Scanning tunneling spectroscopy on crossed carbon nanotubes

Crossing nanotubes were investigated using scanning tunneling microscopy ~STM! and spectroscopy. From the analysis of the measured mechanical deformation of the nanotubes, the contact force between the nanotubes is estimated to be 1 nN. Spectroscopy measurements showed two effects on the electronic structure: ~i! band bending, which we attribute to a position-dependent interaction with the substrate, and ~ii! the formation of localized states, as signalled by additional peaks in the density of states at the crossing point. The existence of localized states at the junction represents a much stronger perturbation of the electronic structure than has generally been assumed. The relevance of these STM results for the interpretation of transport measurements is discussed.