Leonor Chico

CARBON NANOELECTRONICS: UNZIPPING TUBES INTO GRAPHENE RIBBONS

We report on the transport properties of novel carbon nanostructures made of partially unzipped carbon nanotubes, which can be regarded as a seamless junction of a tube and a nanoribbon. We find that graphene nanoribbons act at certain energy ranges as perfect valley filters for carbon nanotubes, with the maximum possible conductance. Our results show that a partially unzipped carbon nanotube is a magnetoresistive device, with a very large value of magnetoresistance. We explore the properties of several structures combining nanotubes and graphene nanoribbons, demonstrating that they behave as optimal contacts for each other, and opening a new route for the design of mixed graphene-nanotube devices.

Electronic transport through bilayer graphene flakes

We investigate the electronic transport properties of a bilayer graphene flake contacted by two monolayer nanoribbons. Such a finite-size bilayer flake can be built by overlapping two semi-infinite ribbons or by depositing a monolayer flake onto an infinite nanoribbon. These two structures have a complementary behavior that we study and analyze by means of a tight-binding method and a continuum Dirac model. We have found that for certain energy ranges and geometries, the conductance of these systems oscillates markedly between zero and the maximum value of the conductance, allowing for the design of electromechanical switches. Our understanding of the electronic transmission through bilayer flakes may provide a way to measure the interlayer hopping in bilayer graphene.

Edge states and flat bands in graphene nanoribbons with arbitrary geometries

Trabajo presentado a la 14th edition of Trends in Nanotechnology International Conference, celebrada en Sevilla (Espana) del 9 al 13 de Septiembre de 2013.

Curvature-induced anisotropic spin-orbit splitting in carbon nanotubes

We have theoretically explored the spin-orbit interaction in carbon nanotubes. We show that, besides the dependences on chirality and diameter, the effects of spin-orbit coupling are anisotropic: spin-orbit splitting is larger for the higher valence or the lower electron band depending on the specific tube. Different tube behaviors can be grouped in three families, according to the so-called chiral index. Curvature-induced changes in the orbital hybridization have a crucial role, and they are shown to be family dependent. Our results explain recent experimental results which have evidenced the importance of spin-orbit effects in carbon nanotubes.

Van der Waals interaction in magnetic bilayer graphene nanoribbons

This work has been partially supported by the Spanish DGES under Grants No. FIS2009-08744 and No. FIS2010-19609-C02-02, the Basque Departamento de Educacion and the UPV/EHU (Grant No. IT-366-07), and the Nanoiker project (Grant No. IE11-304) under the ETORTEK program funded by the Basque Research Departament of Industry.

Electronic properties of twisted trilayer graphene

This work has been partially supported by MEC-Spain under Grant No. FIS2012-33521. E.S.M. acknowledges DGIP/USM for the internal Grant No. 111217. M.P. thanks FONDECYT Grant No. 1100672 and DGIP/USM internal Grant No. 11.11.62.

Gate-controlled conductance through bilayer graphene ribbons

This work was partially supported by MEC-Spain under Grant No. FIS2009-08744 and by the CSIC/CONICYT program, Grant No. 2009CL0054. J.W.G. gratefully acknowledges helpful discussions with M. Pacheco, the ICMM-CSIC for their hospitality, and the financial support of MECESUP research internship program,CONICYT (CENAVA,Grant No. ACT27), and USM 110856 internal grant

Electron-phonon deformation potential interaction in core-shell Ge-Si and Si-Ge nanowires

This work was partially supported by Spanish MINECO through Grant No. FIS2012-33521. D.G.S.-P., C.T.-G., and G.E.M. acknowledge support from the Brazilian Agencies FAPESP and CNPq. R.P.-A. acknowledges CONACyT (Mexico) support through Grant No. 208108 and hospitality at ICMM-CSIC, Madrid, Spain.

Electronic properties of graphene grain boundaries

Grain boundaries and defect lines in graphene are intensively studied for their novel electronic and magnetic properties. However, there is not a complete comprehension of the appearance of localized states along these defects. Graphene grain boundaries are herein seen as the outcome of matching two semi-infinite graphene sheets with different edges. We classify the energy spectra of grain boundaries into three different types, directly related to the combination of the four basic classes of spectra of graphene edges. From the specific geometry of the grains, we are able to obtain the band structure and the number of localized states close to the Fermi energy. This provides a new understanding of states localized at grain boundaries, showing that they are derived from the edge states of graphene. Such knowledge is crucial for the ultimate tailoring of electronic and optoelectronic applications.

Quantum confinement in carbon-nanotube systems

Carbon nanotubes are graphene cylinders of nanometric diameter which can be either semiconducting or metallic depending on their geometry. Joining different kinds of nanotubes by means of topological defects, one can design all-carbon quantum dots and, in principle, achieve electronic confinement in quasi-zero dimensional systems. In this work, we review different ways of quantum electron confinement in carbon nanotubes: by matching a finite metallic nanotube portion to two semi-infinite semiconducting nanotubes, quantum dot states appear in the system due to confinement by energy barriers; all-metallic carbon nanotube structures are shown to have completely localised states because of the symmetry gap between the nanotube components; quasi-localised states, showing up as sharp resonances, are demonstrated to arise as a result of wave vector mismatch in all-metallic systems made of nanotubes without any common symmetry. The different conductance behaviour of the various structures is also studied.