  The surface reconstruction of the Fe catalyst films due to high temperature
processing in hydrogen prior to nanotube nucleation and its effect on the
growth morphologies of partially filled carbon nanotubes (CNTs) synthesized
using atmospheric pressure chemical vapor deposition (APCVD) of propane was
investigated. Results show that pre-heating of the catalyst film deeply
influences the particle size distribution, which governs the growth
morphologies of the corresponding CNTs. The distribution of the catalyst
particles over the Si substrate was analyzed before and after the heat
treatment by atomic force microscopy (AFM) which reveals that heat treatment
causes clusters of catalyst to coalesce and form macroscopic islands. The X-ray
diffraction (XRD) pattern of the grown material indicates that they are
graphitic in nature. Scanning electron microscopy (SEM) analysis suggested that
the growth density strongly depends on the pre heat treatment of the Fe
catalyst film. Multiwalled CNTs with partial catalyst filling were observed via
high-resolution transmission electron microscopy (HRTEM) measurements. The
degree of graphitization of the CNTs also depends on the pre heating as
demonstrated by Raman analysis. A simple model for the growth of partially
catalyst filled nanotubes is proposed.
