Elastic deformation of a carbon nanotube adsorbed on a stepped surface

Carbon nanotubes prepared by thermal decomposition of acetylene on cobalt catalysts were investigated by scanning tunnelling microscopy (STM). One of the STM images revealed a nanotube with a diameter ca 1 nm getting over atomic steps on the (HOPG) graphite substrate on which the samples were deposited. The deformation and the stresses in this nanotube were evaluated from continuous-medium elasticity, using 12-6 C-C pair potentials to describe the interaction with the substrate. A good agreement was found between the computed shape of the deformed nanotube and that revealed by the STM. The calculations also indicated that the stresses only slowly increased with increasing step height and, for that reason, a nanotube adsorbed on a surface can get over sharp steps a few nanometres high without breaking. This result attests to the high flexibility of the carbon nanotube.