Fine structure analysis of spherical carbon particles produced in a methane plasma

We have investigated the growth mechanism as well as the structure of spherical carbon particles grown to micron sizes in a low pressure columnar CH4/H2 plasma by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). From SEM observations, we found a fact that the spherical carbon particles were formed not on the substrate surface but in the sheath. From TEM observations, it was clarified that the spherical carbon particles were composed of graphite onions ranging from 2 to 10nm and diamonds of ca. 5nm were growing at the same time. ► The growth of spherical carbon particles of micron sizes was discovered. ► The spherical particles are produced at the plasma sheath. ► The particles are composed of graphite onions ranging from 2 to 10nm. ► The diamond crystalline grows together with the graphite onion.