Plasma Chemistry and Plasma Processing (v.36, #2)

The chemical interaction between non-thermal plasma species and aqueous solutions is considered in the case of discharges in humid air burning over aqueous solutions with emphasis on the oxidizing and acidic effects resulting from formed peroxynitrite ONOO and derived species, such as transient nitrite and stable HNO3. The oxidizing properties are mainly attributed to the systems ONOO/ONOOH [E°(ONOOH/NO2) = 2.05 V/SHE], ·OH/H2O [E°(·OH/H2O) = 2.38 V/SHE] and to the matching dimer system H2O2/H2O [E°(H2O2/H2O) = 1.68 V/SHE]. ONOOH tentatively splits into reactive species, e.g., nitronium NO+ and nitrosonium NO 2 + cations. NO+ which also results from both ionization of ·NO and the presence of HNO2 in acidic medium, is involved in the amine diazotation/nitrosation degradation processes. NO 2 + requires a sensibly higher energy than NO+ to form and is considered with the nitration and the degradation of aromatic molecules. Such chemical properties are especially important for organic waste degradation and bacterial inactivation. The kinetic aspect is also considered as an immediate consequence of exposing an aqueous container to the discharge. The relevant chemical effects in the liquid result from direct and delayed exposure conditions. The so called delayed conditions involve both post-discharge (after switching off the discharge) and plasma activated water. An electrochemical model is proposed with special interest devoted to the chemical mechanism of bacterial inactivation under direct or delayed plasma conditions.
Keywords: Plasma activated water (PAW); Post-discharge; Peroxynitrite; Oxidizing degradation; Bacterial inactivation; Non-thermal air plasmas

Inactivation of Candida albicans Biofilms on Polymethyl Methacrylate and Enhancement of the Drug Susceptibility by Cold Ar/O2 Plasma Jet by G. M. Wang; P. P. Sun; H. Pan; G. P. Ye; K. Sun; J. Zhang; J. Pan; J. Fang (383-396).
The antimicrobial effects of the cold plasma for the dental pathogenic microorganism propose a promising approach to the Denture Stomatitis (DS) treatment. However, it is crucial to understand that the complexity of the biofilm microenvironment may compromise the efficiency of the therapy. As one of the major issue for DS, Candida albicans biofilms (ATCC10231) formed on denture base resins were treated by cold Ar/O2 (2 %) plasma jet. Spatial viability of the biofilms was investigated with confocal scanning laser microscopy through evaluating their inside cross-section properties. Results showed Candida albicans biofilms with thickness of ~100 µm was completely inactivated by 8 min plasma treatment. Morphology change of the fungi was also observed by the scanning electron microscopy. Drug susceptibilities, the sessile minimum inhibitory concentration (SMIC50) of the biofilm for amphotericin B and fluconazole were decreased from >32 and >256 µg/mL to 8 and 64 µg/mL after 1 min’s plasma treatment, respectively. The reactive species produced from plasma were monitored by optical emission spectroscopy. The successfully inactivation of Candida albicans biofilms and the significant enhancement of its drug susceptibilities induced by the plasma released reactive species propose a promising strategy for the treatment of DS caused by drug-resistant Candida albicans biofilms.
Keywords: Candida albicans biofilms; PMMA; Cold plasma; Inactivation; Drug susceptibility

Effect of Cold Atmospheric Pressure Plasma on the Wheat Seedlings Vigor and on the Inactivation of Microorganisms on the Seeds Surface by A. Zahoranová; M. Henselová; D. Hudecová; B. Kaliňáková; D. Kováčik; V. Medvecká; M. Černák (397-414).
Effects of a cold atmospheric pressure plasma (CAPP) treatment on the germination, production of biomass, vigor of seedlings, uptake of water of wheat seeds (Triticum aestivum L. cv. Eva) were investigated. The CAPP treatment influence on the inactivation of microorganisms occurring on the surface of wheat seeds was investigated also. The so-called Diffuse Coplanar Surface Barrier Discharge generating a cold plasma in ambient air with high power volume density of some 100 W/cm3 was used for the treatment of seeds at exposure times in the range of 10–600 s. The optical emission spectroscopy and the electrical measurements were used for estimation of CAPP parameters. The obtained results indicate that the germination rate, dry weight and vigor of seedlings significantly increased for plasma treatment from 20 to 50 s. The plasma treatment of seeds led to an extensive increase in wettability and faster germination comparing with the untreated seeds. The growth inhibition effect of CAPP on the surface microflora of wheat seeds increased with the increase of the treatment time. The efficiency of the treatment of wheat seeds artificially contaminated with pure cultures of filamentous fungi decreased in the following order: Fusarium nivale > F. culmorum > Trichothecium roseum > Aspergillus flavus > A. clavatus.
Keywords: Cold atmospheric pressure plasma; Wheat seed; Germination; Filamentous fungi; Inactivation

Chemical Composition, Physical Properties and Populating Mechanism of Some O(I) States for a DC Discharge in Oxygen with Water Cathode by Sergeiy A. Smirnov; Dmitriy A. Shutov; Elena S. Bobkova; Vladimir V. Rybkin (415-436).
This paper reports the results of the experimental study of parameters for a DC oxygen discharge with water cathode in the pressure range of 0.1–1 bar and the discharge current of 40 mA. The radius of positive column, the cathode voltage drop, the cathode current density and the electric field strength were measured. Rotational temperatures of N2 (C3Πu, V = 0) and OH (A2Σ, V = 0) and absolute line intensities of atomic oxygen with wave length of 845 and 777 nm were determined as well. Plasma composition modeling was carried out by the combined solution of the Boltzmann equation for electrons, the equations of vibrational kinetics for ground states of N2, O2, H2O molecules, and the equations of chemical kinetics, and the plasma conductivity equation. Calculations were carried out taking into consideration the discharge radial heterogeneity and using experimental values of E/N and gas temperatures. The main particles being formed in plasma were shown to be ·OH, H2O2, O(3P), O2(a1Δg), O2(b1Σ g + ), H(1S). On the basis of this calculation and experimental values of line intensities, the populating mechanism of (3p 3P) level of atomic oxygen was discussed. The comparison of some properties of discharges in O2, N2 and air was done.
Keywords: DC oxygen discharge; Water cathode; Modeling; Active species; Levels populating mechanism

High-Efficient Conversion of CO2 in AC-Pulsed Tornado Gliding Arc Plasma by Jing-Lin Liu; Hyun-Woo Park; Woo-Jae Chung; Dong-Wha Park (437-449).
An AC-pulsed tornado gliding arc plasma was employed for CO2 conversion via CO2 decomposition and dry reforming reactions. A stable and high-efficient constant arc length discharge mode was obtained in this plasma reactor. And then, CO2 conversion was studied under this discharge mode. In the case of CH4/CO2 = 0, CO2 was converted to CO and O2 via the CO2 decomposition reaction. Energy efficiency of 29 % was attained at CO2 conversion of 6 %. With strong reducing agent CH4 added into CO2, the main contributor of CO2 conversion changed from CO2 decomposition to dry reforming of CH4. Conversions of CH4 and CO2, energy efficiency and energy cost changed sharply at CO2/CH4 ratios lower than 1/4, while they changed slowly at CH4/CO2 ratios above 1/4. In the case of CH4/CO2 = 2/3, energy efficiency of 68 % and syngas energy cost of 1.6 eV/mole were achieved at CH4 conversion of 29 % and CO2 conversion of 22 %.
Keywords: Gliding arc; CO2 decomposition; Dry reforming; Energy efficiency

The catalytic naphtha reforming is one of the largest processes of petroleum industry that is used to rebuild the low-octane hydrocarbons in the naphtha to more valuable high-octane gasoline called reformate without changing the boiling point range. An atmospheric pressure pin to plate dielectric barrier discharge (DBD) plasma was used to remove carbonaceous contaminant from the coked Pt–Sn/Al2O3 catalysts during the naphtha reforming process. The effects of treatment time and flow ratios of O2/Ar and O2/He on the carbon content of the coked catalysts were investigated. The produced radicals and active species of the plasma process were identified by optical emission spectroscopy. To confirm removing the coke from the catalyst, thermal gravimetric/differential thermal analysis and temperature programmed oxidation analysis were done. Effects of treatment time and flow ratios of O2/Ar and O2/He on the carbon content of the coked catalysts were investigated by applying elemental analysis. The results of X-ray diffraction, X-ray fluorescence, Brunauer–Emmett–Teller, and CO adsorption showed that the structure and specifications of regenerated catalysts remained without significant changes during the plasma treating. The catalyst performance test revealed that DBD plasma regenerated catalysts increased the aromatic content of the feed as well as the fresh catalysts. The results showed that the plasma treatment method for regeneration of Pt–Sn/Al2O3 can be applied at lower temperature and pressure relative to the thermal regeneration method.
Keywords: Catalyst regeneration; Pt–Sn/Al2O3 catalyst; Plasma; Pin to plate dielectric barrier discharge; Naphtha reforming

Removal of Elemental Mercury from Simulated Flue Gas by Combining Non-thermal Plasma with Calcium Oxide by Jun Zhang; Yufeng Duan; Weixin Zhao; Chun Zhu; Qiang Zhou; Min She (471-485).
Mercury emission from coal combustion has been the fourth biggest pollutant in China, following the dusts, SO2 and NOX. The technology of non-thermal plasma has been widely studied for oxidizing gaseous elemental mercury at low temperature. In this paper, a new method of combining non-thermal plasma with calcium oxide was proposed to remove elemental mercury from simulated flue gas. The effects of non-thermal plasma, input energy, combination mode of plasma and calcium oxide on Hg0 removal were investigated in a wire-cylinder non-thermal plasma reactor, whose energy was supplied by a high voltage alternating current power. The peak voltage and energy of the non-thermal plasma were measured by an oscilloscope and a high voltage probe (1000:1). The results showed that most of Hg0 was converted to oxidized mercury in simulated flue gas by non-thermal plasma treatment. The Hg0 removal efficiency of CaO was improved remarkably strengthened by the non-thermal plasma, which was closely related to input energy, and the maximum mercury removal efficiency was about 80 % at an optimal input energy. Through temperature-programmed decomposition and desorption and energy dispersive spectroscopy analysis, the majority of mercury species on CaO surface were Hg2O and HgO3 rather than HgO. Therefore, it can be concluded that O3 plays an important role in Hg0 oxidation under the condition of non-thermal plasma.
Keywords: Non-thermal plasma; Elemental mercury; Calcium oxide sorbents; Ozone; Mercury oxidation

Experimental Investigation on the Effect of a Microsecond Pulse and a Nanosecond Pulse on NO Removal Using a Pulsed DBD with Catalytic Materials by V. R. Chirumamilla; W. F. L. M. Hoeben; F. J. C. M. Beckers; T. Huiskamp; E. J. M. Van Heesch; A. J. M. Pemen (487-510).
In this study, an experimental investigation of the removal of NO from an atmospheric air stream has been carried out with a non-thermal plasma dielectric barrier discharge reactor filled with different catalytic materials. TiO $$_2$$ 2 , CuO–MnO $$_2$$ 2 –TiO $$_2$$ 2 , CuO–MnO $$_2$$ 2 –Al $$_2$$ 2 O $$_3$$ 3 catalysts were used to study the synergy between the plasma and the catalysts. The NO $$_mathrm{{x}}$$ x removal efficiency and by-products formation were studied as a function of energy density, pulse rise time and width using a plasma catalytic configuration. It was observed that the shorter pulses are more efficient for NO $$_mathrm{{x}}$$ x removal but at the expense of higher by-products formation such as N $$_2$$ 2 O and O $$_3$$ 3 . A comparison has been made between an in-plasma catalytic configuration and a post-plasma catalytic configuration. Among all the three catalysts that were studied, CuO–MnO $$_2$$ 2 –TiO $$_2$$ 2 catalyst showed the best performance with respect to the removal efficiency as well as the by-products formation in both the in-plasma and the post-plasma catalytic configuration. In general, the post-plasma configuration showed better results with respect to low by-products formation.
Keywords: Non-thermal plasma; Dielectric barrier discharge; N $$_{2}$$ 2 O; O $$_{3}$$ 3 ; NO conversion

Flue Gas Desulfurization by Dielectric Barrier Discharge by Mindi Bai; Baiyu Leng; Shoulei Mao; Chaoqun Li (511-521).
There are many problems with flue gas desulfurization by traditional gas ionization discharge, including the large size of the plasma source, high energy consumption, and the need for a traditional desulfurization method. This paper introduces oxidization of SO2 to sulfuric acid (H2SO4) in a duct by reactive oxygen species (O2 +, O3) produced by strong ionization dielectric barrier discharge. The entire plasma reaction process is completed within the duct without the use of absorbents, catalysts, or large plasma source. The reactive oxygen species O2 + reacts with gaseous H2O in the flue gas to generate ·OH radicals, which can oxidize trace amounts of SO2 in large volumes of the flue gas to produce H2SO4. Sulfuric acid is also produced by O3 oxidation of SO2 to SO3, and SO3 reacting with gaseous H2O in the flue gas. Experimental results showed that with a gas temperature of 22 °C and reactive oxygen species injection rate of 0.84 mg/L, the SO2 removal rate was 81.4 %, and the SO4 2− concentration in the recovered liquid H2SO4 reached 53.8 g/L.
Keywords: Dielectric barrier discharge; Reactive oxygen species; ·OH radical; SO2 removal rate

Controlled chemical transformation of water vapor in dielectric barrier discharge (DBD) of argon into hydrogen and hydrogen peroxide for its usability as in situ or ex situ H2 and H2O2 source are reported. Online analysis of the product gas mixture by conventional wet-chemical colorimetric method using buffered KI absorber solution revealed typical H2O2 G-value = 6.4 × 10−3 µmol J−1 (G-value defines as the number of molecules produced/consumed per 100 eV of energy; in SI unit G-value is expressed in µmol J−1) in the absence of ozone. On the other hand, H2 in product mixture analyzed in gas chromatograph-thermal conductivity detector (GC-TCD) with argon carrier revealed its G-value = 0.134 µmol J−1. Enhancements in products’ yields were explored by varying gas residence time inside the plasma zone, and applied voltage and frequency on the dielectric surfaces. Employing a double-DBD reactor, at applied high voltage ~2.5 kV mm−1 @50 Hz and gas residence time ~20 s resulted in the highest yields of H2O2. However, the H2 yield increased continuously with increase in gas residence time. On the other hand, the single-dielectric barrier surface reactors were more efficient for high and exclusive generation of ex situ H2 (e.g. maximum 1260 ppm; G-value typically 0.498 µmol J−1).
Keywords: Dielectric barrier discharge; Argon; Water vapor; Hydrogen; Hydrogen peroxide; Free radical reactions; Gas chromatograph

The Formation of Gas Bubbles by Processing of Liquid n-Heptane in the Microwave Discharge by Yu. A. Lebedev; A. V. Tatarinov; I. L. Epstein; K. A. Averin (535-552).
Numerical modeling of the process of formation of gas bubbles during initiation of the microwave discharge in liquid n-heptane at atmospheric pressure has been performed. The developed model has an axial symmetry. The model is based on joint solution of the Maxwell equations, Navier–Stokes equation, heat equation, continuity equations for electrons (written in the ambipolar diffusion approximation) and the n-heptane concentration (including its thermal decomposition and dissociation by electron impact) and the Boltzmann equation for free electrons of the plasma. The calculations allowed to describe the dynamics of the formation of gas bubbles in the liquid, to evaluate the role of electron impact in the decomposition of n-heptane, and to estimate the characteristic times of various processes in the system. The results of new experiments are compared with the simulation results. On the basis of this comparison one could explain the presence in the spectra of the discharge only bands of C2.
Keywords: Microwave discharge; Discharge in liquid; n-Heptane; 2D modeling; Two-phase fluid

Oxidized Derivatives of n-Hexane from a Water/Argon Continuous Flow Electrical Discharge Plasma Reactor by Stefan Bresch; Robert Wandell; Huihui Wang; Igor Alabugin; Bruce R. Locke (553-584).
A non-thermal continuous flow plasma reactor with a liquid water stream and argon carrier gas is shown to convert n-hexane and water into alcohols, alkenes, ketones, hydroperoxides, alpha-hydroxy-ketones and diketones. Fragmented (short chain) primary alcohols, fragmented aldehydes and fragmented carboxylic acids are also formed. The variation of the supply voltage and oxygen concentration allows moderate fine-tuning of yield and selectivity of this organic “diversity-oriented” synthetic process. A (pH based) procedure for rapid separation of the organic hydroperoxides has been developed. Computationally determined thermodynamic and kinetic parameters of several reaction pathways support their feasibility. The construction of a mechanistic pathway map was accomplished, providing deeper insight into this radical and plasma based transformation process.
Keywords: Organic plasma synthesis; Diversity oriented synthesis; n-Hexane; Hydroxyl radical; Non-thermal plasma; Argon discharge; Continuous flow reactor; Hydroperoxide

Distinguish the Role of DBD-Accompanying UV-Radiation in the Degradation of Bisphenol A by Hong Zhang; Qing Huang; Lamei Li; Zhigang Ke; Qi Wang (585-598).
Discharge plasma oxidation has been widely applied in treatment of organic pollutants including bisphenol A (BPA). However, the conventionally accepted mechanism of BPA degradation is mainly ascribed to oxidation by the active species produced from discharge plasma. Ultraviolet (UV) radiation as one source of plasma discharge energy release is intrinsically accompanied with plasma discharge, yet its role in degradation of BPA has not been explicitly identified. In present study, the light emission from the dielectric barrier discharge (DBD) at spectral region 190–620 nm for different working discharge gases was determined and the role of the UV radiation in the degradation of BPA was carefully scrutinized. It was confirmed for the first time that in the DBD treatment of BPA, the UV radiation accompanied with the plasma discharge could work together with hydrogen peroxide generated from the plasma discharge so that the efficiency of BPA degradation could be improved remarkably.
Keywords: Non-thermal plasma; Dielectric barrier discharge (DBD); Ultraviolet (UV) radiation; Bisphenol A (BPA); Hydrogen peroxide (H2O2)

The present study describes surface modification of leather using environment friendly atmospheric pressure dielectric barrier discharge (DBD) process to improve dyeing with natural dyes. Leather samples were exposed to dielectric barrier discharge produced in air. DBD plasma treatment changes morphology and chemical composition of the surface of leather samples. The chemical changes at leather surface are confirmed by Fourier transform infrared spectrometer. The morphology and chemical composition of leather surface is studied using scanning electron microscope and X-ray photoelectron spectroscopy. We observed significant improvement in dye uptake properties after air plasma treatment. Different species formed in plasma are identified using optical emission spectroscopy. Untreated and plasma treated samples were dyed with Eco-Garnet Brown, Eco-Hill Brown III, Eco-Turkey Red and Eco-Smoke Grey natural dyes. Dyeing behavior was assessed by spectroscopic measurement and by measuring fastness (wash and rub) properties. This has clearly indicated an increase in color intensity of plasma exposed leather as well as an increase in the dye uptake as compared to the untreated leather. Best results were obtained with Eco-Hill Brown III and Eco-Smoke Grey dyes. The study reveals that atmospheric pressure plasma has potential to become dry and eco-friendly process to modify leather surface to improve dye uptake properties with natural dyes.
Keywords: Dielectric barrier discharge; Atmospheric pressure plasma; Fourier transform infrared spectrometer; X-ray photoelectron spectroscopy; Scanning electron microscope; Natural dyes

In the present study, efficient dechlorination and decomposition of dichloromethane (DCM) induced by glow discharge plasma (GDP) in contact with an aqueous solution was investigated. Experimental results showed that DCM underwent effective dechlorination and decomposition under the action of GDP. Both the removal and the dechlorination of DCM increased with increasing pH and with the presence of hydroxyl radical scavengers and decreased with quenchers of hydrated electrons. Formic acid and formaldehyde were the major intermediate byproducts. Final products were carbon dioxide and chloride ion. Hydrated electrons were the most important active species responsible for initiation of the reaction. Hydrolysis of the resulting chloromethyl radicals played an important role in mineralization of chlorine atoms of the molecule. Hydroxyl radicals were mainly involved in the oxidation of the intermediate byproducts. Reaction mechanism was proposed based on the dechlorination kinetics and the distribution of intermediate byproducts.
Keywords: Glow discharge; Dechlorination; Reaction mechanism; Aqueous

Stability of Plasma Treated Non-vulcanized Polybutadiene Surfaces: Role of Plasma Parameters and Influence of Additives by Alicia Henry; Marie-France Vallat; Gauthier Schrodj; Philippe Fioux; Vincent Roucoules; Gregory Francius; Jalal Bacharouche (627-650).
Surface modification studies of non-vulcanized BR elastomers (butadiene rubber) by low-pressure air plasma treatment and the effect on ageing and adhesion performances are presented in this paper. In particular, the influence of discharge power and distance from the glow discharge, and impact of antioxidant molecules in the BR formulation were examined. To characterize the changes to the BR surface, XPS spectroscopy, contact angle measurements, AFM nanoindentation experiments and tack measurements were utilized. Oxidation and crosslinking were the main mechanisms observed on the polymer chains regardless of the plasma conditions used. Beyond a certain threshold of plasma energy (in our case, discharge power of ~60 W and exposure time of ~30 s), a steady state was reached irrespective of the distance from the glow discharge. The presence of antioxidant molecules considerably reduced crosslinking phenomena while maintaining oxidation processes on polymer chains and increasing the nitrogen content in the near surface region. The mechanisms responsible for these differences have been identified. Interestingly, the COOH/C=O ratio changed according to the balance between oxidation and crosslinking. The hydrophobic recovery rate was mainly driven by temperature-dependent dynamics and varied according to the degree of crosslinking in the surface region. It was found to be lower in air atmosphere in the presence of antioxidant molecules. Finally, the presence of antioxidant molecules in the BR formulation allowed the adhesion performances after plasma exposure to significantly increase.
Keywords: Air plasma treatment; Polybutadiene rubber; Antioxidant; Adhesive bonding

Controlling the concentration and nature of functional groups in plasma polymer films by adjusting the flow ratio of constituent precursor gases can be exploited to tune the surface charge of the resulting coating. Plasma polymer films containing various concentrations of nitrogen and oxygen functional groups were deposited in a low-pressure capacitively-coupled glow discharge reactor by plasma polymerization of binary gas mixtures of a hydrocarbon (ethylene or butadiene) and a heteroatom source gas (ammonia and/or carbon dioxide). Increasing the flow ratio of heteroatom to hydrocarbon gases increased the concentration of bonded nitrogen or oxygen, including that of primary amine or carboxylic groups as determined by X-ray photoelectron spectroscopy and chemical derivatization procedures. The zeta potential of samples was measured using an electro-kinetic analyser in a diluted sodium chloride solution. The deposition parameters controlled the composition of the coatings, allowing to tune the surface charge to either positive (ammonia based films)—or negatively (carbon dioxide base films) values at physiological pH.
Keywords: Plasma polymer; Oxygen-rich; Nitrogen-rich; Surface charge; Functional groups

Initial Growth of Functional Plasma Polymer Nanofilms by Marianne Vandenbossche; Maria-Isabel Butron Garcia; Urs Schütz; Patrick Rupper; Martin Amberg; Dirk Hegemann (667-677).
To gain deeper insights into the initial growth mechanism, with respect to functional group density and cross-linking, plasma polymer films (PPFs) were deposited from C2H4/NH3 discharges. Keeping gas phase processes and electrical discharge conditions constant all over the deposition process, the mass deposition rate of the PPF was found to be initially lower and regularly increasing before reaching steady-state conditions after a film thickness of about 5 nm on metal oxide substrates. The first gradient nano-layer, i.e. the first 5 nm deposited, were observed to possess less amino functional groups and to be more cross-linked and thus more stable compared to the film prepared in steady state conditions, in which the uniform film comprises more amino functional groups, yet is less cross-linked and thus less stable. Due to its sticking probability, the substrate thus influences the initial deposition rate. Over plasma exposure time, the substrate becomes covered by an initial layer of PPF and the film-forming species are no longer deposited onto the pristine substrate but onto the already deposited organic polymer film. The preparation of the highly stable functional nanofilm, i.e. the initial PPF layer, can lead to new possible applications and fast deposition processes.
Keywords: Plasma deposition; Initial growth; Nanofilm; Sticking probability; Amino group density

Influence of Working Pressure on the Al2O3 Film Properties in Plasma-Enhanced Atomic Layer Deposition by M. Hur; D. J. Kim; W. S. Kang; J. O. Lee; Y.-H. Song; S. J. Kim; I. D. Kim (679-691).
The effect of working pressure on the properties of Al2O3 films was investigated in direct-type plasma-enhanced atomic layer deposition. Increasing pressure yielded a denser Al2O3 film and a thinner SiOx interlayer, but only slightly affected the Al2O3 film thickness. The diffusivity of O atoms was evaluated by using time-averaged emission intensities of the He I and O I lines. The consumption rate of O radicals and the production rate of H radicals, as functions of plasma exposure time, were deduced from analyzing temporal evolutions of emission intensities of the O I and Hα lines, respectively. The amounts of C and H impurities in the film were confirmed by using an X-ray photoelectron spectroscopy. Finally, the mechanisms by which the working pressure affected the properties of Al2O3 films were discussed based on the experimental results.
Keywords: Al2O3 ; Direct-type; Plasma-enhanced atomic layer deposition; Pressure effect; SiOx

Design and Characteristics of a Laminar Plasma Torch for Materials Processing by Xiuquan Cao; Deping Yu; Meng Xiao; Jianguo Miao; Yong Xiang; Jin Yao (693-710).
Thermal plasma jets have been widely used in various materials processing techniques. However, the conventional thermal plasma torches usually generate turbulent plasma jets with the disadvantages of high axial temperature gradient, a short jet length and difficulties in the process control relatively, limiting its applications to materials processing. Therefore, this paper proposes a new laminar plasma torch (LPT) working with pure nitrogen to generate laminar plasma jet (LPJ). Its design and structural characteristics, e.g. segmented anode, axial gas injection, parallel water cooling structure, etc., are detailed to ensure the stability, the favorable temperature and velocity distribution of the generated LPJ. Experiments on the characteristics of the LPT showed that the generated LPJ possessed high specific enthalpy (ranging between 10 and 90 kJ/g), long jet length (maximum length: 480 mm) and low axial temperature gradient, and its output power a current and the gas flow rate. In addition, the thermal efficiency of the LPT was experimentally determined to be ranging between 25 and 45 %. Furthermore, experiment and simulation on the application of the LPJ for surface quenching verified the even radial temperature distribution of the plasma jet and high heat flux density brought to the surface.
Keywords: Laminar plasma torch; Laminar plasma jet; Specific enthalpy; Jet length; Materials processing

Laser-Induced Plasma on a Titanium Target, a Non-equilibrium Model by Amina Ait Oumeziane; Bachir Liani; Jean-Denis Parisse (711-730).
We use a comprehensive model to investigate the interaction of ultraviolet nanosecond laser pulses with a titanium material. We calculate plasma ignition thresholds and study the effect of the laser-plasma interaction and the importance of the electronic non-equilibrium in the laser-induced plume and its expansion in the background gas. Our calculations of plasma ignition thresholds on titanium targets are validated and compared with experimental and theoretical results. A comparison with experimental data indicates that our results agree well with those reported in the literature. Results for titanium and copper are also compared under the same conditions. The inclusion of electronic non-equilibrium in our work indicates that this important process must be included in laser ablation and plasma plume formation models.
Keywords: Laser ablation; Laser induced plasma; Ultraviolet lasers; Nanosecond pulses; Titanium