Evidence for nonclassical nucleation at solid surfaces in diamond deposition from the gas phase

Abstract

In the framework of a previously developed kinetic model, a discriminating criterion is established to distinguish between classical and nonclassical nucleation of diamond at solid surfaces. The two-step model gives the non-steady-state nucleation density function in terms of the rate constants for active site → germ, germ → active site, and germ → nucleus kinetic steps. The criterion states that α/β > 6 is a necessary condition for classical nucleation at surfaces to occur, α and β being functions of the rate constants which can be obtained by appropriate analysis of the experimental data. This criterion is applied to recent results on diamond nucleation at silicon surfaces and indicates nonclassical results The expression of the nonequilibrium Zeldovich factor, Z, is also found in the form Z = [1 + K/n_d]⁻¹, K and n_d being the rate constants for the germ → nucleus and germ → active site steps, respectively. An estimation of the rate constants is reported and the corresponding Zeldovich factor is evaluated to be 0.6 for nucleation at both Si(100) and Si(111) substrates.