Scanning tunneling spectroscopy signature of finite-size and connected nanotubes: A tight-binding study

We present tight-binding-based simulations of the scanning tunneling spectroscopic signal of different types of carbon nanotubes. Capped, finite, and connected nanotubes have been investigated. We have computed scanning tunneling spectroscopy (STS) maps of each nanotube on different parts of the systems for various tip-sample bias potentials. STS reflects the electronic structure, which depends on the arrangement of atoms in the systems, and can be drastically different even for similar geometries. The computations are in good agreement with recently measured STS spectra. Furthermore, the STS spectra of pentagon and heptagon, which are needed for connecting different carbon nanotubes, constitute characteristic marks of topological defects.