| AVS 66th International Symposium & Exhibition | |
| Plasma Science and Technology Division | Thursday Sessions |
| Session PS-ThM |
| Session: | Plasma Diagnostics and Sources II |
| Presenter: | Austin Woodard, University of California, Riverside |
| Authors: | A. Woodard, University of California, Riverside L. Mangolini, University of California, Riverside K. Shojaei, University of California, Riverside C. Berrospe, University of California, Riverside |
| Correspondent: | Click to Email |
Dusty plasmas are characterized as plasmas containing micro- to nano-sized particles. Probing the plasma physics inherent in these systems is a daunting, but critical, task necessary for the engineering design and optimization of many common-place industrial manufacturing processes utilizing plasma, such as thin film etching and fabrication. We present the development of a test-bed for the characterization of dusty plasmas via a simple Langmuir probe. This diagnostic tool allows for the precise determination of the electron energy distribution function (EEDF) and subsequent plasma parameters but is notoriously difficult to use in dust-forming chemistries due to the inevitability of an insulating coating. To combat this, we have designed a two-stage reactor scheme that overcomes this limitation. In the first plasma reactor, the particle production cell, we synthesize graphitic carbon nanoparticles from the complete dissociation of acetylene, confirmed by a residual gas analyzer, which are then directly injected into the primary chamber volume. The quality of the measurement is minimally affected by the presence of a graphitic nanoparticle coating on the probe tip due to its high electrical conductivity, thus creating a more forgiving environment in which to employ this technique. Additionally, the approach has the advantage of decoupling the nucleation and growth-phase kinetics of the nanoparticles from the primary chamber discharge thus allowing us to study the plasma properties when varying processing parameters such as primary plasma power and chamber pressure. Due to the particle trapping induced in the primary plasma, a continues wave laser (532 nm) was used to investigate the actual particle density in the primary chamber volume, and from this, the average charge per particle. The analysis of the EEDF as a function of the plasma parameters highlights the onset of unexpected trends in plasma the properties which are not predicted by traditional OML theory; we observe secondary peaks in the EEDF that change with the processing parameters, indicating not an electronic transition, but a phenomenon directly related to the presence of dust. To investigate this theoretically, we performed simulations with a Boltzmann-solver modified to account for the effect of secondary electron emissions. These simulations also exhibited a secondary peak, at the same energy levels observed experimentally; thus, we tentatively attribute this observation to secondary emission processes directly tied to the floating potential of the particles.