Theoretical studies on the geometrical and electronic structures of supramolecule bis(2,2′-bipyridine)-5-amino-1,10-phenanthroline ruthenium(II)/functionalized SWCNT dyads

Functionalization of carbon nanotube (CNT) with multiple redox and photo active entities is one of the extensive processes due to its importance in building molecular or supramolecular electronic devices, solar energy storage and conversion systems. Thus, to have better understanding about structural aspects and correct electronic structure of these large systems, the quantum studies have gained increased popularity. In present study, we have investigated the structural and electronic properties of functionalized CNTs (fCNTs) with [Ru(bpy)₂(5-NH₂-1,10-phen)]⁺², (Ru-bpy-phen)⁺², supramolecule based on DFT calculations. Main attention has been applied to obtain stable configuration, binding energies and effect of functionalization on electronic behavior of the selected supramolcule. We also evaluate the effect of nanotube’s diameter and chirality on electronic properties of considered supramolecule. Calculated binding energies show that interaction between the (Ru-bpy-phen)⁺² and the host CNTs depends on the tube diameter while the chirality doesn’t affect significantly on the binding nature of respected complex. We have also investigated the influence of non-local dispersion interactions (vdW) and temperature on the stability and electronic structure of the considered system. Results obtained from the ab initio MD simulations showed that increasing the temperature can affect the distance between C and N atoms in the linkage position. The charge analysis indicates the existence of remarkable charge transfer between (Ru-bpy-phen)⁺² as donor and fCNTs as acceptor moieties in the isolated molecule. In the presence of vdW forces and at higher temperature, the charge transfer was decreased but the direction of transferred charge remains unchanged.     

Calculation of the energy of binding of titanium and scandium complexes to the surface of carbon nanotubes

Complexes of zigzag-type carbon nanotubes (CNTs) with transition metal atoms, scandium and titanium, were studied. It was demonstrated that the energy of binding of both atoms with a carbon surface decreases whereas the rate of diffusion along the surface increases with increasing nanotube diameter. The rate constant of migration of scandium atoms over a CNT surface are several orders of magnitude higher than that for titanium atoms, because the CNT surface—Sc atom binding energy is substantially lower.     

基于铟锡氧化物/Ti复合电极的高亮度碳纳米管场致发射冷阴极

通过制作亲碳性铟锡氧化物(ITO)/Ti复合电极,改善移植型碳纳米管(CNT)冷阴极的导电电极与CNT膜层之间附着性能,从而消除CNT与电极间的界面势垒和非欧姆接触对CNT阴极场发射均匀性和稳定性的影响.采用磁控溅射技术和丝网印刷工艺制作了ITO/Ti基CNT阴极.用X射线衍射仪和场致发射扫描电子显微镜表征CNT阴极结构,结果显示热处理后的ITO/Ti基CNT阴极中可能有TiC相生成,从而使得导电电极与CNT形成有中间物的强作用体系.该体系降低甚至消除电极与CNT之间的界面势垒,增加了CNT与电极间形成欧姆接触的概率.用四探针技术分析电阻率,结果表明ITO/Ti复合电极具有电阻并联效果,CNT阴极导电性能提高.场致发射特性测试表明ITO/Ti基CNT阴极的场致发射电流达到384μA/cm2,较普通ITO基CNT阴极的场致发射电流有显著提高,能够激发测试阳极发出均匀、稳定的高亮度荧光.制作ITO/Ti复合电极是实现场致发射稳定、均匀的低功耗CNT阴极的有效途径.     

Universal correlations in pion-less EFT with the resonating group method: Three and four nucleons

The Effective Field Theory “without pions” at next-to-leading order is used to analyze universal bound-state and scattering properties of the 3- and 4-nucleon system. Results of a variety of phase shift equivalent nuclear potentials are presented for bound-state properties of ³H and ⁴He , and for the singlet S -wave ³He -neutron scattering length a ₀(³He-n) . The calculations are performed with the Refined Resonating Group Method and include a full treatment of the Coulomb interaction and the leading-order 3-nucleon interaction. The results compare favorably with data and values from AV18(+UIX) model calculations. A new correlation between a ₀(³He-n) and the ³H binding energy is found. Furthermore, we confirm at next-to-leading order the correlations, already found at leading order, between the ³H binding energy and the ³H charge radius, and the Tjon line. With the ³H binding energy as input, we get predictions of the effective field theory “without pions” at next-to-leading order for the root mean square charge radius of ³H of (1.6±0.2) fm, for the ⁴He binding energy of (28±2.5) MeV, and for Re{a ₀(³He-n)} of (7.5±0.6) fm. Including the Coulomb interaction, the splitting in binding energy between ³H and ³He is found to be (0.66±0.03) MeV. The discrepancy to data of (0.10±0.03) MeV is model independently attributed to higher-order charge independence breaking interactions. We also demonstrate that different results for the same observable stem from higher-order effects, and carefully assess that numerical uncertainties are negligible. Our results demonstrate the convergence and usefulness of the pion-less theory at next-to-leading order in the ⁴He channel. We conclude that no 4-nucleon interaction is needed to renormalize the theory at next-to-leading order in the 4-nucleon sector.     

Preparation of NiO decorated CNT/ZnO core-shell hybrid nanocomposites with the aid of ultrasonication for enhancing the performance of hybrid supercapacitors

Supercapacitor (SC) electrodes fabricated with the combination of carbon nanotubes (CNTs) and metal oxides are showing remarkable advancements in the electrochemical properties. Herein, NiO decorated CNT/ZnO core-shell hybrid nanocomposites (CNT/ZnO/NiO HNCs) are facilely synthesized by a two-step solution-based technique for the utilization in hybrid supercapacitors. Benefitting from the synergistic advantages of three materials, the CNT/ZnO/NiO HNCs based electrode has evinced superior areal capacity of ~67 µAh cm⁻² at a current density of 3 mA cm⁻² with an exceptional cycling stability of 112% even after 3000 cycles of continuous operation. Highly conductive CNTs and electrochemically active ZnO contribute to the performance enhancement. Moreover, the decoration of NiO on the surface of CNT/ZnO core-shell increases the electro active sites and stimulates the faster redox reactions which play a vital role in augmenting the electrochemical properties. Making the use of high areal capacity and ultra-long stability, a hybrid supercapacitor (HSC) was assembled with CNT/ZnO/NiO HNCs coated nickel foam (CNT/ZnO/NiO HNCs/NF) as positive electrode and CNTs coated NF as negative electrode. The fabricated HSC delivered an areal capacitance of 287 mF cm⁻² with high areal energy density (67 µWh cm⁻²) and power density (16.25 mW cm⁻²). The combination of battery type CNT/ZnO/NiO HNCs/NF and EDLC type CNT/NF helped in holding the capacity for a long period of time. Thus, the systematic assembly of CNTs and ZnO along with the NiO decoration enlarges the application window with its high rate electrochemical properties.     

Study of adhesion of vertically aligned carbon nanotubes to a substrate by atomic-force microscopy

The adhesion to a substrate of vertically aligned carbon nanotubes (VA CNT) produced by plasmaenhanced chemical vapor deposition has been experimentally studied by atomic-force microscopy in the current spectroscopy mode. The longitudinal deformation of VA CNT by applying an external electric field has been simulated. Based on the results, a technique of determining VA CNT adhesion to a substrate has been developed that is used to measure the adhesion strength of connecting VA CNT to a substrate. The adhesion to a substrate of VA CNT 70–120 nm in diameter varies from 0.55 to 1.19 mJ/m², and the adhesion force from 92.5 to 226.1 nN. When applying a mechanical load, the adhesion strength of the connecting VA CNT to a substrate is 714.1 ± 138.4 MPa, and the corresponding detachment force increases from 1.93 to 10.33 μN with an increase in the VA CNT diameter. As an external electric field is applied, the adhesion strength is almost doubled and is 1.43 ± 0.29 GPa, and the corresponding detachment force is changed from 3.83 to 20.02 μN. The results can be used in the design of technological processes of formation of emission structures, VA CNT-based elements for vacuum microelectronics and micro- and nanosystem engineering, and also the methods of probe nanodiagnostics of VA CNT.     

A new force field for the adsorption of H2, O2, N2, CO,H2O,and H2S gases on alkali doped carbon nanotubes

The main goal of this work is the generation of a new force field data set to the interaction of several gases such as H₂, O₂, N₂, CO, H₂O, and H₂S with alkali cation-doped carbon nanotubes (CNTs) using ab initio calculations at the MP2(full)/6-311++G(d,p) level of theory. Different alkali cations including Li⁺, Na⁺_, K⁺ and Cs⁺ were used to dope in the CNT. The calculated potential energy curve for the interaction of each gas molecule with each alkali cation-doped CNTs was fitted to an analytical potential function to obtain the parameters of the potential function. A modified Morse potential function was selected for the fitting in which the electrostatic interactions has been accounted by adding the β/r term to the Morse potential. The accuracy of the calculated force field was checked via Grand Canonical Monte Carlo (GCMC) simulation of the H₂ adsorption on Li-doped graphite and Li-doped CNT. The results of these simulations were compared with the experimental measurements and the closeness of the simulation results with the experimental data indicated the accuracy of the proposed force field. The main merit of this work is the derivation of a specific force field for interaction of each of six gases with four alkali cation-doped CNT, which can be used in molecular simulation of these 24 of systems. The simulation results showed the increase of the H₂ adsorption capacity of nanotube and graphite up to 50% and 10%, respectively, due to the insertion of Li ions.     

Electrochemical synthesis and lithium storage properties of three-dimensional porous Sn–Co alloy/CNT composite

Three-dimensional (3-D) porous copper with stable pore structure is prepared by electroless plating. 3-D porous Sn–Co alloy/carbon nanotube (CNT) composite is synthesized by electrodeposition using 3-D porous copper as the substrate. The scanning electron microscope results indicate that 3-D porous Sn–Co alloy/CNT composite contains a large amount of interconnected pores with the diameter size of ~3 μm. Upon cycling, the pore structure gradually disappears, but no serious exfoliation appears due to porous structure and reinforcement by CNT. The charge/discharge results demonstrate that the 3-D porous Sn–Co alloy/CNT composite electrode delivers high first reversible specific capacity of 490 mAh g^?1, and remains 441 mAh g^?1 after 60 cycles tested at different current densities. Even at the current density of 3,200 mA g^?1, the reversible specific capacity remains 319 mAh g^?1, which is 65 % of the first specific capacity cycled at the current density of 100 mA g^?1.     

外加磁场下抛物型量子线中的带电激子

在一维等效模型下采用有效差分法对抛物型量子阱线中带电激子的束缚能进行了计算,分析了约束势以及磁场对带电激子束缚能的影响,并对带正电激子(X⁺)和带负电激子(X^-)的情况进行了比较.结果表明:电子和空穴的振子强度对带电激子的稳定性有重要影响,X⁺的束缚能不总是比X^-的大,随着空穴振子强度的增加束缚能的函数曲线将会出现交叉,这同实验得到的结果符合;磁场的存在会增加粒子间的束缚,并且磁场对束缚能的影响同振子强度大小有关. 关键词： 带电激子 量子线 束缚能 磁场     

Carbon nanotubes as nanoparticles collector

This communication reports on a new method for the collection of nanoparticles using carbon nanotubes (CNT) as collecting surfaces, by which the problem of agglomeration of nanoparticles can be circumvented. CNT (10–50 nm in diameter, 1–10 μm in length) were grown by thermal CVD at 923 K in a 7 v/v% C₂H₂ in N₂ mixture on electroless nickel-plated copper transmission electron microscopy (TEM) grids and Monel coupons. These samples were then placed downstream of an arc plasma reactor to collect individual copper nanoparticles (5–30 nm in diameter). It was observed that the Cu nanoparticles preferentially adhere onto CNT and that the macro-particles (diameter >1 μm), a usual co-product obtained with metal nanoparticles in the arc plasma synthesis, are not collected. Cu–Ni nanoparticles, a catalyst for CNT growth, were deposited on CNT to grow multibranched CNT. CNT-embedded thin films were produced by re-melting the deposited nanoparticles.     

Efimov Physics in Small Bosonic Clusters

We study small clusters of bosons, A = 2, 3, 4, 5, 6, characterized by a resonant interaction. Firstly, we use a soft-gaussian interaction that reproduces the values of the dimer binding energy and the atom-atom scattering length obtained with LM2M2 potential, a widely used ⁴He-⁴He interaction. We change the intensity of the potential to explore the clusters’ spectra in different regions with large positive and large negative values of the two-body scattering length and we report the clusters’ energies on Efimov plot, which makes the scale invariance explicit. Secondly, we repeat our calculation adding a repulsive three-body force to reproduce the trimer binding energy. In all the region explored, we have found that these systems present two states, one deep and one shallow close to the A ? 1 threshold, and scale invariance has been investigated for these states. The calculations are performed by means of Hyperspherical Harmonics basis set.     

DFT computational study on the phosphate functionalized SWCNTs as efficient drug delivery systems for anti-osteoporosis zolendronate and risedronate drugs

The pristine (4,4)-armchair SWCNT as well as its three phosphate functionalized (CNT-nH₂PO₄, n=1–3) forms were studied as novel drug delivery systems for the two commercially famous anti-osteoporosis drugs including risedronate (RIS) and zolendronate (ZOL) using the density functional theory (DFT) computations at both B3LYP and B3PW91 levels. Results revealed that the binding energy was increased by increasing number of H₂PO₄ moieties attached on the CNT with the most negative binding energy was measured for the CNT-3H₂PO₄ carrier. The dipole moments of all phosphate containing CNTs were much greater (~1.5–4.5 D) than that of pristine CNT (~0 D). The contour maps verified that when the CNT was functionalized by H₂PO₄ groups, the symmetric distribution of electric charge was vanished so that the highest and the lowest asymmetric charge distributions were achieved for the CNT-2H₂PO₄ and CNT-3H₂PO₄, respectively, leading to the greatest and the smallest dipole moments for the CNT-2H₂PO₄ (4.177 D) and the CNT-3H₂PO₄ (1.614 D). The compounds RIS-CNT-3H₂PO₄ and ZOL-CNT-3H₂PO₄ displayed the greatest electronegativity and electrophilicity index which were appropriate for the binding of drugs onto the bone surface (having partial positive charge due to the presence of Ca²⁺) and therefore effectively inhibiting the osteoporosis. Consequently, it was proposed that the drug-CNT-3H₂PO₄ was the most appropriate drug-carrier system for both of the RIS and ZOL drugs which could be employed as the most efficient vehicle.     

Pyridine-thermal synthesis and high catalytic activity of CeO2/CuO/CNT nanocomposites

Carbon nanotubes (CNTs) were controllably coated with the uninterrupted CuO and CeO₂ composite nanoparticles by a facile pyridine-thermal method and the high catalytic performance for CO oxidation was also found. The obtained nanocomposites were characterized by transmission electron microscopy, scanning electron microscopy, X-ray diffraction as well as X-ray photoelectron spectroscopy. It is found that the CuO/CeO₂ composite nanoparticles are distributed uniformly on the surface of CNTs and the shell of CeO₂/CuO/CNT nanocomposites is made of nanoparticles with a diameter of 30-60 nm. The possible formation mechanism is suggest as follows: the surface of CNTs is modified by the pyridine due to the π-π conjugate role so that the alkaline of pyridine attached on the CNT surface is more enhanced as compared to the one in the bulk solvent, and thus, these pyridines accept the proton from the water molecular preferentially, which result in the formation of the OH⁻ ions around the surface of CNTs. Subsequently, the metal ions such as Ce³⁺ and Cu²⁺ in situ react with the OH⁻ ions and the resultant nanoparticles deposit on the surface of CNTs, and finally the CeO₂/CuO/CNT nanocomposites are obtained. The T₅₀ depicting the catalytic activity for CO oxidation over CeO₂/CuO/CNT nanocomposites can reach ∼113 °C, which is much lower than that of CeO₂/CNT or CuO/CNT nanocomposites or CNTs.     

Control of morphology for energy dissipation in carbon nanotube forests

This study focuses on the effect of carbon precursor on the carbon nanotube (CNT) morphology and energy dissipation. Benzene, toluene, and m-xylene were used as carbon precursors for the synthesis of CNT forests following a chemical vapor deposition process. The results indicate that substituents on the benzene ring increase entanglement in the CNT forests. The absorbed energy was slightly greater for CNT forests synthesized using m-xylene than for toluene, but was much smaller for benzene. When compressed to a strain of 0.67, the toluene CNTs absorbed more energy than the m-xylene CNTs. The restitution was much higher for the forests synthesized with m-xylene than toluene while it further decreased for the forests made with benzene. A strong correlation is also observed between the average diameter of the CNTs and the number of methyl substituents on the benzene ring. The control of the entanglement of the CNT forests can potentially be used to design high energy absorbing composites for blast energy dissipation.     

Effects of concentration on magnetization in a diluted magnetic semiconductor quantum dot

The donor bound spin polaron in a Cd_1?xMn_xTe quantum dot is investigated theoretically. Spin polaronic shifts are estimated using a mean field theory. Magnetization is calculated for various concentrations of Mn²⁺ ions with the dot sizes. The lowest binding energies in a diluted magnetic semiconductor of a Cd_1?xMn_xTe quantum dot are also estimated. Using the effective mass approximation, calculations are presented with and without spatial dependent effective masses. It is found that (i) the lowest binding energy decreases with the dot radius (ii) position dependent mass gives larger binding energy for smaller dots (iii) the ionization energy becomes more when spin interaction energy is included (iv) variation of increase in ionization energy is sharper for smaller dots with increase in concentration and (v) the magnetization of Mn subsystem increases when concentration of Mn²⁺ ions increases and it has appreciable changes for smaller dots.     

Modulating the diameter of carbon nanotubes in array form via floating catalyst chemical vapor deposition

Based on the analysis of catalyst particle formation and carbon nanotube (CNT) array growth process in floating catalyst chemical vapor deposition (CVD), delicately controlled gaseous carbon sources and catalyst precursors were introduced into the reactor for the controllable growth of CNT array. The low feeding rate of ferrocene was realized through low-temperature sublimation. With less ferrocene introduced into the reactor, the collision among the in situ formed iron atoms decreased, which led to the formation of smaller catalyst particles. The mean diameter of the CNT array, grown at 800^oC, decreased from 41 to 31 nm when the ferrocene-sublimed temperature reduced from 80 to 60^oC. Furthermore, low growth temperature was adopted in synthesis, through the modulation of the CNT diameter, by controlling the sintering of catalyst particles and the collision frequency. When the growth temperature was 600^oC, the as-grown CNTs in the array were with a mean diameter of 10.2 nm. If propylene was used as carbon source, the diameter can be modulated in similar trends. The diameter of CNT can be modulated by the parameter of the operation using the same substrate and catalyst precursor without other equipment or previous treatment. Those results provide the possibility for delicately controllable synthesis of CNT array via simple floating catalyst CVD.     

Structural dependence of exciton in carbon nanotubes

The binding energies and sizes of excitons, and energy splitting of the bright-dark excitons in single-walled carbon nanotubes have been calculated using the nonorthogonal tight-binding model, supplemented by the long-range Coulomb interaction. It is found that the binding energies and the sizes of excitons not only depend on tube's diameter d, but also its chirality. However, the splitting of the bright-dark excitons mostly depends on 1/d². Our obtained results show that the curvature effect is very important for the exciton excitations in the SWNTs, especially in the smaller diameter ones.     

分层掺B和吸附H2O碳纳米管的结构稳定性及电子场发射性能

运用基于第一性原理的密度泛函理论,系统研究了处于外电场中分层掺B并吸附不同数目H₂O碳纳米管体系的结构稳定性和电子场发射性能. 研究表明:第3层掺B并吸附5个H₂O的B₃CNT+5H₂O体系结构最稳定,管帽处Mulliken电荷最密集,尤其与单独掺B的B₃CNT和单独吸附H₂O的B₃CNT+5H₂O相比,其Fermi能级处态密度分别     

A new class of MO<Subscript>2</Subscript> dioxide nanotubes (M=Si,Ge, Sn,Pb) composed of “square” lattices of atoms: Their structure and energy characteristics

New dioxide nanotubes are described. These nanotubes are rolled up of a “square” lattice of atoms differing from the conventional hexagonal lattice isoelectronic to graphite. The dependence of the strain energy on the nanotube diameter D departs from a 1/D² behavior, and the optimum shape at the same diameter corresponds to “zigzag” tubelenes. Two-layer nanotubes consisting of an MO₂ layer bonded to a carbon nanotube (CNT) are characterized by a considerably lower strain energy, which points to the possibility of using CNTs as a template for the synthesis of such MO₂ nanotubes.     

Electrical, dielectric and surface wetting properties of multi-walled carbon nanotubes/nylon-6 nanocomposites

This paper reports that the multi-walled carbon nanotubes(MWCNT)/nylon-6 (PA6) nanocomposites with different MWCNT loadingshave been prepared by a simple melt-compounding method. Theelectrical, dielectric, and surface wetting properties of theCNT/PA6 composites have been studied. The temperature dependence ofthe conductivity of the CNT/PA6 composite with 10.0 wt{\%} CNTloading ($\sigma _{\rm RT} \sim 10^{-4}$ S/cm) are measured, andafterwards a charge-energy-limited tunnelling model (ln $\sigma (T)\sim T^{-1/2})$ is found. With increasing CNT weight percentage from0.0 to 10.0 wt%, the dielectric constant of the CNT/PA6composites enhances and the dielectric loss tangent increases twoorders of magnitude. In addition, water contact angles of theCNT/PA6 composites increase and the composites with CNT loadinglarger than 2.0 wt%even become hydrophobic. The obtainedresults indicate that the electrical and surface properties of thecomposites have been significantly enhanced by the embedded carbonnanotubes.