AVS 52nd International Symposium
    Nanometer-Scale Science and Technology Thursday Sessions
       Session NS-ThM

Paper NS-ThM10
Topologically Induced Localized States in Single Wall Carbon Nanotubes

Thursday, November 3, 2005, 11:20 am, Room 210

Session: Nanotube-based Devices
Presenter: S.-J. Kahng, Korea University
Authors: S.-J. Kahng, Korea University
S. Lee, Seoul National University, Korea
H. Kim, Seoul National University, Korea
J. Lee, Seoul National University, Korea
Y. Kuk, Seoul National University, Korea
Correspondent: Click to Email
The local electronic structures of semiconducting single wall carbon nanotubes was studied with scanning tunneling microscopy. We performed scanning tunneling spectroscopy measurement at selected locations on the center axis of carbon nanotubes, acquiring a map of the electronic density of states. Spatial oscillation was observed in the electronic density of states with the period of atomic lattice. Defect induced interface states were found at the junctions of the two semiconducting nanotubes, which are well-understood in analogy with the interface states of bulk semiconductor heterostructures. The electronic leak of the van Hove singularity peaks was observed across the junction, due to inefficient charge screening in a one-dimensional structure. Several paired, localized gap states were observed in semiconducting single-wall carbon nanotubes. A pair of gap states is found far from the band edges, forming deep levels. Another pair is located near the band edges, forming shallow levels. The deep levels are explained by a vacancy-adatom complex while the shallow levels are explained by a pentagon-heptagon structure. Our experimental observation indicates that the presence of the gap states provides a means to perform local band-gap engineering as well as doping without impurity substitution.