Abstract:
The effect of nitrogen addition during flame deposition of diamond on the growth rate, morphology and spatial distribution of luminescent point defects in the layers has been studied. For this, well-defined amounts of nitrogen were added to the acetylene and oxygen source gases. The samples were grown under conditions that are known to give diamond deposits with a central area which is unaffected by in-diffusion of nitrogen from the ambient. Consequently, the observed features in this region must be totally ascribed to the deliberately added nitrogen. Upon nitrogen addition, the diamond growth rate in the central area of the deposits initially increases from 54 to 125 mu m/h, while at the same time a {001} texture develops. With further increasing nitrogen concentrations, the growth rate drops again while the diamond crystallites in the layer start to deteriorate and become increasingly separated from each other. This results in a morphology which is usually observed in an annulus around the central area of flame deposited diamond. Photoluminescence spectroscopy and cathodoluminescence topography reveal an increasing incorporation of nitrogen as nitrogen-vacancy pairs and a loss of homogeneity in the central area of the diamond layers with increasing nitrogen addition. Based on the results of the present study, a recipe is given for reproducible flame deposition by the use of a commercially available welding torch and 99.6% pure acetylene.