Diameter-controlled multiwalled carbon nanotubes (MWNTs) have been grown by hot-filament chemical vapor deposition using nickel nanoparticles as catalyst. The nanoparticles were generated by laser ablation, classified with a differential mobility analyzer, and deposited onto silicon substrate. The particle size is tunable down to 2-3 nm, and particles with a geometric mean diameter of 5.1 nm (geometric standard deviation: 1.1) were used for carbon-nanotube growth. MWNTs were grown on the substrate using acetylene at 550 C. The particles did not coalesce during growth, and the MWNTs had outer diameters matching the particle sizes, indicating that the current method can produce diameter-controlled MWNTs. (C) 2003 Elsevier B.V. All rights reserved.