The present invention concerns a method for modyfing at least an electronic property of a carbon nanotube or nanowire comprising exposing said nanotube or nanowire to an acid having the formula (I) wherein R.sub.1, R.sub.2 and R.sub.3 are chosen in the group comprising (H, F, Cl, Br, I) with at least one of R.sub.1, R.sub.2 and R.sub.3 being different from H. At least part of the nanotube or nanowire may be a channel region of a field effect transistor. ##STR00001##