Abstract
Carbon and boron nitride nanotubes have been studied by transmission electron microscopy. Comparison between experiments and simulations showed contrasts in the imaging mode, leading to a delicate evaluation of the diameter of the nanotubes ((dis)appearing fringes due to focus versus chirality of ropes of nanotubes) or to a misinterpretation of their real shape which can appear as non-circular. Focus series are thus necessary to estimate the structural parameters of nanotubes once discrepancies that appear between image simulations and experiments are understood. Electron diffraction was also used to determine both the helicity and the diameter of nanotubes; simulations fit the observations very well. In order to simulate the images of the nanotubes, we have developed a program to calculate the atom coordinates. This program is presented here.