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Solid carbon nanofibers (CNFs), hollow CNFs, metal-filled carbon nanotubes (CNTs), and carbon onions were synthesized by chemical vapor deposition (CVD) using a novel Ni/Y catalyst supported on Cu at different reaction temperatures. XRD, TEM, and EDS analyses reveal that the structure of the catalyst changes with increasing reaction temperature. The evolution of Y doped in Ni directly influences the morphologies of the products. At relatively low temperature, Y is doped in Ni and causes CNF formation, and when the temperature is increased to above 650 °C, Y separates from Ni as yttria nanoparticles and carbon onions are synthesized. The catalyst evolution and carbon nanostructure growth mechanism are discussed in detail. [ABSTRACT FROM AUTHOR]

Abstract: The multiply twinning structure (MTS) of nanodiamonds synthesized by pulsed-laser irradiation was investigated theoretically and experimentally. The thermodynamic calculation shows MTS is more stable than single crystal structure (SCS) in a certain size range and statistical results experimentally accords with the theory. A mechanism on the formation of MTS in nanodiamonds was proposed based on Transmission Electron Microscopy (TEM) observation, in which SCS successively grows into MTS through intermediate states, such as simple twin and triple twin. Furthermore, the dispersive nanodiamonds exhibit strong photoluminescence (PL) after surface passivation. [Copyright &y& Elsevier]

Abstract: A mass of multi-wall carbon nanohorns (CNHs) were synthesized by simple chemical vapor deposition of methane over Ni/Al2O3. Transmission electron microscopy was used to characterize these CNHs. The results showed that the purity of CNHs was about 40–50% and these CNHs were with well graphitized multi-walled structures. The mean diameter of CNHs was about 20nm, which is larger than those prepared by the CO2 laser method, and the length of CNHs was in the range of 50–500nm. Moreover, the growth mechanism of CNHs was discussed. [Copyright &y& Elsevier]

Abstract: A mass of carbon nanotubes with straight and short bodies was produced by chemical vapor deposition of methane over Ni/Al2O3. Scanning electron microscopy, transmission electron microscopy and thermogravimetric analysis were used to analyze the synthesized carbon nanotubes. The results showed that they were well-graphitized multi-walled nanotubes and had not tangled together. Their average length was several hundreds of nanometers, suitable for their use as a nanometer-scale material. [Copyright &y& Elsevier]

Abstract: Changes in the thermogravimetrically determined oxidation behaviors of CVD-grown multi-walled carbon nanotubes (MWNTs) over Ni/Al catalyst with different Ni content were examined. Catalyst type was found to have a measurable impact upon nanotube stability, suggesting differing levels of crystalline perfection in the resulting nanotubes. With increasing the Ni content in the Ni/Al catalyst, the CNTs obtained became less stable during heat treatment in air. Furthermore, high-resolution transmission electron microscopy was employed to investigate the defect sites of as-grown MWNTs. The results provide evidence showing that defect sites along the walls and at the ends of the raw MWNTs facilitate the thermal oxidative destruction of the nanotubes. [Copyright &y& Elsevier]

Abstract: Novel binary and triple carbon nanotubes (CNTs) with one common catalytic particle encapsulated have been synthesized using Ni/Cu/Al2O3 catalyst, which was produced by a sol–gel method. But when using Ni/Al2O3 as catalyst, a mass of common CNTs, that is, one CNT with one catalytic particle encapsulated, was obtained. The results showed that copper-element doping to the Ni/Al2O3 catalyst played a key role in the synthesis of CNTs, signifying a novel approach to modify the Ni/Al2O3 catalyst. Based on the transmission electron microscopy observations, a simple growth mechanism was developed to describe the growth of the binary or triple CNTs, which could be well explained by a diffusion segregation process. [Copyright &y& Elsevier]

Abstract: The initial stage growth of bamboo-shaped carbon nanotubes (CNTs) synthesized by catalytic decomposition of methane is investigated. A special experimental procedure has been developed to stop the process after short durations (0s to 3min). It has found that during the early stages (60s), carbon cluster-encapsulated nanoparticles are formed. With prolonging synthesis time (3min), some CNTs coexisted with carbon cluster-encapsulated nanoparticles are formed. HRTEM observations show that these CNTs display multi-walled and bamboo structure and the encapsulated catalytic particles are quasi-cone morphologies. At the same time, the catalytic particles only encapsulated with carbon clusters present quasi-sphere structures. For growth up to 60min, two kinds of bamboo mode structures are observed: conical, and cylindrical, which are developed by quasi-cone and quasi-sphere catalytic particles, respectively. Moreover, the early stage growth mode of the CNTs is predominantly of the base growth mode according to TEM observations. [Copyright &y& Elsevier]