Dynamics of Silicon Nanoparticle Synthesis by Pulsed Laser Ablation

Abstract

Si nanoparticles have been synthesized by ablating a Si target in Ar with 355 nm laser radiation. The nanoparticle size distribution has been determined in real time by laser-induced time of flight mass spectrometry. Under these conditions, nanoparticles that are formed in 1.0 and 2.0 Torr of background Ar gas exhibit log-normal size distributions with most probable diameters of 2.6 and 3.0 nm, respectively. The speed distribution of the nanoparticles has been determined by varying the time delay between the ablation and photoionization lasers. The results indicate that the most probable speed of the nanoparticles, after formation and a 25 mm drift in background Ar, is 100 m/s. Finally, there is a deviation of the size distribution from the log-normal distribution at small nanoparticle sizes. This is attributed to multiple ionization of the nanoparticles. Confirming evidence for multiple ionization is provided by the atomic and mass spectra which show peak broadening due to Coulomb explosion.