Density of particles on center axis of arc frame for generation of carbon nanotubes

Abstract

This study analyzes the growth process of nanotubes. Using helium as the inert gas, an arc discharge plasma is generated between carbon electrodes, and the spatial distribution of the emission and its dependency on the gas pressure are examined. Based on the emission intensities of C+ at wavelengths of 657.8 and 723.6 nm, the plasma temperature is determined by two-spectral line intensity comparison. It is seen that the plasma temperature rises from the anode to the cathode and falls with increase of the gas pressure. The temperature near the cathode, where the nanotubes grow, is between 5500 and 6000 K. Based on the particle density-temperature relation derived by a theoretical calculation, the neighborhood of the cathode, where the nanotubes grow, seems mostly occupied by the monomer C. The particle density, which is derived from the emission intensity and the temperature distribution, decreases from the anode to the cathode, indicating that C is transported by diffusion from the anode toward the cathode. The diffusion rate of C near the cathode increases with increase of the gas pressure, which enhances the transport of C toward the cathode. The particle density of C+ derived by the same method decreases from the anode to the cathode, indicating that there exists a diffusion in addition to the drift from the anode to the cathode. The particle density increases with gas pressure. This suggests that the density of the carbon monomer and its transport are the important factors for the growth of nanotubes in an arc discharge. © 1998 Scripta Technica.