Nucleation and growth during the chemical vapor deposition of diamond on SiO 2 substrates
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I. INTRODUCTION
II. DESCRIPTION OF EXPERIMENTS
The chemical vapor deposition of diamond films on silicon has received considerable attention and is reviewed in several recent articles.1'2 There has also been interest in depositing diamond on glass substrates.3'4 The current study focuses on the earliest stages of the process on SiO2 surfaces, at times where diamond grows as isolated grains (i.e., prior to the coalescence of these grains). These results are compared with deposition on Si surfaces, under the same deposition conditions. The early stages of microstructure evolution during the CVD of polycrystalline materials depend on nucleation and growth, and on other relevant kinetic mechanisms such as mass transport. Deconvoluting nucleation and growth kinetics from a single set of experiments is potentially difficult. The easiest way to decouple these two mechanisms is to measure the growth rates independently. This was accomplished by depositing diamond under conditions where a limited number of nuclei formed in a relatively short amount of time, such that the particle size distribution was relatively uniform. Parallel experiments with Si and SiO2 substrates show that both the nucleation and growth kinetics were affected by the substrate material.
Diamond deposition was conducted in a microwaveplasma system (ASTex, model HPM/M). This reactor consists of a vertical, 6 in. diameter, water-cooled, stainless steel resonating cavity. The samples were positioned on a 4 in. diameter, induction-heated graphite stage. Three different substrate materials were investigated: (100) Si, oxidized (100) Si, and high-purity fused silica (Asahi Glass Co., total impurities
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