Carbon nanotubes (CNTs) can potentially revolutionize the electronics industry. However, the electronic properties of CNTs are sensitive to its chirality. Current techniques produce bundles of nanotubes with a wide variety of chiralities. A better control of the chirality of nanotubes during synthesis is highly desired. A chiral-selective growth of nanotubes requires detailed microscopic knowledge at the early stages of nanotube synthesis. A laser-based in-situ probe of nanomaterials is a prerequisite to understand the nucleation and growth dynamics of nanotubes and eventually to gain control. We report a theoretical analysis showing that Rayleigh scattering could be used to monitor the growth of nanoparticles under arc discharge conditions. We compute the Rayleigh scattering cross sections of the nanoparticles by combining light scattering theory for gas-particle mixtures with calculations of the dynamic electronic polarizability of the nanoparticles. We find that the resolution of the Rayleigh scattering probe is adequate to detect nanoparticles as small as C60 at the expected concentrations of synthesis conditions in the arc periphery. Larger asymmetric nanoparticles would yield brighter signals, making possible to follow the evolution of the growing nanoparticle population from the evolution of the scattered intensity. Observable spectral features include characteristic resonant behaviour, shape-dependent depolarization ratio, and mass-dependent line shape. Direct observation of nanoparticles in the early stages of growth with unobtrusive laser probes should give insight on the particle formation mechanisms and may lead to better-controlled synthesis protocols. In general, such non-intrusive in-situ detection of nanoscale objects is important in a wide range of applications, from contamination and emission control to biosensors and health monitoring systems to flow diagnostics and analysis devices.

• "In situ characterization of nanoparticles using Rayleigh scattering". B. Santra, M. N. Shneider, and R. Car. Scientific Reports (Nature Group) 7, 40230 (2017)