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  • 1
    Electronic Resource
    Electronic Resource
    Positron-trap centers in neutron-irradiated silicon containing hydrogen (1995)
    Springer
    Applied physics 60 (1995), S. 81-85 
    Details
    ISSN: 1432-0630
    Keywords: PACS: 61.72–y; 61.80.Hg; 78.70.Bj
    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 defect evolution as a function of the annealing temperature has been studied in monocrystalline silicon grown in a hydrogen atmosphere and irradiated with 3.6×1017 neutrons/cm2. Positron lifetime spectroscopy has been used and the results compared with infrared absorption measurements. Vacancy-H, vacancy-2H, vacancy-O-H and divacancy complexes with m hydrogen atoms (m〈6) have been identified for the first time as possible positron traps.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01577618
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  • 2
    Electronic Resource
    Electronic Resource
    Positron mobility in polyethylene in the 60–400 K temperature range (1995)
    Springer
    Applied physics 60 (1995), S. 447-453 
    Details
    ISSN: 1432-0630
    Keywords: 78.70.Bj ; 36.10.Dr ; 61.41.+e
    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 determined the positron mobility (μ+) in polyethylene samples (67.2% crystalline, glass transition temperatureT g=151 K) in the 64–400 K temperature range by Doppler shift measurements. A method based on the simulataneous observation of two γ lines from133Ba and137Cs radioactive sources together with the positron annihilation γ line, was employed to measure the Doppler shift of the 511 keV γ line as a function of the electric field applied to the samples. With this method we were able to measure at the same time the drift velocity of positrons and theS parameter. This parameter is very important in the interpretation of the mobility trend in samples where the positron states change with temperature. The positron mobility was corrected for positronium formation. μ+ at 64 K is 31.7±0.8 cm2 V−1 s−1 then decreases up to 123 K, increases at 148 K and decreases again up to 170 K (μ+=26.9±0.8 cm2 V−s−). This sharp change in mobility is centred around the glass transition temperature of our samples. Then the mobility remains almost constant up to 230 K. From 250 K to 377 K, μ+ increases and reaches the value of 38.4±1.0 cm2 V−1s−1. The corrected experimental data were well fitted by a simple model taking into account scattering and a thermally activated process (hopping mechanism).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01538768
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  • 3
    Electronic Resource
    Electronic Resource
    Cylinder radioactive source for slow-positron beams (1985)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 56 (1985), S. 1531-1533 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The geometrical efficiency is calculated for a radioactive source-moderator assembly, which is often used for the production of slow-positron beams, and comparisons are made between a cylinder source, touching the circumference of the moderator, and a spot source, facing the center of the moderator. It is shown that higher beam intensity and brightness can be obtained with the cylinder source in most practical situations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1138149
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  • 4
    Electronic Resource
    Electronic Resource
    He-implantation induced defects in Si studied by slow positron annihilation spectroscopy (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 2390-2397 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Open volume defect profiles have been obtained by performing Doppler broadening measurements with a slow positron beam on p-type Si samples implanted near liquid nitrogen temperature with He ions at 20 keV and at 5×1015 and 2×1016 cm−2 fluence. The evolution of the defect profiles was studied as a function of isothermal annealing at 250 °C. The fraction of released He was measured by thermal programmed desorption. The defects could be identified as a coexistence of monovacancies stabilized by He-related defects and divacancies. The number of defects decreases for annealing time of a few minutes, then increases at longer annealing times. The mean depth of the defect profiles in the as-implanted samples was found to be very near the surface. After annealing, the mean depth increases to less than one half of the projected He range. This complex dynamics has been interpreted as due to passivation of vacancies by He during the implantation process and the first annealing step when no appreciable He is lost, and to subsequent depassivation during He desorption. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.369555
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  • 5
    Electronic Resource
    Electronic Resource
    Positron annihilation study of vacancy-like defects related to oxygen precipitates in Czochralski-type Si (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 79 (2001), S. 1492-1494 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the direct measurement of vacancy-like defects related to oxygen in the oxygen precipitation process in Czochralski Si. The vacancy-like defects were detected by measuring the positron lifetime and narrowing of the positron–electron annihilation momentum distribution. Oxygen atoms surrounding the vacancy-like defects were detected by analyzing the high-momentum part of the positron–electron momentum distribution measured by a Doppler broadening coincidence technique. It was found that the majority of the defects associated with oxygen have an effective open volume smaller than that of a silicon monovacancy. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1401782
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  • 6
    Electronic Resource
    Electronic Resource
    Copper thin films used as transmission remoderators for slow positron beams (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 1476-1478 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The positron remoderation efficiency of self-supported copper films 1000–5000 Å thick was measured by a slow positron beam at impinging positron energies between 1 and 20 keV. A maximum efficiency of 11.5 (−1+3)% was found. It has been shown that copper films are easily produced. A relatively low temperature annealing ((similar, equals)450 °C) is needed to remoderate positrons. These properties make them good candidate for positron beams with brightness enhancement stage in transmission geometry. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.126068
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  • 7
    Electronic Resource
    Electronic Resource
    Positron-trap centers in neutron-irradiated silicon containing hydrogen (1995)
    Springer
    Applied physics 60 (1995), S. 81-85 
    Details
    ISSN: 1432-0630
    Keywords: 61.72-y ; 61.80.Hg ; 78.70.Bj
    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 defect evolution as a function of the annealing temperature has been studied in monocrystalline silicon grown in a hydrogen atmosphere and irradiated with 3.6×1017 neutrons/cm2. Positron lifetime spectroscopy has been used and the results compared with infrated absorption measurements. Vacancy-H, vacancy-2H, vacancy-O−H and divacancy complexes withm hydrogen atoms (m〈6) have been identified for the first time as possible positron traps.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01577618
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  • 8
    Electronic Resource
    Electronic Resource
    Experimental study of positron motion in Kapton (1992)
    Springer
    Applied physics 54 (1992), S. 233-238 
    Details
    ISSN: 1432-0630
    Keywords: 66.30 ; 71.60 ; 78.70 B
    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 drift of positrons under the action of an electric field in Kapton has been observed by using a variable-energy positron beam and the Doppler broadening technique. Even if the maximum applied field (2 MV/cm) is so high that the electrostatic work for a displacement of less than 0.15 nm is larger than the thermal energy, the experimental data can be fit by the diffusion model with a field-independent mobility. The best-fit value of the mobility (ca. 1×10−3 cm2 V−1 s−1) is extremely low in comparison with other dielectrics. The results are discussed with regards to the interaction of positrons with the molecular field.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00323842
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  • 9
    Electronic Resource
    Electronic Resource
    Positron mobility in polyethylene in the 60–400 K temperature range (1995)
    Springer
    Applied physics 60 (1995), S. 447-453 
    Details
    ISSN: 1432-0630
    Keywords: PACS: 78.70.Bj; 36.10.Dr; 61.41.+e
    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 determined the positron mobility (μ+) in polyethylene samples (67.2% crystalline, glass transition temperature T g=151 K) in the 64–400 K temperature range by Doppler shift measurements. A method based on the simultaneous observation of two γ lines from 133Ba and 137Cs radioactive sources together with the positron annihilation γ line, was employed to measure the Doppler shift of the 511 keV γ line as a function of the electric field applied to the samples. With this method we were able to measure at the same time the drift velocity of positrons and the S parameter. This parameter is very important in the interpretation of the mobility trend in samples where the positron states change with temperature. The positron mobility was corrected for positronium formation. μ+ at 64 K is 31.7±0.8 cm2 V-1 s-1 then decreases up to 123 K, increases at 148 K and decreases again up to 170 K (μ+=26.9±0.8 cm2 V-1 s-1). This sharp change in mobility is centred around the glass transition temperature of our samples. Then the mobility remains almost constant up to 230 K. From 250 K to 377 K, μ+ increases and reaches the value of 38.4±1.0 cm2V-1s-1. The corrected experimental data were well fitted by a simple model taking into account scattering and a thermally activated process (hopping mechanism).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01538768
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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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