Controlling the size of nanoparticles grown in low pressure plasmas using pulsed power

Low temperature plasmas are a preferred method for synthesizing nanoparticles (NPs) in part due to their ability to produce particles with narrow size distributions.  Particles in plasmas primarily charge negative thereby minimizing agglomeration by mutual repulsive forces.  Current methods for growing NPs in plasmas are fine-tuned to carefully balance operating conditions to achieve control over particle size and composition.  One method that has not been investigated is to use pulsed plasmas to control growth.  During a power pulse, negatively charged NPs can be trapped in the positive plasma potential and grow to a desired size.  In the pulse afterglow, the plasma potential dissipates, NPs discharge, are de-trapped and can flow out of the reactor.  In this work, the impact of pulsing the power on NP growth was computationally investigated and corroborated through experiments.  The growth and trajectories of particles were tracked using a 3D kinetic model (Dust Transport Simulator) under simulated pulsed plasma conditions from a 2D multi-fluid plasma model (Hybrid Plasma Equipment Model).  Silicon NPs grown in Ar/SiH₄ mixtures of a few Torr using inductive power were investigated.  Experiments of pulsed plasmas under similar conditions confirm particle trapping.  Results for particle growth rates, final particle sizes, and the viability of using pulsed plasmas to grow NPs will be discussed