Analysis and application of Silicon Nano-Particles Produced via Continous Flow Non-Thermal Plasmas

Doctor of Philosophy, Graduate Program in Mechanical Engineering
University of California, Riverside, December 2015
Dr. Lorenzo Mangolini Chairperson

Continuous flow non-thermal plasma reactors are being investigated for their ability to efficiently produce high quality nanoparticles. While many nanomaterials can  be  produced  via  continuous  flow  non-thermal  plasma  reactors,  silicon  is  of particular interest, due to its abundance and relevance in many energy related fields. Significant gaps still exist in the understanding of the kinetics responsible for particle growth, structural evolution, and surface termination of continuous flow non-thermal plasma reactor produced particles. Particle interaction with plasma radicals results in the heating of the particles, which in turn affects the kinetics of particle growth, structural evolution, and surface termination during synthesis and processing.  We have investigated the details of plasma-nanoparticle interaction by using in-flight and in-situ  characterization  techniques.  For  the  first  time,  we  have measured  the temperature  of  a  free-standing  particle  immersed  in  a  non-equilibrium  processing plasma.

In  parallel,  we  have  utilized  continuous  flow  non-thermal  plasma reactor-produced nanoparticles to create bulk nanostructured materials.  The ability to tune  size,  structure,  and  surface  termination  of  the  continuous  flow  non-thermal plasma reactor produced nanoparticles allows for significant control of the precursor powders used in the densification processes.  Hot pressing processes allow for the production of samples with bulk-like densities while limiting grain growth, allowing for  the  creation  of  nanostructured  bulk  systems.    Nanostructured  bulk  silicon represents an ideal system to study the role of nano-structuring on transport of charge carriers and phonons in bulk materials. Initial results show that small particle and narrow  particle  size  distributions  allows  for  the  creation  of  bulk  nanostructured silicon  with  high  ZT  values.  This  system  has  shown  to  be  relevant  for  direct conversion of heat into electrical power, but is also a model for the optimization of phonon and charge carrier transport in similar material systems.