Spectroscopic evaluation of a compact magnetically boosted radiofrequency glow discharge for time-of-flight mass spectrometry

A compact magnetically boosted radiofrequency glow discharge (GD) has been designed, constructed and its analytical potential evaluated by its coupling to a mass spectrometer (MS). Simple modifications to the original source configuration permitted the insertion of permanent magnets. Small cylindrical Nd–Fe–B magnets (∅ = 4 mm, h = 10 mm) were placed in an in-house-modified GD holder disc that allows easy and fast exchange of the magnets. The different processes taking place within the GD plasma under the influence of a magnetic field, such as sputtering, ionisation processes and ion transport into the MS, were studied using different GD operating conditions. Changes to the ionisation and ion transport efficiency caused by the magnetic field were studied using an rf-GD-TOFMS setup. A magnetic field of 60–75 gauss (G) was found not to affect the sputtering rates but to enhance the analyte ion signal intensities while decreasing the Ar species ion signals. Moreover, magnetic fields in this range were shown not to modify the crater shapes, enabling the fast and sensitive high depth resolved analysis of relatively thick coated samples (micrometre) by using the designed compact magnetically boosted rf-GD-TOFMS.

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.     

射频等离子体对合成低碳醇用CuCoAl催化剂的改性作用

采用共浸渍法制备了CuCo/γ-Al₂O₃催化剂,应用射频等离子体技术对催化剂进行改性处理。以CO加氢合成低碳醇为模型反应对催化剂进行活性评价,通过X射线物相分析(XRD)、氢氧滴定(HOT)、CO程序升温脱附(CO-TPD)和程序升温还原(TPR)等技术对催化剂进行表征,研究了射频等离子体技术强化处理对催化剂结构、吸附性能和还原性能的影响。结果表明,等离子体技术改性处理提高了催化剂活性组分的分散度,细化了铜物种的晶粒尺寸,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,等离子体改性处理的催化剂比未处理的样品CO加氢反应活性和低碳醇的时空产率显著提高。     

辉光放电质谱技术应用进展

对辉光放电质谱(GDMS)在金属与半导体、非导体、薄层与深度分析、分子信息分析方面的应用和一些新装置、新方法进行了综述.着重介绍了近20年来我国学者在辉光放电质谱方面的成就,并结合国际上的报道对该领域的发展现状进行了总结.     

Electrical characteristics of a millisecond pulsed glow discharge

A μs and ms pulsed argon glow discharge was investigated with respect to the breakdown condition (Paschen curve). Moreover, current–voltage profiles were acquired for different discharge frequencies, pulse durations, cathode–anode spacing and discharge pressures. The breakdown voltage was dependent on the cathode material (Cu, steel, Ti and Al). No severe change in the breakdown voltage was observed for a 1 ms pulse at different frequencies. However, the theoretical breakdown curve, calculated based on the Paschen equation did not fit the experimental data. The current plots for different cathode–anode spacing showed a maximum at intermediate distance (8–10 mm). These data were consistent with mass spectrometric data acquired using the same instrument in a GC-GD-TOFMS chemical speciation study.     

Mass spectrometric diagnosis of the surface nitriding mechanism in a d.c. glow discharge

Reactive constituents have been investigated in a molecular beam generated in the cathode surface glow area and surface boundary layer. Mixtures of nitrogen and hydrogen form NH_x(x=0–4) compounds, which are of relevance in heterogeneous, plasma vs. metal nitriding reactions. Ammonia decomposition leads to NH_x(x=2–4). Strong cataphoretic enrichment of hydrogen has been observed in the cathode glow area. Heterogeneous reactions of NH_x with iron lead to the formation of iron nitrides via intermediates such as FeNH_2–3. In a pulsed d.c. glow discharge, increased sputtering and decreased hydrogen enrichment have been observed.     

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.     

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.     

Hydrogen sulfide dissociation in ozonizer discharges and operation of ozonizers at elevated temperatures

A high-temperature ozonizer device has been developed to stud v the conversion of hydrogen sulfide (H₂S) into elemental sulfur and hydrogen. To allow for continuous operation, the process must be carried out at temperatures high enough to remove the sulfur in the liquid (=156°C) or in the vapor state (>435°C). A double quartz wall ozonizer which tolerates the high electrical and chemical requirements was constructed. Its electrical characteristics in the temperature range of 130–560°C and the influence of experimental parameters on conversion and energetic elficiency are described.     

Pulsed glow discharges for analytical applications

Non equilibrium plasmas such as glow discharges have become a commonly used tool in direct surface and interface analysis of solid materials. The application of pulsed glow discharges to material analysis has been studied by several research groups over the last 20 years. Two European projects, EMDPA and GLADNET currently work on the analytical applications of glow discharges, giving a particular attention to pulsed discharges. This review demonstrates the advantages of pulsed discharge operation by showing how the specific excitation and ionisation processes observed during the plasma ignition phase and the afterglow can be used for analytical applications.     

In situ preparation of ultrafine Ru nanocatalyst supported on nitrogen-doped layered double hydroxide by nitrogen glow discharge plasma for catalytic hydrogenation of N-ethylcarbazole

Ultrafine Ru nanoparticles (RuNPs) supported on nitrogen-doped layered double hydroxide (Ru/LDH) were in situ prepared by nitrogen glow discharge plasma (nGDP) without adding any chemical reducing agents or stabilizers. The as-synthesized Ru/LDH catalysts were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, and Fourier transform infrared spectroscopy. During treatment with nGDP, the reduction of Ru³⁺ and nitrogen doping were carried out simultaneously. The resulting RuNPs has a narrow particle size distribution of 1.41–2.61 nm, an ultrafine average particle size of 1.86 nm, and were uniformly dispersed on nitrogen-doped LDH. The complexation of RuNPs and O/N-containing functional groups on LDH improve the catalytic activity and stability of Ru/LDH. The catalyst exhibited excellent properties for the hydrogenation reaction of N-ethylcarbazole (NEC). The conversion of NEC and the selectivity of 12H-NEC were 100% and 99.06% for 1 hr at 120°C and 6 MPa H₂, respectively. The mass hydrogen storage capacity was 5.78 wt%. The apparent activation energy was 35.78 kJ/mol.     

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 semiconducting materials by high-resolution radiofrequency glow discharge mass spectrometry

The analytical capabilities of a high-resolution mass spectrometer in combination with a 13.56 MHz glow discharge ion source for the analysis of semiconducting materials (silicon carbide and gallium arsenide) were studied. It was shown that single positively charged ions of sample material have about 10 eV higher average energy than the ions of the discharge and residual gas. Therefore effective energy separation of the ions of analyte from the ions of the discharge and residual gas was achieved by adjusting the ion transfer optics (breadth and position of energy slit), which improves the analytical capabilities of the developed method.Some analytical applications are presented to illustrate the performance of r.f. GDMS for the bulk analysis of semiconducting materials. The results of the trace element analysis of gallium arsenide and silicon carbide samples are compared with data of independent methods (LIMS, ICP-AES, SIMS).Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthdayOn leave from the Institute of Inorganic Chemistry, 630090 Novosibirsk, Russia     

Argon glow discharge plasma‐reduced palladium nanoparticles supported on activated carbon for Suzuki and Heck coupling reactions

Palladium nanoparticles supported on activated carbon were prepared by argon glow discharge plasma reduction (Pd/C‐P) without any chemical reducing agents and protective agents. The as‐prepared Pd/C‐P catalyst was characterized using nitrogen adsorption–desorption, X‐ray diffraction and transmission electron microscopy analyses. The results showed that the palladium nanoparticles reduced by plasma are well dispersed with a smaller particle size than commercial Pd/C. Pd/C‐P exhibited a high catalytic activity in Suzuki and Heck coupling reactions. Moreover, there was no obvious loss of catalytic activity even after eight repeated cycles, showing good reactivity and recyclability.     

Model of microsecond pulsed glow discharge in hollow cathode for mass spectrometry

A new model for microsecond pulsed glow discharge in a hollow cathode and its afterglow is described. The model is based on the Monte-Carlo method together with a new method for electrical field calculation, which is based on some phenomenological laws of plasma behavior. The afterglow model uses continuity and Poisson equations. A qualitative agreement between the model results and results published in experimental and theoretical works is demonstrated. Some processes in the microsecond pulsed discharge in the hollow cathode, such as sputtering, ionization and transfer of sample, are investigated. The model is successfully used for the optimization of the operational parameters of the time-of-flight mass spectrometer with ionization by microsecond pulsed glow discharge in a hollow cathode.     

Development of a membrane reactor for decomposing hydrogen sulfide into hydrogen using a high-performance amorphous silica membrane

We have successfully developed a membrane reactor for decomposing hydrogen sulfide into hydrogen using an amorphous silica membrane for the first time. The membrane was prepared by the CVD method with tetramethoxysilane and oxygen, and showed excellent hydrogen permeance at 873 K of the order of 10⁻⁷ mol m⁻² s⁻¹ Pa⁻¹ and high hydrogen/nitrogen permselectivity of 10⁴. The membrane reactor constructed with our membrane and a commercially available catalyst decomposed hydrogen sulfide into hydrogen with higher conversion than the equilibrium conversion. This conversion enhancement was because of the selective extraction of hydrogen from the reaction side to the permeate side by the silica membrane.     

Dusty Plasma in Inhomogeneous Magnetic Fields in a Stratified Glow Discharge

We study the dynamics of dust particles in a stratified glow discharge in inhomogeneous magnetic fields. Dust structures are formed in standing striations, in which traps for dust particles arise. When a magnetic field is applied, these structures begin to rotate. The observations were carried out in striations near the end of the solenoid, where the region of an inhomogeneous magnetic field begins. With an increase in the magnetic field, the dusty structure can be deformed. The rotation of a dusty structure in an inhomogeneous magnetic field has been studied in detail; it has its own peculiarities in comparison with rotation in a uniform field. We have considered the mechanisms of such rotation and estimated its velocity.     

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.     

辉光放电质谱法测定高纯材料中痕量硫杂质

准确测定并控制材料中杂质元素含量是发挥高纯材料性能不可或缺的环节。辉光放电质谱法(GDMS)是准确、快速、高灵敏分析高纯材料中痕量及超痕量硫的理想方法。对GDMS分析高纯铜和镍基高温合金中痕量硫的质谱干扰进行了讨论,优化了放电电流和放电电压,采用多种标准物质对硫的相对灵敏度因子(RSF)进行了校准和验证,并与二次离子质谱法(SIMS)进行分析结果比对,验证了GDMS定量分析结果的准确性和可靠性。     

Application of Spray-Type Atmospheric Pressure Glow Plasma Reactor: Ashing of Organic Compounds II

When plasma treatment is carried out in the after glow region of an electrical discharge, the decay rate and the density of the active species are very important factors for the treatment efficiency. They are known to depend on the linear gas flow rate (gas velocity) and on the residence time of the treatment gas in the discharge zone, respectively. In our previous study, we found that the spray-type atmospheric pressure glow plasma reactor with O₂/He or O₂/Ar mixture treatment gases had a satisfactory ashing rate of a solid organic compound (OFPR-800; a photoresist). However, the relationships between the gas velocity or the residence time and the ashing rate had not yet been examined. The present study showed clearly that the gas velocity influenced only the transit time, that is the time which the gas mixture took to progress from the slit nozzle to the sample surface, but it did not influence the generation of the active species. On the other hand, the generation rate of active species in the discharge zone was found to be strongly dependent on the residence time. The ashing rate was found to increase with increasing the residence time up to about 30 ms, beyond which it saturated. From optical emission spectroscopy measurements, the maximum ashing rate could be correlated with the emission intensities corresponding to He 3p³P-2s³S (388.8 nm) and O 3d⁵D-3p⁵P (926.5 nm) bands. These results are of practical interest.