Characteristics Of Microplasma Research Articles

Microplasma characteristics of direct-current atmospheric pressure glow discharge in dependence of gap distance and discharge current

Microplasma at atmospheric pressure has been widely used in many fields due to the lower power consumption, higher plasma density, as well as better uniformity and stability. In this work, the microplasma characteristics of direct current atmospheric pressure glow discharge, including discharge morphology and electrical properties have been investigated with various interelectrode gaps (10–600 μm) and discharge currents (1–6 mA), and simultaneously, a finite element simulation has been conducted to obtain the distribution of the electric field and particle density. The evolution of cathode layer, anode layer and Faraday dark space at this scale was captured with a higher spatial resolution (∼1 μm) for the first time, demonstrating that the cathode layer, especially the cathode sheath rather than the positive column, plays a dominant role in the transition of the microplasma. As the gap shrinks to a size less than cathode layer (∼40 μm), the cathode sheath with a high electric field is compressed, leading to a rapid decrease of the discharge voltage. The discharge voltage remains basically unchanged regardless of the discharge current, because the electric field in the cathode sheath is limited by the accumulated space charge. The experimental results are well verified and explained by the simulation results. This study provides an in-depth understanding of the glow discharge mechanism at microscale, and of the stability of glow discharge at atmospheric pressure, and benefits to future research on the atmospheric pressure large-area microplasma and its related application.

Design of microplasma electrodes for plasma-on-chip devices

Plasma-on-chip (POC) devices have been developed to achieve plasma treatment of individual cells. However, the microcathode of a POC can be easily damaged during plasma firing. In this study, microplasma electrodes for POC devices were designed to enhance the lifetime of plasma electrodes while maintaining their microplasma characteristics. An electrode comprising a 20 nm-thick titanium layer and a 200 nm-thick gold layer on a silicon substrate was fabricated by photolithography and evaporation. Experimental results illustrated that a microelectrode with a blunt-ended cathode and a flat anode can extend the firing lifetime by as much as 30 times that of a double-tip electrode. We also fabricated a 220 nm-thick pure titanium electrode to further extend the lifetime of the electrode. Experimental results showed that the pure titanium electrode can further extend the lifetime 60 fold when compared with an Au / Ti hybrid electrode. However, the voltage requirement for the pure titanium electrode is only 20 V higher than that for the Au/Ti electrode. The pure titanium microelectrode proposed in this study possesses several advantages such as low cost, simple fabrication, and high biocompatibility. Hence, it is highly feasible for POC applications.

Non-destructive control of critical defects and diagnostics of InGaN/GaN heterostructures in power LEDs by using their microplasma characteristics

In this work, we studied the controlled microplasma breakdown of InGaN/GaN heterostructures in power light-emitting diodes (LEDs) prepared on various substrates (SiC, AuSn/Si, Al2O3). It was ascertained that LED microplasma characteristics are related to their functional parameters. It was shown that nondestructive control of the critical defects and diagnostics of the InGaN/GaN power LEDs are possible because they are based on the following parameters of microplasmas: (1) voltage of the first microplasma; (2) current of the first microplasma; (3) amount of the microplasmas; (4) integrated luminescence intensity of the microplasmas; (5) ratio of the blue and yellow band luminescence peak intensities for the microplasmas; (6) displacement between electroluminescence peaks for forward and reverse biases. It was ascertained that the majority of microplasmas arise near the faces of the crystallites’ grain boundaries.

Basic study on force induction using dielectric barrier microplasma array

Kinetic force induction using dielectric barrier microplasma at atmospheric was experimentally investigated in this study. Owing to a micrometer-scale (25 µm) gap, microplasma was generated at only −1.4 kV in atmospheric air. Emission spectrum measurements were determine to identify the microplasma characteristics. Light emission of the N2 second positive system (SPS) was observed. The lifetime of emission signals for the N2 SPS for the microplasma was about 50 ns. SiO2 glass beads of 50 µm diameter were distributed on the surface of an electrode to observe the kinetic force generated by microplasma. Glass bead movements were observed using the Nd; YVO4 laser of 532 nm wavelength and a high-speed camera. When the microplasma electrodes were energized at −1.4 kV, the glass beads moved. Analysis of the obtained photo data showed that the glass beads rose to 5 mm above the microplasma electrodes at a velocity of 1 mm/ms.

Microplasma enhancement via the formation of a graphite-like phase on diamond cathodes

Enhanced electron field emission (EFE) properties in microcrystalline diamond (MCD) films that have been Fe-coated and postannealed are observed. Additionally, improved microplasma characteristics are also observed when these materials are used as cathodes. The turn-on field for inducing the EFE process decreases from 4.7 V/μm for pristine MCD films to 2.2 V/μm for the Fe-coated/postannealed ones, whereas the EFE current density at an applied field of 8.8 V/μm increases from 36.5 to 5327.1 μA/cm2. Transmission electron microscopy, in conjunction with high-angle annular dark field and 3D-tomography studies, reveals that enhanced EFE in the Fe-coated/postannealed MCD films is due to the graphite-like phase on the surface of diamond films. The authors infer that the Fe-coating interacts with the diamond in the postannealing process to dissolve carbons and reprecipitate them in nanographite networks. This process is similar to the formation of carbon nanotubes by the dissolution and reprecipitation of carbon species at the presence of nanosized Fe catalysts. The utilization of high EFE diamond films as cathode materials enhances the microplasma, as the ignition field for initiating the plasma is lowered and a high plasma current density is attainable.

Characterization of inverted pyramidal hollow cathode microplasma devices operating in reactive gases for maskless scanning plasma etching

In the cantilever-based microplasma etching system proposed by our group, the stable discharge characteristics of microplasma device in reactive gases is the foundation of the maskless scanning etching of material. In this paper, the cantilever probe integrated with 100μm2 inverted pyramidal hollow cathode microplasma device and nano-aperture at the hollow tip is successfully fabricated. The electrical and optical characteristics of the dc-driven microplasma devices operating in SF6, CHF3 reactive gases and their mixtures with Ar at different gas pressure are investigated. The etching profile and etching rate for silicon in SF6 microplasma exported from the nano-aperture are simulated to predict the etching effect under maskless microplasma etching system. The results of this paper may lay a foundation for upcoming experiments of maskless scanning plasma etching of silicon and its compounds, and also have implications in microplasma material processing in reactive gases using other devices configuration.

Microcavity Plasma Devices

Traditionally plasma systems have required high operating power, low operating pressure and are relatively large in size, limiting the technology to mostly immobile, large-scale industrial applications. In recent years, microplasma devices have emerged due especially to improvements in microchip fabrication technology. Microplasmas improve on plasma performance, allow for atmospheric operation, permit portability and significantly reduce both the cost of manufacturing and the cost of electrical power. These developments allow for technological improvements in fields such as displays, medicine, alternate energy and chemical analysis. This review will first introduce the concept of man-made plasmas and the distinctive characteristics of microplasmas, then discuss some of the most recent patents of microplasmas with specific regard to devices possessing a microcavity. These patents relate to device types, fabrication improvements and the various applications of microplasma technology.

Two-dimensional particle-in-cell Monte Carlo simulation of a miniature inductively coupled plasma source

Two-dimensional axisymmetric particle-in-cell simulations with Monte Carlo collision calculations (PIC-MCC) have been conducted to investigate argon microplasma characteristics of a miniature inductively coupled plasma source with a 5-mm-diameter planar coil, where the radius and length are 5 mm and 6 mm, respectively. Coupling the rf-electromagnetic fields to the plasma is carried out based on a collisional model and a kinetic model. The former employs the cold-electron approximation and the latter incorporates warm-electron effects. The numerical analysis has been performed for pressures in the range 370–770 mTorr and at 450 MHz rf powers below 3.5 W, and then the PIC-MCC results are compared with available experimental data and fluid simulation results. The results show that a considerably thick sheath structure can be seen compared with the plasma reactor size and the electron energy distribution is non-Maxwellian over the entire plasma region. As a result, the distribution of the electron temperature is quite different from that obtained in the fluid model. The electron temperature as a function of rf power is in a reasonable agreement with experimental data. The pressure dependence of the plasma density shows different tendency between the collisional and kinetic model, implying noncollisional effects even at high pressures due to the high rf frequency, where the electron collision frequency is less than the rf driving frequency.

Application of Microplasma for $\hbox{NO}_{\rm x}$ Removal

In this paper, microplasma is investigated, which occurs between the narrow gap of the electrodes covered with dielectric materials. The discharge gap is set on the order of micrometers by changing a spacer from 0 to 100 mum. In this paper, the characteristics of microplasma, such as discharge voltages, discharge currents, and discharge power that is obtained with the help of Lissajous figures, and the relationships between these electric characteristics are presented. The characteristics of ozone generation by a microplasma electrode are investigated. Treatment by microplasma for the simulated exhaust gas, which contains NOx and C3H8 as a role of HC and CO, is estimated experimentally. In the absence of O2, the exhaust gas is decomposed by nitrogen atomic species in particular. In the presence of O2, it is decomposed by nitrogen atomic species and oxidized by ozone. By-product analysis of treated gases is carried out by Fourier transform infrared spectroscopy and gas chromatography-mass spectrometry. When HC, NOx, and N2 are included in the simulated exhaust gas, HCN, N2O, and CH4 are confirmed as by-products of the microplasma treatment.

Comparison analysis of formation and some characteristics of microplasma coatings on aluminum and titanium alloys

The electrolyte and parameters of high-voltage anodic-cathodic process, which enable one to apply rather thick (to 340 μm) oxide coatings to titanium alloys, are selected. Characteristics of the coating formation on aluminum and titanium alloys are compared. It is found that, on the titanium alloys, the stage of microarc discharges occurs only at relatively high anodic and cathodic components of the current density. The voltage chronograms and oscillograms also have pronounced specific features.

Microcavity plasma devices and arrays: a new realm of plasma physics and photonic applications

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.

ミクロ反応場の生成と応用 -マイクロプラズマ研究の現状と将来展望- 4.マイクロプラズマの応用

In addition to generation and diagnostics of microplasma, application studies of microplasmas have been performed intensively. Based on the unique characteristics of microplasmas, such as an extraordinary locality and high density, developments of various new application technologies are in progress. Those include, e.g., novel materials processing, biomaterials treatment, chemical analysis, light sources of ultra-short wavelengths, three-dimensional micromachining tools and other functional plasma devices. In this chapter, an overview of our studies mentioned above on the applications will be introduced.

Non-spectral and spectral interferences in inductively coupled plasma high-resolution mass spectrometry : Part I. Optical characteristics of micro-plasmas observed just behind the sampler and the skimmer in inductively coupled plasma high resolution mass spectrometry

In order to explain the mechanism of matrix effects in inductively coupled plasma high resolution mass spectrometry (ICP-HRMS), physical properties of micro-plasmas observed just behind the sampler and the skimmer of the MS interface were measured with an optical fiber system. The optical fiber system showed: some remarkable differences between emission characteristics observed behind the sampler and behind the skimmer; band emission of polyatomic species; and spatial distribution of Ar emission lines. In the micro-plasma behind the sampler, band emission due to water (OH and H2O+) was strong and the excitation temperature for Ar (Ar Tex) was 3230 K, while, in the micro-plasma behind the skimmer, extensive N2 band emission was observed and the Tex value was 8120 K. An accelerating voltage added to the MS interface was the most important parameter affecting physical properties and ionization efficiencies of the analytes. In the micro-plasma behind the sampler, all of the temperatures obtained experimentally, Ar Tex, rotational temperature for OH and ionization temperature for Mg, were independent of the accelerating voltage. Ar Tex and the vibrational temperature for N2 decreased with an increase in the accelerating voltage in the micro-plasma behind the skimmer. Also the accelerating voltage affected the formation of polyatomic ion species, because weakly bound polyatomic ion species such as ArX+ were formed in the micro-plasma after the sampler through collision-induced reactions of neutral Ar with X+. Theoretical dissociation equilibrium temperatures for ArX+ showed a tendency to decrease with increasing accelerating voltage, showing the same trend as the observed plasma temperatures in the micro-plasma, not after the sampler but after the skimmer.