Time-resolved diagnostics of single wall carbon nanotube synthesis by laser vaporization

Three questions important to nanosecond laser ablation synthesis of single wall carbon nanotubes (SWNTs) have been addressed using in situ spectroscopic diagnostics: determining the temperature of the nanoparticles within the propagating plume at different times after ablation, monitoring the aggregation of the nanoparticles in the plume, and measuring the growth rates of the SWNTs. Short SWNTs were synthesized using nanosecond Nd:YAG-laser ablation of a C-Ni-Co target inside a high-temperature laser vaporization reactor by controlling and restricting the growth times. The time spent by the plume inside the oven was varied by positioning the target at various locations and imaging the plume using Rayleigh scattered light induced by a 308 nm XeCl laser. Statistical analysis of the short SWNT length distribution was performed using TEM images. The upper and lower limits of the growth rates of SWNTs were estimated as 0.6 and 5.1 μm/s. The particle temperature within the propagating plume was measured at different times after ablation through time-resolved measurements of the plume's blackbody emission. The onset of SWNT growth was estimated based on the time when the particle temperature drops below the eutectic temperature for C/Co, C/Ni. For the first time, absorption spectroscopy was employed to study the aggregation of carbon nanoparticles in the propagating plume. It was shown that the aggregation rate increases rapidly at lower oven temperatures. A general picture of SWNT growth by laser ablation based on imaging, spectroscopy, and pyrometry of ejected material at different times after ablation is discussed.