Microbalance studies of diamond nucleation and growth rates

In situ measurements of diamond nucleation and growth rates using a microbalance within a hot-filament reactor were made. Methane, acetylene, ethylene and ethane in hydrogen, with and without the addition of oxygen, were used as source gases. The measured reaction orders strongly support the view that the bulk of the atom addition is by single-carbon species, e.g. CH,. The reaction order shifts to zero at high hydrocarbon concentrations, suggesting that diamond growth is a surface-site-limited process. Diamond nucleation on virgin substrates shows an initial period in which d(2)M/dt(2) < 0, which is attributed to the incorporation of carbon into the substrate.