Synthesis of CVD diamond at atmospheric pressure using the hot-filament CVD method

At low pressure, chemical vapor deposition (CVD) diamond growth by conventional techniques such as micro-wave plasma and hot-filament have been achieved by metastable precursor species. Moreover, bulk diamond at extremely high pressures and temperatures was consistently originated by the nature of diamond-graphite phase transition. CVD diamond growth has four problems with these conventional techniques. Excluding contaminated air from low pressure reactive systems has been problematic. It is very difficult to control the concentration of atomic hydrogen at high pressures. The growth rate is unsatisfactory and the running cost of gases are high. However, the hot-filament CVD technique at atmospheric pressure overcomes these problems. We have found that in order to control the concentration of atomic hydrogen, the residence time of the input gas and the methane-hydrogen concentration ratio needed to be varied at each pressure. The relationship between the quality of deposited diamond and the pressure have been also investigated by Raman spectroscopy and X-ray diffraction patterns (XRD). The growth rate at atmospheric pressure (1060.1000 Pa) was found to be greater than that at the conventional pressure (5000 Pa). At atmospheric pressure, the growth rate abruptly increases with the residence time. XRD analysis revealed that the quality of diamonds grown at atmospheric pressure was higher than that of diamonds produced at low pressures. Furthermore, high quality diamond growth was achieved with a long residence time of the input gas at atmospheric pressure. (C) 1999 Published by Elsevier Science S.A. All rights reserved.