Search

Observations of crystal-like ordering of fine particles in plasmas were first reported in 1994, when we succeeded to observe it by growing carbon fine particles in a methane plasma. Video cameras and Mie-scattering ellipsometry were applied for the analyses of fine particles and their crystal ordering. 3D and 2D crystal structures were observed for smaller and larger particles, respectively. The former structures were fcc, fco, and bct, but bcc structure was not observed. The result is due to the fact that the rearrangement from fcc to fco or bct occurs with both constant particle density in horizontal planes and constant interplane vertical distance. Behaviors of fine particles under microgravity were observed and analyzed using ready-made and injected fine particles. Its experimental result showed that the resultant force composed of electrostatic and ion drag forces pushes fine particles outward from the center forming a void.

The size and refractive index of particles can be analyzed through the measurement of polarization state of scattered light. The change of polarization state in Mie scattering has been represented by ellipsometric parameters, Ψ and Δ, like the reflection ellipsometry. The analysis method is called Mie-scattering ellipsometry. By in-process Mie-scattering ellipsometry, the growth processes of carbon particles in argon plasma and in methane plasma were analyzed. It was found that carbon particles grow by coagulation in argon plasma, while they grow by carbon coating in methane plasma. It is also shown that imaging Mie-scattering ellipsometry has the potential for the easier confirmation of optical adjustment from a long distance, as well as for the analysis of spatial distribution of particle size.