Pressure Glow Research Articles

Effect of discharge time on the size control of AgNPs prepared by non-thermal atmospheric plasma discharge

In this work, well-controlled and high stability colloidal silver nanoparticles (AgNPs) were attained via atmospheric-pressure plasma glow discharge in AgNO3 aqueous solution by controlling the discharge time. DC glow discharge with (6 kV) applied voltage and (1.8 mA) discharge current for discharge time (5, 10 and 15 min) was carried out in home–made cell at room temperature to prepare specific sizes and form of (AgNPs). Atmospheric pressure plasma between stainless steel capillary tube cathode electrode above the (AgNO3) electrolyte solution and platinum disk as an anode immersed in an (AgNO3) electrolyte solution for fast generation of colloidal nanoparticles. Structural properties of Ag NPs layer were examined via studying of field emission scanning electron microscope (FE-SEM) and X-ray diffraction (XRD) pattern. Optical properties of (AgNPs) were characterized by a UV–Vis beam spectrophotometer. The obtained results showed that (AgNPs) were uniformly distributed on the silicon substrate. Grain size and specific surface area of AgNPs intensely be influenced by the discharge time.

Measurements of the Potential Profiles of Glow Discharges Using an Emissive Probe

Glow discharges are produced in air in a ~1-m-long glass vacuum tube under the pressure of 12-113 mtorr. We present the full potential profiles throughout the glow discharge regions characterized using a cold emissive probe with the current-bias method. Secondary electron emission from the probe likely determines the local plasma potential, which replaces the role of thermionic emission that fails in relatively high-pressure plasmas. The measured potential profiles show good agreement with the theoretical expectations. A large potential drop is measured in the cathode dark space followed by a potential plateau through the negative glow and Faraday dark space regions. Striations in the positive column are shown as stair-step-like multiple potential double layers with a potential step close to the ionization energy. This cold emissive probe method can be used for characterizing potentials in even higher pressure (>1 torr) glow discharges that are not yet well understood.

Formation and energy relaxation of a fast electron beam in cathode regions of a glow discharge in helium

Results of a three-dimensional direct statistical simulation of formation and energy relaxation of a group of high-energy electrons in cathode regions of the low pressure (p < 1 Torr) glow discharge in helium are given. It is demonstrated that the electron distribution function at the exit from the cathode sheath contains a group (beam) of high-energy electrons which did not suffer inelastic collisions and had energy close to the cathode fall potential. The beam is shown to be a main source of charged particle production in the negative glow region. The calculated electron energy distribution function is compared with experimental data.

LIF Imaging of OH radicals in Atmospheric DC Glow Discharge Using Miniature Gas Flow and Electrolyte Cathode

ABSTRACTIn this paper, we report the spatial distribution of OH radical density in atmospheric-pressure DC glow discharge using a miniature helium flow and an electrolyte cathode. Laser-induced fluorescence imaging was applied for the measurement of the OH radical density. The effect of collisional quenching was considered in obtaining the spatial distribution of the OH density. The spatial distribution of the OH radical density showed that the peak of the OH density was located at a separated distance from the electrolyte surface. However, the OH radicals kept contact with the electrolyte surface. It was suggested that the OH radicals were generated mainly in a region separated from the electrolyte surface and some fraction of the generated OH radicals reached to the liquid phase.

One-Dimensional Modeling on the Asymmetric Features of a Radio-Frequency Atmospheric Helium Glow Discharge Produced Using a Co-Axial-Type Plasma Generator

In this paper, a one-dimensional transient fluid model is used to investigate the asymmetric characteristics of the radio-frequency atmospheric-pressure helium glow discharges produced using a co-axial-type plasma generator. Based on the analysis of the particle and energy balance processes in the discharge region, the modeling results show that the asymmetric features of the time-averaged plasma parameters, e.g., the species number densities, electron energy and the electric field, become significant resulting from the increase in the discrepancy between the surface areas of the inner and outer electrodes. And the influence of the inner electrode radius on the asymmetric features of the discharges becomes more significant compared with the electrode gap spacing for the cases with smaller inner electrode radius. The calculated asymmetric features of the discharges are also validated by the experimental analysis on the discharge images using the visible image processing technique qualitatively.

Gliding Glow Discharge in Tornado

The gliding-arc-in-tornado discharge is an example of a “warm plasma” source and is an attractive tool for fuel conversion processes. This paper demonstrates that, at relatively low currents below 530 mA, this discharge is an atmospheric-pressure normal or abnormal glow discharge. This implies applicability of the glow discharge theory and experimental data for evaluation of plasma parameters in technological systems.

Gas barrier properties of carbon films synthesized by atmospheric pressure glow plasma

High gas barrier carbon films were successfully synthesized on top of polymer substrates using an atmospheric-pressure glow (APG) plasma CVD equipment by reducing the discharge area and by changing the size of the electrodes of the equipment. Homogeneous and highly stable plasma was constantly generated under an atmosphere of acetylene gas (C 2H 2) without using any other dilution gases such as He, Ar and N 2 that are generally used in order to stabilize the plasma. The absence of the dilution gases led to form rigid carbon-to-carbon bonds. The rigid C bonds constructed dense carbon films at the very surface of the coated films with high gas barrier properties. The oxygen transmission rates of the polyethylene terephthalate (PET) film coated with this amorphous carbon (a-C:H) material was therefore dramatically improved (23 times less in transmission rate) compared with that of an uncoated PET film. The microstructures of the films were investigated by Fourier transform infrared spectroscopy (FT-IR) and the surface morphology was observed by a scanning electron microscope (SEM).

Properties of Amorphous Carbon Films Synthesized by Atmospheric Pressure Glow Plasma CVD Method

Amorphous carbon films were synthesized on top of polyethylene terephthalate (PET) substrates using atmospheric-pressure glow (APG) plasma CVD equipment which we originally designed and set up. Plasma was generated between two metal electrodes one of which was covered with a dielectric plate. By varying dielectric constant of the plate, the deposition rate of the carbon films was controlled. From the oxygen transmission test, the resulting PET coated with thin carbon films exhibited high gas barrier property. Using the material with high dielectric constant, we finally synthesized a nearly complete gas barrier films at the deposition rate of 15 sec.

Two-dimensional numerical study of atmospheric pressure glows in helium with impurities

A two-dimensional numerical model of an atmospheric pressure glow (APG) discharge was developed. The simulation of the APG in helium with some nitrogen impurities successfully reproduced the discharge evolution during the breakdown process observed in experiments. The results show that the breakdown first appears at the central region of the discharge followed by the axial and radial propagation of the ionization wave. The space charge induced electric field is the main reason for the radial propagation. Penning ionization is the dominant ionization mechanism in the discharge. It leads to an elevated pre-ionization level before the discharge pulse that is essential for maintaining a uniform discharge. Increasing the driving frequency favours a transition from a filamentary to a uniform glow discharge. An increasing number of filaments with driving frequency are observed. The coalescence of the filaments at sufficiently high frequency leads to a uniform discharge. Decreasing the dielectric permittivity of the barriers limits the discharge current and leads to a shift of the discharge towards a uniform Townsend discharge.

Pulse-modulated, high-frequency plasma sterilization at atmospheric-pressure

We studied atmospheric-pressure glow (APG) plasma excited with pulse-modulated RF at 27.12 MHz, using dielectric barrier electrodes. The antibacterial effect of APG plasma was examined using spore-forming bacteria: Bacillus atrophaeus, Geobacillus stearothermophilus, and the following selected species of bacteria, a mold, and yeast-like fungus: Salmonella enteritidis, Staphylococcus aureus, Candida albicans, and Aspergillus niger. Optimum experimental conditions were sought, to find commonality among several conditions: antibacterial effect, neutral gas temperature, and homogeneity over the electrode surface.

Atmospheric pressure glow discharge initiation from a single electron avalanche

Atmospheric pressure glow (APG) discharges are attractive for many applications due to their transversely homogeneous plasma properties. The discharge initiation mechanism for the APG is so far not well understood. Based on a two-dimensional fluid model the discharge initiation process is studied starting from a single initial electron avalanche. Images of the APG development at different phases during the discharge initiation are presented.

Development of a Plasma Source Using Atmospheric-Pressure Glow Discharge in Contact with Solution

A novel plasma source of atmospheric-pressure glow (APG) discharge in contact with solution is developed. Liquid paraffi n consisting of hydrocarbons is used as solution for the purpose of the formation of carbon nanotubes at the gas-liquid interface, i.e., the boundary between glow discharge (gas-phase) and solution (liquid-phase) layers. We have succeeded in generating a stable APG discharge plasma in contact with liquid paraffi n by using a capacitively coupled plasma method with mesh electrode.

Evolution of the radial structure of a negative corona during its transformation into a glow discharge and a spark

With the proper stabilization of a negative corona, it is possible to increase the threshold current at which the corona discharge in the point-plane gap in air transforms into a spark. Then, in the current range corresponding to the transition region between the corona discharge and the spark, a new type of discharge arises—an atmospheric-pressure diffuse glow discharge. The transformation of the negative corona into a glow discharge and then into a spark is accompanied by the rearrangement of the discharge structure. The experiments show that, as the corona current increases, the radial current profile at the anode shrinks and the glow diameter near the anode increases. The radial profiles of the current and the corona glow during the transition to a glow discharge are measured. The longitudinal structure of the corona is computed using a 1.5-dimensional model that, unlike the other available models, includes gas ionization in the drift region of the corona. The experimental data are used to determine the effective cross section of the current channel at the anode. The radial glow profile near the anode is calculated using the measured current profile and assuming that the field profile is parabolic.

Development of powder antifoamer by atmospheric pressure glow plasma

Atmospheric pressure glow (APG) plasma treatment does not require a vacuum pump that is equipped with a low pressure plasma device. With treatment for organic powder, APG plasma can modify the surface roughness and wettability. In this study, we treated polystyrene films and powder by APG plasma, surveyed the changes of surface morphology, and examined the antifoaming effects of powders. A high exposure time (for this study, 20 min) in He+CF 4 plasma, polystyrene powders were introduced onto approximately 55% of fluorine atoms. This powder gave a better result for antifoaming properties.

Adhesive Strength Study and Surface Analysis Using Gas-Phase Chemical Reactions of Atmospheric Pressure Plasma-treated Polypropylene

Adhesive strength of Atmospheric Pressure Glow (APG) plasma-treated polypropylene was studied for various gas mixtures by a scratching test. An explanation of the high adhesive strength obtained after He/N2 APG plasma treatment was given. Formation of carbonyl, alcohol, carboxylic and primary amines was investigated by gas-phase chemical reaction. Their evolution during the ageing of the treated samples was followed. Most changes take place during the first few hours of contact with the atmospheric medium. Contact angle measurements on APG plasma-treated PP were done. These results were compared with PP treated by Silent Electric Discharge (SED). The ageing of the wettability properties of the surface after APG plasmas is better than after SED discharge.

Spatial and Temporal Profiles of Indium in a Furnace Atomization Plasma Excitation Spectrometry Source

Spatially resolved emission and absorption intensities from the indium 303.94-nm resonance line were measured in a furnace atomization plasma excitation spectrometry (FAPES) source. These measurements show that the spatial structure observed in the analyte emission is due to two effects. The first is the spatial distribution of analyte atoms in the source. The absorption measurements show that this spatial distribution is fairly uniform. There is a slight gradient, with analyte concentrations increasing from the cuvette wall to the center electrode. The fine structure in the emission intensity profiles must therefore be caused by the dependence of the degree of analyte excitation on position within the cuvette. This structure suggests that the FAPES source operates as an atmospheric-pressure radio-frequency glow discharge. Negative glows are seen adjacent to the graphite cuvette wall and center electrode.

Subject Index of Volume 90

This paper presents a method of novel plasma treatment for fine particles by the atmospheric-pressure glow (APG) discharge, in which particles were circulated and repeatedly plasma-treated at atmospheric pressure. Using this method, plasma-polymerized tetrafluoroethylene (TFE) film formations on the porous granulated silica particles of 152 μm mean diameter were investigated. The XPS C(1s) spectrum of the treated surfaces deconvoluted into five peaks, which indicates that the films on the particles were composed of highly branched and crosslinked fluoro-carbon segments. The film-coated particles were very hydrophobic. Sound absorption measurements showed that the film-coated particles had a larger elastic coefficient than that of the untreated particles, indicating that dense films were coated on the porous silica particles.

Plasma-polymerized tetrafluoroethylene coatings on silica particles by atmospheric-pressure glow discharge

This paper presents a method of novel plasma treatment for fine particles by the atmospheric-pressure glow (APG) discharge, in which particles were circulated and repeatedly plasma-treated at atmospheric pressure. Using this method, plasma-polymerized tetrafluoroethylene (TFE) film formations on the porous granulated silica particles of 152 μm mean diameter were investigated. The XPS C(1s) spectrum of the treated surfaces deconvoluted into five peaks, which indicates that the films on the particles were composed of highly branched and crosslinked fluoro-carbon segments. The film-coated particles were very hydrophobic. Sound absorption measurements showed that the film-coated particles had a larger elastic coefficient than that of the untreated particles, indicating that dense films were coated on the porous silica particles.

Photoresist Ashing by Atmospheric Pressure Glow Plasma.

We investigated the mechanism and application of photoresist ashing by means of atmospheric pressure glow (APG) plasma. APG plasma using a mixture gas of He and O2 could ash the photoresist with a rate of about 1μm•min-1, which was roughly the same value as that of O2 plasma ashing at a low pressure. The dependences of etch-rate on O2 gas flow rate, discharge power and substrate temperature suggested that the APG plasma ashing process was mainly the oxidation of the photoresist by oxygen radicals. The XPS and optical emission spectroscopy suggested that excited helium promoted the desorption of oxides on the surface of the photoresist. To reduce cost, we tried to use Ar, acetone (Ac) and O2 mixture gas instead of He and O2 mixture gas. Ar/Ac/O2 plasma could etch the photoresist as fast as He /O2 plasma, although the O2 content was one sixth of that of He/O2 plasma. Minute area ashing using a pray type discharge tube was also investigated. Its ashing rate was the fastest, about 4.0μm•min-1, when Ar/O2 mixture gas was used.

The reduction of copper oxide thin films with hydrogen plasma generated by an atmospheric-pressure glow discharge

The reduction of copper oxide thin films by a hydrogen plasma generated by an atmospheric-pressure glow (APG) discharge was investigated. The copper oxide films were prepared by heating the sputtered copper films to C in the air (heat-formed copper oxide) or by sputtering (sputtered copper oxide). Both films were composed of . The reduction occurs first on the surface, then the interface gradually shifts from the surface into the inner region and finally the whole layer is reduced to metallic copper. This process is approximately explained by assuming that the diffusion of the atomic hydrogen in the reduced layer is the rate-deyermining step. By transmission electron microscopic (TEM) observation, a layer of 3 - 5 nm thickness composed of many microcrystals was observed along the surface of the heat-formed copper oxide. After the APG hydrogen plasma treatment, the crystal layer disappeared and the crystalline lattice was re-arranged to form large crystal Cu grains.