Direct observation of molecular orbital at carbon nanotube end

We report the appearance of superstructures in the topological images of scanning tunneling microscopy of single wall carbon nanotubes in the regions near the cap. These structures are localized with 6-7 nm from nanotubes ends and provide wavy pattern parallel to the armchair direction. Our molecular orbital calculation indicates that the superstructure shows a good agreement with calculated lowest unoccupied molecular orbital state. We consider the observed structures are the appearance of real (or imaginary) part of the Bloch state, which occurs as the result of the quantum interference between forward and backward waves. This suggests that the scattering of wave vector from k to -k occurs in two-dimensional manner at the end of the tube.