Formation studies and controlled production of carbon nanohorns using continuous in situcharacterization techniques

Abstract

The formation of carbon nanohorns by laser ablation was investigated using a scanningdifferential mobility analyzer combined with an ultrafine condensation particle counter. Themeasurement technique provided time-resolved size distributions for the carbonnanoparticles every minute during the course of the production run. The instrumentperformance was reasonably stable most of the time; however, during laser ablation,shockwave oscillations leading to significant transient flow and pressure variations wereshown to disrupt the DMAs ability to measure accurate distributions. On thebasis of the general trend observed in the data taken during the laser-ablationexperiments, we found that the geometric mean diameter of the produced populationshifted to larger particle sizes with increases in pulse width. For a given laserpeak power and repetition rate, carbon nanoparticles of mobility diameter closeto 100 nm were produced in a large abundance using longer laser pulse lengths(e.g., 10 ms) as compared to the shorter pulse lengths (e.g., 1 ms). A quantitativeassessment of the particle size dispersion (using statistics like the geometric standarddeviation) in relation to the laser pulse width could not be done with certaintyas the shockwave disturbances produced by the laser-ablation process causedsignificant disruption to SMPS measurements. When laser ablation was not inoperation, it was found that carbon nanoparticles with mobility diameters centred atabout 20 nm could be produced by thermally desorbing the previously depositedcarbon nanoparticles from the reactor wall at temperatures greater than 1300 K.