Bulletin of the American Physical Society
63rd Annual Gaseous Electronics Conference and 7th International Conference on Reactive Plasmas
Volume 55, Number 7
Monday–Friday, October 4–8, 2010; Paris, France
Session VF3: Dusty Plasmas II |
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Chair: Laifa Boufendi, GREMI, CNRS-Universite d'Orleans Room: 262 |
Friday, October 8, 2010 4:00PM - 4:15PM |
VF3.00001: The effect of discharge frequency on the charge of dust particles T. Antonova, S.A. Khrapak, C.-R. Du, B. Steffes, H.M. Thomas, G.E. Morfill The effect of varying excitation frequency of a capacitively coupled gas discharge results in certain changing of plasma properties, which can be important for industrial plasma applications as well as for fundamental plasma studies. In this presentation we estimate the influence of the discharge excitation frequency on the charge of dust particles injected externally in the plasma. The experiments are performed in the chamber with two parallel plate electrodes, the upper one is radio-frequency driven and the lower one is grounded. The micrometer sized particles are injected in the discharge and levitate in the plasma sheath near the lower electrode. The particles are illuminated using the diode laser and their positions are recorded by the CCD camera. The experiments are performed in argon gas at pressures of 20, 50 and 80 Pa with the discharge frequencies varied between 13.56 and 200 MHz. The particle charge can be estimated from their positions in the (pre)sheath region using the force balance condition and a suitable model for the pre-electrode sheath area. On the other hand it can be estimated from the balance of electron and ion fluxes absorbed on the particle surface. In order to account for varying discharge frequency we employ frequency dependent Margenau electron velocity distribution. [Preview Abstract] |
Friday, October 8, 2010 4:15PM - 4:30PM |
VF3.00002: The energy distribution of ions impinging on nanoparticles in collisional plasmas Federico Galli, Meenakshi Manunuru, Uwe Kortshagen Plasmas are a versatile source for crystalline nanoparticles. The mechanism by which nanoparticles in a plasma crystallize is not yet fully understood. While selective nanoparticle heating through energetic surface reactions has been proposed as one mechanism, the effect of ions hitting the nanoparticle surface has not yet been explored. A self-consistent molecular dynamics simulation is used here to calculate the ion energy distribution (IED) function of ions impinging on the surface of nanoparticles in low-pressure argon plasmas. The computation includes the effects of resonant charge exchange and elastic collisions between ions and neutrals through a Monte Carlo null-collision method and considers both Maxwellian and non-Maxwellian electron energy distributions. Results show a strong dependence of the IED on pressure. Pressures of 1-10 Torr yield a remarkable reduction in the average ion energy and an enhancement in the ion flux to the surface of the nanoparticles. [Preview Abstract] |
Friday, October 8, 2010 4:30PM - 4:45PM |
VF3.00003: Thermal creep flux in a complex plasma Mierk Schwabe, Sergey Zhdanov, Milenko Rubin-Zuzic, Hubertus Thomas, Gregor Morfill Complex plasmas are plasmas containing microparticles in addition to ions, electrons and neutrals. Under gravity conditions, the microparticles are pulled towards the lower part of the plasma chamber, where they are levitated by the strong electric field in the sheath. In order to perform experiments in the bulk of the discharge, the experimental set-up can either be transported to microgravity conditions (e.g. on board the International Space Station or during parabolic flights), or gravity can be compensated by an additional force. A force capable of compensating gravity is the thermophoretic force, which is the result of a temperature gradient between the upper and lower part of the plasma reactor. The application of a strong temperature gradient, however, has ``side effects.'' One of those effects is that a convection of the neutral gas is induced by the thermal creep effect, which is relevant especially in rarefied gases. We present measurements of this gas convection using microparticles levitated in the plasma and show that thermal creep is relevant in conditions typical for complex plasma experiments. As example for the strong influence of this convection, we show that it can induce a Rayleigh-Taylor instability in the complex plasma fluid. [Preview Abstract] |
Friday, October 8, 2010 4:45PM - 5:15PM |
VF3.00004: Behavior of particles in plasma etching apparatus Invited Speaker: The behavior of particles in a plasma etching apparatus was investigated with an in-situ particle monitor. The properties of particles can be classified into three types according to the particle velocity. Slow-velocity particles (much less than 1 m/s) are trapped by a plasma-sheath boundary and rarely fall on the wafer during plasma discharge. These particles should be removed from the region above the wafer before turning off the plasma. Medium-velocity particles (a few meters per second) travel above the wafer surface due to a balance between ion drag and electrostatic forces during plasma discharge. The number of particles that attach to the wafer can be reduced by supplying wafer bias power. Fast-velocity particles (a few dozen meters per second or more) are generated by the reflection of particles in a turbo molecular pump (TMP), and these may damage the fine photoresist pattern on the wafer by colliding with it. It is therefore important to decelerate the fast-velocity particles by using gas viscous force. [Preview Abstract] |
Friday, October 8, 2010 5:15PM - 5:30PM |
VF3.00005: The Spatiotemporal Evolution of an RF Dusty Plasma: Comparison of Numerical Simulations and Experimental Measurements Steven Girshick, Adam Boies, Pulkit Agarwal, Johannes Berndt, Eva Kovacevic, Laifa Boufendi Nonthermal RF plasmas in which dust particles nucleate and grow have been the subject of many experimental studies, but few comparisons exist with numerical simulations of the spatiotemporal evolution of the nanoparticle-plasma system. In the present work numerical simulations using a 1D self-consistent plasma-aerosol model are compared to experimental measurements of a dusty argon-silane plasma with corresponding operating conditions. Experimental measurements were made of the profiles of both plasma radiative emission and laser light scattering from particles. These were compared to the numerical model, which predicts that neutral gas drag causes the light scattering profile to peak near the grounded electrode, opposite the showerhead gas inlet, while the profile of radiative emission intensity is predicted to behave oppositely, due to the depletion of electrons by nanoparticles. [Preview Abstract] |
Friday, October 8, 2010 5:30PM - 5:45PM |
VF3.00006: Dynamics of Ar* metastables atoms in dust free and dusty argon plasmas Ilija Stefanovic, Brankica Sikimic, Nader Sadeghi, Joerg Winter Generation of nano-sized hydrocarbon particles through RF plasma polymerization of Ar diluted C$_{2}$H$_{2}$ could be suppressed or enhanced by proper plasma-pulsing, depending upon the pulsing frequency. Thus, the processes in afterglow play important role for dust generation. We applied Laser Absorption Spectroscopy to trace the time evolution of metastable density in different gas mixtures: pure Ar, Ar/ C$_{2}$H$_{2}$, Ar/C$_{2}$H$_{2}$/dust and Ar/dust. By introducing C$_{2}$H$_{2}$ in argon plasma, a very fast decay of metastables in the afterglow was detected, caused by a strong quenching rate in Ar* - C$_{2}$H$_{2}$ collisions. From the decay time we deduced that about 98{\%} of C$_{2}$H$_{2}$ was dissociated in the plasma. After formation of the dust particles, the metastable density enhanced and reached the ten time larger density in argon/dust mixture, for the same pressure and input power. The reason is the formation of dusts, which give the additional source of particle losses. These losses are compensated by increasing the electron temperature, thus the ionization rate. [Preview Abstract] |
Friday, October 8, 2010 5:45PM - 6:00PM |
VF3.00007: Nonlinear Oscillations of a Dust Cloud in a rf Plasma Maxime Mikikian, Lenaic Couedel, Marjorie Cavarroc, Yves Tessier, Laifa Boufendi, Olivier Vallee In a plasma, dust particles acquire a negative charge. Thus, a high density of dust particles strongly reduces the free electron density and can drastically alter the plasma equilibrium leading to a wide variety of instabilities (as in electronegative plasmas). One of these instabilities concerns the dust-free region (void) often appearing in the center of the discharge. This void is maintained by two forces of opposite directions and a break in this equilibrium can lead to strongly nonlinear oscillations of the void size. In this presentation we analyze these low-frequency oscillations on the dust cloud and the plasma thanks to high-speed imaging. Correlations are made with the evolution of the discharge current which shows a nonlinear behavior similar to mixed-mode oscillations (MMOs) well-known in other fields like chemistry or neuronal science. We perform an analogy between MMOs in these fields and the ones we obtained. These MMOs are also highly studied through dynamical system theories which can provide a new approach for studying plasma instabilities. [Preview Abstract] |
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