Nucleation processes leading to Si nanoparticle growth in low temperature flowing plasmas*

Flowing low temperature plasmas (LTPs) are viable alternatives to traditional methods for synthesizing nanoparticles (a few to tens of nms in size) [1].  Nanoparticle (NP) size, composition, and structure are tunable by changing plasma operating parameters (gas composition, pressure, power, and reactor geometry).  NPs in LTPs are synthesized in two stages: (1) nucleation - conception and growth of molecular clusters and (2) growth – agglomeration of clusters or surface deposition.  The stages occur simultaneously, but initial nucleation is necessary.  Nucleation in silane containing plasmas occurs by reactions between anion clusters and neutral or radical Si_nH_m species.  The conditions for the onset of nucleation are not well characterized.  In this work we computationally investigate silicon NP nucleation and growth rates in a flowing LTP.  The Hybrid Plasma Equipment Model (HPEM), a 2D reactor scale multi-physics model, was used to track NP formation processes in a Ar/He/SiH₄ plasma.  Results for trends in silicon NP nucleation and growth as functions of reactor tube diameter, inlet gas composition, pressure, and power are discussed, and compared to experiments for the threshold conditions that produce initial nucleation.

[1]  U. R. Kortshagen. Plasma Chem. Plasma Proc. 36, 73 (2016).