**Abstract**

Carbon nanotubes (CNTs) have attracted considerable attention due to their high aspect ratio, whisker-like form for best possible geometrical field enhancement, high electrical conductivity, and extraordinary thermal stability. Ion beam technology is a potential technique for controlled construction of CNTs. During collision with energetic ions, carbon atom of CNTs can get an adequate amount of energy to escape from the graphite lattice and produce a large number of defects. These defects are advantageous for adding some new functional groups and nanoparticles to modify CNTs. Meanwhile, the structure and atoms in the region of the defects can be rearranged and changed into amorphous structure, onion structure, and so on. These defects also can be used to form the junctions of CNTs and realize welding of CNTs and network formation of amorphous carbon nanowires.

**Keywords:** carbon nanotubes, ion beam, modification, welding, structural change
