Electronic structure of polychiral carbon nanotubes

Most of the works devoted so far to the electronic band structure of multiwall nanotubes have been restricted to the case in which the individual layers have the same chirality. By comparison, much less is known on the electronic properties of multiwall nanotubes that mix different chiralities. These are interesting systems, however, since they can be composed of both metallic and semiconducting layers. For the present work, tight-binding calculations were undertaken for polychiral two-layer nanotubes such as (9,6)@(15,10), (6,6)@(18,2), and others. The recursion technique was used to investigate how the densities of states of the individual layers are affected by the intertube coupling. Constant-current scanning-tunneling-microscopy (STM) images were also calculated for these systems. The result obtained is that the image of a two-wall nanotube is pretty much the same as that of the isolated external layer. It is only in the case of monochiral, commensurate structures such as (5,5)@(10,10) that interlayer effects can be seen in the STM topography.