Amorphous structure transformation of multiwalled carbon nanotubes (MWCNTs) irradiated by 70 keV protons at room temperature was investigated.It was found that some of the proton-irradiated MWCNTs were covered with homogeneous amorphous structure with the inner tube walls in graphite structure.Moreover

the amorphous structure continuously proceeds and the graphite structure was reduced during the proton irradiation until the irradiated MWCNTs become amorphous nanowires with a hollow structure.The proton-induced structural transformation of MWCNTs was a unique graphite-to-amorphous structural transition from the outer walls to the inner walls of the irradiated MWCNTs.The structural evolutionary mechanism of proton-beam-irradiated MWCNTs has been discussed.