In situ optical absorption spectroscopy, incandencence, and light scattering characterization of single-wall carbon nanotube synthesis by the laser vaporization technique

In this paper we discuss three optical methods for in situ characterization of single wall carbon nanotube (SWNT) growth by laser vaporization at elevated temperatures: optical absorption spectroscopy, optical incandescence, and light scattering. Optical absorption spectroscopy was successfully used to estimate the size of carbon nanoparticles and to monitor the atomic metal catalyst in the propagating laser ablation plume. These measurements indicate that the aggregation rate of carbon nanoparticles increases rapidly at lower oven processing temperatures. The second method, incandescence, was applied to measure the particle temperature within the propagating plume at different times after ablation. The third approach, imaging of the plume using Rayleigh scattered light, was used to monitor the ejected material inside the hot furnace as well as to observe the plume when it exits the furnace, i.e., in the cold zone of a quartz tube reactor. We demonstrated that Rayleigh scattering imaging combined with TEM analysis of the produced material was very useful for controlling the length of SWNTs and estimation of the growth rates. A general picture of SWNT growth by laser vaporization based on in situ diagnostics of ejected material at different times after ablation is discussed.