Comparative study of pulsed laser ablated plasma plumes from single crystal graphite and amorphous carbon targets. Part II. Electrostatic probe measurements

In an ongoing effort to investigate plasma plume features yielding high qua lity diamond-like carbon films, we have applied plasma plume diagnosis and film characterization to examine plume character distinction from KrF laser ablation of both amorphous carbon (a-C) and single crystal graphite (SCG) targets. The advancing plasma plume produced by these structurally differen t targets are observed to possess quantitatively similar total heavy partic le inventory, ionized fraction, and electron thermal content, yet quite dif ferent ion kinetic energy, plume profile, C-2 formation mechanism, and conc entration of complex molecules. Plume electron temperatures are observed to reside in the range 1-3 eV, with those in SCG plumes similar to 10%-30% gr eater than a-C at all spatial positions downstream of the target. For both target cases, we find T-e drop off with position away from the target with radiation as the most likely loss mechanism for these noninteracting plumes propagating in vacuum. Electron density is found to be similar to 10%-12% lower near the target in SCC than a-C plumes consistent with mass loss inve ntory measurements, whereas ion fractions are estimated in the range simila r to 10%-15% for both target cases. All recorded data support the conclusio n that the SCG target plasma plume is populated with heavier, more complex molecules than those in a-C which have been shown to be predominantly compr ised of C and C+ under vacuum conditions with the addition of C2 at high fi ll pressure. A significantly smaller profile peaking factor for SCG plumes supports this conclusion. Less energetic and slightly lower temperature SCG plume conditions are consistent with reduced peaking and more massive plum e species. Plasma plumes from SCG targets exhibit laser energy (El) depende nt peaking, again consistent with more complex molecules increasingly disas sociated with EI increase. The El dependence further suggests the potential for control of particle size distribution and plume profile peaking, thoug h not independently. Consistent with this scenario is the observation of ha rder films produced from SCG targets at lower E-l. Micro-Raman results indi cate strongly heterogeneous films deposited by SCG target ablation even und er vacuum conditions further supporting the case for more complex structure s with greater hardness. Energy balance estimates indicate that ion kinetic energy dominates the balance and that SCG ablation liberates about twice t he number of C-12 atoms from the target per unit E-l. As well, high pressur e background fill indicates lesser plume energy attenuation for SCG plumes, again suggesting the presence of higher mass particles. (C) 2000 American Institute of Physics. [S0021-8979 (00)08223-2].