A 2D-ACAR STUDY OF POSITRON INTERACTIONS WITH SURFACES OF ALUMINUM AND SILICON (POSITRON PHYSICS, ANNIHILATION RADIATION).
Item
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Title
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A 2D-ACAR STUDY OF POSITRON INTERACTIONS WITH SURFACES OF ALUMINUM AND SILICON (POSITRON PHYSICS, ANNIHILATION RADIATION).
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Identifier
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AAI8708279
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identifier
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8708279
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Creator
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CHEN, DONG MIN.
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Contributor
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Leonard O. Roellig
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Date
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1987
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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
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Abstract
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Using a high intensity slow positron beam and an UHV surface chamber constructed at Brookhaven National Laboratory, we have applied the well established technique of 2-Dimensional Angular Correlation of Annihilation Radiation to study the interactions of positrons with three low index surfaces of aluminum, Si(111)-(7 x 7), and Si(100)-(2 x 1) surfaces. Effects of the adsorption of oxygen on Al surfaces and hydrogen on a Si(111)-(7 x 7) surface have also been explored. Our measurements confirmed three important processes: spontaneous positronium (Ps) formation and emission, positrons bound in a surface state, and thermally desorbed as Ps atoms. A method has been developed to accurately separate these components. The Ps momentum distributions exhibit some unique structures that are sensitive to the surface conditions, and are found to reflect the electron density of states near the surfaces thus suggesting a new surface spectroscopy: angle-resolved Ps spectroscopy. The positron surface state spectrum has an essentially isotropic distribution with respect to the components perpendicular and parallel to the surface, indicating lateral localization of the surface state positron. This is inconsistent with either the image potential induced positron surface state model, or the physisorbed Ps surface state model for ideal surfaces. The extracted thermal Ps momentum distributions are in good agreement with the theoretical description of a thermodynamical emission process. This thesis provides the first systematic discussion of these extended techniques, and the important results obtained to date.
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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.
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Program
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Physics
