Defect identification using analysis of core electrons contribution to Doppler broadening of the positron annihilation line and measurements of positron lifetime.
Item
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Title
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Defect identification using analysis of core electrons contribution to Doppler broadening of the positron annihilation line and measurements of positron lifetime.
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Identifier
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AAI9917703
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identifier
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9917703
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Creator
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Szpala, Stanislaw.
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Contributor
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Advisers: Martin Kramer | Leonard O. Roellig
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Date
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1999
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Language
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English
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Publisher
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City University of New York.
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Subject
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Physics, Condensed Matter | Engineering, Materials Science
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Abstract
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Positron lifetime and Doppler broadening of the positron annihilation line are well recognized techniques capable of characterization of small open-volume defects (0.1 nm to 5 nm) in buried layers. Due to high level of background, the Doppler broadening measured with a single-detector setup contains information only on the dominating annihilation events, mostly the annihilation with the conduction and valence band electrons. The observability of the contribution of the core electrons to the annihilation can be enhanced upon reduction of the background obtained with the use of coincidence techniques. For the first time, the analysis of the contribution of the core electrons of various elements to the function describing the annihilation line was used to investigate the microstructure of foreign-atom decorated open volume defects. An antimony atom tied to a vacancy in the silicon lattice was identified as the acceptor-behaving defect responsible for the doping saturation in Sb-doped Si grown using low-temperature molecular beam epitaxy. The ground state of the DX center in Si-doped AlGaAs was shown to consist of a vacancy with one Si and one As atom at the nearest-neighbor sites. This is consistent with the theoretical model of the defect in which a small vacancy is formed by the shift of the Si atom away from the As atom.;A prototype of variable-energy positron lifetime spectrometer was built and tested. The timing resolution was characterized by FWHM of 470 ps. The new spectrometer was applied to characterize the defects in a novel material of low dielectric constant (methylsilsesquioxane custom-altered by IBM) intended to replace silicon dioxide in the integrated circuits of the next generation. Dielectric constant reducing voids of the radius of 1.4 nm were found in the foamed specimen in addition to the voids of the radius of 0.65 nm present in the base material.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
