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| The molecular dynamics method is adopted in this paper to investigate single vacancy defect reconstruction in zigzag single-walled carbon nanotubes (SWCNTs) at different temperatures, and the effects of the defect ratio on their elastic properties. The results show that there are two types of reconstruction in zigzag (9,0) SWCNTs. A single vacancy begins to reconstruct into a 5-1DB-P configuration when the temperature is about or higher than 1600 K, and a 5-1DB-T configuration at about or higher than 2600 K. However, these reconstructions do not always take place at these temperatures, i.e., the reconstruction temperatures are discrete. For this reason, a new idea has been put forward: that there are two sets of noncontinuous potential barriers between the three dangling bond (3DB) states and the reconstructions, which correspond to the 5-1DB-P and 5-1DB-T barriers. At room temperature, the Young’s moduli of zigzag (9,0) and (18,0) SWCNTs with no defects are 804 and 860 GPa, respectively. With an increase in the single vacancy defect ratio in these SWCNTs, the Young’s moduli decrease. When the vacancy defect achieves a certain ratio, there is a sudden slowdown in the curves of the Young’s moduli versus the vacancy defect ratio, and a platform phenomenon emerges. Based on analysis of this phenomenon, the following conclusions are derived. The reconstruction of vacancy defects can be carried out not only by way of temperature, but also by the defect ratios in SWCNTs because of the activity of the dangling bonds and their spaces. Vacancy defects bring about a decrease in the Young’s modulus, but their reconstruction is an important factor in stabilizing this modulus. SWCNTs with vacancy defects are also expected to become energy suppliers through the control of vacancy reconstruction. |
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| The molecular dynamics method was adopted in this paper to investigate single vacancy defect reconstruction in zigzag single-walled carbon nanotubes (SWCNTs) at different temperatures, and the effects of the defect ratio on their elastic properties. The results show that there are two types of reconstruction in zigzag (9,0) SWCNTs. A single vacancy begins to reconstruct into a 5-1DB-P configuration when the temperature is about or higher than 1600 K, and a 5-1DB-T configuration at about or higher than 2600 K. However, these reconstructions do not always take place at these temperatures, i.e., the reconstruction temperatures are discrete. For this reason, a new idea has been put forward: that there are two sets of noncontinuous potential barriers between the three dangling bond (3DB) states and the reconstructions, which correspond to the 5-1DB-P and 5-1DB-T barriers. The Young’s moduli decreased with the increase of the single vacancy defect ratio in these SWCNTs, and the decreasing speed suddenly decelerated at a certain vacancy defect ratio, i.e., a platform phenomenon emerges. Based on the above results, it can be concluded that the vacancy defects can be reconstructed not only by way of temperature, but also by the defect ratios in SWCNTs. |
2楼2009-02-09 21:37:38