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  • 1995-1999  (6)
  • 1975-1979  (3)
  • 1970-1974  (1)
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  • 1
    Electronic Resource
    Electronic Resource
    Vacancy-type defects in molecular beam epitaxy low temperature grown GaAs, a positron beam lifetime study (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 1867-1869 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Positron beam lifetime spectroscopy has been utilized to study the depth distribution of vacancy-type defects in molecular beam epitaxy GaAs grown at low temperature. Lifetime spectra were measured as a function of positron energy. From the analysis of the positron lifetime in as-grown and annealed low temperature grown GaAs, the concentrations of Ga monovacancies and voids are estimated. Our results show that in an as-grown sample the Ga monovacancy concentration is 〉3×1018 cm−3. It is also known that vacancy-cluster concentration in an annealed sample exceeds 1018 cm−3 with a nonuniform spatial distribution. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.117460
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  • 2
    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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  • 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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  • 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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  • 5
    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: PACS: 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: 18 cm-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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  • 6
    Electronic Resource
    Electronic Resource
    Monovacancy formation energy in copper, silver, and gold by positron annihilation (1975)
    Springer
    Applied physics 6 (1975), S. 177-180 
    Details
    ISSN: 1432-0630
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Monovacancy formation energies in copper, silver, and gold have been deduced from the temperature variation of the peak counting rate in the angular correlation curve of positron annihilation radiation from these metals. The counting rate was temperature dependent over the entire temperature range, including temperatures so low that no trapping of positrons at vacancies is effective. At these temperatures the increase in counting rate results from thermal expansion of the lattice. By separating this thermal expansion effect from the vacancy trapping effect at higher temperatures, we obtained values for the monovacancy formation energyE 1v for copper, silver, and gold to 1.29±0.02 eV, 1.16±0.02 eV, and 0.97±0.01 eV, respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00883748
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  • 7
    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: PACS: 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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  • 8
    Electronic Resource
    Electronic Resource
    Positron angular correlation measurements on single-crystal aluminum at various temperatures (1974)
    Springer
    Applied physics 5 (1974), S. 177-178 
    Details
    ISSN: 1432-0630
    Keywords: Positron annihilation
    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 tested the trapping model by comparing the temperature dependence of the peak and the tail of the angular correlation curve from single crystal aluminum. The integral over the tail decreased as the integral over the peak increased with temperature, in such a way that the same vacancy formation energy could be deduced from both integrals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00928232
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    Paper (German National Licenses)
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  • 9
    Electronic Resource
    Electronic Resource
    μ+SR diffusion studies at LAMPF (1978)
    Springer
    Hyperfine interactions 4 (1978), S. 838-843 
    Details
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01021947
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    Paper (German National Licenses)
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  • 10
    Electronic Resource
    Electronic Resource
    A concept of a scanning positron microscope (1995)
    Springer
    Fresenius' Zeitschrift für analytische Chemie 353 (1995), S. 594-597 
    Details
    ISSN: 1618-2650
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The concept of a scanning positron microscope which is under construction in München and Trento will be shown. A beam with a variable energy from 1 to 30 keV and a spot diameter of 1 μm, which can be scanned over an area of (0.6×0.6) mm2, is formed after a double stage stochastic cooling of the positrons emitted from a radioactive source. Additionally, the beam will be pulsed to have a well-defined time base for positron lifetime measurements. The design of the microscope is dominated by special demands of positron physics. Therefore, the microscope contains electron optical elements which are well known but rarely used. These are the through the lens reflection remoderator and the optical column with a magnetic side gap lens as probe forming lens.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00321331
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