Tamm states and quantum dots in carbon and heteroatomic nanotubes

The electronic structure of C-BN nanotubes is discussed in the pi approximation. Two types of such structures with (n,0)-tubulet topology are investigated: 1) semiinfinite C-BN and C nanotubes and 2) C-BN nanotubes, consisting of two semiinfinite BN nanotubes coupled by a ring-shaped carbon fragment C-mn. It is shown that, in the first case, energy levels (Tamm levels) whose wave functions are localized on the terminal fragment can exist under certain conditions. In the second case, bound states localized on atoms of the carbon fragment exist. It is established that if a quite extended, cylindrical, carbon cluster is present at the end of a semiinfinite BN nanotube, then such a system can be viewed as a very simple model of a quantum dot. C-BN nanotubes where the carbon fragment couples two semiinfinite BN nanotubes can also be interpreted similarly. A simple analytic method is proposed for finding the Tamm energy levels in heteroatomic nanotubes. (C) 1999 American Institute of Physics. [S1063-7834(99)03208-6].