Study On Electron Beam-induced Amorphization Of Multiple-wall Carbon Nanotube

Since the carbon nanotube(CNT)was found in 1991,it has been widely studied due to its unique one-dimensional hollow graphite structure and electrical and mechanical properties.Among these studies,the tuning or modification of the CNT's structure is an important aspect because the properties of the CNT are strongly depended on its structure.Irradiation by energetic beam,such as ion,proton,laser,or electron beams is an effective technique to create defects on the CNT that can change the structure and thus properties of the CNT via a highly controlled manner.In the existing studies,including amorphization of multi-walled carbon nanotube(MWCNT)induced by ion beam,proton beam and laser beam,the traditional solid physics theory or its approximation have not been broken through whereas the nanocurvature effect and the energetic beam-induced nonthermal effect which play a key role on the amorphization of MWCNT have been neglect.On the other hand,compared with the ion beam and the laser beam,the electron beam(especially in the high-resolution transmission electron microscope)has great advantage in monochromaticity and stability,however,the amorphization of MWCNT induced by electron beam irradiation has not been systematically studied yet.Based on the above considerations,using the well-developed TEM in-situ observation technique,we systematically investigated the amorphization of MWCNT with two ends fixed as induced by electron beam irradiation,we in particular investigated effects of the factors such as MWCNT diameter,electron beam current density,and amorphous carbon on MWCNT surface on the amorphization of MWCNT.The results show:(1)under the same irradiation,the MWCNT with smaller diameter or larger nanocurvature amorphized with a faster rate.Meanwhile,carbon atoms on the MWCNT:"evaporated"with the faster rate,and thus the diameter of the MWCNT shrunk with the faster rate;(2)For MWCNT with similar diameter and number of wall layers,under irradiation with higher electron beam current density,the MWCNT was amorphized at a faster rate..Meanwhile,carbon atoms on the MWCNT"evaporated”with the faster rate,and thus the diameter of the MWCNT shrunk with the faster rate;.(3)under the same irradiation,the MWCNT with the amorphous carbon on its surface amorphized with a faster rate.Meanwhile,carbon atoms on the MWCNT"evaporated"with the faster rate and thus the diameter of the MWCNT shrunk with the faster rate.In addition,we studied as well the amorphization of free cap of MWCNT with its one end fixed.we also found that the different amorphization and atom evaporation processes occurred due to the non uniform distribution of nanocurvature over the MWCNT surface.That is,a faster amorphization and atom evaporation always occurred at the location with a lager nanocurvature.The above results all reveal that the nanocurvature effect and the electron beam athermal activation effect play a key role in the amorphization of MWCNTs and the details of the experimental phenomena were explained by the crystalline defect creation,accumulation and annihilation and the carbon atoms"evaporation"and"diffusion"mechanisms which newly developed based on these two effects.