Bulletin of the American Physical Society
61st Annual Gaseous Electronics Conference
Volume 53, Number 10
Monday–Friday, October 13–17, 2008; Dallas, Texas
Session BT3: Dusty Plasmas |
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Chair: Doug Ernie, University of Minnesota Room: Addison Room |
Tuesday, October 14, 2008 8:00AM - 8:15AM |
BT3.00001: Diffraction of Electromagnetic Waves in Dusty Magnetoplasma Andrey Yatsenko, Nikolay Gorobets It is known, that the plasma in an external magnetic field (magnetoplasma) becomes anisotropy. For example, the Earth ionosphere has such properties. It's possible to present the interaction of electromagnetic waves with dusty magnetoplasma as a diffraction of electromagnetic waves on the macroscopic particles located in the anisotropic plasma. This problem solved by a method of the integral equations of macroscopic electrodynamics, constructed on the basis of Green's function for anisotropic magnetoplasma. According to this method, the boundary problem of electrodynamics is represented as internal and external problems. At the first stage the internal problem is solved. The field exciting in every macroscopic particle by an external source of electromagnetic energy is defined. At the second stage the external problem is solved, the complete electromagnetic field is defined which is a sum of an external field and scattering field. The diffraction of electromagnetic waves on linear structures in magnetoplasma is also considered on the basis of the received integral equations. The features of waves dispersion in different frequency ranges, the conditions of a resonance are determined. The dispersal equations are received which establish the accordance between parameters of linear structure and plasma at a resonance. The scattering electromagnetic fields are determined. [Preview Abstract] |
Tuesday, October 14, 2008 8:15AM - 8:30AM |
BT3.00002: Anisotropic interaction forces between two vertical particles in the plasma sheath Jay Kong, Lorin Matthews, Truell Hyde In a GEC reference cell, charged dust grains are levitated above the negative electrode, usually forming horizontal layers in the plasma sheath. Fast-moving ions in the sheath generate wake fields, creating vertical particle chains where the interaction forces between each particle in a pair are generally different due to the wake-field effect. This presentation will focus on an attenuated oscillation method designed to examine the resulting anisotropic interaction forces. This method is based on an experimental technique whereby dust particles are raised to a height $\Delta $h above their natural equilibrium employing an applied DC bias. Removal of this DC bias causes the dust particles to oscillate with attenuated amplitude, eventually returning to their original equilibrium position. The resulting oscillation spectrum displays features unique to the interaction between the particles. Recent experimental results will be presented. [Preview Abstract] |
Tuesday, October 14, 2008 8:30AM - 8:45AM |
BT3.00003: Self consistent modeling of dusty plasma experiments within a GEC reference cell Victor Land, Erica Shen, Lorin Matthews, Truell Hyde CASPER conducts dusty plasma experiments in two GEC cells. Micrometer sized dust particles are introduced from the top. During their fall toward the lower electrode, they collect ions and electrons from the plasma and charge up. Due to the high electron mobility, this charge is negative and the dust particles are trapped in the electric field above the bottom electrode. There, dust structures form, which might be crystalline. To describe these, knowledge of the local plasma parameters is needed. These could be obtained with probes, but these inevitably perturb the plasma and the dust, and probe contamination makes the collected data unreliable. Since the absorption of plasma on the dust changes the plasma, data obtained with probes in dust free plasma doesn't represent the parameters of dusty plasma. In this paper, the results of a self-consistent model that solves the plasma and the dust parameters simultaneously are presented, which aim to support data obtained from experiments, and to provide a better understanding of the forces acting on the dust, and of the changes in the plasma due to the presence of the dust. [Preview Abstract] |
Tuesday, October 14, 2008 8:45AM - 9:00AM |
BT3.00004: Analytical model for the charge and temperature distributions of nanoparticles in a low pressure plasma accounting for ion-neutral collisions Federico Galli, Uwe Kortshagen An analytical model predicting the nanoparticle charge and temperature distributions in a low pressure plasma is developed. The model includes the effect of collisions between ions and neutrals in proximity of the particles. In agreement with experimental evidence for pressures of a few Torr a charge distribution that is less negative than the prediction from the collisionless orbital motion limited theory is obtained. Under similar plasma conditions an enhanced ion current to the particle is found. Ion-electron recombination at the particle surface, together with other particle heating and cooling mechanisms typical of silane-argon plasmas, is included in a particle heating model which predicts the nanoparticle temperature distribution. The effect of plasma parameters on the nanoparticle temperature distribution is discussed and the predictive power of the model is demonstrated against experimental evidence of temperature induced crystallization of silicon nanoparticles. [Preview Abstract] |
Tuesday, October 14, 2008 9:00AM - 9:15AM |
BT3.00005: Spatial distributions of the size and the density of Cu particulates in high--pressure magnetron sputtering plasmas N. Nafarizal, N. Takada, K. Sasaki It has been observed that magnetron sputtering plasmas are sometimes dusty, namely, they contain a large amount of particulates when they are operated at gas pressures higher than $\sim 100$ mTorr. In this work, we evaluated the spatial distributions of the size and the density of Cu particulates in the gas phase of a magnetron sputtering plasma source employing a Cu target. The evaluations of the size and the density were based on Rayleigh/Mie scattering of laser lights at two wavelengths of 457 and 672 nm. The size of particulates was estimated from the ratio of the scattered laser intensities, while the density was evaluated from the absolute intensity of the scattered laser light. A remarkable experimental result was that no Cu particulates were observed in the bright plasma region which was located near the target surface in all the discharge conditions. At an argon pressure of 400 mTorr and a discharge power of 4 W, we observed that the size of particulates in the outside of the bright plasma was relatively uniform, and more than 50\% of particulates have diameters between 120 and 200 nm. On the other hand, the particulate density had a significant spatial distribution. The absolute particulate density ranged between 10$^7$ and 10$^9 $cm$^{-3}$, and it decreased monotonically with the axial distance from the bright plasma. [Preview Abstract] |
Tuesday, October 14, 2008 9:15AM - 9:30AM |
BT3.00006: Complex Plasma with Two Distinct Particle Sizes Bernard Smith, Lorin Matthews, Truell Hyde Dust particle clouds can be found in almost all plasma processing environments including both plasma etching devices and in plasma deposition processes. Dust particles suspended within such plasmas acquire an electric charge from collisions with free electrons in the plasma. If the ratio of inter-particle potential energy to the average kinetic energy is sufficient, the particles will form either a ``liquid'' structure with short range ordering or a crystalline structure with long range ordering. Otherwise, the dust particle system will remain in a gaseous state. The preponderance of prior experiments used monodisperse spheres to form complex plasma systems. In order to determine the effects of a size distribution, multiple monodisperse particle sizes need to be examined to determine the manner in which phase transitions and other thermodynamic properties depend upon the overall dust grain size distribution. In this experiment, two-dimensional plasma crystals were formed from mixtures of 11.9 $\mu $m and 6.50 $\mu $m monodisperse particles in Argon plasma. With the use of various optical techniques, the pair correlation function was determined at different pressures and powers and then compared to measurements obtained for experiments employing a single size distribution of monodisperse spheres. Additionally, vibrational data was examined to determine other dust and plasma parameters. [Preview Abstract] |
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