Interactions between transition metals and defective carbon nanotubes

Interactions between 3d transition-metal atoms (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn) and (5,5) carbon nanotube (CNT) with a vacancy defect are quantitatively characterized using first-principles calculations. The binding energies between CNT and transition metals are found to be significantly enhanced when vacancy defects are introduced into the CNT. For the defective CNTs doped with Sc, Cr and Zn atoms, the structures of defective CNTs are found to be intact. The doping of Ti, Mn, Cu, Fe, Ni and Co alternates the structures of defective CNTs. Among all 3d transition metals, only the ferromagnetic metal atoms Fe, Co and Ni form bonds with carbon atoms of CNT, suggesting the important role of magnetic exchange interaction in the p-d hybridisation between carbons and transition-metal atoms. The results also indicate that the 3d transition-metal atoms acting as substitutional defects can substantially modify the electronic structure of CNT. It is suggested that these stable CNT-metal systems could become promising engineering materials in many fields such as CNT devices for various spintronics applications and CNT metal-matrix composites.