Growing a carbon nanotube atom by atom: "and yet it does turn".

We use field emission microscopy (FEM) to observe directly the growths of individual carbon nanotubes (CNTs) from the nucleation stage and discover that the CNTs often rotate axially during growth, thus supporting a recently proposed "screw-dislocation-like" (SDL) model. One particularly revealing case is emphasized here in which the CNT turned approximately 180 times during its 11 min growth. Even more remarkable is the frame-by-frame analysis of the video which shows that the rotation proceeds by discrete steps with about approximately 24 per rotation, half the number of atoms on the circumferences of common single wall carbon nanotubes (SWNTs). The conclusion is that we directly observed the SDL growth of a SWNT one carbon dimer at a time. This observation should aid researchers to precisely understand and control the growth of SWNTs.