Striations in electronegative capacitively coupled radio-frequency plasmas: Analysis of the pattern formation and the effect of the driving frequency

Yong Xin Liu, I. Korolov, Edmund Schüngel, You Nian Wang, Z. Donkó, Julian Schulze

Research output: Contribution to journalArticle

11 Citations (Scopus)

Abstract

Self-organized striated structures of the plasma emission have recently been observed in capacitive radio-frequency CF4 plasmas by phase resolved optical emission spectroscopy (PROES) and their formation was analyzed and understood by particle in cell/Monte Carlo collision (PIC/MCC) simulations (Liu et al 2016 Phys. Rev. Lett. 116 255002). The striations were found to result from the periodic generation of double layers due to the modulation of the densities of positive and negative ions responding to the externally applied RF potential. In this work, an in-depth analysis of the formation of striations is given, as well as the effect of the driving frequency on the plasma parameters, such as the spatially modulated charged species densities, the electric field, and the electron power absorption is studied by PROES measurements, PIC/MCC simulations, and an ion-ion plasma model. The measured spatio-temporal electronic excitation patterns at different driving frequencies show a high degree of consistency with the simulation results. The striation gap (i.e., the distance between two ion density maxima) is found to be inversely proportional to the driving frequency. In the presence of striations the minimum ( ) ion densities in the bulk region exhibit an approximately quadratic increase with the driving frequency. For these densities, the eigenfrequency of the ion-ion plasma is near the driving frequency, indicating that a resonance occurs between the positive and negative ions and the oscillating electric field inside the plasma bulk. The maximum ion densities in the plasma bulk are found not to exhibit a simple dependence on the driving frequency, since these ion densities are abnormally enhanced within a certain frequency range due to the ions being focused into the 'striations' by the spatially modulated electric field inside the bulk region.

Original languageEnglish
Article number055024
JournalPlasma Sources Science and Technology
Volume26
Issue number5
DOIs
Publication statusPublished - Apr 20 2017

Fingerprint

striation
radio frequencies
optical emission spectroscopy
ions
positive ions
negative ions
electric fields
collisions
simulation
cells
frequency ranges
modulation
electronics
excitation

Keywords

  • capacitively coupled rf plasma
  • ion-ion plasma model
  • PIC/MCC simulation
  • PROES
  • striations, electronegative gas

ASJC Scopus subject areas

  • Condensed Matter Physics

Cite this

Striations in electronegative capacitively coupled radio-frequency plasmas : Analysis of the pattern formation and the effect of the driving frequency. / Liu, Yong Xin; Korolov, I.; Schüngel, Edmund; Wang, You Nian; Donkó, Z.; Schulze, Julian.

In: Plasma Sources Science and Technology, Vol. 26, No. 5, 055024, 20.04.2017.

Research output: Contribution to journalArticle

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