摘要:

Bundles of carbon single wall nanotubes (SWNTs) are produced by sublimating selected metal mixtures and carbon in an inert atmosphere during an electric arc [1]. Various experimental parameters such as the nature and relative proportions of metallic catalysts [1] or the kind and pressure of gas can influence the quantity and geometry of bundles produced by the arc process. In this paper, we particularly focus on the role of the nature and pressure of gas used. Systematic studies have been made and we present the results obtained by Scanning Electron Microscopy (SEM), High Resolution Transmission Electron Microscopy (HRTEM), X-Ray Diffraction (XRD) and High Resolution Raman Spectroscopy (HRRS). ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.56481

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A batch method for the gas phase production of carbon nanotubes by the catalytic decomposition of acetylene has been developed. Metal clusters are formed by laser vaporization of solid nickel in situ in the hot reaction tube containing a mixture of acetylene and argon. The laser generated clusters act as catalysts for the growth of nanotubes. With this method multi-walled tubes were obtained with inner diameters of 3–10 nm and outer diameters of 10–100 nm, respectively. TEM analysis shows that the tubes are well graphitized. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.56445

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Carbon nanotubes can now be produced in large scale by catalytic decomposition of acetylene in the presence of various supported metal catalysts. However, purification of the tubes obtained by this process is very difficult because it requires the separation both from the catalyst (support and metal particles) and the amorphous carbon which is a product of the thermal decomposition of hydrocarbons. In this work, separation of nanotubes from the catalyst has been carried out using an acidic treatment. On the other hand, the elimination of amorphous carbon by hydrogenation has also been investigated. The quality of the nanotubes was characterized by means of transmission electron microscopy and the yield of pure nanotubes was also determined. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.56451

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Acetylene decomposition over supported cobalt (or iron) catalysts proved to be an effective method for the preparation of well-graphitized carbon nanotubes. Compared to other techniques, catalytic synthesis is operated under relatively mild reaction conditions (700&hthinsp;°C, atmospheric pressure) and experimental apparatus is very simple. In order to improve catalyst performance, we try to understand the reaction mechanism. Catalysts were prepared by the impregnation method using different materials as catalyst support. Physico-chemical characterization of the samples were carried out by XRD, IR, etc. Surface acidity was measured by pyridine adsorption technique. Catalyst samples were tested in the decomposition of acetylene in a fixed bed flow reactor at 722&hthinsp;°C. The quantity of carbon deposit was weighted (catalyst activity). The quality of carbon nanotubes produced was characterized by means of transmission electron microscopy. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.56459

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Highly graphitised needle-like elongated carbon nanostructures containing encapsulated Ni, are produced by heating alternating thin films ofC60and Ni on a silica plate at 950&hthinsp;°C. High Resolution Transmission Electron Microscopy (HRTEM) studies reveal that these tapering structures are fully filled with Ni and are closed at both ends. The diameters of the needles (ca.2–5 &mgr;m in length) range between 10–20 nm at one end and 30–200 nm at the other. A surprisingly high degree of graphitisation was observed for the nanostructures. They may prove to be useful as Scanning Tunnelling Microscope (STM) tips due to their shape. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.56468

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Laser etching of Co, Ni and Fe films, in conjunction with the pyrolysis of solid organic precursors (e.g.aminodichlorotriazine, melamine,etc.) generates aligned carbon nanotube bundles and films of uniform length (<200 &mgr;m) and diameter (30 Å–80 Å). However, nanotube alignment strongly depends upon laser etching conditions (e.g.laser power, pulse duration and focus distance). Additionally, condensed-phase techniques, using mixtures of molten LiCl and soft metals (e.g.Bi, Pb,etc.) as electrolytes, generate high yields of metallic nanowires (<45&percent; overall material and <2 &mgr;m in length, <100 nm OD). Finally, it is shown that novel 3-D flower-like silica nanostructures are produced by a simple and surprising solid-phase approach. It is observed that single catalytic nanoparticles act as nucleation sites, leading to unusual morphologies of silicon oxide nanofibres (20–120 nm OD and <200 &mgr;m). The latter structures may be useful in the context of catalysis, 3-D composite materials, and optoelectronic devices, thus breaking new ground in nanowire and nanofibre technology. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.56529

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Pulsed laser ablation (PLA) has been scaled up to yield several grams/day of single-walled nanotubes. Annealed, purified material is highly crystalline, essentially free of amorphous carbon, fullerenes and catalyst residues, and about 3 times denser than the highly porous, as-grown product. In principle the interactions between tubes in a rope, and/or between rope crystallites, may be “tuned” by 3 different approaches—chemical doping, hydrostatic pressure, or purification/annealing, all of which have a dramatic effect on the temperature dependence of resistivity. In particular, we suggest that the crossover from positive to negative dR/dT at low temperature is a 3D effect and not an intrinsic property of isolated neutral SWNT. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.56530

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The efficient purification of single-wall and multi-wall carbon nanotubes (NTs) by columnar size exclusion chromatography (SEC) is reported. In this process, carbon nanospheres (polyhedra), amorphous carbon and metal particles are removed from aqueous surfactant-stabilised dispersions of NT raw material. TEM and AFM investigations revealed that more than 40–50&percent; of the purified material consists of individual tubes. In addition, length separation of the tubes is achieved. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.56531

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Surfactant-stabilised aqueous dispersions of carbon single-walled nanotubes (SWNTs) provide attractive possibilities for different types of assembling processes. The adsorption behaviour of chromatographically purified, micellar suspended SWNTs on silica substrates and metal electrodes is presented. Chemical modifications of the substrate surface allow to control the adsorption kinetics and the fraction between adsorbed individual SWNTs and bundles of SWNTs. Tube alignment occurs presumably due to flow effects upon removal of the surfactant. As a second assembling technique, we describe the preparation of Langmuir-Blodgett films consisting of SWNTs embedded in a surfactant matrix. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.56545

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Heat-treated catalytic multiwall carbon nanotubes (MWNTs) were intercalated by K andFeCl3in vapor phase, using the two-bulb technique. A first stageKC9intercalation compound was formed with potassium. After elimination of potassium, the tubular morphology is still preserved showing that intercalation is a reversible phenomenon. In the case ofFeCl3,the saturated compound is less rich than with graphite. However, well defined in planehkbands prove the intercalation. Due to the position of the002line at 0.345 nm, it is likely that intercalation is incomplete and that the material is a mixture of intercalated and non intercalated zones. A model of catalytic nanotubes is presented which accounts for the reversibility of the intercalation reactions. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.56546

出版商:AIP    

年代:1998

数据来源: AIP