Armchair Single-walled Nanotubes Research Articles

Electronic and half-metallic behavior of copper-doped silicon carbide armchair single-walled nanotubes using density functional theory

Due to their remarkable mechanical, thermal and electrical characteristics, silicon carbide (SiC) single-walled nanotubes (SWNTs) are an unusual and promising class of materials. Density functional theory (DFT) is used in this study to examine the electrical and structural characteristics of copper-doped SiC armchair SWNTs. It has been discovered that copper doping of SiC armchair SWNTs alters the materials’ electrical characteristics. SiC SWNTs band gap plays a significant role in influencing the electrical conductivity and optical characteristics of the substance. The energy bands i.e., valence band and conduction band of SiC armchair SWNTs overlapped as copper doping concentration increased, altering the materials’ electrical conductivity and optical characteristics. Additionally, a continuous density of states plot and a narrower band gap are frequently employed as markers of ferroelectric behaviour which indicates the existence of a polarizable and highly delocalized electronic system. The significance of copper doping in SiC SWNTs is understood by this study, along with the effects of the doping on the material’s electrical properties.

Tunable Photocatalytic Water Splitting Performance of Armchair MoSSe Nanotubes Realized by Polarization Engineering.

The photocatalytic properties of Janus transition metal dichalcogenide (TMD) nanotubes are closely correlated with the electrostatic potential difference between their inner and outer surfaces (ΔΦ). However, due to some distraction from the tubular structures, it remains a great challenge to calculate their ΔΦ directly. Here, we creatively work out the ΔΦ of Janus MoSSe armchair single-walled nanotubes (A-SWNTs) with their corresponding building block models by first-principles calculations. The ΔΦ increases as the diameter reduces. After considering ΔΦ, we find that all of these MoSSe A-SWNTs possess suitable band-edge positions required for water redox reactions and high solar-to-hydrogen (STH) conversion efficiencies. The built-in field induced by the ΔΦ promotes the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) to proceed separately on the inner and outer surfaces. Especially, the photoexcited carriers exhibit adequate driving forces for OER and HER. Besides, constructing a double-walled nanotube can dramatically increase ΔΦ, which also further improves the separation and redox capacity of photoexcited carriers as well as the STH conversion efficiency. Moreover, all of these MoSSe armchair nanotubes have outstanding optical absorption in the visible light range. Our studies provide an effective strategy to improve the photocatalytic water-splitting performance of Janus TMD nanotubes.

Modeling Interactions of Iron Atoms Encapsulated in Nanotubes

The behavior and electronic structure of the carbon and boron nitride nanotubes that interact with the iron atom were studied using the Lennard–Jones potential and hybrid discrete-continuum approach. The iron-filled nanotubes were explored by means of classical applied mathematics in order to develop an understanding of the underlying mechanisms of the encapsulation of metal atoms inside nanotubes. Herein, we examined the suction energy and then the equilibrium offset positions of the iron atoms inside zigzag and armchair single-walled nanotubes, to obtain the optimal radii of the tubes and encapsulate the iron atom by determining the radii that provide the minimum interaction energies. Our observations indicate that the encapsulation behaviour depends on the radii of the nanotubes, and we predict that it is less likely for an iron atom to be enclosed inside the nanotubes when the value of the tube radius is less than ≈2.5 Å. The optimal nanotube necessary to fully enclose the iron atom has a radius of ≈4.2 for both carbon and boron nitride nanotubes, which approximately corresponds to the interaction energies of −1.8 kcal/mol. In its entirety, this work presents an approach that might further the understanding of the encapsulation of metal atoms inside nanotubes.

Effect of power law index for vibration of armchair and zigzag single walled carbon nanotubes

This research deals with the study of vibrational behavior of armchair and zigzag single-walled carbon nanotubes invoking extended Love shell theory. The effects of different physical and material parameters on the fundamental frequencies are investigated. By using volume fraction for power law index, the fundamental natural frequency spectra for two forms of single-walled carbon nanotubes are calculated. The influence of frequencies against length-to-diameter ratios with varying power law index are investigated in detail for these tubes. To discretize the governing equation in eigen-value form, wave propagation approach is developed. Complex exponential functions have been used and the axial model depends on boundary condition that has been described at the edges of carbon nanotubes to calculate the axial modal dependence. Computer software MATLAB is utilized for the frequencies of single-walled carbon nanotubes and current results shows a good stability with comparison of other studies.

Chemical reactivity and adsorption properties of pro-carbazine anti-cancer drug on gallium-doped nanotubes: a quantum chemical study.

In this study, we propose new armchair single-walled nanotubes (SWNTs) for stable adsorption, increasing drug delivery performance and decreasing side effects of pro-carbazine (Pro-CB) anti-cancer in the framework of B3LYP/6-31g*/Lanl2DZ level of theory. Indeed, doping gallium (Ga) metal in SWNTs is naturally followed by changing of geometry, increasing dipole moment, and creating one site with high reactivity in order to better adsorption of the drug molecule. Chemical reactivity descriptors show that SWNTs and Pro-CB have electrophile and nucleophile roles in interaction, respectively. More importantly, high local and dual softness in Ga-doped SWNTs indicate improvement of drug adsorption. Parallel and perpendicular complexes result from their interaction in the N and the O sites. Negative values of binding energy (Ebind) show that composed complexes are energetically stable especially in the O site in comparison with the N site. On the other hand, more negative value of the Ebind in SWCNTs shows that these nanotubes are more effective for drug adsorption than their boron nitride counterparts. Graphical abstract The Ga dopping results in reducing of HOMO-LUMO gap and increasing charge transfer between SWNTs and Pro-CB, and formation better complex, especially SWCNT.

Reactivity of cycloparaphenylenes: Studying the possible growth of single-walled carbon nanotubes with DFT methods

We perform a theoretical study on a set of carbon nanorings (CycloParaPhenylenes or CPP) envisioned as molecular templates for the selective synthesis of carbon nanotubes. The shape of these precursors, originating from bending n phenylene units in para position until forming the corresponding nanoring [n]CPP, may drive the growth of armchair single-walled nanotubes. This kinetic and thermodynamic study covers a set of molecules with different diameters, analyzing the exothermicity and the reaction path of a CPP-based radicaloid mechanism. The methodology employed is based on validated density functionals for mechanistic studies, shedding light on the viability of this synthetic pathway.

Torsional properties of hexagonal boron nitride nanotubes, carbon nanotubes and their hybrid structures: A molecular dynamics study

The torsional mechanical properties of hexagonal single-walled boron nitride nanotubes (SWBNNTs), single-walled carbon nanotubes (SWCNTs), and their hybrid structures (SWBN-CNTs) are investigated using molecular dynamics (MD) simulation. Two approaches - force approach and energy approach, are adopted to calculate the shear moduli of SWBNNTs and SWCNTs, the discrepancy between two approaches is analyzed. The results show that the shear moduli of single-walled nanotubes (SWNTs), including SWBNNTs and SWCNTs are dependent on the diameter, especially for armchair SWNTs. The armchair SWNTs show the better ability of resistance the twisting comparable to the zigzag SWNTs. The effects of diameter and length on the critical values of torque of SWNTs are obtained by comparing the torsional behaviors of SWNTs with different diameters and different lengths. It is observed that the MD results of the effect of diameter and length on the critical values of torque agrees well with the prediction of continuum shell model. The shear modulus of SWBN-CNT has a significant dependence on the percentages of SWCNT and the hybrid style has also an influence on shear modulus. The critical values of torque of SWBN-CNTs increase with the increase of the percentages of SWCNT. This phenomenon can be interpreted by the function relationship between the torque of different bonds (B-N-X, C-C-X, C-B-X, C-N-X) and the angles of bonds.

Theoretical study of the adsorption of aromatic units on carbon allotropes including explicit (empirical) DFT dispersion corrections and implicitly dispersion-corrected functionals: the pyridine case.

The suitability of implicitly dispersion-corrected functionals, namely the M06-2X, for the determination of interaction energies and electron polarization densities in adsorption studies of aromatic molecules on carbon allotropes surfaces is analysed by comparing the results with those obtained using explicit dispersion through Grimme's empirical corrections. Several models of increasing size for the graphene sheet together with one-dimensional curved carbon structures, (5,5), (6,6) and (7,7) armchair single-walled nanotubes, and two-dimensional curved carbon structures, C60 fullerene, have been considered as substrates in this work, whereas pyridine has been chosen as an example for the adsorbed aromatic molecule. Comparison with recent experimental estimations of the adsorption energy and calculations using periodic boundary conditions on a supercell of 72 carbon atoms indicates that a finite model containing ninety six carbon atoms (C96) approaches quite well the adsorption on a graphene sheet. Analysis of the interaction energy components reveals that the M06-2X functional accounts for most of the dispersion energy implicitly, followed far by wB97X and B3LYP, whereas B97 and BLYP do not differ too much from HF. It has been found that M06-2X corrects only the energy component associated to dispersion and leaves the rest, electrostatic, Pauli and induction "unaltered" with respect to the other DFT functionals investigated. Moreover, only the M06-2X functional reflects the effect of dispersion on the electron polarization density, whereas for the remaining functionals the polarization density does not differ too much from the HF density. This makes the former functional more suitable a priori for the calculation of electron density related properties in these adsorption complexes.

Structures, Energetics, and Electronic Properties of Layered Materials and Nanotubes of Cadmium Chalcogenides

Geometric structures, energetics, and electronic properties of single-layer sheets, multilayer stacks, and single-walled nanotubes (SWNTs) of cadmium chalcogenides CdX (X = S, Se, Te) have been studied using ab initio density functional theory, along with spin–orbit coupling, van der Waals (vdW) interactions, and the GW approximation. Methodologies applied to the rationally designed materials have been validated through the experimental structural parameters and band gaps of 3D bulk zinc blende and wurtzite phases of CdX. The 2D single-layer sheet of CdS is found to be completely planar, while those of CdSe and CdTe are slightly corrugated, all showing a honeycomb lattice. The 2D sheets are destabilized with respect to the bulk zinc blende and wurtzite phases, but can be significantly stabilized by forming 3D multilayer stacks as a result of interlayer interactions. 1D (5,5) armchair and (9,0) zigzag SWNTs are also stabilized from their single-layer sheet counterparts. Both SWNTs consist of two concentric...

A molecular dynamics simulation study for the mechanical properties of different types of carbon nanotubes

Carbon nanotubes have caught tremendous attention of the researchers during the last decade due to their excellent mechanical, electrical, optical and thermal prop- erties. The exploitation of these fibers as reinforcing agents in making strong fiber composites has been a primary research topic in the recent investigations on composite materials. Although the theoretical results are rather opti- mistic, the goal of achieving high strength of the carbon nanotube composites is still not satisfactorily realized. We report here a comparative study of the mechanical properties of single-walled, multi-walled and bundle of single-walled carbon nanotubes. Their mechanical behavior is investigated by molecular dynamics simulation, considering Brenner's second generation reactive empirical bond order interatomic potential between the carbon atoms making a tube. For a long range interaction, we have defined a weak van der Waals force which acts between different layers of a multi-walled tube or between different tubes of a bundle. Samples of three isolated armchair single-wall carbon nanotubes of different diameters, a multi-wall armchair carbon nanotube and finally a bundle of three armchair single-walled nanotubes of same diameter are taken. Their fracture pattern and buckling behavior are modeled and compared. Significant changes are observed in the mechanical properties of the samples of different types of carbon nanotubes which arise due to the interaction between the shells of a multi-walled tube or the tubes in a bundle.

STUDY OF PRISTINE CARBON NANOTUBE UNDER TENSILE AND COMPRESSIVE LOADS USING MOLECULAR DYNAMICS SIMULATION

After the discovery, carbon nanotubes (CNTs) have received tremendous scientific and industrial interests. This is due to their exceptional mechanical, electrical, and thermal properties. CNTs having pristine structure (i.e., structure without any defect) hold very high mechanical properties. In this article, mechanical properties of CNTs are studied under both tensile and compressive loads using molecular dynamics (MD) simulations. Four armchair single-walled nanotubes (SWNTs) having indexes of (3,3), (4,4), (5,5) and (6,6) with pristine structure are simulated with MD. Molecular simulations are carried out using the classical MD method, in which the Newtonian equations of motion are solved numerically for a set of atoms. The velocity- Verlet algorithm is used for solving the Newtonian equations of motion. The Brenner potential is used for carbon-carbon interaction in the CNT and temperature of the system is controlled by velocity scaling. Simulation results show that modulus of elasticity of CNTs varies significantly with CNT diameter. The results obtained from the compressive test by MD simulations are in well agreement with the results obtained from theoretical Euler equation and parabolic equation for long and short column respectively.Keywords: Carbon nanotubes; Molecular dynamics; Young’s modulus; Failure strength; Failure strain.DOI: 10.3329/jme.v40i2.5346Journal of Mechanical Engineering, Vol. ME 40, No. 2, December 2009 72-78

C-BN Single-Walled Nanotubes from Hybrid Connection of BN/C Nanoribbons: Prediction by ab initio Density Functional Calculations

We demonstrated for the first time by ab initio density functional calculation and molecular dynamics simulation that C(0.5)(BN)(0.5) armchair single-walled nanotubes (NT) are gapless semiconductors and can be spontaneously formed via the hybrid connection of graphene/BN Nanoribbons (GNR/BNNR) at room temperature. The direct synthesis of armchair C(0.5)(BN)(0.5) via the hybrid connection of GNR/BNNR is predicted to be both thermodynamically and dynamically stable. Such novel armchair C(0.5)(BN)(0.5) NTs possess enhanced conductance as that observed in GNRs. Additionally, the zigzag C(0.5)(BN)(0.5) SWNTs are narrow band gap semiconductors, which may have potential application for light emission. In light of recent experimental progress and the enhanced degree of control in the synthesis of GNRs and BNNR, our results highlight an interesting avenue for synthesizing a novel specific type of C(0.5)(BN)(0.5) nanotube (gapless or narrow direct gap semiconductor), with potentially important applications in BNC-based nanodevices.

The effects of the grafted hydroxyl on the elastic properties of single-walled carbon nanotubes

The molecular dynamics method was used to investigate the elastic properties of armchair and zigzag single-walled carbon nanotubes grafted by hydroxyl on their ports. The results showed that the Young's moduli of ungrafted armchair (5, 5)，(10,10) and zigzag (9, 0) , (18,0) single-walled carbon nanotubes were 948，901 and 804, 860GPa, respectively. When the single-walled carbon nanotubes were grafted by 2 to 8 hydroxyl functional groups, the Young's modulus of the zigzag single-walled carbon nanotubes was little changed, while the Young's modulus of the armchair single-walled nanotubes first decreased significantly due to the grafting, then increased appreciably to some steady value with increasing of the grafts after having been grafted to certain numbers. The reasons were analyzed in terms of the isoline structure of deformation electron density, C—C bond-length and the system binding energy variation of the carbon nanotubes with different graft numbers.

Topochemical strategies and experimental results for the rational synthesis of carbon nanotubes of one specified type

A generic topochemical route for the rational synthesis of carbon single walled nanotubes (SWNTs) of one specified type is proposed and analyzed using theoretical and experimental results. This route uses crystal-controlled 1,4-addition polymerization of diacetylene groups in cyclic monomer molecules to make organic nanotubes, whose three-dimensional covalent network combines carbon–carbon bonds of the cyclic monomer and four parallel polydiacetylene chains formed by solid-state reaction. Up to 75% of the carbon–carbon bonds of the target carbon nanotube are correctly connected in the organic nanotube, and none are incorrectly connected. Target monomers are down selected by using molecular mechanics calculations to predict the allowable crystal packing parameters, from which topochemical reactivity is predicted using a well-established reactivity diagram. This approach correctly predicts the solid-state polymerizability of a cyclic diacetylene that we experimentally demonstrated forms a targeted hydrocarbon nanotube. Substituent extrusion is the final step in forming the carbon nanotube from the organic nanotube, which should occur cleanly because the covalent connectivity of the organic nanotube holds the structure in place. Using this two-step topochemical control of reaction and structure, during formation of the organic nanotube and during substituent extrusion, routes to armchair and zigzag SWNTs having different ring diameters are proposed.

Local Softness versus Local Density of States as Reactivity Index

The definition of softness and local softness using the density of states (DOS) and local density of states (LDOS) given by Yang and Parr for metals has been casted into working equations and applied to sequences of finite cylindrical fullerenes modeling the (5,5) and (10,10) single-walled capped carbon nanotubes. The behavior of DOS, LDOS, and global and local softness as functions of length and tube type is investigated in the simplest Huckel approximation. DOS-based calculation of global softness gives results that depend less on the details of the electronic structure than those based on the finite-difference approximation. Armchair single-walled nanotubes with larger diameters are softer than those with smaller diameters at the same tube length. Local softness, after fluctuations in the end-cap region, settles down within the first 20 layers of hexagons of the tube body to a constant (diameter-dependent) value.

Superconductivity in armchair carbon nanotubes

We use the momentum space renormalization group to study the influence of phonons and the Coulomb interaction on the superconducting response function of armchair single-walled nanotubes. We do not find superconductivity in undoped single nanotubes. When doped, superconducting fluctuations can develop because of the phonons but remain small and are easily destroyed by the Coulomb interaction. The origin of superconductivity in ropes of nanotobes is most likely an intertube effect. Projections to zigzag nanotubes indicate a more favorable disposition to superconducting fluctuations.

First-principles band structures of armchair nanotubes

Recent work by Thess et al. suggests that (10,10) carbon nanotubes with diameters of 1.38 nm have been observed with high conductivities. Other experimental results have directly measured the density of states of single-wall carbon nanotubes with diameters in the range 1-1.5 nm. Herein we examine the expected electronic properties of armchair single-wall nanotubes with diameters in this range, and present first-principles local-density functional results for band structure and density of states of these SWNTs. We find our results support the validity of the simple graphene sheet model, and are in close agreement with experimental measurements of the density of states of these materials.

Carbon nanotubes as long ballistic conductors

Early theoretical work on single-walled carbon nanotubes1,2,3 predicted that a special achiral subset of these structures known as armchair nanotubes3 should be metallic. Tans et al.4 have recently confirmed these predictions experimentally and also showed directly that coherent electron transport can be maintained through these nanowires up to distances of at least 140 nm. But single-walled armchair nanotubes are one-dimensional conductors with only two open conduction channels (energy subbands in a laterally confined system that cross the Fermi level)1,2,3. Hence, with increasing length, their conduction electrons ultimately become localized5 owing to residual disorder in the tube which is inevitably produced by interactions between the tube and its environment. We present here calculations which show, however, that unlike normal metallic wires, conduction electrons in armchair nanotubes experience an effective disorder averaged over the tube's circumference, leading to electron mean free paths that increase with nanotube diameter. This increase should result in exceptional ballistic transport properties and localization lengths of 10 µm or more for tubes with the diameters that are typically produced experimentally6.