Patterns of diamond nucleation from the gas phase

On the basis of an analysis of experimental data on nucleation rates performed in the preceding paper in this issue, patterns of the process of diamond nucleation from the gas phase on Si(100) substrates have been drawn. A kinetic scheme is proposed which is apparently able to describe the complex behavior of the system in the temperature range 750 K-1225 K, at (CH4/H2) ratios between 0.5 and 2% and at a total pressure of 100 mbar. The model postulates a distribution function of the nucleation centers over the heats of adsorption of active gaseous species and introduces a cut-off criterion based on the necessary condition that adjacent active sites coexist for times longer than the characteristic time of germ growth. Nucleation centers, active sites, germs, and nuclei have been defined by simple molecular models and their rates of transformation discussed, using available literature data.