Atmospheric Pressure Micro Research Articles

Mode Transition Induced by Gas Heating Along the Discharge Channel in Capacitively Coupled Atmospheric Pressure Micro Plasma Jets

The effects of neutral gas heating along the direction of the gas flow inside the discharge channel of a parallel plate micro atmospheric pressure plasma jet, the COST-jet, on the spatio-temporal dynamics of energetic electrons are investigated by experiments and simulations. The plasma source is driven by a single frequency sinusoidal voltage waveform at 13.56 MHz in helium with an admixture (0.05–0.2%) of nitrogen. Optical emission spectroscopy measurements are applied to determine the spatio-temporally resolved electron impact excitation dynamics from the ground state into the He I (3s)3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^3$$\\end{document}S1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_1$$\\end{document} state and the rotational temperature of nitrogen molecules at different positions along the direction of the gas flow inside the 30 mm long discharge channel. The gas temperature, which is assumed to be equal to the N2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_2$$\\end{document} rotational temperature, is found to increase along the discharge channel. This effect is attenuated as the nitrogen concentration is increased in the gas mixture, leading to an eventually constant temperature profile. The experimental data also reveal a plasma operating mode transition along the discharge channel from the Ω\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Omega$$\\end{document}- to the Penning-mode and show good agreement with the results of 1d3v kinetic simulations, which spatially resolve the inter-electrode space and use the gas temperature as an input value. The simulations demonstrate that the increase of the gas temperature leads to the observed mode transition. The results suggest the possibility of using the nitrogen admixture and the feed gas temperature as additional control parameters, (i) to tailor the plasma operating mode along the direction of the gas flow so that the production of specific radicals is optimized; and (ii) to control the final gas temperature of the effluent. The latter could be particularly interesting for biological applications, where the upper gas temperature limit is dictated by the rather low thermal damage threshold of the treated material.

Local enhancement of electron heating and neutral species generation in radio-frequency micro-atmospheric pressure plasma jets: the effects of structured electrode topologies

The effects of structured electrode topologies on He/O2 radio frequency micro-atmospheric pressure plasma jets driven at 13.56 MHz are investigated by a combination of 2D fluid simulations and experiments. Good qualitative agreement is found between the computational and experimental results for the 2D spatio-temporally resolved dynamics of energetic electrons measured by phase resolved optical emission spectroscopy, 2D spatially resolved helium metastable densities measured by tunable diode laser absorption spectroscopy and 2D spatially resolved atomic oxygen densities measured by two photon absorption laser induced fluorescence. The presence of rectangular trenches of specific dimensions inside the electrodes is found to cause a local increase of the electron power absorption inside and above/below these surface structures. This method of controlling the electron energy distribution function via tailored surface topologies leads to a local increase of the metastable and atomic oxygen densities. A linear combination of trenches along the direction of the gas flow is found to result in an increase of the atomic oxygen density in the effluent, depending linearly on the number of trenches. These findings are explained by an enhanced Ohmic electric field inside each trench, originating from (a) the low electron density, and, consequently, the low plasma conductivity inside the trenches, and (b) the presence of a current focusing effect as a result of the electrode topology.

Investigation on electrical characteristics of TFTs fabricated with germanium films crystallized by atmospheric-pressure micro thermal plasma jet irradiation

Crystalline germanium (c-Ge) is an attractive material for a thin-film transistor (TFT) channel because of its high carrier mobility and applicability to a low-temperature process. We present the electrical characteristics of c-Ge crystallized by an atmospheric-pressure micro thermal plasma jet (μ-TPJ). The μ-TPJ-crystallized c-Ge showed a maximum Hall mobility of 1070 cm2 V−1 s−1 with a hole concentration of ∼1016 cm−3, enabling us to fabricate a TFT with a field-effect mobility (μ FE) of 196 cm2 V−1 s−1 and an ON/OFF ratio (R ON/OFF) of 1.4 × 104. R ON/OFF and μ FE were dependent on the scanning speed of the TPJ, implying different types of defects were induced in the channel regions. These findings show the possibility of TPJ irradiation as a promising method for making c-Ge TFTs on insulating substrates.

Plasma Enhanced Chemical Vapor Deposition of Hydrogenated Diamond Like Carbon Films by Atmospheric Pressure Micro Plasmas

Plasma Enhanced Chemical Vapor Deposition of Hydrogenated Diamond Like Carbon Films by Atmospheric Pressure Micro Plasmas

2D spatially resolved O atom density profiles in an atmospheric pressure plasma jet: from the active plasma volume to the effluent

Two-dimensional spatially resolved absolute atomic oxygen densities are measured within an atmospheric pressure micro plasma jet and in its effluent. The plasma is operated in helium with an admixture of 0.5% of oxygen at 13.56 MHz and with a power of 1 W. Absolute atomic oxygen densities are obtained using two photon absorption laser induced fluorescence spectroscopy. The results are interpreted based on measurements of the electron dynamics by phase resolved optical emission spectroscopy in combination with a simple model that balances the production of atomic oxygen with its losses due to chemical reactions and diffusion. Within the discharge, the atomic oxygen density builds up with a rise time of 600 µs along the gas flow and reaches a plateau of 8 × 1015 cm−3. In the effluent, the density decays exponentially with a decay time of 180 µs (corresponding to a decay length of 3 mm at a gas flow of 1.0 slm). It is found that both, the species formation behavior and the maximum distance between the jet nozzle and substrates for possible oxygen treatments of surfaces can be controlled by adjusting the gas flow.

Synthesis of Silicone Films Using Atmospheric Pressure Micro Plasma Jet by Rectangular Nozzle with Three Layered Structure

Synthesis of Silicone Films Using Atmospheric Pressure Micro Plasma Jet by Rectangular Nozzle with Three Layered Structure

Formation of reactive chlorine species in saline solution treated by non-equilibrium atmospheric pressure He/O2 plasma jet

The aqueous-phase chemistry of reactive chlorine species initiated in saline solution by the gas phase discharge plasma above the liquid surface was investigated. A micro-atmospheric pressure 13.56 MHz plasma jet operating with a 0.6% O2 in He was used to promote reactions of plasma-generated oxygen atoms with chloride anions at the gas-liquid interface. Physiological NaCl solution and phosphate buffered saline (PBS) were used. Three chlorine oxoacids or their conjugate bases were detected in the plasma treated saline: hypochlorites HOCl/OCl−, chlorites ClO2−, and chlorates ClO3−, being formed in the concentration ratio 4.5:1:1, respectively. In addition, chlorine dioxide ClO2 was formed in minor amounts. The final pH value of the plasma treated saline was typically 10.2. The total hypochlorite production, [HOCl] + [OCl−], was directly proportional to the initial NaCl concentration, supporting the idea of a direct reaction of Cl− with O atoms. Subsequent post-discharge chemical processes in the bulk plasma treated saline solution were found to lead to the disproportionation of hypochlorite into different oxidation states of chlorine with formation of ClO3− as the final product. The reactivity of O atoms in NaCl solution was studied using taurine and phenol as chemical probes. Experiments with 50 mM taurine revealed a very high initial formation rate of OCl− in PBS (up to 4 μM s−1). Chlorinated products of phenol (2- and 4-chlorophenol) in addition to the hydroxylated products (hydroquinone and catechol) demonstrated chlorination of phenol by hypochlorite. The rate of Cl− oxidation by O atoms was estimated to be 2–3 orders slower than the reaction of O atoms with phenol.

Characteristics of Atmospheric Pressure Micro Plasma Jet by Double Coaxial Pipe and Application to Synthesis of Silicone Films

Characteristics of Atmospheric Pressure Micro Plasma Jet by Double Coaxial Pipe and Application to Synthesis of Silicone Films

Effect of Substrate Heating on Formation of Silicone Films Using Atmospheric Pressure Micro Plasma Jets

Effect of Substrate Heating on Formation of Silicone Films Using Atmospheric Pressure Micro Plasma Jets

Application of Atmospheric Pressure Micro Plasma Jets to Formation of Silicone Films

Application of Atmospheric Pressure Micro Plasma Jets to Formation of Silicone Films

Synthesis and spectroscopic characterization of gold nanoparticles via plasma-liquid interaction technique

Fabrication of non-functionalized gold nanoparticles is interesting owing to their potential applications in sensing and biomedicine. We report on the synthesis of surfactant-free gold nanoparticles (AuNPs) by Plasma-Liquid Interaction (PLI) technique, using micro-atmospheric pressure D.C. plasma. The effects of discharge parameters, such as discharge current, precursor concentration and gas flow rates on the structure and morphology of AuNPs have been investigated. Optical Emission Spectroscopy (OES) was employed to estimate the UV radiation intensity and OH radical density. Scanning electron microscopy (SEM) and ultraviolet-visible (UV-Vis) optical spectroscopy were employed to study the morphology and structure of AuNPs. The normalized intensities of UV radiation and OH radical density found to increase with increase in discharge current. We observed that the particle size can be tuned by controlling any of the following parameters: intensity of the UV radiation, OH radical density, and concentration of the Au precursor. Interestingly, we found that addition of 1% Ar in the feedstock gas results in formation of relatively uniform size distribution of nanoparticles. The surfactant-free AuNPs, due to their bare-surface, exhibit excellent surface-enhanced Raman scattering (SERS) properties. The SERS study of Rhodamine 6G using AuNPs as substrates, shows significant Raman enhancement and fluorescence quenching, which makes our technique a potentially powerful route to detection of trace amounts of dangerous explosives and other materials.

Spatially resolved measurements and diagnostics of digitally controlled rotating field pulsed plasma operated in helium at 20 kHz

Using optical emission spectrometry, fundamental properties are investigated of a stable, planar atmospheric pressure micro discharge, several dozen microliters in volume, driven by a digitally controlled 20kHz rotating microsecond pulsed power. The discharge is generated by rectangular wave pulses using helium as the working gas. At a low cost, the digitally controlled plasma source produces a highly symmetrical, non-stationary helium discharge maintained in open air within 5 electrodes positioned in the plane toward the center. It has been shown that the geometrical shapes of the momentary discharges, which occur between the electrodes, are not arc-like shaped, but rather have a diffusive character and the resulting plasma can become doughnut-like in shape.Rotational and vibrational temperatures from OH and N2 bands, excitation temperatures from He lines and ionization temperatures from Ca lines, as well as electron number densities from Hβ Stark broadening have been estimated along the plasma diameter using axial viewing. The results demonstrated that Texc (He) reaches stable value of 3800K for selected plasma generation conditions (one anode and two cathodes commutation mode, cathode pulse width 8 microseconds, supplied power 200W, helium gas flow 1L·min−1), while the Trot (OH) is considerably lower (1700K). The electron number density has been evaluated to be (1.7–3.3)×1014cm−3 and both Tion (Ca) and Tvib (N2) varied, throughout in the 4500–5100K and 4000–4800K ranges respectively, reaching its peak value near 2mm off the plasma axis.Spatial measurements revealed symmetrical distribution of the plasma parameters, while the measurements of calcium and nitrogen ionic emission confirmed symmetrical doughnut shape of the discharge. Moreover, the processes running inside the discharge and their interaction with the surrounding atmosphere have been described in accordance to the recorded spectra. Spectroscopic observation has shown the existence of N2+ molecular ions, although their emission profile differs significantly from neutral N2. Namely, the population of ionic molecules forms a doughnut shape, while the N2 population exhibits disk shape, indicating that plasma ionization zone is located off-axis.

305 大気圧マイクロプラズマジェットの特性に及ぼす同軸二重管構造の効果(OS4-1 熱および物質輸送現象の基礎と応用(1),OS4 熱および物質輸送現象の基礎と応用)

305 大気圧マイクロプラズマジェットの特性に及ぼす同軸二重管構造の効果(OS4-1 熱および物質輸送現象の基礎と応用(1),OS4 熱および物質輸送現象の基礎と応用)

Surface Finishing by Atmospheric Pressure Micro Plasma Beam Irradiation

A metal surface finishing method by micro plasma beam irradiation was examined and presented in this study. Gray cast iron was used as the experimental material to examine the finishing effect by the micro plasma beam. This experimental setup consists of a compressed air system, a plasma torch, and a power supply. The compressed gas was ignited by high voltage direct current pulsed gas discharge and facilitated the generation of plasma, as well as a plasma beam with a maximum diameter of 0.6 mm was used for finishing the metal surface instantly. The experimental results show that it was possible to remove the peak points which exist on the metal surface. It was showed clearly that after the irradiation by the micro plasma beam, the initial rusty and rough surface becomes a clean and smooth surface under a proper finishing condition.

186 同軸二重管を用いた大気圧マイクロプラズマジェットの特性に及ぼすガス種の影響

186 同軸二重管を用いた大気圧マイクロプラズマジェットの特性に及ぼすガス種の影響

Contribution of ions in radio frequency properties of atmospheric pressure microgaps

In this paper, the contribution of ions in RF permittivity and electrical conductivity of atmospheric pressure micro- and sub-microgaps in both pre-breakdown and post-breakdown regimes is investigated. It is shown that ions are ignorable in post-breakdown conditions, while their role becomes significant in pre-breakdown mode especially for gaps on the right side of Paschen's curve. Also, it is demonstrated that the contribution of ions in RF properties increases by decreasing the operating frequency in comparison with ion-neutral collision frequency.

Detection of atomic oxygen and nitrogen created in a radio-frequency-driven micro-scale atmospheric pressure plasma jet using mass spectrometry

In this paper we show mass spectrometry results for a radio-frequency-driven micro-atmospheric pressure plasma jet (μ-APPJ) discharge obtained using a mass analyzer with triple differential pumping allowing us to sample directly in ambient atmospheric pressure environment (Hiden HPR-60). The flow of the buffer gas (mixture of helium and 1% oxygen) was 2 slm and 3 slm and the excitation frequency was 13.56 MHz. We monitored production of atomic oxygen and nitrogen in the plasma for different flows and powers given by the RF power supply. These measurements were made for energies of electrons emitted from the ionization filament below the threshold for dissociation of O2 and N2. In addition to oxygen and nitrogen atoms, yields for O2, N2, NO and O3 are recorded for different powers and gas flows. It is shown that the μ-APPJ is symmetrical and operates in α-mode. The power transmitted to the discharge was below 5 W in all measurements.

J164031 MEMSノズルを利用したマイクロプラズマ照射

Recently, application of the plasma technology in medical fields attracts a number of researcher's attention. Especially, direct plasma irradiation to a cell is thought to be effective reducing doses of medicine Essence of the plasma irradiation depends on how much the plasma irradiation affects a cell in a tissue. Micro plasma is suitable for the above objective because it can be confined in micrometric area and operated at atmospheric pressure. Asano et al. realized an atmospheric-pressure micro plasma source. The micro plasma is generated within a capillary tube(Φ1 mm). Compared to a typical size of a cell (average 10μm), it is still large.za The micro plasma should be shaped to be comparable with the cell size In this research, MEMS nozzles which has holes(diameter:4〜20μm) are fabricated for localizing the plasma irradiation area. The MEMS nozzles are bonded to the end of capillary tubes. The plasma is irradiated onto a sample as the shape of apertures. Onion cell is used as a sample, and it is patterned as ordered circles by the plasmas.

Electron Dynamics in a Radio-Frequency-Driven Microatmospheric Pressure Plasma Jet

Space and phase resolved optical emission spectroscopy and numerical simulations are employed to investigate the excitation dynamics of a radio-frequency-driven microatmospheric pressure plasma jet. Different power coupling modes can be identified by characteristic structures obtained from the spectroscopic measurements. Numerical results from a 1-D fluid code with semikinetic treatment of the electrons show very good agreement with the experimental results.

Spatially resolved simulation of a radio-frequency driven micro-atmospheric pressure plasma jet and its effluent

Radio-frequency driven plasma jets are frequently employed as efficient plasma sources for surface modification and other processes at atmospheric pressure. The radio-frequency driven micro-atmospheric pressure plasma jet (μAPPJ) is a particular variant of that concept whose geometry allows direct optical access. In this work, the characteristics of the μAPPJ operated with a helium–oxygen mixture and its interaction with a helium environment are studied by numerical simulation. The density and temperature of the electrons, as well as the concentration of all reactive species are studied both in the jet itself and in its effluent. It is found that the effluent is essentially free of charge carriers but contains a substantial amount of activated oxygen (O, O3 and O2(1Δ)).The simulation results are verified by comparison with experimental data.