Tube-tube interaction in double-wall carbon nanotubes

In a Raman map of double-wall carbon nanotubes, the radial breathing modes of the inner tubes are grouped into clusters with similar resonance behavior. These clusters are located close to the resonances of SDS wrapped HiPco tubes and can spread over 30 cm(-1). Compared to the HiPco tubes the resonances of the inner tubes are shifted about 50 meV to the red. Each cluster represents one fixed inner tube type in several different outer tube types and each component of a cluster originates from a well defined inner/outer tube pair. Elaborate inter-shell interaction models showed an increasing charge transfer from the outer to inner tube with decreasing diameter difference. Additionally, many DWCNTs systems seem to be metallic, i.e. they have a finite density of states at the Fermi level.