The effects of nitrogen addition on flame deposition of diamond

Abstract

The influence of nitrogen addition on oxyacetylene flame deposition of diamond has been investigated by controlled addition of nitrogen to the combustion gases. Heretofor, the nitrogen incorporation into the diamond layer, the growth rate, and the diamond morphology were determined as a function of the nitrogen flow and compared to gas-phase distributions of the CN radical close to the deposition substrate. Two-dimensional laser induced fluorescence (LIF) was applied for the gas-phase measurements: cathodoluminescence (CL), scanning electron microscopy (SEM), and optical microscopy were used for the determination of the nitrogen incorporation, morphology and growth rate, respectively. In the studied range of nitrogen flows, a linear relation was observed between the added amount of nitrogen and the CN LIF signal in the center of the flame. It was found that that diamond deposition in the central region is largely influenced by the deposition parameters, whereas deposition in the outer zone depends mainly on the interaction with the ambient air: the annulus of enhanced growth marks the transition between those areas. In the central area, a correlation was observed between the onset of quenching of the CL signal and the occurrence of secondary nucleation on the diamond {111} facets. The observation that both the CN LIF signal and the nitrogen incorporation in the central region increase with the added amount of nitrogen indicates, together with the changes in central growth rate and morphology that are observed upon nitrogen addition, that CN or a closely related species plays an important role in the influence of nitrogen addition on flame deposition of diamond.