Direct Current Glow Discharge Research Articles

Development of soft ionization using direct current pulse glow discharge plasma source in mass spectrometry for volatile organic compounds analysis

This study describes an ionization source for mass analysis, consisting of glow discharge plasma driven by a pulsed direct-current voltage for soft plasma ionization, to detect toxic volatile organic compounds (VOCs) rapidly and easily. The novelty of this work is that a molecular adduct ion, in which the parent molecule attaches with an NO+ radical, [M+NO]+, can be dominantly detected as a base peak with little or no fragmentation of them in an ambient air plasma at a pressure of several kPa. Use of ambient air as the discharge plasma gas is suitable for practical applications. The higher pressure in an ambient air discharge provided a stable glow discharge plasma, contributing to the soft ionization of organic molecules. Typical mass spectra of VOCs toluene, benzene, o-xylene, chlorobenzene and n-hexane were observed as [M+NO]+ adduct ion whose peaks were detected at m/z 122, 108, 136, 142 and 116, respectively. The NO generation was also confirmed by emission bands of NO γ-system. The ionization reactions were suggested, such that NO+ radical formed in an ambient air discharge could attach with the analyte molecule.

Photoelectrochemical performance of N-doped ZnO branched nanowire photoanodes.

A ZnO branched-nanowire (BNW) photoanode was doped with N for use in a photoelectrochemical cell (PEC) to generate H2 from water splitting. First, ZnO BNWs were synthesized by chemical bath deposition method. Two experimental methods were used for N-doping: the time-controlled direct-current glow discharge plasma (DCGDP) and the DC magnetron plasma (DCMP) methods, to optimize N-doping of the NW structure. X-ray photoelectron spectroscopy (XPS) provided the N distribution and atomic percentage in the BNWs. The XPS results confirmed that N distribution into ZnO BNWs occurred by N substitution of O sites in the ZnO structure and through well-screened molecular N2. The morphologies and structures of the fabricated nanostructures were investigated by field-emission scanning electron microscopy and X-ray diffraction respectively. The photoanode performance was demonstrated in photoelectrochemical studies at various power densities under both dark and illuminated conditions. Increasing the N amount in the ZnO BNWs increased the photocurrent in the PEC.

Slow electron energy balance for hybrid models of direct-current glow discharges

In this paper, we present the formulation of slow electron energy balance for hybrid models of direct current (DC) glow discharge. Electrons originating from non-local ionization (secondary) contribute significantly to the energy balance of slow electrons. An approach towards calculating effective energy brought by a secondary electron to the group of slow electrons by means of Coulomb collisions is suggested. The value of effective energy shows a considerable dependence on external parameters of a discharge, such as gas pressure, type, and geometric parameters. The slow electron energy balance was implemented into a simple hybrid model that uses analytical formulation for the description of non-local ionization by fast electrons. Simulations of short (without positive column) DC glow discharge in argon are carried out for a range of gas pressures. Comparison with experimental data showed generally good agreement in terms of current-voltage characteristics, electron density, and electron temperature. Simulations also capture the trend of increasing electron density with decreasing pressure observed in the experiment. Analysis shows that for considered conditions, the product of maximum electron density ne and electron temperature Te in negative glow is independent of gas pressure and depends on the gas type, cathode material, and discharge current. Decreasing gas pressure reduces the heating rate of slow electrons during Coulomb collisions with secondary electrons, which leads to lower values of Te and, in turn, higher maximum ne.

1D kinetic simulations of a short glow discharge in helium

This paper presents a 1D model of a direct current glow discharge based on the solution of the kinetic Boltzmann equation in the two-term approximation. The model takes into account electron-electron coulomb collisions, the corresponding collision integral is written in both detailed and simplified forms. The Boltzmann equation for electrons is coupled with continuity equations for ions and metastable atoms and the Poisson equation for electric potential. Simulations are carried out self-consistently for the whole length of discharge in helium (from cathode to anode) for cases p = 1 Torr, L = 3.6 cm and p = 20 Torr, L = 1.8 mm, so that pL = 3.6 cm·Torr in both cases. It is shown that simulations based on the kinetic approach give lower values of electron temperature in plasma than fluid simulations. Peaks in spatial differential flux corresponding to the electrons originating from superelastic collisions and Penning ionization were observed in simulations. Different approaches of taking coulomb collisions into account give significantly different values of electron density and electron temperature in plasma. Analysis showed that using a simplified approach gives a non-zero contribution to the electron energy balance, which is comparable to energy losses on elastic and inelastic collisions and leads to significant errors and thus is not recommended.

Low Pressure DC-Plasma System for the Modification of Polymeric Membrane Surfaces

The main objectives of this work were to develop a lab-scale direct current (DC) glow discharges plasma system for modification of organic and inorganic membranes. Characteristics of plasma system were presented under the discharge of five gases (Ar, N2, air, O2, and CO2). A Langmuir double probe was used for the evaluation of the electron temperature (Te) and electron density (ne) of plasmas. The current and voltage (I-V) characteristic curves were analyzed. Relationships between breakdown voltage (VB) of gases and products of gas pressure and inter-electrode gap (pd) were studied in form of Paschen curves. The results showed that Te of plasma in various gases was in the range of 4-13 eV, while the ne varied between 108 and 109 cm-3. The plasma generated at different gas pressure and applied voltage is in the normal and abnormal modes. Finally, the constructed DC-plasma system was utilized for modification of polymeric membrane surfaces. Treatment time, discharge power and type of gas were varied. The tailoring of membrane surfaces was analyzed through the water contact angle and percent-weight loss (PWL) measurements, DMTA, AFM, XPS and FTIR spectrum. It could be shown that DC-plasma from this system can be used to modify the surface of polymeric membranes.

Sensitive Determination of Cd in Small-Volume Samples by Miniaturized Liquid Drop Anode Atmospheric Pressure Glow Discharge Optical Emission Spectrometry.

A novel liquid drop anode (LDA) direct current atmospheric pressure glow discharge (dc-APGD) system was applied for direct determination of Cd in liquid microsamples (50 μL) by optical emission spectrometry (OES). The microdischarge was generated in open-to-air atmosphere between a solid pin type tungsten cathode and a liquid drop placed on a graphite disk anode. The arrangement of the graphite disk placed on a PTFE chip platform as well as the solid pin type cathode was simple and robust. The limit of detection (LOD) of Cd for the developed LDA-APGD-OES method was 0.20-0.40 μg L-1, while precision (as the relative standard deviation for the repeated measurements) was within 2-5%. By using the liquid drop of 50 μL, the linearity range of 1-1000 μg L-1 was achieved. The effect of addition of the low-molecular weight (LMW) organic compounds, easily ionized elements (EIEs), i.e., Ca, K, Mg, and Na, as well as the foreign ions (Al, Cu, Fe, Mn, Zn) to the solution on the in situ atomization and excitation processes occurred during operation of the LDA-APGD system, and the response of Cd was studied. Validation of the proposed method was demonstrated by analysis of Lobster hepatopancreas (TORT-2), pig kidney (ERM-BB186), and groundwater (ERM-CA615) certified reference materials (CRMs) and recoveries of Cd from water samples spiked with 25 μg L-1 of Cd. Very good agreement between the found and certified values of Cd in the CRMs (the recoveries were within the range of 96.3-99.6%) indicated trueness of the method and its reliability for determination of traces of Cd. In the case of the spiked water samples, the recoveries obtained were in the range from 95.2 to 99.5%.

Наноструктурированные углеродные материалы в эмиссионной электронике

This paper considers the influence of formation conditions on the composition and structure of polycluster diamond films, diamond-like carbon films and carbon nanowalls. Polycluster diamond films were obtained from a gas mixture of hydrogen and methane activated with arc and microwave discharges as well as by applying heat (i.e. hot-wire method). Diamond-like carbon films were obtained by using the methods of high-frequency magnetron sputtering, high-frequency diode discharge in a gas mixture of cyclohexane and hydrogen, graphite ion-beam sputtering. Carbon nanowalls were obtained from a gas mixture of hydrogen and methane activated with a direct current glow discharge. The composition and structure of synthesized carbon materials are explored by using the methods of electron and atomic force microscopy, X-ray diffractometry and Raman spectroscopy. Finally, the authors also study the interconnection between the composition and structure of synthesized carbon materials and electric and functional characteristics of cold cathodes based on them.

Characterization of the DC glow discharge in longitudinal flowing helium at atmospheric pressure

A one-dimensional self-consistent fluid model was developed to study the direct-current (DC) glow discharge in longitudinal flowing helium (He) at atmospheric pressure. Distinct dynamical features of charged particles are observed at different He flow velocities, which is accompanied by a dramatic change of spatial discharge structure. The positive He flow leads to the reduction of charged particle densities in the positive column and negative glow regions, and even makes the negative glow region disappear. The negative He flow allows for the enhancement of charged particle densities in the negative glow regions. These observations above mainly lie in the fact that the convection effects due to the He gas flow influence the transport properties of charged particles through different ways by comparing the He flow velocity with the ion drift one. These findings are of guiding significance for the improvement of the chemical activity and work efficiency of plasma source by controlling the gas flow in practical industrial fields.

Direct current atmospheric pressure glow discharge generated between a pin‐type solid cathode and a flowing liquid anode as a new tool for silver nanoparticles production

Direct current atmospheric pressure glow discharge (dc‐APGD), generated between a pin‐type tungsten solid cathode and the surface of a flowing liquid anode (FLA), was used to synthesize Ag nanoparticles (AgNPs) and gelatin‐stabilized Ag nanoparticles (GEL‐AgNPs) in a flow‐through plasma‐reaction system. To characterize the nanostructures, UV/Vis absorption spectrophotometry, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were applied. Resulting GEL‐capped AgNPs were more stable and lower in size than AgNPs. By applying attenuated total reflectance Fourier transform infrared spectroscopy (ATR FT‐IR) and FT‐Raman spectroscopy, possible functionalization of the AgNPs surface by GEL after dc‐APGD treatment was examined. The described method was robust and provided high amounts of the suspensions of nanocolloidal Ag.

Growth of mirror-like ultra-nanocrystalline diamond (UNCD) films by a facile hybrid CVD approach**Development of CVD ultra-nanocrystalline diamond films and related high-precision machining products (International S&T Cooperation, No. S2015ZR1100).

In this study, growth of mirror-like ultra-nanocrystalline diamond (UNCD) films by a facile hybrid CVD approach was presented. The nucleation and deposition of UNCD films were conducted in microwave plasma CVD (MPCVD) and direct current glow discharge CVD (DC GD CVD) on silicon substrates, respectively. A very high nucleation density (about 1 × 1011 nuclei cm−2) was obtained after plasma pretreatment. Furthermore, large area mirror-like UNCD films of Φ 50 mm were synthesized by DC GD CVD. The thickness and grain size of the UNCD films are 24 μm and 7.1 nm, respectively. In addition, the deposition mechanism of the UNCD films was discussed.

Study on plasma pre-functionalized PVC film grafted with TiO2/PVP to improve blood compatible and antibacterial properties

Research into the design of new biopolymers/polymer functionalized with nanoparticles is of tremendous interest to the medical sector, particularly with regard to blood-contacting devices. In this present study, a steady blood compatible and active antibacterial coating was fabricated by the grafting of titanium dioxide (TiO2)/polyvinylpyyrolidone (PVP) onto a polyvinyl chloride (PVC) film surface via the direct-current glow discharge plasma method. To enhance the chemical interaction between TiO2/PVP and PVC, the surfaces of the PVC films were functionalized by different plasmas (air, argon, and oxygen) before coating. In this study, the plasma parameters were varied, such as treatment time of about 5–20 min for a constant power of 100 W, potential 300 V, and a constant gas pressure of 2 Pa for air, argon, and oxygen gas environment. Then, the different plasma treatments on the PVC films, TiO2/PVP were grafted using a simple dip-coating method. In addition, the TiO2/PVP-grafted PVC films were characterized by contact angle, attenuated total reflectance Fourier transform infrared spectroscopy, field-emission scanning electron microscope, and x-ray photo electron spectroscopy. Importantly, TiO2/PVP is grafted onto the PVC surface due to the plasma-based retained functionality and demonstrates adhesive efficiency, which was observed by XPS. The bio-stability of the TiO2/PVP-modified PVC film was evaluated by in vitro platelet activation analysis and protein adsorption analysis. Then, the antibacterial properties were evaluated by the agar diffusion method against Escherichia coli. The result reveals that the grafting of TiO2/PVP was slightly higher for the 15 min oxygen plasma-functionalized PVC, which significantly decreases the platelet adhesion and protein adsorption. Moreover, the antibacterial properties of the 15 min oxygen plasma-functionalized PVC with TiO2/PVP-grafted film is also greatly improved compared with an air- and argon-functionalized surface. Our present study demonstrates that the plasma treatment is a beneficial and eco-friendly method to achieve higher hydrophilicity. Furthermore, our results indicated that the plasma-modified PVC exhibits appropriate anti-fouling performance.

On the effect of laser irradiation and heat treatment on the structure and field-emission properties of carbon nanowalls

The composition and structure of carbon nanowalls formed on silicon substrates from the gas phase of hydrogen and methane activated by a direct-current glow discharge are studied by methods of scanning electron microscopy, X-ray diffractometry, IR spectroscopy, and Raman spectroscopy. It is shown that nanowalls are comprised of a porous material consisting of curved lamellar (flaky) crystallites with a thickness of 3–10 nm. The effect of heat treatment and laser irradiation in air on the structure of the carbon nanowalls is studied, and the current–voltage characteristics of field-emission cathodes on their basis are obtained. The heating temperatures and laser-radiation power densities at which the morphology of the surface of carbon nanowalls changes and the characteristics of field-emission cathodes on their basis are determined.

Battery-Operated Atomic Emission Analyzer for Waterborne Arsenic Based on Atmospheric Pressure Glow Discharge Excitation Source.

In this paper, a sensitive atomic emission spectrometer (AES) based on a new low power and low argon consumption (<8 W, 100 mL min-1) miniature direct current (dc) atmospheric pressure glow discharge (APGD) plasma (3 mm × 5 mm) excitation source was developed for the determination of arsenic in water samples. In this method, arsenic in water was reduced to AsH3 by hydride generation (HG), which was then transported to the APGD source for excitation and detected by a compact CCD (charge-coupled device) microspectrometer. Different parameters affecting the APGD and the hydride generation reactions were investigated. The detection limit for arsenic with the proposed APGD-AES was 0.25 μg L-1, and the calibration curves were found to be linear up to 3 orders of magnitude. The proposed method was successfully applied to the determination of certified reference material (GBW08605), tap water, pond water, groundwater, and hot spring samples. Measurements from the APGD analyzer showed good agreement with the certified value/values obtained with well-established hydride generation atomic fluorescence spectrometry (HG-AFS). These results suggest that the developed robust, cost-effective, and fast analyzer can be used for field based arsenic determination and may provide an important tool for arsenic contamination and remediation programs.

Computational model of a direct current glow discharge used as an ambient desorption/ionization source for mass spectrometry

A new model of a plasma ionization source anchored by experimental data giving a comprehensive view of the discharge mechanism.

Flowing dusty plasma experiments: generation of flow and measurement techniques

A variety of experimental techniques for the generation of subsonic/supersonic dust fluid flows and means of measuring such flow velocities are presented. The experiments have been carried out in a -shaped dusty plasma experimental device with micron size kaolin/melamine formaldehyde particles embedded in a background of argon plasma created by a direct current glow discharge. A stationary dust cloud is formed over the cathode region by precisely balancing the pumping speed and gas flow rate. A flow of dust particles/fluid is generated by additional gas injection from a single or dual locations or by altering the dust confining potential. The flow velocity is then estimated by three different techniques, namely, by super particle identification code, particle image velocimetry analysis and the excitation of dust acoustic waves. The results obtained from these three different techniques along with their merits and demerits are discussed. An estimation of the neutral drag force responsible for the generation as well as the attenuation of the dust fluid flow is made. These techniques can be usefully employed in laboratory devices to investigate linear and non-linear collective excitations in a flowing dusty plasma.

Blistering of mechanically polished molybdenum upon its exposure to deuterium-containing plasma

Recent data on the blistering process in polished polycrystalline Mo for the case of direct-current glow discharge in deuterium and D2/2–4 mol % O2 or N2 admixtures, at an energy of incident molecular ions of 70–120 eV and a pressure of 14 Pa, are reported. Depending on the method of metal surface polishing, the initial metal grains are broken up into mutually disordered regions of smaller sizes (subgrains); the chemical composition of the damaged layer changes. In the formed structure, blistering can develop easily or be impeded. Small additions of O2 or N2 to deuterium facilitate the blistering.

Numerical simulation of a direct current glow discharge in atmospheric pressure helium**Project supported by the National Natural Science Foundation of China (Grant Nos. 11575050 and 10805013), the Midwest Universities Comprehensive Strength Promotion Project, the Natural Science Foundation of Hebei Province, China (Grant Nos. A2016201042 and A2015201092), and the Research Foundation of Education Bureau of Hebei Province, China (Grant No. LJRC011).

Characteristics of a direct current (DC) discharge in atmospheric pressure helium are numerically investigated based on a one-dimensional fluid model. The results indicate that the discharge does not reach its steady state till it takes a period of time. Moreover, the required time increases and the current density of the steady state decreases with increasing the gap width. Through analyzing the spatial distributions of the electron density, the ion density and the electric field at different discharge moments, it is found that the DC discharge starts with a Townsend regime, then transits to a glow regime. In addition, the discharge operates in a normal glow mode or an abnormal glow one under different parameters, such as the gap width, the ballast resistors, and the secondary electron emission coefficients, judged by its voltage–current characteristics.

A chemical stability study of trimethylsilane plasma nanocoatings for coronary stents

Trimethylsilane (TMS) plasma nanocoatings were deposited onto stainless steel coupons in direct current (DC) and radio frequency (RF) glow discharges and additional NH3/O2 plasma treatment to tailor the coating surface properties. The chemical stability of the nanocoatings were evaluated after 12 week storage under dry condition (25 °C) and immersion in simulated body fluid (SBF) at 37 °C. It was found that nanocoatings did not impact surface roughness of underlying stainless steel substrates. X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy were used to characterize surface chemistry and compositions. Both DC and RF nanocoatings had Si- and C-rich composition; and the O- and N-contents on the surfaces were substantially increased after NH3/O2 plasma treatment. Contact angle measurements showed that DC-TMS nanocoating with NH3/O2 treatment generated very hydrophilic surfaces. DC-TMS nanocoatings with NH3/O2 treatment showed minimal surface chemistry change after 12 week immersion in SBF. However, nitrogen functionalities on RF-TMS coating with NH3/O2 post treatment were not as stable as in DC case. Cell culture studies revealed that the surfaces with DC coating and NH3/O2 post treatment demonstrated substantially improved proliferation of endothelial cells over the 12 week storage period at both dry and wet conditions, as compared to other coated surfaces. Therefore, DC nanocoatings with NH3/O2 post treatment may be chemically stable for long-term properties, including shelf-life storage and exposure to the bloodstream for coronary stent applications.

Erratum: “Control of plasma properties in a short direct-current glow discharge with active boundaries” [Phys. Plasmas 23, 024501 (2016)

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Influence of reacting gas content on structural and electro-physical properties of nanostructured diamond films grown by chemical vapor deposition with crossed E/H field glow discharge stabilization

The method and setup for polycrystalline diamond films deposition from the gas-phase using the direct current (DC) glow discharge stabilized by crossed E/H field are presented. The mentioned method was used for the preparation of nanostructured diamond films. The nanostructure formation was realized by N2 addition to Ar/CH4/H2 plasma. The detailed study of electro-physical, morphological and structural properties was done using simple two-electrodes scheme of resistivity measurements, atomic force and scanning electron microscopies as well as Raman spectroscopy. The data of electro-physical measurements is in good correlation with the data of optical measurements and complement each other showing the complete picture of the processes of modification of the diamond films structure induced by nitrogen atoms incorporation.