The Experts below are selected from a list of 708 Experts worldwide ranked by ideXlab platform
Jeffrey Hopwood - One of the best experts on this subject based on the ideXlab platform.
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split post dielectric resonator plasma generators
International Conference on Plasma Science, 2016Co-Authors: Zane Cohick, Wei Luo, Douglas E Wolfe, Michael T Lanagan, Jeffrey HopwoodAbstract:Recently, it has been shown that Microplasmas can be generated via the use of split-ring-resonator metamaterial structures. However, it has been suggested that high Q-factors may lead to even more efficient microplasma generation1. This inspired the use of dielectric resonators with high Q-factors to generate plasmas. Unlike all previous plasma generators, dielectric resonator plasma generators may be ideal for interaction with high-frequency electromagnetic radiation since conductor losses can be eliminated or minimized. In addition, the dielectric resonator can enhance the electric field via dielectric contrast. One potential application is to use low-loss dielectrics to generate plasmas which may then act as metamaterials for GHz-THz radiation. The electromagnetic properties of plasmas can be tuned rapidly via changing external parameters such as input power and pressure, which makes them an interesting candidate for tunable metamaterials. We explore the properties of dielectric resonator plasma generators as well as the plasmas which are generated by the resonators. In addition, the use of low work function thin films is explored in order to enhance plasma generation properties and reduce damage to the dielectrics.
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low voltage switchable microplasma arrays generated using microwave resonators
IEEE Electron Device Letters, 2013Co-Authors: Alan R Hoskinson, Pramod K Singh, Sameer Sonkusale, Jeffrey HopwoodAbstract:Microplasmas are generated at atmospheric pressure using an array of microstrip resonators and controlled by diode switches. These Microplasmas are sustained by continuous microwave power, but can be individually switched on and off by applying +2/-5 VDC to the diodes. Each diode allows the capacitance between the resonator and reference electrode to be switched in or out of the circuit, shifting the resonant frequency and modulating power delivered to the microplasma. We present models of the resonator circuit including plasma loading and demonstrate the circuit's efficacy for the addressable control of Microplasmas in a five-resonator array.
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stable linear plasma arrays at atmospheric pressure
Plasma Sources Science and Technology, 2011Co-Authors: Alan R Hoskinson, Jeffrey HopwoodAbstract:A non-thermal microplasma has been intensively investigated because of its ability to generate high electron densities with low gas temperatures, even at atmospheric pressure. This work demonstrates linear arrays of Microplasmas generated in atmospheric pressure argon driven by a series of microstrip resonators. Small arrays of such resonators were previously shown to sustain up to five Microplasmas, but intrinsically weak coupling between resonators is shown to be insufficient to form wider uniform arrays. An electrical connection between each resonator is shown to enhance the coupling among resonators, allowing arrays composed of at least 88 elements that extend 11?cm in width. The application of coupled-mode theory to this system shows good agreement with measurements of microplasma emission intensity as well as with electromagnetic simulations of these devices. Operation of arrays at microwave frequencies allows a nearby ground electrode to participate in the resonance. These findings may allow for future low-cost plasma processing using roll-to-roll techniques at pressures of one atmosphere.
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spatially resolved argon microplasma diagnostics by diode laser absorption
Journal of Applied Physics, 2011Co-Authors: Naoto Miura, Jeffrey HopwoodAbstract:Microplasmas were diagnosed by spatially resolved diode laser absorption using the Ar 801.4 nm transition (1s5-2p8). A 900 MHz microstrip split ring resonator was used to excite the microplasma which was operated between 100–760 Torr (13–101 kPa). The gas temperatures and the Ar 1s5 line-integrated densities were obtained from the atomic absorption lineshape. Spatially resolved data were obtained by focusing the laser to a 30 μm spot and translating the laser path through the plasma with an xyz microdrive. At 1 atm, the microplasma has a warm core (850 K) that spans 0.2 mm and a steep gradient to room temperature at the edge of the discharge. At lower pressure, the gas temperature decreases and the spatial profiles become more diffuse.
J G Eden - One of the best experts on this subject based on the ideXlab platform.
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spatially periodic Microplasmas in complex microchannel networks wall plasma interactions and dynamic behavior
Journal of Physics D, 2019Co-Authors: Jin Hoon Cho, Hong Yang, Sungjin Park, J G EdenAbstract:Wall-plasma interactions have been observed for spatially-periodic Microplasmas generated in 300–700 µm wide channels fabricated in nanoporous alumina. Examination of Ne microplasma discs produced in a standing-wave pattern in Al2O3 channels illustrates the competition between electron production at the sheath-wall interface and loss by recombination in an atmospheric pressure background. Two topologies of the microplasma arrays are observed. For channel widths (d) less than 450 µm, the Microplasmas are generally centered in the channel and sustained by electron generation at both plasma sheath/channel wall interfaces, presumably including the release of charge residing in the hexagonal alumina pores. As d is progressively increased from 300 to 450 µm, the microchannel plasma cross-section is gradually transformed from circular to elliptical, and its surface area declines by as much as 50% so as to minimize e − losses to the background gas. Increasing d above ~450 µm abruptly switches the topology to one in which plasmas having a triangular cross-section attach to one of the channel walls in a pattern that alternates along the channel axis. Microfabricating trapezoidal cross-section channels into complex geometries, including the Cornu spiral and intersecting linear arrays, also reveals dynamic behavior in the propagation of Microplasmas. For a common spiral structure, observations of plasma expansion show the wavefront propagates over the corrugated surface or within the channel with radial and azimuthal velocities of 3 ± 1 km s−1 and 8 ± 1.5 km s−1, respectively. Plasma formation is initiated in each ring of the spiral through electron seeding by streamers propagating radially outward at velocities approaching 200 km s−1. In addition to electrostatic charge-mediated variations in the mean separation between adjacent Microplasmas, the time-dependent interference between two 1D microplasma arrays has been observed during plasma expansion. Reproducible ignition of a microplasma ensemble along ridges micromachined into channels near the intersections of two linear arrays has also been realized. The results reported here demonstrate that microchannels with the walls overcoated with any of a variety of materials provide a promising platform for examining in detail the interaction of low temperature plasma with a surface of arbitrary composition and topography.
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pulsed Microplasmas generated in truncated paraboloidal microcavities simulations of particle densities and energy flow
Journal of Physics D, 2012Co-Authors: Hojun Lee, S J Park, J G EdenAbstract:Microplasmas generated within cavities having the form of a truncated paraboloid, introduced by Kim et al (2009 Appl. Phys. Lett. 94 011503), have been simulated numerically with a two-dimensional, fluid computational model. Microcavities with parabolic sidewalls, fabricated in nanoporous alumina (Al2O3) and having upper (primary emitter) and lower apertures of 150??m and 75??m in diameter, respectively, are driven by a bipolar voltage waveform at a frequency of 200?kHz. For a Ne pressure of 500?Torr and 2??s, 290?V pulses constituting each half-cycle of the driving voltage waveform, calculations predict that ?10?nJ of energy is delivered to each parabolic cavity, of which 26?30% is consumed by the electrons. Once the cathode fall is formed, approximately 65% and 8% of the input energy is devoted to driving the atomic ion and dimer ion currents, respectively, and the peak electron density of ?6???1012?cm?3 is attained ?90?ns following the onset of the first half-cycle (positive) voltage pulse. Specific power loading of the microplasma reaches 150?kW?cm?3 and the loss of power to the wall of the microcavity drops by as much as 24% when the excitation voltage is increased from 280 to 310?V. The diminished influence of diffusion with increasing pressure is responsible for wall losses at 600?Torr accounting for <20% of the total electron energy.
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Pulsed Microplasmas generated in truncated paraboloidal microcavities: Simulations of particle densities and energy flow
2012 Abstracts IEEE International Conference on Plasma Science, 2012Co-Authors: S J Park, J G EdenAbstract:Summary form only given. Microplasmas generated within cavities having the form of a truncated paraboloid, introduced by Kim et al. [Appl. Phys. Lett. 94, 011503 (2009)], have been simulated numerically with a two-dimensional, fluid computational model. Microcavities with parabolic sidewalls, fabricated in nanoporous alumina (Al2O3) and having upper (primary emitter) and lower apertures of 150 μm and 70 μm in diameter, respectively, are driven by a bipolar voltage waveform at a frequency of 200 kHz. For a Ne pressure of 500 Torr and 2 μs, 290 V pulses constituting each half-cycle of the driving voltage waveform, calculations predict that ~10 nJ of energy is delivered to each parabolic cavity, of which 26-30 % is consumed by the electrons. Once the cathode fall is formed, approximately 65% and 8% of the input energy is devoted to driving the atomic ion and dimer ion (Ne2+) currents, respectively, and the peak electron density of ~6·1012 cm-3 is attained ~90 ns following the onset of the first half-cycle (positive) voltage pulse. Specific power loading of the microplasma reaches 150 kW-cm-3 and the loss of power to the wall of the microcavity drops by as much as 22% when the excitation voltage is increased from 280 V to 310 V. The diminished influence of diffusion with increasing pressure is responsible for wall losses at 600 Torr accounting for 20% of the total electron energy.
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confinement of nonequilibrium plasmas in microcavities with diamond or circular cross sections sealed arrays of al al2o3 glass microplasma devices with radiating areas above 20cm2
Applied Physics Letters, 2006Co-Authors: S J Park, K S Kim, A Y Chang, L Z Hua, J C Asinugo, T Mehrotra, T M Spinka, J G EdenAbstract:Arrays of Al∕Al2O3/glass microplasma devices with microcavities having diamond or circular cross-sectional geometries and radiating (active) areas >20cm2 have been operated sealed-off in Ne, Ar, and Ar∕D2 gas mixtures. Microcavities are fabricated in only one of the two electrodes, and the thickness of the completed package is ∼170μm (excluding the quartz output window). Excited by a sinusoidal 20kHz voltage wave form, arrays with active areas of 4.5×3cm2 exhibit ignition voltages as low as 110±5V rms for Ne pressures of 400–700Torr. Mixtures of 1% D2 in Ar at a total pressure of 300Torr produce wavelength-integrated (λ∼250–400nm) intensities of ∼1mWcm−2 over a 25cm2 area. Optical micrographs show the operation of the Microplasmas in two well-defined modes. For current densities below a threshold value (∼53mAcm−2 for 250μm dia. cavities and pNe=400Torr), diffuse uniform plasma is produced in each cavity but, with higher currents, a positive column having near-cylindrical geometry appears, as evidenced by ...
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microcavity plasma devices and arrays a new realm of plasma physics and photonic applications
Plasma Physics and Controlled Fusion, 2005Co-Authors: J G Eden, S J ParkAbstract:The confinement of low temperature, non-equilibrium plasmas to cavities having characteristic spatial dimensions <1 mm is providing new avenues of inquiry for plasma science. Not only is a previously unexplored region of parameter space now accessible, but the interaction of the plasma with its material boundaries raises fascinating questions and opportunities. Other scientific issues that come to the fore include scaling relationships and the collisional processes that become prevalent in a high pressure environment. The general characteristics of Microplasmas, as well as several emerging applications, are briefly described here. With regard to the latter, emphasis will be placed on photonics and, specifically, the demonstration of large (500 × 500) arrays of microcavity plasma devices in Si, the observation of photodetection in the visible, near-infrared and ultraviolet by a microplasma, and the measurement of optical gain in the blue (λ ~ 460 nm) from a linear array of Microplasmas in a ceramic structure.
S J Park - One of the best experts on this subject based on the ideXlab platform.
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pulsed Microplasmas generated in truncated paraboloidal microcavities simulations of particle densities and energy flow
Journal of Physics D, 2012Co-Authors: Hojun Lee, S J Park, J G EdenAbstract:Microplasmas generated within cavities having the form of a truncated paraboloid, introduced by Kim et al (2009 Appl. Phys. Lett. 94 011503), have been simulated numerically with a two-dimensional, fluid computational model. Microcavities with parabolic sidewalls, fabricated in nanoporous alumina (Al2O3) and having upper (primary emitter) and lower apertures of 150??m and 75??m in diameter, respectively, are driven by a bipolar voltage waveform at a frequency of 200?kHz. For a Ne pressure of 500?Torr and 2??s, 290?V pulses constituting each half-cycle of the driving voltage waveform, calculations predict that ?10?nJ of energy is delivered to each parabolic cavity, of which 26?30% is consumed by the electrons. Once the cathode fall is formed, approximately 65% and 8% of the input energy is devoted to driving the atomic ion and dimer ion currents, respectively, and the peak electron density of ?6???1012?cm?3 is attained ?90?ns following the onset of the first half-cycle (positive) voltage pulse. Specific power loading of the microplasma reaches 150?kW?cm?3 and the loss of power to the wall of the microcavity drops by as much as 24% when the excitation voltage is increased from 280 to 310?V. The diminished influence of diffusion with increasing pressure is responsible for wall losses at 600?Torr accounting for <20% of the total electron energy.
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Pulsed Microplasmas generated in truncated paraboloidal microcavities: Simulations of particle densities and energy flow
2012 Abstracts IEEE International Conference on Plasma Science, 2012Co-Authors: S J Park, J G EdenAbstract:Summary form only given. Microplasmas generated within cavities having the form of a truncated paraboloid, introduced by Kim et al. [Appl. Phys. Lett. 94, 011503 (2009)], have been simulated numerically with a two-dimensional, fluid computational model. Microcavities with parabolic sidewalls, fabricated in nanoporous alumina (Al2O3) and having upper (primary emitter) and lower apertures of 150 μm and 70 μm in diameter, respectively, are driven by a bipolar voltage waveform at a frequency of 200 kHz. For a Ne pressure of 500 Torr and 2 μs, 290 V pulses constituting each half-cycle of the driving voltage waveform, calculations predict that ~10 nJ of energy is delivered to each parabolic cavity, of which 26-30 % is consumed by the electrons. Once the cathode fall is formed, approximately 65% and 8% of the input energy is devoted to driving the atomic ion and dimer ion (Ne2+) currents, respectively, and the peak electron density of ~6·1012 cm-3 is attained ~90 ns following the onset of the first half-cycle (positive) voltage pulse. Specific power loading of the microplasma reaches 150 kW-cm-3 and the loss of power to the wall of the microcavity drops by as much as 22% when the excitation voltage is increased from 280 V to 310 V. The diminished influence of diffusion with increasing pressure is responsible for wall losses at 600 Torr accounting for 20% of the total electron energy.
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confinement of nonequilibrium plasmas in microcavities with diamond or circular cross sections sealed arrays of al al2o3 glass microplasma devices with radiating areas above 20cm2
Applied Physics Letters, 2006Co-Authors: S J Park, K S Kim, A Y Chang, L Z Hua, J C Asinugo, T Mehrotra, T M Spinka, J G EdenAbstract:Arrays of Al∕Al2O3/glass microplasma devices with microcavities having diamond or circular cross-sectional geometries and radiating (active) areas >20cm2 have been operated sealed-off in Ne, Ar, and Ar∕D2 gas mixtures. Microcavities are fabricated in only one of the two electrodes, and the thickness of the completed package is ∼170μm (excluding the quartz output window). Excited by a sinusoidal 20kHz voltage wave form, arrays with active areas of 4.5×3cm2 exhibit ignition voltages as low as 110±5V rms for Ne pressures of 400–700Torr. Mixtures of 1% D2 in Ar at a total pressure of 300Torr produce wavelength-integrated (λ∼250–400nm) intensities of ∼1mWcm−2 over a 25cm2 area. Optical micrographs show the operation of the Microplasmas in two well-defined modes. For current densities below a threshold value (∼53mAcm−2 for 250μm dia. cavities and pNe=400Torr), diffuse uniform plasma is produced in each cavity but, with higher currents, a positive column having near-cylindrical geometry appears, as evidenced by ...
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microcavity plasma devices and arrays a new realm of plasma physics and photonic applications
Plasma Physics and Controlled Fusion, 2005Co-Authors: J G Eden, S J ParkAbstract:The confinement of low temperature, non-equilibrium plasmas to cavities having characteristic spatial dimensions <1 mm is providing new avenues of inquiry for plasma science. Not only is a previously unexplored region of parameter space now accessible, but the interaction of the plasma with its material boundaries raises fascinating questions and opportunities. Other scientific issues that come to the fore include scaling relationships and the collisional processes that become prevalent in a high pressure environment. The general characteristics of Microplasmas, as well as several emerging applications, are briefly described here. With regard to the latter, emphasis will be placed on photonics and, specifically, the demonstration of large (500 × 500) arrays of microcavity plasma devices in Si, the observation of photodetection in the visible, near-infrared and ultraviolet by a microplasma, and the measurement of optical gain in the blue (λ ~ 460 nm) from a linear array of Microplasmas in a ceramic structure.
Mg Kong - One of the best experts on this subject based on the ideXlab platform.
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Microplasmas: Sources, particle kinetics, and biomedical applications
'Wiley', 2019Co-Authors: Iza F, Gj Kim, Sm Lee, Jk Lee, Jl Walsh, Yt Zhang, Mg KongAbstract:Thanks to their portability and the non-equilibrium character of the discharges, Microplasmas are finding application in many scientific disciplines. Although microplasma research has traditionally been application driven, Microplasmas represent a new realm in plasma physics that still is not fully understood. This paper reviews existing microplasma sources and discusses charged particle kinetics in various microdischarges. The non-equilibrium character highlighted in this manuscript raises concerns about the accuracy of fluid models and should trigger further kinetic studies of high-pressure microdischarges. Finally, an outlook is presented on the biomedical application of Microplasmas.X11360sciescopu
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Characterisation of a 3 nanosecond pulsed atmospheric pressure argon microplasma
'Springer Science and Business Media LLC', 2010Co-Authors: Jl Walsh, F. Iza, Mg KongAbstract:This study details the generation and characterisation of a 3 nanosecond pulsed atmospheric pressure argon microdischarge, and provides a comparison with a comparable DC microplasma. There is a growing interest in short pulsed excitation of Microplasmas as a gateway to access highly non-equilibrium discharge chemistry that is inaccessible using other excitation mechanisms. By combining time-resolved electrical and optical diagnostics the repetitive 3 nanosecond pulses considered in this study are shown to produce a highly transient plasma with a peak dissipated power above 160 kW and electron densities in excess of 1017 cm-3. During the afterglow period electrons rapidly cool below the excitation threshold suggesting emission from excited argon neutrals should also diminish rapidly. However, argon emissions are observed for several microseconds after each applied pulse, far in excess of their radiative lifetimes. Potential repopulation mechanisms are considered and it is concluded that electron-ion recombination is the most likely repopulation process
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evolution of discharge structure in capacitive radio frequency atmospheric Microplasmas
Physical Review Letters, 2006Co-Authors: J J Shi, Mg KongAbstract:Conventional radio-frequency (rf) nonthermal atmospheric plasmas are generated in a millimeter gap. In this Letter, we present a self-consistent numerical study of rf atmospheric Microplasmas in a submillimeter gap comparable to their sheath thickness. It is shown that the narrow electrode gap deforms the discharge structure, ultimately removing the bulk-plasma region and disabling electron trapping. Significantly, these properties permit rf atmospheric Microplasmas to operate at very high current densities thus simultaneously achieving higher stability and greater chemical reactivity.
Jae Koo Lee - One of the best experts on this subject based on the ideXlab platform.
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electron heating mode transition induced by ultra high frequency in atmospheric Microplasmas for biomedical applications
Applied Physics Letters, 2012Co-Authors: H C Kwon, I H Won, Jae Koo LeeAbstract:The electron heating mode transition induced by ultra-high frequency in atmospheric-pressure Microplasmas was investigated using particle-in-cell simulation with a Monte Carlo collision. Interestingly, this discharge mode transition is accompanied by non-monotonic evolution of electron kinetics such as effective electron temperature, plasma density, and electron energy on the electrode. In this study, the highest flux of energetic electrons (ɛ > 4 eV) usable for tailoring the surface chemistry in atmospheric Microplasmas is obtained at the specific frequency (400 MHz), where an optimal trade-off is established between the amplitude of sheath oscillations and the power coupled to electrons for sub-millimeter dimensions (200 µm).
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Microplasmas: sources, particle kinetics, and biomedical applications
Plasma Processes and Polymers, 2008Co-Authors: Felipe Iza, Jae Koo Lee, Gon Jun Kim, Seung Min Lee, James L. Walsh, Yuantao T. Zhang, Michael G. KongAbstract:Thanks to their portability and the non-equilibrium character of the discharges, Microplasmas are finding application in many scientific disciplines. Although microplasma research has traditionally been application driven, Microplasmas represent a new realm in plasma physics that still is not fully understood. This paper reviews existing microplasma sources and discusses charged particle kinetics in various microdischarges. The non-equilibrium character highlighted in this manuscript raises concerns about the accuracy of fluid models and should trigger further kinetic studies of high-pressure microdischarges. Finally, an outlook is presented on the biomedical application of Microplasmas.
