Quantitative analysis of microstructure of carbon materials by HRTEM

The main object of the present research is to make a quantitative evaluation on the microstructure of carbon materials in terms of microcrystal. The digitized images acquired from finely pulverized carbon materials under HRTEM at a high magnification were processed by the image processing software so as to extract the fringes of （002） lattice of graphite crystal from the background image, and an FFT-IFFT filtering operation was performed followed by processes as binarization for the image and skeletonization for the fringes. A set of geometrical parameters including position, length and orientation was set up for every lattice fringe by calculating the binarized image. Then, the above obtained fringe parameters were put into an algorithm, which was especially developed for such fringe images so as to find fringes that could be regarded as those belonged to one single graphite microcrystal. The fringe was subjected sequentially to comparing procedures with every other fringe on aspects as parallelism, relative position and spacing, and the above comparisons were repeated till the last fringe. Eventually, the microcrystal size, its stacking number, and the distribution of the microcrystal in the whole sample, as well as other related structure information of such microcrystal in carbon materials were statistically calculated. Such microstructure information at nanometer level may contribute greatly to the interpretation of the properties of carbon materials and a better correlation with the same macrostructure.     

Functionalization of multiwalled carbon nanotubes and related polyimide/carbon nanotubes composites

A low molecular weight tree-type polyimide was used to modify the surface of multiwalled carbon nanotubes. The modified carbon nanotubes exhibited excellent dispersion in organic solvent; and the polyimide/carbon nanotubes composite film basic on such carbon nanotubes shows enlarged combination property compared with the composite film from acid-carbon nanotubes. Meanwhile, an electric conductivity was introduced to the composite film, and the thermal properties have also been developed.     

Properties of copper/graphite/carbon nanotubes composite reinforced by carbon nanotubes

Electroless Cu plating was used for flake G powder and CNTs, Cu-G-CNTs (copper/graphite/carbon nanotubes) composites were manufactured by means of powder metallurgical method. The influences of CNTs on the mechanical properties, conductivity properties, friction, and wear performance of the composite were examined. The results indicate that adding a small amount of CNTs can improve comprehensive property of the composites, especially mechanical property. However, excessive CNT, which is easily winding reunion and grain boundary segregation, results in performances degradation.     

Linearly joined carbon nanotubes

Linearly joined carbon nanotubes (CNTs) have been fabricated on well-ordered porous anodic aluminum oxide (AAO) nanotemplates prepared by a multi-step anodization and pore widening process. The location and shape of the junctions are very uniform. The electronic properties of the tubes will be affected critically by the junctions. Therefore, one could design CNTs which have specific properties by changing the ratio of the two diameters of linearly joined CNTs. The linearly joined tubes could be used in fabrication of nanoscale electronic devices like field-effect transistor (FET).     

SERS,FT-IR and photoluminescence studies on single-walled carbon nanotubes/conducting polymers composites

Surface-enhanced Raman scattering (SERS), Fourier transform infrared (FT-IR) and photoluminescence (PL) spectroscopies were used to investigate composites based on single-walled carbon nanotubes (SWNTs) and different conducting polymers like polyaniline (PANI), poly-paraphenylene vinylene (PPV) and poly 3-hexylthiophene (3-PHT). In the case of SWNTs/PANI, different composites are obtained by adding dispersed SWNTs powder to the polymer solutions and by chemical polymerization of aniline in presence of SWNTs. The difference originates in the irreversible chemical transformation of SWNTs in the polymerization medium. The synthesis medium used for the preparation of PANI transforms SWNTs in fragments of shorter length like closed-shell fullerenes. This explains the similarity of SERS and FT-IR spectra of the composites PANI/SWNTs and PANI/C₆₀, chemically synthesized. Electrochemical polymerization of aniline in an HCl solution on a SWNT film leads to a covalent functionalization of SWNTs with PANI. In this case, Raman scattering data suggest an additional nanotubes roping with PANI as a binding agent. A post treatment with the NH₄OH solution of polymer-functionalized SWNTs involves an internal redox reaction between PANI and carbon nanotubes. As a result, the polymer chain undergoes a transition from the semi-oxidized state into a reduced one. In the case of PPV and 3-PHT, the effect of the concentration of SWNTs on the photoluminescence properties will be described and compared, as probes of interaction.     

Lithium interaction with carbon nanotubes

Lithium interaction with catalytic carbon nanotubes under high-pressure conditions was studied. A large amount of Li (2Li/C) reacted with the carbon nanotubes forming an intercalation compound (I_c~4.1 Å) which follows from X-ray diffraction and IR spectroscopy data. We cannot exclude also the possibility of insertion of a part of Li into the channel of the nanotubes.     

SERS spectroscopy studies on the electrochemical oxidation of single-walled carbon nanotubes in sulfuric acid solutions

Surface-enhanced Raman scattering (SERS) and cyclic voltammetry (CV) were used to investigate oxidation–reduction processes of single-wall carbon nanotube (SWNT) films deposited on Au supports in 0.5 M H₂SO₄ solutions. In the potential range (0; +1000) and (0; +1500) mV versus saturated calomel electrode (SCE), the oxidation–reduction reactions of SWNT films are quasi-reversible and irreversible, respectively. Anodic polarization of SWNT films until +1000 mV versus SCE produced compounds similar to the bisulfate intercalated graphite. Regardless of excitation wavelength, i.e. 1064 or 676.4 nm, variation in the Raman spectra exhibited a decrease in the intensity of the bands associated with the radial breathing mode (RBM) situated in the 120–240 cm⁻¹ spectral range. Also an increase in the intensity of the D band is accompanied an up-shift of this band. A gradual decrease of the Breit–Wigner–Fano component was observed at λ_exc=676.4 nm. Partial restoration of the Raman spectra was achieved by a subsequent alkaline solution treatment. Potentials higher than +1000 mV versus SCE resulted in SWNTs breakage and fragments of different length were formed such as closed-shell fullerene. This was observed in the SERS spectrum by: (i) the disappearance of the RBM band, (ii) the increased D-band shifted to ca. 1330 cm⁻¹ and (iii) the appearance of a new band at 1494 cm⁻¹, frequently observed also in the Raman spectrum of fullerenes on the type C₇₀, C₈₄, C₁₁₉, as well as in its derivative compounds (e.g. C₆₀O, clathrates, etc.). Appearance and increase in the intensity of the Raman band at 1494 cm⁻¹ as result of an anodic polarization of the SWNT film in solution of H₂SO₄ 0.5 M in 1-butanol is a further evidence of the nanotubes breakage.     

Transformation of singlewalled carbon nanotubes to multiwalled carbon nanotubes and onion-like structures by nitric acid treatment

We have obtained various phases during the refluxing process of singlewalled carbon nanotubes (SWNTs) in 30% HNO₃ acid solution at 100 °C. From the similar treatment in HCl acid solution, we observe no structural phase transformation but enlargement of the bundle size of SWNTs. This strongly suggests that the intercalation of nitric acids into the bundles, which is evidenced by the distribution of smaller diameters of bundles, induces the disintegration of tubes by oxidative etching first and the reformation into multiwalled nanotubes, cone-capped phase, and further onion-like structures. The origin of such a transformation mechanism is further discussed.     

Decorating Mg/Fe oxide nanotubes with nitrogen-doped carbon nanotubes

Mg/Fe oxide nanotubes decorated with nitrogen-doped carbon nanotubes (CN_x) were fabricated by catalytic chemical vapor deposition of ethylenediamine on the outer surface of oxide nanotubes. Mg/Fe oxide nanotubes were prepared using a 3:1 molar precursor solution of Mg(NO₃)₂ and Fe(NO₃)₃ and anodic aluminum oxide as the substrate. The obtained samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and vibrating sample magnetometer (VSM). The XRD pattern shows that the oxide nanotubes are made up of MgO and Fe₂O₃. TEM and SEM observations indicate the oxide nanotubes are arrayed roughly parallel to each other, and the outer surface of oxide nanotubes are decorated with CN_x. XPS results show the nitrogen-doped level in CN_x is about 7.3 at.%. Magnetic measurements with VSM demonstrate the saturated magnetization, remanence and coercivity of oxide nanotubes are obvious improved after being decorated with CN_x.     

HRTEM and EELS studies of defects structure and amorphous-like graphite induced by ball-milling

Deformation structures and amorphization kinetics of graphite with high crystallinity upon ball-milling (BM) are studied by high-resolution transmission electron microscopy (HRTEM) and electron energy-loss spectroscopy (EELS). Basal plane stacking disorder, cleavage, delamination cracks, misorientation bands and low-angle (0002) twist boundaries are observed. The basal plane stacking disorder is probably produced by simultaneous shearing of all the lattice planes involved. Other defects such as half Frank loops or interstitial loops and significant bending and buckling of the basal planes are also frequently observed. Sustained shearing of (0002) planes acting in parallel with the increase of the Frank loops finally leads to the breakage of the hexagonal network in a very fine scale until an amorphous-like structure results. Although the amorphous-like phase exhibits amorphous halo diffraction patterns, HRTEM investigations indicate that it consists of highly curled small flakes with average basal plane diameter less than 5 nm and thickness (normal to the basal planes) less than 2 nm. EELS investigations demonstrate that its bonding is essentially sp². The present study clarifies the defect configuration appearing in heavily deformed graphite and also shows evidence that the amorphization of graphite is a defect-controlled process.     

碳纤维表面生长纳米碳管及其增强的炭/炭复合材料

采用化学气相沉积工艺在碳纤维表面生长了纳米碳管,将此种碳纤维作为增强材料,以中间相沥青为基体炭前驱体采用浸渍炭化工艺制备了炭/炭复合材料.观察了所得复合材料断口的微观形貌,测试了抗弯强度及热物理性能.结果表明,碳纤维表面的纳米碳管可以有效地提高纤维与基体的粘结力,复合材料的抗弯性能提高了50%,而对复合材料的导热性能影响较小.     

Conducting textiles from single-walled carbon nanotubes

In this paper we present a simple and straightforward route to prepare conducting textiles by incorporating carbon nanotubes through a dyeing approach. This process consists of immersing textiles in an aqueous sulfonated polyaniline-carbon nanotube dispersion acting as a dye. Incorporating carbon nanotubes into textiles increased the conductivity by four orders of magnitude and doubled the capacitance compared to textiles dyed with sulfonated polyaniline. Textile durability and their applicability as strain gauges were also demonstrated.     

Excitons in semiconducting single-walled carbon nanotubes

We report correlated-electron calculations of optically excited states in 10 semiconducting single-walled carbon nanotubes with a wide range of diameters. Optical excitation occurs to excitons whose binding energies decrease with the increasing nanotube diameter, and are smaller than the binding energy of an isolated strand of poly-(paraphenylene vinylene). The ratio of the energy of the second optical exciton polarized along the nanotube axis to that of the lowest exciton is smaller than the value predicted within single-particle theory. The experimentally observed weak photoluminescence is an intrinsic feature of semiconducting nanotubes, and is consequence of dipole-forbidden excitons occurring below the optical exciton. Excited states absorption calculations show photoinduced absorption energies are lower than or comparable to the binding energy of the lowest exciton.     

Conduction mechanisms in single-walled carbon nanotubes

The transport properties of single-walled carbon nanotubes (SWNTs) were examined to investigate their conduction mechanisms. By measuring the temperature dependence of the resistance, it was clarified that the conduction mechanism in SWNT mats can be changed from the non-metallic to the coexistence of metallic and non-metallic modes as the thickness of the mats changed. This change is attributable to the quality and the quantity of metallic nanotubes.     

The oxidation kinetics of multi-walled carbon nanotubes

The kinetics of isothermal oxidation of multi-walled carbon nanotubes (MWNTs) in air has been investigated in the experimental range of 573-823 K using thermogravimetry. The results show that the oxidation of MWNTs is both chemically controlled and diffusion controlled depending on the temperature range. Chou’s model has been applied to treat the oxidation behavior of MWNTs and the comparison of the experimental data with the theoretical ones validates the applicability of the model. This model offers a quantitative expression for the weight loss as a function of time at constant temperature conditions. The possible mechanism for oxidation has also been discussed briefly.     

On the mechanics of single-walled carbon nanotubes

This review paper discusses some basics in using continuum mechanics and molecular dynamics to characterize the deformation of single-walled carbon nanotubes (SWCNTs). It identifies that the van der Waals force between SWCNTs in a bundle distributes symmetrically and influences the bundle formation, and that to avoid misleading results from a molecular dynamics simulation, the interaction potential, thermostat scheme and simulation parameters must be carefully selected. The paper then points out that when the necessary condition proposed by Vodenitcharova and Zhang and a compatibility condition for elastic constants are satisfied, the intersect of the bending and in-plane stiffness curves in the modulus-thickness plane can determine a unique effective wall thickness of an SWCNT and hence its Young's modulus.     

Electrical measurement on individual multi-walled carbon nanotubes

The characterization of electrical property of multi-walled carbon nanotubes （MWCNTs） on a nanometer scale is essential for their potential application in nano-electronic devices. The MWCNTs were synthesized on Fe2O3/SiO2/Si substrate and Pt plate substrate by simple thermal chemical vapor deposition （STCVD） technique and the electrical measurements of individual MWCNT grown on silicon substrate and Pt plate substrate were performed by home-made ＇nano-manipulator＇, respectively. According to current-voltage curves obtained in the experiments the current density that the MWCNTs can carry is calculated to be about 10^7 A/cm^2, which is much larger than that of normal metals.