title: Orientation and morphological evolution of catalyst nanoparticles during carbon nanotube growth.
abstract: We examined the structure, morphology, and orientation of catalyst nanoparticles used for seeding and growing multiwall carbon nanotubes (MWCNTs) by plasma enhanced chemical vapor deposition in CH4/H2 gas mixtures. Iron catalyst nanocrystals are converted to Fe3C in CH4/H2 plasmas and the MWCNTs grow from Fe3C nanocrystals. Initially faceted and equiaxed catalyst nanocrystals are distorted and elongated significantly once a tubular CNT structure is formed around the catalyst particles. Eventually, catalysts deform into elongated tear-drop shapes. Once this morphology forms, CNT structures produced are straight and have uniform diameters. Surprisingly, the Fe3C nanocrystals located inside the base of well-graphitized nanotubes do not exhibit a preferred orientation relative to the nanotube axis. Catalyst nanocrystals in a variety of orientations relative to the nanotube axis still produce well-graphitized nanotubes with similar diameters and structures.
authors.affiliation: Department of Chemical Engineering & Materials Science, University of Minnesota, Minneapolis, Minnesota 55455, USA.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Behr
authors.forename: K Andre
authors.initials: KA
authors.lastname: Mkhoyan
authors.forename: Eray S
authors.initials: ES
authors.lastname: Aydil