Abstract View
Understanding the Depletion of Electron Density in Dusty Plasmas at Atmospheric Pressure
NABIEL H ABUYAZID, Xiaoshuang Chen, Davide Mariotti, Paul D Maguire, Christopher J. Hogan, R Mohan Sankaran, University of Illinois
Abstract Number: 574
Working Group: Dusty Plasma
Abstract
Dust formation in plasmas, once an undesired phenomenon, is now relatively well-established for the gas-phase synthesis of stabilizer-free, high-melting point nanoparticle materials including carbon and silicon.[1] These complex multiphase systems are characterized by two-way interactions between plasma species and the precursor vapor and nucleated particles. For example, it has been shown that nanoparticles preferentially obtain a negative charge because of the higher mobility of electrons as compared to ions, which leads to a decrease in the electron density and other effects on the plasma.[2] However, many of these studies have focused on low-pressure plasmas where the concentrations of nanoparticles and plasmas species as well as the nature of plasma-particle interactions may be very different from those at atmospheric pressure.
Here, we present a combined experimental and modeling study of nanoparticle-containing plasmas at atmospheric pressure. A tandem plasma system was set up consisting of a RF-powered plasma to nucleate and grow carbon nanoparticles from hexane vapor, and a second, identical plasma where the particles were introduced. On-line, non-contact diagnostics were applied to both plasmas including ion mobility spectrometry to measure particle size distributions, electrical conductivity to obtain electron density, and optical emission spectroscopy to obtain gas temperature, electron density, and electron temperature. A constant number Monte Carlo (CNMC) simulation was developed to predict nucleation and growth in the first plasma and particle charging in the second plasma. Nanoparticle formation was confirmed both experimentally by IMS measurements and by CNMC simulations in the first plasma. Electrical conductivity and spectroscopic measurements show that there is an observable electron depletion in the second plasma when the particle-laden flow from the first plasma is introduced. However, control experiments supported by simulations reveal that the main contribution to electron depletion is a molecular vapor species that is either unreacted precursor or a reaction byproduct. Based on these results, we present a unifying picture for particle charging in a plasma at different pressures that shows that at atmospheric pressure, in contrast to low pressure, the electron density in the plasma is too high relative to the particle concentration for the particles to have a significant impact.
[1] Kortshagen, Sankaran, Pereira et al., Chem. Rev. 2016
[2] Woodard, Shojaei, Berrospe-Rodriguez et al., J. Vac. Sci. Technol. A 2020