Argon-oxygen Plasma Research Articles

Nanocrystalline gamma alumina coatings by inverted cylindrical magnetron sputtering

Alumina coatings were deposited on glass, silicon and stainless steel substrates by magnetron sputtering of two cylindrical aluminum targets in argon–oxygen plasma using a mid frequency AC power supply operated at 41 kHz and 5 kW. No substrate heating was used during the deposition process. Reactive sputtering was carried out in the poisoned mode of the targets at low deposition rates of about 0.09 nm s − 1 . The coatings were characterized by X-ray diffraction studies and found to be nano-crystalline, γ-phase of aluminum oxide. The coatings thickness was measured using the optical interference effects in the UV–visible spectrum of thin films deposited on glass substrates. Thin film thickness after 4 h of reactive sputtering was found to be 1.3 μm. We further studied the oxidation resistance of the alumina coatings produced on stainless steel substrates at a temperature of 400 °C. Coatings were found to be completely stable at this temperature and prevented the oxidation of underlying stainless steel substrate.

Modeling of non-equilibrium argon–oxygen induction plasmas under atmospheric pressure

Modeling of induction thermal plasmas has been performed to investigate chemically non-equilibrium effect for dissociation and ionization. Computations were carried out for argon–oxygen plasmas under atmospheric pressure. The thermofluid and concentration fields were obtained by solving two-dimensional modeling. This formulation was presented using higher-order approximation of the Chapman–Enskog method for the estimation of transport properties. A deviation from the equilibrium model indicates that argon–oxygen induction plasmas should be treated as non-equilibrium for dissociation and ionization. The present modeling would give the guidance for the rational design of new material processing using thermal plasmas.

Second derivative Langmuir probe diagnostics of Ar/O2 gas discharge for DC YBCO-124 sputtering

Second derivative Langmuir probe measurements of the electron energy distribution function (EEDF) in an argon–oxygen d.c. gas discharge in conditions close to the optimal for on-axis sputter deposition of YBa2Cu4O8 films have been performed. Taking into account the effect of plasma depletion caused by the electron sink of the probe surface, an extension of Druyvesteyn's method for determination of the plasma potential and the EEDF (respectively, the electron temperature, T and the electron density, n) of the argon–oxygen plasma in the vicinity of the substrate was used. The film composition was monitored as a function of the deposition parameters and related to the relevant plasma characteristics.

Modification of Aliphatic Self-Assembled Monolayers by Free-Radical-Dominant Plasma: The Role of the Plasma Composition

Modification of octadecanethiolate self-assembled monolayers on Au by nitrogen-oxygen or argon-oxygen downstream microwave plasma with a low oxygen content (estimated below several percent) has been studied by synchrotron-based high-resolution X-ray photoelectron spectroscopy and water contact angle measurements. For both types of plasma, the primary processes were found to be the loss of conformational and orientational order and the oxidation of the alkyl matrix and headgroup-substrate interface. At the same time, the film modification occurred much faster and with different intermediates for the nitrogen plasma than for the argon plasma. The reasons for these differences are considered in terms of the different reactivities and different efficiencies of the energy transfer between the plasma constituents in these two types of plasma.

Kinetic pathways to visible emission from a moly–oxide–argon discharge bulb

A low-pressure mercury-free moly-oxide–argon (MoO3–Ar) electrodeless discharge is investigated with potential application to lighting. The inductive discharge is driven by a 13.56 MHz radio frequency (RF) generator at input powers between 100 and 200 W. Calibrated emission spectra in the near ultraviolet (UV), visible, and near infrared regions are recorded and the corresponding powers emitted as radiation are obtained. An extensive set of transition probabilities and rate coefficients for electron impact excitation between Mo states is assembled and a detailed collisional radiative model of the plasma is developed. The model includes 11 states of neutral Mo, the evaporative and recycling chemistry of MoO3 into Mo and back, and the relevant species and reactions in argon–oxygen plasma. The possible paths for visible and UV radiation are analyzed in detail. The measured light output at 200 W RF input power is ∼40 lumens per watt (lpw) with a potential to reach ∼60–80 lpw. Comparison of the model with data for various radiated powers and electron density shows reasonable agreement.

RuO 2–SiO 2 composite thin films with wide resistivity range

RuO 2–SiO 2 composite thin films were deposited on oxidised silicon wafers by reactive sputtering of Ru and quartz in argon–oxygen plasma. Post-deposition annealing was performed in a furnace in the temperature range from 200 to 600 °C in nitrogen ambient. The composition of the films was determined by Rutherford backscattering, while the crystallographic properties were monitored by X-ray diffraction and Raman spectroscopy. Electrical characterisation of the films was carried out using the Van der Pauw technique. A wide range of resistivity between 200 × 10 −6 and 120 × 10 −3 Ω cm was obtained by varying the proportion of SiO 2 in the films. It was shown that by appropriate annealing conditions, tuning of the thermal coefficient of resistance to almost zero value could be obtained for most of the resistivity range of the investigated films.

Plasma cleaning of dental instruments

The theoretical risk of prion transmission via surgical instruments is of current public and professional concern. These concerns are further heightened by reports of the strong surface affinity of the prion protein, and that the removal of organic material by conventional sterilization is often inadequate. Recent reports of contamination on sterilized endodontic files are of particular relevance given the close contact that these instruments may make with peripheral nerve tissue. In this paper, we report the effective use of a commercial gas plasma etcher in the cleaning of endodontic files. A representative sample of cleaned, sterilized, files was screened, using scanning electron microscopy and energy-dispersive X-ray analysis, to determine the level of contamination before plasma cleaning. The files were then exposed for a short-term to a low-pressure oxygen–argon plasma, before being re-examined. In all cases, the amount of organic material (in particular that which may have comprised protein) was reduced to a level below the detection limit of the instrument. This work suggests that plasma cleaning offers a safe and effective method for decontamination of dental instruments, thus reducing the risk of iatrogenic transmission of disease during dental procedures. Furthermore, whilst this study focuses on dental files, the findings indicate that the method may be readily extended to the decontamination of general surgical instruments.

Argon–oxygen plasma treatment of deposited organosilicon thin films

Organosilicon thin films deposited on silicon (1 0 0) substrates from hexamethyldisiloxane and oxygen by means of an expanding thermal plasma have been exposed to an argon–oxygen plasma. From this it is possible to obtain more information of the reaction mechanism between oxygen radicals in the plasma and the deposited films. It has been shown that the carbon content of the deposited films, present in the form of methyl groups, can be almost fully removed. Therefore, the deposited films need to have a significant porosity. The oxygen from the exposing plasma is also incorporated into the films forming SiOSi and SiOH bonds. The dependencies of the various bonding types present in the film as function of exposure time and as function of the oxygen content of the exposure plasma are simulated using two simple models; one for the plasma gas phase and one for the film. Implications from these simulations for the oxygen treatment mechanism and atomic oxygen on the film surface are discussed.

Fotocromismo em filmes finos de óxidos de tungstênio de diferentes composições

Tungsten oxide thin films with three different compositions were deposited by reactive sputtering in an oxygen-argon plasma. In a system composed of a home made photochemical reactor coupled with an optic fiber spectrophotometer, the photochromic effect was studied in these oxide films as function of UV irradiation time, in ethanol, methanol and formaldehyde atmospheres. It was observed that the photochromic efficiency depends on the vapor chemical nature where the film is irradiated as well as the film composition. Kinetic analysis suggest that two kinds of optical absorption centers should respond by the photochromic effect in these films, one generated at film surface and other inside it, which one presenting a different time constant.

Zirconium sputtering by argon–hydrogen and argon–oxygen plasma

The effects on the sputtering of zirconium by mixing hydrogen or oxygen with argon plasma were investigated. Plasmas were generated by electron cyclotron resonance (ECR) heating. The zirconium target was cylindrical, 7 cm in diameter, 2 cm in length and 0.1 mm in thickness, and was set on the downstream side from the ECR point. The zirconium sputtering rate was evaluated from the amount of zirconium deposited onto the copper sample collector, which was dissolved with aqua regia after plasma sputtering experiments, and then the zirconium concentration was measured by ICP-AES. The chemical sputtering effect is discussed based on comparison with the physical sputtering effect. It was found that the sputtered zirconium flux depends on the oxygen partial pressure. It is concluded that the sputtering of zirconium in Ar–O 2 is governed by chemical interaction between oxygen radicals and the zirconium target.

Condition and Effects of Various Plasmas after Passing through the Slits

The conditions and effects of various plasmas after passing through narrow slits have been investigated. It is important to know them in order to improve solid materials of complex structure. We have studied them, using a sample which simply represents the complex solid materials. This sample consists of slit plates, spacers and a base plate. Modification sources, which modify the material, were introduced into the sample through the slit plates. The conditions and effects of various plasmas were estimated by measuring the change between the contact angles before the plasma improvement and those after the plasma improvement. The material was treated in oxygen plasma, argon plasma and nitrogen plasma mainly. These kinds of plasma were generated by a discharge reactor of induction (coil) type. It has been found that these plasma gases can pass through a very complex route with twists and turns and treat a part behind the material. However, the processing effect is different with every plasma. Oxygen plasma’s effect was the strongest of the gases that we used. Argon plasma’s effect was not very strong in the condition of our experiment. In case of nitrogen plasma, its effect became low rapidly near the slits.

On the Use of Global Kinetics Models for the Investigation of Energy Deposition and Chemistry in RF Argon–Oxygen Plasmas Working in the Torr Regime

A global plasma model is used to investigate the chemistry and energy deposition in 13.56 MHz radio-frequency capacitively coupled oxygen–argon discharges under conditions usually used for the deposition of tin oxide films. These models are based on the solution of a stationary electron Boltzmann equation coupled to species balance equations including the vibrational kinetics equations of O2. The results obtained showed that vibrational non equilibrium of O2-molecule is not significant. The dissociation degree of O2 was found to be around a few percents and the discharge was often moderately electronegative even for small O2 contents in the feed gas. The ionization and energy dissipation mechanisms are mainly governed by the collisional processes involving O2 for an oxygen feed gas composition greater than 20%. Results also showed that the predicted densities of the charged species and the electronegative character of the discharge are strongly linked to the assumption made on the homogeneity of the power deposition. On the contrary, the predicted density of O-atom is not sensitive to this assumption.

Analysis of biodiesel by argon–oxygen mixed-gas inductively coupled plasma optical emission spectrometry

The determination of Ca, Cl, K, Mg, Na and P in biodiesel samples by ICP optical emission spectrometry was investigated using a new ICP spectrometer with CCD detectors and radial plasma viewing. Prior to analysis the samples were diluted 1∶4 (m/m) with kerosene. The effect of added oxygen to the intermediate gas, outer gas and nebulizer gas was studied. An overall increase of the signal to background ratios for Na I 588.995 nm, Na I 589.592 and K I 766.490 nm was observed due to reduced background emission of carbon and carbon compounds when oxygen was added. The addition of 0.35 l min−1 oxygen and 0.8 l min−1 argon to the nebulizer gas flow was found to be the most efficient in order to improve the detection limits for Na and K. The application of this cold argon–oxygen plasma enables Na and K determination at µg kg−1 concentrations in biodiesel. The limits of detection for Na I 588.995 nm, Na I 589.592 nm and K I 766.490 nm after the dilution of biodiesel with kerosene are 1.6, 1.4 and 7.1 µg kg−1, respectively, compared with 59, 74 and 220 µg kg−1, respectively, calculated for typical ICP operating conditions. The determination of environmentally relevant organic chlorine at low mg kg−1 levels is possible using the intense spectral lines in the vacuum ultraviolet spectral range at 134.724 or 135.166 nm. Limits of detection for these lines are 0.4 and 0.9 mg kg−1, respectively, after sample dilution as described above.

Surface Modification of EPDM Rubber by Reactive Argon-Oxygen Plasma Process

The ethylene-propylene diene monomer (EPDM) rubber is an important material for rocket engine technology due to its thermal and mechanical characteristics. The improvement of the adhesion character...

Surface Modification of EPDM Rubber by Reactive Argon-Oxygen Plasma Process

The ethylene-propylene diene monomer (EPDM) rubber is an important material for rocket engine technology due to its thermal and mechanical characteristics. The improvement of the adhesion characteristics of EPDM on other kinds of polymers, using plasma technology, has been the major subject of many research works carried out during the last years. In this work, the EPDM surface activation process was carried out in a reactive ion etching reactor (RIE) operated at 13,54 MHz using pure oxygen and a gas mixture of argon and oxygen. These essays were performed varying the process pressure from 70 mTorr to 1000 mTorr, process time from 1 min to 10 min and RF power input from 50 W to 200: W. The surfaces of the treated samples were analyzed by Fourier transform infrared attenuated total reflection spectroscopy (FTIR- ATR). The evolution of the C-OH, and C=O and R-O chemical groups were observed as a function of the plasma process parameters. The analysis of the IR spectra showed that there are experimental condition of the process in which the production of new radical groups on this rubber surface is maximized.

Plasma assisted room temperature bonding for MST

A room temperature wafer bonding process based on oxygen plasma treatment or argon plasma treatment has been studied for surfaces of silicon, silicon dioxide and crystalline quartz. The surface energy of the bonded samples was measured after different storage times at room temperature. After 24 h the bonded interfaces exhibit high surface energies, comparable to what can be achieved with annealing steps in the range of 600–800°C using normal wet chemical activation before bonding. Subsequent annealing of the bonded silicon/silicon samples caused substantial generation of voids while void generation did not occur in bonded silicon dioxide/silicon dioxide samples. The void generation is influenced by process parameters such as the chamber pressure and the coil. The silicon/silicon interfaces formed at room temperature show electrical properties comparable to those of bonded silicon/silicon interfaces formed using wet chemical activation and high temperature annealing.

Synthesis of Crystalline Micron Spheres of Titanium Dioxide by Thermal Plasma Oxidation of Titanium Carbide

Spherical micron particles of crystalline titanium dioxide (TiO 2 ) were synthesized by inflight oxidation of titanium carbide (TiC) micron powders (mean diameter: 28 μm) in argon-oxygen thermal plasma. The extent of oxidation of TiC powders increases with the flow rate of oxygen in the plasma gases (Ar + O 2 ), and a nearly complete oxidation was achieved at a higher oxygen input (10 L/min) yielding TiO 2 powders as the oxidized product. Morphology examination showed that the particles generated by this process are monodispersed and are perfectly spherical. Particle sizes of the as-produced powders range from submicron to several tens of micrometers and are characterized by a bimodal size distribution. A simple sedimentation treatment was applied to separate the as-formed powders with alcohol solvent to give uniform spherical particles with monomodal size distributions. Microstructure analysis of individual particle by aid of selected area Raman spectrum revealed that all the spherical particles are totally crystalline, comprised of either rutile or anatase or their composite. The formation mechanism of the TiO 2 particles in the plasma oxidation was discussed.

Elaboration and adhesion of zinc oxide coatings on poly-ether-ether-ketone films

Zinc oxide coatings are deposited by r.f. magnetron sputtering from a ZnO target. A systematic study has been made on the influence of the sputtering parameters (oxygen partial pressure, total pressure, and r.f. power) both on the structure and on the chemical composition of the zinc oxide deposits. These thin films exhibit the zincite form with a preferred orientation along the [002] axis. The grain size becomes important once the ejected atoms reach high energies. The zinc oxide deposits have a microstructure, which varies from a large columnar structure to a more regular one depending on the process parameters. The density decreases with increasing total pressure and decreasing r.f. power during sputtering. Their composition (O/Zn atomic ratio), established by RBS, depends on the sputtering conditions. An oxygen excess is observed at low pressures. The 180° peeling test is used to evaluate the adhesion between ZnO deposits and PEEK films. This adhesion is indeed very high. This can be explained by the rupture that takes place in the ceramic rather than in the interface between the two materials as shown by X-ray energy dispersion spectrometry measurements. The surface free energies of virgin- and plasma-treated PEEK (polar and dispersive components) are determined by one and two liquid methods. The plasma treatments are found to change the polar component. The highest values are obtained with an argon–oxygen plasma mixture. XPS analyses are performed to observe the modification induced by plasma treatment of the PEEK surface and to investigate the ZnO/PEEK interface for a better understanding of the coating adhesion mechanisms of PEEK film. The improvement of the adhesion of zinc oxide coatings induced by plasma treatments is characterised by fragmentation tests.

Formation of Silicon Structures by Plasma‐Activated Wafer Bonding

A room temperature wafer bonding process based on oxygen plasma treatment or argon plasma treatment has been studied for surfaces of silicon, silicon dioxide, and crystalline quartz. The surface energy of the bonded samples was observed at different storage times. Atomic force microscope measurements, multiple internal reflection infrared spectroscopy, electrical characterization, secondary ion mass spectroscopy, and post‐processing steps were performed to evaluate the plasma‐treated surfaces and the formed bonded interfaces. Electrical measurements were used to investigate the usefulness of plasma‐bonded interfaces for electronic devices. The bonded interfaces exhibit high surface energies, comparable to what can be achieved with annealing steps in the range of 600–800°C using normal wet chemical activation before bonding. The high mechanical stability obtained after bonding at room temperature is explained by an increased dynamic in water removal from the bonded interface allowing covalent bonds to be formed. © 2000 The Electrochemical Society. All rights reserved.

Adhesion of Hydroxyapatite Layer Prepared by Thermal Plasma Spraying to Titanium or Titanium (IV) Oxide Substrate.

Hydroxyapatite (HAp) was sprayed onto titanium substrates in argon-hydrogen thermal plasma or onto titanium (IV) oxide substrates in argon-oxygen thermal plasma. In the latter case, no adhesive strength by a tensile test could be measured because of high fragility of the titanium (IV) oxide. Comparison of the width of peeled-off layers by a scratch test suggested a higher adhesive strength of HAp layers sprayed onto titanium (IV) oxide than onto titanium substrates. It seemed that the surface oxide layer of the titanium substrate would give a positive contribution to adhesion. In both the above experiments, adhesive strength increased with the substrate temperature up to 1130°C and the maximum adhesive strength was 19.2MPa for layers sprayed onto titanium.