All ETDs from UAB

Advisory Committee Chair

Yogesh K Vohra

Advisory Committee Members

Shane A Catledge

Joseph G Harrison

Raymond G Thompson

Uday K Vaidya

Document Type

Dissertation

Date of Award

2009

Degree Name by School

Doctor of Philosophy (PhD) College of Arts and Sciences

Abstract

In this dissertation research, the roles of three basic parameters in homoepitaxial diamond growth by microwave plasma chemical vapor deposition on planar (type Ib yellow diamond plates) and non-planar (type Ia brilliant cut natural diamonds) substrates have been investigated. Isotopically enriched carbon-13 methane gas has been utilized in the experiments as the source of carbon to clearly distinguish the grown diamond layer from the underlying substrate using Raman spectroscopy. Nitrogen showed a catalytic effect in the growth of diamond on diamond anvil substrates. In the standard H2/O2/N2/13CH4 feed gas mixture, when nitrogen was varied between 0 to 3500 parts per million (ppm), an optimum value of 1250 ppm nitrogen resulted in the highest growth rate and smoothest surface morphology. This particular chemistry resulted in 100% success rate during the fabrication of designer diamond anvils. No such optimum value in nitrogen concentration was found for planar substrates indicating a strong dependence of diamond growth rate on the substrate geometry. On planar substrates, the effects of nitrogen concentration, methane concentration and substrate temperatures were studied independently by varying each parameter carefully over a broad range. Dramatic changes in surface morphologies and growth rates were observed by optical and atomic force microscopy. The nitrogen incorporation in carbon-13 diamond layers was monitored through photoluminescence spectroscopy of nitrogen-vacancy complexes. A twentyfold increase in growth rate has been reported as a result of this research. An optimum substrate temperature of 1050 C resulted in the highest growth rate when 2% CH4/H2 was used in feed gas mixture. Use of high methane concentration in the feed gas mixture resulted in diamond films where twinning on the surface was completely absent. Aggressive incorporation of nitrogen in CVD diamond has been observed at substrate temperatures above 1050 C indicating that species such as HCN, CN and NHX play an active role on the surface at those temperatures. The optimum temperature has been observed to shift to higher values as the C/N ratio in the feed gas mixture increased. The roles of various growth parameters in high growth rate and high quality homoepitaxial diamond growth are discussed in this thesis.

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