Laser-induced particle formation and coalescence in a methane discharge

Laser-induced formation of submicrometer dust particles and the subsequent coalescence phenomena in a low-pressure methane radio-frequency plasma have been analyzed. Six distinct phases can be distinguished: (a) nanoparticle synthesis by laser interaction with the plasma species, (b) particle conglo meration and the formation of ordered Coulomb lattices at the plasma-sheath region above the powered electrode, (c) coalescence of grains within the C oulomb lattice and formation of submillimeter strings, (d) condensation of the strings in the discharge and the formation of V-shaped structures, (e) condensation of the V structures into a single network of several centimete rs in diameter suspended in the plasma, (f) deposition of the network on th e electrode and its subsequent growth on the surface. Large carbon structur es as well as nanoparticles have been analyzed in situ by He-Ne laser light scattering and laser ablation and ex situ by an optical and a scanning ele ctron microscope, and by micro-Raman spectroscopy. (C) 1999 American Vacuum Society. [S0734-2101(99)01106-9].