Session GT1: Poster Session I (4:00pm - 6:00 pm)

Electron Transport in Water Vapour

Sets of electron collision cross sections for water vapour previously reported are examined by comparing calculated electron swarm parameters with measured parameters. Further, reliable cross section set of water vapour is estimated by the electron swarm method using Monte Carlo simulation to ensure the accuracy of the swarm parameter calculation. The values of an electron drift velocity, a longitudinal diffusion coefficient, and an effective ionisation coefficient calculated from Yousfi and Benabdessadok's set [J. Appl. Phys. 80, 6619 (1996)] and those calculated from Itikawa and Mason's set [J. Phys. Chem. Ref. Data 34, 1 (2005)] do not necessarily agree with measured data. A new cross section set of water vapour, which consists of three kinds of rotational excitation, two kinds of vibrational excitation, three kinds of electron attachment, twenty-six kinds of electronic excitation, and six kinds of ionisation cross sections, and an elastic collision cross section, is estimated, and an anisotropic electron scattering for elastic and rotational excitation collision is considered. The swarm parameters calculated from the estimated cross section set is in good agreement with measured data in a wide range of reduced electric field.   

Low energy electron scattering from atomic oxygen and nitrogen

Recent considerations of the depth of understanding of laboratory and astrophysical plasmas has drawn attention to theoretical and experimental data for electron collisions with atoms, molecules and ions, particularly for atomic oxygen, nitrogen and carbon atoms [1]. We report accurate experimental differential elastic cross sections from 10 to 150 degrees with energy analysis of the scattered electrons. Phase shifts parameterization [2] of oxygen and nitrogen data enabled calculation of integral elastic and momentum transfer cross sections. Subsequently ionization and excitation processes in nitrogen atoms were explored to see the influence of electronic structure such as the 2$s^{2}$ 2$p^{3}$ $^{2}D$ and $^{2}P$ metastable states in the autoionization region [3]. The apparatus used crossed modulated electron and atomic beams with energy selection of the incident electron beam and absolute cross sections determined from experimental parameters using a relative gas flow method. \\[4pt] [1] K. Bartschat and O Zatsarinny, Phys. Scri. 90 (2015) 054006;\\[0pt] [2] J. F. Williams and L. J. Allen, J. Phys. B 22 (1989) 3529;\\[0pt] [3] Y. K. Kim and J Desclaux, Phys Rev A \textbf{66}, 012708 (2002)   

Electron-impact population transfer rates between metastable and resonance states of argon

Electron-impact population transfer between metastable and resonance 1s states of argon is studied by time resolved laser pump-probe technique in a surfatron generated argon plasma. A nanosecond laser pulse tuned to a 1s-2p or 1s-3p transition depletes one of the 1s metastable or resonance states of argon and the time variations of the densities in that state and the other three 1s states are then simultaneously monitored by laser absorption diagnostic with different cw diode lasers. Plasma parameters are: 6 mm diameter plasma tube, p$=$5-20 mbar, n$_{\mathrm{e}}=$1-6 x 10$^{19}$ m$^{-3}$, T$_{\mathrm{e}}=$1-2 eV. At such high n$_{\mathrm{e}}$ values e-impact transfers between 1s states dominates over all other loss processes, $i.e.$ diffusion, Ar-impact transfers and radiative losses. A simple collisional-radiative model is used to deduce the transfer rates from the time evolution of the densities in the four 1s states following the pulsed laser depletion. At T$_{\mathrm{e}}\ge $1.2 eV, k$_{\mathrm{ij}}$ rate coefficients (in units of 10$^{19}$ m$^{3}$.s$^{-1})$, for transfers between metastables and neighboring resonance states are k$_{54}=$1.6 and k$_{32}=$9, respectively. The population transfer with change of ion-core is weak for 1s$_{2}$ to 1s$_{5}$ (k$_{\mathrm{25}}$\textless \textless 1) but resonance states are efficiently mixed, k$_{24}=$k$_{42}=$2. Recent quantum mechanical calculation by Zatsarinny \textit{et al} seems to underestimate by factor 2 or more the corresponding cross-sections.   

B-spline R-matrix with pseudostates calculations for electron-impact excitation and ionization of aluminum

A systematic study of angle-integrated cross sections for electron scattering from neutral aluminum is reported. The calculations, carried out with our \hbox{B-spline} R-matrix with Pseudo-States (BSRMPS) method [1,2], cover elastic scattering, ionization, and excitation of the 14~states $(3s^2np)^2P^o$ $(n = 3-6)$, $(3s^2ns)^2S$ $(n = 4-6)$, $(3s^2nd)^2D$ $(n = 3,4)$, $(3s3p^2) ^{4,2}P,\;^2D,\;^2S$, and $(3s^24f)^2F^o$ of aluminum. The sensitivity of the predictions is checked by comparing results obtained in different approximations, including a large-scale model with over 500 continuum pseudo-states in the close-coupling expansion. The current results represent an extensive, effectively complete, and highly accurate (believed to be within a few percent) set of electron collision data for neutral aluminum, which is readily suitable for modelling applications.\\[4pt] [1] O.\ Zatsarinny, Comp. Phys. Commun.~{\bf 174} (2006) 273.\\[0pt] [2] O.\ Zatsarinny and K.\ Bartschat, J.\ Phys.\ B {\bf 47} (2014) 061001.   

Electron impact elastic scattering and vibrational excitation of ethylene

Experimental and theoretical (Schwinger Multi-Channel model) differential scattering cross sections for low energy electron elastic scattering plus vibrational excitation (4 energy loss features) of ethylene are presented. The incident electron energy range is from 0.5eV to 100eV and scattering angles of 5 to 130 degrees. Comparisons with theory and past available measurements show good agreement in general.   

Vibrational excitation of methyl chloride by low energy electron impact

Differential scattering cross sections for low energy vibrational excitation of methyl chloride are presented. The experimental and theoretical (Schwinger Multi-Channel model) results comprise 5 vibrational excitation energy loss features of methyl chloride. The incident electron energy range is from 1eV to 15eV and scattering angles from 10 to 130 degrees. Comparisons with other available results will be presented.   

Electron impact of CO, CO$_{2}$, and N$_{2}$ using the MAVEN IUVS flight spare

The Imaging Ultraviolet Spectrograph (IUVS) flight spare, part of the Mars Atmosphere and Volatile and EvolutioN (MAVEN) mission, was used to observe the fluorescence resulting from electron-impact on CO, CO$_{2}$, and N$_{2}$. The experimental investigation was carried out using a large vacuum chamber, a detector platform that provided vertical and horizontal movement, and the MAVEN IUVS flight spare. An electron gun and Faraday cup, along with suitable Helmholtz coils, were mounted $\sim$ 0.5m apart and perpendicular to the line-of-sight of the IUVS. The IUVS consists of far-ultraviolet (FUV) and a middle-ultraviolet (MUV) detectors, covering the 110-190nm and 180-340nm wavelength ranges, which observed the photon emissions resulting from an optically-thin swarm of gas that was excited by electrons of fixed energies. The imager platform allowed the fluorescence to be observed at multiple vertical positions relative to the on-center measurement, thus enabling direct observation of photons from long-lived metastable states. Absolute emission cross sections, glow profiles, and lifetimes of numerous transitions will be presented.   

A (e,2e$+$ion) study of low-energy electron-impact ionization of THF

We have investigated the Fully Differential Cross Sections (FDCS) for electron impact induced ionization of THF (C4H8O) by low-energy (E$_o$=26 eV) for three different orbital states of the highest, next highest, and next-next highest occupied molecular orbitals (HOMO, NHOMO, and Next NHOMO). Theoretical results are compared with experiment for in plane scattering with projectile scattering angles of $15^{\circ}$, $25^{\circ}$, $35^{\circ}$, and $50^{\circ}$. Different theoretical models are examined - the molecular 3 body distorted wave (M3DW), and the distorted wave Born approximation (DWBA), with the effects of the post collision interaction (PCI) treated either exactly or with the Ward-Macek approximations.   

Electron impact ionization of CH$_{4}$, H$_{2}$O and NH$_{3}$ with a Sturmian approach

The study of ionization of molecular systems is more complex and challenging than in the atomic case because the Hamiltonian is generally multicenter and highly non-central. Additionally, in most experiments the molecular spatial orientation is not resolved, so that the random orientation of the molecule must be taken into account through an adequate angular average. In this contribution, we illustrate our implementation of a Sturmian approach, based on Generalized Sturmian Functions [1], for the study of single electron impact ionization of small molecules. Molecular model potentials are proposed to describe the interaction between the ejected electron with the parental ion. A similar approach was used before to study photoionization of molecules [2]. The calculated triple differential cross sections for ionization from valence orbitals of CH$_{4}$, NH$_{3}$ and H$_{2}$O will be reported, and compared with different available theoretical and experimental data.\\[4pt] [1] G. Gasaneo et al, Adv. Quantum Chem. 57, 153 (2013). \newline [2] C. M. Granados-Castro, Adv. Quantum Chem. (2015), accepted for publication.   

Primary dissociation channels of SiH4

The primary dissociation channels of SiH4 were investigated using computational chemistry. The results showed the very similar properties to those of CH4. The main dissociation product was SiH2 and the second dissociation product was SiH3. SiH was produced through SiH3 to SiH$+$H2 reaction, by electronic excitation.   

Closed Orbits in Phase Space

We report characteristics of closed classical orbits in an electric field in phase space produced in photoabsorption. Rydberg states of atomic and molecular hydrogen and helium are considered. The core potential used for the hydrogen molecule is an effective one electron one center core potential evaluated at the internuclear equilibrium distance. Poincare surfaces of section in phase space are generated by integrating the equations of motion in semiparabolic coordinates $u =$ ($r +$ $z)^{1/2}$ and $v =$ ($r - z)^{1/2}$, and plotting the location in phase space (p$_{v}$ versus $v)$ whenever $u =$ 0, with the electric field in the z direction. Combination orbits produced by Rydberg electron core scattering are studied and the evolution in phase space of these combination orbits due to scattering from one closed orbit into another is investigated. Connections are made to measured laser photoabsorption experiments that excite Rydberg states (20 \textless\ n \textless\ 30) and produce accompanying scaled energy recurrence spectra. The phase space structures responsible for the spectra are identified.   

Third-order transport coefficients for electron and positron swarms in gases

A multi term solution of the Boltzmann equation has been used to calculate third-order transport coefficients of charged particle swarms in neutral gases under the influence of electric and magnetic fields. The hierarchy resulting from a spherical harmonic decomposition of the Boltzmann equation in the hydrodynamic regime is solved numerically by representing the speed dependence of the phase-space distribution function in terms of an expansion in Sonine polynomials about a Maxwellian velocity distribution at an internally determined temperature. A group projector technique is employed to determine the structure and symmetries along individual elements of the skewness tensor when both electric and magnetic fields are present. Results are given for electron and positron swarms for certain model and real gases over a range of electric and magnetic field strengths. The results of the Boltzmann equation analysis are compared with those obtained by a Monte Carlo simulation technique. Various aspects in the behavior of skewness tensor elements are investigated, including the existence of correlation with low-order transport coefficients, sensitivity to post-ionization energy partitioning and errors of two-term approximation for solving Boltzmann's equation.   

Experimental and Theoretical Study of Ion Velocity Distribution Functions in Two- Dimensional Velocity Space

Ion Velocity Distribution Functions (IVDF) in two-dimensional velocity space were measured by one-sided disk probe in He, Ar, N$_{2}$, and Hg in the range of dc electric field $\frac{E}{P}\sim 10\div 20\frac{V}{cm\, Torr}$ , where IVDF is anisotropic and strongly departs from a Maxwellian. Analytical solution of the Boltzmann equation is obtained for IVDF taking into account charge exchange and elastic scattering cross sections. IVDFs were also calculated using Monte Carlo method. Measured and simulated IVDFs agree well with analytical solution and yield known values of mobility and perpendicular and parallel diffusion coefficients.   

Collisional quenching reaction rate coefficients of $N_{2} (A^{3}\Sigma _{u}^{+}$) by C$_{2}$F$_{6}$ and C$_{3}$F$_{8}$

The collisional quenching reaction rate coefficient of $N_{2} (A^{3}\Sigma _{u}^{+} )$ by various air pollutant gases [1,2] were determined from the measurement of the effective lifetime of $N_{2} (A^{3}\Sigma_{u}^{+} )$in pure N$_{2}$ (5-nine) with a small amount of air pollutant gases as an admixture. Derivation of the rate coefficient was performed the waveform analysis of the transient ionization current after turning off the UV light in the Townsend discharge. In this paper, we report that the obtained collisional quenching reaction rate coefficients of $N_{2} (A^{3}\Sigma _{u}^{+}$) by C$_{2}$F$_{6}$ and C$_{3}$F$_{8}$ are (2.3 $\pm$ 1.8) $\times$ 10$^{-15}$ cm$^{3}$/s and (1.6 $\pm$ 0.8) $\times$ 10$^{-14}$ cm$^{3}$/s, respectively. Furthermore, we investigate the relationship between the rate coefficient and the mass number of their quenching molecular gases. Firstly, it is confirmed that the rate coefficient take large value with an increase in the mass number of the quenching gases. Secondly, if H atom is included in the gas molecules such as CH$_{4}$, C$_{2}$F$_{6}$ and C$_{3}$F$_{8}$ the rate coefficient take large value, but if the molecules including F atom such as C$_{2}$F$_{6}$ and C$_{3}$F$_{8}$ instead of H atom in this study, more smaller values of the collisional quenching reaction rate coefficient are observed. \\[4pt] [1] S. Suzuki, H. Itoh, H. Sekizawa and N. Ikuta, J. Phys. Soc. Jpn., 62, No.8, 2692-2697 (1992)\\[0pt] [2] S. Suzuki, H. Itoh, Europhysics Conference on Atomic and Molecular Physics of Ionized Gases XXII, P2-03-03 (2014)   

Attraction during binary collision of fine particles in Ar plasma

Forces exerted on fine particles in plasmas play central roles in their transport, agglomeration, as well as Coulomb crystals and liquids. The forces are complicated because of charge fluctuation of fine particles, charge screening in plasma, anisotropy of plasma flow, and so on. Various formulas of such forces have been theoretically predicted but many of them have not been supported by experimental results yet. Here we carried out experiments on binary collision of fine particles using Ar rf-discharge plasmas. PMMA fine particles of 10$\mu $m diameter were injected into the plasma and they were levitated around the plasma sheath boundary. The number of fine particles levitated was so small that we can observe non-collective pair interaction. We observed binary collisions of fine particles with a high speed and high resolution camera. We found that repulsion of two fine particles takes place in short distances, whereas attraction takes place in middle distances. These results indicate that inter-molecular like potential exists between them. The attraction corresponds to non-collective fine-particle attraction due to shadow effects.   

Microwave photonic bandgap devices with active plasma elements

A 3-D alumina rod based microwave photonic crystal device with integrated gaseous plasma elements is designed and characterized. Modulation of the plasma density of the active plasma elements is shown to allow for high fidelity modulation of the output signal of the photonic crystal device. Finite difference time domain (FDTD) simulations of the device are presented, and the functional effects of the plasma electron density, plasma collision frequency, and plasma dimensions are studied. Experimental characterization of the transmission of the device shows active tunability through adjustments of plasma parameters, including discharge current and plasma size. Additional photonic crystal structures with integrated plasma elements are explored.   

A global model study of oxygen discharges -- formation and annihilation of the singlet molecular metastables and effects of the electron energy distribution function

A revised reaction set for oxygen plasma modelling was implemented in a volume average global model that considers only Maxwellian electron energy distribution function. The results showed that the state could be present in the discharge in amounts higher than the state. A further study has been realized through changes in the electron energy distribution function. Differences in the results calculated using Maxwellian and non-Maxwellian distributions demonstrate the importance of using a proper electron energy distribution function in plasma modelling.   

Excitation of N2(C3$\Pi $u,v) and N2$+$(B2$\Sigma $u$+$,v) vibronic levels by streamer discharge in atmospheric pressure air

Ionizing waves in air often take the form of thin filaments called streamers. Propagating streamer head is a place where the major part of reactive species is produced and that is of considerable interest for various applications, such as pollution control, ozone formation, etc. Knowledge of vibrational distributions of N2(C3$\Pi $u,v) and N2$+$(B2$\Sigma $u$+$,v) electronic states induced by the streamer head electrons is of particular interest, namely for determination of the self-enhanced electric field in the nitrogen/air streamer discharge. Indeed, vibrational distributions of N2(C3$\Pi $u,v) and N2$+$(B2$\Sigma $u$+$,v) states are very sensitive to the electric field variations occurring due to the streamer head action and might be used as a complementary spectrometric tool for monitoring streamer head parameters. In this work, a numerical study on streamer induced excitation of N2(C3$\Pi $u,v$=$0-4) and N2$+$(B2$\Sigma $u$+$,v$=$0-4) vibronic levels in air is presented and discussed from the point of view of improved determination of the streamer head parameters.   

Correlating Metastable-Atom Density, Reduced Electric Field, and Electron Energy Distribution in the Early Stages of a 1-Torr Argon Discharge

Temporal measurement of electron density, metastable-atom density, and reduced electric field are used to infer the dynamic behavior of the excitation rates describing electron-atom collision-induced excitation in the positive column of a pulsed argon discharge plasma by invoking plausible assumptions regarding the shape of the electron energy distribution function (EEDF), specifically, inelastic electron-metastable collisions produce high-energy electrons and electron-electron collisions will cause the EEDF to become more Maxwellian [1]. Direct observation of these excitation rates have been used to predict the temporal behavior of metastable-atom density in the post-transient stage of a pulsed plasma discharge [2]. Ignoring the Maxwellianizing effect of electron-electron collisions allows for the examination, in this poster, of correlations between the aforementioned quantities in the transient stage of the discharge. We conclude that the observed line-emission ratio and the predicted line-emission ratio are in quantitative agreement with each other in the transient phase of the discharge and qualitatively agree with each other in the initiation phase of the discharge. Ignoring electron-electron collisions allows insight into hard-to-measure or expensive-to-measure plasma conditions and their time dependence in the transient phase of the discharge. [1] Pitchford et al., J. Appl. Phys. 92, 6990. [2] Franek et al., Plasma Sources Sci. Technol. 24 (2015) 034009.   

Monte Carlo Simulation of the Effect of ``Hot'' Atoms on Active Species Production in High-Voltage Pulsed Discharges

Atoms and radicals produced in the discharge plasma possess excessive translational energy (a few electron-volts) that is lost after several elastic collisions with neutral particles. It was shown that, prior to the energy degradation of ``hot'' particles they can be involved in chemical reactions with high energy threshold. This leads to an additional production of chemically active species. The purpose of this work was to simulate numerically this effect and to calculate the amount of active species produced in discharge plasmas taking into account chemical reactions with ``hot'' atoms and radicals. The simulation was carried out by a Monte Carlo method allowing competitive consideration of elastic and inelastic collisional processes leading to the translational energy relaxation of particles with excessive initial energy. Using a Monte Carlo technique, energy degradation of ``hot'' H and O atoms was simulated in CH$_{\mathrm{4}}$:O$_{\mathrm{2}}$ and CH$_{\mathrm{4}}$:air mixtures. It was shown that during the relaxation of H and O translational energy the additional generation of CH$_{\mathrm{3}}$, OH and H$_{\mathrm{2\thinspace }}$takes place. This affects the total amount and composition of active species produced in high-voltage pulsed discharges.   

Mode analysis for a microwave driven plasma discharge: A comparison between analytical and numerical results

The market shows in recent years a growing demand for bottles made of polyethylene terephthalate (PET). Therefore, fast and efficient sterilization processes as well as barrier coatings to decrease gas permeation are required. A specialized microwave plasma source -- referred to as the plasmaline -- has been developed to allow for depositing thin films of e.g. silicon oxid on the inner surface of such PET bottles. The plasmaline is a coaxial waveguide combined with a gas-inlet which is inserted into the empty bottle and initiates a reactive plasma. To optimize and control the different surface processes, it is essential to fully understand the microwave power coupling to the plasma and the related heating of electrons inside the bottle and thus the electromagnetic wave propagation along the plasmaline. In this contribution, we present a detailed dispersion analysis based on a numerical approach. We study how modes of guided waves are propagating under different conditions, if at all.   

Measurement of supersonic plasma interacting with stationary plasma by electric probes

Supersonic plasma is generally related to the formation of young star object (YSO), active galactic nuclei (AGN) and new galaxies via plasma bubble expansion during the event of super nova. Capacitive coupled plasma (CCP) is produced by RF power of 13.56 MHz and the plasma is accelerated by negatively biased cascade grid to produce supersonic flow. Electron temperature, plasma density and Mach number are measured by using a single probe and a Mach probe. Electron temperature and plasma density of CCP are 0.8 eV and 1.8 $\times$ 10$^{9}$ cm$^{-3}$, respectively. Mach number of supersonic plasma flow is about 2 and 50 W RF power at 52 mTorr. Ambient plasma is generated by DC filament discharge and its electron temperature and plasma density are 0.5 eV and 3 $\times$ 10$^{10}$ cm$^{-3}$, respectively. When the supersonic plasma flow interact with ambient plasma, electron temperature is increased higher than ambient plasma up to 4 eV, and plasma density is decreased from 4 $\times$ 10$^{10}$ cm$^{-3}$ to 1 $\times$ 10$^{10}$ cm$^{-3}$. Density contrast $\eta $ of supersonic plasma flow of our experiment is about 0.04, while AGN jets in universe are observed to have density contrast $\eta $ of lower than 10$^{-2}$.   

Streamer discharge inception from a dielectric body with a frequency dependent dielectric permittivity

Dielectric bodies are polarized by an external electric field; this polarization is characterized by their dielectric permittivity. However, if the electric field changes fast enough, the dipoles inside the dielectrics cannot follow these changes and their dielectric permittivity drops, eventually to 1 for an electric field that changes infinitely fast. Now the characteristic time scale of streamer discharge development at atmospheric pressure is order of nanoseconds. On this time scale many dielectrics respond to a changing electric field with a smaller dielectric permittivity than to a time independent field. Here we study positive streamer inception from a dielectric tip made of ice. The dielectric permittivity of ice drops from 93 to 3 already on the timescale of milliseconds. We demonstrate that this effect is important and that it can make a streamer propagate with only half of the speed as for a constant dielectric permittivity.   

A characterization of atmospheric pressure plasma jets (APPJs) through a spatio-temporal map of the APPJ's optical emission spectra

APPJs have become increasingly important in the past years in medical, science, and industry. However, there still remains a largely unsolved problem of characterizing APPJs to determine the quantity of species they deliver; the type of atomic, molecular, and radical species they deliver, both charged and neutral; as well as the energy of the species they deliver. In this paper, we will present our work on the characterization of the type of charged species delivered by our APPJ through a spacial and temporal map of the APPJ's optical emission spectra. This spatial-temporal emission spectra enables us to track how the relative abundance of individual emitting species changes as a function of distance from the jets central axis and as a function of time (distance from the APPJ's orifice). Using a helium working gas, we tested our method of characterization by measuring the relative abundances of different helium, nitrogen, and oxygen emitting species under three different conditions: using a shielding gas of oxygen, using a shielding gas of nitrogen, and using no shielding gas at all-just the He jet directly into the atmosphere. The results of this study will be presented.   

Second harmonic generation as nonlinear bifurcation phenomenon at various positions in plasma-metamaterial composite

Plasma has been a research target as a nonlinear material to generate harmonic waves because of its dynamics. Its nonlinearity has been limited due to the cutoff density beyond which permittivity is negative. Metamaterial is a novel artificial material with extraordinary electromagnetic responses, and an array of double split ring resonators (DSRRs) is a typical one with negative permeability [1]. So far we have successfully confirmed microwave propagation in composites of negative-permeability DSRRs and negative-permittivity plasma whose high electron density enhances its nonlinear phenomena; one of them is second harmonic generation detected at one fixed position along the microwave propagation. In this report, we demonstrate the experimental results about the spatial profiles of the monitored fundamental (2.45 GHz) and the second harmonic (4.9 GHz) wave signals with corresponding measurement of electron density profiles. A significant intensity of the second harmonic wave was detected at a spatially separated position from the input port, which implies that the nonlinearity by the combination of plasma and DSRRs is sustained at overall parts of this composite.\\[4pt] [1] J. B. Pendry, A. J. Holden, D. J. Robbins, and W. J. Stewart, IEEE Trans. Microw. Theory Tech. 47, 2075 (1999).   

Measurements of Striation Phenomena in Low Energy Atmospheric Pressure Plasma Using the Optical Emission Spectroscopy

Plasma technology has been used in many fields. It is considered that reactive species produced by plasma play an important role on those plasma applications. There are many unknown phenomena in those application mechanisms. Recently, the striation phenomena was found along the plasma column ejected from a low energy atmospheric pressure plasma equipment using neon gas. In this work, the visible emission of neon plasma flare was measured by using the optical emission spectroscopy, and mainly neon atom and nitrogen molecule neutral lines were observed. Especially, the emission of neon atoms was dominant, and Ne I (683.3 nm) emission intensity of negative current phase was larger than that of positive current phase. Furthermore, the emission distribution of Ne I (683.8 nm) along the striation was measured, and it was found that Ne I also shows intermittent features along the plasma flare.   

Radio-frequency sheaths in grazing angle magnetic fields

Radio-frequency sheaths are a well-known phenomenon in low-temperature plasmas, but they also occur in magnetically confined plasmas designed for fusion applications, particularly when electromagnetic heating techniques are employed. The behaviour of the sheaths in this context is of interest both because of the effect on erosion of plasma facing surfaces by sputtering and possible effects on the stability of the plasma near the wall, with possible consequences for the efficiency of plasma heating. With these problems in mind, in this paper we use a particle-in-cell simulation to investigate the behaviour of a model radio-frequency discharge with a magnetic field at grazing incidence, that is, not quite parallel to, the electrode surface. The plasma parameters are chosen so that, in a normalized sense, they are comparable with those encountered in fusion devices. We discuss the behaviour of the plasma under these conditions, with reference to the adequacy of conventional radio-frequency sheath models under these conditions.   

Ion sound instability driven by the ion flow in a system of the finite length

Ion sound instabilities driven by the ion flow in a system of a finite length are considered by analytical and numerical methods. The ion sound waves are modified by the presence of stationary ion flow resulting in negative and positive energy modes. The instability develops due to coupling of negative and positive energy modes mediated by reflections from the boundary. It is shown that the wave dispersion due to deviation from quasineutrality is a crucial parameter that determines the stability. In finite length system, the disperson is characterized by the length of the system measured in units of the Debye length. The instability is studied analytically and the results are compared with direct, initial value numerical simulations. It is shown that boundary effects result in the instability under the conditions when the standard kinetic ion sound instability does not occur.   

Study on the Striation of an Atmospheric Pressure Plasma Flare Using a High Speed Camera

Characteristics of a low energy atmospheric pressure plasma (LEAPP) specially designed for a medical application has been studied by the visualization of plasma emissions using a high speed camera. The formation of striations in the LEAPP was observed between a nozzle exit and a target material. This result indicates that the plasma propagation is not a bullet type. Detail structure of the striation phenomena will be presented in the conference.   

A transition of the electron energy distribution function through ratio of driving frequency to the energy relaxation frequency

Over the past twenty years, atmospheric pressure plasma (APP) devices including sub-millimeter dielectric barrier discharges (micro DBDs) have been developed for plasma medicine. They have great advantage of stable and high density plasmas, but there are still many unknown phenomena of which experimental diagnostics are difficult. In this study, a one-dimensional particle-in-cell simulation with Monte Carlo Collisions (MCC) was adopted to investigate the characteristics of electron energy probability function (EEPF) as a self-consistent kinetic model with no assumptions. Spatio-temporal analysis compares well with theoretical estimation of micro DBDs driven with RF frequencies from 13.56 MHz to 500 MHz~in APP. The result indicates that the ratio of the driving frequency to the energy relaxation frequency contributes to the drastic transition of EEPF. The kinetic theory with two-term approximation explains that the electron transport follows the non-local kinetics even in the APP device for specific conditions.   

Is the Bohm Criterion satisfied in magnetized plasmas, and how does ion-neutral collisionality matter?

It is taken for granted that the usual Bohm criterion must be satisfied for weakly collisional, magnetized plasmas at the plasma-wall boundary for the case in which the magnetic field is normally incident on the boundary, but there is a paucity of experimental works that confirm it. Beyond this, theorists view the Bohm criterion as approximately true, holding only for collisionless plasmas. The question is whether Bohm's criterion really is satisfied in weakly collisional magnetized plasmas in the simplest case ( $\mathbf{ \hat{n} } \parallel \mathbf{ B }$/B, where $\mathbf{\hat{n}}$ is the boundary surface normal vector) and how that criterion (the ions reaching a sonic point at the end of the presheath) is modified as collisionality rises. Experiments are conducted in a linear magnetized helicon plasma source at the University of Wisconsin, Madison, an upgraded version of MARIA (MARIA-Magnetized Anisot Ropic Ion-distribution Apparatus), in order to address these questions. Experimental results are discussed in light of relevant theoretical works.   

Radio-frequency Plasma Sheath Studies

The response of ion-electron plasma as well as two-component plasma to RF fields is studied via PIC simulation. In each case, the light species responds strongly to the RF and the heavy species does not. By varying the external electrode geometry, RF waveform, and driving voltage and frequency, light species of certain charge-to-mass ratios may experience a trapping effect within the RF structure. The space charge of this species creates a potential well for the oppositely-charged, heavy species. Simulation results are presented, as well as plans for experimental investigation of the same effect. Applications to plasma processes in which a plasma boundary is subjected to external RF fields are discussed.   

Developing Chemistry and Kinetic Modeling Tools for Low-Temperature Plasma Simulations

We discuss the use of proper orthogonal decomposition (POD) methods [del-Castillo-Negrete et al., PoP {\bf 15}, 092308 (2008)] in VSim, a FDTD plasma simulation code capable of both PIC/MCC and fluid modeling. POD methods efficiently generate smooth representations of noisy self-consistent or test-particle PIC data, and are thus advantageous in computing macroscopic fluid quantities from large PIC datasets (e.g. for particle-based closure computations) and in constructing optimal visual representations of the underlying physics. They may also confer performance advantages for massively parallel simulations, due to the significant reduction in dataset sizes conferred by truncated singular-value decompositions of the PIC data. We also demonstrate how complex LTP chemistry scenarios can be modeled in VSim via an interface with MUNCHKIN, a developing standalone python/C++/SQL code that identifies reaction paths for given input species, solves 1D rate equations for the time-dependent chemical evolution of the system, and generates corresponding VSim input blocks with appropriate cross-sections/reaction rates. MUNCHKIN also computes reaction rates from user-specified distribution functions, and conducts principal path analyses to reduce the number of simulated chemical reactions.   

Comparative Shock-Tube Study of Autoignition and Plasma-Assisted Ignition of C$_{2}$-Hydrocarbons

The dynamics of pulsed picosecond and nanosecond discharge development in liquid water, ethanol and hexane Using a shock tube with a discharge cell, ignition delay time was measured in a lean ($\varphi \quad =$ 0.5) C$_{2}$H$_{6}$:O$_{2}$:Ar mixture and in lean ($\varphi \quad =$ 0.5) and stoichiometric C$_{2}$H$_{4}$:O$_{2}$:Ar mixtures with a high-voltage nanosecond discharge and without it. The measured results were compared with the measurements made previously with the same setup for C$_{2}$H$_{6}$-, C$_{2}$H$_{5}$OH- and C$_{2}$H$_{2}$-containing mixtures. It was shown that the effect of plasma on ignition is almost the same for C$_{2}$H$_{6}$, C$_{2}$H$_{4}$ and C$_{2}$H$_{5}$OH. The reduction in time is smaller for C$_{2}$H$_{2}$, the fuel that is well ignited even without the discharge. Autoignition delay time was independent of the stoichiometric ratio for C$_{2}$H$_{6}$ and C$_{2}$H$_{4}$, whereas this time in stoichiometric C$_{2}$H$_{2}$- and C$_{2}$H$_{5}$OH-containing mixtures was noticeably shorter than that in the lean mixtures. Ignition after the discharge was not affected by a change in the stoichiometric ratio for C$_{2}$H$_{2}$ and C$_{2}$H$_{4}$, whereas the plasma-assisted ignition delay time for C$_{2}$H$_{6}$ and C$_{2}$H$_{5}$OH decreased as the equivalence ratio changed from 1 to 0.5. Ignition delay time was calculated in C$_{2}$-hydrocarbon-containing mixtures under study by simulating separately discharge and ignition processes. Good agreement was obtained between new measurements and calculated ignition delay times.   

Effect of low temperature in nitriding of SiC using a remote

The surface nitriding of SiC using a remote nitrogen plasma is a candidate method for passivating the interface between the gate insulator and the channel region in a SiC-based power transistor. This work was motivated by the decrease in the weight density of the SiC surface by the irradiation of a remote nitrogen plasma. The decrease in the weight density is considered to be mainly due to desorption of C$_2$N$_2$ and HCN from the SiC surface during nitriding. In this work, we cooled the SiC sample below $-100$ $^\circ$C to minimize the damage induced by the plasma irradiation. The sample which was irradiated by a remote nitrogen plasma for 1 minute showed the following effects of the sample cooling. 1) A deeper nitride layer was formed in the cooled sample, while the dislocation of the crystalline structure was milder. 2) The composition ratio of Si/C was roughly 1/1 in the region at a depth of $>1$ nm in the cooled sample. A cooled sample which was irradiated for 3 minutes had a nitride layer without oxygen at a depth of $>1.6$ nm. This structure is thought to be stable for the C-face of 4H-SiC. The irradiation of a remote nitrogen plasma to low-temperature SiC could work effectively for forming the passivation layer between the gate insulator and the channel region.   

Diagnostic signature of low-energy secondary electron emission at the boundary of a partially-ionized plasma

Effects of secondary electron emission (SEE) from a solid surface in contact with plasma are important for conducting and interpreting plasma experiments and modeling. Those effects are especially strong for contaminated surfaces. Measurements of SEE reported here are conducted in a plasma having a nearly mono-energetic population of electrons that is energetically well resolved and separated from a broader-energy-range electron population. By performing the SEE measurement in an afterglow or afterglow-like plasma, we take advantage of the nearly mono-energetic electron population that arises in ionizing plasma-chemical reactions, such as binary like-particle collisions of metastable atoms. We demonstrate a diagnostic method for measuring the low-energy electron absorption coefficient across the broader energy range and the effects of contamination on the swept-bias probe characteristic trace.   

Current Status of Divertor Plasma Simulator (DiPS-2) for Dust Interactions with Plasma and Surfaces

The divertor plasma simulator (DiPS-2) which is a linear plasma machine with $\sim$ 8 MW/m$^{2}$ power density emitted from a DC plasma discharge source with a LaB$_{6}$ cathode is under installation for experiments of dust interactions with plasma and surfaces in fusion research fields. Specifications of DiPS-2 have weakly magnetized helium plasmas (density $\sim$ 10$^{13}$ cm$^{3}$, electron temperature $\sim$ 1 - 10 eV, particle flux $\sim$ 10$^{23}$/(sec$\cdot$m$^{2}$), which are of the order of plasma parameters in a typical divertor. Currently, a vacuum chamber with the diameter of 560 mm and the length of 800 mm called as ``dust interaction with surface chamber (DiSC)'' is being setup to an end flange of DiPS-2. The DiSC has a load-lock system for easily changing material targets and plasma diagnostics systems such as laser induced fluorescence (LIF), laser Thomson scattering (LTS), thermocouples and fast scanning probes (FSP) with SP, TP and MP. Using the measured dust and plasma parameters, SOL heat flux width ($\lambda_{\mathrm{q}}$) and sheath heat transmission factor ($\gamma_{\mathrm{s}}$) will be experimentally deduced for the analysis of the dust effects to plasmas. Initial probe data will be addressed.   

Surface charge measurements in barrier discharges on different time scales

The deposition of surface charge in barrier discharges is a process that influences the ongoing discharge significantly. This contribution presents the measurement of absolute surface charge densities and their dynamics in a laterally extended setup. An electro-optic BSO crystal is used as dielectric. The absolute charge density on its surface is deduced from the change of polarisation of light passing the crystal. Using different temporal resolutions, the behavior of charge is investigated on three different time scales. The highest temporal resolution of the technique is in the order of hundreds of nanoseconds. Therefore it is possible for the first time to observe the charge deposition process during an active discharge. On the time scale of the applied voltage period (several microseconds), the conservation mechanisms of a lateral discharge pattern is investigated. For this, the influence of surface charge and metastable species in the volume is estimated. Further, the behavior of the surface charge spots on a variation of the external voltage and gas pressure is studied. Measurements on a time scale in the magnitude of seconds reveal charge decay and transport phenomena. This work was funded by the Deutsche Forschungsgemeinschaft.   

Patterned Surface Functionalization of Dot-Arrayed CNTs for Biochip Sensor Using Scannable Ultrafine Atmospheric Pressure Plasma Jet

The present results show that the feasibility of using a dot-arrayed CNT as a biochip sensor was demonstrated by successfully fabricating CNTs in an array form and performing patterned surface functionalization of amino and carboxyl groups onto CNT. The vertically aligned CNT was fabricated in an array form using a combined thermal-plasma CVD for realizing the development of biochip sensors. Patterned surface functionalization was developed by ultrafine APPJ in two stages: (1) pretreatment by He gas with -500V dc bias and (2) posttreatment without bias by a He/NH3 gas mixture for amino group or by a He/O2 gas mixture for carboxyl group functionalization. The analysis results of chemical derivatization indicate that amino and carboxyl groups successfully functionalized the CNT dot array without interfering with each other. The optimum period of ultrafine APPJ treatments was achieved by balancing the following 3 aspects: (1) effective area of modification, (2) amount of surface functionalization, and (3) damage of the CNT. Finally, the patterned surface functionalization of amino and carboxyl groups was successfully conducted in the arbitrary pattern by using ultrafine APPJ automatically scanned by computer-controlled precision stage.   

BCA-kMC Hybrid Simulation for Hydrogen and Helium Implantation in Material under Plasma Irradiation

Ion implantation by plasma irradiation into materials achieves the very high concentration of impurity. The high concentration of impurity causes the deformation and the destruction of the material. This is the peculiar phenomena in the plasma-material interaction (PMI). The injection process of plasma particles are generally simulated by using the binary collision approximation (BCA) and the molecular dynamics (MD), while the diffusion of implanted atoms have been traditionally solved by the diffusion equation, in which the implanted atoms is replaced by the continuous concentration field. However, the diffusion equation has insufficient accuracy in the case of low concentration, and in the case of local high concentration such as the hydrogen blistering and the helium bubble. The above problem is overcome by kinetic Monte Carlo (kMC) which represents the diffusion of the implanted atoms as jumps on interstitial sites in a material. In this paper, we propose the new approach ``BCA-kMC hybrid simulation'' for the hydrogen and helium implantation under the plasma irradiation.   

Cross correlation analysis of plasma perturbation in amplitude modulated reactive dusty plasmas

Interactions between plasmas and nano-interface are one of the most important issues in plasma processing. We have studied effects of plasma perturbation on growth of nanoparticles in amplitude modulated reactive dusty plasmas and have clarified that amplitude modulation (AM) leads to suppression of growth of nanoparticles [1]. Here we report results of cross correlation analysis of time evolution of laser light scattering intensity from nanoparticles in reactive plasmas. Experiments were carried out using a capacitively-coupled rf discharge reactor with a two-dimensional laser light scattering (LLS) system. We employed Ar$+$DM-DMOS discharge plasmas to generate nanoparticles. The peaks at higher harmonics and subharmonics in spectra of laser light scattering intensity were detected, suggesting nonlinear coupling between plasma and nanoparticle amount. We found high cross correlation t between waves at AM frequency and its higher harmonics. Namely, perturbation at $f_{AM}$ closely correlates with those at higher harmonics.   

Study of the secondary electron emission in the limit of low electron energies using Q-machine in transverse magnetic field

The secondary electron emission (SEE) from surfaces plays an important role in plasma, accelerator and high power microwave applications [2-3]. A recent study proposed that the SEE yield, which is ratio of secondary to primary electron fluxes, approaches unity in the limit of zero energy of incident electron [3]. The high SEE has profound implications especially for plasma applications, including, for example, plasma thrusters for spacecraft propulsion and electric probes. High SEE at low electron energies may be caused by variety of surface effects. In specially cleaned metal surfaces numerous previous experimental studies of the secondary electron emission did not observed high SEE [1]. This talk presents a technique for measurements of SEE yield in a low-pressure plasmas in the presence of transverse magnetic field. It is shown that for poly-crystal surfaces, the SEE yield can be indeed very high ($\sim$ 0.8) but still not approaching unity. This result is explained by additional reflection of primary electrons from a potential barrier near the poly-crystal surface. The contribution of electron reflection from the potential barrier and the surface has been identified and studied. [1] A. Andronov, I. Kaganovich, et al. Bull. of the APS, Vol.58, No.16, p.306, 2013. [2] A. Mustafaev, M. Kaganovich, et all. Bull. of the APS, Vol.58, No.8, p.62, 2013. [3] R. Cimino, et al., Phys.Rev.Lett. 93, 014801, 2004.   

Ablation of CsI by XUV Capillary Discharge Laser

XUV capillary discharge laser (CDL) is suitable source for ablation of ionic crystals as material which is difficult to ablate by conventional laser. Single crystal of CsI was irradiated by 2.5 ns pulses of a 46.9 nm radiation at 2 Hz. The CDL beam was focused by Sc/Si multilayer spherical mirror. Attenuation length of CsI for this wavelength is 38 nm. Ablation rate was calculated after irradiation of 10, 20, 30, 50 and 100 pulses. Depth of the craters was measured by optical profiler (white light interferometry). Ablation threshold was determined from craters after irradiation with the changing fluence and compared with modeling by XUV-ABLATOR.   

Active interrogation of plasma-liquid~boundary using 2D plasma-in-liquid apparatus

Plasma medicine and plasma-based water purification technologies rely on the production and transport of plasma-derived (direct or indirect) reactive species into the bulk medium. This interaction takes place at the interface between the gas phase plasma and the liquid medium. The nature of radical production and subsequent radical transport from this region or boundary layer is not well understood due to the difficulty of implementing diagnostics to interrogate this region. We present a 2-D plasma-in-liquid water apparatus that makes the interface region assessable to optical diagnostics. Using colorimetric chemical probes, acidification and oxidation fronts are tracked using high-speed imaging and spectroscopy. Additionally, observed, plasma-induced fluid dynamical effects are also discussed. Forces at the interface can play a key role in the transport of radicals into the bulk solution. The role of plasma-driven interfacial forces as well as that of the applied, local electric field on chemical front propagation velocity and induced circulation are also discussed.   

Modifications in Structural, Electrical, Electronic and Mechanical Properties of Titanium Thin Films under different Gas Plasmas

In the recent past, Titanium thin films can be grown over different substrates such as silicon, glass and quartz by using versatile deposition techniques DC, RF sputtering, electronic beam and thermal evaporation etc. The grown films are then exposed in different gas environments for individual application. It has been found that Titanium nitride exhibits good chemical stability, mechanical and electrical properties. To investigate these properties in titanium nitride thin films, we have developed a new approach hot cathode arc discharge plasma system. By using this technique, we can measure plasma and nitriding parameters independently. In the present work, we have investigated gases mixture (Nitrogen, Argon and Hydrogen) effect on the structural, mechanical, electrical and electronic properties in plasma system. We have used 100\% N2, 50\% N2 + 50\% Ar and 50\% N2 + 50\% H2 gases ratio for plasma nitriding. Structural and electronic structure properties are measured from X-ray diffractions (XRD) and X-ray photoelectron spectroscopy (XPS) respectively. The surface morphology of these films were measured using Atomic Force Microscopy (AFM) and the nano-indentation mode is used to find out the hardness of the samples.   

The Effect of Anode Material and Secondary Gas Injection on Self-organized Patterns in Atmospheric Pressure Glows

Plasma self-organization on anode surfaces in DC glow discharges remains poorly understood. This effort aims to elucidate the nature of self-organization through the study of resulting patterns on both liquid and metal electrode surfaces. Self-organization pattern formation and behavior were studied as a function of inter-electrode spacing, electrode material type, gas composition and gas flow rate using emission spectroscopy and fast camera imaging. The response of the patterns to variation in these parameters is reported. These results are used as a basis for speculating upon the underlying physical processes that give rise to the self-organization.   

Plasma surface kinetics studies of etch process in inductively coupled fluorocarbon and hydrogen-containing fluorocarbon plasmas

Ultra-high deep contact-hole etching is one of the critical issues in fabrication processes of the nanoscale devices. The fluorocarbon (FC) plasmas have been used to obtain the ideal etch profiles. To achieve ultra-high deep contact hole, we present a plasma-surface kinetic studies based on the experimental plasma diagnostic data for silicon dioxide and nitride etch process under inductively coupled FC and HFC plasmas. For this work, the cut-off probe and QMS were used for measuring the electron densities and the ion and neutral radical species. Furthermore, the systematic surface analysis was performed to investigate the thickness and chemical bonding of polymer passivation layer during the etch process. The proposed semi-global surface kinetic model can consider deposition of polymer passivation layer and silicon oxide {\&} nitride etching self-consistently. In this model, thickness of the passivated polymer layer on substrate is calculated from steady-state polymer consumption balance which is composed of sputtered consumption and polymer deposition during oxide etching. Finally, this work will provide better insights to understand basic phenomena of the plasma etching process, leading to the predictable and reliable 3D topography simulation (K-SPEED).   

Spectroscopic Examination of Molecular Spectra in Mixture Gaseous Microwave Discharge (N2-O2 and N2-H2)

We develop some theoretical calculations of spectra of molecular electronic transitions. By using spectroscopic measurement, spectra range at 200-800-nm can be obtained and are compared with the calculation results to exam the molecular properties. We use N$_{2}$-H$_{2}$ microwave discharge to exam NH and N$_{2}$-O$_{2}$ microwave discharge to exam NO.   

Real-time monitoring of GaN films in processing plasma

The use of plasma is expected when fabricating devices on a gallium nitride (GaN) substrate. However, the plasma can make some significant damages that are caused by irradiating particles etc., in particular, high-energy ions generated in the plasma. In order to understand the mechanism to create these damages, we so far utilized photoluminescence (PL) emissions from the GaN film to make real-time monitoring of any changes relating to optical properties of the film that was exposed in the plasma. In this presentation, we will show our preliminary measurements with PL from the GaN exposed in argon or argon-chlorine plasma. Argon plasma is expected to give physical damages, while chlorine-containing plasma is expected to give both physical and chemical damages. Our measurements showed that the exposure in argon plasma degraded PL emission property from the GaN film, while the exposure of chlorine-containing plasma did not. This is likely because the speed of chemical reactions (etching) was simply faster than the speed of creation of physical damages according to our thickness measurement. Our presentation will give the following results from the real-time monitoring measurements.   

Evaluation of Plasma Temperature from the OH Violet Molecular Emission System

The violet OH system (A$^{2}\Sigma^{+}$ - X$^{2}\Pi_{\mathrm{i}})$ molecular emission spectrum is frequently observed in plasma sources containing water it is a good tool for diagnosing plasmas containing this molecule. We have simulated the spectrum of (0,0) band of this system from 3064 {\AA} for different rotational temperature. The method proposed permit to evaluate, by comparing point to point a real spectrum with the simulated one, temperature and apparatus function, approximated by the gauss function (the half-width at 1/e height). Moreover, it is shown, by noised spectra simulation, the influence of noise to signal ratio at the calculated temperature values. If the noise to signal ratio is about 10{\%} we found an error of 6{\%} at temperature 3000K and 10{\%} at 6000K. This method has been used to determine the combustion temperature from a real spectrum recording in Polymethyl methacrylate rocket plume taken 0 mm from the nozzle of fuel grain. The rotational temperature of about 3000 $\pm$ 350 K, has been found and noise to signal ratio is about 20{\%}.   

Investigation on measurement of effective sheath width using a cutoff probe

The plasma density is the key parameter showing electric plasma property as well as processing rate. Therefore, various diagnostic methods have been developed and researched for measuring the absolute plasma density. One of them, cutoff probe, has been developed for more accurate measurement of the plasma density. The cutoff probe is the promising diagnostics method having diagnostic advantages: high accuracy in measured plasma density, simple assumption in measurement process, and readily use and interpretation of results for diagnostics. The sheath is also an important parameter in plasma researches and applications. In this presentation, we introduce measurement method of the effective sheath width using equivalent circuit model of S21 phase spectrum of the cutoff probe. The reliability of this method was verified by investigation of the FDTD simulation and comparative experiment with calculated Child-Langmuir law sheath width from Langmuir probe data. The results show that measured sheath width has an acceptable error when it was compared with input sheath width in the FDTD simulation. Furthermore, the measured sheath width was found to be in good agreement with the floated sheath width calculated from the Child-Langmuir sheath law.   

Matched dipole probe for precise electron density measurements in magnetized and non-magnetized plasmas

We present a plasma diagnostics method based on impedance measurements of a short matched dipole placed in the plasma. This allows measuring the local electron density in the range from 10$^{12}$-10$^{15}$ m$^{-3}$ with a magnetic field of at least 0-50 mT. The magnetic field strength is not directly influencing the data analysis and requires only that the dipole probe is oriented perpendicularly to the magnetic field. As a result, the magnetic field can be non-homogeneous or even non-defined within the probe length without any effect on the final tolerance of the measurements. The method can be applied to plasmas of relatively small dimensions (\textless\ 10 cm) and doesn't require any special boundary conditions. The high sensitivity of the impedance measurements is achieved by using a miniature matching system installed close to the probe tip, which also allows to suppress sheath resonance effects. We experimentally show here that the tolerance of the electron density measurements reaches values lower than 1{\%}, both with and without the magnetic field. The method is successfully validated by both analytical modeling and experimental comparison with Langmuir probes. The validation experiments are conducted in a low pressure (1 mTorr) Ar discharge sustained in a 10 cm size plasma chamber with and without a transversal magnetic field of about 20 mT.   

Optical emission spectroscopy of argon and hydrogen-containing plasmas

Optical emission spectroscopy (OES) on neutral argon is applied to investigate argon, hydrogen and hydrogen-silane plasmas. The spectra are analyzed using an extensive collisional-radiative model (CRM), from which the electron density and the electron temperature (or mean energy) can be calculated. The CRM also yields insight into the importance of different excited species and kinetic processes. The OES measurements are performed on pure argon plasmas at intermediate pressure. Besides, hydrogen and hydrogen-silane plasmas are investigated using argon as a trace gas. Especially for the gas mixture discharges, CRMs for low and high pressure differ substantially. The commonly used line-ratio technique is found to lose its sensitivity for gas mixture discharges at higher pressure. A solution using absolutely calibrated line intensities is proposed. The effect of radiation trapping and the shape of the electron energy distribution function on the results are discussed in detail, as they have been found to significantly influence the results. (S. Siepa et al., J. Phys. D: Appl. Phys. 47 (2014) 445201)   

Ion energy distributions in dual frequency RF plasmas

For many surface-processing applications involving plasmas operated at RF frequencies it has been found helpful to combine two sources of power operating at different frequencies. By choosing suitable input powers at the two frequencies and varying the phase relationship set between the two inputs, the energy distributions (IEDs) for the ions arriving at the target surface can be optimised. There have been, however, only a limited number of published reports of measured or modelled distributions. In the present work IEDs for both positive and negative ions formed in plasmas in argon and nitrous oxide have been measured for mass-identified ions in two different reactors, one of which is a parallel-plate, capacitatively-coupled, system and the other is an inductively-coupled system. Typical data for 13.56 and 27.1 MHz inputs are presented for a range of phase relationships. The IEDs show clearly significant differences between the data for different species of ions which result in part from the ion-molecule collisions occurring, particularly in the plasma/surface sheath regions.   

Quantification of the VUV radiation in low pressure hydrogen and nitrogen plasmas

Low pressure plasmas with hydrogen and/or nitrogen emit intense radiation in a broad wavelength region in the VUV. In order to quantify this radiation measurements in the wavelength region from 120 nm to 280 nm have been carried out using RF discharges. In case of molecular hydrogen dominant transitions are the Werner band (C--X), the Lyman band (B--X), and the continuum (a--b) as well as the Lyman lines from the hydrogen atom. Depending on the pressure, for hydrogen up to 20{\%} of the RF power of 600 W, is found in the VUV, whereas only about 2{\%} are emitted in the VIS represented by the Balmer series emission (H$_{\alpha}$ - H$_{\varepsilon}$) and the Fulcher emission (d--a). For nitrogen, the Lyman-Birge-Hopfield system (a-X) is most prominent in the wavelength region between 125 nm and 230 nm as well as some nitrogen resonance lines whereas in the visible range the first and second positive systems dominate. In hydrogen-nitrogen mixtures NH radiation appears due to the plasma chemistry. The measured radiant power will be compared with results from collisional radiative models for H$_{2}$ and N$_{2}$ which make use of electron density and temperature from spectroscopic measurements. Extrapolations to a wider parameter range are provided.   

Improved tunable external filter for Langmuir probe measurement at low density plasmas

Measurement of the electron energy probability function (EEPF) at low density plasma, especially in molecular gas discharge, is difficult due to large RF fluctuation. To overcome the problem, an improved tunable external filter was developed. In contrast to an internal filter, the external filter can tune the resonance frequency of the choke filter. However, conventional external filter has low impedance due to a large stray capacitance between a probe tip and the external filter. To reduce the effect of the stray capacitance, an appropriate inductor was connected to the probe tip, and the external filter was designed to tune the first and the second harmonic frequencies independently. Using our filter, the EEPFs were measured at low density plasma with various gases, and the results show the improved performance of the filter as compared to the previous studies.   

Two-dimensional time-resolved measurement of plasma parameters on a wafer-level using floating harmonic method

Two-dimensional time-resolved plasma diagnostic system is developed to observe transient plasma behaviors. The system is composed of wafer-type probe array, 16-channel/simultaneous data acquisition system, and driving circuit for floating harmonic method (FHM). The FHM can measure the electron density and electron temperature with high time resolution up to 200 microsec. By using the diagnostic system, transient plasma behaviors, such as effects of gas inlet and antenna power absorption, were observed. When the gas is distributed non-uniformly, the plasma density is relatively high near the gas inlet. In addition, antenna-shape plasma profiles are observed when the plasma is turned on and off.   

Spatial Resolution of Combined Wavelength Modulation Spectroscopy with Integrated Cavity Output Spectroscopy for Atomic Oxygen Detection

For developments of thermal protection system, atomic oxygen plays important role. However, its measurement method has not been established because the pressure in front of TPS test materials is as high as a few kPa. Our group proposed combined wavelength modulation and integrated output spectroscopies based on the forbidden transition at OI 636 nm to measure the ground-state number densities. In this study, WM-ICOS system is developed and applied to a microwave oxygen plasma to evaluate measurable region. As a result, the estimated number density by ICOS could be measured as low as 10$^{21}$ m$^{21}$. For the condition, WM-ICOS was applied. The signal to noise ratio of the 2f signal was 40.4. Then, the sensitivity was improved about 26. This result corresponding to the measurement limit of the partial atomic oxygen pressure of 250 Pa. The sensitivity of WM-ICOS was found to enough to diagnose the shock layer in high enthalpy flows. However, the spatial resolution was as large as 8 mm. The size of the beam pattern depends on the cavity length, robust ness of the cavity and accuracy of the cavity alignment. In this presentation, the relationship among these parameters will be discussed.   

Quantification Approach of Gas Temperate Distribution in Atmospheric Positive DC Glow Discharge Measured by Spectroscopic Imaging

In our previous work, a two-dimensional (2D) gas temperature distribution in a positive DC steady-state glow corona was qualitatively measured by spectroscopic imaging. Spectral images of its glow corona were taken using ICCD camera with ultra-narrow band-pass filters, and they were corresponded to the head and tail of a second positive system bands of nitrogen (2PS N$_{\mathrm{2}}$ (0-2)). The qualitative gas temperature was obtained from the emission intensity ratio ($I_{2Ptail}$/$I_{2Phead})$ between the head and tail of 2PS N$_{\mathrm{2}}$ (0-2). This emission intensity ratio also equals the rotational temperature ($T_{R})$, and $T_{R}$ almost equals the gas temperature ($T_{G})$ in atmospheric pressure. In this work, the qualitative 2D gas temperature distribution was derived from 2D $I_{2Ptail}$/$I_{2Phead}$ plots, and the calibration date of $I_{2Ptail}$/$I_{2Phead}$ for $T_{R}$ was accumulated by investigating the relationship between the spatially average absolute gas temperature ($T_{av})$ obtained by single-point spectroscopic measurement and the average value of $I_{2Ptail}$/$I_{2Phead}$ plots. On the basis of the calibration date, a spectroscopically-imaged qualitative 2D $I_{2Ptail}$/$I_{2Phead}$ distribution in a positive DC glow corona was converted to a quantitative 2D image of gas rotational temperature.   

Three electrode atmospheric pressure plasma jet in helium flow

Plasma jets are widely used in various types of applications and lately more and more in the field of plasma medicine. However, it is not only their applicability that distinguishes them from other atmospheric plasma sources, but also the behavior of the plasma. It was shown that plasma plume is not continuous, but discrete set of plasma packages. Here we present iCCD images and current voltage characteristics of a three electrode plasma jet. Our plasma jet has a simple design with body made of glass tube and two transparent electrodes wrapped around it. The additional third metal tip electrode was positioned at 10 and 25 mm in front of the jet nozzle and connected to the same potential as the powered electrode. Power transmitted to the plasma was from 0.5 W to 4.0 W and the helium flow rate was kept constant at 4 slm. For the 10 mm configuration plasma is ignited on the metal tip in the whole period of the excitation signal and in the positive half cycle plasma ``bullet'' is propagating beyond the metal tip. In contrast to that, for the 25 mm configuration at the tip electrode plasma can be seen only in the minimum and maximum of the excitation signal, and there is no plasma ``bullet'' formation.   

Measurement of the negative hydrogen ions temperature by using an omegatron mass analyzer in the sheet plasma

The production mechanisms of negative ions in hydrogen plasma are not easily understood because of the complex phenomena of atomic and molecular reactions. A mainstream measurement of H$^{-}$ is a laser photodetachment technique. We had measured negative ions using a laser photodetachment technique. Consequently, under a secondary hydrogen gas supply entering into the plasma, the H$^{-}$ is distributed in the periphery of the sheet plasma. In addition, it has been reported that the negative hydrogen ions transport velocity evaluated by the relaxation time of optically released electron current. Nevertheless, this technique a laser photodetachment cannot be used as a mass analyzer. In this paper, we have measured the temperature of the negative hydrogen ions T$_{H-}$ by using an omegatron mass analyzer in the sheet plasma. The T$_{H-}$ is determined by measuring the collection ion currents I$_{H-}$ as a function of the ion repeller voltage V$_{G2}$ by using an omegatron mass analyzer. From the fitting an exponential region of the measured I-V characteristics curve, T$_{H-}$ is around 1.40 eV at the gas pressure of 0.23 Pa in the periphery region of the sheet plasma.   

Laser Thomson scattering in a pulsed atmospheric arc discharge

Laser scattering measurements, including Rayleigh, Raman, and Thomson scattering have been performed on an atmospheric pulsed arc discharge. Such laser scattering techniques offer a non-invasive diagnostic to measure gas temperature, electron temperature, and electron density in atmospheric plasma sources, particularly those with feature sizes approaching 1 mm. The pulsed discharge is ignited in a pin to pin electrode geometry using a 6 kV pulse with 10 ns duration. The electrodes are housed in a glass vacuum chamber filled with argon gas. The laser signal is produced by a Nd:Yag laser supply, repetitively pulsed at 10 Hz and frequency quadrupled to operate at 266 nm. The scattered laser signal is imaged onto a triple grating spectrometer, which is used to suppress the Rayleigh scatter signal in order to measure the low amplitude Thomson and Raman signals. Preliminary results include measurements of electron temperature and electron density in the plasma column taken during the evolution of the discharge. The laser system is also used to measure the Rayleigh scattering signal, which provides space and time resolved measurements of gas temperature in the arc discharge.   

Diagnostics of capacitively-coupled hydrocarbon plasmas for deposition of diamond-like carbon films using quadrupole mass spectrometry and Langmuir probe

Diamond-like carbon (DLC) films are the hydrogenated amorphous carbon films, which contains a mixture of sp$^{2}$- and sp$^{3}$-bonded carbon. The DLC films have been widely used for various applications, such as automotive, semiconductors, medical devices, since have excellent material properties in lower friction, higher chemical stability, higher hardness, higher wear resistance. Until now, numerous investigations on the DLC films using plasma assisted chemical vapor deposition have been done. For precise control of coating technique of DLC films, it is enormously important to clarify the fundamental properties in hydrocarbon plasmas, as a source of hydrocarbon ions and radicals. In this paper, the fundamental properties in a low pressure radio-frequency hydrocarbon (Ar/CH$_{4}(1~\%)$ gas mixture) plasmas have been diagnosed using a quadrupole mass spectrometer (HIDEN ANARYTICAL Ltd., EQP-300) and Langmuir probe system (HIDEN ANARYTICAL Ltd., ESPion).   

Laser induced fluorescence measurements of ion velocity in a DC magnetron microdischarge with self-organized drift wave modes propagating in the direction opposite the E x B electron drift velocity

Evidence is presented of rotating azimuthal wave structures in a planar DC magnetron microdischarge operating in argon and xenon. Plasma emission captured using a high frame rate camera reveals waves of varying azimuthal modes propagating in the negative E x B direction. The dominant stable mode structure depends on discharge voltage. The negative drift direction is attributed to a local field reversal arising from strong density gradients that drive excess ions towards the anode. The transition between modes is shown to be consistent with models of gradient drift-wave dispersion in the presence of such a field reversal when the fluid representation includes ambipolar diffusion along the direction parallel to the magnetic field. Time-average and time-synchronized laser induced fluorescence measurements are carried out to elucidate the anode-bound ion dynamics driven by the field reversal.   

Emission Spectroscopy measurement of hybrid ECR-Helicon plasma source parameters

Optical emission spectroscopy measurement of plasma temperature and density were conducted on KACST hybrid plasma source. The hybrid source involves ECR and helicon source operated simultanously. The results indicate that the ECR alone density is higher than the density of the combined sources while the combined temperature is lower.   

Simulation of Ion Energy and Angular Distribution Functions using a Multidimensional RF Sheath Model

We have developed a novel numerical tool to rapidly and precisely predict the ion energy and angular distribution functions (IEDF and IADF) for an rf sheath formed around an arbitrary surface geometry in a single- or dual-frequency capacitively coupled plasma (CCP). A Monte Carlo method coupled with our multidimensional rf sheath model [1] is utilized to simulate ion trajectories and collisions with neutrals in an oscillating sheath. The IEDF calculated for a one-dimensional sheath in a dual-frequency CCP agreed very well with data measured using the In-wafer Ion Energy Analyzer [2]. We also present the IEDF and IADF obtained for a two-dimensional sheath around a wafer edge and an adjacent focus ring in another dual-frequency CCP to demonstrate the multidimensional capability of the present model. The model should be of practical use for the research and development of semiconductor device manufacturing equipment. \\[4pt] [1] K. Denpoh and T. Shirafuji, Jpn. J. Appl. Phys., 50 (2011), 036001.\\[0pt] [2] M. Funk, et al., presented at 59th Int. Symp. American Vacuum Soc., 2012.   

Investigation of ion energy and angular distributions at the wafer edge in rf capacitively coupled reactors using CFD-ACE+

Dual frequency capacitively coupled reactors are now commonly used in microelectronics fabrication. The extent of possible independent control of ion fluxes and ion energy and angular distribution (IEADs) by varying HF and LF signals is currently a topic of great interest [1]. In this study, we report on investigations of IEADs in single and dual frequency CCPs, including the wafer edge refinement using CFD-ACE+. The current algorithms in CFD-ACE+ allow the determination of total power at the electrode or in the discharge. To account for the presence of two or more rf sources connected to a powered electrode, the existing numerical algorithms for power targeting were enhanced to track current at the electrode as a function of time, vary voltage and determine power as a function of frequency. The Monte Carlo transport module for heavy species in CFD-ACE+ was recently enhanced to compute IEADs in rf discharges. Results for the effect of varying power and pressure on IEADs were compared to semi-analytical models and data reported in Gahan et al [1]. The validated model was applied to investigate the effect of details of HF and LF signals on IEADs in Argon discharges.\\[4pt] [1] Y. Zhang et al, J. Vac. Sci. Technol., A33, 031302, 2015\\[0pt] [2] D. Gahan, et al, Plasma Sources Sci. Technol., 21, 024004, 2012   

Uniformity Control in Capacitively Coupled Plasmas

In the fabrication of microelectronics devices, the volume production at mature yield is ultimately determined by the uniformity of the plasma. Plasma uniformity associated with patterning and hard mask open (HMO) steps are especially critical as the feature scale becomes smaller (\textless 20 nm) than the limitation of ArF lithography. Capacitively coupled plasmas (CCP) are attractive for these processes as the uniformity of radical and ion fluxes onto the wafer can be made quite uniform. In the case of dual frequency CCP (DF-CCP) sources, the high frequency (HF) power may be applied to an upper electrode and low frequency (LF) power is applied to a lower electrode where a substrate is located. The upper electrode can be divided into inner and outer electrode segments in order to provide plasma uniformity control. In this presentation we describe the ion flux and energy distributions and radical flux to the substrate for a DF-CCP source generated using a 2-dimensional plasma hydrodynamics model. We compare simulated results with the experimental measurements. The ability to control the plasma uniformity is demonstrated showing how changing electrode gap distance and splitting power on the upper electrodes impacts species and energy flux to the substrate. Gap variations introduce trade-offs. We find that a more uniform ion flux can be obtained for smaller gaps. As we split the HF power more towards the outer electrode, the fluxes to the wafer becomes more uniform.   

The effect of realistic energy dependent gamma-coefficients on heating dynamics and process control in capacitive radio frequency plasmas

In most PIC/MCC simulations of capacitively coupled plasmas (CCPs), only ion induced secondary electron emission from boundary surfaces is included. The corresponding emission probability, $\gamma $, is assumed to be constant and independent of the ion energy and surface conditions. It is usually guessed to be 0.1. However, in reality, $\gamma $-electron emission is known to be energy dependent and to be induced by fast atom impact and other processes, too. Here, we demonstrate that including realistic energy dependent $\gamma $-coefficients due to ion and fast atom impact strongly affects a variety of crucial plasma parameters under different discharge conditions: In single frequency CCPs operated in Argon at 13.56 MHz, the plasma density, ion flux, and electron heating mode are found to be significantly affected by including realistic emission coefficients. In dual-frequency CCPs driven at 2 MHz and 27 MHz, the separate control of the mean ion energy and flux is demonstrated to be sensitive to a realistic modeling of secondary electron emission. By switching individual processes on and off in the simulation, we identify the dominant physical mechanisms causing these effects.   

Particle-in-Cell Simulations of Atmospheric Pressure He/2\%H2O Discharges

Atmospheric pressure micro-discharges in contact with liquid surfaces are of increasing interest, especially in the bio-medical field. We conduct 1D3v particle-in-cell (PIC) simulations of a voltage-driven 1 mm width atmospheric pressure He/2\% H2O plasma discharge in series with an 0.5 mm width liquid H2O layer and a 1mm width quartz dielectric layer. A previously developed two-temperature hybrid global model of atmospheric pressure He/H2O discharges [Ke Ding, M.A. Lieberman and A.J. Lichtenberg, J. Phys. D: Appl. Phys. 47, 305203 (2014)] was used to determine the most important species and collisional reactions to use in the PIC simulations. We found that H13O6+, H5O3-, and electrons were the most prominent charged species, while most of the metastable helium He* was quenched via Penning ionization. The ion-induced secondary emission coefficient $\gamma_i$ was assumed to be 0.15 at all surfaces. A series of simulations were conducted at 27.12 MHz with $J_{\rm rf}\approx$ 800--2200 A/m$^2$. The H2O rotational and vibrational excitation losses were so high that electrons reached the walls at thermal temperatures. We also simulated a much lower frequency case of 50 kHz with $V_{\rm rf}=$ 10 kV. In this case, the discharge ran in a pure time-varying $\gamma$-mode.   

3D simulation of integrated multi-coil ICP source with azimuthal modes

Integrated multi-coil (IMC) planar ICP source with azimuthal motion is presented. Scaling ICP sources to larger substrate size is always complicated due to many technical issues and is challenged by the plasma chemistry. The source described in this work has capability of azimuthally moving plasma and has potential for large area and high density plasma applications. Hence, this system does not have an ideal axial symmetry, the 3D model approach has to be used to assess its transient performance. Moreover, reactor walls are imposing stronger boundary conditions on distribution of the radicals in ``off-axis reactive plasma.'' Intrinsic asymmetry of source and plasma were investigated by 3D fluid model developed under Plasma Module framework and supported by COMSOL Multiphysics solvers. Operation modes have potential to control plasma distribution, reaction chemistry and increase/modulate radicals' production. Simulation confirmed assumption that plasma distribution may essentially change in different gas. Under specific conditions integrated multi-coil ICP source is producing pulsed plasma. Temporal, spatial and population plasma characteristics were investigated in an inert carrier gas (Ar) and reactive plasma consisting of several gases (Ar, H2, CO and CH4).   

Energy transfer model in non-equilibrium e-O2-O high temperature flows

In the contribution to conference will be presented the first preliminary results of a kinetic model for the energy exchange in thermal and chemical non-equilibrium oxygen-containing high temperature flows.   

Mobility of Ar$^{+}$ in CF$_4$

In this work we present a complete cross section set for Ar$^{+}$ in CF$_4$ where existing experimentally obtained data are selected and extrapolated. Monte Carlo simulation method is applied to accurately calculate transport parameters in hydrodynamic regime. We discuss new data for Ar$^{+}$ ions in CF$_4$ where flux and bulk values of reduced mobility are given as a function of E/N (E-electric field, N-gas density). We find that internally resonant exothermic dissociative charge transfer cross section for CF$_3^{+}$ production significantly increases zero field ion mobility with respect to the polarization limit.   

Simulating the charging of a particle on a surface in a plasma

It is common knowledge that a floating surface will charge negative when a plasma is applied over it. One can imagine that any macroscopic dust particle on the surface will also get charged. The theory that describes this charging is, however, underdeveloped. It has been suggested that the particle will share its charge with the surface, leading to roughly the same surface charge density. This is, however, only valid when both the surface and the particle are electrically conductive. In this contribution, we show a novel model to simulate the charge on a non-conducting particle on a surface in a plasma. It is based on balancing the ion and electron fluxes through the plasma sheath towards the particle. With this, we show that the charge on a particle on a surface can be five orders of magnitude higher than what was previously assumed. Knowledge of the charge on a particle on a surface is important, because it, combined with the plasma sheath electric field, will lead to an electric force on the particle. It has been proposed that this force is important in the lofting of dust from the surface of extra-terrestrial bodies. Additionally, it has been suggested, that it can be used for cleaning in high-tech applications, such as lithography machines and spacecrafts.   

Coupling discharge and gas dynamics in streamer-less spark formation

We present simulations of streamer-less spark formation with a new 2D cylindrically symmetric model. The model incorporates the coupling between the electric discharge (described by a reaction-drift-diffusion model on the timescale of ion motion and Poisson's equation) and the gas (described by Euler equations and an energy balance equation for the heat generated). The model is employed to study electrical breakdown in supercritical N2 between planar electrodes under the application of pulsed voltages. We present the modeling results of gas heating by the electrical discharge and the back coupling of the thermally driven gas expansion on the discharge. Our model captures space-charge effects, thermal shocks and induced pressure waves. Because of secondary-electrode emission, we observe a cycle of electrons being released from the cathode, heating the gas, the gas affecting the discharge and the electrons being absorbed at the anode. This cycle might either lead to spark formation or to discharge decay.   

Conservation laws in embedding theory

In this work is considered embedding theory, a theory in which independent variables which describe gravity are functions of the space-time embedding into a ten-dimensional pseudo-Euclidean space. Neother's theorem is used to find conservation laws for energy and angular momentum as a result from the action's invariance in relation to the rotation and translation of the system. The form of these conservation laws and their consequences depending on the different formulations of embedding theory is discussed. It is also analyzed a transition from embedding theory to a field theory in a flat space-time with a number of dimensions greater than four. The same procedure is followed in this case to find conservation laws, resulting in the solution of the problem of time present in Einstein's theory of general relativity.   

Numerical band structure calculations of plasma metamaterials

Metamaterials (MM) are materials engineered to display negative macroscopic permittivity and permeability. These materials allow for designed control over electromagnetic energy flow, especially at frequencies where natural materials do not interact. Plasmas have recently found application in MM as a negative permittivity component. The permittivity of a plasma depends on its electron density, which can be controlled by an applied field. This means that plasmas can be used in MM to actively control the transmission or reflection of incident waves. This work focuses on a plasma MM geometry in which microplasmas are generated in perforations in a metal plate. We characterizethis material by its band structure, which describes its interaction with incident waves. The plasma-EM interactions are obtained by coupling Maxwell's equations to a simplified plasma momentum equation. A plasma density profile is prescribed, and its effect on the band structure is investigated. The band structure calculations are typically done for static structures, whereas our current density responds to the incident waves. The resulting band structures are compared with experimental results.   

Estimation of Photon Effects on Townsend Discharges for SecondaryElectronEmission Coefficient Measurements

A Monte Carlo simulation (MCS) is applied to investigate the secondary electron emission in Argon Townsend discharges. The influxes of ions, photons and metastable species onto the cathode surface are estimated simply from the number of inelastic collisions. The effect of photons becomes significant especially under higher pd conditions since the photon influx increases. This suggests the possibility of the estimation of the secondary electron emission coefficient of photons by examining breakdown voltage characteristics (Paschen curves). The effect of metastable species is much smaller than those of ions and photons and is negligible. The Paschen curves evaluated with MCS agrees well with the results of one-dimensional fluid model simulation when the photon effect is neglected, showing the necessity of further improvement.   

A Stabilization of LIBMESH Based Finite Element Method in Two-Dimensional Fluid Simulation of Capacitively Coupled Plasma

LIBMESH is a library for providing a framework for the numerical simulation of partial difference equations using arbitrary unstructured discretizations on serial and parallel platforms. A two-dimensional axisymmetric fluid simulation based on the finite element method which is supported by LIBMESH is introduced. Stabilization of this simulation is accomplished by using the test functions of Petrov-Galerkin scheme. An example of capacitively coupled plasma is modelled by the simulation and the results are compared with of other literatures.   

A hybrid model in inductively coupled plasma discharges with bias source: Description of model and experimental validation in Ar discharge

Traditional fluid simulation and Particle-in-Cell/Monte-Carlo collision (PIC/MCC) are very time consuming in inductively coupled plasma. In this work, a hybrid model, i.e. global model coupled bidirectional with parallel Monte-Carlo collision (MCC) sheath model, is developed to investigate inductively coupled plasma discharge with bias source. The global model is applied to calculate plasma density in bulk plasma. The sheath model is performed to consistently calculate the electric field, ion kinetic and the sheath thickness above the bias electrode. Moreover, specific numbers of ions are tracked and ultimately ion energy distribution functions (IEDFs) incident into bias electrode are obtained from MCC module. It is found that as the bias amplitude increases, the energy width of both IEDFs becomes wider, and the total outlines of IEDFs move towards higher energy. The results from the model are validated by experimental measurement and a qualitative agreement is obtained. The advantage of this model is that plasma density, ion flux and IEDF, which are widely concerned in the actual process, could be obtained within an hour.   

Hybrid Modeling of SiH$_{4}$/Ar Discharge in a Pulse Modulated RF Capacitively Coupled Plasma

Pulsed plasmas have offered important advantages in future micro-devices, especially for electronegative gas plasmas. In this work, a one-dimensional fluid and Monte-Carlo (MC) hybrid model is developed to simulate SiH$_{4}$/Ar discharge in a pulse modulated radio-frequency (RF) capacitively coupled plasma (CCP). Time evolution densities of different species, such as electrons, ions, radicals, are calculated, as well as the electron energy probability function (EEPF) which is obtained by a MC simulation. By pulsing the RF source, the electron energy distributions and plasma properties can be modulated by pulse frequency and duty cycle. High electron energy tails are obtained during power-on period, with the SiHx densities increasing rapidly mainly by SiH$_{4}$ dissociation. As the RF power is off, the densities in the bulk region decrease rapidly owing to high energy electrons disappear, but increase near electrodes since diffusion without the confinement of high electric field, which can prolong the time of radials deposition on the plate. Especially, in the afterglow, the increase of negative ions near the electrodes results from cool electron attachment, which are good for film deposition.   

Radio-frequency breakdown in oxygen and synthetic air

Parallel plate rf discharges have a long history in the materials processing industry, but much of their behavior is still poorly understood, particularly processes taking place during the breakdown. In order to test some simple models of RF breakdown we have performed detailed simulations using well tested Monte Carlo code that allows also verification against RF and DC benchmarks but also treatment of temporal spatial non-localities. This work contains our simulation results of the breakdown voltage curves in oxygen and synthetic air. At first, electrons were released from the middle of the gap and any further development is due to the applied field, random number generator and solutions of kinetic and balance equations. The obtained results qualitatively agree with the existing experimental and simulation results. In addition, spatial distributions of electron concentration, energy and rates of elastic scattering and ionization are also presented and discussed in light of the processes leading to the breakdown. We analyze the role of low threshold inelastic collisions and non-conservative attachment as compared to the previous results for argon.   

PlasmaPIC: A tool for modeling low-temperature plasma discharges

PlasmaPIC is a three-dimensional particle in cell (PIC) code. It consists of an electrostatic part for modeling dc and rf-ccp discharges as well as an electrodynamic part for modeling inductively coupled discharges. The three-dimensional description enables the modeling of discharges in arbitrary geometries without limitations to any symmetry. These geometries can be easily imported from common CAD tools. A main feature of PlasmaPIC is the ability of an excellent massive parallelization of the computation, which scales linearly up to a few hundred cpu cores. This is achieved by using a multigrid algorithm for the field solver as well as an effective load balancing of the particles. Moreover, PlasmaPIC includes the interaction of the neutral gas and the plasma discharge. Because the neutral gas and the plasma simulation are acting on different time scales we perform the simulation of both separately in a self-consistent treatment, whereas the neutral gas distribution is calculated using the direct simulation Monte Carlo method (DSMC). The merge of these features turns PlasmaPIC into a powerful simulation tool for a wide range of plasma discharges and introduces a new way of understanding and optimizing low-temperature plasma applications.   

Verification of particle-in-cell simulations against exact solutions of kinetic equations

Demonstrating correctness of computer simulations (or verification) has become a matter of increasing concern in recent years. The strongest type of verification is a demonstration that the simulation converges to an exact solution of the mathematical model that is supposed to be solved. Of course, this is possible only if such an exact solution is available. In this paper, we are interested in kinetic simulation using the particle-in-cell method, and consequently a relevant exact solution must be a solution of a kinetic equation. While we know of no such solutions that exercise all the features of a typical particle-in-cell simulation, in this paper we show that the mathematical literature contains several such solutions that involve a large fraction of the functionality of such a code, and which collectively exercise essentially all of the code functionality. These solutions include the plane diode, the neutron criticality problem, and the calculation of ion energy distribution functions in oscillating fields. In each of theses cases, we can show the the particle-in-cell simulation converges to the exact solution in the expected way. These demonstrations are strong evidence of correct implementation.   

PLASIMO modelling of a helium atmospheric plasma jet

Atmospheric plasma jets are intensively studied because of their wide range of potential applications, in particular for surface treatments and in plasma medicine. The PLASIMO modeling toolkit is used to simulate the capillary plasma-jet in order to quantify the delivery of fluxes and fields to the treated sample. The setup under study consists of capillary powered electrode through which helium gas flows and a grounded ring electrode placed a distance of few mm in front of the capillary. The discharge is excited by sinusoidal voltage with amplitude of 2kV and 30KHz repetition rate. The plume emanating from the jet, or the plasma bullets, propagates through a Pyrex tube and the gas phase channel of helium exits into the surrounding air. The drift-diffusion module of PLASIMO is used to construct a model of the helium plasma jet with the aim to study the dynamics of the plasma inside and outside the source. We discuss the properties of the plasma source and the plasma plume or bullet emitted into the atmosphere. The modeling results are qualitatively compared with experimental observations.   

A volume averaged global model for inductively coupled HBr/Ar plasma discharge

A global model for inductively coupled HBr/Ar plasma was developed. The model was based on a self-consistent global model had been developed by Kwon et al., [J. Appl. Phys. 109, 073311 (2011)] and a set of chemical reactions in the HBr/Ar plasma was compiled by surveying theoretical, experimental and evaluative researches. In this model vibrational excitations of bi-atomic molecules and electronic excitations of hydrogen atom were taken into account. Neutralizations by collisions between positive and negative ions were considered with Hakman's approximate formula achieved by fitting of theoretical result. For some reactions that were not supplied from literatures the reaction parameters of Cl$_2$ and HCl were adopted as them Br$_2$ and HBr, respectively. For validation calculation results using this model were compared with experimental results from literatures for various plasma discharge parameters and it showed overall good agreement.   

Spectral Kinetic Simulation of the Ideal Multipole Resonance Probe

The term Active Plasma Resonance Spectroscopy (APRS) denotes a class of diagnostic techniques which utilize the natural ability of plasmas to resonate on or near the electron plasma frequency $\omega_{pe}$: An RF signal in the GHz range is coupled into the plasma via an electric probe; the spectral response of the plasma is recorded, and a mathematical model is used to determine plasma parameters such as the electron density ne or the electron temperature Te. One particular realization of the method is the Multipole Resonance Probe (MRP). The ideal MRP is a geometrically simplified version of that probe; it consists of two dielectrically shielded, hemispherical electrodes to which the RF signal is applied. A particle-based numerical algorithm is described which enables a kinetic simulation of the interaction of the probe with the plasma. Similar to the well-known particle-in-cell (PIC), it contains of two modules, a particle pusher and a field solver. The Poisson solver determines, with the help of a truncated expansion into spherical harmonics, the new electric field at each particle position directly without invoking a numerical grid. The effort of the scheme scales linearly with the ensemble size N.   

The influence of electrohydrodynamic flow on the distribution of chemical species in positive corona

A numerical simulation of positive corona discharge in air, including the effect of electrohydrodynamic (EHD) motion of the gas, has been carried out. Air flow is assumed to be confined between two parallel plates, and corona discharge is produced around a thin wire, midway between the plates. Therefore, fluid dynamics equations, including electrical forces, have been solved together with the continuity equation of each neutral species. The plasma chemical model included 24 chemical reactions and ten neutral species, in addition to electrons and positive ions. The results of the simulation have shown that the influence of EHD flow on the spatial distributions of the species is quite different depending on the species. Hence, reactive species like atomic oxygen and atomic nitrogen are confined to the vicinity of the wire, and they are weakly affected by the EHD gas motion. In contrast, nitrogen oxides and ozone are efficiently dragged outside the active region of the corona discharge by the EHD flow.   

3D PIC Modeling of Microcavity Discharge

We present a number of techniques and challenges in simulating the transient behavior of a microcavity discharge. Our microcavities are typically cylindrical with diameters approximately 50 - 100 $\mu$m, heights of 50 - 200 $\mu$m, pressure near atmospheric, and operate at a few hundred volts. We employ a fully kinetic simulation methodology, the Particle-in-Cell (PIC) method, with interparticle collisions handled via methods based on direct simulation Monte Carlo (DSMC). In particular, we explicitly include kinetic electrons. Some of the challenges we encounter include variations in number densities, external circuit coupling, and time step resolution constraints. By employing dynamic particle weighting (particle weights vary over time by species and location) we can mitigate some of the challenges modeling systems with 10$^{7}$ variations in number densities. Smoothing mechanisms have been used to attempt to mitigate external circuit response. We perform our simulations on hundreds or thousands of processing cores to accommodate the computational work inherent in using relatively small time step sizes (e.g., 50 fs for a 100 ns calculation). In addition, particle weighting issues inherent to three-dimensional low temperature plasma systems will be mentioned.   

Generation of Diffuse Large Volume Plasma by an Ionization Wave from a Plasma Jet

Low temperature plasma jets emitted in ambient air are the product of fast ionization waves that are guided within a channel of a gas flow, such as helium. This guided ionization wave can be transmitted through a dielectric material and under some conditions can ignite a discharge behind the dielectric material. Here we present a novel way to produce large volume diffuse low pressure plasma inside a Pyrex chamber that does not have any electrodes or electrical energy directly applied to it. The diffuse plasma is ignited inside the chamber by a plasma jet located externally to the chamber and that is physically and electrically unconnected to the chamber. Instead, the plasma jet is just brought in close proximity to the external wall/surface of the chamber or to a dielectric tubing connected to the chamber. The plasma thus generated is diffuse, large volume and with physical and chemical characteristics that are different than the external plasma jet that ignited it. So by using a plasma jet we are able to ``remotely'' ignite volumetric plasma under controlled conditions. This novel method of ``remote'' generation of a low pressure, low temperature diffuse plasma can be useful for various applications including material processing and biomedicine.   

Microwave Plasma Excitation Using Cylindrical Cavity with Dual Injection

Large high-density plasmas have been generated by injecting magnetron-based microwaves radiated from slots cut on a wall of a rectangular or coaxial waveguide. However, a standing structural microwave in the waveguide often causes non-uniformity of plasma density. To minimize such inhomogeneity excited by the conventional waveguide, we adopt a resonant cylindrical cavity combined with a solid-state microwave amplifier. Microwave is injected into the cavity from two ports azimuthally apart by 90 degrees to each other (\textit{dual injection}). FDTD simulations are performed for a \textit{TE}$_{111}$ mode resonant cavity excited by \textit{single} or \textit{dual} microwave injection. In the case of the dual injection with a phase difference of $\pi $/2, the wave field azimuthally rotates in the cavity, and hence the slots cut on a cavity bottom wall launch travelling waves, thus minimizing the azimuthal inhomogeneity of the resultant plasma. 40-cm-diameter plasmas are experimentally generated in argon at 0.1 $\sim$ 5 Torr with microwaves of 2.4--2.5GHz and 400W. Threshold powers for plasma ignition are much less in \textit{dual} injection than those in \textit{single }injection. Optical emission images of the cylindrical plasmas show that the plasma uniformity is considerably improved in \textit{dual} injection, particularly at high-pressure and low-power.   

Time evolution of the plasma column structure and gas temperature in pulsed surface wave discharges produced at microwave frequencies in helium at intermediate pressure

Pulsed surface wave discharges produced at microwave frequency in helium at intermediate pressure (1-50 Torr) were investigated. The time-evolution of the spatial structure of the plasma column was studied by using iCCD imaging. An ionization front is observed that propagates with a typical velocity of a few km/s soon after plasma ignition and decreases rapidly afterwards until the plasma reaches its steady state. A ``plasma bullet'' of a few cm long is also observed several tens of microseconds after breakdown especially at lower pressure. On the other hand, by using the rotational structure of OH molecular band emission, the gas temperature was determined as a function of time at different axial positions. Depending on the operating conditions, its value is typically in the range 400-900$^{\circ}$ C. It is also found that the gas temperature reaches its steady-state value within a few hundreds of microseconds after ignition and that it decreases as the plasma columns expands.   

Positive column of the glow discharge in argon

We report the measurements we performed of the reduced electric field strength $E/p$ in the positive column in the range of the gas pressure and tube radius product of 0.01~\textless ~\textit{pR}~\textless ~30~Torr$\cdot $cm. We got good agreements with numerical models and experimental data of other authors. We also present two analytical models for the reduced electric field $E/p$. The first model deals with the ambipolar mode of the positive column of the constant current discharge in noble gases. We consider the case of a balance between the rate of charged particle production due to direct ionization of gas molecules through electron impact and their escape to the discharge tube walls. Simple expressions for the reduced electric field $E/p$ in the positive column in argon are obtained. The second model consists in considering the production and loss of charged particles and metastable atoms and obtaining a simple equation for the reduced electric field $E/p$ depending on the discharge current density, gas pressure and tube radius. These models furnish a good description of experimental data in the whole range of \textit{pR} values studied.   

Mechanisms of gas breakdown in non-uniform electric field between flat electrodes

This paper studies how the electric field non-uniformity and the electron diffusion escape affect the DC gas breakdown between flat electrodes. We registered the breakdown curves of the DC discharge between the electrodes having the radius of $R_{e}$~$=$~6~mm with the inter-electrode gap values $L$ between 3 and 72 mm in the tubes of inner diameter values of 13 and 56 mm within the nitrogen pressure range $p$ from 0.02 to 120 Torr. We found that the breakdown curves for the gap of 3 mm actually match in the total pressure range, the diffusion escape of electrons to the tube walls playing no role in the gas breakdown process. In a narrow tube the minimum breakdown voltage is constant in the range of $L$/$R_{e}$~$\le $~1 but with the subsequent gap growth it increases linearly in order to compensate for the diffusion loss to the tube walls. For the wide tubes of 56 mm in diameter and for the gap of 72 mm the breakdown curves possess more flat minima and they run in the range of lower breakdown voltage values than one for a narrow tube. The minimum breakdown voltage grows slowly only in the range of $L$/$R_{e}$~\textgreater ~2.   

Modes of burning and axial structure of dc discharge with transverse diaphragm

This paper reports the CVCs of the dc discharge with a diaphragm located between the electrodes. We determined the conditions when normal and abnormal modes of such a dc discharge can exist. The axial profiles of the plasma parameters (electron temperature, plasma potential and concentration) from the anode to the cathode sheath boundary were also registered with a single Langmuir probe. We demonstrated that at low nitrogen pressure of 0.1 Torr and the discharge current of 1 mA a double layer was formed near the diaphragm only in the cathode part of the tube whereas with the current of 10 mA the double layer expanded to the anode part too. At the nitrogen pressure of 0.5 Torr a positive column was observed in the anode part of the tube, and the double layers were formed on both sides of the diaphragm (in the anode as well as in the cathode parts of the tube). These layers accelerated electrons into the orifice. In all cases the maximum of the plasma concentration is located inside the orifice.   

Plasma Discharge Effect on Secondary Electron Yield of Various Surface Locations on SRF Cavities

Electron activity (field emission and multipacting) has been identified as the main limiting factor of Superconducting Radiofrequency (SRF) cavity performance. Secondary Electron Yield (SEY) is highly dependent on the state of the cavity's surface, which is investigated before and after plasma exposure. Current methods for simulating the electron activity in SRF cavity consider it as a uniform surface. Due to fabricating procedure there are three distinct areas of the cavity's microstructure: weld zone, heat affected zone, and base metal zone. Each zone has a characteristic microstructure even after the treatments that are currently used to clean the surface of the cavities. Improvement of existing surface treatment techniques, or use of a new is required in order to increase the limit of Q factor towards the theoretical limit of Nb. RF discharge is a promising technique for this purpose. In order to test the effect of the plasma on the SEY of the various cavity surface zones we have developed the experimental setup to measure the energy distribution of the SEY from coupon-like samples. Samples are made in a way that all three zones of cavity surface will be included in the examination. We will present the SEY changes in these three zones before and after plasma treatment.   

Three Modes of Air Atmospheric Pressure Plasma

Atmospheric pressure plasma jet operating in air have gained a high interest due to its various applications in industry and biomedical [1]. The presented air plasma jet system is consisted of stainless steel hollow needle electrode of 1 mm inner diameter which is covered with a quartz tube with a 1 mm diameter side hole. The hole is above the tube nozzle by 5 mm and it is covered by a copper ring which is connected to the ground. The needle is connected to sinusoidal 27 kHz high voltage power supply (25 kV) though a current limiting resistor of 50 k$\Omega$. The tested distance between the needle tip and the side hole was 1 mm or 2.1 mm gape. The electric and plasma jet formation characteristics show three modes of operations. Through these modes the plasma length changes with air flow rate to increase in the first mode and to confine inside the quartz tube in the second mode, then it start to eject from the nozzle again and increase with flow rate to reach a maximum length of 7 mm at 4.5 SLM air flow rate in the third mode. The measured gas temperature of the plasma jet can approach room temperature (300 K). Moreover, the plasma jet emission spectra shows the presence of reactive O and OH radical in the plasma jet. These results indicate that the generated air plasma jet can be used a plasma sterilization. \\[4pt] [1] A-A.H. Mohamed, J.F. Kolb, Schoenbach, Eur. Phys. J. D 60, 517-522 (2010).   

Optical Emission Spectroscopy in PECVD Helps Modulate Key Features in Biofunctional Coatings for Medical Implants

We explore the use of optical emission spectroscopy (OES) diagnostic tools as a process feedback control strategy in plasma-assisted deposition of biofunctional coatings. Hydrogenated carbon nitride coatings are deposited on medical-grade metallic substrates using radio-frequency (rf) discharges sustained in C$_{\mathrm{2}}$H$_{\mathrm{2}}$/N$_{\mathrm{2}}$/Ar gaseous mixtures. The discharge is generated by capacitively coupling the rf power (supplied at $f \quad =$ 13.56 MHz) to the plasma and the substrates are electrically biased using a pulse generator to provide microsecond square profiled pulses at voltages in the range \textbar $V_{\mathrm{bias}}$\textbar $=$ 250 V -- 1000 V. Nitrogen content and CN bonding configurations in the coatings follow similar trends to those of CN radicals and nitrogen molecular ions in the discharge. OES is used as a non-intrusive diagnostic technique to identify a suitable window of process parameters and ultimately achieve biofunctional interfaces compatible with current clinical demands. Importantly, we demonstrate that key features of the coatings can be modulated and made suitable for blood and/or tissue contacting medical implants, such as coronary stents and orthopaedic implants. The coatings are mechanically robust, inherently non-thrombogenic and can be readily modified, enabling an easy functionalization through the immobilization of biological molecules in a bioactive conformation.   

Development of Simplified Atmospheric-Pressure Plasma Nitriding

Nitriding treatment is one of the surface hardening technologies, applied to dies and automobile components. In recent industry, low-pressure nitriding treatment using vacuum system is mainstream. On the other hand, we have originally developed an atmospheric-pressure plasma nitriding which do not need vacuum system. However we needed an air-tight container to purge residual oxygen and external heater to control treatment temperature. To make this technique practical, we addressed to construct a simplified treatment system, where treatment temperature is controlled by thermal plasma itself and oxygen purging is achieved by a simple cover. This means that any air-tight container and external heater is not necessary. As a result, surface temperature is controlled by changing treatment gap from nozzle tip to steel surface. We succeeded in controlling well thickness of hardened layer by adjusting treatment temperature even in such a simplified system. In the conference, we also discuss experimental results for hardening complex shaped materials by using our simplified nitriding.   

Sterilization Efficiency of Spore forming Bacteria in Powdery Food by Atmospheric Pressure Plasmas Sterilizer

To provide food sterilization method capable of killing highly heat resistant spore forming bacteria, we have studied effects of plasma treatment method at atmospheric pressure in order to develop a new high speed plasma sterilization apparatus with a low cost and a high efficiency. It is also difficult even for the plasma treatment to sterilize powdery food including spices such as soybean, basil and turmeric. This paper describes that an introduction of mechanical rotation of a treatment space increases the efficiency so that perfect inactivation of spore forming bacteria in these materials by a short treatment time has been demonstrated in our experiments. We also will discuss the sterilization mechanism by dielectric barrier discharge.   

Development of High-Density Plasma Photonic Crystals Using High-Power Lasers

A plasma photonic crystal (PPC) is an array of plasma structures that interacts with electromagnetic (EM) waves in ways not possible with natural materials. 2D PPCs can be used for generating a band gap, which is a range of wave frequencies in which no waves are transmitted through the structure. Such gap forms when an EM wave travels through a 2D PPC with spacing equal to half the wavelength of the wave and plasma frequency ($\omega_p$) on the order of the frequency of the wave. Until recently, research on PPCs has been limited to $\omega_p < 30~GHz$, which is equivalent to a plasma density of $n_e < 10^{13}~cm^{-3}$. Over the last year, PPCs of $n_e > 10^{15}~cm^{-3}$ have been generated at Stanford through the use of high-power lasers. The PPCs are generated by expanding the laser beam from a Q-switched Nd:YAG laser through a Galilean beam expander and subsequently focusing the beam through an optical micro-lens array. The intense photoionization of air that occurs at the focus of the individual lenses leads to the formation of a 2D array of very dense plasma spots. Photomultiplier measurements show a plasma lifetime of $\sim$150 ns during which the plasma array functions as a PPC, representing a first step towards advancing the field forward into the low THz regime.   

Fast Rise Time and High Voltage Nanosecond Pulses at High Pulse Repetition Frequency

Eagle Harbor Technologies (EHT), Inc. is conducting research to decrease the rise time and increase the output voltage of the EHT Nanosecond Pulser product line, which allows for independently, user-adjustable output voltage (0 -- 20 kV), pulse width (20 -- 500 ns), and pulse repetition frequency (0 -- 100 kHz). The goals are to develop higher voltage pulses (50 -- 60 kV), decrease the rise time from 20 to below 10 ns, and maintain the high pulse repetition capabilities. These new capabilities have applications to pseudospark generation, corona production, liquid discharges, and nonlinear transmission line driving for microwave production.   

Analysis and utilization of plasma treated water for food and agricultural interest

Attention on aqueous chemical species produced in plasma-treated solutions through plasma-liquid interactions has been increased because of its strong relation to bio/medical and food applications. The long-lived and reactive oxygen and nitrogen species such as hydrogen peroxide, ozone, superoxide anion, and oxyacids play a crucial role in those applications. The plasma treatment brings about absorption of these species into the target liquid and also induces changes in liquid characteristics and composition via photolysis by plasma UV emission and post-discharge reactions. In this presentation, we discuss the result of our investigation of the chemical properties related to the two main oxyacids, HNO$_{2}$ and HNO$_{3}$, in plasma treated water (PTW). Water was treated in close proximity by our SDBD system developed specifically to meet the application requirements. The chemical properties of the solution varied gradually over the treatment time and storage time. Here we report the result of our experiment, theoretical analysis, and their consistency. Furthermore, the dependence of the nitrite ion production yield on the dissipated power, treatment time, and dielectric material will be discussed. Based on the revealed fundamental characteristics, the utilization of PTW in the meat curing process as one of the nitrite sources will be briefly demonstrated. In terms of sausage quality, there were no noticeable effects of PTW on the total aerobic bacteria counts, color, and peroxide values of sausages compared with those using celery powder and sodium nitrite.   

Magnetic and structural properties of CaMn$_{0.9}$Mo$_{0.1}$O$_3$ perovskite synthesized in abnormal glow discharge

In this work we use the abnormal glow discharge (AGD) to produce the CaMn$_{0.9}$Mo$_{0.1}$O$_3$ perovskite through decarbonize, calcination and sintering steps. Structural characterization was carry out by Rietveld refinement of X-ray diffraction on samples after sintering step. The magnetic properties was analysed through magnetization curves as a function of temperature for applied magnetic fields in the range of 20 Oe to 20 kOe by the ZFC-FC method and magnetization curves in function of the applied field at 50 K and 300 K temperatures. The CaMn$_{0.9}$Mo$_{0.1}$O$_3$ perovskite was also produced by conventional method in resistive furnace and its behaviour was compared with those of the plasma synthesized. The X-ray analysis reveals that the samples produced by both methods crystalized in a Pnma structure, the lattice parameters change and one second phase appears when the AGD is applied in the last production steps. The magnetization measurements allow analysing the behaviour of the sample at low temperatures and comparing the magnetic transitions in the samples produced by both methods; these are influenced according to production method employed. The results shows that the use of AGD is an alternative method to produce ceramic materials, which reduced ostensibly the production time and allow to obtain similar magnetic and structural properties with respect to conventional method.   

Effects of Plasma Formation on the Cesium Diode (DPAL) and Excimer (XPAL) Pumped Alkali Laser

Diode pumped alkali lasers (DPALs) and excimer pumped alkali lasers (XPALs) are being investigated as a means to convert optical pumps having poor optical quality to laser radiation having high optical quality [1]. DPALs sustained in Cs vapor are pumped on the D$_{\mathrm{2}}$(852.35 nm), Cs(6$^{\mathrm{2}}$S$_{\mathrm{1/2}})\to $ Cs(6$^{\mathrm{2}}$P$_{\mathrm{3/2}})$, transition and lase on the D$_{\mathrm{1}}$(894.59 nm) transition, Cs(6$^{\mathrm{2}}$P$_{\mathrm{1/2}})\to $ Cs(6$^{\mathrm{2}}$S$_{\mathrm{1/2}})$. Collisional mixing (spin orbit relaxation) of the Cs(6$^{\mathrm{2}}$P$_{\mathrm{3/2}})$ and Cs(6$^{\mathrm{2}}$P$_{\mathrm{1/2}})$ levels is a key part of this three-level (in fact, a quasi-two-level) laser scheme. In the five-level XPAL pumping scheme, the CsAr(B$^{\mathrm{2}}\Sigma ^{\mathrm{+}}_{\mathrm{1/2}})$ state is optically pumped by 836.7 nm pulses, which later dissociates and produces Cs(6$^{\mathrm{2}}$P$_{\mathrm{3/2}})$. As in DPAL, a collisional relaxant transfers the population of Cs(6$^{\mathrm{2}}$P$_{\mathrm{3/2}})$ to Cs(6$^{\mathrm{2}}$P$_{\mathrm{1/2}})$, which enables lasing on D$_{\mathrm{1}}$ transition. A first principals global computer model has been developed for both systems to investigate the effects of plasma formation on the laser performance. Argon is used as a buffer gas and nitrogen or ethane are used as a collisional relaxant at total pressure of 600 Torr at temperatures of 350-450 K, which produces vapor pressures of Cs of \textless 0.1 Torr. In both systems, a plasma formation in excess of 10$^{\mathrm{14}}$ - 10$^{\mathrm{16\thinspace \thinspace }}$cm$^{\mathrm{-3}}$ occurs, which potentially reduces laser output power by electron collisional mixing of upper and lower laser levels [2]. [1] W.F. Krupke, et. al., Opt. Lett. \textbf{28} 2336 (2003). [2] B.D. Barmashenko, et. al. Opt. Comm. \textbf{292}, 123 (2013).   

Ultraviolet Light Source Using Electrodeless Microwave Discharge

Surface treatment technologies using ultraviolet (UV) light, such as organic residue removal, surface modification or sterilization, are widely used. So far, UV lamps using DC discharge with electrodes inside the lamp tube is commonly used. However, sputtering of electrode materials sometimes causes deposition on the inner tube surface as well as degradation of the electrodes, resulting in short life time of the lamp tube. In this study, we propose an electrodeless UV mercury (Hg) lamp source using microwave power. 2.45 GHz Microwave power (\textless 4 kW) from a power supply is divided into four power lines using branch waveguides. A mercury lamp tube (diameter: 9.6 mm, length: 42 cm, Hg: 13.5 mg, Ar: 1 Torr) is inserted into the branch waveguides and microwave power is coupled to the plasma. Emission from the lamp is monitored by a monochromator and an 254 nm UV monitor. Lamp temperature is also measured by a thermography camera and tube temperature up to 900 K with good uniformity along $\sim$ 30 cm was observed. Uniformity of the 254 nm UV light intensity was $+$15 {\%} along the lamp tube. The maximum UV light intensity of 64 mW/cm$^{2}$ was observed at a microwave power of 4 kW.   

EUV nanosecond laser ablation of silicon carbide, tungsten and molybdenum

In this paper we present results of study interaction of nanosecond EUV laser pulses at wavelength of 46.9 nm with silicon carbide (SiC), tungsten (W) and molybdenum (Mo). As a source of laser radiation was used discharge-plasma driver CAPEX (CAPillary EXperiment) based on high current capillary discharge in argon. The laser beam is focused with a spherical Si/Sc multilayer-coated mirror on samples. Experimental study has been performed with 1, 5, 10, 20 and 50 laser pulses ablation of SiC, W and Mo at various fluence values. Firstly, sample surface modification in the nanosecond time scale have been registered by optical microscope. And the secondly, laser beam footprints on the samples have been analyzed by atomic-force microscope (AFM).   

Radiative properties of Ceramic Metal-Halide High Intensity Discharge lamps (CMH) containing additives in argon plasma

The lighting represents a consumption of about 19{\%} of the world electricity production. We are thus searching new effective and environment-friendlier light sources. The Ceramic Metal-Halide High Intensity Lamps (CMH) are one of the options for illuminating very high area. The new CMH lamps are mercury free and contain additives species which lead to a richer spectrum in specific spectral intervals, a better colour temperature or colour rendering index. This work is particularly focused on the power radiated by these lamps, estimated using the Net Emission Coefficient, and depending on several additives (calcium, sodium, tungsten, dysprosium, thallium or strontium).   

Time resolved EUV spectra from Z{\-}pinching capillary discharge plasma

We developed [1] symmetrically charged driver to obtain high voltage, high current Z-pinching capillary discharge. Plasma is created by up to 70~kA, 29~ns rise{\-}time current pulse passing through a 5~mm inner diameter, 224~mm long capillary filled with gas to initial pressure in the range of 1~kPa. Due to the low inductance design of the driver, the pinch is observable directly from the measured current curve. Time-integrated and time-resolved spectra of discharge plasma radiation are recorded together with the capillary current and analyzed. The most encouraging spectra were captured in the wavelength range 8.3 $\div$ 14 nm. This spectral region contains nitrogen Balmer series lines including potentially lasing NVII~2~--~3 transition. Spectral lines are identified in the NIST database using the FLY kinetic code. The line of 13.38~nm wavelength, transition NVII~2~--~3, was observed in gated, and also in time-integrated spectra for currents \textgreater 60~kA. \\[4pt] [1] Nevrkla, M., Jancarek, A., Nawaz, F.: Discharge driver for 13.4 nm XUV laser, 2013 19th IEEE Pulsed Power Conference, PPC 2013; San Francisco, CA; United States; 16 June 2013~through~21 June 2013; Code~101034   

Spectroscopic studies of Cr VI species in a laser produced plasma

We present measurements characterizing a laser generated, highly ionized microplasma suitable to extend the cut-off energy of High Harmonic Generation (HHG) to energies up to 5 keV. The HHG process occurs when a strong ultrafast laser hits a gaseous target producing coherent radiation with a much higher photon energy than the driving laser. Commonly, noble gases are used and typical photon energies of several 100 eV are obtained. We plan to use Cr$^{5+}$ species as the target for HHG as generated by a double pulse method: the first pulse creates the plasma, the second pulse is used to obtain the temperature required for Cr$^{5+}$. Here, we present results on the optimization of plasma parameters such as the plasma temperature, the number density and the dynamics of Cr$^{5+}$ by means of spectroscopic techniques in the optical and the XUV regime.   

Temperature Dependence of Nitro-Quenching by Atmospheric-Pressure Plasma

A lot of techniques exist as the hardening method of steels, such as nitriding, carburizing and quenching. However, low-alloy steels cannot be hardened by nitriding because hardening by nitriding requires nitride precipitates of special alloy elements such as rare metals. Recently, nitro-quenching (NQ) was developed as a new hardening process, where nitrogen invokes martensitic transformation instead of carbon. NQ is adaptable to hardening low-alloy steels because it does not require alloy elements. In industrial NQ, nitrogen diffusion into steel surface is operated in high temperature ammonia gas. As a new technology, we have developed surface hardening of low-alloy steel by NQ using an atmospheric-pressure plasma. Here the pulsed-arc plasma jet with nitrogen/hydrogen gas mixture is sprayed onto steel surface and then water quench the sample. As a result, the surface of low-alloy steel was partially hardened up to 800 Hv by producing iron-nitrogen martensite. However, the hardness profile is considerably non-uniform. We found that the non-uniform hardness profile can be controlled by changing the treatment gap, the gap between the jet nozzle and the sample surface. Eventually, we succeeded in hardening a targeted part of steel by optimizing the treatment gap. Moreover, we propose the mechanism of non-uniform hardness.   

A Kinetic Plasma-Pumped Rare Gas Laser

Extending from diode-pumped alkali vapor lasers (DPAL), Han and Heaven [\textit{Opt. Lett.} \textbf{37} 2157-9] have shown that rare gas metastable states, $np^{5}(n+1)s[3/2]_{2}$, can operate as the base of a three-level laser with excition of the $(n+1)s \rightarrow (n+1)p$ transitions. Though both the rare gas lasers (RGL) and DPALs can be excited with incoherent optical pumping, RGLs do not suffer from the highly reactive behavior of alkali metals. Since metastable populations are maintained via electric discharge, we propose using a tuned electron energy distribution function (EEDF) to modify RGL efficiencies and drive the population inversion. The EEDF is maintained by the discharge along with the introduction of electron sources. Using our kinetic global modeling framework (KGMf) and three gas systems (helium buffered argon and krypton along with pure argon), we first validate the intracavity intensity laser model and then generate gain and energy efficiency baselines for each system. Parameter scanning methods are then used to find optimized EEDFs and system parameters for metastable production, generation of a lasing population inversion, and increasing RGL operation efficiencies. Finally, we determine if an RGL can operate without optical pumping.   

Atomic layer etching of SiO$_{2}$ under Ar/ C$_{4}$F$_{8}$ plasmas with pulsed bias

The purge steps in the atomic layer etching (ALE) reduce the throughput and increase the costs. By elaborately choosing bias pulse waveforms, ALE can be achieved without alternating feedstock gas, although compromises are needed between throughput and precision. In this study, a multi-scale model is used to simulate ALE of SiO$_{2}$ with a pulsed bias in Ar/C$_{4}$F$_{8}$ plasmas. Firstly, a commercial software CFD-ACE$+$ is used to calculate the reactant fluxes towards the substrate in a CCP reactor. The ion bombardment energy and angular distributions at substrate are calculated with a hybrid sheath model, where electric field is got from fluid equations, and the ion-neutral collisions are considered applying the Monte Carlo(MC) method. Then, the reactant transport and surface MC reaction algorithm are coupled in a feature scale model. Influences of bias pulse frequency and duty ratio on atomic precision control are studied. Also, comparisons are made between conventional ALE and pulsed bias etching. Results show that when pulsed bias is used instead of alternating the feedstock gas, we can still achieve certain self-limiting nature in etching, with higher throughput and acceptable loss of precision.   

Many flaked particles generated by electric field stress working as an impulsive force in mass-production plasma etching equipment

Particles generated in plasma etching significantly lower production yield. In plasma etching, etching reaction products adhere to the inner chamber walls, gradually forming films, and particles are generated by flaking of the deposited films due to electric field stress that acts boundary between the inner wall and the film. In this study, we have investigated the mechanism of instantaneous generation of many flaked particles using the mass-production reactive ion etching equipment. Particles, which flake off from the films on the ground electrode, are detected by the in-situ particle monitoring system using a sheet-shaped laser beam. The results indicate that the deposited films are severely damaged and flake off as numerous particles when the floating potential at the inner wall suddenly changes. This is because the rapid change in floating potential, observed when unusual wafer movement and micro-arc discharge occur, causes electric field stress working as an impulsive force. The films are easily detached by the impulsive force and many flaked particles are instantaneously generated. This mechanism can occur on not only a ground electrode but a chamber walls, and cause serious contamination in mass-production line.   

Plasma discharge characteristics in compact SF${_6}$ radio-frequency plasma source for plasma etching application

In order to create a compact plasma etching reactor, plasma discharge characteristics in compact SF${_6}$ radio-frequency (RF) plasma source which has a chamber diameter of 40 mm have been studied. Convergent magnetic field configuration produced by a solenoid coil and a permanent magnet located behind substrate is employed for efficient plasma transport downstream of plasma source. A discharge characteristics with the changes in relative emission intensity of fluorine atom of FI at 703.7 nm in compact SF${_6}$ plasma source are discussed: the dependence of relative emission intensity on the magnetic field strength, the RF input power, and the mass flow rate of the SF${_6}$ gas. The relative emission intensity was significantly increased when the RF input power is $\sim$150 W. We present the fundamental etching performance (especially etching rate) of compact plasma source, and then the etching rate of 0.1-1.0 $\mu$m/min was obtained under the condition of a RF input power of 50-200 W, a mass flow rate of SF${_6}$ of 5.5 sccm and a bias RF power of 20 W. The results of test etching will be shown in presentation.   

Study on the decontamination of surface of radioactive metal device using plasmatron

Radioactive waste contiguously produced during operation of NPP (nuclear power plant). Therefore, KHNP (korea hydro {\&} nuclear power co., ltd) decided to disband the NPP unit 1 in the Kori area. Since most of the metallic radioactive wastes are not contaminated ones themselves but rather ones containing polluted nuclides on their surface, the amount of wastes can be sharply reduced through decontamination process. In this study DC plasmatron and isotope sheet of radioactive cobalt was used to study the decontamination process. Decontamination can be achieved by etching the contaminated layer from the surface. Due to the restricted usage of radioactive materials, we have studied etching of Cobalt (Co) sheet to imitate the radioactive contamination. Plasma was generated using mixture gas of CF4/O2 in the ratio of 10:0, 9:1, 8:2, 7:3, 6:4 maintaining the plasma sample distance of 20 mm, 30 mm, 40 mm and exposed time of 60 sec, 120 sec, 180 sec using fixed Ar carrier gas flow rate of 1000 sccm. As a result, we obtained maximum etching rate of 9.24 $\mu$m/min when the mixture ratio of CF4/O2 gas was 4:1, which was confirmed by SEM and mass-meter. It was confirmed that more close positioning the Co samples to the plasmatron nozzle yields maximum etching rate.   

A new method of dry cleaning after plasma etching of MRAM materials

This paper describes a new method for dry cleaning after etching of MRAM materials. Problems such as repeatability or particle generation after etching of MRAM materials are due to the non-volatile nature of etch products. A new etch concept for MRAM is to etch each material such as carbon, metal, or silicon compounds step by step. There are 4 steps in this cleaning: 1) carbon removal by N2/H2, 2) metal removal by Ar, 3) silicon removal by CF4/O2, 4) carbon, oxygen, and fluorine removal by N2/H2. Etch repeatability and particle level reduction have been demonstrated to result from this cleaning method.   

Antifouling Transparent ZnO Thin Films Fabricated by Atmospheric Pressure Cold Plasma Deposition

One problem with outdoor-mounted solar panels is that power generation efficiency is reduced by face plate dirt; a problem with electronic touch panels is the deterioration of screen visibility caused by finger grease stains. To solve these problems, we should fabricate antifouling surfaces which have superhydrophobic and oil-repellent properties without spoiling the transparency of the transparent substrate. In this study, an antifouling surface with both superhydrophobicity and oil-repellency was fabricated on a glass substrate by forming a fractal microstructure. The fractal microstructure was constituted of transparent silica particles 100 nm in diameter and transparent zinc-oxide columns grown on silica particles through atmospheric pressure cold plasma deposition; the sample surface was coated with a chemically adsorbed monomolecular layer. Samples were obtained which had a superhydrophobic property (with a water droplet contact angle of more than 150$^{\circ}$) and a high average transmittance of about 90{\%} (with wavelengths ranging from 400 nm to 780 nm).   

New Method for Production of High-Energy Neutral Molecules of Reactive Gases

For the surface modification of dielectric substrates by reactive gas molecules with energy of 100 keV they are usually produced due to charge exchange collisions of ions extracted from a plasma emitter and accelerated by high-voltage pulses. As generation of the ion plasma emitter at a 100-kV potential is quite difficult, it was proposed to extract the ions from a ground potential emitter, accelerate them by high voltage between the emitter and a negatively biased high-transparency grid and transform them into fast neutral molecules in the positive space charge sheaths of the grid. As the energy of fast molecules is defined by potentials of charge exchange collision points inside the sheath their spectrum ranges from zero to a value corresponding to the pulse amplitude. A reverse beam is always generated due to acceleration of ions from the plasma on the other side of the grid. The lower the latter density, the higher the ratio of the primary to the reverse beam currents. When the grid is composed of parallel flat plates, the charge exchange due to reflections from the plates substantially contributes at low gas pressure to production of molecules with the energy corresponding to the pulse amplitude.   

Effects of sputtering mode on the microstructure and ionic conductivity of yttria-stabilized zirconia films

The microstructure and ionic conductivity of reactively sputtered yttria-stabilized zirconia (YSZ) films in various sputtering modes are systematically studied using a closed-loop controlled system with plasma emission monitoring. A transition-mode sputtering corresponding to 45{\%} of target poisoning produces a microstructure with ultrafine crystallites embedded in an amorphous matrix, which undergoes an abnormal grain growth upon annealing at 800$^{\circ}$C. At 400$^{\circ}$C, its measured ionic conductivity is higher, by about a half order of magnitude, than that of its 86{\%}-target-poisoning counterpart, which is in turn higher than the YSZ bulk by about one order of magnitude. The abnormally-grown ultra-large grain size is believed to be responsible for the former comparison due to the suppression of the grain boundary blocking effect, while the latter comparison can be attributed to the interface effect.   

Preparation of hydrogenated diamond-like carbon films by reactive Ar/CH$_4$ high power impulse magnetron sputtering with negative pulse voltage

High power impulse magnetron sputtering (HiPIMS) has been attracted, because sputtered target species are highly ionized. High densities of active species such as radical ions and neutral radicals can be also achieved owing to high density reactive HiPIMS plasmas. We investigate properties of hydrogenated diamond-like carbon films prepared by reactive HiPIMS of Ar/CH$_4$ gas mixture. The properties of the films strongly depend on the plasma compositions and the kinetic energy of the carbon-containing ions which can enter into the films. The film preparation is performed at an average power of 60 W and a repetition frequency of 110 Hz, changing CH$_4$ fraction up to 15\%. Total pressure ranges between 0.3 and 2 Pa. The maximum of instantaneous power is about 20-25 kW, and the magnitude of the current is 36 A. A negative pulse voltage is applied to the substrates for about 10 $\mu$s after the target voltage changed from about -600 V to 0 V. The structural properties are characterized by Raman spectroscopy and nano-indentation method. Film hardness strongly depends on the magnitude of negative pulse voltage. By adjusting the magnitude of negative voltage, the film hardness ranges between about 10 and 22 GPa.   

Formation of hydrogenated amorphous carbon films by reactive high power impulse magnetron sputtering containing C$_2$H$_2$ gas

Diamond-like carbon (DLC) films have attracted interest for material industries, because they have unique properties. Hydrogenated amorphous carbon films are prepared by reactive high power impulse magnetron sputtering (HiPIMS) containing C$_2$H$_2$ gas and the properties of the films produced in Ar/C$_2$H$_2$ and Ne/C$_2$H$_2$ HiPIMS are compared. Production of hydrocarbon radicals and their ions strongly depends on both electron temperature and electron density in HiPIMS. Therefore, the influence of the difference in buffer gas (Ar and Ne) on the film properties is also valuable to investigate. The film preparation is performed at an average power of 60 W and a repetition frequency of 110 Hz. Total pressure ranges between 0.3 and 2 Pa. The maximum of instantaneous power is about 20-25 kW, and the magnitude of the current is 35 A. A negative pulse voltage is applied to the substrates for about 15 $\mu$s after the target voltage changed from about -500 V to 0 V. Hardness of the films prepared by Ar/C$_2$H$_2$ HiPIMS monotonically decreases with increasing the total pressure, whereas that of the films prepared by Ne/C$_2$H$_2$ HiPIMS does not strongly depend on the total pressure.   

Open Air Silicon Deposition by Atmospheric Pressure Plasma under Local Ambient Gas Control

In this paper, we report open air silicon (Si) deposition by combining a silane free Si deposition technology and a newly developed local ambient gas control technology. Recently, material processing in open air has been investigated intensively. While a variety of materials have been deposited, there were only few reports on Si deposition due to the susceptibility to contamination and the hazardous nature of source materials. Since Si deposition is one of the most important processes in device fabrication, we have developed open air silicon deposition technologies in BEANS project. For a clean and safe process, a local ambient gas control head was designed. Process gas leakage was prevented by local evacuation, and air contamination was shut out by inert curtain gas. By numerical and experimental investigations, a safe and clean process condition with air contamination less than 10 ppm was achieved. Si film was deposited in open air by atmospheric pressure plasma enhanced chemical transport under the local ambient gas control. The film was microcrystalline Si with the crystallite size of 17 nm, and the Hall mobility was 2.3 cm$^{2}$/V$\cdot$s. These properties were comparable to those of Si films deposited in a vacuum chamber.   

PECVD of SiOC Films Using a Sheet-type Atmospheric Pressure Plasma Jet

Packaging industries have used SiOC thin films for gas barrier coatings on the membranes for packaging foods, drug, and so on. PECVD is the most extensively employed method for preparing the SiOC films. However, PECVD is a process performed at a low pressure in general and requires expensive vacuum systems, especially in the case of large area coatings. Atmospheric pressure PECVD is a candidate to overcome this issue. If we simply apply atmospheric pressure plasma to CVD processes, however, we will encounter the problem of particle formation because of the high collision frequency in the environment of atmospheric pressure. In this work, we have developed a reactor that utilizes a unique gas-flow scheme for avoiding the particle formation. We have successfully deposited SiOC films by using this reactor, in which the source material is hexamethyldisiloxane and discharge/carrier gas is He. XPS measurements on the SiOC films have revealed that the films contain relatively higher concentrations of unfavorable methyl groups that reduce gas barrier performances. However, no particulates are involved in and on the deposited films as long as characterizing the films with eye observation and with transmission electron microscopy.   

Effect of Low-Energy Ions on Plasma-Enhanced Deposition of Cubic Boron Nitride

The effect of low-energy ions on deposition of cubic boron nitride (cBN) films in an inductively coupled plasma with the chemistry of fluorine is studied in terms of ion energy, ion flux, and ion to boron flux ratio onto the substrate [1]. The ion energy and the ion to boron flux ratio are determined from the sheath potential and the ratio of incident ion flux to net deposited boron flux, respectively. For negative substrate biases where sp$^{2}$-bonded BN phase only or no deposit is formed, both the ion energy and the ion to boron flux ratio are high. For positive substrate biases where cBN phase is formed, the ion energy and the ion to boron flux ratio are estimated in the range of a few eV to 35 eV and 100 to 130, respectively. The impact of negative ions is presumed to be negligible due to their low kinetic energy relative to the sheath potential over the substrate surface. The impact of positive ions with high ion to boron flux ratios is primarily responsible for reduction of the ion energy for cBN film deposition.\\[4pt] [1] K. Teii and S. Matsumoto, Thin Solid Films \textbf{576}, 50-54 (2015).   

Raman Spectroscopy of $a$-C:H Films Deposited Using Ar $+$ H$_{2}+$ C$_{7}$H$_{8}$ Plasma CVD

We investigated the effects of ion energy on Raman spectra of $a$-C:H films prepared by Ar $+$ H$_{2}+$ C$_{7}$H$_{8}$ plasma CVD. Raman spectra were measured with a laser Raman spectrometer (JASCO NRS-3100). Both the D-peak position and G-peak position shift toward higher wavenumbers as ion energy increases. The intensity ratio of the D-peak and G-peak, $I_{\mathrm{D}}$/$I_{\mathrm{G}}$ increases with increasing the ion energy, indicating that the amount of ring-like \textit{sp}$^{2}$ clusters increases. The H content in $a$-C:H derived from photoluminescence (PL) background decreases with increasing the ion energy. The full width at half maximum of the G-peak, FWHM$_{\mathrm{G}}$ related to the C-C \textit{sp}$^{3}$ content and H content increases with increasing the ion energy to 100 eV, whereas it decreases with increasing further the ion energy to 105 eV. The variation of FWHM$_{\mathrm{G}}$ is consistent with that of mass density. There results indicate that the structure of $a$-C:H films transforms from polymer-like carbon to diamond-like one with increasing the ion energy above the threshold value of $\sim$ 100 eV.   

Preparation of mixed metal thin films by a PVD method using several kinds of powder targets

Bismuth iron garnet (Bi$_{3}$Fe$_{5}$O$_{12})$ and aluminum doped zinc oxide (AZO) thin films were prepared by a physical vapor deposition method using mixed metal powder targets. The X-ray powder diffraction and X-ray photoelectron spectroscopy results suggest that crystalline thin films can be prepared using powder targets with quality similar to that of the films prepared using bulk targets. Bi$_{3}$Fe$_{5}$O$_{12}$ films prepared using the pulsed laser deposition method were Bi rich, which may be due to the lower melting temperature of Bi (544 K) compared with that of Fe (1811 K). The mean transparency and resistivity of the AZO films prepared by the sputtering method were approximately 79{\%}--84{\%} and 0.5$--$1.4 ohm/cm, respectively.   

Plasma-Enhanced Deposition of Nanocrystalline Diamond/Carbon Nanowall Composite Films for Field Emitters

Two methods of substrate scratching pretreatment using diamond powder are employed to fabricate nanocrystalline diamond/carbon nanowall (CNW) composite films [1]. The surface after scraping for undulation has continuous undulant scratches with a number of residual diamond grains exclusively along the scratches, while that after scratching with ultrasonic vibration shows irregular distributions of residual diamond grains and scratches, depending upon the size of the powder. Nanocrystalline diamond film/CNW composites are obtained with either pretreatment method by moderate-pressure microwave plasma-enhanced chemical vapor deposition using an Ar/N$_{2}$/CH$_{4}$ mixture. With increasing the duration of scratching, the morphology of the deposits changes from CNWs to a film/CNW composite and lastly to CNWs on a film, accompanied by an overall increase in wall spacing. The turn-on field for field emission decreases from 2.1 V/$\mu $m without scratching down to 1.2 V/$\mu $m with scratching due to suppression of electric field screening between the walls as evidenced by the larger field enhancement factor.\\[4pt] [1] C.Y. Cheng, M. Nakashima, K. Teii, Diamond Relat. Mater. \textbf{27-28}, 40-44 (2012).   

Substrate temperature dependence of Au-induced crystalline Ge film formation using sputtering deposition

We are developing Au-induced crystalline Ge film formation using sputtering deposition. For the method, very thin Au films were deposited on SiO$_{2}$ substrates and then Ge atoms were irradiated to the Au films by sputtering. We found two kinds of Ge film growth: one is Ge film formation on Au films, and the other is Ge film formed between Au films and SiO$_{2}$. The latter film formation, however, takes place in a narrow temperature range around 140$^{\circ}$C. Here we report two kinds of substrate temperature dependence of Ge film formation: one is annealing temperature of Au films, and the other is the substrate temperature dependence during Ge sputtering. 30nm-thick Au films were deposited quartz glass as a catalyst at room temperature by sputtering. Then the Au films were annealed in a temperature range from room temperature to 190 $^{\circ}$C in a vacuum. Au grain grows and crystal orientation shows better alignment as the annealing temperature rises. We found that the smaller grain size with random orientation is better for Ge film formed between Au films and SiO$_{2}$.   

Measurements of nitrogen atom density in N2/Ar sputtering plasma for fabrication of high-mobility amorphous In2O3:Sn films

Amorphous In2O3:Sn (a-ITO) has attracted attention because of the advantages such as smooth surface and high etching rate. We have recently succeeded in sputtering deposition of a-ITO films with high mobility 61 cm$^{\mathrm{2}}$/Vs by introducing N2 into the deposition atmosphere. Here, aiming to clarify effects of N of a-ITO film growth, we measure absolute density of N atom in N2/Ar sputtering plasma by using vacuum UV absorption spectroscopy. ITO films were fabricated by RF magnetron sputtering on glass substrates at 150C with Ar-N2 mixed gas. We observed that the morphology is changed from polycrystalline to amorphous by introducing N2 into the deposition atmosphere. Furthermore the mobility of a-ITO films was found to be greatly dependent on N2 flow rate. The electron Hall mobility increases from 48 to 55 cm$^{\mathrm{2}}$/Vs with increasing N2 flow rate ratio from 3 to 5{\%}, where the absolute density of N atom in the plasma increases from 3.78 to 7.44 (10$^{\mathrm{10}}$ cm$^{\mathrm{-3}})$. Since the N composition ratio in ITO films is almost constant for N2 flow rate ratio of 3--5{\%}, the difference in the adsorption/desorption behavior of N atoms on the growth surface brings about the change in the film properties.   

Magnetic properties of Fe/FeSi$_{2}$/Fe$_{3}$Si trilayered films prepared by facing targets sputtering deposition

Whereas giant magnetoresistance and tunnel magnetoresistance films generally employ nonmagnetic metal and insulator spacers, respectively, we have studied Fe$_{3}$Si/FeSi artificial lattices, in which FeSi$_{2}$ is semiconducting and its employment as spacers is specific to our research. For the formation of parallel/antiparallel alignments of layer magnetizations, the employment of ferromagnetic layers with different coercive forces is required. There have been few studies on the fabrication of Fe-Si system spin valves comprising ferromagnetic layers with different coercive forces. In this work, Fe$_{3}$Si and Fe were employed as ferromagnetic layer materials with different coercive forces. Fe/FeSi$_{2}$/Fe$_{3}$Si trilayered spin valve junctions by facing targets direct-current sputtering deposition combined with a mask method, and their electrical and magnetic properties were studied. An Fe$_{3}$Si layer was epitaxially grown on Si(111) substrate as a bottom layer. After that, An Fe layer with a large coercive force was deposited as a top layer, posterior to a FeSi$_{2}$ layer being deposited. From magnetization curves measured by a vibrating sample magnetometer, it was confirmed that the parallel and antiparallel magnetization alignments of ferromagnetic layers are clearly realized.   

Cluster Incorporation into A-Si:H Films Deposited Using H$_{2}$+SiH$_{4}$ Discharge Plasmas

Light-induced degradation is the most important issue for hydrogenated amorphous silicon (a-Si:H) solar cells. Our previous results have suggested that incorporation of clusters into films is responsible for the light-induced degradation. Therefore, it is important to control the incorporation of clusters. Recently, we have developed multi-hollow discharge plasma CVD method, by which clusters are driven toward the downstream region and high quality a-Si:H films can be deposited in the upstream region [1]. Here, we report effects of H$_{2}$ dilution on cluster incorporation. Cluster size was measured by TEM, and the incorporation amount of clusters was measured with quartz crystal microbalances [2]. H$_{2}$ dilution leads to smaller clusters and the cluster incorporation in the upstream region increases with H$_{2}$ dilution because the diffusion velocity of such small clusters much surpasses gas flow velocity.\\[4pt] [1] K. Koga, et. al., Jpn. J. Appl. Phys. \textbf{44} (2005) L1430.\\[0pt] [2] Y. Kim, et. al., Jpn. J. Appl. Phys. \textbf{52} (2013) 01AD01.   

Development of DLC cone for fast ignition experiment

In fast ignition research, a divergence of laser-generated hot electrons is a serious problem. Using DLC cones is one of actions against this problem. However, it is difficult to make a stand alone DLC cone because it needs a thick DLC layer. In this reserch, we studied preparation conditions for thick DLC layers and characteristics of DLC layers. We prepared a DLC layer on a brass conical bar by using a plasma-based ion implantation and deposition (PBIID) system. Acetylene gas or toluene vapor was used as a source. It was found that low gas pressure and low RF pulse power is suitable for thick DLC layer deposition. It was found that the toluene vapor had an advantage in thick layer deposition because of its high deposition rate. These DLC layers showed SP3 rich property in Near edge X-ray absorption fine structures (NEXAFS) spectra. Based on these results, we succeeded in making stand alone DLC cones.   

Measurements of absolute densities of nitrogen and oxygen atoms in sputtering plasma for fabrication of ZnInON films

Control of chemical composition in films is of great importance in controlling the physical properties. Recently, we have developed ZnInON (ZION) with tunable band gap over the entire visible spectrum [1]. Due to the deviation from its pseudo-stoichiometry ((ZnO)$_{\mathrm{x}}$(InN)$_{\mathrm{1-x}})$, however, the films have a number of crystal defects. In this study, with the aim of precise control of the chemical composition, we have measured absolute densities of N and O in sputtering plasma during deposition. ZION films were deposited with Ar/N2/O2 gas mixtures. The absolute densities of N and O were measured by vacuum ultraviolet absorption spectroscopy. With increasing O2/N2 flow rate ratio from 0 to 15{\%}, N density increases from 2.7 to 9.7 $\times$ 10$^{11}$ cm$^{-3}$, while O density is almost constant with the value of 4.5 $\times$ 10$^{11}$ cm$^{-3}$. These results indicate that incorporation of O atoms into ZION films increases with increasing the O2 flow rate ratio. Furthermore, we found that ZION films with pseudo-stoichiometric composition are grown at the O$_{2}$/N$_{2}$ flow rate ratio of 15{\%}, where ZION films have low defect density. \\[4pt] [1] N. Itagaki, et al., Mater. Res. Express 1, 036405 (2014).   

Measurement of absolute density of N atom in sputtering plasma for epitaxial growth ZnO films via nitrogen mediated crystallization

ZnO has attracted attention as a potential alternative to GaN in light emitting diodes because of the wide band gap and large exciton binding energy. Recently, we have developed a fabrication method of ZnO by sputtering, nitrogen mediated crystallization (NMC), enabling us to make epitaxial films with low defect density. By utilizing the buffer layers fabricated by NMC method, we have succeeded in fabrication of single crystalline ZnO films even on 18{\%} lattice mismatched substrates. Here, aiming to clarify effects of nitrogen during NMC process, we measured absolute density of N atom in sputtering plasma by means of vacuum ultra violet absorption spectroscopy. First, NMC--ZnO buffer layers were deposited in Ar/N2 atmosphere. Then, ZnO films were deposited in Ar/O2 atmosphere. With increasing N2 flow rate ratio from 4 to 12{\%}, the N density increases from 3.2 $\times$ 10$^{10}$ to 1.4 $\times$ 10$^{11}$ cm$^{-3}$. By utilizing the NMC--ZnO buffer layer fabricated at under these conditions, single crystalline ZnO films are grown. However, large number of pits are observed on the surface of ZnO films under N-rich conditions, indicating that N density is of importance in controlling the morphology of ZnO films.   

Plasma-Assisted Mist Chemical Vapor Deposition of Zinc Oxide Films for Flexible Electronics

Plasma-assisted mist chemical vapor deposition of ZnO films was performed for transparent conductive oxide formation of flexible electronics. In this study, ZnO films deposition using atmospheric-pressure He plasma generated by a micro-hollow cathode-type plasma source has been demonstrated. To obtain detail information according to generation of species in the plasma, the optical emission spectra of the atmospheric pressure He plasma with and without mist were measured. The result without mist shows considerable emissions of He lines, emissions attributed to the excitation and dissociation of air including N$_{2}$ and O$_{2}$ (N, O, and NO radials, and N$_{2}$ molecule; N$_{2}$ second positive band and first positive band), while the results with mist showed strong emissions attributed to the dissociation of H$_{2}$O (OH and H radicals). The deposition of ZnO films was performed using atmospheric-pressure He plasma. The XRD patterns showed no crystallization of the ZnO films irradiated with pure He. On the other hand, the ZnO film crystallized with the irradiation with He/O$_{2}$ mixture plasma. These results indicate that the atmospheric-pressure He/O$_{2}$ mixture plasma has sufficient reactivity necessary for the crystallization of ZnO films at room temperature.   

Laser-induced metal plasmas for pulsed laser deposition of metal-oxide thin films

Metal and metal-oxide thin films, e.g. ZnO, MgO, Al$_{\mathrm{2}}$O$_{\mathrm{3}}$ and TiO$_{\mathrm{2}}$, are widely used in e.g. microelectronics, catalysts, photonics and displays. Pulsed Laser Deposition (PLD) is a plasma-based thin-film deposition technique that is highly versatile and fast, however it suffers from limitations in control of film quality due to a lack of fundamental understanding of the underlying physical processes. We present experimental and modelling studies of the initial phases of PLD: laser ablation and plume expansion. A 2D hydrodynamic code, POLLUX, is used to model the laser-solid interaction of a Zn ablation with a Nd:YAG laser. In this early phase of PLD, the plasma plume has temperatures of about 10 eV, is highly ionized, and travels with a velocity of about 10-100 km/sec away from the target. Subsequently, the plasma enters the plume expansion phase in which the plasma cools down and collision chemistry changes the composition of the plume. Time-integrated optical emission spectroscopy shows that Zn I and Zn II emission lines dominate the visible range of the light emission. Comparison with the Los Alamos plasma kinetics code ATOMIC shows an average temperature around 1 eV, indicating a significant drop in plasma temperature during the expansion phase.   

Plasma polymerization for cell adhesive/anti-adhesive implant coating

Plasma polymerization of ethylenediamine (C$_{\mathrm{2}}$H$_{\mathrm{8}}$N$_{\mathrm{2}}$, EDA) and perfluoropropane (C$_{\mathrm{3}}$F$_{\mathrm{8}}$, PFP) with admixture of argon and hydrogen, respectively, was studied using an asymmetric 13.56 MHz CCP. The analysis of the plasma chemical gas phase processes for stable molecules revealed consecutive reactions: C$_{\mathrm{2}}$H$_{\mathrm{8}}$N$_{\mathrm{2}}$ consumption, intermediate product NH$_{\mathrm{3}}$, and main final product HCN. In C$_{\mathrm{3}}$F$_{\mathrm{8}}$-H$_{\mathrm{2}}$ plasma the precursor molecule C$_{\mathrm{3}}$F$_{\mathrm{8}}$ and molecular hydrogen are consumed and HF as well as CF$_{\mathrm{4}}$ and C$_{\mathrm{2}}$F$_{\mathrm{6}}$ are found as main gaseous reaction products. The deposited plasma polymer films on the powered electrode are strongly cross-linked due to ion bombardment. The stable plasma polymerized films from EDA are characterized by high content of nitrogen with N/C ratio of about 0.35. The plasma polymerized fluorocarbon film exhibit a reduced F/C ratio of about 1.2. Adhesion tests with human osteoblast cell line MG-63 on coated Ti6Al4V samples (polished) compared with uncoated reference sample yielded both, the enhanced cell adhesion for plasma polymerized EDA and significantly reduced cell adhesion for fluorocarbon coating, respectively. Aging of the plasma polymerized EDA film, in particular due to the reactions with oxygen from air, showed no significant change in the cell adhesion. The fluorocarbon coating with low cell adhesion is of interest for temporary implants.   

A thermocouple-based remote temperature controller of an electrically floated sample to study plasma CVD growth of carbon nanotube

Plasma chemical vapor deposition (CVD) is now gathering attention from a novel viewpoint, because it is easy to combine plasma processes and electrochemistry by applying a bias voltage to the sample. In order to explore electrochemistry during the plasma CVD, the temperature of the sample must be controlled precisely. In traditional equipment, the sample temperature is measured by a radiation thermometer. Since emissivity of the sample surface changes in the course of the CVD growth, it is difficult to measure the exact temperature using the radiation thermometer. In this work, we developed new equipment to control the temperature of electrically floated samples by thermocouple with Wi-Fi transmission. The growth of the CNT was investigated using our plasma CVD equipment. We examined the temperature accuracy and stability controlled by the thermocouple with monitoring the radiation thermometer. We noticed that the thermocouple readings were stable, whereas the readings of the radiation thermometer changes significantly (20 $^{\circ}$C) during plasma CVD. This result clearly shows that the sample temperature should be measured with direct connection. On the result of CVD experiment, different structures of carbon including CNT were obtained by changing the bias voltages.   

Non-contact temperature measurement of silicon substrate in sputtering plasma using optical interferometer

The substrate temperature is one of important parameters to control the plasma processing and involve the film properties or the chemistry of gas phase. High power impulse magnetron sputtering (HIPIMS) realizes a very significant fraction of the ionized species and which induced onto the substrate and heated it. It is essential to analyze the substrate temperature and the heating mechanisms. In this study, we have measured the silicon substrate temperature in HiPIMS by using the optical low-coherence interferometry. The reflected light from the front surface interferes that from back surface. The optical path length of Si wafer is obtained by the inverse Fourier transform of spectral interferogram and varies with the change in the silicon temperature. The silicon temperatures with various resistivities were measured and the change in the optical thickness increased with decreasing the resistivity owing to the carrier density of the silicon substrate. The time variation of Si substrate temperatures at various applied voltages in the HiPIMS using the titanium target was measured and the silicon temperatures increased with increasing the applied voltage.   

Correlation between energy of depositing particles and mobility of ITO films in the Reactive Plasma Deposition with dc arc discharge

A correlation between the energy of depositing particle and the mobility of ITO film has been investigated in order to elucidate the optimal energy required to form high-quality ITO film. ITO films were deposited with controlling the energy of depositing particles and according to it the condition of oxygen atmosphere was changed to get a constant carrier density of the deposited ITO films. The mobility of ITO film deposited at the substrate temperature of 200$^{\circ}$C was found dependent on the energy of depositing particles and we concluded that the optimal energy is greater than 13 eV for ITO film deposition.   

Glutamate biosensor based on carbon nanowalls grown using plasma enhanced chemical vapor deposition

Carbon nanowalls (CNWs) are composed of few-layer graphene standing almost vertically on the substrate. Due to the large surface area of vertical nanographene network, CNWs draw attention as platform for electrochemical sensing, biosensing and energy conversion applications. In this work, CNWs were grown on nickel substrate using inductively coupled plasma with methane/Ar mixture. After the CNW growth, the surface of CNWs was oxidized using Ar atmospheric pressure plasma to obtain super-hydrophilic surface. For the biosensing application, the surface of CNWs was decorated with platinum (Pt) nanoparticles by the reduction of hydrogen hexachloroplatinate (IV) solution. The resultant Pt particle size was estimated to be 3-4 nm. From the XPS analysis, pure Pt existed without being oxidized on the CNW surface. Electrochemical surface area of the Pt catalyst was evaluated by cyclic voltammetry. Pt-decorated CNWs will be used as an electrode for electrochemical glutamate biosensing. L-glutamate is one of the most important in the mammalian central nervous system, playing a vital role in many physiological processes. Nanoplatform based on vertical nanographene offers great promise for providing a new class of nanostructured electrodes for electrochemical sensing.   

In situ Plasma Exposure for Improved Interfaces in Atomic Layer Deposited Dielectrics on GaSb

Among compound semiconductors, GaSb possesses one of the highest hole mobilities, making it a promising candidate for p-channel devices for III-V-based MOS technologies. However, the requirement of a low-defect interface between the GaSb device layer and gate dielectric represents a formidable hurdle to full MOS implementation. Native oxidation of the GaSb surface typically results in a highly defective interface, trapping charge and preventing free Fermi level movement. Wet chemical approaches to removing the native oxide often lead to mixed, irreproducible results and fail to prevent rapid reoxidation upon atmospheric exposure. As an alternative to wet chemical treatments, we have investigated the use of in-situ H$_{\mathrm{2}}$/Ar plasma for improving the interface between GaSb and atomic layer deposited (ALD) dielectrics. We have found that by exposing the native-oxide-covered GaSb to mild H$_{\mathrm{2}}$/Ar plasma immediately prior to ALD of high-k dielectrics, one can decrease the density of interface states by two orders of magnitude, unpinning the Fermi level and enabling carrier modulation. The effectiveness of the treatment can be tuned by varying the RF plasma power, the plasma exposure time, or the substrate temperature during exposure, with higher powers, longer exposures, and higher temperatures (up to 300C) resulting in improved electrical interfaces.   

Plasma-Modified Atomic Layer Deposition

PEALD is known to grow thin films with differing properties from those grown purely via chemical reactions, or thermal ALD processes. However, material properties are still limited when compared to films grown by other deposition techniques. We have used non-growth plasma steps in each ALD cycle to modify properties, in a technique we refer to as plasma-modified ALD. To study how non-growth plasma steps modify properties, we have grown metal oxides with various plasma processing steps from CCPs of Ar, O$_{\mathrm{2}}$, N$_{\mathrm{2}}$, and H$_{\mathrm{2}}$ gases at relatively high pressures of 1-2 mbar. A grid is used to screen ion bombardment of the samples within a commercial Beneq TFS-200 reactor, making this plasma configuration indirect, but not remote. Several properties show significant differences between the films grown with and without these additional steps. These altered properties include crystalline orientation as indicated by XRD, plasmon resonances, photoluminescence, electron paramagnetic resonance, optical dispersion, mobilities, carrier concentrations, and resistivities. Selected plasma-initiated modifications to ALD-grown oxides of zinc, vanadium, and hafnium, and their anticipated applications in novel materials systems will be presented.   

A Study of Current and Voltage Relationships in a PECVD Process Plasma

Commercial PECVD reactors present several challenges to problem of plasma diagnosis. Among them is the scarcity of available plasma metrology which can provide genuine insight and still satisfy commercial constraints. The VI probe is one of the few instruments that can meet both of these needs. This work presents a study of voltage, current, impedance, phase and harmonic trends acquired by off-the-shelf VI probes. Voltage vs Current plots in 1 to 2 Torr CCP plasmas at moderate (\textless\ 3 kW) RF power levels are discussed for process relevant gasses. Non-linear features in these plots have been observed and their possible relation to Alpha-Gamma mode transitions, on-set of plasma instabilities and on wafer process results are discussed. Following S.J. You, et.al. the use of these data to identify the primary RF power absorption mechanism is discussed. Additionally, study of harmonics can be related to plasma asymmetry, the onset of parasitic plasma and system faults. Results from both pulsed and continuous plasmas are also discussed. \\[4pt] [1] S.J. You, et.al. Journal of Applied Physics V94 N12 (2003)   

Surface Passivation of ZrO2 Artificial Dentures by Magnetized Coaxial Plasma deposition

Recent growth and fabrication technologies for functional materials have been greatly contributed to drastic development of oral surgery field. Zirconia based ceramics is expected to utilize artificial dentures because these ceramics have good biocompatibility, high hardness and aesthetic attractively. However, to apply these ceramics to artificial dentures, this denture is removed from a dental plate because of weakly bond. For improving this problem, synthesis an Al passivation-layer on the ceramics for bonding with these dental items is suitable. In order to deposit the passivation layer, we focused on a magnetized coaxial plasma deposition (MCPD). The greatest characteristic of MCPD is that high-melting point metal can be deposited on various substrates. Additionally, adhesion force between substrate and films deposited by the MCPD is superior to it of general deposition methods. In this study, we have reported on the growth techniques of Al films on ZrO2 for contributing to oral surgery by the MCPD. Surface of deposited films shows there were some droplets and thickness of it is about 200 nm. Thickness is increased to 500 nm with increasing applied voltage.   

Current-Voltage Characteristics and Deposition of AlTiN Thin Films by High Power Impulse Magnetron Sputtering Process

In this study, AlTiN thin films were deposited using a high power impulse magnetron sputtering (HiPIMS) process under a unipolar mode. The AlTi target had a composition of 70 at{\%} Al and 30 at{\%} Ti. Nitrogen was used as the reactive gas to deposite AlTiN thin films along with Ar gas at a working pressure of 1x10-3 torr. The target voltage and current were measured at different conditions including various duty cycles from 1 to 5{\%}, pulse durations from 50 to 400 $\mu $s, target powers from 0.6 to 1.8 kW, and N2/Ar ratios from 0 to 1. Depending on the deposition condition, peak powers in the range of 104 to 105 W were observed. The effect of deposition conditions were discussed. For film deposition, the pulse duration and the duty cycle were fixed at 100 $\mu $s and 3{\%}, respectively. A fixed bias of -150 V was applied to the substrates, including Si wafer, 304 stainless steel, and tungsten carbide.It was found that the nitrogen content increases with the N2/Ar ratio and then saturates. With increasing target power, a higher N2/Ar ratio was required for the AlTiN thin films to have a better mechanical properties. Meanwhile, the hardness of the AlTiN thin films also increases with the target power. The highest hardness of 41 GPa was observed as the N2/Ar ratio was 0.9 and the power was 1.8 kW. It was found that the amount Al-N bonding and the distribution of AlN phase within the AlTiN thin films play an important role in determining the mechanical properties.   

Study of plasma induced flow forming mechanism using the Schlieren method

As one of the active flow control device, a non-thermal dielectric barrier discharge plasma actuator is well known and paid attention. However, the effect of applied voltage waveform to the spatial distribution of the electric discharge and induced flow is not understood. We visualized spacio-temporal evolution of an air density due to the induced flow by Schlieren imaging method with high speed camera, and discuss the relationship between the time variation of applied voltage dV/dt and induced flow. Sinusoidal and triangular waveform voltages were applied to the plasma actuator. It was observed that induced flow was formed with phase of dV/dt\textless 0 of sinusoidal voltage waveform. In the case of triangular voltage waveform, it found that the induced flow is faster with increasing the time of dV/dt\textless 0 in one cycle. These phenomena can be considered as follows. In the phase dV/dt\textgreater 0, the streamer easily progresses to the dielectric surface, and the dielectric surface is charged up immediately and electric field is weakened by the surface charge, and then induced flow is not formed. On the other hand, in the case of dV/dt\textless 0, because streamer is difficult to progress, the electric field to accelerate the positive ions is not cancelled with surface charge.   

Simulation of inductive flow controlled by using Microplasma Actuator

Plasma actuator is a novel device for flow control because it has many advantages such as simple construction, no moving part, and quick response. In this study, microplasma actuator with four independent channels was used to generate upward and downward flow. The discharge gap was set at 25 $\mu $m, enabling the discharge to occur at the voltage of about 1 kV. Due to low discharge voltage the applied high-voltage could be controlled using FET switches easily. This enables to generate flexible flow. When a AC voltage of 1.4 kV and 20 kHz was applied, 0.6 m/s upward flow and 0.2 m/s downward flow were obtained. The numerical simulation using Suzen model was also carried out to investigate the flow velocity near the electrode surface since flow observation was difficult due to the reflected light from electrodes in PTV. In the simulation, we confirmed that the intensity of upward and downward flow was close to that in experiments. After applying a AC voltage for 2.5 ms, flow control was not finished, and considered to be the transient state. Vortices with the height of about 1.5 mm were occurred in both cases of experiments and the numerical simulations. On the other hand, after driving for 60 ms, the vortex development stopped and this stage was considered to be the steady state.   

Experimental results of an iodine plasma in PEGASES gridded thruster

In the electric gridded thruster PEGASES, both positive and negative ions are expelled after extraction from an ion-ion plasma. This ion-ion plasma is formed downstream a localized magnetic field placed a few centimeters from the ionization region, trapping and cooling down the electron to allow a better attachment to an electronegative gas. For this thruster concept, iodine has emerged as the most attractive option. Heavy, under diatomic form and therefore good for high thrust, its low ionization threshold and high electronegativity lead to high ion-ion densities and low RF power. After the proof-of-concept of PEGASES using SF6 as propellant, we present here experimental results of an iodine plasma studied inside PEGASES thruster. At solid state at standard temperature and pressure, iodine is heated to sublimate, then injected inside the chamber where the neutral gas is heated and ionized. The whole injection system is heated to avoid deposition on surfaces and a mass flow controller allows a fine control on the neutral gas mass flow. A 3D translation stage inside the vacuum chamber allows volumetric plasma studies using electrostatic probes. The results are also compared with the global model dedicated to iodine as propellant for electric gridded thrusters.   

Electron Extraction Mechanisms of a Micro ECR Neutralizer

A neutralizer is one of the indispensable components for ion propulsion systems. To design a better performance neutralizer the mechanisms of electron extraction from its plasma source through orifices should be elucidated. In the present study, three-dimensional particle simulations have been carried out for a 4.2-GHz microwave discharge neutralizer, where the size of the discharge chamber is 20 $\times$ 20 $\times$ 4 mm$^3$ and a xenon electron cyclotron resonance plasma is employed. The numerical model is composed of a particle-in-cell simulation with a Monte Carlo collision algorithm for the kinetics of charged particles, a finite-difference time-domain method for the electromagnetic fields of microwaves, and a finite element analysis for the magnetostatic fields of permanent magnets. The calculations were conducted at the gas pressure of 1 mTorr and the absorbed power of 0.3 W. The simulation results have indicated that the electrostatic field of the plasma has a dominant influence on the electron extraction, where electrons are not extracted unless the effect of the electrostatic field is taken into account in the calculations.   

Measurement of erosion in helicon plasma thrusters using the VASIMR\textsuperscript{\textregistered} VX-CR device

The helicon plasma source is one of the principal stages of the high-power VASIMR\textsuperscript{\textregistered} electric propulsion system. The VASIMR\textsuperscript{\textregistered} VX-CR experiment focuses solely on this stage, exploring the erosion and long-term operation effects of the VASIMR helicon source. We report on the design and operational parameters of the VX-CR experiment, and the development of modeling tools and characterization techniques allowing the study of erosion phenomena in helicon plasma sources in general, and stand-alone helicon plasma thrusters (HPTs) in particular. A thorough understanding of the erosion phenomena within HPTs will enable better predictions of their behavior as well as more accurate estimations of their expected lifetime. We present a simplified model of the plasma-wall interactions within HPTs based on current models of the plasma density distributions in helicon discharges. Results from this modeling tool are used to predict the erosion within the plasma-facing components of the VX-CR device. Experimental techniques to measure actual erosion, including the use of coordinate-measuring machines and microscopy, will be discussed.   

Trajectory Control of Small Rotating Projectiles by Laser Sparks

The possibility of controlling the trajectory of the supersonic motion of a rotating axisymmetric projectile using a remotely generated laser spark was investigated. The dynamic images of the interaction of thermal inhomogeneity created by the laser spark with the bow shock in front of the projectile were obtained. The criterion for a strong shock wave interaction with the thermal inhomogeneity at different angles of a shock wave was derived. Significant changes in the configuration of the bow shock wave and changes in the pressure distribution over the surface of the rotating projectile can appear for laser spark temperature of $T'$~$=$~2500-3000~K. The experiment showed that strong interaction takes place for both plane and oblique shock waves. The measurement of the velocity of the precession of the rotating projectile axis from the initial position in time showed that the angle of attack of the projectile deviates with a typical time of perturbation propagation along the projectile's surface. Thus the laser spark can change the trajectory of the rotating projectile, moving at supersonic speed, through the creation of thermal heterogeneity in front of it.   

Plasma Assisted Combustion Mechanism for Hydrogen and Small Hydrocarbons

The main mechanisms of nonequilibrium gas excitation and their influence on the ignition and combustion were briefly discussed. Rotational excitation, vibrational excitation, electronic excitation, dissociation by electron impact and ionization were all analyzed, as well as the ways in which the selectivity of the gas excitation in the discharge can be controlled. The model consists of two parts. The first part describes gas excitation by electron impact -- rotational, vibrational and electronic states population by pulsed discharges. The second part considers energy relaxation in the plasma (formation of Maxwell-Boltzmann equilibrium across translational, vibrational and electronic degrees of freedom of molecules), quenching and decomposition of excited states, their reactions and recombination -- with formation of thermally-equilibrium pool of radicals, which could be considered as initial conditions for any detailed combustion kinetic mechanism. The mechanism was verified against available kinetic data in a wide temperature range. Despite of some lack of knowledge of mechanism details, nonequilibrium plasma demonstrates great potential for controlling ultra-lean, ultra-fast, low-temperature flames and is an extremely promising technology for a very wide range of applications.   

Non-equilibrium Numerical Analysis of Microwave-supported Detonation Threshold Propagating through Diatomic Gas

Microwave-supported Detonation (MSD), one type of Microwave-supported Plasma (MSP), is considered as one of the most important phenomena because it can generate high pressure and high temperature for beam-powered space propulsion systems. In this study, I numerically simulate MSD waves propagating through a diatomic gas. In order to evaluate the threshold of beam intensity, I use the physical-fluid dynamics scheme, which has been developed for simulating unsteady and non-equilibrium LSD waves propagating through a hydrogen gas.   

Ion and neutral dynamics in Hall plasma accelerator ionization instabilities

Hall thrusters, the extensively studied $E \times B$ devices used for space propulsion applications, are rife with instabilities and fluctuations. Many are thought to be fundamentally linked to microscopic processes like electron transport across magnetic field lines and propellant ionization that in turn affect macroscopic properties like device performance and lifetime. One of the strongest oscillatory regimes is the ``breathing mode,'' characterized by a propagating ionization front, time-varying ion acceleration profiles, and quasi-periodic 10-50 kHz current oscillations. Determining the temporal and spatial evolution of plasma properties is critical to achieving a fundamental physical understanding of these processes. We present non-intrusive laser-induced fluorescence measurements of the local ion and neutral velocity distribution functions synchronized with the breathing mode oscillations. Measurements reveal strong ion velocity fluctuations, multiple ion populations arising in narrow time windows throughout the near-field plume, and the periodic population and depopulation of neutral excited states. Analyzing these detailed experimental results in the context of the existing literature clarifies the fundamental physical processes underlying the breathing mode.