The Study Of The Interaction Between Carbon Nanotubes And Transition Metal Clusters By First-principles Calculation

Carbon nanotube considered as a novel nano-material has been paid much attention during the last decade. Owing to their unique quasi-one-dimensional atomic structure and superb mechanical and electronic properties, the single-walled carbon nanotubes (SWNTs) has been playing a significant role in emerging nanotechnology and becoming the important building blocks for nanoelectronic applications, chemical and biological sensing, and nano-composites. However in reality, vacancy defects can appear in CNTs during growing process, purification or irradiation. Some recent experiments indicate the effect of defects can't be neglected. The defects in CNTs may not only influence the mechanical properties but the electronic, magnetic and chemical characteristics. In the same time, many experiments and theory calculations show the 3d transition metal (TM) atomic clusters have larger magnetic moment than bulk. Despite of purification there are catalytic cluster can remaining on the tip ends or the tube-wall of carbon nanotubes, and metal clusters can be intentionally coated outside of nanotubes. As typical magnetic transition metal and frequently used catalyst in the growing process of carbon nanotubes, Fe filled in or adsorbed on CNTs has been therefore the subjects of many theoretical and experimental studies. The SWNT with periodic carbon-carbon networks has its specific electronic properties, and in the same time, the magnetic metal cluster as impurity can adjust the electronic properties of the compound by inducting the notable difference between the majority and minority densities of states near the Fermi level. These imply that the compound system of magnetic atomic cluster and SWNTs should lead to an even more diverse range of applications. Understanding the interaction between the magnetic cluster and SWNTs should be the kernel of the whole design.In this thesis, we performed the calculation with a DFT-based spin-polarized first-principles method and the main results and conclusion are summarized as follow:(1) The mechanical, electronic and magnetic properties of the carbon nanotubes with different concentrations of vacancy defects have been investigated. Comparing the carbon nanotube with different defects concentrations and different styles, the infection of mechanical properties of carbon nanotube were quantitative analysed. Then the electronic and magnetic properties changes show the effect of vacancy defect is remarkable.(2) Based on the study of Fe₄ cluster confined in SWNT, the interaction between the metal nanoparticle and SWNT was discussed in detail. The final stable geometrical structure of Fe₄ cluster adsorbed on the inside and outside of SWNTs, is dominated by the two competitive Fe-Fe and Fe-C interactions in the Fe₄+SWNT compound systems. The Fe-C interaction can be considered as templating effect and depends on the charity and diameter of SWNTs. The electronic, magnetic and mechanical properties of "Fe4+CNT" system show it is a good balance between the manipulation and spin-polarized property for nano-device design.(3)The Fe₄ cluster adsorbed on graphene was also investigated. The tetrahedral structure is still the most stable configuration. Comparing the various cases of the Fe₄ cluster adsorbed on SWNTs and graphene, we discuss the changes of binding energy, electronic and magnetic properties depended on the curvature C-C networks.In summary, we consider that the study on the SWNTs with vacancy defects is a practical subject for nano-mechanical, and the interaction between the carbon nanotube and metal nanoparticle is an important, interesting and challenging research field. Our study suggests that the carbon nanotube can be further exploited as a template or regulator for the design of nanoscale magnets with controllable properties. We are still considering this design in the ongoing project.