investigated the excitation spectrum in an external magnetic field up to 6 T applied perpendicular to thec-axis. Preliminary measurements in zero field show that dipolar effects lead to a shift of the minimum of the dispersion curve away from theK-point. We show that with increasing magnetic field the whole dispersion sheet is shifted towards higher frequencies and a splitting appears. With the help of a local Hamiltonian which neglects exchange interactions between all neighbours we give a qualitative explanation of the intensity of the magnetic excitations in dependence of the magnetic field. A more sophisticated theory (RPA-diagonalisation of the Heisenberg-Hamiltonian that is used to describe the magnetic behaviour of CsFeCl3) yields — apart from a mismatch for the modes at high energy transfers — a satisfactory description of the magnetic excitations of CsFeCl3 in dependence of the magnetic field.
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  • 8
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The magnetic excitations in CsFeBr3 have been measured with inelastic scattering of cold neutrons to high precision at 80 mK. The fact that the lowest frequency mode softens with decreasing temperature but stabilizes at 0.11 THz below 2.5 K is the indication that CsFeBr3 remains a SGS system forT→0. From dispersion curves measured earlier in a magnetic field along the chain axis experimental intensities were derived and in turn correlation lengths. Correlation lengths were also calculated using the new parameters for exchange and anisotropy. The experimental results and the calculations both show that the correlation lengths increase for increasing magnetic field, flatten off around the phase transformation at 4.1 Tesla with a maximum of about 35 Å and then decrease again for higher fields. No critical phenomena connected with this phase transformation could be detected. The “Mirror Mode” published earlier was found to be of spurious origin due to double scattering. It does not exist.
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  • 9
    ISSN: 1434-601X
    Keywords: 25.70.Np
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The longitudinal-momentum distributions of projectile fragments from 0.8 A GeV136Xe and 1 A GeV197Au projectiles impinging on targets of beryllium and aluminium, respectively, have been measured using the projectile-fragment separator FRS at GSI. Different momentum distributions have been found for two different classes of fragmentation processes: the abundant hot fragmentation with several nucleons evaporated from the prefragments, and the rare cold fragmentation with only protons removed from the projectile, but no nucleons evaporated. The data are compared to model calculations.
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  • 10
    ISSN: 1434-601X
    Keywords: 21.10.−k ; 27.20.+n ; 25.70.Np ; 21.10.Re
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Total interaction cross sections have been measured for8Li on C and Pb targets, for9Li on C, Al, Cu, Sn and Pb targets as well as for11Li on C, Sn and Pb targets. For each beam, we also used a plastic scintillator as target. The measurements with the scintillator targets are used to extract reduced nuclear radii of the lithium isotopes. These radii are then used for the calculation of the nuclear part of the total cross section for the other targets. The total electromagnetic-dissociation (EMD) cross sections have been deduced and are compared to different models. A strong target-charge-dependent EMD cross section is measured for11Li reaching 2.96 −0.82 +0.84 b for the Pb target. In the9Li case, a large EMD cross section for high-Z targets has been observed which amounts to 0.75 ± 0.45 b for the Pb target. The EMD cross sections of both,9Li and11Li, may be understood by the giantdipole-resonance model.
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