Investigations of single-wall carbon nanotube growth by time-restricted laser vaporization

Abstract

The growth times of single-wall carbon nanotubes ͑SWNT's͒ within a high-temperature laser-vaporization ͑LV͒ reactor were measured and adjusted through in situ imaging of the plume of laser-ablated material using Rayleigh-scattered light induced by time-delayed, 308-nm laser pulses. Short SWNT's were synthesized by restricting the growth time to less than 20 ms for ambient growth temperatures of 760-1100°C. Statistical analysis of transmission electron microscope photographs indicated most-probable lengths of 35-77 nm for these conditions. Raman spectra ͑E ex ϭ1.96 and 2.41 eV͒ of the short nanotubes indicate that they are wellformed SWNT's. The temperature of the particles in the vortex-ring-shaped plume during its thermalization to the oven temperature was estimated by collecting its blackbody emission spectra at different spatial positions inside the oven and fitting them to Planck's law. These data, along with detailed oven temperature profiles, were used to deduce a complete picture of the time spent by the plume at high growth temperatures ͑760-1100°C͒. The upper and lower limits of the growth rates of SWNT's were estimated as 0.6 and 5.1 m/s for the typical nanosecond Nd:YAG laser-vaporization conditions used in this study. These measurements permit the completion of a general picture of SWNT growth by LV based on imaging, spectroscopy, and pyrometry of ejected material at different times after ablation, which confirms our previous measurements that the majority of SWNT growth occurs at times greater than 20 ms after LV by the conversion of condensed phase carbon.

Evolution of catalyst particle size during carbon single walled nanotube growth and its effect on the tube characteristics

“…1 Even though extensive effort has been made to control the diameter, chirality, and type ͑metallic or semiconducting͒ of the nanotubes, by varying the catalyst size and composition, support/substrate materials, synthesis temperature, and hydrocarbon gases, [2][3][4][5][6][7][8][9][10][11][12] synthesis of nanotubes with given characteristics is still very challenging. The size of catalyst particles is one of the key issues in the growth of SWNTs.…”

Novel Catalysts, Room Temperature, and the Importance of Oxygen for the Synthesis of Single-Walled Carbon Nanotubes

“…However, the laser ablation reaction is highly dynamic in that the ablated materials from each laser pulse form a vapor cloud immediately in front of the target that grows outward in a vortex. 4 As the cloud grows, clusters and particles form catalysts particles from which SWCNTs stem. These catalysts particles, from which SWCNTs grow, are generally accepted to be in a molten state.…”

“…The strength of laser ablation is that it produces high yield and high quality SWCNTs. 4 The available catalysts for laser ablated SWCNT production, until now, have been limited to the requirement of at least one of a select few transition metals 5 (Co, Ni, Rh, Pt) being present in the reaction. These require a relatively high synthesis temperature.…”

Laser Interactions for the Synthesis and In Situ Diagnostics of Nanomaterials

“…7.4c), or Rayleigh scattering from aggregated clusters (e.g., the vortex rings in Fig. 7.4g) [37,38]. A time-delayed, gated, intensified CCD-array detector with variable gate ([3 ns) is typically used to capture images or optical spectra during, or at a well-defined delay with respect to, the probe laser pulse.…”