A comparative study of structure and phonon dynamics single wall carbon and boron nitride nanotubes

The recent discovery of Carbon Nanotubes and other non-carbon nanostructured materials, have attracted great interest and inspired many theoretical and experimental investigations. There has also been intense activity in exploring the fascinating physical properties of these newer forms of Nanomaterials namely, fullerenes and Single Wall Carbon NanOtnbes (SWCNT), Filled nanotubes and Boron Nitride Nanotubes (BNNT) etc. Currently single wall nanotubes (SWNT) are receiving focused attention, as they are ideal candidates for future nanoscale electronic and mechanical devices due to their structural and electronics properties. Nanotubes exhibits some unexpected and very interesting electronic properties, like they may be metallic or narrow or moderate gap semiconductors, depending on their chirality, which is defined by the orientation of hexagons with respect to nanotube axis. Soon after the discovery of carbon nanotube it was speculated that other materials could possibly form similar nanostructures. The viable candidate was hexagonal Boron Nitride. Boron Nitride Nanotubes (BNNT) has attracted focused attention due to their potentials to serve as semiconductor of constant energy gaps. They were theoretically predicted to be stable structures with an electronic band gap, independent of their radius and chirality. In the present paper we have studied in details the structural symmetry of both Carbon (monoatomic) and Boron Nitride (diatomic) nanotubes in respect of phononic band structure. The phonon spectrum (10, 10) armchair structures for both SWCNT and BNNT are calculated using de Launay type force constant model considering the nearest and next nearest radial and angle bending forces. and zone folding technique. The calculated phonon density of states show multi-peak structures and predict correctly all the Raman modes. The application of the present theory has also been used to predict the diameter dependence of the radial breathing mode and effect of chirality on phonon spectrum of both Carbon and Boron nitride nanotubes.