Bulletin of the American Physical Society
72nd Annual Gaseous Electronics Conference
Volume 64, Number 10
Monday–Friday, October 28–November 1 2019; College Station, Texas
Session TF1: Negative-ion and Dust-Particle Containing Plasmas |
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Chair: Larry Overzet, The University of Texas at Dallas Room: Century I |
Friday, November 1, 2019 8:00AM - 8:30AM |
TF1.00001: Plasma Characteristics Revealed Through Dust Dynamics Invited Speaker: Lorin Matthews The plasma characteristics within a sheath near a charged boundary are difficult to determine experimentally, as most probes perturb the sheath structure they are intended to measure. However, micron-sized dust grains can be levitated within the sheath with minimal perturbative effects. The charged dust can self-assemble into ordered structures which are very sensitive to changes in the confining electric fields. The dynamics of the grains can be used to map the forces due to electric fields present in the sheath, but the particle charge and electric field are difficult to measure independently. The problem is further complicated by the ion wake field which develops downstream of the dust grains in a flowing plasma. Here we use a molecular dynamics simulation of ion flow past dust grains to investigate the interaction between the charged dust particles and ions. The charging and dynamics of the grains are coupled self-consistently and derived from the ion-dust interactions. Comparison of the modeled dust-plasma interactions with experimental data allows determination of quantities such as the charge on individual grains, the electric field within the region, the ion density, and the ion flow velocity. [Preview Abstract] |
Friday, November 1, 2019 8:30AM - 8:45AM |
TF1.00002: The charge of single micro-particles in a low pressure spatial plasma afterglow Boy Van Minderhout, Judith Van Huijstee, Antoine Post, Ton Peijnenburg, John Vogels, Paul Blom, Gerrit Kroesen, Job Beckers We have measured the charge of individual micro-particles in the spatial afterglow of an inductively coupled plasma. In our setup micro-particles fall through a spatially limited region of plasma where through interaction with the plasma they are charged. The particle charge is measured using their acceleration in an externally applied electric field. Up to now research has focused on the plasma charging of spherical particles. However in almost all applications particles are not spherical, for which the charging processes can significantly differ from that of single particles. We have developed an \textit{in situ} cluster size detection technique based on the settling velocity of these clusters. Using this method, first cluster charge measurements are presented. We compare our results to an analytical particle decharging model. [Preview Abstract] |
Friday, November 1, 2019 8:45AM - 9:00AM |
TF1.00003: Spores of bacteria treated in dusty plasmas Kazuo Takahashi, Hiroto Tanaka, Rui Togashi, Eigo Ito, Gaetan Herry, Marie Henault, Laifa Boufendi Treating bacteria in plasmas has been focused attention on for this decade from the point of view of developing new sterilization methods in medical and food industries. Regarding the bacteria as small particles, combination of the bacteria and the plasmas leads to a new form of the dusty plasma, which contains electron, ion and massive small particles. This new form is expected to open new applications with help from understanding physics of dusty plasmas. In this study, we observed spores of bacteria injected to a discharge plasma. The plasma was generated by an rf (13.56 MHz) voltage with parallel-plate electrodes. The spores of a kind of bacteria, Bacillus subtilis were levitated in the plasma. It looked like the same as a dusty plasma. The spores were treated on the electrode as well as in the plasma. They were collected after treatment on the surface or in the gas phase. Survival rate of the bacteria treated in the gas phase was found to be lower than that on the surface. The spores on the surface were irradiated by ions through the Bohm sheath. Conversely, those in the gas phase were exposed to the ion flux expressed by the orbit-motion-limited (OML) theory. The ion flux of the OML sheath much larger than the Bohm sheath contributed to efficiently kill the bacteria. [Preview Abstract] |
Friday, November 1, 2019 9:00AM - 9:15AM |
TF1.00004: Particle Decharging and Agglomeration in Pulsed Dusty RF Plasmas Toshisato Ono, Zichang Xiong, Chris Hogan, Uwe Kortshagen The spatiotemporal evolution of dust particles in plasmas is of interest for applications in semiconductor processing and particle synthesis in plasmas. In this work, particle visualization by laser light scattering and ion density measurements by a double Langmuir probe have been conducted carried out in a dusty argon plasmas generated in an RF capacitive reactor. We particularly focus on the particle dynamics in the afterglow of a pulsed plasma. We find that periodic pulsing of the plasma containing micrometer-sized particles leads to particle decharging, and at high particle loadings, rapid particle agglomeration, which is made possible because Coulombic repulsion is minimized upon decharging. A double Langmuir probe was utilized to obtain ion densities through comparison between measured probe characteristics and a model accounting for collisional ion motion. The Pparticle visualization showed that the mechanism of decharging is not simply ion-particle collisions, but may be driven by electron emission, which is material (dielectric constant) dependent. High dielectric constant particles appear to agglomerate significantly less, suggesting they decharge more slowly. [Preview Abstract] |
Friday, November 1, 2019 9:15AM - 9:30AM |
TF1.00005: Kinetic Modeling of Nanoparticle Growth in Low Pressure Dusty Plasmas Steven Lanham, Jordyn Polito, Himashi Andaraarachchi, Zhaohan Li, Zichang Xiong, Uwe Kortshagen, Mark J. Kushner Low pressure ``dusty'' plasmas can be used to synthesize high quality nanoparticles (NPs) from feedstock gases with controllable properties based on operating conditions. Negatively charged NPs can be trapped by the positive plasma potential, enabling growth by collisions with precursors. Understanding the coupled effects between the plasma and particles is fundamental to improving production of nanoparticles. In this paper, we discuss results from a computational investigation of the effects of operating conditions on the growth rate of Si NPs in low pressure plasmas. The Hybrid Plasma Equipment Model (HPEM), a multi-fluid model, was used in the study. Kinetics algorithms which allow for particle growth and subsequent size-dependent forces were incorporated into the Dust Transport Simulator (DTS) to track three-dimensional trajectories and growth of NPs. The demonstration system examines Si NP growth in an argon inductively-coupled-plasma sustained in a flow tube in which SiH$_{\mathrm{4}}$ is injected [1]. Scaling of NP growth rates, agglomeration, particle trapping, and formation of Coulomb solids will be discussed as a function of operating conditions such as pressures, flow rates, and power. [1] U. Kortshagen et al. Chem. Rev. 116, 11061 (2016). [Preview Abstract] |
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