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  • 1
    Electronic Resource
    Electronic Resource
    Molecular beam flux measurements and equilibria for As4, P4, As2, P2, and AsP (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 4444-4448 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The dynamic equilibrium between P2, As2, and AsP at 1000 °C has been studied by mass spectrometry of fluxes from a double effusion cell. From simple ion gauge measurements of heated and unheated fluxes we determined the ionization efficiency for the dimers P2 and As2 relative to the tetramers, P4 and As4. Simultaneous mass spectrometer and ion gauge measurements of the effusion fluxes allowed the relative ionization sensitivities for P2, As2, and AsP to be determined. From the mass spectrometry data it was possible to determine the equilibrium constant 1.9±0.4 and free energy −0.55 eV molecule−1 for the process As2+P2(large-closed-square)2 AsP. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359852
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  • 2
    Electronic Resource
    Electronic Resource
    Phosphorus cracking efficiency and flux transients from a valved effusion cell (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 1664-1668 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The transient behavior of the flux from a valved effusion cell containing red phosphorus is shown to result from a low elemental sublimation coefficient (α=1.3×10−7) and not from the presence of white phosphorus in the sublimator region. The criteria for generating white phosphorus in the sublimator are given. The conversion from tetramers to dimers is modeled as a function of temperature and pressure. At higher pressures, higher temperatures are needed to convert P4 to P2. Experimental results are shown to be in qualitative agreement with results from thermodynamic equilibrium arguments. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360261
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  • 3
    Electronic Resource
    Electronic Resource
    Raman study of Al0.54In0.46P/GaAs interfaces grown by solid source molecular beam epitaxy (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 63 (1993), S. 2402-2404 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An Al0.54In0.46P/GaAs superlattice was grown using a new approach to molecular beam epitaxy that employs solid-source valved crackers to supply the As4 and P2 group V fluxes. The superlattice sample was characterized by off-resonance Raman backscattering spectroscopy. In comparison to other III-V superlattices, the acoustic region of the Raman spectrum from this superlattice was especially rich, and phonon doublets up to the seventh order were visible in the spectrum. The interface roughness in the superlattice was determined to be two monolayers using a simple photoelastic model to characterize the intensities of the folded longitudinal-acoustic phonon peaks. The minimal intermixing present at the interfaces demonstrates the ability to abruptly switch between group V fluxes using the solid-source valved crackers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.110488
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  • 4
    Electronic Resource
    Electronic Resource
    Use of a valved, solid phosphorus source for the growth of Ga0.5In0.5P and Al0.5In0.5P by molecular beam epitaxy (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 59 (1991), S. 342-344 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on a new method for the generation of phosphorus beams in molecular beam epitaxy: the use of a valved, solid cracker source. The valved solid source avoids previous difficulties associated with the use of solid phosphorus, and provides an attractive alternative to the use of phosphine. The use of red phosphorus does not interfere with the subsequent growth of high quality arsenides in the same growth chamber. The performance of this valved phosphorus source is illustrated by the growth of two ternary phosphides, Ga0.5In0.5P and Al0.5In0.5P. The quality of the phosphides reported here is comparable to the best results reported by other growth techniques. The effects of composition, growth temperature, and P2 flux on the films' characteristics are reported. Indium desorption during growth is found to be substantially greater in AlInP than in GaInP.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.105590
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  • 5
    Electronic Resource
    Electronic Resource
    Raman scattering from square profile, sinusoidal profile, and tilted AlxGa1−xAs/AlyGa1−yAs superlattices (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 62 (1993), S. 1925-1927 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Al-like and Ga-like longitudinal optic phonons from square profile, sinusoidal profile, and tilted AlxGa1−xAs/AlyGa1−yAs superlattices are examined using Raman spectroscopy. The Raman spectrum from a superlattice with a square composition profile and an Al composition modulation of 18% (x−y=0.18) exhibits Al- and Ga-like longitudinal optic phonon peaks that are doublets. These doublets are no longer resolvable for a square profile superlattice with a 10% composition modulation (x−y=0.1), and the spectrum contains only single, broadened Al- and Ga-like longitudinal optic phonon peaks. The spectra from sinusoidal profile superlattices also exhibit single, broadened phonon peaks for composition modulations that are less than or equal to 22% (x−y≤0.22). The spectrum of a tilted superlattice is similar to that of a square profile superlattice with a 10% composition modulation and to that of a sinusoidal profile superlattice with a composition modulation of 16%. The assignment of the sinusoidal profile with a 16% composition modulation to the tilted superlattice is consistent with a previous photoluminescence study of tilted superlattices.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.109546
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  • 6
    Electronic Resource
    Electronic Resource
    The sediment column as a record of trophic status: examples from Bosherston Lakes, SW Wales (1991)
    Springer
    Hydrobiologia 214 (1991), S. 171-180 
    Details
    ISSN: 1573-5117
    Keywords: sediment geochemistry ; 210Pb dating ; diatom analysis ; eutrophication ; phosphorus ; Chara ; marl lakes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Bosherston Lakes are a series of interconnected, mesotrophic to hypereutrophic, artificially-created coastal marl lakes in Dyfed, South West Wales. Progressive eutrophication of the lake system has been produced by a high external phosphorus loading which includes phosphorus-rich effluent from a sewage treatment works (STW) in the catchment of the Lakes. Cores were taken from four sites of varying eutrophic status within the Lakes. In the surface sediment layer, organic C, N and P concentrations generally correlate directly with trophic status and reflect distance from the source of P input. At one site, sediment stratigraphy records a clear transition at 20–15 cm depth, marked by a sharp upward increase in porosity, organic C, N, and P, and ‘iron-associated’-P; decreases in organic matter C/N, C/P and N/P ratios; a sharp decrease in carbonate, and a change in the subfossil diatom assemblage. Lead-210 dating indicates that this change occurred in the period 1919 to 1938. The diatom stratigraphy and sediment geochemistry suggest that this transition reflects an increase in trophic status at this site, probably as a result of the influx of nutrient-rich water. This took place when the management of the Stackpole estate surrounding the lake system, fell into decline during the period 1919–1938.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00050947
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