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Enhancement and control of carrier lifetimes in p-type 4H-SiC have been investigated. In this study, thermal oxidation and carbon ion implantation methods, both of which are effective for lifetime enhancement in n-type SiC, were attempted on 147-μm thick p-type 4H-SiC epilayers. Effects of surface passivation on carrier lifetimes were also investigated. The carrier lifetimes in p-type SiC could be enhanced from 0.9 μs (as-grown) to 2.6 μs by either thermal oxidation or carbon implantation and subsequent Ar annealing, although the improvement effect for the p-type epilayers was smaller than that for the n-type epilayers. After the lifetime enhancement, electron irradiation was performed to control the carrier lifetime. The distribution of carrier lifetimes in each irradiated region was rather uniform, along with successful lifetime control in the p-type epilayer in the range from 0.1 to 1.6 μs. [ABSTRACT FROM AUTHOR]

Abstract: H and D retention characteristics in the near top surface of the JT-60U plasma facing carbon tiles were investigated by means of elastic recoil detection analysis. From the result, H was dominantly retained within 1μm depth because of the H discharges for the wall cleaning carried out before the removal of sample tiles. (H+D)/C ratios were small: it was ∼0.07 at a maximum in the divertor samples except for the deposition on the dome outer wing tile which was ∼0.13, and it was ∼0.15 at a maximum in the first wall samples. The hydrogen concentration in the redeposited carbon layers is strongly influenced by the temperature. Consequently, (H+D)/C ratios at the observed low level are a result of the operation of JT-60U at wall temperatures of 300°C or higher. [Copyright &y& Elsevier]

Based on a molecular mechanics coupled with atomistic-based continuum theory, a closed-form formula is presented to examine the elastic properties of single- and double-walled carbon nanotubes subjected to hydrostatic pressure. Following the present model, the effects of the armchair and zigzag CNT structures on the pressure behavior are theoretically investigated. The computational result indicates that the bulk modulus is less sensitive to the chiral structures except for very small tube diameters. Moreover, closed-end nanotubes under hydrostatic pressure exhibit a larger bulking modulus than open ended nanotubes. The cap of the zigzag tubes has a larger effect on the bulk modulus when compared to the armchair tubes, especially in small diameter nanotubes. The predicted strain and the bulk modulus are in good agreement with existing theoretical results. [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: 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]

High purity single crystals of Mo5SiB2(D8l), Mo5Si3(D8m), Mo5Si3C(D88) and Ti5Si3(D88) and polycrystals of Nb5SiB2(D8l) and V5SiB2(D8l) have been grown and their electrical and thermal properties have been measured. The resistivity of all transition metal 5-3 silicides exhibit a negative curvature with a tendency towards saturation when it is plotted as a function of temperature. The resistivity of Mo5SiB2, Mo5Si3 and Mo5Si3C is saturated at a lower value than that of Ti5Si3, Nb5SiB2 and V5SiB2. In Mo5Si3C where room temperature resistivity is large because of large residual resistivity, resistivity saturation is pronounced and results in almost temperature independent resistivity. Thermal conductivities for Mo5SiB2, Mo5Si3, Mo5Si3C and Ti5Si3 are about 27, 19, 8.5 and 11 W/mK, respectively. Mo5Si3C exhibits almost temperature independent thermoelectric power along [112¯0]. On the other hand, thermoelectric power of Mo5Si3C along [0001] and Mo5SiB2 decreases monotonically with increasing temperature. [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]

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]

High yields of graphitic conical nanofibres (5-70 nm OD; <5 µm in length) are produced by pyrolysing various palladium precursors under an Ar atmosphere at 850-1000°C. The fibres exhibit diamond-shaped Pd particles at their tips, which are responsible for the carbon aggregation and its subsequent diffusion. This carbon replication phenomenon on the Pd particles results in the formation of stacked graphene cones, which grow aligned along a common axis, thus creating graphitic nanofibres. The cones within the fibres can be either open (lamp-shade type) or closed. The material has been analysed using sophisticated electron microscopy (HRTEM, SEM, ED) and spectroscopic techniques (Raman, EELS, EDX). Due to the large number of open edges, we envisage that these novel nanofibres may find important applications in the fabrication of field emitters, gas storage devices and composites. [ABSTRACT FROM AUTHOR]

Carbon nanotubes have a whisker-like structure so an extremely high strength and lack of plasticity are generally predicted. In-situ observations made by transmission electron microscopy, however, prove that carbon nanotubes bend plastically at room temperature. The bending process at the atomic level is suggested by a molecular mechanics calculation: a nanotube deforms elastically until certain critical curvature is attained; then the atomic bonding in the stressed side changes from a graphite-like bonding state to a diamond-like state. [ABSTRACT FROM AUTHOR]

The authors report a significant enhancement in the thermal conductivity of a conventional carbon fiber/phenolic resin composite system when adding highly crystalline multiwalled carbon nanotubes. They demonstrate that 7 wt % of carbon nanotubes dispersed homogeneously in a phenolic resin acted as an effective thermal bridge between adjacent carbon fibers and resulted in an enhancement of the thermal conductivity (e.g., from 250 to 393 W/m K). These results indicate that highly crystalline carbon nanotubes can be used as a multifunctional filler to enhance simultaneously the mechanical and thermal properties of the carbon fiber/phenolic resin composites. [ABSTRACT FROM AUTHOR]

Double-walled carbon nanotubes are needed in a pure, highly crystalline form before features such as their electronic properties, thermal transport and mechanical behaviour can be investigated. Here we fabricate a paper-like material that consists of hexagonally packed bundles of clean, coaxial carbon nanotubes whose double walls vary little in diameter; it is prepared in high yields using chemical-vapour deposition with a conditioning catalyst and two-step purification. Our results will enable investigation of the physical properties of double-walled carbon nanotubes, which are predicted to be superior to those of both their single- and multiwalled relatives. [ABSTRACT FROM AUTHOR]

A comparison of the microtexture and structure of the low temperature heat-treated polyparaphenylene (PPP)-based carbons which are promising for the Li ion battery has been performed using high-resolution transmission electron microscopy and electron energy loss spectroscopy. It is found that the PPP-based carbon prepared by Kovacic method remains in suitable microtexture for high Li storage over a wider temperature range relative to that obtained by Yamamoto method. This characteristic of the Kovacic PPP-based carbon could lead to a more controlled microtexture for obtaining a higher Li storage capacity for Li ion battery applications. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

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: 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 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]

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]

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: 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]

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]

A morphological characterization of activated AR-resin was carried out. The time and temperature effect of the EDLC (electric double layer capacitor) properties of AR-resin were investigated. In order to clarify the relation between the electric double layer capacitance and the ion mobility in the organic solvent, a computer simulation was used to calculate the possible solvation size of Et4NBF4 in propylene carbonate. The sample (HTT 700) activated at a heat treatment temperature (HTT) of 700 °C for 2 h has a specific capacitance as high as 35.27 F g−1 (equivalent to 141.08 F g−1 for a single electrode), when it is charged to 2.5 V and discharged at 1 mA cm−2. The capacitance increase by using a longer activation time at each HTT was as follows: 2.3 times at HTT 600, 1.6 times at HTT 700, 1.3 times at HTT 800 and 1.2 times at HTT 900. This variation could be forecast from image analysis using a TEM photograph. Furthermore, a possible ion size of electrolyte (Et4NBF4) in a solvent was calculated and it is related to the mobility of charge carriers in a micropore. [Copyright &y& Elsevier]

Abstract: Retention and depth profile of all hydrogen isotopes (hydrogen, deuterium and tritium) in the carbon tiles of outer divertor, outboard baffle plate and outboard first wall in JT-60U, which were mostly eroded, were measured by TDS, SIMS and TIPT, and discussed from view points of tile temperature, incident energy and flux of impinging H, D and T. The distribution of T in the analyzed tiles was compared with the impinging flux of tritium produced by DD reactions, which was calculated by the OFMC code. In this paper, H, D and T retention mechanisms and isotopic replacement effects are summarized. [Copyright &y& Elsevier]