Time-resolved diagnostics and mechanisms of single-wall carbon nanotube synthesis by the laser vaporization technique

Abstract

Single-wall carbon nanotubes are formed by Nd:YAG laser vaporization of a graphite/(1 at. % Ni, 1 at. % Co) target into flowing argon (500 Torr) within a quartz tube furnace (1000 degree(s)C). Here, this process is investigated for the first time with time-resolved laser-induced luminescence imaging and spectroscopy of Co atoms, C 2 and C 3 molecules, and clusters. These measurements under actual synthesis conditions show that the plume of vaporized material is segregated and confined within a vortex ring which maintains an approximate 1 cm 3 volume for several seconds. Using time-resolved spectroscopy and spectroscopic imaging, the time for conversion of atomic and molecular species to clusters was measured for both carbon (200 microsecond(s) ) and cobalt (2 ms). This rapid conversion of carbon to nanoparticles, combined with transmission electron microscopy analysis of the collected deposits, indicate that nanotube growth occurs during several seconds of time from a feedstock of mixed nanoparticles in the gas-suspended plume. By adjusting the time spent by the plume within the high- temperature zone using these in situ diagnostics, single- walled nanotubes of controlled length were grown at an estimated rate of 0.2 micrometers /s. Ex situ annealing of short, 100-200 nm-long SWNT seeds collected after limited growth inside the hot oven resulted in continued growth of longer SWNT bundles, supporting the condensed phase conversion mechanism for SWNT growth.