Relation between gas phase CN radical distributions, nitrogen incorporation, and growth rate in flame deposition of diamond

Abstract

Controlled amounts of nitrogen were added during oxyacetylene flame deposition of diamond to investigate the possible role of the CN radical in the effects of nitrogen addition. CN radical distributions were visualized using two-dimensional laser induced fluorescence (LIF) and compared with nitrogen incorporation into the layer and with the diamond growth rate, which were measured by means of cathodoluminescence (CL) and optical microscopy, respectively. For the studied range of nitrogen flows, it was found that the CN LIF signal in the center of the flame is linearly dependent on the added amount of nitrogen. Diamond deposition in the central region is mainly influenced by the deposition parameters, whereas deposition in the outer zone is largely determined by the interaction of the flame with the ambient; the annulus of enhanced growth is affected by both the deposition parameters and the ambient. By a simple consideration, in which the growth rate is separated in nitrogen dependent and independent contributions, an observed positional difference between CN LIF and growth rate maxima can be explained. Comparison of the CN LIF signal, the CL signal and the diamond deposition rate indicates that CN (or a closely related species) may be the species or one of the main species responsible for the effects of nitrogen addition during oxyacetylene flame deposition of diamond.