The growth times of single-wall carbon nanotubes ͑SWNT's͒ within a high-temperature laser-vaporization ͑LV͒ reactor were measured and adjusted through in situ imaging of the plume of laser-ablated material using Rayleigh-scattered light induced by time-delayed, 308-nm laser pulses. Short SWNT's were synthesized by restricting the growth time to less than 20 ms for ambient growth temperatures of 760-1100°C. Statistical analysis of transmission electron microscope photographs indicated most-probable lengths of 35-77 nm for these conditions. Raman spectra ͑E ex ϭ1.96 and 2.41 eV͒ of the short nanotubes indicate that they are wellformed SWNT's. The temperature of the particles in the vortex-ring-shaped plume during its thermalization to the oven temperature was estimated by collecting its blackbody emission spectra at different spatial positions inside the oven and fitting them to Planck's law. These data, along with detailed oven temperature profiles, were used to deduce a complete picture of the time spent by the plume at high growth temperatures ͑760-1100°C͒. The upper and lower limits of the growth rates of SWNT's were estimated as 0.6 and 5.1 m/s for the typical nanosecond Nd:YAG laser-vaporization conditions used in this study. These measurements permit the completion of a general picture of SWNT growth by LV based on imaging, spectroscopy, and pyrometry of ejected material at different times after ablation, which confirms our previous measurements that the majority of SWNT growth occurs at times greater than 20 ms after LV by the conversion of condensed phase carbon.

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Single-wall carbon nanotubes (SWNT) were grown to micron lengths by laser-annealing nanoparticulate soot containing short (∼50 nm long) nanotube “seeds.” The “seeded” nanoparticulate soot was produced by restricting the time spent by an ablation plume inside an 800 °C oven following laser vaporization of a C–Ni–Co target. The soot collected from the laser vaporization apparatus was placed inside graphite crucibles under argon, and heated by a CO2 laser. In situ pyrometry was used to estimate the sample temperature. Length distributions of SWNT bundles in the unannealed and annealed samples were measured by transmission electron microscopy and field emission scanning electron microscopy. Annealing treatments exceeding 1600 °C produced no increase in nanotube length, while lower temperatures in the 1000–1300 °C range were optimal for growth. These experiments indicate that SWNT grow by the conversion of condensed phase nanomaterial during annealing, a similar mechanism to that proposed for growth during normal laser–vaporization production.

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Three questions important to nanosecond laser ablation synthesis of single wall carbon nanotubes (SWNT) 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.