Studies of diamond films/crystals synthesized by oxyacetylene combustion flame technique

High-quality diamond films/crystals were synthesized using the oxyacetylene combustion flame technique at atmospheric pressure in a narrow acetylene-rich region. Three nozzle configurations, single-, tilted- and multi-nozzle, were used to explore possible ways to improve the uniformity of diamond films and to increase the deposition areas. It was found from the systematic investigation that the surface morphology and crystal structure of diamond films are strongly dependent on the processing parameters such as the gas mixture ratio, r, of acetylene to oxygen, substrate temperature, and nozzle configurations. The appearance of two-dimensional spiral steps on (1 1 0) diamond surfaces was observed, which have not previously been reported in the literature. This phenomenon is explained using the concept of surface reconstruction. The observed layered steps on (1 0 0), (1 1 0), and (1 1 1) diamond planes strongly suggest that under certain conditions the synthetic diamond crystals could grow with a layer mechanism on any major plane, at least in the case of films made using combustion flames. Experimental results from X-ray diffraction and Raman spectroscopy show the presence of compressive stress along the 1 0 0 direction in the diamond films. The films also have good optical transparency, indicating potential for optical coating applications. The hardness, growth rate, film uniformity, and deposition areas of diamond films are discussed. Advantages and limitations of these three flame-torch deposition techniques are also presented.