Emission spectroscopy and size distribution of gas phase nanoparticles generated by laser-based methods

Abstract

Tungsten and iron/carbon composite nanoparticles were generated via ArF excimer laser-assisted CVD from WF 6/H 2/Ar gas mixture and photolytic decomposition of ferrocene (Fe(C 5H 5) 2), respectively. Time-resolved spectroscopic measurements were performed and the emitted black-body-like radiation from these particles, due to the laser heating, was analyzed determining the temperature of the particles. Dominant cooling processes as evaporation and heat transfer by the ambient gases were identified; thermionic emission and black-body-like radiation were found to be negligible. Melting of tungsten and boiling of iron nanoparticles were observed. The size distributions of the particles were found lognormal and it was explained by the residence time approach model, functioning at the limit with no coagulation of the particles. Amorphous carbon nanoparticles were formed via laser ablation of a highly oriented pyrolytic graphite target at 193 nm excimer laser wavelength in N 2 atmosphere at normal pressure. The size distribution of the particles was in situ monitored by a differential mobility analyzer in the size-window of 7–130 nm. Change of size distributions was monitored as the laser fluence was varied. The observed effects are discussed and related to the ablation dynamics. Compositional and structural examinations of deposited particle-films were performed by Raman spectroscopy, X-ray and electron diffraction techniques.