Exploring the simultaneous existence of Stone-Wales and carbon ad-dimer defects in the zigzag single-walled carbon nanotubes

We have applied density functional calculations to investigate simultaneous existence of Stone–Wales (SW) and carbon ad-dimer (CD) defects in the zigzag (n, 0) n=5, 6, 7, 8, 9, and 10 SWCNTs, with an extensive search by considering two different orientations of defects. According to our results, the adsorption of a carbon dimer on a hexagonal ring of SWCNTs is easier than the rotation of a C–C bond trough the SW rearrangement. Moreover, the formation of a carbon dimer on the exterior sidewalls of an SW defective SWCNT or the rotation of a C–C bond of a CD defective SWCNT is more favorable than those on the perfect ones. Defect formation energy shows a strong dependence on the both SWCNT radius and defect orientation. The reactivity of SW–CD defective SWCNTs through chemisorption of hydrogen atoms on the central bonds of defect sites shows the thermodynamically lower preference of additions for the CD defective sites in comparison to SW defective sites. Histograms of the ¹³C NMR chemical shifts of SW–CD defective SWCNTs exhibit individual signals for defect sites, which can be attributed to azupyrene- and pentalelene-like structures for SW and CD defect sites, respectively.     

Quantum Chemical Study on the adsorption of metformin drug on the surface of pristine,Si- and Al-doped (5, 5) SWCNTs

Adsorption properties of metformin (MF) drug onto pristine, Si- and Al-doped (5, 5) armchair single-wall carbon nanotubes (SWCNTs) were studied using density functional theory (DFT) calculations at the B3LYP and ωB97XD methods with the standard 6–311 G** basis set. The most stable geometries of the MF drug molecule onto pristine, Si- and Al-doped (5, 5) CNTs were selected and evaluated in the gaseous and aqueous environments. We calculated the natural bond orbitals (NBO), Frontier molecular orbital (FMO), density of states (DOS) and molecular electrostatic potential (MEP) of systems upon adsorption of MF drug. It was found that the reaction of MF drug with pure SWCNT is physisorption in nature, while high chemisorption can be achieved by using Al- and Si-doped SWCNTs. Despite Al-doped SWCNT provides stronger adsorption, however the change in the energy gap of Si-doped SWCNT is more pronounced. It is predicted that MF drug incorporating Si-doped SWCNT can be extended as drug delivery system.     

Molecular dynamics study of effects of nickel coating on torsional behavior of single-walled carbon nanotube

The effects of nickel coating on the torsional behaviors of single-walled carbon nanotubes (SWCNTs) subject to torsion motion are investigated using the molecular dynamics (MD) simulation method. The simulation results show that regardless of chirality, defect or radius, nickel coating can considerably enhance the critical torque of SWCNTs. However, by comparing the critical torsion angle between nickel-coated SWCNTs and corresponding pristine SWCNTs, it is found that nickel coating in small-radius nanotubes does induce a reduction in the critical torsion angle. The results also show that the structural failure of nickel coated imperfect (9,0) SWCNT occurs at an obviously higher critical torque in comparison with uncoated (9,0) SWCNT with a vacancy defect. Furthermore, we also find that the critical torque of a short nickel coated SWCNT is bigger than that of a long one, while the critical torsion angle for a short tube is smaller than that for a long one.     

Liquid dimethyl sulphoxide confined by carbon nanotubes

Here, we report the molecular dynamics simulation on liquid dimethyl sulphoxide (DMSO) confined by single-walled carbon nanotubes (SWCNTs) in comparison with DMSO in the bulk phase at 298 K. The local order of DMSO, analysed in terms of radial distribution functions is similar to that in the bulk except the case with the SWCNT (8, 8) where the anomalous structure pattern is realized. Meanwhile, the translational self-diffusion coefficients of DMSO in confinements are much lower then in the bulk phase (by a factor of 2–3) and correlate with a value of the SWCNT internal diameter. Using cylindrical distribution functions of DMSO atoms we elucidate that the slowdown of self-diffusion coefficient of DMSO confined in the SWCNTs is reduced by the first layer of DMSO molecules close to the SWCNT wall.     

Sidewall fluorination and hydrogenation of single-walled carbon nanotubes: a density functional theory study

The fluorination and hydrogenation reactions on (6, 6) and (10, 0) single-walled carbon nanotubes (SWCNTs) have been examined via computing the reaction energy for the chemisorption. The examined nanotubes have comparable lengths and diameters, with or without Stone-Wales defects on the sidewall. The two fluorine or hydrogen atoms are anchored to the external walls of the SWCNTs. The computed chemisorption energies of these virtual reactions reveal that the fluorination and hydrogenation of the nanotubes are moderately sensitive to the nanotube chirality and the sidewall topology, and the (10, 0) SWCNT with Stone-Wales defect can be easily fluorinated and hydrogenated.      

Axisymmetric vibration of single-walled carbon nanotubes in water

A double shell-Stokes flow model is developed to study the axisymmetric vibration of single-walled carbon nanotubes (SWCNTs) immerged in water. In contrast to macroscopic solid-liquid system, a submerged SWCNT is coupled with surrounding water via the van der Waals interaction. It is shown that this unique feature substantially reduces viscous damping of the axisymmetric radial, longitudinal and torsional vibrations and significantly up-shifts the frequency of the radial vibration of an SWCNT. The study offers a theoretical explanation for the experimental observation and molecular dynamics simulations available in particular cases, and provides an efficient modelling tool and useful guidance for the study of the general dynamic behaviour of SWCNTs in a fluid.     

Dominoes in carbon nanotubes

We demonstrate by molecular dynamics simulations that the domino process can be developed in single-walled carbon nanotubes (SWCNTs). Once a section of a SWCNT with an appropriate diameter (>3.5 nm) is collapsed, the successive collapse of the neighboring portions can generate a domino wave along the longitudinal direction of the tube. The wave is driven by van der Waals potential energy and its natural speed can be up to 1 km/s. Molecules inside the SWCNT can be accelerated by the domino wave and finally shot out. The finding shows for the first time that a SWCNT can be an energy supplier, which provides opportunities for designing new concept (domino-driven) nanoelectromechanical system devices.     

First principles study on magnetic and electronic properties with rare-earth atoms doped SWCNTs

The adsorptions of rare-earth (RE) atoms on (6, 0) and (8, 0) single-walled carbon nanotubes (SWCNTs) have been investigated by using the first-principles pseudopotential plane wave method within density functional theory (DFT). The binding energy, Mulliken charge, magnetic properties, band structure and DOS were calculated and analyzed. Most of RE atoms including Nd, Sm and Eu have a magnetic ground state with a significant magnetic moment. Some electrons transfer between RE-5d, 6s and C-2p orbitals. Owing to the curvature effect, the values of binding energy for RE atoms doped (6, 0) SWCNT are lower than those of the same atoms on (8, 0) SWCNT. The pictures of DOS show that hybridizations between RE-5d, 6s states and C-2p orbitals and between RE-4f and C-2p orbitals appear near the Fermi level. Results indicate that the properties of SWCNTs can be modified by the adsorptions of RE atoms.     

Enhanced luminance of MEH-PPV based PLEDs using single walled carbon nanotube composite as an electron transporting layer

An efficient electron transporting layer (ETL) based on single walled carbon nanotube (SWCNT) composites has been developed for poly [2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) based orange polymer light emitting diodes (PLEDs) and its effect on the performance of PLEDs has been examined. It is observed that with increase in SWCNT concentration, in ETL, the luminance and luminous efficiency of the PLEDs increase (about 5 times increase in luminance is observed at 5% w/w SWCNT concentration). The SWCNTs present in the MEH-PPV ETL boost the mobility of electrons injected from the cathode towards the emissive layer by establishing highly conducting percolation paths. This balances the concentration of holes and electrons in the emissive layer, which leads to enhanced emission from the PLEDs.     

Mechanical properties of nickel-coated single-walled carbon nanotubes and their embedded gold matrix composites

The effects of nickel coating on the mechanical behaviors of armchair single-walled carbon nanotubes (SWCNTs) and their embedded gold matrix composites under axial tension are investigated using molecular dynamics (MD) simulation method. The results show that the Young's moduli and tensile strength of SWCNTs obviously decrease after nickel coating. For armchair SWCNTs, the decreased ratio of the Young's moduli of SWCNTs with smaller radius is larger than that of SWCNTs with larger radius. A comparison is made between the response to Young's modulus of a composite with parallel embedded nanotube and the response of a composite with vertically embedded nanotube. The results show that the uncoated SWCNT can enhance the Young's modulus of composite under the condition of parallel embedment, but such improvement disappears under the condition of vertical embedment because the interaction between SWCNT and gold matrix is too weak for effective load transfer. However, the nickel-coated SWCNT can indeed significantly improve the composite behavior.     

The mechanical property of single-walled carbon nanotube under combined electromechanical loading

The mechanical properties and failure process of single-walled carbon nanotube (SWCNT) under combined electric field and tensile loading are investigated using the semi-empirical quantum mechanical method. The local and global structural deformation and variation of mechanical properties of SWCNT under different directions and intensity of external electric field are discussed systematically. It is shown that the electric field induced deformation in the radial and axial directions of the SWCNT are strongly dependent on the direction of electric field. The analysis of mechanical properties shows that the structure stiffness, tensile strength and failure strain of the SWCNT all decrease with the increase of the field intensity, which is particularly evident under the longitudinal electric field. The Young's modulus of SWCNTs vary with the tube diameter and are affected by the electric field. The increase of the length of the tubes intensifies the charge concentration at the tube ends under the electric field and lead to the decrease of mechanical properties of SWCNTs. The failure process of SWCNTs under the coupling effect of electric field and tensile loading is found to be controlled by the field strength and also affected by the electric charge accumulation.     

Compressive characteristics of single walled carbon nanotube with water interactions investigated by using molecular dynamics simulation

The elastic properties of single walled carbon nanotube (SWCNT) with surrounding water interactions are studied using molecular dynamics simulation technique. The compressive loading characteristic of carbon nanotubes (CNTs) in a fluidic medium such as water is critical for its role in determining the lifetime and stability of CNT based nano-fluidic devices. In this paper, we conducted a comprehensive analysis on the effect of geometry, chirality and density of encapsulated water on the elastic properties of SWCNT. Our studies show that defect density and distribution can strongly impact the compressive resistance of SWCNTs in water. Further studies were conducted on capped SWCNTs with varying densities of encapsulated water, which is necessary to understand the strength of CNT as a potential drug carrier. The results obtained from this paper will help determining the potential applications of CNTs in the field of nano-electromechanical systems (NEMS) such as nano-biological and nano-fluidic devices.     

曲率对Rh在锯齿型单壁碳纳米管内外吸附影响的研究

利用密度泛函理论系统的研究了单壁碳纳米管的曲率对Rh原子在锯齿型碳管内外的吸附行为, 发现Rh原子在管外吸附比管内稳定; 随着碳管管径的增加, 曲率减小, 管内外吸附能的差值逐渐减小, 接近Rh原子在石墨烯上的吸附能. 电荷密度分析表明, 由于卷曲效应使碳纳米管管外的电荷密度大于管内, 随着曲率减小, 这种差别逐渐减小. 管内外吸附Rh原子的Bader电荷差值及局域态密度差别亦随着曲率的下降而减小, 这与Rh原子在管内外吸附能的变化规律相一致.     

A first-principles investigation on the effect of the divacancy defect on the band structures of boron nitride (BN) nanoribbons

On the basis of the comprehensive first-principles computations, we investigated the geometries, electronic and magnetic properties of zigzag and armchair boron nitride nanoribbons (BNNRs) with the divacancy defect of 5–8–5 ring fusions formed by removing B–N pair, where the defect orientation and position are considered. Our computed results reveal that all of the defective BNNRs systems can uniformly exhibit nonmagnetic semiconducting behavior, and the formation of the divacancy 5–8–5 defect can significantly impact the band structures of BNNRs with not only the zigzag but also armchair edges, where their wide band gaps are reduced and the defect orientation and position play an important role. Clearly, introducing divacancy defect can be a promising and effective approach to engineer the band structures of BNNRs, and the present computed results can provide some valuable insights for promoting the practical applications of excellent BN-based nanomaterials in the nanodevices.     

Anisotropic tight-binding model applied to zigzag ultra-small nanotubes

A single-wall carbon nanotube (SWCNT) can be visualized as a graphene rolled into a cylinder. Tight-binding band structure calculations, with hopping between nearest-neighbor π orbitals only (NNTB), established rules by which both the mode in which the graphene is rolled up and the diameter determine whether the SWCNT is a metal or a semiconductor. However, when the diameter of the SWCNT is ultra-small its large curvature results in the breakage of these rules. In this work, we studied zigzag (n, 0) SWCNTs with diameters smaller than 0.7 nm using a π orbital-only tight-binding model including anisotropy in the hopping between next-nearest-neighbor sites (ANNNTB). Band overlaps were found in the electronic band structures of the zigzag SWCNTs for n=3, 4, 5, and 6, indicating that they are metals. The reason why the band structures of armchair and chiral SWCNTs are less affected by curvature effects becomes clear with the ANNNTB model, as does the reason why non-degenerate states cause band overlaps of the zigzag SWCNTs for n=3, 4, 5, and 6. Our results show that a π orbital-only tight-binding model is able to describe both the band overlaps and gaps obtained by ab initio calculations for zigzag SWCNTs.     

Position-controlled synthesis of single-walled carbon nanotubes on a transparent substrate by laser-induced chemical vapor deposition

The synthesis of single-walled carbon nanotubes (SWCNTs) on a transparent substrate with multiple-catalyst layer (Fe/Al/Cr: 0.5/15/500 nm) using laser-induced chemical vapor deposition is reported. Ethylene (C₂H₄) mixed with hydrogen (H₂) and a continuous wave Nd:YVO₄ laser (532 nm) were used as the precursor gas and the irradiation source, respectively. It was found that the density and quality of the SWCNT dots varied sensitively to laser irradiance and chamber pressure. From subsequent micro-Raman analyses at different excitation sources (488, 514, 633, and 785 nm), the diameters of the SWCNTs were estimated to be within the range of 0.8-2 nm and that the SWCNT dots were composed of both semiconducting and metallic SWCNTs. It is demonstrated that an array of SWCNT dots can be fabricated at precisely controlled positions of a transparent substrate at room temperature with no need of catalysis patterning.     

Atomistic simulations of divacancy defects in armchair graphene nanoribbons: Stability,electronic structure,and electron transport properties

Using the first principles calculations associated with nonequilibrium Green?s function, we have studied the electronic structures and quantum transport properties of defective armchair graphene nanoribbon (AGNR) in the presence of divacancy defects. The triple pentagon–triple heptagon (555–777) defect in the defective AGNR is energetically more favorable than the pentagon–octagon–pentagon (5–8–5) defect. Our calculated results reveal that both 5–8–5-like defect and 555–777-like defect in AGNR could improve the electron transport. It is anticipated that defective AGNRs can exhibit large range variations in transport behaviors, which are strongly dependent on the distributions of the divacancy defect.     

Vanishing of the Breit-Wigner-Fano component in individual single-wall carbon nanotubes

In order to decide definitely on the dependence of the intensity of the Breit-Wigner-Fano (BWF) component with the size of the bundle, we have measured the radial breathing modes and tangential modes (TMs) of well defined metallic individual single-wall carbon nanotubes (SWCNTs) and individual SWCNT bundles. In this aim, a complete procedure including the preparation of the substrates, the sample preparation, atomic-force-microscopy imaging and Raman spectroscopy has been developed. From this procedure, we show unambiguously that the BWF component vanishes in isolated metallic SWCNTs. In other words, the observation of a BWF component in the TM bunch is an intrinsic feature of the metallic SWCNT bundle.     

Electronic transport properties of a diarylethene-based molecular switch with single-walled carbon nanotube electrodes: The effect of chirality

We have studied the electronic transport properties of an optical molecular switch based on the diarylethene molecule with two single-walled carbon nanotube (SWCNT) electrodes using first-principles transport calculations. It is shown that the closed form shows an overall higher conductance than the open form at low bias which is independent of the SWCNTs’ chirality. Meanwhile, the conductance of the molecular switch can be tuned by changing the chirality of the SWCNTs.     

Molecular Dynamics Study of Effects of Si-Doping Upon Structure and Mechanical Properties of Carbon Nanotube

In this paper, a Si-doped single-walled carbon nanotube (SWCNT) (7,7) and several perfect armchair SWCNTs are investigated using the classical molecular dynamics simulations method. The inter-atomic short-range interaction is represented by empirical Tersoff bond order potential. The computational results show that the axial Young's modulus of the perfect SWCNTs are in the range of 1.099 ± 0.005 TPa, which is in good agreement with the existing experimental results. From our simulation, the Si-doping decreases the Young's modulus of SWCNT, and with the increased strain levels, the effect of Si-doped layer in enhancing the local stress level increases. The Young's modulus of armchair SWCNTs are weakly affected by tube radius.