Plasma diagnostics during pulsed laser deposition of diamond-like carbon using single crystal graphite and amorphous carbon

Optical emission study of ablation plasma plumes from single crystal graphite (SCG) and amorphous carbon (a-C) targets during the preparation of diamond-like carbon (DLC) films by KrF excimer pulsed laser deposition (PLD) has been investigated. The C I emission intensity increases with laser energy density (E_L) increase, while the C₂ emission changes drastically with E_L for both ablated plasma plumes. The C₂/C emission intensity ratio for the a-C plume decreases with E_L increase, while the C₂/C ratio for the SCG plume decreases with E_L increase up to 3.0 J/cm², then increases slightly with further E_L increase. Nanohardness of the DLC films decreases with the C₂/C ratio increase. It is suggested that the C₂ molecule in the plasma plume does not play an important role in producing high quality DLC films, and that the C₂/C ratio is a good parameter to monitor the PLD process.