Comparative study of pulsed laser ablated plasma plumes from single crystal graphite and amorphous carbon targets. Part I. Optical emission spectroscopy

A comparative study of ablation plasma plumes originated from single crysta l 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 carried out by means of a monochromator equipped with an inte nsified optical multichannel analyzer. In high vacuum, the emission lines o f carbon neutral C and ions of C+, C2+, and C3+ can be observed from both t he SCG and a-C plasma plumes. The emission intensity from C atoms increases with laser energy density (E-L) increase for both cases. The C-2 emission intensity from the SCC plasma plume changes drastically with E-L, while tha t from the a-C plasma plume is almost constant. The C-2/C emission intensit y ratio for the a-C case decreases with E-L increase. As for the SCG case, the C-2/C ratio decreases with E-L increase up to 3.0 J/cm(2), and increase s slightly with further E-L increase. Nanohardness of the deposited films d ecreases with the increase of the C-2/C emission intensity ratio. It is sug gested that for both the SCG and a-C target cases, the C-2 molecule in the ablated plasma plume may not play an important role in producing high quali ty DLC films. It is further proposed that the threshold of laser fluence fo r the formation of diamond-like character film using KrF excimer PLD is 2.1 J/cm(2) (0.84 x 10(8) W/cm(2)) for the a-C target and 3.0 J/m(2) (1.2 x 10 (8) W/cm(2)) for the SCG target. The C-2 vibrational temperature of the SCG and the a-C plasma plumes show different features on both the laser energy density and nitrogen pressure dependencies. Through optical emission spect roscopy and Langmuir probe measurements in vacuum and nitrogen background, it is concluded that there are many particles with higher mass in the SCG p lasma plume, especially at relatively lower laser energy density below 3.0 J/cm(2). (C) 2000 American Institute of Physics. [S0021-8979(00)08123-8].