Carbon nanostructures filled with Fe were synthesized. It was found that both the shape and the phase of the carbon nanocapsulate may be controlled during the growth, and controlled ferrous amorphous-crystalline phase transformation may be realized via electron beam irradiation. Since an electron beam may be focused into a nanoscale probe, this method may in principle be used for fabricating amorphous-crystalline heterostructures inside carbon nanotubes. (C) 2003 Elsevier Science B.V. All rights reserved.