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 conglomeration and the formation of ordered Coulomb lattices at the plasma-sheath region above the powered electrode, (c) coalescence of grains within the Coulomb 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 centimeters in diameter suspended in the plasma, (f) deposition of the network on the electrode and its subsequent growth on the surface. Large carbon structures 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 electron microscope, and by micro-Raman spectroscopy. (C) 1999 American Vacuum Society. [S0734-2101(99)01106-9].