A. Belkind

Time-resolved optical emission spectroscopy of pulsed DC magnetron sputtering plasmas

Reactive magnetron sputtering of dielectrics using pulsed DC power in the frequency range between 5–350 kHz provides a deposition process without arcing. We studied the optical emission spectra of aluminium, argon and oxygen during the magnetron sputter deposition of Al in Ar and the reactive sputter deposition of Al2O3 in an Ar/O2 gas mixture using a fast intensified CCD camera. Time-resolved as well as time-averaged optical emission spectroscopic studies were carried out. The time-resolved studies focused on the temporal behaviour of the various emissions during the decay of the plasma after the power is turned off. Decay times ranging from 1 to 4 µs were observed. A detailed analysis of the various processes that contribute to the emission of a particular emission line and its decay was carried out and an attempt was made to relate the various decay times to the dynamics of, respectively, the decay of the fast electrons, the Ar metastables, the Al atoms (metallic mode) and the O atoms (oxide mode).

Pulsed electrical discharge in bubbled water for environmental applications

Summary form only given. Pulsed electrical discharges are frequently used for generating ozone, hydrogen peroxide, O, H and OH radicals and other chemically active species utilized for water sterilization, decoloration, and decontamination. This study investigates radical production and water purification by electrical discharges in water in the presence of oxygen bubbles. The organic dye, Rhodomine WT at an initial concentration of 200-400 ppb is used as a model compound to access the effectiveness of the cleaning process for several reactor designs and experimental parameters. The rhodomine concentration is determined using fluorescence spectroscopy. Significant reductions in the dye concentrations have been achieved by applying 12-16 kV pulses at a rate of up to 80 Hz to a reactor with horizontal parallel mesh electrodes, 5 mm apart and water flowing and bubbles passing vertically through the electrodes. Several other reactor designs have been investigated. The experiments reported here explore the effect of varying the power delivered to the system, the electrode configuration, the oxygen gas flow rate and solution flow rate, and the initial pH and conductivity of the solution on the decoloration process and on the production of hydrogen peroxide and ozone in the solution. Mechanisms are discussed that are responsible for the importance of the background solution properties such as pH and conductivity on the effectiveness of the production of active species.

Time-resolved investigation of pulsed-DC magnetron reactive plasma

Summary form only given, as follows. DC reactive sputter deposition of dielectric films can be greatly affected by arcing. Observations have indicated that arcing is due to breakdown of the dielectric (oxide) film, which grows on the surface of the metal target as a result of positive charge accumulation. The use of pulsed-DC power in the pulsing frequency range of 20-350 kHz has been employed to reduce or eliminate arcing. Using duty cycles, which could be varied between 50% and 90%, plasma dynamics were studied. The relationships between various deposition process parameters (power, pressure, pulsing frequency, duty cycle, etc.) were studied using time-resolved general electrical, Langmuir probe and optical emission measurement techniques and the results are discussed.

Characterization of the Remote Plasma Generated in a Pulsed-DC Gas-Flow Hollow-Cathode Discharge

In this paper, the remote plasma generated in a pulsed-dc powered gas-flow hollow-cathode discharge in Ar with Al and Cu targets used for reactive sputter-deposition processes was investigated using time-resolved optical emission spectroscopy and Langmuir probe measurements. It was found that the Ar emission intensity during the ldquooff-timerdquo of the discharge cycle decays in two steps: A fast decay due to the initial disappearance of the energetic electrons is followed by a subsequent more gradual decay of the plasma density. The plasma potential reaches the highest positive values in the system during the ldquo off-time.rdquo A capacitive current related to the formation of the cathode sheath was detected at the beginning of the ldquoon-timerdquo of the pulsing cycle. At the beginning of plasma re-establishment, the Ar and Al emission intensity peaks coincide with the peak in the electron temperature. At later times, the Ar and Al emission intensities follow the temporal variations of the discharge current.

Electrical discharges in bubbled water

Summary form only given. Electrical discharges in gas bubbles in water are investigated by applying microsecond long rectangular pulses of 6-20 kV to needle-to-plane electrodes submerged in water. Ar or O2 bubbles; 1-5 mm in diameter, are introduced through the Pt needle that serves as the negative electrode. A bubble remains on the needle through numerous discharge processes. The voltage across the electrodes and the current to the ground are measured. Electrical measurements suggest that a corona-type atmospheric-pressure discharge is ignited in the gas bubble (composed of Ar or O2 gas and water vapor) without the electrical breakdown of the entire water filled electrode gap. The discharge characteristics are investigated as a function of the applied voltage, the distance between the electrodes, the bubbled gas (Ar or O2), the size of the gas bubble, and the pH and conductivity of the water. Optical and electrical measurements are used to explore the properties of the discharge. The size of the bubble as compared to the electrode distance affects the electrical characteristics of the discharge. The liquid water-metal interface and the liquid water-gas interface both play an important role in the initiation and the development of the electrical discharge in the gas bubbles. Evidence from environmental application studies supports the strong dependence of the discharge properties, active species production, and cleaning efficiency on all the parameters mentioned above including the applied voltage, the electrode distance, bubble size, and the initial characteristics of the solution

Environmental Applications of Pulsed Electrical Discharges in Bubbled Water

Summary form only given. Pulsed electrical discharges in water find environmental applications in water sterilization and decoloration due to the production of active species, such as ozone, hydrogen peroxide, O, H, and OH radicals. We investigated the production of active species and the decomposition of organic compounds using electrical discharges between horizontal mesh-to-mesh electrodes in water with Ar or Oxygen bubbles passing vertically through the electrodes. The production of active species was investigated using optical emission spectroscopy and a variety of chemical analytical methods. These methods have been used to investigate Rhodamine decoloration and the production of hydrogen peroxide under varying experimental conditions, such as gas flow rate, solution flow rate, mesh size, distance between the electrodes, and electrical power delivered to the system. The ratio of bubble size to mesh size and the distance between the electrodes affect the type of the discharge. The discharge changes from a streamer-discharge to a spark discharge with streamers propagating along the bubble surface. The spark mode with Ar bubbles was shown to be the most effective in the production of active species and Rhodamine WT decoloration. The following observations are noteworthy: The electrical characteristics of the discharge in DI water resemble those of a barrier discharge. Experiments with SiO2 coated electrodes confirm these similarities.

Optical Emission Spectroscopy of a Pulsed Electrical Discharge in Gas Bubbles in Water

Summary form given only. Pulsed electrical discharges in water have been investigated for water decontamination and decoloration. The optimization of the cleaning process requires detailed knowledge of the discharge process, particularly in terms of the formation of active species such as OH, O, and other radicals. Rectangular voltage pulses of 1 mus duration are applied to single Ar or oxygen bubbles in water and optical emissions from the discharge are studied as a function of applied voltage, power delivered to the discharge, and the total energy supplied or the number of pulses applied to each bubble. Average and time-resolved spectra have been recorded from Ar and oxygen bubbles in various spectral ranges from 285 nm to 880 nm. We observed increases in emission intensity with power for OH and other emissions confirming that the radical formation increases with increasing power. Ar lines and OH vibrational bands were used to determine the electron, vibrational, and rotational temperature in the discharge. Spectra were taken in 200 ns time windows during a single pulse and additional time-resolved information has been obtained using a fast photomultiplier tube with band-pass filters. This information allows us to speculate on the dynamics of the radical production and other processes in the pulsed discharge.

Plasma treatment of a heated diesel/steam mixture for use in ship service fuel cell systems

Summary form only given. Fuel Cell Energy (FCE), Inc. is a leading manufacturer of high-temperature internal reforming fuel cells for distributed power generation. FCE is currently developing a 625 kW power module fueled by naval logistics fuels for ship service applications. The design of this power generator includes provisions for desulfurization of NATO F-76 marine diesel fuel and preparation of methane-rich gas for use in the internal reforming Direct Fuel Cell/sup /spl reg// (DFC/sup /spl reg//). Non-thermal plasma technology provides an attractive alternative to conventional catalytic routes for steam reforming of high molecular weight hydrocarbon fuels such as diesel and naval distillates. The prospects for the development of the compact non-thermal plasma technology for the ship service fuel cell application are currently under investigation. We are using a plasma reactor with a large number of micro-rods, each of which generates a surface discharge that is similar to a dielectric barrier discharge. Each micro-rod consists of an inner conductor of small-diameter, which is connected to the discharge-sustaining high voltage. The inner conductor is surrounded by an insulating dielectric material. A bare wire, tightly wrapped around the insulated conductor, serves as the second electrode, which is typically grounded. A large number of these micro-rods are packed inside the plasma reactor. The surface discharges from the individual micro-rods overlap and form a more or less homogeneous plasma volume. The heated fuel/steam mixture is passed through the plasma reactor either in the direction of the micro-rods (parallel flow) or perpendicular to it (cross flow). Preliminary experiments indicate that this plasma reactor is capable of converting a significant fraction of the complex aromatic hydrocarbons in the diesel vapor into small, aliphatic hydrocarbons (methane, ethane, propane). Further details will be presented at the Conference.