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Abstract: We present a high temperature heat treatment study of CVD-grown graphene nanoribbons annealed up to 2800°C, demonstrating a progressive annihilation of lattice defects as the heat treatment temperature is raised. Starting at 1500°C, single and multiple loop formation were observed on the ribbons edges as the temperature was increased. The structural changes of the samples are documented by X-ray diffraction, Raman spectroscopy, TGA, SEM, and HRTEM. This work indicates that nanoribbon annealing eventually leads to defect-free samples, through graphitization and edge loop formation. The annealed material exhibits structural differences that could be tailored for a variety of specific applications. [Copyright &y& Elsevier]

Abstract: Here we describe synthesis of very unusual multi-walled carbon nanotubes through a catalytic chemical vapor deposition method using a floating reactant method and subsequent thermal treatment up to 2600°C in a large quantity. Main characteristics of these nanotubes are (1) relatively wide distribution of diameters ranging from 20 to 70nm and linear, long macro-morphology (aspect ratio >100), (2) highly straight and crystalline layers, (3) high purity through removal of metallic impurity, (4) very low interlayer spacing (0.3385nm) and low R value (I D/I G =0.0717), (5) high G′ intensity over intensity of G band (G′/G=0.85) and strongly negative magnetoresistance value of −1.08% at 77K and 1T. The unusual microstructure of thin multi-walled carbon nanotubes with a partially facetted cross-sectional shape caused by thermal treatment is mainly ascribed to abrupt density changes (from 1.89 to 2.1g/cm3) within a confined nanosized space, accompanying with the phase separation. [Copyright &y& Elsevier]

Abstract: Chemically reduced solid-state mesophase pitch carbon fibers below 1000°C in a flow of hydrogen gas were treated up to 3000°C in an argon atmosphere in order to evaluate the effect of hydrogen on the graphitization behavior. Major phenomena observed during the reduction process are chemical transformation from an ether to a hydroxyl group (corresponding to the rupture of the C–O–C bond) and their subsequent evolution as gases. Finally, oversupplied hydrogen might be utilized to satisfy the dangling bond. For the sample heat treated at 3000°C, the low crystallinity indicates that hydrogen atoms covalently bonded to the end planes of graphitic layers act as an effective barrier to crystallite growth. [Copyright &y& Elsevier]

We describe, for the first time, the sequential structural changes of bundles of double-walled carbon nanotubes (DWNTs) as a function of heat treatment temperature. DWNTs (inner diameters >0.9 nm) are structurally stable up to 2000 °C. Above 2100 °C, the outer walls of adjacent DWNTs start coalescing into large diameter tubes. At temperatures higher than 2100 °C, three different types of structures were observed: (a) large-diameter DWNTs; (b) multi-walled carbon nanotubes (MWNTs), and (c) flaky carbons. The results demonstrate that DWNTs are much more stable than SWNTs, and their stability is comparable to that of MWNTs. [Copyright &y& Elsevier]

Highly disordered carbon nanotube is obtained through a catalytic thermal chemical vapor deposition method, especially, using the floating reactant method. The results of annealing highly disordered carbon nanotube are (1) removal of metallic compounds, (2) structural conversion into multi-wall carbon nanotube with a little faceted cross-section, and (3) development of a tug morphology in carbon nanotubes. The characteristic observed in annealed multi-wall carbon nanotubes make them useful as a filler in advanced composite. [Copyright &y& Elsevier]

Systematic studies of structural changes in stacked cup carbon nanofibers by heat treatment from 1800 to 3000 °C are carried out. The most prominent feature upon heat treatment of these nanofibers is the formation of energetically stable loops between adjacent active end planes both on the inner and outer surfaces. The appearance of the jagged outer and inner surfaces at 3000 °C is due to a combinational effect, perhaps caused by improved stacking within domains connected by loops having limited crystallite size, accompanied by structural reorganization between domains. Consequently, a low degree of graphitizability is ascribed to this unusual stacked cup morphology of pristine carbon nanofibers. [Copyright &y& Elsevier]

Cone-stacked nanotubes with thick layers of deposited carbon obtained by a catalytic chemical vapor deposition method are annealed at high temperature. Phase separation between cone-stacked nanotubes and amorphous carbon layers occurs during annealing due to different structural transformation behaviors, resulting in the formation of multi-wall carbon nanotubes containing a cone-type multi-shell arrangement. The apex angles of the nanocones are about 40°. This type of carbon nanotube shows different physical and electrical properties. [Copyright &y& Elsevier]

The effect of grinding on cup-stacked carbon nanotubes is studied. The application of a bending force on the sidewall of such carbon nanotubes, that is higher than the Van der Waals force acting between the cups, results in the shortening of carbon nanotubes and the formation of nano-barrels exhibiting an increased number of accessible active sites (represented by the ends of graphitic planes) and anisotropic properties at both ends. [Copyright &y& Elsevier]

In this paper, we report high-pressure Raman experiments (0 − 28 GPa) in two different systems, i.e. , linear carbon chains encapsulated by multi-walled (C n @MWCNTs) and double-walled (C n @DWCNTs) carbon nanotubes. By running high-pressure cycles, it is observed basically two changes in the Raman spectra of chains that are the softening and disappearance of C n modes. We attributed the irreversible redshift of the C n band to the coalescence between adjacent chains. On the other hand, the disappearance of the C n band at the onset of the CNT collapse pressure is assigned to the tube-chain cross-linking. This effect appears to be independent of the C n length and the number of walls of the tubes, depending only on the innermost CNT diameter. We show that the pressure to coalesce longer chains is higher than 10 GPa. Density functional theory and molecular dynamics calculations were performed in order to support the interpretation of experimental data. The calculations show an irreversible pressure-induced softening of frequency of the confined linear carbon chain. Furthermore, molecular dynamics calculations showed that coalescence between the shorter chains occurs in a region of lower pressure than that of the longer chains, thus supporting the experimental observations. Our findings shed new light on the understanding of the C n @CNT system stability and pave the way for using high-pressure to obtain ultra-long chains (at lower pressures) and ultra-hard composites (at higher pressures). [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: Thin, flexible and tough bucky paper fabricated by filtering a stable suspension of double-walled carbon nanotubes (DWNTs) was characterized from the viewpoint of its pore structure and oxidation stability as compared with that derived from single-walled carbon nanotubes (SWNTs). The N2 adsorption isotherms of DWNTs and SWNTs at 77K were of type II and type IV, respectively, and also the micropore volume in DWNTs was three times greater than that in SWNTs. The onset temperature of oxidation in DWNTs was enhanced by ca. 200°C due to their coaxial structure. The expected high mechanical and electrical properties when combined with their high surface area and high structural integrity make the DWNTs bucky paper promising materials for numerous applications. [Copyright &y& Elsevier]

Abstract The radial stability and the irreversible transformation of triple-wall carbon nanotubes (TWCNTs) bundles are investigated at high pressure conditions both experimentally and theoretically (exp. up 72 GPa). The tubes having a mean internal diameter of 0.83 nm and graphite-like intertube distance, show an onset of the radial collapse evidenced by the evolution of optical phonons. The nanotube collapse onset is observed at ∼ 22 GPa completes for the two external tubes at ∼ 29 GPa, however the innermost tube remains stable up to ∼ 37 GPa. Molecular dynamic calculations performed on smaller diameter TWCNTs bundles, as a model system, confirmed the multiple-stage pressure-induced collapse process. An analytical expression for the collapse pressure of carbon nanotubes having an arbitrary number of walls is proposed. Our experiments and modelling show that for pressures beyond ∼ 60 GPa an irreversible structural transformation of TWCNTs takes place. Ex situ transmission electron microscopy characterization on the recovered sample from 72 GPa revealed the mechanical failure of carbon nanotubes which evolve towards ribbon-like structures as corroborated by Raman spectroscopy. Modelling the tubes evolution at high pressure and high temperature showed the formation of new structures ranging from ribbon-like to graphite-like with either different degrees of amorphization or s p 3 interlinking. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

The unique electronic and vibrational properties of linear carbon chains (LCCs) have attracted close attention from the scientific community in recent years. Raman spectroscopy addressing the LCC spectral signature around 1850 cm−1 has been widely used to identify the LCC and probe electronic and vibrational properties as a function of carbon length. Despite the number of works available in literature, some aspects of the LCC's aforementioned properties remain unclear. Using a combination of confocal and Tip-enhanced Raman Spectroscopy (TERS), along with different laser lines, this work addresses important aspects of the optical resonance window of LCCs encapsulated by multi-walled carbon nanotubes (MWCNTs) (i.e. LCC@MWCNT) as well as an elusive Raman signature around 1637 cm−1, which is assigned to the LCC's longitudinal acoustic (LA) phonon mode at the X point (zone edge), which becomes Raman active likely due to disorder effects. First-principles calculations endorse our conclusions. [Display omitted] [ABSTRACT FROM AUTHOR]

High-pressure resonance Raman experiments were performed on linear carbon chains Cn confined in double-wall carbon nanotubes (Cn@DWCNT). Our results indicate that the frequency of the chain mode undergoes a non-linear decreasing as pressure increases, in agreement with previous studies of the behavior of carbon chains into multi-wall carbon nanotubes. After the pressure cycle, the Cn modes present an irreversible frequency downshift together with an irreversible upshift (downshift) of the RBM modes (G + band) of the inner tube. These spectral changes are interpreted as evidence of cross-linking between the carbon chain and the wall of the inner tube. Density functional theory (DFT) calculations were performed in order to shed light on the interpretation of the experimental data. The theoretical calculations show a pressure-induced charge transfer from the nanotube to the carbon chain, thus resulting in an increasing of the C≡C bond length, and consequently, a softening frequency of the Cn Raman mode. Furthermore, an irreversible cross-linking between the tube and Cn is observed when the maximum applied pressure is higher than the pressure of radial tube collapse is predicted by modelling, thus supporting the experimental results. [ABSTRACT FROM AUTHOR]

In this paper we report the characterization of linear carbon chains encapsulated in multiwalled carbon nanotubes by using Raman spectroscopy and transmission electron microscopy. The chains are characterized by strong vibrational peaks around 1850 cm −1 and both the frequency and intensity of these peaks were found to be dependent on laser excitation energy. Furthermore, resonance Raman spectroscopy was used for constructing the resonance window of the linear carbon chains. The Raman spectroscopy data showed that long chains have lower highest occupied molecular orbital–lowest unoccupied molecular orbital energy gaps and weaker carbon–carbon bonds. Besides the spectroscopy evidence for the linear carbon chain, we used scanning transmission electron microscopy/electron energy loss spectroscopy analysis of the nanotube cross section to unambiguously show the existence of a 1D structure present within the innermost carbon nanotube with an unprecedented clarity compared to previous reports on this kind of system. [ABSTRACT FROM AUTHOR]

Abstract: Transmission electron microscopy (TEM) is one of the highest resolution analysis methods of materials. The three dimensional recognition of the materials is difficult by TEM because the observation data is projection images through the materials. In this study, space structure of carbon nanotubes loaded with metal particles was analyzed by three dimensional TEM (3D-TEM) [1,2]. The nano structured carbons are also observed by high resolution transmission electron microscopy (HRTEM) with Cs corrector. Cup-stack type carbon nanotubes (CSCNTs) loaded with Pt particles (2–3nm in diameter) prepared by GSI Creos Corporation were analyzed by these methods. Pt particles are bound selectively to the edges of hexagonal carbon layers of inside and outer surface of CSCNTs efficiently and can be expected to work well as catalysts of electrodes of fuel cell. It is sometimes difficult that the nano sized area is analyzed by selected area electron diffraction (SAD) because the selected area aperture cannot be so small. The HRTEM and image processing technique give similar results of SAD when it works and revealed to be useful to analyze nano structured carbons. [Copyright &y& Elsevier]

Abstract: Hepatocyte and various hepatic stem cell transplantations have been studied as alternative therapies to orthotopic liver transplantation for liver injury. The engraftment of transplanted cells into the parenchyma requires transmigration through sinusoidal endothelial cells (SECs), the only cellular barrier. In this study, we constructed a SEC-imaging perfusion culture system that mimics sinusoids with respect to hemorheologic properties. SECs were successfully maintained for 24 hours. Human liver stem cells (HLSCs) were used as a model of transplanted cells for in vitro engraftment to SECs under perfusion culture conditions. Conditions of high shear stress perfusion with 0.34 dyne/cm2 significantly reduced cell adhesion in contrast to lower shear stress conditions of 0.1 and 0.03 dyne/cm2. Among the biologic perfusion fluids, namely, fetal bovine serum (FBS), pig plasma, and 5% human albumin solution, HLSCs showed significantly greater attachment to SECs when perfused with FBS, which is well known to contain abundant amounts of adhesion molecules. This biomimetic SEC perfusion culture system may provide a useful tool to study engraftment mechanisms and to evaluate the effects of various enhancers as an alternative to animal models. [Copyright &y& Elsevier]

Abstract: Compositional changes of the residual iron compounds in isothermally treated catalytic chemical vapor deposition derived multi-walled carbon nanotubes have been monitored using 57Fe transmission Mössbauer spectroscopy and X-ray fluorescence. The iron phases entrapped in the as-synthesized carbon nanotubes consist of γ-iron, α-iron, Fe3C and Fe1−x S. The Fe1−x S phase decomposes completely around 1500°C while the iron carbide phase decomposes in the temperature range of 1500–2400°C. The obtained apparent activation energy of ca. 76kcal/mol suggests that the entrapped iron was removed via a diffusion process during thermal treatment. [Copyright &y& Elsevier]

This study demonstrates the ability to fabricate lightweight, ductile but mechanically strong magnesium alloy (AZ91D) composites by introducing a small number of high crystalline multi-walled carbon nanotubes. It is demonstrated that 1% of relatively short and straight carbon nanotubes distributed homogeneously on the outer surface of magnesium powders act as an effective reinforcing filler to prevent deformation, thereby contributing to the enhanced tensile strength of magnesium alloy composites (e.g., from 315 to 388MPa). [Copyright &y& Elsevier]

Abstract: This manuscript reports the analysis of the G′ band profile in the Raman spectra of nanographites with different degrees of stacking order. Since the G′ band scattering coming from the 2D and 3D phases coexisting in the same sample can be nicely distinguished, the relative volumes of 3D and 2D graphite phases present in the samples can be estimated from their Raman spectra. The comparison between Raman scattering and X-Ray diffraction data shows that Raman spectroscopy can be used as an alternative tool for measuring the degree of stacking order of graphitic systems. [Copyright &y& Elsevier]

Abstract: Here we demonstrated the ability to fabricate ultra-fine carbon fibres through electrospinning of the polymer blends of polyacrylonitrile (PAN) and polyamic acid (PAA) and subsequent thermal treatment. The good spinnability of the polymer blends was achieved by reducing the solution’s viscosity by the addition of PAN. There was a close correlation between the fibre diameter developed in the spinning process and the physical properties of the carbonized fibres; the smaller diameter fibre gave rise to the higher crystallinity of the single carbonized fibre and, furthermore, a higher electrical conductivity and mechanical strength of the carbonized fibre web. The high anisotropy in the mechanical strength of the carbonized fibre webs was ascribed to the partial alignment of the resulting fibres along the winding direction through the electrospinning process. [Copyright &y& Elsevier]

Abstract: Systematic isothermal annealing has been carried out on catalytic chemical vapor deposition-derived highly disordered multi-walled carbon nanotubes in order to understand the structural evolution of carbon nanotubes kinetically. After specified isothermal time the crystallographic parameters strongly depend on annealing temperature, and can be divided into three stages. Rapid structural enhancement in the range from 1800 to 2200°C originates from the abrupt evolution of the residual catalytic compounds and is seen as partially aligned small fringes along the tube length. The lack of further structural ordering at temperatures above 2400°C and the low activation energy (ca. 90kJ/mol) are thought to be the result of the limited space available for further structural development considering the nano-sized multi-walled carbon nanotubes. [Copyright &y& Elsevier]

Abstract: We describe the synthesis of N-doped single-walled carbon nanotubes (N-SWNTs), that agglomerate in bundles and form long strands (<10cm), via the thermal decomposition of ferrocene/ethanol/benzylamine (FEB) solutions in an Ar atmosphere at 950°C. The amount of benzylamine in the solution was varied from 0% to 26% by weight. Using Raman spectroscopy, we noted that as the N content is increased in the starting FEB solution, the growth of large diameter tubes is inhibited. We observed that the relative electrical conductivity of the strands increases with increasing nitrogen concentration. Thermogravimetric analysis (TGA) showed novel features for highly doped tubes that are related to chemical reactions on N sites. [Copyright &y& Elsevier]

Abstract: Leymus chinensis (Trin.) Tzvel., a xerophilous grass, is adapted to high pH (8.5–11.5) sodic soils. Consequently, the species must have developed molecular and physiological mechanisms to adapt itself under such stress conditions during the course of evolution. In order to identify and characterize the complexity of this adaptation, it is important to identify genes by large-scale sequencing of cDNA clones or expressed sequence tags (ESTs). cDNA libraries were constructed from leaf tissue collected from the plants growing in the natural habitat, and from root by subjecting the seedlings to Na2CO3 stress. Of the 998 cDNA clones from each leaf and root tissues, 869 and 773, respectively, showed high quality sequences. In the leaf cDNA library, 574 clones were non-redundant, of which 295 had homology to the known transcripts, and 183 to unclassified proteins. The remaining 96 ESTs had no homology in the databases searched. Similar analysis of root cDNA library revealed that, of the 654 non-redundant clones, 269 had homology to the known transcripts, whereas 148 were novel. Sequence comparison of these clones using BLASTX led to the identification of 39 and 31 putative abiotic stress related genes from leaf and root cDNA library, respectively. The putative ESTs will serve as useful resource to understand the molecular basis of high pH sodic soil tolerance in plants. [Copyright &y& Elsevier]

Abstract: We describe the synthesis of cm-long strands consisting of single-walled carbon nanotube ropes. The method involves the thermolysis of ferrocene (FeCp2)–alcohol solutions under an Ar atmosphere at 800–950 °C. The tubes within strands could exhibit large diameters (2–3.5nm OD) in high yields by either increasing the ferrocene concentration in the alcohol solution or by increasing the pyrolysis temperature. We noted that the nanotube material with the highest degree of crystallinity was produced at 950°C, and as the ferrocene concentration in the alcohol solution increases (e.g., 1.2 wt%), the tubes tend to be metallic. This method appears to be simple, safer and more efficient than others reported in the literature because it does not require vacuum, sulphur agents, relatively high temperatures or large amounts of H2. [Copyright &y& Elsevier]

Abstract: Thermal annealing of graphitic conical nanofibers, produced by pyrolysing Pd precursors under an Ar atmosphere at 850–1000°C, results in the coalescence of adjacent cones. These novel cone-like arrangements exhibit heptagonal and pentagonal carbon rings located in the cauterized rims between adjacent cones. We propose molecular models that resemble such structures and calculate their electronic properties using a self-consistent local approach based on a realistic tight-binding Hamiltonian. The calculations demonstrate that coalesced cones exhibit a conducting behaviour and a local analysis of the density of states (DOS) reveals that curvature is crucial in modifying the electronic structure. [Copyright &y& Elsevier]

Abstract: We report H2 storage capacities up to 2.7wt% at 77K in spherical nanoporous carbons exhibiting periodic arrays of pores and surface areas between 946 and 1646m2/g. The materials were produced via the pyrolysis of sucrose (C12H22O11) embedded inside a spherical form of MCM-48 at 1000°C in an inert atmosphere. Our results open up new possibilities for producing carbon nanomaterials with large surface areas, which are able to store hydrogen with attractive yields. [Copyright &y& Elsevier]

We review the latest advances in the production and state-of-the art characterization of B- and N-doped carbon nanotubes (CNTs) and nanofibers. We briefly discuss different approaches to producing these novel doped nano-systems. The use of high-resolution transmission electron microscopy (HRTEM), electron energy loss spectroscopy (EELS), scanning tunneling spectroscopy (STS), Raman spectroscopy, and allied techniques to characterize these doped systems is reviewed. The field emission properties as well as some applications to the fabrication of novel polymer composites, Li+ batteries, and gas sensors are also discussed. It is clear that these materials possess outstanding properties when compared with pure CNTs, and it is foreseen that these systems will revolutionize some aspects of nanotube science and technology, thus opening a vast field of experimental and theoretical research. [Copyright &y& Elsevier]

We review the latest advances in the production and state-of-the art characterization of B- and N-doped carbon nanotubes (CNTs) and nanofibers. We briefly discuss different approaches to producing these novel doped nano-systems. The use of high-resolution transmission electron microscopy (HRTEM), electron energy loss spectroscopy (EELS), scanning tunneling spectroscopy (STS), Raman spectroscopy, and allied techniques to characterize these doped systems is reviewed. The field emission properties as well as some applications to the fabrication of novel polymer composites, Li+ batteries, and gas sensors are also discussed. It is clear that these materials possess outstanding properties when compared with pure CNTs, and it is foreseen that these systems will revolutionize some aspects of nanotube science and technology, thus opening a vast field of experimental and theoretical research. [Copyright &y& Elsevier]

Focuses on the use of modified Hodge and EDTA-disk synergy tests in screening metallo-beta-lactamase-producing strains of Pseudomonas and Acinetobacter species. Interpretation of the presence of a distorted inhibition zone after incubation; Tests used in determining the characteristics; Evaluation of the usefulness of the synergy tests.

Background Many types of stem cells have been widely used for the treatment of liver diseases. The therapeutic effect of stem cells is predominantly based on the immune regulatory properties of these cells. Methods We isolated human liver stem cells (HLSCs), which are considered intrahepatic stem cells, and examined their suppression of T-cell proliferation induced by phytohemagglutinin. Results HLSCs inhibited phytohemagglutinin-induced T-cell proliferation not only in direct co-culture but also in indirect co-culture in a cell number–dependent manner. That is, T-cell proliferation was substantially inhibited by cell-to-cell contact regardless of soluble factor(s). B7-H1, a co-inhibitory molecule that relies on cell-to-cell contact, was found to be constitutively expressed at low levels on HLSCs. Furthermore, its expression was upregulated moderately by tumor necrosis factor-α and dramatically by interferon-γ. Conclusions These results suggest that HLSCs would have therapeutic effects through T-cell suppression in acute liver diseases. [ABSTRACT FROM AUTHOR]

Abstract: In situ Raman scattering measurements of pristine and fluorinated double-walled carbon nanotube samples under high pressure have been performed. Due to the mechanical shielding effect of the outer tubes of the double-walls to the applied pressure, the Raman scattering lines from the inner tubes of both samples remained to be observed even at high pressure. [Copyright &y& Elsevier]