Local electronic density of states of a semiconducting carbon nanotube interface

The local electronic structure 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.

Figure 1

Typical STM images of CNTs on the Au(111) surface. (a) $300\times 250{\mathrm{nm}}^2$. (b) $220\times 220{\mathrm{nm}}^2$. Inset shows the herringbone reconstruction of a terrace of the Au(111) surface near CNTs.

Figure 2

(a) An STM image of a CNT. The image length is 7.6 nm. The sample bias voltage is $-0.5\mathrm{V}$. (b) Spatially resolved LDOS of the CNT. (c) Cross section of (b) along the vertical lines of “A” and “B.” (d) Cross section of (b) along the horizontal line of “C.”

Figure 3

(a) STM image of a CNT. The image length is 7.6 nm. The sample bias voltage for the upper image is $-0.3\mathrm{V}$ and that for the lower image is 0.5 V. (b) Spatially resolved LDOS of the CNT. (c) Cross section of (b) along the vertical lines of “A” and “B.” (d) Cross section of (b) along the horizontal lines of “C,” “D,” and “E.”

Figure 4

LDOS data for a CNT with a defect. Upper data was taken at the defect, while lower data was taken far from the defect.