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A three-dimensional kinetic Monte Carlo model has been developed to simulate the chemical vapor deposition of a diamond (100) surface under conditions used to grow single-crystal diamond (SCD), microcrystalline diamond (MCD), nanocrystalline diamond (NCD), and ultrananocrystalline diamond (UNCD) films. The model includes adsorption of CH<inf>x</inf> (x = 0, 3) species, insertion of CH<inf>y</inf> (y = 0-2) into surface dimer bonds, etching/desorption of both transient adsorbed species and lattice sidewalls, lattice incorporation, and surface migration but not defect formation or renucleation processes. A value of ∼200 kJ mol<sup>-1</sup> for the activation Gibbs energy, ΔG<sup>‡</sup><inf>etch</inf>, for etching an adsorbed CH<inf>x</inf> species reproduces the experimental growth rate accurately. SCD and MCD growths are dominated by migration and step-edge growth, whereas in NCD and UNCD growths, migration is less and species nucleate where they land. Etching of species from the lattice sidewalls has been modelled as a function of geometry and the number of bonded neighbors of each species. Choice of appropriate parameters for the relative decrease in etch rate as a function of number of neighbors allows flat-bottomed etch pits and/or sharp-pointed etch pits to be simulated, which resemble those seen when etching diamond in H<inf>2</inf> or O<inf>2</inf> atmospheres. Simulation of surface defects using unetchable, immobile species reproduces other observed growth phenomena, such as needles and hillocks. The critical nucleus for new layer growth is 2 adjacent surface carbons, irrespective of the growth regime. We conclude that twinning and formation of multiple grains rather than pristine single-crystals may be a result of misoriented growth islands merging, with each island forming a grain, rather than renucleation caused by an adsorbing defect species.