Growth Dynamics of Single-Wall Carbon Nanotubes Synthesized by CO₂ Laser Vaporization

Abstract

Single-wall carbon nanotubes (SWNTs) were synthesized by the irradiation of a 20-ms CO2 laser pulse (1-kW peak power) onto a graphite−Co/Ni composite target at 25−1200 °C. Characterization of carbonaceous deposits using Raman scattering, scanning electron microscopy, and transmission electron microscopy showed that SWNTs were formed by laser irradiation even at room temperature. At 1100−1200 °C, the SWNT yield significantly increased (> 60%). A high-speed video imaging technique was used to observe the expanding vaporization plume and the emerging carbonaceous materials in an Ar atmosphere. Carbonaceous materials containing SWNTs became visible after ∼3 ms from the initiation of laser irradiation of the target. At 1000−1200 °C, blackbody emission from large carbon clusters and/or particles was observed for more than 1 s after the end of the laser pulse. We suggest that the growth of the SWNTs occurs from a liquidlike carbon−metal particle via supersaturation and segregation. A continuous supply of hot carbon clusters to the particles due to the 20-ms laser pulse and the maintenance of the hot growth zone for SWNTs, performed with the help of a furnace, are thought to play a crucial role in the SWNT formation.