title: CVD growth of carbon nanostructures from zirconia: mechanisms and a method for enhancing yield.
abstract: By excluding metals from synthesis, growth of carbon nanostructures via unreduced oxide nanoparticle catalysts offers wide technological potential. We report new observations of the mechanisms underlying chemical vapor deposition (CVD) growth of fibrous carbon nanostructures from zirconia nanoparticles. Transmission electron microscope (TEM) observation reveals distinct differences in morphological features of carbon nanotubes and nanofibers (CNTs and CNFs) grown from zirconia nanoparticle catalysts versus typical oxide-supported metal nanoparticle catalysts. Nanofibers borne from zirconia lack an observable graphitic cage consistently found with nanotube-bearing metal nanoparticle catalysts. We observe two distinct growth modalities for zirconia: (1) turbostratic CNTs 2-3 times smaller in diameter than the nanoparticle localized at a nanoparticle corner, and (2) nonhollow CNFs with approximately the same diameter as the nanoparticle. Unlike metal nanoparticle catalysts, zirconia-based growth should proceed via surface-bound kinetics, and we propose a growth model where initiation occurs at nanoparticle corners. Utilizing these mechanistic insights, we further demonstrate that preannealing of zirconia nanoparticles with a solid-state amorphous carbon substrate enhances growth yield.
authors.affiliation: Department of Materials Science and Engineering, Massachusetts Institute of Technology , 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States.
authors.forename: Akira
authors.initials: A
authors.lastname: Kudo
authors.forename: Stephen A
authors.initials: SA
authors.lastname: Steiner
authors.forename: Bernhard C
authors.initials: BC
authors.lastname: Bayer
authors.forename: Piran R
authors.initials: PR
authors.lastname: Kidambi
authors.forename: Stephan
authors.initials: S
authors.lastname: Hofmann
authors.forename: Michael S
authors.initials: MS
authors.lastname: Strano
authors.forename: Brian L
authors.initials: BL
authors.lastname: Wardle