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Previous work on thermally induced arsenic deactivation in highly doped silicon has proven the generation bf vacancies and suggests the formation of arsenic-vacancy clusters as the deactivation mechanism. Using positron annihilation spectroscopy in the two-detector coincidence geometry, we are able ...
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A polycrystalline sample of Al63Cu25Fe12 has been studied as a function of thermal treatment by positron annihilation and X-ray diffraction techniques. Results suggest the presence of an icosahedral-to-rhombohedral microcrystalline phase transition near 300-degrees-C. Below this transition, a large ...
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Samples of the stable Al75Pd15Fe10 decagonal quasicrystal have been studied both in the as-cast state and after annealing. Structural properties were investigated using X-ray diffraction and Fe-57 Mossbauer effect studies. X-ray patterns show that annealing improves the degree of order in the decago...
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Amorphous Al-Y-Ni alloys, prepared by rapid solidification from the melt, have shown a unique combination of low density and high tensile strength. In the present work amorphous alloys of the composition Al87Y8Ni5-xFex (2 less-than-or-equal-to x less-than-or-equal-to 5) have been studied using room ...
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Al-Cu-Fe alloys of several different stoichiometries have been prepared using a variety of sample preparation methods and have been studied using Fe-57 Mossbauer effect spectroscopy. Well ordered icosahedral, phason disordered icosahedral and rhombohedral crystalline phases were investigated. The re...
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A Doppler broadening positron annihilation technique which allows for the study of near surface defects in bulk samples is described. The method is capable of observing changes in the homogeneous bulk defect concentration in a sample acid is also able to characterize spatially localized near-surface...
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Doppler-broadening positron-annihilation-spectroscopy experiment that utilizes an in situ Cu-64 source for the study of Cu and Cu-containing materials is described. This technique is particularly useful for the investigation of defect structure at elevated temperatures, and the present instrumentati...
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Using a low-temperature stage X-ray diffractometer, we have investigated the temperature dependence of the lattice parameters of single crystal superconductors Bi2.2Sr1.8CaCu2Ox. The experimental results show that (i) the lattice constants increase linearly with increasing temperature above about 10...
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The positron beam technique is shown to be a sensitive indicator of the presence of arsenic within the grain boundaries of poly-silicon. Variable-energy positron beam and secondary-ion mass spectrometry studies have been performed on As+-implanted pre-amorphized Si samples as a function of dose and ...
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Electrical deactivation of arsenic in highly doped silicon has been studied using the positron-beam technique. Direct experimental evidence linking the formation of arsenic-vacancy complexes (i.e., As-n-v) to the deactivation process is reported. The average number of arsenic atoms per complex, (n) ...
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Positron annihilation spectra of arsenic- and gold-implanted silicon are compared:with spectra from bulk samples of arsenic and gold. Spectra with strongly reduced background intensities were recorded using a two detector coincidence system with a variable-energy positron beam. It is shown that feat...
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Room temperature Fe-57 Mossbauer effect measurements of the one- and two-dimensional quasicrystalline phases of Al75Pd15Fe10 are reported. Both materials show Mossbauer spectra with asymmetric doublets which have been analyzed in terms of a distribution of quadrupole splittings, and in terms of a di...
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Structural studies of conventionally solidified Al80-2xPd20CrxFex alloys have shown that the formation of a well ordered icosahedral phase occurs for a composition where the free-electron Fermi sphere is coincident with the first pseudo-Brillouin zone boundary. This condition indicates the importanc...
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Amorphous alloys of the composition Al65Gd15Cu20 and Al1Gd1Fe1 have been prepared by rapid quenching from the melt. The alloys have been studied by X-ray diffraction, thermal analysis and SQUID magnetization methods. Thermal analysis results show crystallization temperatures of 647 and 945 K for Al-...
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In situ Doppler-broadening temperature scans and room temperature positron-lifetime measurements are reported for Al63CU25Fe12, Al62.5CU25Fe12.5, Al62CU25.5Fe12.5, and Al62Cu22.8Fe15.2 face-centered-icosahedral (FCI) quasicrystalline samples. Quenched-in disorder has been observed and found to annea...