Growth rate enhancement by nitrogen in diamond chemical vapor deposition-a catalytic effect

The diamond growth rate enhancement factor A([N-2],[CH4]) of nitrogen has been measured in situ by laser reflection interferometry using thin reflecting iridium interlayers on on-axis and off-axis single crystals. A shows a characteristic linear decrease with the methyl radical concentration in the gas phase. The resulting local maximum in the growth rate curve yields conditions for which growth is accelerated when the methane concentration is decreased. In a model that fits the measurements quantitatively nitrogen catalyzes growth and competes with the hydrocarbon growth species for adsorption sites. The data allow excluding of several alternative models for nitrogen induced growth rate enhancement.