The Dynamics Of Movements And Reconstructions Of Defect In Single-walled Carbon Nanotube Junction

Intramolecular junctions in single-walled carbon nanotubes are potentially ideal structures. Ouyang et al reported that the (22,-5)/(21,-2) and (11,8)/(9,6) junctions had been made in science journal. Hashimoto et al made a SWNT of mixed chirality (17,0)/(18,0) sigle carbon nanotube junction by electron bombardment. Consequently, carbon nanotubes junction exist or be made by radiation. We have used molecular dynamics simulation to study the formation regularity of the junctions between two single-walled carbon nanotubes and the motion and reconstruction of the defect in junctions. Furthermore, we studyed the microscopic mechanism of the motion and reconstruction of these single-walled carbon nanotube junctions.First, employing semiempirical Tersoff potential to describe the C-C interactions in single-walled carbon nanotube junctions, we simulated the formation of the junctions between two adjacency zigzag and adjacency armchair single-walled carbon nanotubes,respectively. The simulation results show that the defects are formed by pentagon-heptagon pairs and there is a pair of pentagon-heptagon in zigzag junctions and a pairs of separate pentagon-heptagon in armchair junctions. These simulation results are in agreement with Hashimoto': pentagon-heptagon pair is the most probably responsible for the serial junctions of two parts of SWNTs with different chiral indices.Taking (7,0)/(8,0) and (6,6)/(7,7) carbon nanotube junctions for examples, we studyed the thermal stability of single-walled carbon nanotube junctions. The results tell us that the two C located at the two wing of the pentagon-heptagon topological defects with lower remove energy can more easily be evaporated and leave the system.Molecular dynamics calculations are performed to study the dynamics of the movement of the (7,0)/(8,0) and (6,6)/(7,7) junction interconnecting two carbon nanotubes. The experimentally observed complex longitudinal and helical movements of the kink are well reproduced in our simulations based on the preferential evaporation of the carbon atoms with high energy and lower remove energy. The defects in the junctions between the two carbon nanotubes moves towards the tube with larger diameter, resulting in an overall reduction of the diameter of the nanotubes without inducing disorder or damage. The movements of the defects in the junctions are found to be chirality dependent. The junction connecting two zigzag nanotubes can have either a pseudoclimb or a spiral movement depending on where the evaporation of carbon atoms occurs, while the junction between the armchair nannotubes has an interesting spiral movement with separations and recombinations of the topological defects. The kink motions are found to be chirality dependent.In accordance with the mechanism of the highest internal energy atoms evaporating, we simulated the change process of (7,0)/(8,0) zigzag and (6,6)/(7,7) armchair single-walled carbon nanotube junction structures when atoms evaporated because of high temperature or radiation. The simulation results that the removal of the atoms lead to the longitudinal or spiral movement of junctions on the tube wall, is in good agreement with the kink motion observed during experiments. Our study suggest a mechanism for synthesis of carbon nanotube semiconductor-metal intramolecular heterojunctions with specific locations and controlled sizes and show the possibility of application to nanoelectronic devices.