Oxygen Glow Discharge Research Articles

Influence of oxygen and argon plasma treatments on the chemical structure and redox state of oxide covered iron

The paper reveals structural changes of the iron surface during the plasma oxidation in an oxygen glow discharge. For this purpose, an in-situ set-up which combines IR-spectroscopy under grazing incidence and quartz crystal micro weighing was used. A Scanning Kelvin Probe was used to measure the influence of the glow discharge on the electronic properties of the iron oxide surface. The glow discharge was initiated by a low power audio frequency voltage source. The results show that an oxygen plasma on iron which is already covered by a natural oxide layer leads to an effective removal of organic contaminations and an increased thickness of the oxide of about 5 to 6 nm. In agreement with the spectroscopic data, the Voltapotential measurements show that the oxide surface is depleted in Fe 2+ states. The structure of the additionally grown oxide is most likely to be γ-Fe 2O 3. This means that the n-semiconducting properties of the oxide are changed. Within an subsequent argon discharge, the Fe 3+ in the oxide surface is again reduced to Fe 2+. The paper illustrates the importance of the consideration of the electronic properties while structuring oxide covered metals and the usefulness of the Scanning Kelvin Probe measurement to reveal electronic properties of semiconducting oxide layers.

Experimental and theoretical investigation of oxygen glow discharge structure at low pressures

An experimental and theoretical investigation of the oxygen glow discharge structure at low pressures has been performed. Radial dependencies of the electron energy distribution function, the ambipolar plasma potential, and the negative ion concentration, as well as the axial electric field and the concentrations of atomic and singlet oxygen were measured. A new approach to the application of laser photodetachment method has been used to measure the negative ion concentration. It allows one to obtain information about fast processes after the photodetachment at low frequencies (/spl sim/100-200 Hz) by using the simplest modulation technique. A self-consistent model involving the electrodynamics and kinetics of the discharge was developed. The observed variations of the negative ion densities with current density and oxygen pressure were explained in the model frame by a dependence of the detachment rate constant of the O/sup -/+O/spl rarr/e+O/sub 2/ process on the effective ion temperature (k=1.9/spl middot/10/sup -10/-/spl radic/1100/T/sub i//sup eff/). It was shown that the feature of oxygen dc discharge at low pressures is a possibility to change the basic type of negative ions from the O/sup -/ to the O/sub 2//sup -/. This effect become more pronounced with decreasing current density.

Experimental investigation and numerical simulation of the energy distribution of positive ions in the negative glow of an oxygen discharge

Using a two-electrode probe, we measured the energy distribution functions of positive ions in the cathode regions of an oxygen glow discharge. The ion distribution functions have two maxima, the magnitude and position of which depend on the gas pressure and the voltage applied to the probe. The proposed approximation of the observed distribution functions is based on the assumption that two groups of ions exist with different mean energies and well described experimental curves. We numerically simulated the measuring process and found an approach for reproducing the ion energy distribution in the plasma unperturbed by the probe.

Oxygen gettering properties of boron film produced by diborane dc glow discharge

Boron film coated on plasma facing walls has been utilized to reduce the oxygen impurity level by the gettering action. The boron film is also useful to reduce the hydrogen recycling. In this study, the boronization was conducted by a dc glow discharge with a mixture gas of diborane and helium both for a graphite and a stainless steel (SS) liners. After the boronization, the oxygen glow discharge was carried out to evaluate the gettered oxygen amount. The state of the oxygen in the surface was also examined. The gettered oxygen amount in the case of the graphite liner was about twice larger than that in the case of the SS liner. The oxygen was trapped in the depth range from the top surface to 100 nm or from the top surface to 20–30 nm in the case of graphite or SS, respectively. The oxygen was observed to be chemically bonded with the boron. After the oxygen discharge, the helium discharge was conducted to recover the oxygen gettering ability. After the helium discharge, the oxygen discharge was again carried out. The gettered oxygen amount in the case of graphite was comparable with that in the case of SS.

Plasma functionalization and reorientation of macromolecules at polymer surfaces

The functionalization of polypropylene surfaces and octadecyltrichlorosilane layers with oxygen-containing groups, and changes in molecular and supermolecular orientations resulting from low pressure oxygen glow discharge plasma treatment were investigated. The main results are the fast reorientation under plasma exposure, and the discrepancy between the slow increase in the functional group concentration and the fast improvement in the maximum adhesion to polyurethane. The reoriented polymer surface should also be a precondition for improved adhesion properties. Labelling reactions allow us to detect low concentrations of OH groups at polymer surfaces by Fourier transform IR spectroscopy combined with ATR spectroscopy. The concentration of OH groups was twofold increased with diborane reduction to convert C=C, C=O, COOH and COOR groups into OH groups.

Plasma Modifications to the Interface in Carbon Fiber Reinforced Thermoplastic Matrices

Abstract Radio frequency glow discharge oxygen plasma was used to modify the surfaces of PAN-based and mesophase pitch-based carbon fibers. Surface chemical changes to the fibers were monitored by X-ray photoelectron spectroscopy and by fiber wetting studies evaluated in terms of dispersive-polar components of surface energy and acid-base contribution to the work of adhesion. Physical changes to these fibers were monitored by scanning electron microscopy. Stress transferability of these fibers was evaluated by the embedded single fiber test in poly(methyl methacrylate), poly(ethyl methacrylate), poly(methacrylonitrile) and poly(vinyl chloride) as these matrices offered varying degrees of dispersive-polar and acid-base character. Experimentally determined critical aspect ratios were compared to the theoretical work of adhesion determined by dispersive-polar interactions and with the Lewis acid-base nature of the matrices.

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.

Cathode sheath subjected to a voltage step: applications to sheath width measurement

We present the current and voltage dynamics of a cathode sheath when a fast downward step of negative voltage is superimposed on the constant cathode bias. Owing to the very different reaction times of electrons and ions, the early interval of the dynamic can be used to measure the stationary cathode sheath width. The method is applied to an abnormal glow discharge in oxygen.

Investigations on Plasma Assisted Surface Cleaning of Aluminum in an Oxygen Glow Discharge

AbstractAluminum plates which are contaminated with hydrocarbon containing compounds (oil, grease) were treated in an Ar‐, O2‐ and Ar/O2‐plasma generated by a dc‐discharge. Besides a variation of the macroscopic discharge parameters (power, pressure) also different modes (anomalous glow regime, hollow cathode regime) have been studied. In most cases the contaminated substrates served as cathodes of an anomalous glow discharge where the combined influence of chemically reactive radicals and energetic ions was very effective.During the plasma process the discharge was monitored by means of power variation and optical emission spectroscopy. The spectral line intensities of several species (etchants and products) have been measured as functions of the process duration. Simultaneously the removal of the contamination layers was observed by means of in‐situ ellipsometry. The temporal change of the ellipsometric parameters ψ and δ during the cleaning process was taken as a measure for the state of the surface. The combination of spectroscopic and ellipsometric measurements which indicate the progress of the plasma treatment gave interesting results on the mechanisms at the surface. In addition, surface analysis was used to assess the quality of the substrates treated.

A comparison of plasma-oxidized and photo-oxidized polystyrene surfaces

High-resolution core-level and valence-band X-ray photoelectron spectroscopic measurements show that polystyrene surfaces become more heavily oxidized during ultraviolet photo-oxidation than under plasma oxidation. A greater proportion of- C O 2-linkages are evident following the former treatment, along with the virtual absence of any phenyl features in the valence region and an attenuated π-π∗ shake-up satellite in the C(1s) spectra. This apparent paradox of the more reactive medium producing a less oxidized surface is explained in terms of the complex plasma-surface interactions associated with the exposure of a polymer surface to an oxygen glow discharge.

Appearance of stable glow discharge in air, argon, oxygen and nitrogen at atmospheric pressure using a 50 Hz source

Unusual glow discharges in air, argon, oxygen and nitrogen at atmospheric pressure can be produced using a 50 Hz source. This technique is introduced on the basis of the idea of a lower dielectric breakdown voltage gas. The electrode system, which is composed of a fine metal wire mesh of specified radius and a dielectric substance, is very useful for plasma surface processes and for chemical reactions in the plasma bulk. The observations of the Lissajous figure of voltage-electric charges and of the current pulse shapes are proposed as a method of distinguishing between the atmospheric pressure glow plasma and the silent electric discharge.

Recovery of Luminous Efficiency of Degraded Willemite Phosphor in an Oxygen Glow Discharge

The luminous efficiency of Willemite phosphor is degraded by electron bombardment. Experiments are reported demonstrating that the luminous efficiency of the degraded phosphor can be recovered by exposure to a low‐pressure oxygen glow discharge.

Plasma oxidation of polystyrene vs. polyethylene

Polyethylene and polystyrene film surfaces have been plasma-oxidized and subsequently characterized by X-ray core level and valence band spectroscopies. The extent of polyethylene surface oxidation was found to be dependent on the power of the oxygen glow discharge employed and the length of time that the treated sample was left exposed to air prior to analysis. In marked contrast to these observations, plasma-oxidized polystyrene surfaces were much less dependent on the oxygen glow discharge power and were also found to retain their oxygenated character over much longer periods of ageing. These differences in oxidative behaviour are explained in terms of the molecular structures of the respective polymers.

Plasma-catalysed surface rearrangement of poly(ethylene) to a poly(propylene) type structure

Exposure of a poly(ethylene) substrate to an oxygen glow discharge, followed by ageing, results in the formation of a poly(propylene)-type structure at the polymer surface.

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.

Surface oxidation of polyethylene, polystyrene, and PEEK: the synthon approach

It is found that surface modification of a polymer by an oxygen glow discharge can be modeled by vacuum-UV oxidation. However, during plasma treatment, competing etching/ablation processes also occur which continuously expose unreacted polymer; this does not happen during UV irradiation and therefore a greater depth of oxidation is found with the latter; UV/O 2 -treated PEEK gives the most highly oxidized surface

Preparation and characterization of superhydrophobic FEP-Teflon surfaces

Abstraet-Supcrhydrophohic FEP-Teflon was prepared by argon ion etching followed by oxygen glow discharge treatment of commercially available FEP-Teflon sheet material. This combined treatment yielded an increase in water contact angle from 109° to > 140°. Ion etching alone caused a small increase in surface roughness and a loss of fluorine from the surface, but the water contact angles increased only to 120°. Scanning electron micrographs of ion-etched surfaces showed stalky protrusions with a diameter of approximatcly 40 nm. Glow discharge treatment of ion-etched surfaces reduced the length of these protrusions and therewith the microscopic surface roughness. However, in all cases the macroscopic surface roughness was less than 1 um (RA value). X-Ray photoelectron spectroscopy indicated major changes in elemental surface composition as a result of the treatments. These modifications did not influence the infrared absorption spectra (attenuated total reflection) of the modified surfaces, indicating that the chemical changes brought about are really superficial. It is concluded that the superhydrophobicity created is mainly due to changes in the specific, microscopic surface topography resulting from ion etching, but also partly due to the role of the glow discharge treatment, restoring a high surface concentration of fluorine after ion etching.

Tunneling spectroscopy on metal-insulator-silicon structures with very thin insulating layers

Tunneling measurements were performed at 4.2 K to investigate metal-insulator-silicon junctions with very thin silicon oxide or silicon nitride layers (2–5 nm) as tunneling barriers. For the measurements at 4.2 K highly degenerate P- or B-doped Si samples were used. Silicon oxide layers were produced by oxidation of Si in dry oxygen at 600 °C or by plasma deposition in an oxygen glow discharge. Silicon nitride films were prepared by nitridation in a NH3 discharge. The effects of interface states, the Si doping density, the metal of the gate electrode and the tunneling barrier material on the tunneling conductivity were studied systematically. Changes in the conductivity were found to be related to changes in the density of interface states, caused by annealing processes or by high-field stress. Vibrational modes of phonons and impurities in the structures were detected by inelastic electron tunneling spectroscopy. Using this approach a direct correlation between the increase in the density of interface states and the decrease of the density of Si-H groups was established.

Kinetics of O(1S) and O(1D) metastable atoms in a DC oxygen glow discharge

The concentrations of O(1D) and O(1S) metastable atoms are measured in the positive column of a DC oxygen glow discharge by vacuum ultraviolet absorption spectroscopy at 115 and 122 nm respectively. In the investigated range of pressures p=0.2-2 torr and discharge currents Id=10-80 mA, the concentrations of O(1D) and O(1S) atoms range from 1011-1012 and from 1010-1011 cm-3 respectively. In these conditions the main creation and destruction processes are discussed: the O(1D) atoms are created by electron impact dissociation of O2(X3 Sigma ) and O2(a1 Delta ), and excitation of O(3P), and lost through quenching by oxygen molecules. It is shown that it is necessary to add to the electron impact excitation another creation term of O(1S) atoms to balance the destruction through quenching by O2(X3 Sigma ), O2(a1 Delta ) and O(3P).

Spectroscopic temperature measurements in oxygen discharges

The rotational temperature of the excited state O2 (b1 Sigma g+, v=0) in an oxygen glow discharge is measured from the intensity distribution of the atmospheric A-band O2 (b1 Sigma g+, v=0) to O2(X3 Sigma g-, v=0) at lambda =760 nm. The kinetic temperature, often called the gas temperature is also deduced using vacuum ultraviolet absorption spectroscopy in the same experimental conditions: pressure p=0.5-5 torr, discharge current up to 100 mA and deposited power up to 2 W cm-1. It is shown that the rotational temperature of the A-band is equal to the rotational temperature of the molecular X3 Sigma g- ground state and of the first metastable as 1 Delta state measured by coherent anti-Stokes Raman spectroscopy. Since the kinetic temperature is in equilibrium with the rotational temperature of the ground state, we conclude that the rotational temperature of the O2 (b1 Sigma g+) state is identical to the gas temperature.