Formation of carbon nanotubes:In situoptical analysis using laser-induced incandescence and laser-induced fluorescence

Abstract

Gas-phase production of carbon nanotubes in presence of a metal catalyst with a continuous wave CO 2 laser is investigated by combining coherent anti-Stokes Raman scattering ͑CARS͒, laser-induced fluorescence ͑LIF͒, and laser-induced incandescence ͑LII͒. These in situ techniques provide a unique investigation of the different transformation processes of the primarily carbon and metal vapors issued from the vaporization of the target by the laser and the temperature at which these processes occur. Continuous-wave laser provides with stable continuous vaporization conditions very well suited for such in situ investigations. Temperature profiles inside the reactor are known from CARS measurements and flow calculations. Carbon soot, density, and size of carbon aggregates are determined by LII measurements. LIF measurements are used to study the gas phases, namely, C 2 and C 3 radicals which are the very first steps of carbon recombination, and metal catalysts gas phase. Spectral investigations allow us to discriminate the signal from each species by selecting the correct pair of excitation/detection wavelengths. Spatial distributions of the different species are measured as a function of target composition and temperature. The comparison of LIF and LII signals allow us to correlate the spatial evolution of gas and soot in the scope of the different steps of the nanotube growth already proposed in the literature and to identify the impact of the chemical nature of the catalyst on carbon condensation and nanotube nucleation. Our study presents the first direct evidence of the nanotube onset and that the nucleation proceeds from a dissolution-segregation process from metal particles as assumed in the well-known vapor-liquid-solid model. Comparison of different catalysts reveals that this process is strongly favored when Ni is present.

Laser-induced incandescence: Particulate diagnostics for combustion, atmospheric, and industrial applications

“…For example, with the use of CW lasers in this process for the ablation of carbonaceous material from a solid target, the resulting thermal radiation in the plume is analyzed for particle temperature [488,489]. Cau et al [490] reported on the measurement of soot-particle sizes via time-resolved pulsed LII in such a process.…”

Laser-induced incandescence for non-soot nanoparticles: recent trends and current challenges

“…Nevertheless, TiRe-LII shows promise for interrogating this morphology, since signal decay rate is roughly proportional to the heat transfer surface area. Cau et al [ 177 ] interpreted TiRe-LII signals from soot and CNTs using a model developed by Krüger et al [ 191 ] for soot, but without accounting for the morphological differences between these two material types. Mitrani and Shneider [ 179 ] presented a simple heat transfer model for MWCNTs, which accounted for their cylindrical shape and allowed for non-uniform temperatures within the nanomaterial.…”

In situ diagnostics for nanomaterial synthesis in carbon arc plasma

“…The principles of Laser Induced Fluorescence as applied to C2 detection in low temperature plasmas are described in refs. [26][27][28]. Because signal detection is at a different wavelength from the laser wavelength, PLIF is insensitive to scattered laser light, which can be significant in the arc environment.…”