Band Structure Of Carbon Nanotubes Research Articles

Multi-electron transfer mechanism and band structures of CNTs in MOF-derived CNTs/Co hybrids for enhanced electromagnetic wave absorption property

Metal-organic framework (MOF)-derived magnetic metal/carbon nanocomposites have received widespread attention for electromagnetic wave (EMW) absorption. The present study introduces a novel approach to MOF composite material design by constructing composites modified with carbon nanotubes (CNTs) and magnetic Co nanoparticles. The carbon confinement effect in CNT/Co not only regulates the electronic structure of Co-C bonds, but also maintains the redox cycle of Co0/2→Co3+→Co0/2+, improving electronic activity and exhibiting synergistic integration characteristics of efficient electromagnetic wave absorption. Particularly, the maximum reflection loss (RLmin) of CNTs/Co-900 reached −52.7 dB at 4.67 GHz in the case of an absorber thickness of 1.6 mm. The excellent microwave absorption performance may be attributed to the interwoven structure formed by novel ZIF-67, CNTs, and Co metal nanoparticles and the double loss of magnetic Co and dielectric CNTs. In addition, the band gap of CNTs was calculated to be Eg = 0.27 eV by the semi-empirical tight-binding method with DFTB+. It is confirmed that CNTs have high electron migration ability, which is beneficial to conductive loss. It is confirmed that CNTs have high electron migration ability, which is beneficial to conductive loss. This study provides a novel strategy for the development of metal-organic framework-based magnetic particles/carbon nanocomposites for electromagnetic wave absorption.

Influence of Tension and Compression on the Band Structure of Carbon Nanotubes as Probed by the Cylindrical Wave Method

Influence of Tension and Compression on the Band Structure of Carbon Nanotubes as Probed by the Cylindrical Wave Method

Influence of Torsional Strains on the Band Structure of Carbon Nanotubes according to the Cylindrical Waves Method

Influence of Torsional Strains on the Band Structure of Carbon Nanotubes according to the Cylindrical Waves Method

Defect effects and electronic structure regulation in low-dimensional materials

Low-dimensional materials have been drawing increasing interest due to the unique structures and fascinating properties which are quite promising for wide-range application ranging from new energy resources to information technology. The exotic electronic states of the low-dimensional materials which arise from the quantum-confinement effects of electrons render a potential strategy to overcome the size-limitation of traditional semiconducting materials and continue the Moores’ law which is difficult for the conventional bulk materials. The electronic structure modulation of low-dimensional materials to meet the relevant requirements serves as the key to reach this goal. Notably, in low-dimensional materials, the defect effects are more remarkable than those in bulk materials due to the high specific surface area and quantum confinement effects. Moreover, the compatibility of low-dimensional materials to nanoscaled devices is crucial for the next-generation device applications. Here, we focus on the role of defects in electronic structure modulation of one- (1D) and two-dimensional (2D) materials to summarize works of our group relevant to this topic in recent years. The point defects, such as vacancies and adatoms (or functional groups) are revealed to have significant contribution to the electron spin-polarization and excited states. The ferromagnetism of the metal-free materials is demonstrated in wide range of materials, such as graphite, hexagonal boron nitride and silicon carbide both theoretically and experimentally. The spin-polarization of p electrons in these materials enriches the family of ferromagnetic materials and offers a promising strategy for spintronics device applications. The hollow structure of carbon nanotubes provides an ideal platform for the study of atomic reaction, diffusion and condensation processes confined in nanospace. The electronic band structures of carbon nanotubes can be effectively regulated by encapsulating metal or hydrogen nanowires. Ultrahigh density of hydrogen nanowires can be confined inside carbon nanotubes, thanks to the excellent mechanical properties, which lead to metallization or superconductivity of the 1D hydrogen systems at relative low pressure and high temperature, due to the “physical compression” effect of carbon nanotubes. The superconducting hydrogen can be well explained in terms of the Eliashberg superconductivity theory for electron-phonon strong-coupling system. The metallization and superconducting phase of hydrogen nanowires encapsulated in carbon nanotubes open a promising platform for study of low-dimensional superconductivity at high pressure. Additionally, metal-organic frameworks (MOFs) which are composed of transition metal (TM) atoms and organic ligands emerged as a new family of 2D materials. Compared with traditional 2D materials, MOFs have the advantages of structural diversity, porous configurations, tunable electronic band structures. Some lattice models, such as Kagome, Lieb and Ruby lattice models can be achieved in 2D MOFs. The synergistic effect of TM atoms and organic ligands leads to exotic properties, such as Kane fermions, topological electronic states (quantum spin Hall effects and quantum anomalous Hall effect), superconductivity, high catalytic activity, etc. The well-distributed TM atoms in the porous structures of 2D MOFs facilitate the catalysis in hydrogen evolution reaction (HER), oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), which hold great promise in water splitting and fuel cells. In view of the experimental progresses on the synthesis of diverse 2D MOFs, the fascinating properties of 2D MOFs bring about new concepts for electronic devices and catalysis design.

Curvature effects in the band structure of carbon nanotubes including spin–orbit coupling

The Kane–Mele model was previously used to describe effective spin–orbit couplings (SOCs) in graphene. Here we extend this model and also incorporate curvature effects to analyze the combined influence of SOC and curvature on the band structure of carbon nanotubes (CNTs). The extended model then reproduces the chirality-dependent asymmetric electron-hole splitting for semiconducting CNTs and in the band structure for metallic CNTs shows an opening of the band gap and a change of the Fermi wave vector with spin. For chiral semiconducting CNTs with large chiral angle we show that the spin-splitting configuration of bands near the Fermi energy depends on the value of .

Modeling of sub-band and diameter effect in carrier concentration of CNTFET

Carbon nanotubes (CNTs) have been seen as a potentially future material to provide an ultrasmall device (CNTFET (Carbon Nanotube Field Effect Transistor)). Therefore, the studies of sub-bands effects are needed in order to find the enhancement of carrier transport in CNTFET.Also in this paper the band structure of the rolled-up nanotube can be obtained by zone-folding from the band structure of the graphene sheet. This method is used in this work and we simulated and analyzed the band structure of carbon nanotube. We present analytical modeling of carrier concentration in a zigzag semiconducting of carbon nanotube field effect transistor (CNFET) using the dispersion relation E(k) (the first three sub-bands) and given the density of states (DOS), the carrier concentration is obtained based on a numerical method as an alternative to the usual Fermi–Dirac integrals. In order to find the influence of the first three sub-bands energy and diameter dt of CNT in non-degenerate and degenerate region of the carrier concentration in CNTFET. The results obtained showed that the diameter and the energy of sub-band have a significant impact on the carrier concentration of CNTFET.

Peierls instability in (5,5) and (9,0) carbon nanotubes: Effect of torsional strain on band gap

Effect of Peierls instability on the electronic band structure of carbon nanotubes (CNTs) under torsional strain is studied by tight-binding approximation. When Kekule structure with two different bond lengths is introduced, armchair (5,5) and zigzag (9,0) CNTs become semiconducting indicating by a small band gap opening at the Fermi level. Numerical calculations show that the increasing of shear strain leads to reduce the band gap of armchair (5,5) carbon nanotube. Shear strain threshold for a semiconductor–metal phase transition depends on the difference in the bond lengths. In the metal state, the torsional strain induces the Fermi wavenumber of (5,5) carbon nanotube deviated from the center of the first Brillouin zone. Under the torsional strain, a semiconductor–metal–semiconductor phase transition appears for (9,0) CNT with Kekule structure as well.

Zitterbewegung of electrons in carbon nanotubes created by laser pulses

We describe a possibility of creating non-stationary electron wave packets in zigzag carbon nanotubes (CNT) illuminated by short laser pulses. After the disappearance of the pulse the packet experiences a trembling motion (Zitterbewegung, ZB). The band structure of CNT is calculated using the tight-binding approximation generalized for the presence of radiation. By employing realistic pulse and CNT parameters we obtain the ZB oscillations with interband frequencies corresponding to specific pairs of energy bands. A choice of optimal parameters is presented in order to observe the phenomenon of ZB experimentally. The use of Gaussian wave packets to trigger the electron Zitterbewegung, as used in the literature, is critically reexamined.

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.

ELECTRONIC BAND STRUCTURE OF CARBON NANOTUBES WITH QUINOID STRUCTURE

In this paper, we fully describe the geometry of atomic structure of carbon nanotube with quinoid structure. Electronic energy band structure of carbon nanotubes with quinoid structure is studied by tight-binding approximation. In the presence of bond alternation, calculations show that only armchair (n, n) carbon nanotube (without twisting) remains metallic and zigzag (3ν - 1, -3ν + 1) CNT becomes metallic at the critical elongation. Effect of deformation on the change of band gap is also calculated and discussed.

Electronic Band Structure of Carbon Nanotubes with Kekule Structure

Electronic band structure of carbon nanotubes with the Kekule structure is studied by the tight-binding approximation. We give a complete geometrical approach to structural properties of carbon nanotubes with bond alternation, including chiral and achiral tubes. When the Kekule is introduced, all carbon nanotubes become semiconducting with a small band gap at the Fermi level. The band gap of the carbon nanotubes depends only on the difference between C—C bond lengths or the resonance integrals.

Radial deformation and band-gap modulation of pressurized carbon nanotubes

We numerically investigate the electronic band structure of carbon nanotubes (CNTs) under radial corrugation. Hydrostatic pressure application to CNTs leads to a circumferential wave-like deformation of their initially circular cross-sections, called radial corrugations. Tight-binding calculation was performed to determine the band gap energy as a function of the amplitude of the radial corrugation. We found that the band gap increased with increasing radial corrugation amplitude; then, the gap started to decline at a critical amplitude and finally vanished. This non-monotonic gap variation indicated the metal-semiconductor-metal transition of CNTs with increasing corrugation amplitude. Our results provide a better insight into the structure-property relation of CNTs, thus advancing the CNT-based device development.

Cohesive band structure of carbon nanotubes for applications in quantum transport

An integrated cohesive band structure of carbon nanotubes (CNTs) applicable to all chirality directions (n, m), starting from the Dirac cone of a graphene nanolayer in k-space, is demarcated, in direct contrast to dissimilar chiral and achiral versions in the published literature. The electron wave state of a CNT is quantized into one-dimensional (1-D) nanostructure with a wrapping mode, satisfying the boundary conditions from one Dirac K-point to an equivalent neighboring one with an identical phase and returning to the same K point. The repetitive rotation for an identical configuration with added band index (n-m)mod3, yields one metallic (M) with zero bandgap corresponding to (n-m)mod3 = 0, semiconducting state SC1 with (n-m)mod3 = 1 and SC2 with (n-m)mod3 = 2. The band gap and effective mass of SC2 state are twice as large as those of SC1 state. A broad-spectrum expression signifying the linear dependence of the effective mass on the bandgap is obtained. Both the Fermi energy and the intrinsic velocity limiting the current to the saturation level is calculated as a function of the carrier concentration. Limitations of the parabolic approximation are pointed out. Several new features of the band structure are acquired in a seamlessly unified mode for all CNTs, making it suitable for all-encompassing applications. Applications of the theory to high-field transport are advocated with an example of a metallic CNT, in agreement with experimental observations. The mechanism behind the breakdown of the linear current-voltage relation of Ohm's law and the associated surge in resistance are explained on the basis of the nonequilibrium Arora's distribution function (NEADF). These results are important for the performance evaluation and characterization of a variety of applications on CNT in modern nanoscale circuits and devices.

Calculation of Cutting Lines of Single-Walled Carbon Nanotubes

Abstract. Carbon nanotubes (CNs) are hexagonally shaped arrangements of carbon atoms that have been rolled into tubes with outstanding properties. Carbon nanotubes are among the stiffest and strongest fibers known, and have remarkable electronic properties and many other unique characteristics. All properties of the carbon nanotubes are determined by its electronic structure. The main focus of this study has been to investigate the basic electronic band structure of carbon nanotubes and to understand the origin of the cutting lines. For this purposes brief introduction to the electronic properties of carbon nanotubes was given and then 3D electronic band structure was plotted. For different chirality vectors (n, m) 1D and 2D first Brillouin zones and cutting lines of SWNT were calculated and plotted. Key words: Single-walled carbon nanotube, Brillouin zone, Cutting line.

A model of the multiple adsorption of hydrogen atoms on the surface of carbon nanotubes

A model of the multiple adsorption of atomic hydrogen on the surface of single-walled carbon nanotubes of the zigzag and arm-chair types was constructed. The adsorption model is based on the Anderson periodic model. An analytic equation for the band structure of carbon nanotubes with adsorbed hydrogen atoms was obtained, and the special features of this structure were studied. The dependence of the band structure of carbon nanotubes on the concentration of adsorbed hydrogen atoms was analyzed. The model constructed can be used to study adsorption of other univalent atoms on the surface of carbon particles.

Magnetoconductance of carbon nanotubes probed in parallel magnetic fields up to 60 T

Magnetoconductance of carbon nanotubes (CNTs) is investigated. We clearly show that a semiconducting CNT can be converted into a metallic one, or vice versa, with the application of a large magnetic field parallel to the tube axis, providing a consistent confirmation of the Aharonov–Bohm (AB) effect on the band structure of CNTs. We also demonstrate that magnetic-field values where the semiconductor-to-metal transition occurs can be tuned by mechanical strain. Combined control of both the strain and the AB effect may open up new possibilities for CNT devices. In addition, we propose an idea to manipulate spin-split subbands of CNTs, resulting from spin–orbit interaction (SOI), by using the magnetic field to generate sizeable spin-polarized currents. Split magnetoconductance peak due to SOI.

Single Wall Carbon Nanotube Field Effect Transistor Model

The low-energy-limit band structure of carbon nanotubes (CNTs) indicates parabolic behavior. However it is not parabolic in other parts of the band energy. Based on the confinement effect we present an analytical model that captures the essence of the physical processes in a carbon nanotube field effect transistor (CNTFET). The model covers seamlessly the whole range of transport from drift-diffusion to ballistic. It has been clarified that the intrinsic speed of CNTs is governed by the transit time of electrons. Although the transit time is more dependent on the saturation velocity than on the weak-field mobility, the feature of high-electron mobility is beneficial in the sense that the drift velocity is always maintained closer to the saturation velocity, at least at the drain end of the transistor where electric field is necessarily high and controls the saturation current. The results obtained are applied to the modeling of the current-voltage characteristics of a CNTFET. The channel-length modulation is shown to arise from the drain velocity becoming closer to the ultimate saturation velocity as the drain voltage is increased.

On the Possibility of Obtaining MOSFET-Like Performance and Sub-60-mV/dec Swing in 1-D Broken-Gap Tunnel Transistors

Tunneling field-effect transistors (TFETs) have gained a great deal of recent interest due to their potential to reduce power dissipation in integrated circuits. One major challenge for TFETs so far has been achieving high drive currents, which is a prerequisite for high-performance operation. In this paper we explore the performance potential of a 1D TFET with a broken-gap heterojunction source injector using dissipative quantum transport simulations based on the nonequilibrium Green's function formalism, and the carbon nanotube bandstructure as the model 1D material system. We provide detailed insights into broken-gap TFET (BG-TFET) operation, and show that it can indeed produce less than 60mV/decade subthreshold swing at room temperature even in the presence of electron-phonon scattering. The 1D geometry is recognized to be uniquely favorable due to its superior electrostatic control, reduced carrier thermalization rate, and beneficial quantum confinement effects that reduce the off-state leakage below the thermionic limit. Because of higher source injection compared to staggered-gap and homojunction geometries, BG-TFET delivers superior performance that is comparable to MOSFET's. BG-TFET even exceeds the MOSFET performance at lower supply voltages (VDD), showing promise for low-power/high-performance applications.

Band structures of carbon nanotube with spin–orbit coupling interaction

We explore the band structures of single-walled carbon nanotubes (SWCNTs) with two types of spin–orbit couplings. The obtained results indicate that weak Rashba spin–orbit coupling interaction can lead to the breaking of four-fold degeneracy in all tubes even though without the intrinsic SO coupling. The asymmetric splitting between conduction bands and valence bands is caused by both SO couplings at the same time. When the ratio of Rashba spin–orbit coupling to the intrinsic spin–orbit coupling is larger than 3, metallic zigzag nanotube is always metallic conductor, on the contrary it becomes semiconducting properties. However, only when this ratio is equal to about 3 or the intrinsic spin–orbit coupling is much weak, the metallic armchair nanotube still holds the metallic behavior in transport.

Electrocatalytic properties of carbon nanotube carpets grown on Si-wafers

Electrocatalytical activity of carbon nanotube carpets grown on oxidized silicon wafers by spray pyrolysis catalytic chemical vapor deposition has been examined for use in electrochemical devices. To determine the influence of electron donor doping on electrochemical quality, N-atoms were incorporated into the nanotube structure during growth. N-doping, as revealed by electron microscopy, Raman spectroscopy and X-ray diffraction data, led to essential changes of the tubule morphology and structure. For the electrochemical investigation of the carbon nanotube electrodes produced, cyclic voltammetry and electrochemical impedance spectroscopy were used, while ferrocene ( FeCp 2 ) and uric acid served as reference redox systems. Results have revealed enhanced electron transfer kinetics on the N-doped electrodes. The electronic band structure of carbon nanotubes and electrochemical gating are shown to be responsible for the charge transfer kinetics on nanotube electrodes.