Formation Mechanism of Amorphous Silicon Nanoparticles Synthesized by Induction Thermal Plasma

Department of Chemical Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan

^* Corresponding author: watanabe@chem-eng.kyushu-u.ac.jp

Abstract

This study focus on the synthesis of amorphous silicon nanoparticles and understanding the formation mechanism. Counter-flow quenching gases with different flow rates were injected from downstream of the torch to understand the effect of quenching gas on the formation of silicon nanoparticles. Transmission electron microscopy show that nanoparticles with spherical shape and agglomerates consist of smaller particles were synthesized. X-ray diffraction analysis is used to calculate the amorphization degree, which is defined as fraction of amorphous silicon in the silicon nanoparticles including both crystal and amorphous. The obtained results show that higher quenching gas flow rate leads to smaller diameter with higher amorphization degree. Electron diffraction patterns reveal that nanoparticles with diameter less than 10 nm are amorphous and agglomerated together, while for the nanoparticles with diameter larger than 10 nm are crystal. The formation mechanism of amorphous silicon nanoparticles is explained by estimated nucleation temperature and experimental results. Consequently, silicon nucleates at about 2400 K and then silicon vapor condenses on the nucleus. Finally, smaller nanoparticles will keep amorphous phase, while nanoparticles with a larger diameter grow to form crystalline.