24 research outputs found
Role of Symmetry in the Transport Properties of Graphene Nanoribbons under Bias
The intrinsic transport properties of zigzag graphene nanoribbons (ZGNRs) are
investigated using first principles calculations. It is found that although all
ZGNRs have similar metallic band structure, they show distinctly different
transport behaviors under bias voltages, depending on whether they are mirror
symmetric with respect to the midplane between two edges. Asymmetric ZGNRs
behave as conventional conductors with linear current-voltage dependence, while
symmetric ZGNRs exhibit unexpected very small currents with the presence of a
conductance gap around the Fermi level. This difference is revealed to arise
from different coupling between the conducting subbands around the Fermi level,
which is dependent on the symmetry of the systems.Comment: 4 pages, 4 figure
Multiple Localized States and Magnetic Orderings in Partially Open Zigzag Carbon Nanotube Superlattices: An Ab Initio Study
Using first-principles calculations, we examine the electronic and magnetic
properties of partially open zigzag carbon nanotube (CNT) superlattices. It is
found that depending on their opening degree, these superlattices can exhibit
multiple localized states around the Fermi energy. More importantly, some
electronic states confined in some parts of the structure even have special
magnetic orderings. We demonstrate that, as a proof of principle, some
partially open zigzag CNT superlattices are by themselves giant (100%)
magnetoresistive devices. Furthermore, the localized(and spin-polarized) states
as well as the band gaps of the superlattices could be further modulated by
external electric fields perpendicular to the tube axis, and a bias voltage
along the tube axis may be used to control the conductance of two spin states.
We believe that these results will open the way to the production of novel
nanoscale electronic and spintronic devices.Comment: In submissio
Spontaneous edge-defect formation and defect-induced conductance suppression in graphene nanoribbons
We present a first-principles study of the migration and recombination of
edge defects (carbon adatom and/or vacancy) and their influence on electrical
conductance in zigzag graphene nanoribbons (ZGNRs). It is found that at room
temperature, the adatom is quite mobile while the vacancy is almost immobile
along the edge of ZGNRs. The recombination of an adatom-vacancy pair leads to a
pentagon-heptagon ring defect structure having a lower energy than the perfect
edge, implying that such an edge-defect can be formed spontaneously. This edge
defect can suppresses the conductance of ZGNRs drastically, which provides some
useful hints for understanding the observed semiconducting behavior of the
fabricated narrow GNRs.Comment: 6 pages, 4 figures, to appear in PR