Oxygen Glow Discharge Research Articles

Negative Ions, Ozone, and Metastable Components in dc Oxygen Glow Discharge

AbstractIn a dc glow discharge in oxygen, the concentrations of minor components of O2(a1Δg), O2(b1 Σg), O3, O(1D), as well as nagative ions and electrons have been measured. Balance equations have been derived which describe satisfactorily the stationary concentrations of these components as functions of gas pressure and discharge current. For the first time, the rate constants of important aeronomical reactions (a) O− + O2(a1Δg) → O3 + e, (b) O2− + O2(a1Δg) → 2O2 + e and (c) e + O3 → O2− +O have been measured as functions of gas temperature T and mean energies of ions Ei and electron E6: Ka = (2.5 ± 0.5) · 10−9 · (T/300)4 ± 0.4· (Ei/0.04)−2.6 ± 0.4 cm3/s for T = 385−605 K and Ei = 0.10 − 0.66 eV; Kb = (1.0 ± 0.3) · 10−10 · (T/300)−2 ± 0.5 · (Ei/0.04)0.23 ± 0.05 cm3/s for T = 330−605 K and Ei = 0.09 + 1.5 eV; Kc for Ee = 0.8÷5 eV.

Effect of plasma surface modification on electrical conduction in polyethylene

AbstractHigh‐density polyethylene films 50 μm thick were exposed to the downstream plasma flow of RF glow discharges in argon, hydrogen, or oxygen. It was found that many transvinylene and unreacted radicals remain after the argon or hydrogen plasma treatment, and that carbonyl groups are formed in the oxygen plasma treatment.The conduction current was smaller in the hydrogen‐plasma treated samples and the samples exposed to oxygen or ozone after hydrogen‐plasma treatment than in the untreated samples. Thermal pulse current measurements indicate that the treated surface layer traps electrons or holes and reduces the field strength at the electrode surface, thus suppressing further injection of electrons or holes.

Theoretical and experimental characterization of positive-column plasmas in oxygen glow discharge

Combined theoretical and experimental studies have been accomplished in order to elucidate the features of positive columns in oxygen glow discharges. The Langmuir probe technique was utilized to measure the plasma parameters such as electron temperature and electric field. A tandem mass spectrometer was used to measure relative concentrations of charged particles. These experimental results were found to be in good agreement with the present theoretical calculations based on a slightly ionized stationary plasma model.

Kinetic model of a DC oxygen glow discharge

A simple kinetic model predicting the concentration of oxygen atoms, metastable singlet molecules O2(a1Δ) and negative ions O — in the positive column of a DC glow discharge is developed. The calculated O and O2(a1Δ) concentrations are compared to previously reported measurements for pressuresp=0.2–2 Torr and discharge currentsI=10–80 mA. The electron density calculated from the continuity equationj=nee vd agrees well with experiment. The rate coefficients for electron impact processes used in the balance equations of O, O2(a1Δ), and O− were taken from the literature as a function of the reduced electric fieldE/N forE/N=40–80 Td. A reasonable agreement is obtained between the model and the experiment with a set of 10 reactions for the production and destruction of the above-mentioned species

Glow-discharge removal of codeposited carbon films in graphite-lined tokamak reactors

In a graphite-lined tokamak reactor, the interaction of the plasma with the graphite first wall will result in the formation of carbon deposits that are highly rich in tritium. This mechanism of tritium retention will be a major contributor to the in-vessel tritium inventory. In this paper, the glow-discharge technique is proposed for removing these films to reduce the inventory buildup. Glow-discharge runs were performed with feed gases of H2, He, N2, and O2. The results show that only oxygen glow discharges can remove carbon films at sufficiently large rates. The impact of this study on the Tokamak Fusion Test Reactor (TFTR) and the Compact Ignition Tokamak (CIT) is discussed. A recipe for effective glow-discharge operation on TFTR and CIT is also described.

Improvement of average film quality in RBa/sub 2/Cu/sub 3/O/sub 7-x/ sputtered films

Thin films of RBa/sub 2/Cu/sub 3/O/sub 7-x/ (R includes Y, Er, and Nd) have been deposited by four-gun DC magnetron sputtering from metallic targets in a Xe-O/sub 2/ gas mixture and postannealed in flowing O/sub 2/. Extensive optimization of the film deposition process has been achieved for erbium-based films which can be produced with good characteristics on a variety of substrates. Fine-grained polycrystalline films with sharp resistive transitions are produced on single-crystal and polycrystalline YSZ, MgO, ZrO/sub 2/-buffered sapphire, and silver-buffered sapphire. Broader transitions are observed on buffered silicon wafers. These erbium films often show grain sizes as small as 20-30 nm and, with the addition of an RF oxygen glow discharge in the deposition system, are quite smooth despite furnace postannealing. Highly-oriented 1-2-3 film growth is observed on SrTiO/sub 3/ and LaAlO/sub 3/ single-crystal substrates. Four-point resistivity measurements show transitions as narrow as 1 K, while magnetization and RF frequency-shift measurements show more detail about film quality. Films are characterized by XRD, SNMS, Auger, XPS, and cross-sectional EDX profiling. The authors also report on the use of in-situ deposition of silver as a passivation layer for the 1-2-3 surface.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The surface analysis of a plasma modified contact lens surface by SSIMS

AbstractThe oxygen glow discharge plasma modification of a contact lens material has been studied using SSIMS. SSIMS provides evidence at the molecular level for the conversion of surface organosiloxane species to inorganic silica functionalities with treatment time. These findings shown an excellent correlation with a dramatic increase in surface hydrophilicity, as derived from surface energy studies, on plasma treatment. This study further illustrates the potenial of SSIMS in the determination of the molecular changes at the surface during the plasma treatment process.

An XPS study of the KCl surface oxidation in oxygen glow discharge

The reaction between the surface of KCl and oxygen in a glow discharge has been studied by X-ray photoemission spectroscopy (XPS). Oxygen glow discharge treatment resulted in the formation of a superoxide, which decomposed under vacuum at room temperature to KO 2 and finally to K 2O. No evidence of KClO 3 or KClO 4 formation has been found. Binding energies of some oxygen species in potassium oxides were determined. The possible role of potassium in K-doped silver catalysts of ethylene epoxidation is discussed.

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(1Δ) 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.

Optical constants of reactively sputtered cupric oxide films

Thin films of cupric oxide are deposited by a rf sputtering method using only oxygen glow discharge and their optical properties are measured in the wavelength region of 0.5–0.8 μm. These films show a band gap of 1.21 ±0.05 eV and a dispersion curve similar to that for Cu 2O and in disagreement with the reported data. The dispersion of CuO can be expressed by an empirical formula of the type of n 2 = 1+4.59λ 2 (λ 2 −0.212) (λ in μm). In the wavelength region quoted above, CuO films show large absorption coefficients, greater than 10 4 cm −1.

A potential fall produced by a space-charge dipole layer moving in an oxygen glow discharge

A potential fall created by a space-charge dipole layer that moves as a solitary wave with a velocity close to that of an electron in the positive column at higher pressure in oxygen is shown. Sometimes only one potential fall exists between electrodes. The number of the potential fall changes with discharge current, by which the hysteresis phenomenon is found. Since the width of a potential fall is much larger than the electron mean-free path, both ionization and attachment play an important role in the potential fall for the formation of a dipole layer. The shape of the small current change when a dipole layer arrives at an anode is examined, suggesting what is existent in a dipole layer. The nature of the self-excitation of a dipole layer in the positive column cannot be found. The reason why a dipole layer appears and how it is maintained in the positive column of the oxygen glow discharge are explained.

Glow-Discharge Cleaning in Oxygen of Carbon-Contaminated Optical Elements

Carbon-contaminated mirrors and gratings have been cleaned by a d.c. glow discharge in oxygen. The reflectance of mirrors and the efficiency of gratings were measured in situ before and after cleaning in the photon-energy range 4 ∼ 40 eV or 100 ∼ 1000 eV using reflectrometers which incorporated a discharge electrode. Angle-resolved scattering of mirrors and diffraction patterns of gratings were also measured. The mirror reflectance was restored to that of original mirror materials and the scattering level was reduced rather than increased by the discharge cleaning. The grating efficiency of the inside first order was drastically improved by cleaning, even by nearly an order of magnitude in some energy regions. Furthermore, the effect of a blaze was shown to be recovered by examining changes in the efficiencies of other orders as well.

Investigation of carbon contamination of synchrotron radiation mirrors

Carbon-contaminated synchrotron radiation mirrors have been successfully cleaned by a dc glow discharge in oxygen. Reflectance and angle-resolved scattering have been measured before and after cleaning. The effect of carbon contamination on reflectance is severe at near normal incidence whereas it is small at grazing incidence. The decrease in reflectance is most noticeable for photons with an energy below about 10 eV. In the discharge arrangement in which the mirror surface did not face an electrode, the reflectance of contaminated mirrors was nearly restored to that of uncontaminated mirrors and the scattering level was reduced. An additional discharge, in which the mirror surface faced the electrode, degraded the reflectance but produced no appreciable change in the scattering level.

Confined oxygen glow discharge cleaning of silicon

The reproducibility of the thickness of SiO2 films deposited on Si or Al surfaces is strongly affected by substrate cleanliness. Consistent correlation between film–substrate and film–quartz crystal data is not obtained when using wet chemical cleaning methods. Auger depth profiling has been used to characterize silicon dioxide films on silicon cleaned by a confined oxygen glow discharge in a commercial electron beam evaporator. Model studies were performed by x‐ray photoelectron spectroscopy of in situ cleaning. Oxygen discharge cleaning is shown to be effective in removing carbonaceous material without damaging the silicon surface and without measurably increasing the silicon native‐oxide thickness.

Electron tunneling into Bi thin films under pressure

We have studied the pressure dependence of the tunneling resistance of tunnel junctions between 300-nm-thick Bi films and 20-nm-thick films of Al deposited at room temperature. Native Al oxide formed by oxygen glow discharge provided the tunnel barrier. The resistance was measured as a function of voltage from 0 to about 1 V. Measurements were made from room temperature to below the superconducting transition temperature of the Al film. The pressure range covered was from 0 to about 8 kbar. The resistance decreases with increasing pressure in a way easily described by simple tunneling theory. In the resistance curves we observe pressure dependence of structure, which has in the past been associated with the pressure dependence of the Bi band structure.

Plasma-induced oxidation of Ag(110)

The exposure of a clean Ag(110) surface to a glow discharge oxygen plasma has been found to induce considerable surface oxidation which otherwise cannot be achieved under the same pressure/temperature conditions. As a result of such treatment several states of oxygen appear to be adsorbed/absorbed onto the crystal, which have been characterised primarily by thermal desorption. Interestingly, the main desorption occurs at 570 K indicating that desorption from bulk oxide occurs at the same temperature as the surface chemisorbed layer. This result explains previous observations of exchange of surface oxygen with subsurface oxygen in desorption experiments.

Differences between the bonding of oxygen in glow discharge deposited a-Si:H and a-Ge:H

We have prepared a-Si:(H,O) and a-Ge:(H,O) films by the glow discharge technique and have studied the bonding of oxygen by IR absorption spectroscopy. We find qualitatively different behavior in these two alloy systems, which we relate to differences in plasma phase interactions in which precursor molecular groups are formed.

Study of O2 (1Δ) production in a glow discharge at large molar flow rates

O2 (1Δ) and O (3P) produced in the oxygen glow discharge at large molar flow rates (3–12 mmol/s) have been measured. Up to 1.1% of initial molecular oxygen is converted into singlet 1Δ oxygen, and 3.3% into atomic oxygen. Incidentally, a new emission band at 5885 Å, not previously reported, has been observed and ascribed to AuO.

Photodetachment as a Control Mechanism for Diffuse Discharge Switches

Photodetachment is considered as a control mechanism for diffuse discharge switches. Experiments have been performed on photodetachment of ions in the flowing afterglow of a dc glow discharge in oxygen. Experiments with different laser wavelengths and the dependence of the optogalvanic signal on the laser energy flux indicate that O- is the dominant negative ion. For an energy flux of 35 mJ/cm2, 50percent of the O- ions can be photodetached.

Effect of glow discharge treatment of substrates on parylene-substrate adhesion

A detailed investigation of the effect of argon, oxygen, and methane glow discharge (plasma) treatment of substrates on the adhesion characteristics of parylene polymer to a variety of substrates is reported. It is found that methane glow discharge treatment, which results in the deposition of a glow discharge polymer of methane on the substrate surface, is most effective in improving the bonding strength of the parylene polymer, while the oxygen glow discharge treatment which produces a hydrophilic substrate surface with no or insignificant polymer deposition is detrimental to parylene adhesion. The effect of argon glow discharge treatment may vary from true cleaning of the substrate surface to deposition of a thin layer of a polymeric coating produced by the simultaneous glow discharge polymerization of the ablated organic materials existing in the reactor and may or may not improve parylene adhesion. These results are supported by the Auger electron spectroscopy and contact angle measurements of the glow discharge-treated surfaces. Model studies using substrates of different surface free energies indicate that water-resistant adhesion of parylene polymer increases with the hydrophobicity of the substrate material and is in harmony with the above findings. From the viewpoint of adhesion the most advantageous and dependable effect is obtained with the methane plasma treatment. The treatment results not only in the formation of a more compatible, hydrophobic surface but also produces radical sites for covalent bonding with the parylene.