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Octagonal Defects as the Source of Gap States in Graphene Semiconducting Structures

100%
Pelc M., Jaskólski W., Ayuela A., Chico L.
Acta Physica Polonica A
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2013
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vol. 124
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issue 5
777-780
EN
We study graphene nanoribbons and carbon nanotubes with divacancies, i.e., local defects composed of one octagon and a pair of pentagons. We show that the presence of divacancies leads to the appearance of gap states, which may act as acceptor or donor states. We explain the origin of those defect-localized states and prove that they are directly related to the zero-energy states of carbon ring forming the octagonal topological defect.
2
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Friedel Oscillations in Carbon Nanotube Quantum Dots and Superlattices

88%
Chico L., Santos H., Ayuela A., Pelc M., Jaskólski W.
Acta Physica Polonica A
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2008
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vol. 114
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issue 5
1085-1091
EN
Interface states of all-metallic carbon nanotube quantum dots and superlattices are studied within a tight-binding model. We focus on achiral systems made by connecting armchair (n,n) and zigzag (2n,0) tubes with a full ring of n pentagon-heptagon topological defects. We show that the coupling between interface states, which arise from the topological defects, reflects the existence of the Friedel oscillations in the (n,n) tube, with an unusually large decay exponent. We expect this interaction to be important for the understanding of other physical properties, such as selective dot growth, magnetic interaction through carbon tubes or optical spectroscopy of interface states.
3
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Unzipped and Defective Nanotubes: Rolling up Graphene and Unrolling Tubes

76%
Chico L., Santos H., Ayuela A., Jaskólski W., Pelc M., Brey L.
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issue 3
433-441
EN
The properties of carbon nanotubes can be dramatically altered by the presence of defects. In this work we address the properties of two different kinds of defective nanotubes: junctions of achiral tubes with topological defects and partially unzipped carbon nanotubes. In particular, we begin by focussing on the interface states in carbon nanotube junctions between achiral tubes. We show that their number and energies can be derived by applying the Born-von Karman boundary condition to an interface between armchair- and zigzag-terminated semi-infinite graphene layers. We show that these interface states, which were thought to be due to the presence of topological defects, are in fact related to the graphene zigzag edge states. Secondly, we study partially unzipped carbon nanotubes, which can be considered as the junction of a carbon nanotube and a graphene nanoribbon, which has edge features giving rise to novel properties. Carbon nanoribbons act as transparent contacts for nanotubes and viceversa, yielding a high conductance. At certain energies, nanoribbons behave as valley filters for carbon nanotubes; this holds considering electron-electron interaction effects. Furthermore, the application of a magnetic field turns the system conducting, with a 100% magnetoresistance. These novel structures may open a way for new carbon-based devices.
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