AVS2004 Session PS-ThM: Atmospheric and Microdischarges

Thursday, November 18, 2004 8:20 AM in Room 213A

Thursday Morning

Start	Invited?	Item
8:20 AM	Invited	PS-ThM-1 Atmospheric and Micro Discharges J.K. Lee, S.S. Yang, M. Radmilovic-Radjenovic, S. Mukherjee (Pohang University of Science and Technology, South Korea) Plasma display panels (PDPs) are micro discharges, operated at high pressures of 400-500 Torr. Using 2-D kinetic simulation code (XOOPIC), we calculated incident angle and energy distributions of ions on the cathode surface in a PDP cell. Kinetic results show that in a coplanar-type PDP cell, most ions impinge on the MgO surface at the cathode region with the incident angle in the range of 10~30 degrees¹ from normal with energies below 50 eV and two temperatures 5 and 50 eV. The calculated electron temperature at the anode striation² region is lower than that between the striation bunches and ranges from 0.5 to 2 eV. We operated the panel at pressures in atmospheric range to study the distinction in the characteristics of the discharge. At a constant pd value by increasing pressure p (in the atmospheric pressure range) and reducing gap length d, we observed similar discharge characteristics to the conventional PDP. We also investigated the difference in the discharge characteristics in the presence and absence of radiation trapping³ and dimers by our 2-D and 3-D fluid simulations and the Paschen breakdown characteristics of microdischarges at high pressures. ¹ S.S. Yang, J.K. Lee, et al., Contri. to Plasma Phys. (to appear in 2004). ² C.H. Shon and J.K. Lee, Phys. Plasmas 8, 1070 (2001). ³ H.C. Kim, S.S. Yang, and J.K. Lee, J. Appl. Phys. 93(12), 9516 (2003).
9:00 AM		PS-ThM-3 Gas and Electrode Temperatures in Non-equilibrium Atmospheric Pressure Plasma with Microwave Excitation M.N. Nagai (Nagoya University, Japan) Gas and Electrode Temperatures in Non-equilibrium Atmospheric Pressure Plasma with Microwave Excitation Plasma processing is the most attractive industrial technology because etching, deposition, or synthesis processings of materials are able to be performed at the low temperature. Recently, atmospheric pressure non-equilibrium plasmas expand the application in not only conventional but also new industrial and science fields. To produce non-equilibrium plasmas, several attempts have been proposed, such as corona discharges and dielectric barrier discharges. The neutral gas temperature is one of the most important plasma parameters for producing non-equilibrium atmospheric pressure plasma. The gas temperature measured gives us the information concerning the chemical reaction in the plasma such as combination and elimination reaction. Excess high gas temperature causes the evaporation of electrodes for producing the plasma, and the melting of materials by the plasma irradiation. In this study, non-equilibrium atmospheric pressure plasma was successfully produced in N₂, Ar, or He gas using a dielectric barrier micro-gap plasma with microwave excitation. We investigated effects of pulse discharge and electrode temperature on gas temperature. We measured gas temperature by N₂ optical emission of the second positive band system and electrode temperature by blackbody emission. It was found that the short pulse modulation of microwave power and water-cooled electrode were effective for reducing the gas temperature. The pulse discharge decreased the gas temperature from 900 K to 600 K, and the water-cooled electrode decreased the gas temperature by more than 200 K. Controlling of the electrode temperature was one of the most effective techniques to reduce the gas temperature because the gas temperature was in equilibrium with the electrode temperature.
9:20 AM		PS-ThM-4 Characterization of the Cold Atmospheric Plasma Hybrid Source L. Bardos, H. Barankova (Uppsala University, Sweden) Parameters of the Hybrid Hollow Electrode Activated Discharge (H-HEAD) source for cold atmospheric plasma applications will be described. The source with a simple cylindrical electrode terminated by a gas nozzle combines the microwave antenna plasma with the hollow cathode plasma generated inside the nozzle by pulsed DC power. The source is capable to produce over 15 centimeters long plasma plume at less than 500 sccm of the argon flow in open air and the microwave power of 500 W (2.4 GHz). Parameters of the hybrid plasma are controlled by both the microwave power and the power delivered to the hollow cathode. An anomalous effect of local maximum in the length of plasma plume at low gas flows is described. Results of the optical emission spectroscopy in argon and neon and electrical parameters of the hybrid discharge will be presented.
9:40 AM		PS-ThM-5 Diagnostics of High Pressure DC Helium Microplasma Discharge Q. Wang (University of Houston); I. Koleva (University of Sofia, Belgium); D.J. Economou, V.M. Donnelly (University of Houston) Gas and plasma diagnostics were performed in a slot-type DC microplasma (200 microns gap) discharge at high pressures. The gas temperature in a helium discharge was estimated by adding small quantities of nitrogen (<100 ppm) into the gas feed. Specific vibrational bands (v'v"), namely (1,3), (0,2) and (1,4) of the N₂ second positive system, were carefully selected to avoid interference with emission from He atoms and He₂ excimer. At 250 Torr pressure and 200 mA/cm² current density, the gas temperature was T_g = 350 ± 25 K. The measured gas temperature was almost independent (to within experimental uncertainty) of pressure (in the range of 150 Torr - 600 Torr), and current density (in the range of 100 mA/cm² - 400 mA/cm²). These measurements were consistent with a simplified heat transfer model. Spatially resolved measurements of electron temperature were also performed using trace rare gas optical emission spectroscopy (TRG-OES). These measurements are greatly complicated by collisional quenching at the high operating pressures. Electron density and electron temperature profiles was deduced by comparing emission intensities from the Paschen 2p_x (x = 1-10) manifold of Ne, Ar, Kr and Xe trace gases. Results suggest that the electron temperature peaks in the cathode sheath region, while the plasma density peaks away from the cathode sheath. A self-consistent fluid model of a DC helium microdischarge was in agreement with the experimental data. Work supported by DOE/NSF.
10:00 AM		PS-ThM-6 Atmospheric-pressure Microdischarges as Short-residence Time Reactors for Silicon Nanoparticle Synthesis R.M. Sankaran, D. Holunga, R.C. Flagan, K.P. Giapis (California Institute of Technology) Microdischarges are investigated as short-residence time reactors for the synthesis of nanoparticles. The application is attractive since nucleation and growth can be limited in the reaction zone, while charging of particles in the plasma may reduce coagulation downstream. We report here on the gas-phase synthesis of silicon nanoparticles in an atmospheric-pressure dc microdischarge. The discharges are formed in silane/argon gas mixtures between a metal capillary tube (d=180 microns) that serves as the cathode and an anode tube of larger size. Incorporation of gas flow through the discharge results in a continuous production of aerosol particles which are size classified in situ using a radial differential mobility analyzer (RDMA). Based on their electrical mobility, the particles were found to possess relatively narrow distributions (σ_g=1.3-1.5) with mean sizes between 2 and 5 nm depending on reactor conditions. Electrical measurements after synthesis in the microreactor show that the particles are charged both negatively and positively. To further characterize the particles, the aerosol stream is bubbled into solvents directly after synthesis in the microreactor. These colloidal dispersions exhibit strong blue photoluminescence with maximum intensity at 440 nm (2.8 eV). Atomic force microscopy on solutions drop cast on silicon substrates have verified that the particles are as small as 2 nm. In this talk, we will discuss features of this new synthesis technique including effects of discharge conditions on particle growth and optical properties.
10:20 AM		PS-ThM-7 Comparison of Atmospheric Pressure Helium Plasmas Operating in the Abnormal Glow and Recovery Modes R.F. Hicks, X. Yang, M. Moravej, G. Nowling (University of California, Los Angeles); S. Babayan, J. Penelon (Surfx Technologies) The properties of a radio-frequency atmospheric pressure plasma fed with helium and nitrogen were investigated. Two discharge modes were identified with current-voltage measurements and optical emission spectroscopy. After the discharge was struck, the plasma entered an abnormal glow regime with a maximum power density of 4.8 W/cm², corresponding to a current density and voltage of 0.73 A/cm² and 317 V. Further increasing the power caused the plasma to shift into a new "recovery" mode with a dramatic reduction of current and voltage and a surge in power to 416 W/cm². This transition is attributed to sheath breakdown. The spatial emission intensity between the electrodes in the abnormal glow reached a maximum 0.25 mm away from the electrodes. In contrast, the recovery mode exhibited maximum emission intensity at the edge of the electrodes, with an intensity 200 times higher than that of the abnormal glow. The neutral gas temperature measured in the abnormal and recovery modes equaled 75 and 250 °C, respectively. The density of nitrogen atoms produced in the plasma was determined by measuring the temporal decay rate of the first-positive emission of nitrogen molecules, i.e., N₂(B) ^__> N₂(A) + hν. It was found that with 0.4 vol.% N₂, the abnormal and recovery modes produced 1.0x10¹⁶ and 1.7x10¹⁶ cm^-3 N atoms at maximum power densities of 4.8 and 416 W/cm², respectively. These results indicate that the abnormal glow is more efficient at dissociating molecules into reactive species. A thorough discussion of the physics and chemistry of the atmospheric pressure plasma will be provided at the meeting.
10:40 AM		PS-ThM-8 Atmospheric He-O₂ DBD Plasma for Steel Decontamination E. Michel (Universite Libre de Bruxelles, Belgium); E. Silberberg (Arcelor Group); F. Reniers (Universite Libre de Bruxelles, Belgium) The use of a DBDs allows the stabilization of cold plasmas at atmospheric pressure which are of a great interest for industrial surface treatments because they do not request expensive vacuum systems. Contrary to wet treatments traditionally used to clean steel surfaces, the plasma treatments are environmental friendly, as they do not produce toxic waste. Standard steel surfaces were covered with various amounts of oil using dip coating. The contaminated surfaces were treated using atmospheric pressure plasma in a DBD. In our configuration, the hot electrode only is covered with the dielectric, whereas the other electrode being the sample. Voltages between 1 to 4 kV were applied between the electrodes, at a frequency varying between 5 and 30 kHz. The plasma gas consisted in a mixture of He-O₂ (2 to 10 % oxygen), at atmospheric pressure. The plasma chemistry was characterized using optical emission spectrometry (OES). The electrical characteristic of the plasma were recorded as a function of the applied voltage, frequency and gas composition. The transition parameters between the homogenous glow discharge and the filamentary one were established for our configuration. The kinetics of decontamination was studied by Auger electron spectroscopy (AES) and infrared spectroscopy (IRRAS- FTIR). The effect of the frequency, the applied voltage, the discharge current, the initial amount of contamination and the plasma gas composition on the kinetics of oil degradation was studied and discussed. The resulting surface state of steel was investigated using AES and X-ray photoelectron spectroscopy. Finally, a macroscopic model for the kinetics of decontamination of steel surfaces by He-O₂ atmospheric plasmas is proposed.
11:00 AM		PS-ThM-9 Line Plasma Generation of Microwave Employing Narrow Width Waveguide T. Fukasawa (Tokai University, Japan); S. Fujii (ADTEC Plasma Technology Co., Ltd., Japan); H. Shindo (Tokai University, Japan) Line plasma over 40 cm in length has been required for large area plasma processing at relatively higher pressure or atmospheric pressure. The line plasma will be applied to surface treatment of rolled organic thin film; furthermore, processing of large area flat panel such as large area LCD. The width of conventional rectangular waveguide is about 10 cm, therefore wavelength(λg) in the waveguide is about 15cm. However, the λg is increased with the decrease of the width of the waveguide. λg = λ/√(1-λ/2W)². λ is wave length in free space and W is width of the waveguide. We manufactured very narrow rectangular waveguide, whose inner widths are 63.5mm, 61.8mm and 61.5mm, respectively. Length and inner thickness of the waveguide are 500mm and 5mm respectively. 2.45 GHz microwave was introduced to the narrow waveguide through TE mode rectangular waveguide (BRJ-2), three-stub tuner and rectangular tapered waveguide. Electric field in the narrow waveguide was measured using electric probe. Measured λg was corresponded to the above-mentioned formula. λg was over 1m at the waveguide width of 61.5mm. A slit was made on the side of the wave-guide of 400mm in length and 1mm in width. A quartz tube was set on the slit, whose inner diameter and outer diameter were 3mm and 4mm, respectively. Length of the quartz tube was 400mm. He gas was introduced into the quartz tube. Pressure was measured by capacitance manometer. At the microwave power of 200W, some sections were observed corresponding to wavelength of microwave in free space. At the microwave power of 1kW, however, uniform optical emission intensity was achieved. Optical emission spectrum (OES) intensity at the wavelength of 656nm was measured in order to measure the distribution of electron density in the quartz tube. At the microwave power of 1kW, uniformity of the OES intensity was +-8.4%.
11:40 AM		PS-ThM-11 Atmospheric Pressure Plasma Liquid Deposition - A New Route to High Performance Coatings S.R. Leadley, L. O'Neill, L.-A. O'Hare, A.J. Goodwin (Dow Corning Ltd., Ireland) Plasma enhanced coating processes are well known as a route to well adhered, conformal, high performance coatings. Dow Corning Plasma Solutions has developed a new coatings approach, which was invented in collaboration with the Department of Chemistry of the University of Durham, UK. Atmospheric Pressure Plasma Liquid Deposition combines atmospheric pressure glow discharge (APGD) technology with a unique precursor delivery system. This process operates at atmospheric pressure and ambient temperature allowing the use of a wide range of liquid precursors. The plasma causes polymerization of the precursor so that it is deposited as a conformal, well-adhered thin-film coating, which retains all the functionality and value of the original liquid monomer precursor. This technology retains flexibility with respect to process chemistry and the capability to deliver a vast range of surface functions through the mixing and matching of precursors. The aim of this presentation is to introduce the technology behind this new process and show examples of coatings that have been prepared using mixed monomers, so that the properties of the coating can be tailored.