Electron-beam engineering of single-walled carbon nanotubes from bilayer graphene

Bilayer graphene nanoribbons (BGNRs) with a predefined width have been produced directly from bilayer graphene using a transmission electron microscope (TEM) in scanning mode operated at 300 kV. The BGNRs have been subsequently imaged in high-resolution TEM mode at 80 kV. During imaging, the interaction of the electrons with the sample induces structural transformations in the BGNR, such as closure of the edges and thinning, leading to the formation of a single-walled carbon nanotube (SWCNT). We demonstrate using molecular dynamics simulations that the produced SWCNT is, in fact, a flattened SWCNT with elliptical circumference. Density functional theory calculations show that the band gap of the flattened semiconducting SWCNTs is significantly smaller than that of the undeformed semiconducting SWCNTs, and this effect is particularly profound in narrow SWCNTs.