55 research outputs found
Modification of the electronic structure in a carbon nanotube with the charge dopant encapsulation
We present the first-principles study of effects of the charge dopants such
as Cesium and Iodine encapsulated on the electronic structure of carbon
nanotubes. An encapsulated cesium atom donates an electron to the nanotube and
produces donor-like states below the conduction bands. In contrast, an iodine
trimer (I) accepts an electron from the nanotube and produces an
acceptor-like state above the valance band maximum. We find that a Cs atom
inside a metallic armchair carbon nanotube gives rise to spatial oscillations
of the density of states near the Fermi level.Comment: Applied Physics Letters (in press), 3 color figure
Reduction of Activation Energy Barrier of Stone-Wales Transformation in Endohedral Metallofullerenes
We examine effects of encapsulated metal atoms inside a C molecule on
the activation energy barrier to the Stone-Wales transformation using {\it ab
initio} calculations. The encapsulated metal atoms we study are K, Ca and La
which nominally donate one, two and three electrons to the C cage,
respectively. We find that isomerization of the endohedral metallofullerene via
the Stone-Wales transformation can occur more easily than that of the empty
fullerene owing to the charge transfer. When K, Ca and La atoms are
encapsulated inside the fullerene, the activation energy barriers are lowered
by 0.30, 0.55 and 0.80 eV, respectively compared with that of the empty
C (7.16 eV). The lower activation energy barrier of the Stone-Wales
transformation implies the higher probability of isomerization and coalescence
of metallofullerenes, which require a series of Stone-Wales transformations.Comment: 13 pages, 3 figures, 1 tabl
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
Origins of anomalous electronic structures of epitaxial graphene on silicon carbide
On the basis of first-principles calculations, we report that a novel
interfacial atomic structure occurs between graphene and the surface of silicon
carbide, destroying the Dirac point of graphene and opening a substantial
energy gap there. In the calculated atomic structures, a quasi-periodic
domain pattern emerges out of a larger commensurate
periodic interfacial reconstruction,
resolving a long standing experimental controversy on the periodicity of the
interfacial superstructures. Our theoretical energy spectrum shows a gap and
midgap states at the Dirac point of graphene, which are in excellent agreement
with the recently-observed anomalous angle-resolved photoemission spectra.
Beyond solving unexplained issues of epitaxial graphene, our atomistic study
may provide a way to engineer the energy gaps of graphene on substrates.Comment: Additional references added; published version; 4 pages, 4 figure
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