Xihuang Zhou

Mass-production of single-wall carbon nanotubes by arc discharge method

Abstract With a Y–Ni alloy composite graphite rod as anode for d.c. arc discharge, a cloth-like soot was produced, containing about 40% single wall carbon nanotubes (SWCNTs). By characterization with high resolution transmission electron microscope (HREM) and Raman spectroscopy, it is found that the SWCNTs have nearly the same diameter of 1.3 nm and belong to armchair (n, n) type carbon nanotubes (n=8, 9, 10 and 11). It is also proposed that a large temperature gradient and the addition of Y–Ni alloy in the anode are the two most important factors influencing the formation of SWCNTs.

TEMPERATURE DEPENDENCE OF THE RAMAN SPECTRA OF CARBON NANOTUBES

We report on a temperature dependence of the frequency of all the major peaks in the Raman spectra of carbon nanotubes, using different excitation laser powers at the sample. The frequency decreases with increasing temperature for all peaks, and the shifts in Raman frequencies are linear in the temperature of the sample. In comparison, a similar dependence is found in active carbon, but no shift is observed for the highly ordered pyrolytic graphite within the same range of variation in laser power. A lowering of frequency at higher temperature implies an increase in the carbon–carbon distance at higher temperature. The relatively strong temperature dependence in carbon nanotubes and active carbon may be due to the enhanced increase in carbon–carbon distance. This enhancement may originate from the heavy defects and disorder in these materials.

Comparative Raman Study of Carbon Nanotubes Prepared by D.C. Arc Discharge and Catalytic Methods

The Raman spectra of carbon nanotubes prepared by catalytic (C-CNT) and d.c. arc discharge (D-CNT) methods are reported. A previously unnoticed third-order Raman peak at ca. 4248 cm-1 was observed in the Raman spectrum of D-CNT. The Raman features of D-CNT and C-CNT are similar to those of highly oriented pyrolytic graphite (HOPG) and active carbon, respectively. The data also suggest that the increase in disorder in D-CNT compared with HOPG is due to structural defects in D-CNT.

Nonresonant third‐order optical nonlinearity of all‐carbon molecules C60

The nonresonant third‐order hyperpolarizability of all‐carbon molecules C60 is measured by nanosecond degenerate four‐wave‐mixing experiment in C60 toluene solution. The value of γ1111 measured is 1.6×10−31 esu, which corresponds to an estimated value of the third‐order nonlinear optical susceptibility χ(3)1111E = 3.3 × 10−9 esu for the solid compound.

Large and ultrafast third-order optical non-linearity of single-wall carbon nanotubes at 820 nm

Single-wall carbon nanotubes (SWCNT) of diameter 1.3 nm have been produced and cut into finite lengths centered at 160 nm. A solution of them in DMF has been prepared for third-order optical non-linearity measurements using the femtosecond optical Kerr effect at a wavelength of 820 nm. The ultrafast second-order hyperpolarizability, gamma, of this SWCNT is estimated to be as large as 2.1 X 10(-28) esu

High-yield preparation of endohedral metallofullerenes by an improved DC arc-discharge method

Abstract The soot containing endohedral metallofullerenes Mx@C2n(M=Y, La, Tb and Sm; x=1, 2, 3; n⩾30) has been prepared by DC arc-discharge method under improved conditions including high helium pressure, low electric current, large gap distance between electrodes and high atomic ratio of M/C, with MNi2 alloys instead of metal oxides or pure metals as the encaged metal source, followed with extraction by CS2. The raw soot and extracts were analyzed by laser desorption mass spectrometry and results show that the relative yields of metallofullerenes, even if the usually low yield ones, Sm@C74 and Sm@C84 for example, are rather high. Some possible reasons leading to the high yield preparation are discussed.

High yield synthesis and growth mechanism of carbon nanotubes

Abstract With Y 2 O 3 /carbon composite rods, Carbon nanotube bundles were synthesized in high yield by d.c. arc-vaporizing method. The carbon nanotube bundles and carbon nanotubes were observed by optical microscope, scan electron microscope and high-resolution transmission electron microscope. According to our observations, a new model is proposed to account for the growth of cathode deposit with nanotube bundles.

Synthesis of C60-NBN and C70-NBN(N=L, 2) by DC arc Burning Method

Abstract Macroscopic quantities of boron-doped fullerenes, such as C60-nBn and C70-nBn(n = 1, 2), were successfully synthesized by DC arc burning method, extracted by CS2, and characterized by field desorption mass spectra. Among them C58B2 and C68B2 were extracted for the first time. The boron-doped fullerenes were found to be less stable than their pristine fullerene analogs. When the electric current becomes too high, no boron doped fullerene, but more higher fullerenes, were formed.

Optical limiting properties of buckminsterfullerene C60/C70

Optical limiting behavior through reverse saturable absorption for the solution of a buckminsterfullerene C60/C70 mixture (85% C60 and 15% C70) in toluene has been observed with 10 ns, 530 nm laser pulses. The solution concentration dependence of optical limiting degree is investigated by using the solutions of various transmissivities. The strong influence of the triplet state quenched in the existence of 3O2 is also investigated by comparing the optical limiting process for the argon-degased solution and the not argon-degased solution. The results indicate that buckminsterfullerence is a kind of promising material for light protector.

Single-wall carbon nanotube colloids in polar solvents

Stable single-wall carbon nanotube (SWCNT) colloids in polar solvents, such as water, ethanol, acetone and DMF, have been prepared and the third-order optical nonlinearity of the SWCNTs measured using the femtosecond optical Kerr effect.