Modeling of the gas-phase chemistry in C–H–O gas mixtures for diamond chemical vapor deposition

Abstract

The boundaries of the diamond deposition region in the C-H-O ͑Bachmann͒ atomic phase composition diagram have been reproduced successfully for 38 different C, H, and O containing gas mixtures using the CHEMKIN computer package, together with just two criteria-a minimum mole fraction of methyl radicals ͓CH 3 ͔ and a limiting value of the ͓H͔/͓C 2 H 2 ͔ ratio. The diamond growth/no-growth boundary coincides with the line along which the input mole fractions of C and O are equal. For every gas mixture studied, no-growth regions are found to coincide with a negligible (Ͻ10 Ϫ10) mole fraction of CH 3 radicals, while for gas mixtures lying within the diamond growth region the CH 3 mole fraction is ϳ10 Ϫ7. Each no-growth→diamond growth boundary is seen to be accompanied by a 2-3 order of magnitude step in CH 3 mole fraction. The boundary between diamond and nondiamond growth is less clearly defined, but can be reproduced by assuming a critical, temperature dependent ͓H͔/͓C 2 H 2 ͔ ratio ͑0.2, in the case that T gas ϭ2000 K͒ that reflects the crucial role of H atoms in the etching of nondiamond phases. The analysis allows prediction of the composition process window for good quality diamond growth for all stable input gas mixtures considered in this study.

Effects of Feed Gas Composition and Catalyst Thickness on Carbon Nanotube and Nanofiber Synthesis by Plasma Enhanced Chemical Vapor Deposition

“…The trends predicted by the present simulations for CNT growth conditions are similar to those estimated by experimental data for diamond growth conditions. The simulations confirm that the atomic hydrogen to acetylene ratio ([H]/[C 2 H 2 ]) demarcates a change in growth products, as suggested by Petherbridge et al 42 This study concludes that changes in catalyst thickness and gas-phase composition exhibited strong effects on the diameters of the nanotubes and nanofibers and the quality of growth. Future planned studies using in situ Effects of Feed Gas Composition and Catalyst Thickness on CNT and Nanofiber Synthesis by PECVD gas-phase laser diagnostics above the growth surface are expected to provide further insights into the effects of local gas phase chemistry on nanotube and nanofiber growth.…”

“…At 2% inlet CH 4 concentration, diamond is typically formed. Petherbridge et al 42 mole fraction in the inlet stream. We note that the results from present study are consistent with the Petherbridge et al criteria in that almost no tubular carbon content was observed at 3% inlet CH 4 mole fraction, while carbon nanotubes and/or nanofibers were observed for all higher inlet methane concentrations.…”

Contiguous Petal-like Carbon Nanosheet Outgrowths from Graphite Fibers by Plasma CVD

“…The likely mechanism of petal growth involves deposition of hydrocarbon radicals at or near the exposed surface graphene edges, which may be accentuated by the hydrogen−oxygen plasma pretreatment. According to Petherbridge et al and supported by recent work by Garg et al , the critical factor in determining the preference for diamond sp 3 lattice structures or graphene sp 2 structures upon deposition is the ratio of atomic hydrogen to acetylene in the plasma mixture. The present deposition pressure and plasma power conditions are similar to those that produce diamond growth , but the gas composition is more similar to that for carbon nanotube growth and is expected to be the most significant factor in determining the hydrogen:acetylene ratio.…”

Nano crystalline diamond MicroWave Chemical Vapor Deposition growth on three dimension structured silicon substrates at low temperature

“…The complex diamond CVD growth mechanisms involve both creation of sp3 carbon bonds and selective etching of the sp2 carbon by hydrogen. In addition to its role as a selective etchant, hydrogen bombardment creates reactive sites on the diamond surface on which CH3 radicals can dock [30,31]. Then, the two neighbouring methyl groups can form a sp3 C-C bond and release two hydrogen atoms.…”