| With the developments of technology, many new materials are found and created to meet the growing needs of people. CNT is a typical one. The logic circuit of transistors based on carbon nanotubes can solve the size limit of the traditional semiconductor devices. It allows for integration of multiple devices on a single chip. The CNT transparent films can be used as the transparent electrode for application in solid state lighting, LCD displays, touch panels, and photovoltaics. However, the defects produced in the production have a great influence in the properties.Classical molecular dynamics is adopted in this paper, while Airebo potential is used to describe the C-C interaction. We have investigated the thermal stability of various chiral SWCNTs, which have several Stone-Wales defects. The formation of composite edge and screw dislocations in double-walled CNTs and their high temperature stability are also explored.Armchair, chiral and zigzag single-walled CNTs with Stone-Wales defects have been studied for the thermal stability at different temperatures in this paper. The above three types are illustrated with examples of (10,10), (13,7) and (18, 0) respectively. The effects of both length and diameter have been excluded. It has been discovered that the Lindemann index curve of armchair CNTs gradually increases linearly with temperatures lower than 3,000 K, which means the atoms near the initial positions are making the typical thermal vibration. So we know armchair CNTs is stable under the temperature of 3,000 K. When the temperature increases from 3,000 K to much higher, the curve deviates from the original linear growth relationship, and transforms into fully rapid growth. From the simulated results, it behaved in a way that a growing number of carbon atoms break away from the tubular axle, ejecting to different directions. Hence, it can be concluded that the melting temperature of the armchair CNTs with Stone-Wales defects is about 3,000 K. Chiral and zigzag CNTs have the melting temperature of around 2,800 K and 2,500 K respectively as well.The cross coupling between different layers have very important significance to the electrical, mechanical and thermal properties of double-walled carbon nanotubes. Because of the cross coupling, electrons and phonons can transport in different walls easily at the same time, comprising without it. The cross coupling can also stop the slip of walls, so the mechanical properties of carbon nanotubes will be enhanced. In this paper, two double-walled CNTs of the same type are put closer axially and staggered in radial direction. A symmetric edge and screw dislocations will be formed between the walls at room temperature. The generated screw dislocations of junction can connect the outermost and the innermost edge dislocations. The difference lines in that the armchair's inner-tube has a stretch-out tendency, while the zigzag's inner-tube has an inward closing trend. Through the thermal stability analysis of composite dislocations, it is discovered that the pre-melting temperature of zigzag dislocation CNT is from 1,500 K to 2,400 K, which is lower than armchair's 2,400 K to 3,000 K. We also find that the double-walled CNTs with dislocation begin melting from the screw components. Also observed in the melting temperature, edge dislocation and screw dislocation present a crossover growth trend. With the increase of time, rang of screw dislocation extend. And when temperature adds screw components begin to turn to edge components. |
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