Growth of single-wall carbon nanotubes dependent on laser power density and ambient gas pressure during room-temperature CO2 laser vaporization

Single-wall carbon nanotubes (SWNTs) were synthesized by the irradiation of 20-ms CO2 laser pulses onto a graphite-Co/Ni target at room temperature. We investigated the effect of laser power density (10-150kW/cm(2)) and ambient At gas pressure (150-760 Torr) on the abundance of SWNTs with lengths of up to about 200 nm in soot-like carbonaceous deposits. For a constant power density (30 kW/cm(2)), depending on the Ar gas pressure, SWNTs with diameters of 1.2-1.4 nm were synthesized. Expansion behavior and temperature-fall rates of clusters and/or particles in laser plumes were also analyzed by high-speed video imaging and temporally and spatially resolved emission spectroscopy. The temperature-fall rates were estimated to be 171-427 K/ms. The SWNT growth on the time scale of a few milliseconds appeared to be related to same features of condensing clusters and/or particles, including resident densities, collision frequencies and temperatures.