Influence of methane concentration on the nucleation and growth stages in diamond film deposition

Optical emission spectroscopy (OES) and mass spectrometry have been used to characterize the reaction species during the CVD synthesis of diamond films using methane and hydrogen gas mixtures in a microwave discharge. In tile low methane concentration range, an increase in the nucleation rate with the methane content in the reactor has been detected by scanning tunneling microscopy (STM), which has been associated to the increase in the atomic hydrogen as well as to the presence of CHx (x < 3) radicals, considered as precursors of amorphous and diamond-like carbon films. Although the further growth of the diamond films is mainly associated with CH3 radicals and/or C2H2 molecules, present in the discharge, other ionized CH+ species have been detected by OES, which are known to favor the attachment of methyl radicals on the growing surface.