Probing electric characteristics and sorting out metallic from semiconducting carbon nanotubes

Differences of the electric response of metallic and semiconducting single-walled carbon nanotubes (SWCNTs) to a DC electric field applied by the tip of a scanning probe microscope are reported. We show that conventional Electric Force Microscopy (EFM) images can be used to directly distinguish metallic from semiconducting SWCNTs on a process-free sample. Not only the magnitudes of their response are different, but, more important, the EFM line profile across a nanotube – its electric signature – is qualitatively distinct for metallic or semiconducting SWCNTs. The influence of nanotube length and diameter on their response to the applied field is also analyzed and shows remarkable differences. Theoretical modeling explains and fits the experimental data, giving support to this very simple, yet extremely accurate and all-encompassing methodology.