Diamond chemical vapor deposition: Thermodynamic analysis and growth studies.
Item
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Title
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Diamond chemical vapor deposition: Thermodynamic analysis and growth studies.
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Identifier
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AAI9130376
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identifier
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9130376
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Creator
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Sommer, Marianne.
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Contributor
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Adviser: Frederick W. Smith
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Date
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1991
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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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The chemical vapor deposition of carbon films is analyzed using the thermodynamic quasiequilibrium (QE) model and a phase diagram for the carbon-hydrogen system is obtained. When the enhanced etching of graphite by hydrogen is included in the model, a region appears in the phase diagram where diamond is predicted to be the only stable phase of carbon, in agreement with the experimental results of Matsumoto et al. (J. Mater. Sci. 17, 3106 (1982)). The QE model can also explain the experimentally observed effects on the CVD of diamond resulting from variations in the available growth parameters (substrate temperature, reactant ratio, etc.). When the QE thermodynamic model is extended to reactions between carbon, hydrogen, and oxygen the stability region of solid carbon in the C-H-O phase diagram is predicted to shrink considerably due to the formation of CO. In particular, it is predicted that no carbon can be deposited from gas mixtures whose C/O ratio equals unity.;In a series of experiments the interactions of tungsten and rhenium filaments with gas mixtures typical of the diamond growth environment have been analyzed. It has been demonstrated that the filaments themselves can act as high temperature substrates for the deposition of graphitic carbon and that the filaments then lose their ability to dissociate the reactant gases. The filament resistance, spectral emissivity, power consumption, and partial pressures of stable gases in the reaction chamber have been found to depend critically both on the filament temperature and on the reactant ratio. Specifically, both W and Re filaments show sharp jumps in power consumption at essentially the same temperature, signaling strong increases in filament activity and, hence, production of atomic hydrogen. This behavior can be related to the removal of nonreactive carbon from the filament surface via etching by atomic hydrogen. Upon the addition of small amounts of oxygen to C-H mixtures these transitions from deposition to etching of graphitic carbon from the filament surface are shifted to lower temperatures. The results of these experimental studies are consistent with the predictions of the QE thermodynamic model for both the C-H and C-H-O systems and the implications of these observations for filament-assisted diamond CVD are discussed.;Samples deposited from various gas mixtures under different growth conditions have been found to be in good agreement with the predictions of the QE model.
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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.
