First-principles study of nanotubes and graphene related structures

Abstract

Based on first-principles calculations, we study some attracting physical properties of nanotubes and graphene-related structures: i) Fe encapsulated carbon nanotubes, ii) telescoping carbon nanotubes, iii) carbon nanotubes with various vacancies, and iv) graphene on the $SiO_2$ substrate. First, we investigate electronic and magnetic properties of Fe-filled carbon nanotubes, as a candidate for spintronic devices. For electron transport properties of carbon nanotubes, we discuss conduction mechanism due to interwall coupling in telescoping nanotubes and formation of various vacancy clusters. Finally, interactions between graphene layers and $SiO_2$ substrate and their doping effects are examined. Within spin-density functional approximation, we study electronic and magnetic properties of Fe nanowires inside single-wall carbon nanotubes. The magnetic properties of Fe-filled carbon nanotubes for the ferromagnetic state are greatly enhanced due to the reduced coordination number of the Fe atoms on the nanowire surface, compared with bulk Fe. The increase of magnetic moments is more effective for thin nanowires, where the Fe atoms interact very weakly with the nanotube and thus their magnetic properties inside the tube are similar to those for the free-standing nanowires. For thick Fe nanowires, undercoordinated Fe atoms interact more strongly with the carbon nanotube, and thereby the magnetic moments are reduced. The analysis of the densities of states near the Fermi level shows that electron conduction mostly occurs along the Fe wires protected from oxidation by carbon coating. Our calculations suggest that for applications to spin transport devices, it is desirable to form thin Fe wires inside single-wall nanotubes with large diameters. For the electron transport of telescoping carbon nanotubes, where the (5,5) and (10,10) nanotubes are coaxially aligned, we perform a comparative study using first-principles and tight-binding nonequilibrium Green`s funct...