Scanning tunneling spectroscopy of a semiconducting heterojunction nanotube on the Au(1Â 1Â 1) surface

The atomic and electronic structures of a single-wall carbon nanotube prepared on the Au(1 1 1) surface was studied. We performed scanning tunneling spectroscopy measurement in a semiconducting nanotube heterojunction, obtaining the local electronic density of states. An interface state was observed within the energy gaps of the semiconducting nanotubes. The interface state is spatially localized within a few nm scales and decays into the two semiconducting CNTs with unequal screening lengths. The interface state is donor-like, possibly originating from a heptagonal atomic structure. The interface state is well-understood, in analogy with that of a conventional semiconductor heterojunction.