  We show that electron irradiation in a dedicated scanning transmission
microscope can be used as a nano-electron-lithography technique allowing the
controlled reshaping of single walled carbon and boron nitride nanotubes. The
required irradiation conditions have been optimised on the basis of total
knock-on cross sections calculated within density functional based methods. It
is then possible to induce morphological modifications, such as a change of the
tube chirality, by removing severals tens of atoms with a nanometrical spatial
resolution. These irradiation techniques could open new opportunities for
nano-engeneering a large variety of nanostructured materials.
