摘要:

This paper describes the results of the synthesis of SWNTs in weak and strong DC magnetic fields. In weak magnetic fields with the maximum intensity of 0.5 T, SWNTs were synthesized only when the applied field was parallel to the current direction. These samples consisted of tubes with a diameter as small as about 0.9 nm. Furthermore, the metal particles were smaller compared to zero field case. On the other hand, at strong magnetic fields with the maximum intensity of 2 T, the yield decreased with increasing magnetic field strengths for the arc discharge current of 70 A. This was believed due to forced convection caused by the temperature rise in the anode resulting from higher current densities due to Lorentz force acting on charged particles non-parallel to the magnetic field direction. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1420043

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

High-quality single-walled carbon nanotubes (SWNTs) have been produced by DC arc discharge in hydrogen ambience. By using Fe 1&percent; catalyst a large amount of SWNTs are produced in pureH2gas. Other transition metals of iron group and its combination are also used as catalyst for preparing SWNTs by adding 1&percent;H2Sgas inH2.Tri-metal catalyst, Fe(0.25&percent;)-Ni(0.9&percent;)-Co(0.9&percent;), is found to be most effective for high yield of SWNTs. The SWNTs diameters are fairly thick ∼1.4–4 nm, and some double-walled carbon nanotubes also exist with them. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1420044

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

The production of isolated single wall carbon nanotubes (SWNTs) is accomplished using the laser oven process. Material is collected on quartz substrates at different locations in the laser oven for a variety of flow conditions. The lengths and diameter distributions of the nanotubes are measured directly (without additional processing steps) using AFM. Preliminary Raman data taken using 2D scans indicate the feasibility of this technique for length and diameter determination. The AFM study indicated the formation of long individual nanotubes, which then seem to coalesce into bigger bundles. The role of the inner tube of the flow-tube set up is confirmed to improve interactions between SWNTs resulting in formation of bundles. Flowing buffer gas seems to influence the dispersion of particulate material in the nanotube product. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1420045

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

Electrochemical doping of single-wall carbon nanotube (SWNT) films and concomtant changes in their electronic states were investigated byin situoptical absorption and Raman spectroscopy as well as by ac resistance measurements using non-aqueous electrolytic solution. Reversible variation of these properties induced by the shift in the electrode potential demonstrated the practicability of fine-tuning of their electronic states. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1420046

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

Carbon nanocoils have been synthesized in great quantities by thermal chemical vapor deposition using the iron catalyst prepared by a convenient electroplating method on indium tin oxide substrates. The fine iron particles can be sufficiently mixed with the indium tin oxide by this method, which induces the high efficient growth of small-sized carbon nanocoils with relatively uniform diameters. The growth of carbon nanocoils is dependent on the deposition temperature, the flow rate of acetylene gas and the deposition time, which is due to the activity of the catalyst particles, the density of acetylene and/or hydrocarbon radicals in the reaction chamber and the tip growth mechanism. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1420047

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

Carbon nanotubes were synthesized using several mesoporous silica with different pore sizes as the templates. TEM observation confirmed that carbon nanotubes with homogeneous diameter can be obtained by the present method. However, it was hard to find the correlation between the pore size of the templates and the diameter of the prepared carbon nanotubes. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1420048

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

Single-wall carbon nanotubes (SWNTs) were synthesized by laser ablation of Ni-Co-graphite composite targets at 1200&hthinsp;°C under flowing argon. The effects of the temperature gradient near the target and the gas flow rate on the diameter distribution of SWNTs were studied in order to understand their growth dynamics. The diameter distribution of the SWNTs, analyzed by Raman spectroscopy, was dependent on the gas flow rate when there was a temperature gradient around the target. Time resolved scattering images from the ablated species at different flow rates indicated that velocities of backward moving species increased with increasing flow rate. These findings are used to estimate the time required for nucleation and the growth of SWNTs. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1420049

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

A new, simple method of carbon nanotube fabrication was developed. The method employed a tungsten-electrode-inert-gas (TIG) welding arc torch, with a graphite electrode used instead of a conventional tungsten electrode in order to prevent contamination of the tungsten vapor and droplets. The substrates used as counterelectrodes for the torch arc were pure graphite and catalyst (Ni, Y)-mixed graphite. The torch arc was operated in open air with both DC and AC modes. Nanotubed surfaces were obtained on catalyst-mixed graphite with DC and AC modes, and on pure graphite with the AC mode. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1420050

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

Multiwalled carbon nanotubes (CNTs) were synthesized on Ni-coated Si substrates by thermal chemical vapor deposition (CVD) with an acetylene gas. Ni thin film with a thickness of 120 nm was prepared at 200&hthinsp;°C under a pressure of3×10−3 Torrby RF magnetron sputtering. The CNTs grown at a growth temperature of 650&hthinsp;°C were uniformly aligned with high tube density. We obtained relatively less aligned CNTs with lower tube density with increasing growth temperatures, in contrast to the general belief. This was explained by the change of the surface morphology of the metal layers, where with increasing the growth temperatures the metal grains were coalesced and thus the grain size became bigger, reducing the grain density. The length of the CNTs increased with increasing growth time and saturated at long growth time. The growth termination at large growth time is explained by the cap growth mechanism. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1420051

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

Vertically aligned carbon nanotubes were grown on Ni-coated Si substrates using microwave-plasma enhanced chemical vapor deposition. The surface morphology of Ni thin films was varied with the rf power density during the sputtering process. It was found that the growth of carbon nanotubes was strongly influenced by the surface morphology of Ni thin film. Pure carbon nanotubes were synthesized on the Ni thin film with uniformly distributed small grain sizes, whereas a lot of carbonaceous particles were produced in addition to the nanotubes, when the nanotubes were grown on the Ni film with widely distributed grain sizes. With decreasing Ni-grain size, the diameter and the wall-number of carbon nanotubes decreased while the length and the density of the nanotubes increased. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1420052

出版商:AIP    

年代:1901

数据来源: AIP