Abstract
The qualities of freestanding single-walled carbon nanotubes (SWCNTs) grown on Co/Si(100) in the gravity-assisted chemical vapour deposition (CVD) process have been investigated. Vertically oriented SWCNTs of high quality appear at a growth time of less than 3 min, verified by the clear radial breathing mode (RBM) in the Raman spectra and by the high resolution images taken by a transmission electron microscope (TEM). At a growth time of 3 min, vertical and looped SWCNTs co-appear on the substrate. A SWCNT longer than ∼1 μm tends to bend into a semicircular loop. At a longer growth time such as 20 min, the coating of amorphous carbon (a-C) on the SWCNT becomes dominant, which is attributed to catalytic poisoning. A relatively long SWCNT (∼10-40 μm) surrounded with a thick a-C layer is the final structure. The bending stiffness of the a-C tube is estimated ∼15 times larger than that of the SWCNT, which helps to keep the a-C/SWCNT composite structure in a nearly vertical shape. A mechanism has been proposed to explain the coating of a-C on SWCNTs. © IOP Publishing Ltd.