Atomically resolved Moiré-type superstructures in double-walled carbon nanotubes

Double-wall carbon nanotubes (DWCNTs) are investigated with high resolution by scanning tunneling electron microscopy at 78 and 4.5 K. Besides the atomic structure of the DWCNT surface, an additional honeycomb-type superstructure is revealed at these low temperatures. This periodic structure can be interpreted in terms of a Moiré pattern resulting from a rotation between the rolled up graphene sheets that constitute the DWCNT. Deviations of the observed Moiré patterns from the perfect hexagonal Moiré patterns that are commonly resolved for multi-graphene layer surfaces are found to be related to the intrinsic different curvature of the inner and outer tube of the DWCNT. Investigation of such Moiré patterns in the surface of DWCNTs allows one to gain more insight into the structure and chirality of the otherwise inaccessible inner shell of the DWCNTs.