Udo Bringmann

Hydrogen Dissociation at Hot Filaments: Determination of Absolute Atomic Hydrogen Concentrations

Several CVD methods, using thermal or plasma activation of the gas phase, are used for the formation of synthetic diamond films1,2. The deposition processes are performed at pressures of a few tens of mbar (microwave plasma-assisted CVD (MWPCVD)3 or hot filament-assisted CVD (HFCVD)4) to atmospheric pressures (plasma jets5 or flame synthesis6) with hydrocarbons and an abundance of molecular hydrogen in the gas phase. Although the detailed mechanisms are still in discussion, the importance of the presence of hydrogen for selective diamond formation is widely accepted. Atomic hydrogen, created by the activation of the gas atmosphere, can react with hydrocarbons to form hydrocarbon species like methyl or acetylene in the gas phase. These species are by some authors assumed to be key species in the process of diamond formation7,8. Furthermore the higher etching rate of H atoms for non-diamond carbon9 is suspected to lead to the formation of thermodynamic metastable diamond as the only phase10. At last H atoms bonded to carbon on the surface may stabilize the sp3-bonds necessary for diamond formation11.