Chemical kinetics in carbon depositing d.c.-arc jet CVD reactorsстатья
Статья опубликована в высокорейтинговом журнале
Информация о цитировании статьи получена из
Web of Science,
Scopus
Статья опубликована в журнале из списка Web of Science и/или Scopus
Дата последнего поиска статьи во внешних источниках: 18 июля 2013 г.
Аннотация:Experimental and theoretical studies of the behaviour of hydrocarbon species in d.c.-arc jet chemical vapour deposition reactors are reported, as a function of carbon source gas flow rate. CH(X) and C-2(a) radical number densities have been measured in absorption (by cavity ring-down spectroscopy) and via their optical emission in an arc jet plume operating with a standard CH4/H-2/Ar feedstock gas mixture. The C-2(a) radical number density is seen to exhibit a linear (or sub-linear) dependence on CH4 flow rate, in accord with previous findings (J. Appl. Phys. 82 (1997) 2072) for both C-2(a) and C-3(X) radicals in a lower power d.c.-arc jet. The present findings, together with the comprehensive set of earlier experimental data on gas velocity and gas temperature measurements (Diam. Relat. Mater. 7 (1998) 165; Plasma Sources Sci. Technol. 10 (2001) 595) have been used in developing a model of the plasma plume. The present calculations suggest that the observed high diamond growth rates (> 50100 mum/h) are most probably related to atomic C, which is present at concentrations as high as 10(14) cm(-3), though C-2 species are calculated to be present at comparable abundance and thus may also contribute to growth. The high temperatures (similar to3200 K) and large H-2 dissociation fraction (tens of percent) result in fast conversion of the input CH4 into C atoms as a result of H-shifting reactions of the form: CHx + H reversible arrow CHx-1 + H-2. The plasma-chemical reaction mechanism and thermochemical data developed here goes some way to unravelling the complex inter-conversion mechanisms linking C, C, and C, hydrocarbons and changing the extent of H-saturation via series of H-shifting reactions of the form: CxHy + H reversible arrow CxHy-1 + H-2, (x = 1-3). The simplified model for carbon source gas incorporation into the free stream introduced in this work is shown to overestimate the C-2(a) density but to provide a very reasonable description of CH densities measured in the Bristol d.c.-arc jet, and to reproduce well the C and CH radical absorbances and broadband absorbance at 248 nm reported in an expanding cascaded arc jet reactor operating with Ar/C2H2 at Eindhoven University of Technology (C) 2002 Elsevier Science B.V. All rights reserved.