Buffered internal stresses in diamond-like carbon films reinforced with single-walled carbon nanotubes

Diamond-like carbon (DLC) films reinforced with single-walled carbon nanotubes (SWCNTs) were fabricated by sputter-deposition of DLC onto a few monolayers of spray-coated SWCNTs on glass substrates. The thickness-averaged internal stress was reduced by 1.5 GPa by incorporation of SWCNTs into 10-nm-thick DLC films. Stress analysis indicates that the internal stress is reduced by 1.8 GPa at the SWCNT-DLC nanocomposite layer and decreases exponentially as a function of film thickness. Microscopy reveals significant cracking and delamination in 150-nm-thick DLC films, while the SWCNT-reinforced films remain essentially intact. The results demonstrate that SWCNTs in DLC films influence the early stage of DLC film growth and act as an effective stress-buffering layer near the boundary between the film and substrate.     

Effect of nucleases on the cellular internalization of fluorescent labeled DNA-functionalized single-walled carbon nanotubes

Nuclease effects on the cell internalization of single-walled carbon nanotubes (SWNTs) functionalized with fluorescent-labeled DNA in serum containing cell growth media were examined. When Cy3-labeled DNA-functionalized SWNT conjugates (Cy3DNA-SWNTs) were incubated with HeLa cells in a fatal bovine serum (FBS) medium, a high fl uorescence intensity was obtained from the cells, indicative for the high level inclusion of Cy3DNA-SWNTs. However, the fluorescence intensity was remarkably reduced if Cy3DNA-SWNTs were incubated with cells in the FBS-free medium. Further systematic control experiments revealed that Cy3 dye molecules were released from Cy3DNA-SWNT conjugates by nuclease, and the free Cy3 dyes penetrate into HeLa cell with high efficiency. Although the actual amounts of SWNTs internalized in the cells were almost identical for both cells incubated in the FBS-present and FBS-absent media according to the Raman measurements, one should be cautious to determine the degree of SWNT internalization based on the fluorescence intensities especially when the coloring dye molecules were linked to oligonucleotides in nuclease containing media. Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users. This article is published with open access at Springerlink.com     

Tailoring the diameter of single-walled carbon nanotubes for optical applications

Single-walled carbon nanotubes (SWCNTs) with specific diameters are required for various applications particularly in electronics and photonics, since the diameter is an essential characteristic determining their electronic and optical properties. In this work, the selective growth of SWCNTs with a certain mean diameter is achieved by the addition of appropriate amounts of CO₂ mixed with the carbon source (CO) into the aerosol (floating catalyst) chemical vapor deposition reactor. The noticeable shift of the peaks in the absorption spectra reveals that the mean diameters of the as-deposited SWCNTs are efficiently altered from 1.2 to 1.9 nm with increasing CO₂ concentration. It is believed that CO₂ acts as an etching agent and can selectively etch small diameter tubes due to their highly curved carbon surfaces. Polymer-free as-deposited SWCNT films with the desired diameters are used as saturable absorbers after stamping onto a highly reflecting Ag-mirror using a simple dry-transfer technique. Sub-picosecond mode-locked fiber laser operations at ∼1.56 μm and ∼2 μm are demonstrated, showing improvements in the performance after the optimization of the SWCNT properties.      

Tunable separation of single-walled carbon nanotubes by dual-surfactant density gradient ultracentrifugation

We present a systematic study of the effects of surfactants in the separation of single-walled carbon nanotubes (SWNTs) by density gradient ultracentrifugation (DGU). Through analysis of the buoyant densities, layer positions, and optical absorbance spectra of SWNT separation using the bile salt sodium deoxycholate (DOC) and the anionic salt sodium dodecyl sulfate (SDS), we clarify the roles and interactions of these two surfactants in yielding different DGU outcomes. The separation mechanism described here can also help in designing new DGU experiments by qualitatively predicting outcomes of different starting recipes, improving the efficacy of DGU and simplifying post-DGU fractionation.      

Nonlocal anisotropic elastic shell model for vibrations of single-walled carbon nanotubes with arbitrary chirality

A nonlocal anisotropic elastic shell model is developed to study the effect of small scale on shell-like vibration of single-walled carbon nanotubes (SWCNTs) with arbitrary chirality. Anisotropic elastic shell model is reformulated using the nonlocal differential constitutive relations of Eringen. The equations of motion are derived and analytical solution for the vibration of anisotropic SWCNTs is presented by using the Flügge shell theory and complex method. The suggested model is justified by a good agreement between the results given by the present model and available data in literature. Furthermore, the model is used to elucidate the effect of small scale on the vibration of zigzag, armchair and chiral SWCNTs. Our results show that small scale is essential for vibration of SWCNTs when the axial wave-length is not extremely long. Moreover, the results show that local model substantially overestimates vibrational frequencies of almost all modes.     

Photoelectrochemical reactions of electrodes modified with composites between conjugated polymer or ruthenium complex and single-walled carbon nanotubes

Composite materials between conjugated polymer; poly[2-methoxy-5-(2'-ethylhexyloxy)-1.4-phenylene vinylene] (MEHPPV), or ruthenium(II)-tris(2,2'-bipyridine) (Ru(bpy)₃²⁺)-poly(sodium 4-styrenesulfonate) (PSS) complex and single-walled carbon nanotubes (SWNTs) were fabricated using polymer wrapping method. Formation of SWNT/MEHPPV or SWNT/PSS/Ru(bpy)₃²⁺ composite was confirmed by absorption and fluorescence spectra, and AFM images. Electrode modified with SWNT/MEHPPV or SWNT/PSS/Ru(bpy)₃²⁺ composite was prepared by casting from DMF solution of SWNT/MEHPPV or aqueous solution of SWNT/PSS/Ru(bpy)₃²⁺. The electrode modified with SWNT/MEHPPV or SWNT/PSS/Ru(bpy)₃²⁺ composite showed photocurrent response due to photoexcitation of MEHPPV or Ru(bpy)₃²⁺. The photocurrents are ascribed to photoinduced electron-transfer reaction from excited state of MEHPPV or Ru(bpy)₃²⁺ to SWNT.     

Thermo-mechanical vibration of a single-walled carbon nanotube embedded in an elastic medium based on nonlocal elasticity theory

A single-elastic beam model has been developed to analyze the thermal vibration of single-walled carbon nanotubes (SWCNT) based on thermal elasticity mechanics, and nonlocal elasticity theory. The nonlocal elasticity takes into account the effect of small size into the formulation. Further, the SWCNT is assumed to be embedded in an elastic medium. A Winkler-type elastic foundation is employed to model the interaction of the SWCNT and the surrounding elastic medium. Differential quadrature method is being utilized and numerical solutions for thermal-vibration response of SWCNT is obtained. Influence of nonlocal small scale effects, temperature change, Winkler constant and vibration modes of the CNT on the frequency are investigated. The present study shows that for low temperature changes, the difference between local frequency and nonlocal frequency is comparatively high. With embedded CNT, for soft elastic medium and larger scale coefficients (e₀a) the nonlocal frequencies are comparatively lower. The nonlocal model-frequencies are always found smaller than the local model-frequencies at all temperature changes considered.     

单壁碳纳米管束的排布

流体排布法是实现碳纳米管定向排列的一种简单的方法。采用流体排布法在具有浸润性图案化的基底上成功地对单壁碳纳米管(SWNTs)束进行了水平方向上的排布。将SWNTs悬浮液滴入光刻胶制成的微通道中,在流体剪切力作用下,弯曲的SWNTs在一定程度上会被拉伸并且平行地排列在纳米级宽度的微通道中。将排列好的SWNTs阵列转移到一些不同间距的金电极对上面,制作成碳纳米管场效应晶体管(CNTFET)。CNTFET的电性能测试结果表明,制备的SWNTs束可以制造出不同电极间距同时具有良好电性能的CNTFET。     

A simple method of producing single-walled carbon nanotubes from a natural precursor: Eucalyptus oil

Single-walled carbon nanotubes (SWNTs) have been synthesized by catalytic decomposition of eucalyptus oil, on a high silica-zeolite support impregnated with Fe/Co catalyst at 850 °C by the spray pyrolysis method. Catalyst with 5 wt.% (molar ratio of Co:Fe = 1:1), impregnated in zeolite was suitable for effective formation of carbon nanotubes (CNTs). As-grown CNTs were characterized by SEM, TEM and Raman spectroscopy. Raman spectroscopy reveals that as-grown CNTs are well graphitized. Raman spectroscopy also reveals that the as-prepared SWNTs have a diameter of about 0.79-1.71 nm.     

Investigation of the thermo-mechanical properties of single-walled carbon nanotubes based on the temperature-related higher order Cauchy-Born rule

In the present study, a nanoscale quasi-continuum constitutive model for predicting the thermal-mechanical properties of single-walled carbon nanotubes (SWCNTs) and graphene sheet is established based on the interatomic potential and the temperature-related higher order Cauchy-Born rule. Helmholtz free energy is used as the corresponding thermodynamic potential. It is a function of some temperature-dependent lattice parameters that can be determined through an energy minimization process. As an application of the proposed quasi-continuum model, temperature dependency and curvature effect of the specific heat, the coefficient of thermal expansion (CTE) and the Young’s modulus of SWCNTs are investigated systematically. Numerical results obtained show the effectiveness of the proposed constitutive model.     

Investigation of temperature effect on the mechanical properties of single-walled carbon nanotubes

A temperature-related higher-order gradient continuum theory is proposed for predicting the mechanical properties of single-walled carbon nanotubes (SWCNTs) at various temperatures. It is found that the axial elastic moduli of zigzag (21, 0), armchair (12, 12) and chiral (15, 9) SWCNTs with similar radii approach 0.7 TPa when T = 0 K, but decline slightly on different slopes. These results indicate that the temperature effect influences the axial Young moduli of zigzag SWCNTs less than those of the other types. Moreover, the parameters λ₁ and λ₂ corresponding to the uniform longitudinal and circumferential stretches at different temperatures are also examined, and the results show that with an increasing temperature, all SWCNTs are stretched in the longitudinal direction, while in the circumferential direction, only the zigzag SWCNTs are stretched, whereas the others are compressed.     

Catalyst effect on the preparation of single-walled carbon nanotubes by a modified arc discharge

Single-walled carbon nanotubes (SWCNTs) were prepared by a modified arc discharge furnace using 500?Torr helium as buffer gas at 600?°C. The effect of the catalyst type on the production of SWCNTs was studied by transmission electron microscopy, X-ray diffraction and Raman spectroscopy. The experimental results indicated that the catalyst composition plays an important role in the production rate and purity of the SWCNTs product. Fe-Ni-Mg and Co-Ni powder catalysts demonstrated excellent catalytic effect at a catalyst content of 3?wt%. The soot production rate was up to 15?g/hr and the mean diameter of SWCNTs was about 1.3?nm.     

An efficient numerical method for analyzing the thermal effects on the vibration of embedded single-walled carbon nanotubes based on the nonlocal shell model

Employing the variational differential quadrature (VDQ) method, the effects of initial thermal loading on the vibrational behavior of embedded single-walled carbon nanotubes (SWCNTs) based on the nonlocal shell model are studied. According to the first-order shear deformation theory and considering Eringen's nonlocal elasticity theory, the energy functionality of the system is presented and discretized using the VDQ method. The effects of thermal loading and elastic foundation are simultaneously taken into account. The use of the numerical discretization technique in the context of variational formulation reduces the order of differentiation in the governing equations and consequently improves the convergence rate. The accuracy of the present model is first checked by comparison with molecular dynamics simulation results and those of other methods. The effects of involved parameters are then investigated on the fundamental frequencies of thermally preloaded embedded SWCNTs. The results imply that the thermal loading has a significant effect on the vibration analysis of embedded SWCNTs.     

Interfacial interactions in clay-based nylon 6 nanocomposites: A density functional theory study

Density functional theory was used to study the interfacial interactions between clay and polymer in polymer/clay nanocomposites, with a focus on nylon 6 matrix. The binding energy and the distance between nylon 6 and clay surface were predicted. The effect of the isomorphic substitution in clay octahedral and tetrahedral layer on the strength of the interfacial interactions was also examined. The interaction strength between nylon 6 and clay surface was found to increase with the degree of isomorphic substitution. And the magnitude of the binding forces, reflected from the calculated binding energies, was found to be higher when the substitution took place in tetrahedral layer (e.g., Al³⁺ for Si⁴⁺). No covalent bonds were observed between nylon 6 and the clay, which means that the chemical structures of the clay and nylon 6 are unchanged during the mixing process.     

Moderate temperature synthesis of single-walled carbon nanotubes on alumina supported nickel oxide catalyst

A simple nickel oxide catalyst has been developed in synthesizing single-walled carbon nanotubes (SWNTs) at moderate temperature. The catalyst used in the experiment was without a preceding reduction in hydrogen flow. The synthesis of SWNTs was performed at a temperature of 700 °C, which represents a moderate reaction temperature. The presence of SWNTs on the catalyst was confirmed by transmission electron microscope (TEM) and Raman spectroscope. The Raman spectrum shows a strong intensity at the radial breathing mode, indicating that the occurrence of SWNTs was dominant. Raman data further reveals that the synthesized SWNTs had the diameters in the range from 0.58 to 2.02 nm.     

Scanning electron microscopy imaging of single-walled carbon nanotubes on substrates

Scanning electron microscopy (SEM) plays an indispensable role in nanoscience and nanotechnology because of its high efficiency and high spatial resolution in characterizing nanomaterials.Recent progress indicates that the contrast arising from different conductivities or bandgaps can be observed in SEM images if single-walled carbon nanotubes (SWCNTs) are placed on a substrate.In this study,we use SWCNTs on different substrates as model systems to perform SEM imaging of nanomaterials.Substantial SEM observations are conducted at both high and low acceleration voltages,leading to a comprehensive understanding of the effects of the imaging parameters and substrates on the material and surface-charge signals,as well as the SEM imaging.This unified picture of SEM imaging not only furthers our understanding of SEM images of SWCNTs on a variety of substrates but also provides a basis for developing new imaging recipes for other important nanomaterials used in nanoelectronics and nanophotonics.     

利用碳纳米管吸附溶液中金属离子的研究进展

碳纳米管具有中空层状结构,大的比表面积和长径比,高的化学稳定性和热稳定性以及端帽、内腔、管壁容易被修饰等特点,是一种较为理想的吸附材料。综述了碳纳米管与吸附相关的结构和性质,分析了经硝酸氧化处理过的碳纳米管对溶液中金属离子的吸附作用原理,以及pH值、离子浓度对吸附作用的影响。讨论了将碳纳米管对金属离子的吸附作用与分离富集技术相联系,应用于元素分析测定,能够提高方法灵敏度,降低了元素检出限。在仪器分析方面将有巨大潜力。     

Comparative experimental study of methane adsorption on multi-walled carbon nanotubes and granular activated carbons

In this study, methane storage capacity of granular activated carbons (GACs) and two types of multi-walled carbon nanotubes (MWCNTs) was investigated and compared. An experimental apparatus consisting a dual adsorption vessel was set up for measurement of equilibrium adsorption of methane on adsorbents using volumetric technique at pressure range of 0–50?bar at different temperatures. The first type of MWCNs has shown lower methane uptake (4.5?mmol?g^?1) compared to GACs (6.5?mmol?g^?1) at the temperature of 283.15?K and the pressure of 50?bar, while 33?mmol?g^?1 of methane storage capacity was achieved using the second type of MWCNTs that is much higher than methane storage on GACs at the same operating conditions. The superior uptake performance for the second type of MWCNTs can be attributed to its specific characteristics such as smaller pore size and higher pore volume. The experimental data of adsorption were almost equally well described by Langmuir, Freundlich and Sips equations to determine the model isotherms. The isosteric heat of methane adsorption on the adsorbent was calculated based on Clausius–Clapeyron and the Sips isotherm model using the experimental data at different temperatures. Results revealed that the isosteric heat of methane adsorption on MWCNTs was lower than the heat of methane adsorption on GACs. Low values obtained for isosteric heats of adsorption indicated dominance of physisorption mechanism for all adsorbents. In general, the obtained data indicated that some well-structured MWCNTs with uniform and narrow size distribution as well as higher pore volume are potential materials for methane storage and deserve further study.     

Structural and electronic properties of Ti-nanowires/C-single wall nanotubes composites by density functional theory calculations

Structural and electronic properties of composite Ti-nanowires/single wall carbon nanotubes ((6,0) and (10,0)) (SWNT) were evaluated by means of density functional theory computations. We considered the cases of monoatomic (MNW), BCC (β-NW) and HCP (α-NW) nanowires that were either inserted or deposited in/on the SWNTs. In all cases the NWs turn the cylindrical SWNTs’ shape to ellipsoid, an effect that is closely related to charge transfer from Ti toward C neighboring atoms. We found that the wires inside the SWNT appear to be more stable compared to the outside cases, while all NWs contribute with new energy states at the Fermi level, transforming the semiconducting (10,0) to a conducting composite. In addition, we found spin up–down differences in the β-NW_on case and electronic charge redistributions e.g. in α-NW_in (charge accumulation internally along the tube's axis) or in α-NW_on (superficial charge accumulation in the vicinity of the NW), accompanied by manifestation of electric dipole moment that reaches the value of 10 Debye in a-NW_on. These results may be of use in the design of new C-based nanocomposite systems suitable for applications in microelectronics, sensors and catalysis.