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  • PACS: 61.70; 68.55; 78.70  (2)
  • PACS: 61.70; 78.70  (1)
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  • 1
    Electronic Resource
    Electronic Resource
    Transmission of positrons with a β+ energy distribution through thin films (1996)
    Springer
    Applied physics 63 (1996), S. 299-301 
    Details
    ISSN: 1432-0630
    Keywords: PACS: 61.70; 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.  The transmission through Al foils of isotropically implanted positrons from a 22Na β+ source has been measured. It is shown that the transmission is reasonably well-described using an exponential profile once backscattering is accounted for, except for thicknesses below approximately 7 mg/cm2. Below this thickness, the measured transmission is slightly less than that predicted by the exponential profile. Such a deviation has previously been observed for collimated positrons, suggesting that the implantation profile has no significant dependence on the spatial distribution of the incident positrons. This deviation is critical for the proper interpretation of positron lifetime experiments on thin films using a conventional positron lifetime spectrometer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01567885
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    An investigation of point defects in silicon carbide (1995)
    Springer
    Applied physics 61 (1995), S. 55-58 
    Details
    ISSN: 1432-0630
    Keywords: PACS: 61.70; 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.  Positron lifetime measurements on bulk samples of single crystal SiC wafers have shown that both 6H and 4H polytypes exhibit a bulk lifetime of 150±2 ps. All samples contained a second, defect-related lifetime component, ranging in value from 250 to about 300 ps with rather low intensities. The defect structure exhibited by the nanocrystalline samples is, not unexpectedly, much more complex. Positron beam experiments on Electron Cyclotron Resonance Chemical Vapour Deposited (ECR-CVD) SiC thin films showed that the positrons are very sensitive to changes in important film parameters as a function of the deposition conditions. It was found that the film density is lower than expected, probably due to hydrogen incorporation; variations in composition among different films were detected through variations in the S parameters, and differences were observed in the electric field at the film–substrate interface due to hydrogen passivation of dangling bonds and different substrate resistivities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01538211
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Microstructural evolution of ZnS during sintering monitored by optical and positron annihilation techniques (1995)
    Springer
    Applied physics 61 (1995), S. 217-220 
    Details
    ISSN: 1432-0630
    Keywords: PACS: 61.70; 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.  Positron lifetime and optical absorption techniques were employed to track the microstructural evolution of polycrystalline ZnS grown by Chemical Vapor Deposition (CVD). As grown material and material treated with Hot Isostatic Pressure (HIP) was sintered at temperatures ranging from 400 to 1000 °C for 2–18 h. A 290 ps defect lifetime could be resolved in all samples, while an additional longer lifetime (τ=430 ps) was found only in samples annealed at low temperatures. This component gradually disappeared during annealing at 800 ° C. Associated with the disappearance of the long-lived component, the apparent bulk lifetime of the material changed from 235 to 215 ps. A 215±2 ps bulk parameter was also found for HIP-treated material annealed at temperatures greater than 400 ° C and hence is taken to represent the delocalized state of the positrons in ZnS. Optical absorption measurements showed that annealing at 800 ° C also caused the absorption profiles of the CVD and HIP samples to converge. The rate of the bulk lifetime transition correlates with the absorption changes. The observed sharpening of the absorption profile is attributed to a decrease in scattering from grain boundaries and voids, and a decrease in absorption from point defects. The 430 ps lifetime is believed to be due to trapping at voids and grain boundaries, while the 290 ps lifetime likely is due to a monovacancy stabilized as a small complex.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003390050194
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    Paper (German National Licenses)
    Fulltext
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