Synthesis of single walled carbon nanotubes by dual laser vaporization

Abstract

Single walled carbon nanotubes were synthesized by the laser vaporization of graphite composite targets in a tube furnace. Two pulsed Nd:Yag lasers operating at fundamental (1064 nm) and 2 nd harmonic (532 nm) were combined, focused and evaporated targets in an inert atmosphere of Ar flowing at 200 sccm at a pressure of 500 mBar. The furnace temperatures of either 1200 or 1000 0 C were used. The targets were either pure graphite or graphite doped with catalysts. The as-evaporated material was collected and characterized by transmission electron microscopy, scanning electron microscopy and Raman Spectroscopy. TEM analysis showed individual single walled tubes with diameters of 1.31 ± 0.02 nm and bundles of single walled tubes up to 10 nm in diameter. Raman Spectroscopy revealed a distribution of chiral, metallic and semiconducting nanotubes, all with very low defect concentration. The majority of the identified tubes were semiconducting. The addition of Fe as catalyst changed the diameter distribution from 1.30 – 1.46 nm to 1.33 – 1.49 nm and significantly lowered the defect concentration. The concentration of metallic nanotubes was also found to have decreased.