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.