Low temperature (500-700 degrees C) synthesis of high-quality single-walled carbon nanotubes (SWNTs) via microwave plasma assisted chemical vapor deposition (MPCVD) was demonstrated by pyrolysis of methane over the Fe-Mo bimetallic catalyst nanoparticles supported on porous MgO powders. In comparison with higher temperature (800 degrees C) growth by the conventional thermal CVD using the same batch of catalyst, the SWNTs grown by the low temperature MPCVD show small diameters with narrow distribution. Moreover, it was found that the lower the growth temperature, the smaller and more homogenous the tube diameter, showing the feasibility of controlling the SWNTs diameters by tuning the growth temperature. (c) 2005 Elsevier B.V. All rights reserved.