| Since the discovery of carbon nanotube (CNT) in 1991, it is found that carbon nanotube with special structure and nanometer scale has many outstanding characteristics, such as high rigidity, excellent electronic and mechanic properties and so on. CNT also has high specific surface area. Therefore it's predicted to be a potential material for absorption. Besides, CNT can be filled with various kinds of matters because of its capsule-like structure, including metals such as copper, lead, iron and mercury, for the purpose of preparation of hybrid materials with different functions. To date, metals have been successfully encapsulated into carbon nanotubes in experiments. And, theoretical research predicts that metals filled in CNTs will possess unique features, for instance, preventing metals from oxidization, making efficient and multi-functional catalysts, as well as realizing compound materials with special electronic, magnetic, mechanic properties and so on. In fact, the interface interaction existing in the hybrid material will affect its structural configuration, and consequently results in different physical characteristics. Therefore, in this thesis, by the means of molecular dynamic simulation and quenched annealing method, we studied the structural features of gold nanowires encapsulated in single-walled carbon nanotubes (SWCNT), and discussed the mechanism that lies in the process of forming those structures.In this work, the carbon-carbon interaction was described with Tersoff-Brenner potential, the carbon-gold interaction with Lennard-Jones potential, and the gold-gold interaction with Finnis-Sinclair potential.First of all, we investigated the dependence of the enclosed Au structure on the radius of SWCNT, while the numbers of atoms kept constant (i.e. N=306 and N=600.). It was found that Au formed a helical multishell, which is different from its bulky counterpart. With the increase of the radius of SWCNT, the number of shells increases correspondingly. The spacing between the shells has much to do with the gold-carbon interaction and gold-gold interaction. The distance between the SWCNT wall and the outmost shell of the Au nanowire is a little over 0.3 nm, which is in the range of the well depth of the C-Au Lennard-Jones potential, meaning the gold-carbon interaction is the minimum at this distance. The intershell distance in the Au nanowire varies from 0.208 nm to 0.233 nm. The nearest neighbor distance (NND) calculated is about 0.287 nm, close to the NND of its fcc bulky crystal.Then we investigated the effect of the number of the filled gold atoms on the configuration of the enclosed Au. We found that, for thin SWCNTs (i.e. n is 8, 10 or 12.), no matter how many atoms are filled, the structure of the Au nanowire remains helical multishell. Due to the confinement of the tube wall, filling more atoms only leads the Au nanowire to grow along the axis direction of the SWCNT. However, for thick SWCNTs (i.e. n is 14, 16 or 18.), the final structure of the enclosed gold transforms from the previous helical multishell to fcc-like when decreasing the Au atoms.In order to explore the mechanism of this structural transformation in detail, we studied the cases of gold filled in even thicker SWCNTs while the amount of the gold atoms is fixed at 306. It is found that, while the radius of the SWCNT increases, the encapsulated gold mainly forms a fcc structure. Furthermore, we extended the radius of the SWCNT to be infinite, or say, employing grapheme as a host to see the structural characteristics of the Au on the graphene. The results showed that the final structure of gold on graphene is exactly fcc. It indicates that there exists a competition between gold-carbon interaction and gold-gold interaction, which plays an important role in the formation of different structures.Our investigation showed that, the radii of the SWCNTs and the numbers of filled Au atoms are all key parameters in deciding the morphology of the Au nanowires enclosed in the SWCNTs over the range of diameters we considered. |
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