A Nucleation and Growth Model of Vertically-Oriented Carbon Nanofibers or Nanotubes by Plasma-Enhanced Catalytic Chemical Vapor Deposition

Abstract

Carbon nanofibers are grown by direct current and hot filaments-activated catalytic chemical vapor deposition while varying the power of the hot filaments. Observations of these carbon nanofibers vertically oriented on a SiO2 (8 nm thick)/Si(100) substrate covered with Co nanoparticles (10-15 nm particle size) by Scanning Electron and Transmission Electron Microscopies show the presence of a graphitic "nest" either on the surface of the substrate or at the end of the specific nanofiber that does not encapsulate the catalytic particle. Strictly in our conditions, the activation by hot filaments is required to grow nanofibers with a C2H2 - H2 gas mixture, as large amounts of amorphous carbon cover the surface of the substrate without using hot filaments. From these observations as well as data of the literature, it is proposed that the nucleation of carbon nanofibers occurs through a complex process involving several steps: carbon concentration gradient starting from the catalytic carbon decomposition and diffusion from the surface of the catalytic nanoparticles exposed to the activated gas and promoted by energetic ionic species of the gas phase; subsequent graphitic condensation of a "nest" at the interface of the Co particle and substrate. The large concentration of highly reactive hydrogen radicals mainly provided by activation with hot filaments precludes further spreading out of this interfacial carbon nest over the entire surface of the substrate and thus selectively orientates the growth towards the condensation of graphene over facets that are perpendicular to the surface. Carbon nanofibers can then be grown within the well-known Vapor-Liquid-Solid process. Thus the effect of energetic ions and highly reactive neutrals like atomic hydrogen in the preferential etching of carbon on the edge of graphene shells and on the broadening of the carbon nanofiber is underlined.

GISAXS study of the alignment of oriented carbon nanotubes grown on plain SiO2/Si(100) substrates by a catalytically enhanced CVD process

“…The sample preparation has already been described elsewhere [4,5] and is only briefly recalled. The substrates were prepared by SiO 2 deposition of a layer of thickness 5 nm by a DECR plasma process on a heavily doped Si(100) sample (Sb n-doped with ρ = 3 mΩ cm; size 8.5 × 6 × 0.245 mm 3 ).…”

Linewidths of C2H2 perturbed by H2: experiments and calculations from an ab initio potential

“…[10] It is known that acetylene also plays a role as an intermediate species in the process of soot formation often observed in combustion research [11,12]. Finally, acetylene is frequently used as a target molecule to measure the temperature of combustion mixtures through the use of rotational or vibrational coherent anti-Stokes Raman spectroscopy (CARS) [Ref.…”

Modelling the effects of nitrogen doping on the carbon nanofiber growth via catalytic plasma‐enhanced chemical vapour deposition process

“…[19] 2. Generation of carbon species on the catalyst nanoparticle surface (which is exposed to plasma) due to the dissociation of hydrocarbons on the catalyst nanoparticle surface.…”