Plasma assisted chemical vapor deposition of diamond and applications: From large-grain polycrystalline diamond to nanocrystalline diamond

Growth of diamond with extreme physical and chemical properties can be achieved in electrical discharges under properly controlled plasma chemistry at temperatures and pressures where graphite, instead of diamond, is thermodynamically stable. This discovery led us to wide open opportunities for applying the extreme hardness, thermal conductivity, optical and microwave transparency, chemical inertness, wear resistance, coefficient of thermal expansion, dielectric strength, carrier saturation velocities, and many other interesting properties of diamond crystals and coatings to industrial and scientific applications. Plasma density, plasma chemistry, as well as physical processes in plasmas such as ion bombardment of substrates and/or the growing diamond surfaces all play important roles in the nucleation and the growth of diamond on various substrates. Plasmas generated in gaseous mixtures such as methane and hydrogen with controlled dilution by argon as well as plasmas generated in vapor mixtures formed from properly mixed liquid solutions alone have been developed and optimized for the nucleation and growth of diamond of selected crystal orientations, grain sizes, and doping levels. A systematic experimental project has also been conducted to explore diamond nucleation and growth by plasmas generated in gas mixtures of methane and hydrogen that are highly diluted by more than 90% argon. Growth of well-faceted microcrystalline diamond films with preferred (100) or (111) crystal orientation as well as nanocrystalline diamond films could be tailored by controlling plasma parameters such as microwave power density, gas pressures and compositions, and substrate temperatures. In this presentation a number of plasma CVD processes being developed in our laboratory for diamond deposition and many current and potential applications of diamond films and coatings fabricated by the plasma CVD processes will be reported. Effects of inert argon gas on the process plasmas and the process parameters that determine the primary and secondary nucleation rates and the growth rate for diamond will be discussed. Plasma CVD, diamond, nucleation, growth.