Spectroscopic Properties and STM Images of Carbon Nanotubes

TL;DR

This paper provides a comprehensive theoretical analysis of the electronic properties and STM imaging of carbon nanotubes, considering environmental effects and defects, revealing how substrate interactions influence their electronic structure.

Contribution

It introduces detailed theoretical insights into how the local environment affects the electronic and STM properties of carbon nanotubes, including defect imaging and substrate interactions.

Findings

STM patterns are unaffected by substrate or tube interactions.

Defects and caps produce voltage-dependent STM images explained by electronic interference.

Substrate interaction modifies energy levels, opening pseudogaps and broadening van Hove singularities.

Abstract

We present a theoretical study of the role of the local environment in the electronic properties of carbon nanotubes: isolated single- and multi-wall nanotubes, nanotube-ropes, tubes supported on gold and cutted to finite length. Interaction with the substrate or with other tubes does not alter the scanning-tunneling-microscopy (STM) patterns observed for isolated tubes. STM-topographic images of topological defects (pentagon/heptagon pair) and tube-caps have also been studied. In both cases the obtained image depends on the sign of the applied voltage and it can be described in terms of the previous catalog of STM-images (interference between electronic waves scattered by the defect). We also have computed the electronic density of states for isolated tubes with different chiralities and radii confirming a correlation between the peak-structure in the DOS and the nanotube diameter, however the metallic plateau in the DOS also depends on the nanotube chirality. Furthermore, the conduction and valence band structures are not fully symmetrical to one another. In contrast to STM images, the interaction with the substrate does modify the energy levels of the nanotube. We observe opening of small pseudogaps around the Fermi level and broadening of the sharp van Hove singularities of the isolated single-walled-nanotubes that can be used to extract useful information about the tube structure and bonding. The combination of STM and spectroscopic studies opens a new technique to address the electronic and structural properties of carbon and composite nanotubes.