Carbon Nanotube Superlattices Research Articles

Thermal conductivity of carbon nanotube superlattices: Comparative study with defective carbon nanotubes**Project supported by the National Natural Science Foundation of China (Grant Nos. 11404278 and 11275163) and the Science Foundation of Hunan Province, China (Grant No. 2016JJ2131).

We use molecular dynamics simulation to calculate the thermal conductivities of (5, 5) carbon nanotube superlattices (CNTSLs) and defective carbon nanotubes (DCNTs), where CNTSLs and DCNTs have the same size. It is found that the thermal conductivity of DCNT is lower than that of CNTSL at the same concentration of Stone–Wales (SW) defects. We perform the analysis of heat current autocorrelation functions and observe the phonon coherent resonance in CNTSLs, but do not observe the same effect in DCNTs. The phonon vibrational eigen-mode analysis reveals that all modes of phonons are strongly localized by SW defects. The degree of localization of CNTSLs is lower than that of DCNTs, because the phonon coherent resonance results in the phonon tunneling effect in the longitudinal phonon mode. The results are helpful in understanding and tuning the thermal conductivity of carbon nanotubes by defect engineering.

First-principles study on the electronic and transport properties of periodically nitrogen-doped graphene and carbon nanotube superlattices

Prompted by recent reports on $\sqrt{3} \times \sqrt{3}$ graphene superlattices with intrinsic inter-valley interactions, we perform first-principles calculations to investigate the electronic properties of periodically nitrogen-doped graphene and carbon nanotube nanostructures. In these structures, nitrogen atoms substitute one-sixth of the carbon atoms in the pristine hexagonal lattices with exact periodicity to form perfect $\sqrt{3} \times \sqrt{3}$ superlattices of graphene and carbon nanotubes. Multiple nanostructures of $\sqrt{3} \times \sqrt{3}$ graphene ribbons and carbon nanotubes are explored, and all configurations show nonmagnetic and metallic behaviors. The transport properties of $\sqrt{3} \times \sqrt{3}$ graphene and carbon nanotube superlattices are calculated utilizing the non-equilibrium Green's function formalism combined with density functional theory. The transmission spectrum through the pristine and $\sqrt{3} \times \sqrt{3}$ armchair carbon nanotube heterostructure shows quantized behavior under certain circumstances.

Transmission spectra and valley processing of graphene and carbon nanotube superlattices with inter-valley coupling

We numerically investigate the electronic transport properties of graphene nanoribbons and carbon nanotubes with inter-valley coupling, e.g., in and superlattices. By taking the graphene superlattice as an example, we show that tailoring the bulk graphene superlattice results in rich structural configurations of nanoribbons and nanotubes. After studying the electronic characteristics of the corresponding armchair and zigzag nanoribbon geometries, we find that the linear bands of carbon nanotubes can lead to the Klein tunnelling-like phenomenon, i.e., electrons propagate along tubes without backscattering even in the presence of a barrier. Due to the coupling between K and valleys of pristine graphene by supercells, we propose a valley-field-effect transistor based on the armchair carbon nanotube, where the valley polarization of the current can be tuned by applying a gate voltage or varying the length of the armchair carbon nanotubes.

Influence of tension-twisting deformations and defects on optical and electrical properties of B, N doped carbon nanotube superlattices**Project supported by the National Natural Science Foundation of China (No. 51371049) and the Natural Science Foundation of Liaoning Province (No. 20102173).

As the era of nanoelectronics is dawning, CNT (carbon nanotube), a one-dimensional nano material with outstanding properties and performances, has aroused wide attention. In order to study its optical and electrical properties, this paper has researched the influence of tension-twisting deformation, defects, and mixed type on the electronic structure and optical properties of the armchair carbon nanotube superlattices doped cyclic alternately with B and N by using the first-principle method. Our findings show that if tension-twisting deformation is conducted, then the geometric structure, bond length, binding energy, band gap and optical properties of B, N doped carbon nanotube superlattices with defects and mixed type will be influenced. As the degree of exerted tension-twisting deformation increases, B, N doped carbon nanotube superlattices become less stable, and B, N doped carbon nanotube superlattices with defects are more stable than that with exerted tension-twisting deformations. Proper tension-twisting deformation can adjust the energy gap of the system; defects can only reduce the energy gap, enhancing the system metallicity; while the mixed type of 5% tension, twisting angle of 15° and atomic defects will significantly increase the energy gap of the system. From the perspective of optical properties, doped carbon nanotubes may transform the system from metallicity into semi-conductivity.

Influences of shear deformation on electronic structure and optical properties of B, N doped carbon nanotube superlattices

Carbon nanotubes, one of the most advanced nanoscale materials, have attracted much research attention since they exhibited semiconductor, metal or insulator properties depending on their geometric structures. Carbon nanotubes have great potential in various applications in electronic and optical device. Dopants to the carbon nanotubes intentionally could offer a possible route to change and tune their electronic, optical properties. Another important and effective method is to deform the carbon nanotubes structure. Superlattice structures can offer extra degrees of freedom in designing electronic, optical devices. To understand the involved mechanism, in this paper, the geometry structures, electronic structures and optical properties of the armchair carbon nanotube superlattices doped cyclic alternately with B and N under different shear deformations are investigated by the first-principles method through using the CASTEP code in MS 6.0. It is found that the structures of carbon nanotube superlattices can be dramatically changed by shear deformation. When the shear deformation is less than 9%, the optimization geometry structures of carbon nanotube superlattices are still similar to tubular structures, when the shear deformation is greater than 12%, the geometry structures of these systems have large distortions. The results about the binding energy show that the shear deformation changes the stability of the armchair doped carbon nanotube superlattice. The larger the shear deformation, the lower the stability of the doped carbon nanotube superlattices is. The analysis of charge population show that the covalent bond and ionic bond coexist in the armchair carbon nanotube superlattices doped cyclically alternately with B and N. The band gap of the carbon nanotube superlattice is affected by N, B dopants, as a result, the carbon nanotube superlattice changes from a metal to a semiconductor. Compared with the (5, 5) nanotube superlattices, the band gaps of the (7, 7), (9, 9) doped carbon nanotube superlattices increase. With increasing the shear deformation, the band gap of the doped carbon nanotube superlattices decreases gradually, when the shear deformation is greater than 12%, the band gap changes into 0 eV, the carbon nanotube superlattice changes back into a metal from a semiconductor. The analysis of density of states obtains the same conclusions as the energy band analysis. In optical properties, compared with the armchair carbon nanotube superlattices doped cyclically alternately with B and N without shear deformation, those systems under shear deformation have the peaks of the absorption coefficient and the reflectivity that are all reduced, and are all red-shifted.

Electronic band structure of a Carbon nanotube superlattice

By employing the theoretical method based on tight-binding, we study electronic band structure of single-wall carbon nanotube (CNT) superlattices, which the system is the made of the junction between the zigzag and armchair carbon nanotubes. Exactly at the place of connection, it is appeared the pentagon–heptagon pairs as topological defect in carbon hexagonal network. The calculations are based on the tight binding model in the nearest-neighbor approximation. We seek to describe electronic band structure in the presence of the pentagonheptagon pairs. Our calculation show that the pentagon–heptagon pairs defect in the nanotube structures is not only responsible for a change in a nanotube diameter, but also governs the electronic behaviour around Fermi level. Also, we obtain the Fermi energy of the system via integration of the density of states and matching it to the number of electron in the unit cell. The numerical results may be useful to design of electronic devices based on CNTs.

Boron carbon nanotube superlattices: Geometry, electronic structure and quantum conductance

The stable boron carbon nanotube superlattices (BCNTSLs) that are constructed by periodically connecting carbon nanotube (CNT) and boron nanotube (BNT) with different lengths and diameters are predicted by employing the density functional first-principles calculations. The geometrical and electronic structures as well as quantum conductance of BCNTSLs are studied. It is found that the superlattices can be metallic or semiconducting depending on tube diameters and the ratio of BNT to CNT segments in a periodic unit. The confined states in the superlattice are observed. The present study could offer a useful way for designing some functional nanodevices.

Multiple localized states and magnetic orderings in partially open zigzag carbon nanotube superlattices: An ab initio study

Using ab initio calculations, we examine the electronic and magnetic properties of partially open (unzipped) 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. We believe that these results will open the way to the production of novel nanoscale electronic and spintronic devices.

Interface bands in carbon nanotube superlattices

AbstractWe study the electronic band structure of several carbon nanotube superlattices built of two kinds of intermolecular junctions: (12, 0)/(6, 6) and (8, 0)/(14, 0). In particular, we focus on the energy bands originating from interface states. We find that in case of the metallic (12, 0)/(6, 6) superlattices, the interface bands change periodically their character from bonding‐ to antibonding‐like vs. increasing length of the (6, 6) tube.We show that these changes are related to the decay of the charge density Friedel oscillations in the metallic (6, 6) tube. However, when we explore other chiralities without rotational symmetry, no changes in bondingantibonding character are observed for semiconductor superlattices, as exemplified in the case of (8, 0)/(14, 0) superlattices. Our results indicate that unless metallic tubes are employed in the junctions, the bondingantibonding crossings are not present (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Friedel Oscillations in Carbon Nanotube Quantum Dots and Superlattices

Proceedings of the XXXVII International School of Semiconducting Compounds, Jaszowiec 2008.

Mesoscale reverse stick-slip nanofriction behavior of vertically aligned multiwalled carbon nanotube superlattices

Characteristics of sliding friction behaviors of vertically aligned multiwalled carbon nanotube (CNT) superlattices have been investigated in this letter. Friction force was measured using both regular atomic force microscopy (AFM) probe and colloidal AFM probe consisting of a 15μm diameter borosilicate sphere attached to the end of regular cantilever. A distinct reverse stick-slip behavior was observed in the current study compared to the usual stick-slip behavior reported in literature. It was found that this reverse stick-slip behavior was primarily due to the combined effects of surface topology and elastic deformation of CNTs, which were verified by experiments and atomistic simulations.

Electronic band structure of carbon nanotube superlattices from first-principles calculations

We report on first-principles calculations for metallic carbon nanotube superlattices $N(12,0)∕N(6,6)$ with $N=1\char21{}4$. Although the calculated band structures show a good overall agreement with the results of the simpler tight-binding $\ensuremath{\pi}$-electron approximation, electron interaction and correlation effects strongly modify some peculiar flatbands, previously found within a tight-binding approach [W. Jask\'olski and L. Chico, Phys. Rev. B 71, 155405 (2005)]. In the ab initio approach, these bands are no longer dispersionless, much closer to the Fermi level, and are always nondegenerate, in contrast to former tight-binding results.

Carbon nanotube superlattices in a magnetic field

AbstractThe influence of magnetic field on the band structure of carbon nanotube superlattices is investigated. In particular, we study superlattices built of finite sections of (6,6) and (12,0) tubes connected by pentagon/heptagon topological defects. Magnetic field is parallel to the axis of the superlattice. We demonstrate that the superlattice band structure does not show periodicity with the flux quantum, which is typical for pure carbon nanotubes. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008

Symmetry and structural properties of carbon nanotube quantum dots and superlattices

The electronic structure and quantum conductance of metallic carbon nanotube quantum dots and superlattices are investigated. We study two kinds of quantum dots and superlattices: rotationally symmetric and rotationally asymmetric ones. It is shown that rotational invariance significantly in.uences the conductance of quantum dots. In contrast, quantum conductance of superlattices (multiple quantum dots) does not critically depend on their rotational symmetry. All the calculations are performed within the tight-binding model and π-electron nearest-neighbors approximation.

Band Structure and Quantum Conductance of Metallic Carbon Nanotube Superlattices

The electronic structure and quantum conductance of rotationally in-variant (6,6)/(12,0) and rotationally non-invariant (5,5)/(8,2) superlatticesmade of metallic carbon nanotubes are investigated. It is shown that, exceptin the limit of very large periods, the quantum conductance of such super-lattices does not critically depend on their rotational invariance, although itdoes in case of quantum dots and single junctions made of these nanotubes.PACS numbers: 73.22.{f, 73.63.{b

Localized and conducting states in carbon nanotube superlattices

The electronic structure and quantum conductance of superlattices made of metallic carbon nanotubes are investigated. It is shown that minibands with the same origin as nonconductive states in metallic quantum dots [L. Chico and W. Jask\'olski, Phys. Rev. B 69, 085406 (2004)] can have a nonzero conductance in superlattices. We also report on a peculiar behavior of some bound states in $(2n,0)∕(n,n)$ superlattices, which originate from dispersionless bands of $(2n,0)$ tubes, but localize exclusively in the neighboring $(n,n)$ sections. They are truly localized and do not yield any conductance.

Quantum conductance of a helically coiled carbon nanotube

Using π-orbital tight-binding model, we investigate the transport properties of a coiled carbon nanotube (also called carbon nanotube spring), which we construct by connecting carbon nanotubes periodically in three-dimensional (3D) space. Theconductance is quantized due to the translational symmetry in the coiled direction. However, the conductance behaviors differ greatly from those of pristine metallic carbon nanotubes but similar to those of carbon nanotube superlattices. We explain that conductance behaviors of the coiled carbon nanotube.

Electronic excitations in coupled armchair carbon nanotubes

We study the low-frequency electronic excitations in two-dimensional armchair carbon nanotube superlattices. The characteristics of the electronic structures and the superlattice geometry are directly reflected in the electronic excitations. The excitation properties, the dielectric function, the excitation spectrum, and the plasmon frequency, strongly depend on the direction and the magnitude of the transferred momentum, and the nanotube radius. There are low-frequency plasmons except that the transferred momentum is perpendicular to the tubular axis. They belong to acoustic plasmons.