Measurement of C6H6 densities in a diamond deposition system

We report the absolute column densities of gas phase C6H6 and upper limits on absolute C4H2 and C2H3 concentrations in a hot filament diamond chemical vapor deposition (CVD) reactor. The steady state density of C6H6 is monito red as a function of C2H2 and H-2 input fractions. The C6H6 column density is a quadratic function of input C2H2 fraction at low C2H2 fractions. Above a critical C2H2 input fraction, the C6H6 column density becomes independen t of C2H2 input fraction. The column density of gas phase C6H6 is relativel y insensitive to the input H-2 fraction. The weak relationship between C6H6 and H-2 input fraction is in contradiction to the conclusion drawn from ch emical kinetics modeling of diamond CVD that H-2 strongly suppresses the fo rmation of aromatic species under diamond CVD conditions. Moreover, compari son of C6H6 column densities with previously measured CH3 column densities under similar conditions indicate that a comparable fraction of gas phase c arbon atoms in the steady state are incorporated in C6H6 as are incorporate d in the growth species CH3. (C) 1999 American Institute of Physics. [S0021 9606(99)51309-3].