Electronic and mechanical properties of C60-doped nanotubes

Using a generalized tight-binding model, we study the changes induced in the electronic and mechanical properties of carbon nanotubes with encapsulated C(60)s. Provided enough overlap exists between the electronic states of the nanotube and those of the C60s, a tiny gap (similar to0.01-0.02 eV) opens in the band structure of a metallic tube. The gap is seen to be wider for smaller separations between the C(60)s. For semiconductor tubes, on the other hand, the encapsulated C(60)s produce donor levels in the gap causing it to narrow. As regards mechanical properties, doped tubes are observed to be slightly 'softer' than undoped ones. This is indicated by reductions of the Young modulus and torsional rigidity of the doped tubes by 0.4-1.8% and 0.6-1.2%, respectively, as compared to those of the pure tubes. Moreover, the Poisson ratio of the doped tubes is seen to be lower by similar to5%. These novel features of the fullerene-doped nanotubes should be of interest in future applications.