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  • 1
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    Wissenschaftliche Monitoringkonzepte für die Deutsche Bucht (WIMO) - Abschlussbericht (2016)
    In:  EPIC3160 p.
    Details
    Publication Date: 2018-02-15
    Description: The state and development of coastal marine systems and an understanding of the interaction of organisms, sea floor, water column, and biochemical and physical processes can only be obtained by a combination of long-term monitoring and modelling approaches of different complexity. A need for the development and evaluation of monitoring strategies is driven by a framework of different European and German regulations. The research project WIMO (Scientific Monitoring Concepts for the German Bight) has developed concepts and methods that aim at a fundamental scientific understanding of marine systems and also meet monitoring requirements of European legislation and regulations like the EU Marine Strategy Framework Directive. In this final report examples of common descriptors of ecosystem state like seabed integrity, eutrophication, and biodiversity are discussed. It has been assessed to what extent established measuring procedures used to survey the characteristics of the sea floor, and newly developed technologies are eligible for governmental monitoring. The significance of integrative modelling for linking and visualising results of measurements and models is illustrated. It is shown how new concepts have been implemented into governmental monitoring in the form of web based data sheets. These insights enable continuous analyses and developments in the future.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Miscellaneous , notRev
    Format: application/pdf
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  • 2
    Electronic Resource
    Electronic Resource
    Resonant Raman scattering in hexagonal GaN (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 2404-2406 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We performed resonant Raman scattering in hexagonal GaN using discrete laser lines in the violet and UV spectral range for optical excitation. To tune the energetic position of the fundamental gap E0 of GaN relative to the exciting photon energy the sample temperature was varied between 77 and 870 K. Analyzing both Stokes and anti-Stokes Raman spectra, the resonance profiles for Fröhlich-induced one-E1(LO) and two-E1(LO) phonon scattering could be deduced, covering the energy range from 0.5 eV below the E0 gap up to the gap energy. The strength of deformation-potential scattering by the A1(TO) mode was used as an internal reference. For excitation slightly above the E0 gap energy E1(LO) multiphonon scattering up to the fourth order was observed, which reflects the stronger polarity of the Ga-N bond as compared to conventional III-V semiconductors. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.116148
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  • 3
    Electronic Resource
    Electronic Resource
    Nitrogen stabilized 〈100〉 texture in chemical vapor deposited diamond films (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 34-36 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have studied the influence of nitrogen impurities in CH4/H2 gas mixtures on the structure and morphology of polycrystalline diamond films prepared by microwave plasma assisted chemical vapor deposition. The nitrogen concentration in the process gas was varied between 1 and 1000 ppm. Optical emission spectroscopy was applied to detect the nitrogen in the plasma via emission from CN radicals. The morphology and texture of polycrystalline films prepared with various N2 impurity levels and CH4 concentrations in the range 0.5%–2% was investigated using scanning electron microscopy and x-ray texture analysis. For the films prepared with low methane concentrations (e.g., 0.5%) only a minor influence of the nitrogen was observed. However, most interestingly, for higher methane concentrations (1%–2%) the addition of small amounts of nitrogen turned out to have a tremendously beneficial effect on the film morphology and structure. Films prepared without additional nitrogen are of nanocrystalline structure and of minor quality, whereas films prepared with nitrogen concentrations in the range 10–100 ppm exhibit a pronounced 〈100〉 texture and a considerably improved crystalline quality as judged by Raman spectroscopy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.113064
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  • 4
    Electronic Resource
    Electronic Resource
    Resonant Raman scattering and spectral ellipsometry on InAs/GaSb superlattices with different interfaces (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 2972-2974 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have used Raman spectroscopy and spectral ellipsometry to investigate InAs/GaSb short-period superlattices (SLs), grown by molecular-beam epitaxy, with either InSb- or GaAs-like interfaces. Room-temperature ellipsometric measurements show spectral features in the dielectric function due to the E1 and E1+Δ1 interband transitions of GaSb and InAs. For SLs with small InAs layer thicknesses (4 ML InAs/10 ML GaSb) the critical point energies are found to depend on the type of interfacial bonding, with an energy shift of up to 50 meV observed between SLs with GaAs- and InSb-like interfaces. Resonant Raman measurements show a pronounced enhancement in scattering efficiency for the superlattice phonons and, in particular, for the interface modes for incident photon energies matching the critical point energies of the SL. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.112480
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  • 5
    Electronic Resource
    Electronic Resource
    Homoepitaxial 13C diamond films studied by micro-Raman and photoluminescence spectroscopy (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 63 (1993), S. 3005-3007 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Raman microscopy has been used to study 13C and 12C/13C isotopically mixed homoepitaxial diamond films grown by chemical vapor deposition on natural diamond substrates. The measured dependencies of the frequency and the width of the first-order zone-center optic phonon line on the isotope composition agree well with those reported for diamond crystals synthesized under high pressure. To study the evolution of the epitaxial layer quality for a 13C diamond film grown on a natural type IIa diamond substrate with an isotopic composition of almost pure 12C, micro-Raman spectroscopy has been performed on a polished cross section. The width of the zone-center phonon line is found to increase in the epitaxial layer from 2.6 up to 3.0 cm−1 with increasing distance from the film/substrate interface and is thus consistently larger than the linewidth of 2.5 cm−1 measured in the substrate. Two photoluminescence bands are observed in the epitaxial film centered at 2.16 and 2.21 eV. The 2.16 eV band, which has been attributed to emission from an interstitial nitrogen-vacancy complex, shows a pronounced maximum in intensity at the film/substrate interface indicating an enhanced nitrogen incorporation at the interface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.110266
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  • 6
    Electronic Resource
    Electronic Resource
    Interface formation in InAs/AlSb and InAs/AlAs/AlSb quantum wells grown by molecular-beam epitaxy (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 1293-1295 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have used resonant Raman scattering from both longitudinal-optical phonons and interface modes to study the chemical bonding across the InAs/AlSb interface in InAs/AlSb quantum wells grown by molecular-beam epitaxy. The effusion cell shutter sequence at the interfaces was selected for the deposition of either one monolayer of InSb or two to three monolayers of AlAs. In all cases an InSb-like interface mode is observed, indicating the preferential formation of In—Sb interface bonds irrespective of the shutter sequence. The deposition of two or three monolayers of AlAs at the InAs/AlSb interface results in the formation of pseudoternary AlSb1−xAsx barriers rather than binary AlAs interfaces and AlSb barriers, indicating a strong exchange among the group-V atoms. Normal (AlSb on InAs) and inverted (InAs on AlSb) InAs/AlSb interfaces have also been compared, revealing a much stronger InSb-like interface mode for the growth of AlSb on InAs than for the case of InAs grown on AlSb.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.112098
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  • 7
    Electronic Resource
    Electronic Resource
    Raman spectroscopic study on the wirelike incorporation of Si dopant atoms on GaAs(001) vicinal surfaces (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 490-492 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Raman scattering by collective electronic excitations from a δ-doping layer has been used to investigate the ordered incorporation of Si dopant atoms on vicinal GaAs(001) surfaces. In a series of δ-doped samples grown by molecular beam epitaxy (MBE) under specific conditions the Si dopant atoms were found to be incorporated predominantly on Ga sites, even at a doping concentration as high as 1.8×1013 cm−2. A pronounced polarization asymmetry in the Raman scattering intensity of collective intersubband plasmon-phonon modes was observed in a sample grown under conditions established by real-time high-energy electron diffraction to be favorable for wirelike Si incorporation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.111139
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  • 8
    Electronic Resource
    Electronic Resource
    Spectroscopic ellipsometry characterization of (InGa)N on GaN (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 1715-1717 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Pseudodielectric function spectra of hexagonal (InGa)N epitaxial layers on GaN were obtained by spectroscopic ellipsometry and compared with photoreflection spectra. Composition and thickness of the InxGa1−xN layers grown by metalorganic chemical vapor deposition, were varied between 0.04≤x≤0.10 and 15–60 nm, respectively. The pseudodielectric function exhibits a clear maximum at the fundamental gap energy of the (InGa)N, which allows a determination of the In content via the composition dependence of that gap energy. The pseudodielectric function spectrum of a complete GaN/(InGa)N/(AlGa)N/GaN light-emitting diode structure shows maxima arising from fundamental gap interband transitions of all constituent layers including the (InGa)N active region. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.122255
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  • 9
    Electronic Resource
    Electronic Resource
    Resonant Raman scattering in GaN/(AlGa)N single quantum wells (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 70 (1997), S. 363-365 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Resonant Raman scattering has been used to study longitudinal optical (LO) phonon modes in 2–4-nm-wide GaN/Al0.15Ga0.85N single quantum wells (QW). Raman spectra recorded using subband gap excitation were found to be completely dominated by the phonon modes of the (AlGa)N barriers. In contrast, for excitation close to resonance with the lowest transition between confined electron and hole states in the GaN QW scattering by the A1(LO) phonon in the QW became dominant in spite of the narrow width of the QW. For well widths of 3 and 4 nm, the frequency of the A1(LO) phonon in the QW was found to be close to that in bulk GaN, whereas for a well width of 2 nm the QW phonon was broadened and shifted towards the frequency of the (AlGa)N A1(LO) phonon mode. This broadening and frequency shift indicate some cation intermixing for the narrowest QW with the widths of the interface regions being comparable to the well width of 2 nm, demonstrating the usefulness of resonant Raman scattering for quality assessment of GaN/(AlGa)N QWs and interfaces. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.118413
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  • 10
    Electronic Resource
    Electronic Resource
    Evidence for compositional inhomogeneity in low In content (InGa)N obtained by resonant Raman scattering (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 241-243 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Resonant Raman scattering has been used to study hexagonal InxGa1−xN films with x(approximate)0.1, grown by metal–organic chemical vapor deposition on sapphire substrates. To vary the energy difference between the fundamental gap energy of the (InGa)N and the photon energy of the discrete laser emission lines used for recording the spectra, the sample temperature was varied between 300 and 870 K. Raman scattering by the (InGa)N A1(LO) phonon shows a clear resonance profile when the fundamental energy gap approaches the incident photon energy, with a maximum enhancement in scattering efficiency of 10 measured relative to the scattering strength of the E2 phonon mode. The (InGa)N A1(LO) phonon was found to shift to higher frequencies with respect to the E2 mode when the experimental conditions were varied from excitation below the fundamental energy gap of (InGa)N to above-band-gap excitation. This frequency shift is explained by the presence of compositional inhomogeneity, which results in localized regions with higher In content, and thus, lower gap energy and phonon frequency, and regions with lower In content, and consequently, higher gap energy and phonon frequency. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.121768
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