Dc Oxygen Glow Discharge Research Articles

Surface recombination in Pyrex in oxygen DC glow discharges: mesoscopic modelling and comparison with experiments

Surface recombination in an oxygen DC glow discharge in a Pyrex (borosilicate glass) tube is studied via mesoscopic modelling and comparison with measurements of recombination probability. A total of 106 experimental conditions are assessed, with discharge current varying between 10 and 40 mA, pressure values ranging between 0.75 and 10 Torr, and fixed outer wall temperatures ( Tw ) of −20, 5, 25 and 50∘C . The model includes O+O and O+O2 surface recombination reactions and a Tw dependent desorption frequency. The model is validated for all the 106 studied conditions and intends to have predictive capabilities. The analysis of the simulation results highlights that for Tw=−20∘C and Tw=5∘C the dominant recombination mechanisms involve physisorbed oxygen atoms ( OF ) in Langmuir–Hinshelwood (L-H) recombination OF+OF and in Eley–Rideal (E-R) recombination O2+OF , while for Tw=25∘C and Tw=50∘C processes involving chemisorbed oxygen atoms ( OS ) in E-R O+OS and L-H OF+OS also play a relevant role. A discussion is taken on the relevant recombination mechanisms and on ozone wall production, with relevance for higher pressure regimes.

Response of the modified GAFCHROMIC EBT2 radiochromic film to DC glow discharge plasma

The response of the modified GAFCHROMIC EBT2 radiochromic film to DC Oxygen glow discharge plasma was investigated using a flatbed scanner and an UV–Vis spectrophotometer. The film was modified by removing the polyester overlaminate, adhesive, and topcoat layers with a total thickness of 80 µm, and is now referred to as EBT2-M. The EBT2-M films were exposed to DC Oxygen plasma for different durations: 0, 0.5, 1, 2, 3, 4, 7, and 10 min. The exposed films exhibit coloration homogeneity with an average variation of (1.6 ± 0.3) × 10−4 pixel values/µm, irrespective of the applied exposure time. The pixel values of the red-and-green channels and weighted grayscale images decreased exponentially with different sensitivity amounts to ∼\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sim$$\\end{document} 39.67, 49.69, and 42.11 min−1, respectively, as the exposure time increased. The two absorption peaks at 580 ± 4 nm and 632 ± 4 nm in the UV–Vis absorption spectra of the exposed GAFCHROMIC EBT2-M radiochromic films are increasing with increasing exposure time up to 4 min, thereafter saturated for prolonged exposure time. The integrated absorbance in the range from 400 to 700 nm is linearly correlated with the exposure time. The indirect and direct optical energy band gaps and Urbach energy of the modified GAFCHROMIC EBT2 film are weakly correlated with the exposure time. These findings suggest the utilization of the modified GAFCHROMIC EBT2 radiochromic film as a novel and simple technique for plasma diagnostics.

Characterization of Gold Oxides Prepared by an Oxygen-dc Glow Discharge from Gold Films Using a Gold Discharge Ring by X-ray Photoelectron Spectroscopy.

Gold oxides (0.1 - 2.0 nm thick) prepared from gold films by an oxygen-dc glow discharge using a gold discharge ring for 0.17 - 30 min at room temperature were characterized by X-ray photoelectron spectroscopy. The oxide thickness increased with increasing discharge time in contrast to the use of an aluminum ring, and thicker oxide films were obtained. The O 1s spectra show four components: I, II, III, and IV. Components I, II, and IV appear during the early formation periods (≤0.5 min). Components I and II are stable and assigned to hydroxyl groups on the surfaces. Component IV changes into component III (gold oxide) after longer discharge times (≥1 min). The gold oxides (2.0 nm thick) decompose after 15 d at room temperature and decompose immediately at temperatures exceeding 117°C. They also decompose under ultraviolet light irradiation (254, 302, and 365 nm) and decompose more rapidly in water vapor at the shorter wavelengths. The thicker nature of the gold oxides is advantageous for their preservation, and they were preserved in their oxidized state for 196 d in anhydrous dodecane in a dark atmosphere.

Reaction Monitoring of Gold Oxides Prepared by an Oxygen-dc Glow Discharge from Gold Films in Various Aqueous Solutions by a Surface Plasmon Resonance-based Optical Waveguide Sensing System and X-ray Photoelectron Spectroscopy.

The chemical properties of thin (∼0.6 nm) gold oxide layers prepared by an oxygen-dc glow discharge from gold films at room temperature in various solvents and solutions were studied using a surface plasmon resonance (SPR)-based optical waveguide sensing system and X-ray photoelectron spectroscopy (XPS). New insights into the stability and reactivity of gold oxides under these conditions were obtained. The O 1s XPS spectra show three oxygen species, comprising components I, II, and III in the gold oxides, and components I and II are present in this order from the top surface of the oxide (component III). The gold oxide is stable in various solvents (water, methanol, ethanol, acetone, acetonitrile, diethyl ether, chloroform, hydrocarbons) for 10 - 30 min at room temperature. The gold oxide decomposes in aqueous 10-2 M solutions of acetaldehyde, hydrochloric acid, and sodium hydroxide during these periods. Gold oxide decomposition in these solutions was monitored by SPR and the decomposition rates were obtained. Decomposition of the gold oxides was confirmed and their surfaces were characterized after decomposition by XPS.

Characterization and preservation of gold oxides prepared by an oxygen-dc glow discharge from gold films and studied by X-ray photoelectron spectroscopy

Gold oxides with thicknesses of less than 1 nm that were prepared by an oxygen-dc glow discharge over various periods (0.5–10 min) from gold films at room temperature were characterized by X-ray photoelectron spectroscopy (XPS), and a preservation method was developed for these oxides. The O 1s spectra show three oxygen species comprising components I, II, and III in the gold oxides. Components I and II are both stable and assigned to hydroxyl groups. The angular dependence of the XPS spectra of the gold oxides indicates that the oxygen species of components I and II are present in this order from the top surface of the gold oxide (component III). The gold oxides decompose after 36 h at room temperature and decompose immediately at temperatures exceeding 121 °C in a dark atmosphere. These gold oxides also decompose under ultraviolet (UV) light irradiation (254, 302, and 365 nm) at room temperature and decompose more rapidly in water vapor at the shorter wavelengths. These findings indicate that the gold oxide decomposition is accelerated via a reaction with excited water molecules produced by UV light absorption. The gold oxide decomposes after 6 h in water but decomposes more slowly in hydrocarbons (hexane, octane, and dodecane) at room temperature in a dark atmosphere. The gold oxide can be preserved in the oxidized state for 84 days in anhydrous dodecane. This simple preservation method of a gold oxide immersed in a hydrocarbon with low water content will be helpful for practical use in future applications.

Formation and decomposition of gold oxides prepared by an oxygen-dc glow discharge from gold films and studied by X-ray photoelectron spectroscopy

Formation and decomposition of thin (<1 nm) gold oxides prepared by an oxygen-dc glow discharge from gold films were studied by X-ray photoelectron spectroscopy (XPS). Four oxygen species comprising O 1s components Ⅰ, Ⅱ, Ⅲ, and Ⅳ are present in the XPS spectra. Component Ⅳ appears in the early formation periods and then changes into the oxide component Ⅲ. Components Ⅰ and Ⅱ are both stable at high temperatures and assigned to hydroxyl groups. The angular dependence of the XPS spectra of the gold oxides indicates that the oxygen species of components Ⅰ and Ⅱ are present in this order from the top surface of the gold oxide (component Ⅲ). The gold oxides decompose after 36 h at room temperature and decompose immediately at temperatures exceeding 121 °C in a dark atmosphere. The oxides also decompose under ultraviolet (UV) light irradiation at 254, 302, and 365 nm and decompose more rapidly at the shorter wavelengths. The decomposition of the gold oxides under UV light irradiation is slower in a high vacuum but is faster in a water vapor atmosphere. The decomposition caused by UV light irradiation and its wavelength dependence indicate reaction of the gold oxides with excited water molecules produced by UV light absorption.

Improved Surface Properties of Copper/PolyMethylMethacrylate nanocomposite films using DC O2 Plasma

Films of Polymethylmethacrylate with copper nanofiller were prepared and treated with low temperature oxygen DC glow discharge plasma. FTIR spectroscopy, AFM, water contact angle (WCA) measurements and UV-Vis spectroscopy were used to detect the produced chemical, morphological and optical changes as a function of plasma treatment time. The FTIR spectra, showed a decreasing value of the main characterizing signals of the composite films in addition to the creation of an oxygen containing functional group. The surface morphology of the treated samples was altered according to the increased values of the average surface roughness, obtained from the AFM images. The WCA also, decreased noticeably with increasing treatment time. The UV-Vis spectroscopic analysis showed a decreasing value of the optical absorption in the wave length range 190-270 nm which is an indication to the loss of carbonyl group. The value direct and inddirect optical band gap decreased with treatment time meanwhile, values of the band tail width were significantly increased.

Fluid model of H‐form of the positive column in DC oxygen glow discharge

In our contribution, the positive column of oxygen DC glow discharge is investigated using methods of computational physics at medium pressures (200–687 Pa) and discharge currents from 20 to 40 mA. Under mentioned conditions, the attributes of the DC oxygen discharge are particular, what is based on the existence of two forms: H‐form and T‐form. One‐dimensional fluid model of the stable H‐form has been developed. Not only radial profiles of various species in cylindrical tube but also the reaction among them and their interaction with the walls are taken into account. The model is built on the continuous description of concentration of species and drift‐diffusion approximation of the particle flux. The results of the simulation are in good agreement with experimental ones.

Influence of the surface morphology of aluminum foil on the probability of heterogeneous recombination of О(3Р) atoms in oxygen plasma

The process of recombining oxygen atoms on the surface of an aluminum foil and thin film is investigated in the positive column of the DC glow discharge in oxygen at a gas pressure of 200 Pa, a discharge current of 50 mA, and surface temperatures of 350–530 K. It is shown that an increase in the average surface roughness leads to a decrease of the probability of the heterogeneous recombination of O(3P) atoms. The values of the apparent activation energy for the process of heterogenic recombination of oxygen atoms are calculated.

Study on structural, morphological and thermal properties of surface modified polyvinylchloride (PVC) film under air, argon and oxygen discharge plasma

The effect of air, argon, oxygen DC glow discharge plasma on the polyvinylchloride (PVC) film synthesized by solution casting technique, were evaluated via changes in physio-chemical properties such as structural, morphological, crystalline, thermal properties. The PVC film was plasma treated as a function of exposure time and different plasma forming gases, while other operating parameters such as power and pressure remained constant at 100 W and 2 Pa respectively. The plasma treated PVC were characterized by static contact angle, ATR-FTIR, XPS, AFM and T-peel analysis. It was found that various gaseous plasma treatments have improved the polar components, surface roughness on the surface of PVC which was confirmed by XPS, AFM, resulting in highly enhanced wettability and adhesion. X-ray diffraction study showed that plasma treatment does not persuade considerable change, even though it vaguely induces the crystallinity. The thermal properties of plasma treated PVC were evaluated by Differential Scanning Calorimetry and it was observed that O2 plasma treatment gives higher glass transition temperature of 87.21 °C compared with the untreated one. The glass transition temperature slightly increased for Oxygen plasma treated material due to the presence of higher concentration of the polar functional groups on the PVC surface due to strong intramolecular bonding.

Synthesis of zinc oxide films in glow discharge of various configurations

The structure of zinc oxide (ZnO) films deposited on silicon substrates using dc glow discharge in oxygen have been studied for two electrode configurations—with tubular (hollow) and planar cathodes. At a substrate temperature of 670 K and oxygen pressure of 0.5 Torr, ZnO films synthesized in the hollow cathode geometry possess a columnar structure, while those obtained in the planar geometry are continuous. A decrease in the oxygen pressure from 0.5 to 0.2 Torr in discharge with the hollow cathode geometry leads to a change from a columnar to continuous film structure, while the morphology of films obtained in the planar geometry remains unchanged. The synthesized films exhibit a high degree of crystallographic orientation [001]ZnO ‖ [001]Si with complete azimuthal disorientation in the plane of film conjugation with the substrate.

Study of plasma–solid interaction in electronegative gas mixtures at higher pressures

Surface treatment at higher pressures has become an important issue of plasma science and technology. The analysis of processes in such plasmas is now often based on computer modelling; however, the main problem of simulation in medium and higher pressures is the increasing number of collisions among plasma particles and because of this, decreasing efficiency of simulations. A combination of experimental and computational approaches was used for the study of this problem in the present work. The measurements were performed in the positive column of a DC glow discharge in oxygen, both pure and in mixtures with rare gases, at medium pressures. These experiments were completed by computer simulations, where an attempt was made to extend the particle simulation technique to higher pressures. It was shown that the standard Particle-In-Cell/Monte Carlo simulation technique loses its applicability at higher pressures and must be replaced by more sophisticated computational methods. In the present work new algorithms for particle treatment in plasma at higher pressures were suggested and successfully tested.

Study of rotational temperature of oxygen DC glow discharge in Silica and Pyrex discharge tubes

Active DC glow discharges in oxygen have been studied in Silica and Pyrex discharge tubes for medium pressures up to 550 Pa and for discharge currents up to 40 mA. Electric field strength measured by a double-probe technique was found to increase with the pressure and to decrease with the discharge current, which is typical for DC glow discharges. We have focused on the emitted radiation. The rotational temperature ( T rot) of molecular oxygen was determined from the PP and PQ branches of the well-resolved atmospheric A-band of molecular oxygen at 760 nm. Good agreement between values of T rot obtained from particular branches was found. The increase of the rotational temperature with increasing pressure and discharge current has been observed in both discharge tubes, however, the values of rotational temperature were systematically higher in the tube made of Pyrex glass. This difference was explained by the particular thermal conductivity of the tube material.

Adsorption State and Morphology of Anthraquinone-2-carboxylic Acid Deposited from Solution onto the Atomically-Smooth Native Oxide Surface of Al(111) Films Studied by Infrared Reflection Absorption Spectroscopy, X-ray Photoelectron Spectroscopy, and Atomic Force Microscopy

The adsorption state and morphology of anthraquinone-2-carboxylic acid (AQ-2-COOH) deposited from acetone solutions (0.02 - 1.00 mg ml(-1)) onto atomically-smooth native oxide surfaces of Al(111) films were investigated by infrared reflection absorption spectroscopy, X-ray photoelectron spectroscopy, and atomic force microscopy. The atomically-smooth oxide surfaces were prepared by vacuum evaporation of Al on mica substrates at 350 degrees C, followed by oxidation in an oxygen-dc glow discharge at room temperature. It was found that AQ-2-COOH is adsorbed on the film surfaces in both the neutral and ionized state, where the amount of the neutral molecules increases with increasing concentration. This molecule is adsorbed as both a uniform nanometer-scale film, and as micrometer-sized particles with heights ranging from 10 to 200 nm above the film surface. The volumes of the particles of deposited AQ-2-COOH increased with increasing concentration. It is concluded that the particles are microcrystallites of neutral AQ-2-COOH and that the thin uniform film results from AQ-2-COOH anion formation on the film surfaces. A comparison of the results obtained by use of these surface analytical techniques clearly shows the features and advantages of these tools.

Adsorption and deposition of anthraquinone-2-carboxylic acid on alumina studied by inelastic electron tunneling spectroscopy, infrared reflection absorption spectroscopy, X-ray photoelectron spectroscopy, and atomic force microscopy

The adsorption state of anthraquinone-2-carboxylic acid (AQ-2-COOH) deposited from acetone solutions (0.01–1.00 mg/ml) on native oxide surfaces of Al films was characterized by inelastic electron tunneling spectroscopy, infrared reflection absorption spectroscopy, and X-ray photoelectron spectroscopy. The oxide was prepared on evaporated Al films at room temperature in an oxygen-dc glow discharge. The morphology of the deposited AQ-2-COOH on the oxide surfaces was observed and analyzed by atomic force microscopy. These surface analyses showed that AQ-2-COOH is adsorbed predominantly as a uniform nanometer-scale film of carboxylate anions on the oxide surfaces deposited from solutions with concentrations lower than or equal to 0.02 mg/ml. It was found that AQ-2-COOH is adsorbed as both a uniform film of anions and as micron-sized particles of neutral molecules with heights of a few tens of nanometers when AQ-2-COOH is deposited from solutions with concentrations higher than 0.02 mg/ml. A comparison of the results obtained by these surface analytical techniques clearly shows the features and advantages of these analytical techniques.

Negative ion destruction by O(3P) atoms and O2(a 1Δg) molecules in an oxygen plasma

Laser photodetachment was used to investigate the dynamics of negative ion density in the positive column of a pure oxygen dc glow discharge over a range of pressure (0.1–5 Torr) and current density (2–40 mA cm−2). Upon discharge current modulation, the negative ion O− concentration decayed with the characteristic loss times of oxygen O(3P) atom and metastable oxygen O2(a 1Δg) molecule concentrations over a wide range of discharge parameters. To determine the rate constants of negative ion loss by reaction with these species, the dynamics of O(3P) atoms and O2(a 1Δg) molecules was investigated using time-resolved actinometry and IR spectroscopy at 1.27 µm, respectively. At pressures greater than ∼0.5 Torr the attachment–detachment dominated regime of the oxygen discharge was realized and the main negative ion was O−. Under these conditions, electron attachment to O2 molecules to produce O− was compensated by detachment of O− with O(3P) and O2(a 1Δg). The rate constants of O− detachment with O(3P) atoms ) and singlet O2(a 1Δg) molecules ), were determined in the plasma itself for the first time.

Spectroscopic determination of oxygen DC glow-discharge temperature: Radial profile of gas temperature

Rotational temperature in the oxygen DC glow discharge is determined from atmospheric A-band of molecular oxygen. Two methods of estimation of this parameter taking into account the quality of the detected spectra are analysed and compared. Radial profile of the rotational temperature is measured. No radial variations of rotational temperature have been observed in the positive column under our experimental conditions.

A study of reactions in DC glow discharge in oxygen

A newly developed, low cost plasma system that works at atmospheric pressure and operates with both DC or AC high voltage power supplies was presented. This system was tested for its biocidal effect on a wide range of micro-organisms in water. Optimal killing parameters such as time, temperature and AC and DC high voltage power levels were tested for bacteria (Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, Streptococcus mutans, Bacillus subtilis), yeast (Candida albicans), fungi (Aspergillus niger) and green algae. Results show this system to have a very efficient biocidal effect on most bacteria, algae and fungi in water.

Energy spectra of heavy particles bombarding the cathode surface in a dc glow discharge and its effects on low energy implantation

Radio frequency glow discharges are employed in surface processing where low energy and low damage conditions are required. Direct current glow discharges are to be preferred, however, for more rapid sputtering and deposition. In order to be able to design glow discharge cells, it is essential to understand energy spectra of ions and neutrals created and accelerated in the discharge and their effects on the parameters associated with particles incident on the bombarded cathode. This paper reviews the important models which may be employed in the determination of energy/angle spectra, describes how energy spectra from these models may be employed in the prediction of implantation characteristics in cathode targets and compares experimental and theoretical results for a polycrystalline copper surface in a dc oxygen glow discharge.

Characterization of ultrathin sputtered SiO films on alumina by inelastic electron tunneling spectroscopy and atomic force microscopy

Amorphous SiO films are prepared by radio-frequency planar magnetron sputtering in a background of argon. Inelastic electron tunneling spectra are presented of the films incorporated in Al/SiO/Pb tunnel junctions with the aluminium films pre- or post-oxidized relative to the SiO deposition stage. Both the aluminium and lead junction electrodes are evaporated in a standard oil diffusion pumped, liquid nitrogen trapped vacuum system at a base pressure of 10−7 Torr; aluminium oxidation is achieved either by admitting oxygen into the vacuum chamber or by performing a low power dc oxygen glow discharge. Spectra obtained are similar, but not identical, to those obtained for evaporated SiO films. Different types of silicon hydride species are observed depending on the environment to which the SiO films are exposed after their deposition. Possible reactions of the films with water vapor are discussed which could produce the observed hydrides which are also assigned. Reverse bias tunneling spectra provide strong evidence that the SiH species reside on the SiO surface, and it is shown that they can be removed by exposure of the surface to a gaseous glow discharge. Atomic force microscopy images are presented of SiO films supported on aluminium and alumina which indicate that their topography is not noticeably modified by exposure to the glow discharge, and that they possess a relatively uniform quasi two-dimensional island structure.