AVS 50th International Symposium
    Applied Surface Science Monday Sessions
       Session AS-MoA

Paper AS-MoA6
Scanning Tunneling Spectroscopy of Boron Nitride Nanotubes; Evidence for a Giant Stark Effect

Monday, November 3, 2003, 3:40 pm, Room 324/325

Session: Nanotube and Nanoparticle Characterization
Presenter: S. Aloni, University of California at Berkeley and Lawrence Berkeley National Laboratory
Authors: S. Aloni, University of California at Berkeley and Lawrence Berkeley National Laboratory
M. Ishigami, University of California at Berkeley
A. Zettl, University of California at Berkeley and Lawrence Berkeley National Laboratory
Correspondent: Click to Email
The Electronic properties of double-walled boron nitride nanotubes BNNT's were studied by scanning tunneling microscopy and spectroscopy at 7K. High resolution topographs of the tubes reveal information about the hexagonal boron nitride lattice as well as information about interlayer coupling between inner and outer tube. Tunneling spectra are also strongly dependent on the electronic coupling between the tube and the substrate. When the tube is well coupled to the substrate the spectra clearly show manifestation of a one dimensionality of the electronic structure and band gaps of 3.5eV. However, weakly coupled tubes display significantly higher apparent band gaps of 7-9.5 eV, indicating that the applied electric field is not fully applied across the tunneling gap between the STM tip and the tube. Simple analysis of the current-distance spectra shows that the actual BNNT bandgap is significantly smaller (3-5 eV) and is attributed to a second tunneling junction present between the tube and the under-laying substrate. Unlike their carbon analogues, BNNT are expected to be semiconducting with a chirality independent band gap of 5-5.5eV. We explain the low measured band gap values by a tip induced giant Stark effect, where the band gap is narrowed due to the high electric field as predicted in recent theoretical calculations by S.Louie et.al.