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  • 1
    Electronic Resource
    Electronic Resource
    Phase transformations and vacancy formation energies of transition metals by positron annihilation (1979)
    Springer
    Applied physics 20 (1979), S. 135-140 
    Details
    ISSN: 1432-0630
    Keywords: 78.70 ; 71.60 ; 61.70
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The technique of the coincidence count rate at the peak of the angular correlation curve (CCR) in positron annihilation has been applied to the investigation of vacancy formation energies in thermal equilibrium in nickel, cobalt, and iron. The monovacancy formation energyE 1v/F has been determined to (1.55±0.05) eV and (1.34±0.07) eV for nickel and cobalt, and (1.60±0.10) eV for α-iron, and (1.40±0.15) eV for γ-iron, respectively. The structural phase transformations in cobalt (693 K) and iron (1183 K, 1663 K) are exhibited by discontinuities of the CCR. In the case of cobalt the CCR follows exactly the change of the thermal expansion at the transition temperature. The temperature dependence of the CCR in the prevacancy region is found to be proportional to the thermal expansion for all metals investigated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00885934
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Vacancy-impurity interaction in dilute iron alloys by positron annihilation (1982)
    Springer
    Applied physics 28 (1982), S. 179-187 
    Details
    ISSN: 1432-0630
    Keywords: 78.70 ; 61.70
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Positron annihilation measurements of the coincidence count rate at the peak of the angular correlation curve (CCR) have been performed as a function of temperature for the alloy systemFeTi in a concentration range up to about 1.3 at. %. The concentration dependence of the effective vacancy formation enthalpy (H 1V F )eff suggests the existence of an attractive interaction between vacancies and the impurity atoms. It will be shown that the description of the vacancy concentration in an alloy according to the Lomer model is not valid in this case, because it neglects binding of vacancies to solute atom pairs and to higher agglomerates. The application of a model proposed by Dorn and Mitchell gives evidence that beyond the binding of a vacancy to a single solute atom in the concentration range investigated also aggregates of a vacancy bound to two and three foreign atoms must be taken into account. The analysis of the measurements according to the method of Hehenkamp and Sander gives values for the respective vacancy-solute-atom(s) binding enthalpies H 1 B =0.25eV, H 2 B =0.53eV and H 3 B =0.91eV. The discussion of the temperature and solute-atoms concentration dependence of the vacancy concentration suggests a much more complicated behaviour than for pure metals even at low solute-atom concentrations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00617984
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    A slow positron lifetime study of the annealing behaviour of an amorphous silicon layer grown by MBE (1995)
    Springer
    Applied physics 61 (1995), S. 71-74 
    Details
    ISSN: 1432-0630
    Keywords: 68.55 ; 78.70
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract We have studied MBE grown amorphous silicon, which was recrystallized at different temperatures for one hour, with a pulsed positron beam. A positron lifetime of 538±10 ps in the as-grown state is attributed to microvoids containing at least 10 vacancies. An incompletely recrystallized sample annealed at 500°C shows an additional long lifetime from ortho-positronium (o-Ps) pick-off annihilation. The o-Ps component disappears for samples, recrystallized at 700°C and above, and the defect lifetime steadily decreases with higher annealing temperature until a value of 310 ps is reached for the layer annealed at 1200°C. This value is explained by positron trapping at dislocations or small vacancy defects stabilized by dislocations or impurities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01538214
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Investigations of positron lifetimes in InP with a pulsed positron beam (1995)
    Springer
    Applied physics 61 (1995), S. 321-324 
    Details
    ISSN: 1432-0630
    Keywords: 78.70 ; 68.55 ; 61.70
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Indium Phosphide layers grown by gas source Molecular Beam Epitaxy, (MBE) have been studied by positron lifetime spectroscopy using the recently modified pulsed positron beam in Munich. The as-grown samples are known to be phosphorous rich and contain a high concentration of vacancy-type defects. On annealing, phosphorous precipitates are formed and the concentration of free volume defects increases. Positron lifetime spectroscopy has identified the grown in defects to be indium vacancies at a concentration around 1018cm−3. The dominant defects after annealing exhibit a positron lifetime characteristic of divacancies and are present at concentrations in excess of 5×1019cm−3.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01538197
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    Paper (German National Licenses)
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