Bimetallic particles of Ti and Co have been used to grow multi-walled carbon nanotubes (MWNTs) to study the effects of Ti on the growth. The particles were generated by laser ablation and size-classified with a differential mobility analyzer. Diameter-controlled MWNTs were grown on a silicon substrate from 5-nm particles by thermal chemical vapor deposition using acetylene at 510 and 610 degreesC. Titanium has been found to enhance the MWNT growth significantly. There is an optimum Ti fraction for the growth, as confirmed by evaluation of the growth probabilities of MWNTs. A possible mechanism of growth enhancement by Ti is discussed. (C) 2004 Elsevier B.V. All rights reserved.