Probing the electronic structure of nanotube peapods with the scanning tunneling microscope

The scanning tunneling microscope (STM) is a powerful tool for examining the electronic structure of carbon nanostructures. We describe experiments in which the STM's capabilities for atomic scale imaging, spectroscopy, and nanoscale manipulation have been used to examine isolated fullerene peapod structures. These measurements demonstrate that the array of encapsulated C ₆₀ molecules in a peapod induce periodic modifications in the nanotube's local electronic structure. To understand these findings, we develop a theory for the mixing of the nanotubes' electronic states and C ₆₀ s' orbitals. The theory provides a good description of the prominent features of the peapods' local electronic structure as probed by STM spectroscopy.