Introduction
Carbon nanotubes (CNTs) have attracted much attention since their discovery in 1991.1-3 Studies have shown that the magnetic phenomenon of CNTs is related to edge effects.4 Compared to symmetrical structures, asymmetrical structures are related to the design of directional transport,5 electromagnetic switches6, 7 and other devices. Studies on heterojunction CNTs with different radii exhibit spin ferromagnetic or antiferromagnetic coupling phenomenon, which are related to the number of carbon atoms at two zigzag edges. In addition, our research on cap-(9, 0)/(10, 0) CNTs shows that the carbon atoms at zigzag edges have spin polarization but do not at the cap end, and increasing or decreasing charges affect the spin density.8, 9 And cap-(5, 5)/(9, 0) CNTs adsorbed with alkali-metal atoms demonstrate that electrons transfer from the alkali atom to the CNTs.10So can we adsorb non-metallic atoms on cap-CNTs to affect the distribution of spin density, thereby adjusting the spin density?
The spin-polarized behavior of electrons is closely related to the design of magnetic materials, spintronic device and so on.11, 12
Previous studies on graphene and CNTs have shown that p electrons at zigzag edges exist spin polarizations.13, 14 These spin-polarized electrons have spin ferromagnetic or spin antiferromagnetic coupling because of the same or different spin arrangement orientations.15-18 But armchair graphene and CNTs do not have spin polarization phenomenon15. Further studies show that eliminating the armchairs edges between the zigzag edges improves their spin-polarized properties.19, 20 In addition, defects such as vacancies, doping, and adsorbed atoms affect the spin polarization phenomenon18, 21-24, and these defects inevitably exist in carbon materials. Therefore, it is necessary to study the spin polarization behavior of the defect structures.
In this paper, based on the cap-(9, 0) CNTs, the defect for adsorbed atoms that may cause spin polarization is introduced on the surface of C30. We used the first-principles density functional theory method (DFT)25-27 to study it. The calculation results show that C adatom induces the generation of spin density, and the spin density distribution is different for different adsorption positions. This work will provide help for the research of spintronic injection and other devices.