Growth of multiwalled carbon nanotubes during the initial stages of aerosol-assisted CCVD

We report a study of the initial stages of growth of aligned multiwalled carbon nanotubes (MWNT) synthesised by catalytic chemical vapour deposition (CCVD) of liquid aerosol obtained from toluene/ferrocene solution. A special experimental procedure has been developed to stop the process after short durations (30 s to 2 min). Two different pyrolysis temperatures are considered: 800 and 850 °C. Both scanning and transmission electron microscopy (SEM, TEM) coupled to energy-dispersive X-ray (EDX) analyses are used in order to determine the location of catalyst particles and to examine their chemical nature, morphology and size distribution when nanotubes start to grow. During the early stages (30 s), we observe the formation of a layer of catalyst particles on silicon substrates before the growth of nanotubes. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) measurements indicate the occurrence of iron oxide (γ-Fe2O3 or Fe3O4). In addition, XPS analysis reveals the formation of graphite-like carbon, demonstrating that iron oxide particles catalyse the decomposition of toluene vapour. SEM and TEM observations show that these particles are most often located at the nanotube root, suggesting a base growth mechanism responsible for the formation of aligned nanotube when prolonging growth time (2 min).