Single-walled carbon nanotubes (CNTs) were synthesized from carbon monoxide and iron catalyst nanoparticles by two different aerosol methods. The catalyst particles were produced by physical vapor nucleation using a resistively heated iron wire (hot wire generator) and by thermal decomposition of ferrocene vapor. The essential role of etching agents (CO2 and H2O) in the CNT formation process was demonstrated. An addition of small amounts of CO2 and H2O vapor in the reactor resulted in an increase in CNT length. Also, the CO2 introduction was found to decrease the minimum temperature for CNT synthesis from 890 degrees C to below 600 degrees C. (c) 2005 Elsevier B.V. All rights reserved.