The effects of gas dilution on the nanoparticles nucleation in a low pressure capacitively coupled acetylene discharge

Abstract

The effects of gas dilution on the chemistry of macromolecules and nucleation of nanoparticles in a low pressure radio-frequency acetylene discharge are investigated by employing a self-consistent, one dimensional multi-fluid model. Ar, He, and H2 are used for the dilution with different percentages, keeping the total gas inlet constant. The results of numerical simulations showed that the nucleation rate decreases monotonically with H2 fraction, when the plasma is diluted in hydrogen. But, for Ar and He diluted plasmas, the nucleation increases with increasing of the dilution up to 40%, and then declines. Diluting acetylene in Ar increases the electron number density and consequently the rate of electron impact hydrocarbon dissociation, the latter in turn leads to a more effective polymerization and nanoparticle nucleation. Radicals are identified as the most important species during the nucleation process and their number density is always higher in Ar diluted plasma than the other two.

Effects of process conditions on the chemistry of an Ar/C2H2 dust‐forming plasma

“…The experiments also revealed that the formation of dust particles in Ar/C 2 H 2 plasmas is accompanied by a decrease of the electron and acetylene densities and by an increase of the electron temperature and the density of metastable argon atoms . Numerical simulations of the nucleation of nanoparticles in C 2 H 2 and Ar/C 2 H 2 plasmas showed that positive and negative ions, as well as hydrocarbon radicals, may take part in the initial stage of particle formation …”

“…We also assume that the plasma contains negative ions C 2 H − with density n − although not measured in our experiment due to mass spectrometer limitations and complexity in extracting negative ions from the positive plasma glow. At large ratio of the argon atom density to that of acetylene molecules, the anions C 2 H − are the dominant negative ions …”

“…In the past two decades, plasmas used for the formation of carbonaceous dust particles have been intensively investigated both by experimental measurements and numerically . The experiments have shown that dust particle growth strongly depends on the concentrations of C 2 H − ions, which are supposed to act as the main species for the initiation of dust formation and C 2 H neutral radicals .…”

“…[11][12][13] In the past two decades, plasmas used for the formation of carbonaceous dust particles have been intensively investigated both by experimental measurements [11][12][13][14][15][16][17][18][19][20][21] and numerically. [21][22][23][24][25][26][27][28] The experiments have shown that dust particle growth strongly depends on the concentrations of C 2 H − ions, which are supposed to act as the main species for the initiation of dust formation [11] and C 2 H neutral radicals. [16] The experiments also revealed that the formation of dust particles in Ar/C 2 H 2 plasmas is accompanied by a decrease of the electron and acetylene densities and by an increase of the electron temperature and the density of metastable argon atoms.…”

“…[16][17][18][19][20] Numerical simulations of the nucleation of nanoparticles in C 2 H 2 and Ar/C 2 H 2 plasmas showed that positive and negative ions, as well as hydrocarbon radicals, may take part in the initial stage of particle formation. [22][23][24][25][26][27] The experiments on nanoparticle growth have also revealed that growth is possible only at certain process conditions (pressure, discharge power, input gas fluxes, etc.). Varying the conditions can affect the internal plasma parameters as the electron, ion and neutral densities, and the electron energy distribution function (EEDF).…”