Ion beam sputtering has been used for the sequential deposition of metal multilayers on various substrates to control the density of single-walled carbon nanotubes (SWNTs) synthesized by chemical vapor deposition. Underlayers (10-20 nm) of Al and Ir were found to activate the substrates for SWNT growth with Fe as active catalyst. Adding Mo as cocatalyst gives increased production of SWNTs and the density can be controlled by varying the thickness of the different metal layers. High-resolution transmission electron microscopy and Raman scattering are used to characterize the SWNTs.