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$_{3}$) 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$_{60}$ 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$_{60}$ 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$_{60}$ (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 $6\times 6$ domain pattern emerges out of a larger commensurate $6\sqrt{3}\times6\sqrt{3}R30^\circ$ 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