Effect of excitation states of nitrogen on the surface nitridation of iron and steel in d.c. glow discharge plasma

The plasma nitriding phenomena that occur on the surfaces of iron and steel were investigated. In particular, the correlation between the kinds of nitrogen radicals and the surface nitriding reaction was investigated using a glow‐discharge apparatus. To control the excitation of nitrogen radicals, noble gas mixtures were used for the plasma gas. The highly populated metastables of noble gases selectively produce excited nitrogen molecules (N₂*) or nitrogen molecule ions (N₂⁺). The optical emission spectra suggested that the formation of N₂*‐rich or N₂⁺‐rich plasma was successfully controlled by introducing different kinds of noble gases. Auger electron spectroscopy and XPS were used to characterize the depth profile of the elements and chemical species on the nitrided surface. The nitride layer formed by a N₂⁺‐rich plasma had a much higher nitrogen concentration than that by a N₂*‐rich plasma, likely due to the larger chemical activity of the N₂⁺ species as well as the N₂⁺ sputtering bombardment to the cathode surface. The strong reactivity of the N₂⁺ species was also confirmed from the chemical shift of N 1s spectra for iron nitrides. An iron nitride formed by the N₂⁺‐rich plasma has higher stoichiometric quantity of nitrogen than that formed by the N₂*‐rich plasma. Besides the effect of nitrogen radicals on surface nitridation, the contribution of the chromium in steel to the nitriding reaction was also examined. This chromium can promote a nitriding reaction at the surface, which results in an increase in the nitrogen concentration and the formation of nitride with high nitrogen coordination. Copyright © 2010 John Wiley & Sons, Ltd.     

Analysis of microscopic modifications and macroscopic surface properties of polystyrene thin films treated under d.c. pulsed discharge conditions

Using a d.c. pulsed plasma for the polymer surface treatment allows the attainment of macroscopic modifications of the surface, such as an important increase in wettability. At the same time microscopic variations of the surface structure are mainly linked to low‐depth chemical modifications, even if very weak roughness changes appear. This technique thus presents two major interests: the low power consumption compared with other techniques such as radiofrequency or microwave plasmas makes it economical; and very significant treatment (macroscopic) is realized under soft conditions without degradation of the polymer. The results of macroscopic and microscopic studies on polystyrene surfaces may allow a macroscopic interpretation to be made of the interaction between the polymer and the d.c. pulsed plasma. Treatment is divided into two temporal stages: cleaning and functionalization. Copyright © 2005 John Wiley & Sons, Ltd.     

Penetration of plasma surface modification. I. Cf4 and C2F4 glow discharge plasmas

Plasma treatment of a polymeric surface could involve at least three major mechanisms: (1) direct interaction of reactive species in the low-temperature plasma state with the surface (line of sight irradiation effect), and (2) chemical reactions of plasma-induced reactive species with the surface, and (3) reactions among reactive species and the surface (plasma polymerization). The first and the third effects are considered to be limited to the surfaces which directly contact with plasma (glow). The second effect is not limited to the surfaces that contact with plasma state but can penetrate beyond the plasma zone by diffusion. Using an assembly of fibers, of which only the top layer contacts with plasma (glow), the penetration of chemical changes caused by plasma exposure was investigated. Results indicate that the fluorination effect (incorporation of fluorine-containing moieties on the surface of polymeric substrate) penetrates through a considerable thickness of the assembly of fibers, depending on the porosity (gas permeability) of the system. Chemical reactions of plasma-induced (chemically) reactive but nonpolymerizing species with the substrate fibers seems to predominate. The direct interactions of energetic species, such as ions, electrons, and electronically excited species, with polymeric surfaces seems to play relatively minor roles in the plasma treatment investigated. The major role of plasma, in this case, seems to be creating such chemically reactive species. © 1994 John Wiley & Sons, Inc.     

Investigation of glow discharge plasma for surface modification of polypropylene

Material surface properties of polymers, plastics, ceramics and textiles can be modified by atmospheric or low‐pressure glow discharge plasma. The aim of the present work is to study the surface modification of biaxially oriented polypropylene (BOPP) film in order to improve its hydrophilic and wetting properties. In this article we used low‐pressure, low‐temperature oxygen plasma for the surface treatment of BOPP. Scanning electron microscopy indicates that plasma treatment causes mainly physical changes by creating microcraters and roughness on the surface and increasing surface friction. Attenuated total reflectance infrared spectra show oxygen‐containing groups such as ? OH at 3513 cm^?1 and C?O at 1695 cm^?1. Microscopic investigations of water droplets on BOPP (treated, untreated) show that the interfacial adhesion of treated surfaces is increased. Copyright © 2003 John Wiley & Sons, Ltd.     

Experimental study of a d.c. oxygen glow discharge by V.U.V. absorption spectroscopy

Vacuum ultraviolet absorption spectroscopy has been used to measure the concentration of oxygen molecules O₂(³), metastable singlet O₂(¹) molecules, atoms, and ozone in a d.c. glow discharge. The axial electric field, the electronic density, and the gas temperature are also determined. This set of measurements is presented for the positive column of a glow discharge created in a 1.6-cm-diameter Pyrex tube, for a pressure between 0.2 and 5 Torr and a d.c. current up to 80 mA.     

Application of a rotating high-pressure glow discharge for the dissociation of hydrogen sulfide

The dissociation of hydrogen sulfide has been studied in an atmospheric-pressure glow discharge rotating between concentric electrodes in an axial magnetic field. Though the electrodes were heated to remove the sulfur formed in the discharge, stable operation was possible. The characteristics of the discharge and the influence of experimental parameters on the conversion of hydrogen sulfide and the energy efficiency are reported.     

Laser Doppler anemometry under plasma conditions. Part I. Measurements in a d.c. plasma jet

A study is presented on the use of laser Doppler anemometry (LDA) techniques for the measurement of the gas and particle velocities under plasma conditions. Experimental data is presented for a d.c. plasma jet in which alumina particles are injected under different operating conditions. The results reveal that the plasma velocity at the exit of the jet is of the order of 200–300 m/s. The intensity of turbulence is as high as 30 to 40% in the free shear layer and the particle velocity distribution is shown to be asymmetric, with particle dispersion in the plane of injection considerably more important than that in the perpendicular direction. The average particle velocity depends on the composition of the plasma gas, the torch current, and power.     

Monte Carlo analysis of the electron thermalization process in the afterglow of a microsecond dc pulsed glow discharge

A Monte Carlo model is utilized for studying the behavior of electrons in the afterglow of an analytical microsecond dc pulsed glow discharge. This model uses several quantities as input data, such as electric field and potential, ion flux at the cathode, the fast argon ion and atom impact ionization rates, slow electron density, the electrical characterization of the pulse (voltage and current profiles) and temperature profile. These quantities were obtained by earlier Monte Carlo — fluid calculations for a pulsed discharge. Our goal is to study the behavior of the so-called Monte Carlo electrons (i.e., those electrons created at the cathode or by ionization collisions in the plasma which are followed by using the Monte Carlo model) from their origin to the moment when they are absorbed at the cell walls or when they have lost their energy by collisions (being transferred to the group of slow electrons) in the afterglow of the pulsed discharge. The thermalization of the electrons is a phenomenon where the electron-electron Coulomb collisions acquire a special importance. Indeed, in the afterglow the cross sections of the other electron reactions taken into account in the model are very low, because of the very low electron energy. We study the electron energy distributions at several times during and after the pulse and at several positions in the plasma cell, focusing on the thermalization and on the behavior of the electrons in the afterglow. Also, the time evolution of the rates of the various collision processes, the average electron energy, the densities of Monte Carlo and slow electrons and the ionization degree are investigated.     

Study of a new direct current atmospheric pressure glow discharge in helium

In this study a new DC-APGD operated in He was developed and characterized. The discharge is operated at 0.9 kV and about 25-35 mA and at a gas flow of 100 ml/min. The source was spectroscopically studied and parameters such as the rotational temperature (T_rot), the excitation temperature (T_exc), the ionization temperature (T_ion) and the electron number density (n_e) were determined. The current-voltage characteristic of the source was studied as well. At optimized conditions the discharge operates in the normal region of the current-voltage characteristic. Rotational and excitation temperatures determined with the use of OH band and Fe I lines as thermometric species were of the order of about 900-1200 and 4500-5500 K, respectively. This indicates that despite of the atmospheric pressure, the discharge is not in LTE. Spatially resolved temperature measurements were performed with axial as well as radial resolution and showed relatively flat profiles. Axially resolved emission intensity profiles for several species such as H, N₂, N₂⁺, OH, He and Hg were determined. It also was found that H₂ introduced into the He by electrolysis of acid solutions such as in ECHG considerably increases the spectroscopically measured gas temperatures but decreases the analyte line intensities, as shown for Hg.     

Chemical structure and surface morphology evolution of glow discharge polymer films by Ar‐ions intermittent etching

The Ar‐ions intermittent‐etching technique was successfully incorporated during the deposition of glow discharge polymer (GDP) films. The ionic components and ion energy distributions (IEDs) of C₄H₈/H₂ and C₄H₈/H₂/Ar plasma were diagnosed by an energy‐resolved mass spectrometer, respectively. The Fourier transform infrared spectroscopy, scanning electron microscope, and white‐light interferometer were used to studying the chemical structure, surface morphology, and roughness of the GDP films, which are deposited with the various time of Ar‐ions intermittent etching. With the introduction of Ar into the chamber, the intensity of the C H absorption peaks becomes weak and the large‐mass C H species were ionized and dissociated from the mass spectrometer results. The surface roughness of GDP films are decreased with Ar‐ions intermittent etching, the lowest surface roughness (Rq) is only 33.6 nm when the intermittent cycle is 60 minutes/15 minutes. The highest sp³CH₃ (sym) absorption peaks are attributed to samples also with 60‐minute/15‐minute intermittent cycle, which shortens the length of the carbon chain and reduces the probability of the cluster formations.     

Dominant reaction channels and the mechanism of silane decomposition in a H2-Si(s)-SiH4 glow discharge

Chemical relaxation mass spectrometry has been used to study the kinetics and mechanism in the silane-hydrogen-solid silicon system under conditions of glow discharge. The emphasis was on the main processes related to the deposition of amorphous and nanocrystalline silicon thin films. It is shown that under conditions of the deposition of a-Si and nc-Si the dominant reaction channel is the electron impact induced fragmentation of silane into molecular hydrogen and SiH₂ radical. The role of other processes, such as hydrogen abstraction, is discussed.     

Evaluation of a pulsed glow discharge time-of-flight mass spectrometer as a detector for gas chromatography and the influence of the glow discharge source parameters on the information volume in chemical speciation analysis

The figures of merit of a pulsed glow discharge time-of-flight mass spectrometer (GD-TOFMS) as a detector for gas chromatography (GC) analysis were evaluated. The mass resolution for the GD-TOFMS was determined on FWHM in the high mass range (²⁰⁸Pb⁺) as high as 5,500. Precision of 400 subsequent analyses was calculated on ⁶³Cu⁺ to be better than 1% RSD with no significant drift over the time of the analysis. Isotope precision based on the ⁶³Cu⁺/⁶⁵Cu⁺ ratio over 400 analyses was 1.5% RSD. The limits of detection for gaseous analytes (toluene in methanol as solvent) were determined to be as low as several hundred ppb or several hundred pg absolute without using any pre-concentration technique. Furthermore, the different GD source parameters like capillary distance, cathode–anode spacing, and GD source pressure with regards to the accessible elemental, structural, and molecular information were evaluated. It was demonstrated that each of these parameters has severe influence on the ratio of elemental, structural, and parent molecular information in chemical speciation analysis.     

等离子体技术对CO2甲烷化用Ni/SiO2催化剂的改性作用

采用浸渍法制备了Ni/SiO₂催化剂,应用等离子体技术对催化剂进行改性处理。以CO₂甲烷化为模型反应对催化剂进行活性评价,通过H₂程序升温还原(H₂-TPR)和CO₂程序升温脱附(CO₂-TPD)技术对催化剂进行表征。研究了等离子体技术强化处理对催化剂吸附性能和还原性能的影响。结果表明,与常规焙烧的催化剂相比,等离子体技术改性处理提高了催化剂活性组分的分散度,增加反应活性位并调变了活性位对吸附物种的吸附强度,改进了催化剂的还原性能,CO₂甲烷化反应活性和甲烷的时空产率显著提高。     

Plasma-induced deposition of titanium nitride from TiCl4 in a direct current glow discharge: Control of the chlorine content and gas-phase nucleation

Titanium nitride thin films have been deposited from TiCl₄, N₂, and H₂, in a low-pressure glow discharge at temperatures of 500°C, which are compatible with most applications. Based on our earlier work on the effect of tire plasma parameters on the chemical pseudoequilibrium in this and in similar systems, the chlorine content could he reduced to less than 2 at %. Suppression of the positive column reduced the gas-phase reaction within the reactor volume and the concomitant homogenous nucleation Dense, vent hard films with golden color could he deposited on various substrates including silicon and steel.     

辉光放电光谱法在深度分析上的应用现状

本文简单地介绍了辉光放电光谱法（GD-OES）的基本原理。分别对深度分析的定量方式、放电方式、应用领域和相关标准进行了详细地阐述。重点描述了商品化仪器中使用的SIMR深度分析定量方法。分别对三种放电方式（如直流、射频和脉冲）在深度分析中的特点进行了介绍。综述了GD-OES在金属镀层、复杂涂镀层、纳米级薄膜和样品制备领域的具体应用。最后,介绍了GD-OES在深度分析方面的标准     

Investigation of the afterglow time regime in pulsed radiofrequency glow discharge time‐of‐flight mass spectrometry

The pulsed power operation mode of a radiofrequency (rf) glow discharge time‐of‐flight mass spectrometer was investigated, for several ions, in terms of intensity profiles along each pulse period. Particular attention was paid to the plateau and transient afterglow regions. An rf pulse period of 4 ms and a duty cycle of 50% was selected to evaluate the influence of discharge parameters in the afterglow delay and shape of Ar⁺, Ar₂⁺ and several analytes (Br, Cl, Cu) contained in polymeric layers. Pulse shapes of Ar⁺ and Ar₂⁺ ions vary with pressure and power. At low pressures the highest intensity is observed in the plateau while at higher pressures (>600 Pa) the afterpeak is the dominant region. Although the influence of the applied power is less noticeable, a widening of the afterglow time regime occurs for Ar⁺ when increasing the power. Maximum intensity of the argon signal is measured in the afterglow at 30 W, while the area of such afterpeak increases with power. The maximum intensity of Ar₂⁺ is obtained at the highest power employed (60 W) and the ratio maximum intensity/afterglow area remains approximately constant with power. Analytes with ionization potentials below (Cu) or just above (Br) the argon metastable energy show maxima intensities after argon ions decay, indicating they could be ionized by collisions with metastable Ar atoms. Chlorine signals are observed in the afterglow despite their ionization potential is well above the energy of argon metastable levels. Moreover, they follow a similar pattern to that observed for Ar₂⁺, indicating that charge‐transfer process with Ar₂⁺ could play a significant role. Copyright © 2011 John Wiley & Sons, Ltd.     

Study of a hollow cathode arc discharge in the presence of chromium oxide

A hollow cathode arc discharge in hydrogen has been used for the purpose of chromium oxide reduction, the solid oxide being placed inside the anode. Mass transport from the oxide to the gas phase and excitation conditions in the plasma have been investigated. The results show that a substantial amount of oxide is transferred to the gas phase with subsequent reduction and deposition inside the cathode cavity, in the form of a pure metal. The residual part condenses on the discharge chamber wall as an amorphous substance, containing 50–60% of Cr metal, and on the anode surface under the form of a mixture of chromium oxide and metal crystals (10%). From spectroscopic investigations it follows that, inside the anode zone, total Cr concentration in the gas phase is of the order of 10¹⁴ cm^–3, the excitation temperature of the atoms and ions being 4500 and 5500 K, respectively, and the ionization temperature being about 6000 K.Notation I absolute spectral line intensity (W cm^–2 sr^–1) - emission coefficient (W cm^–3 sr^–1) - A relative absorption - absorption coefficient (cm^–1) - L plasma diameter (mm) - f _tk oscillator strength - _D full Doppler width (cm^–1) - S( ₀ L) Ladenburg-Levy function - wave number (cm^–1) - k _pl mass transport rate (mol cm^–2 s^–1) - k _th thermal reduction rate (mol cm^–2 s^–1) - u ion mobility (mm V^–1 s^–1 ) - E electric field strength (V mm^–1) - drift velocity (cm s^–1)     

DC plasma etching of silicon by sulfur hexafluoride. Mass spectrometric study of the discharge products

Polycrystalline silicon wafers were etched in dc discharges of SF₆. SF_x species were extracted from the discharges and measured with a mass spectrometer. A systematic procedure was used to measure the SF _x ⁺ signals such that they are indicators of events in the discharge close to the sample undergoing etching. The picture that emerges is remarkably simple and shows the relative stability of several SF_x species including SF₆, SF₄, SF₂, and SF which are shown to be extracted from the discharge both in the presence and absence of the silicon sample. When silicon is being etched on the cathode of the discharge cell, the only significant additional products are SiF₄ and S₂F₂. A comparison of blank and sample data for opposite substrate polarities shows that there is only a small cation-assisted etching effect and suggests that ions do not play an important role in the etching of silicon by SF₆ discharges.     

Mass spectrometric studies on the decomposition of trialkylgallium on gaas surfaces

The thermal decomposition of trimethylgallium [(CH₃)₃Ga] and triethylgallium [(C₂H₅)₃Ga] on gallium arsenide (GaAs) surfaces was studied under an ultra-high vacuum using mass spectrometry. It was observed that the decomposition process of (CH₃)₃Ga and (C₂H₅)₃Ga depends on the arsenic coverage of the substrate surface. On a (100)-oriented surface, increasing the arsenic coverage basically enhances the decomposition of (CH₃)₃Ga and (C₂H₅)₃Ga to gallium atoms above 350 and 300°C, respectively. The decomposition of (CH₃)₃Ga proceeds by emitting CH₃ radicals. On a surface with low arsenic coverage, the decomposition of (CH₃)₃Ga is imperfect and fewer than three methyl groups of alkylgallium are desorbed. On a (111)B-oriented surface, however, an increase in the surface arsenic coverage suppresses the decomposition of alkylgallium, which is different from the case for a (100) surface.