High purity, aligned multi-wall carbon nanotube (CNT) films were grown on quartz substrates in a chemical vapor deposition (CVD) process. In the CVD process, a solution of ferrocene in toluene was injected in a carrier gas of Ar/H-2, into a horizontal quartz tube. The CNTs were analyzed by scanning and transmission electron microscopy, thermogravimetric analysis, and Raman spectroscopy. Results for CNTs synthesized using a wide range of toluene concentrations indicated that, for carbon concentration in the gas phase higher than similar to 9.6 mol/m(3), catalyst deactivation due to encapsulation of metal particles occurs. Sectional analysis of the CVD reactor products showed that more than 40% of the iron particles were deposited in the first 10 cm section of the reactor, wherein diameters of nanotubes (similar to 28 nm) and iron particles are smaller than that of (similar to 48 nm) in the exit region of the reactor. The CNT diameter is closely related to the iron particle size on which they grow. In the area close to the reactor inlet. as the nanotube film grows the iron particles become trapped and attached to the dense film of nanotubes and turn into carbon-coated nanospheres on top of the nanotube array. (C) 2009 Elsevier B.V. All rights reserved.