Glow Discharge Conditions Research Articles

Surface modification of poly(tetrafluoroethylene) films by plasma polymerization and UV-induced graft copolymerization for adhesion enhancement with electrolessly-deposited copper

Surface modification of H2 plasma-pretreated poly(tetrafluoroethylene) (PTFE) films, either by plasma polymerization and deposition of GMA, or by UV-induced graft copolymerization with glycidyl methacrylate (GMA), was carried out for adhesion enhancement with the electrolesslydeposited copper. XPS and FTIR results revealed that the epoxide groups in the plasma-polymerized GMA (pp-GMA) layer had been preserved to various extents, depending on the glow discharge conditions. The T-peel adhesion test results showed that the adhesion strengths of the electrolesslydeposited copper on both the pp-GMA modified PTFE (pp-GMA-PTFE) film and the GMA graftcopolymerized PTFE (GMA-g-PTFE) film were much higher than that of the electrolessly-deposited copper on the pristine or the H2 plasma-treated PTFE film. The high adhesion strength between the electrolessly-deposited copper and the surface-modified PTFE film was attributed to the fact that the plasma-polymerized and the UV graft-copolymerized GMA chains were covalently tethered on the H2 plasma-pretreated PTFE surface, as well as the fact that these GMA chains were spatially and interactively distributed into the copper matrix.

Modification of Si(100) surface by plasma-enhanced graft polymerization of allylpentafluorobenzene

- Hydrophobic fluoropolymer thin films were deposited on Si(100) substrates by plasma polymerization of allylpentafluorobenzene (APFB) under different glow discharge conditions, and in the presence and absence of Ar plasma pre-activation of the substrate surfaces. The FTIR and X-ray photoelectron spectroscopy (XPS) results suggested that the plasma polymerization proceeded mainly through the C=C bond of APFB, and the fluorinated aromatic structure in the deposited polymer films was preserved to different extents, depending on the radio-frequency (RF) power used for plasma polymerization. The use of a low RF power (~5 W) readily resulted in the deposition of thin films having nearly the same fluorinated aromatic structure as that of the APFB homopolymer. For the plasma-polymerized APFB (pp-APFB) films deposited on the Ar plasma-preactivated Si(100) surfaces, solvent extraction results suggested that the pp-APFB films became covalently tethered onto the silicon substrate surfaces. Thermogravimetric (TG) analysis results indicated that the thermal stability of the pp-APFB films had been enhanced substantially after annealing at 270°C in a vacuum oven.

Biodegradable biocomposite non-woven matrices based on PDLLA- and elastin-solubilized proteins/elastin

Poly(D,L-lactide) (PDLLA) was synthesized by ring-opening polymerization of D,Llactide. Non-woven PDLLA matrices were prepared by an extrusion/winding process. The process conditions were optimized and the surfaces of these matrices were modified by glow-discharge treatment and/or glutaraldehyde incorporation for immobilization of elastin-derived proteins (ESP) to the matrix to increase the biocompatibility and also to improve the bioactivity of the matrix. Glow-discharge conditions were optimized. Ethylene diamine (EDA) and Ar were used as the active monomers in the plasma phase. When EDA was used, the glow-discharge treated PDLLA matrices were first allowed to be reacted with glutaraldehyde, although, when Ar used, the treated matrices were used directly for ESP immobilization. The higher degree of immobilization was obtained for EDA and glutaraldehyde. The ESP-incorporated PDLLA matrices were further treated with elastin by cross-reaction of the ESP molecules on the matrix surfaces with elastin. Scanning electron microscopy (SEM) studies showed that ESP were homogeneously deposited the surface of the matrix.

Improved hybrid Monte Carlo–fluid model for the electrical characteristics in an analytical radio-frequency glow discharge in argon

An improved hybrid Monte Carlo–fluid model for electrons, argon ions and fast argon atoms, is presented for the rf Grimm-type glow discharge. In this new approach, all electrons, including the large slow electron group in the bulk plasma, are treated with the Monte Carlo model. The calculation results presented here are the electrical characteristics (voltage, current and power as a function of time in the rf cycle, as well as the electrical potential and field distribution in the discharge), the electron and argon ion densities, and the electron, fast argon ion and atom impact ionization rates. In particular, the newly calculated electron impact ionization rate is more reliable now, because it is explicitly calculated in the electron Monte Carlo model instead of using an approximate formula, as in the earlier fluid model. Consequently, the major difference with our previous calculation results is found in the electron impact ionization rate. The calculated electrical characteristics (voltage, current and power) are, however, very similar to the results of our previous model. The new model confirms that the plasma displacement current is lower than the ion and electron conduction currents at the typical analytical rf Grimm-type glow discharge conditions, and therefore that the plasma current and voltage are in phase with each other. This is in contrast to other modeling results published recently, but in agreement with experimental observations where the capacitive current of the measuring circuit had also been subtracted from the total current.

Conditioning procedures in Tokamak: Tore Supra application

In this paper, conditioning procedures presently used in tokamaks are described. Long discharge operation has been achieved in the Tore Supra. Moreover, Tore Supra is the only Tokamak in the world which operates with a permanent magnetic field as foreseen in future fusion reactors. Normal glow discharge conditioning appears to be inefficient in this case. Therefore, special conditioning procedures have been developed at Tore Supra which are addressed in this paper.

Properties of surface layers produced on the Ti–6Al–3Mo–2Cr titanium alloy under glow discharge conditions

The recent rapid progress in surface treatment techniques requires that titanium alloys should have an improved resistance to frictional wear without any loss of their high corrosion resistance. These requirements can be satisfied by producing surface layers of specified microstructure and phase composition. The paper presents the results of examinations of the structure and properties of surface layers formed on the Ti–6Al–3Mo–2Cr titanium alloy by glow discharge assisted nitriding and modified process known as carbonitriding (characterized by an alteration of the gaseous atmosphere in which the process is conducted). The investigations included: metallographical examinations, determination the phase and chemical composition of the layers, measurements of their corrosion and frictional wear resistance and scratch tests. The carbonitriding process increases the hardness and improves the wear and corrosion resistance compared to the nitriding technique.

Corrosion resistance of chromium nitride and oxynitride layers produced under glow discharge conditions

The paper presents the results of investigations of the structure and corrosion resistance of chromium nitride, oxynitride and oxide layers produced on steels by electrochemical chromium deposition combined with glow discharge assisted nitriding, oxynitriding and oxydizing processes. The layers obtained were of the types: CrN+Cr 2N+Cr+(Cr,Fe); Cr 2N+Cr+(Cr,Fe); CrN+Cr 2N+Cr+(Cr,Fe) 7C 3; Cr 2N+Cr+(Cr,Fe) 7C 3; Cr(N,O)+Cr+(Cr,Fe) 7C 3 and Cr 2O 3. The corrosion resistance of the layers is high and can be modified by changing the process parameters, such as the temperature and chemical composition of the gas atmosphere.

The influence of the residual stresses on the corrosion and wear resistance of nitrided layers produced isothermally and cyclically on Ti–1Al–1Mn titanium alloy under glow discharge conditions

One of the important effects occurring during surface treatments is the development of certain states of residual stresses that are localized in the surface layers and affect the useful properties of the treated parts, such as the corrosion resistance and resistance to frictional wear of the layers. The paper presents the results of metallographical examinations, determination of the residual stresses state and measurements of the corrosion and frictional wear resistance of the surface layers produced on the Ti–1Al–1Mn titanium alloy by isothermal and cyclic nitriding under glow discharge conditions. These techniques permit controlling the microstructure and thickness of the layers as well as the state of residual stresses induced in them, i.e. the parameters which essentially affect their performance properties.

Prebreakdown and breakdown investigation of needle-plane vacuum gaps in the micron/submicron regime

This article reports investigations of insulation failure of needle-plane gaps of micrometric dimensions. Using a piezoelectric translational stage it is possible to set the gap spacing in the range between 0.1 and 40 μm with a resolution less than 0.04 μm. The prebreakdown and breakdown characteristics of the needle-plane gap were investigated as a function of the gap spacing, emitter radius, ambient pressure, and conditioning effects. The experimental results showed that the breakdown voltage of a microtip-plane gap is relatively high. For a 2 μm radius tip set at a 1 μm gap distance from a planar electrode, the breakdown voltage was about 500 V. It was found that an increase of pressure from 10−6 to 10−2 Torr did not influence the value of the threshold voltage for breakdown. dc glow discharge conditioning in air at a pressure of ∼1 Torr increased the value of threshold voltage for breakdown in vacuum by about 20%–30%. The obtained prebreakdown characteristics of microtip type gaps is very important for the development of vacuum microelectronic devices; specifically, these data provide valuable insights to the practical limits to which microtip-gate gaps can be stressed in practical field emitter arrays in field emission displays.

Nano-diamond films deposited by direct current glow discharge assisted chemical vapor deposition

Continuous carbon films are deposited by the direct current (DC) glow discharge assisted chemical vapor deposition method using a hydrogen–methane gas mixture. As a result of the DC-glow discharge–surface interaction, the substrate is covered by a film whose properties are strongly affected by the glow discharge and substrate conditions. It was found that under appropriate combination of the experimental parameters, a nano-sized carbon composite film containing a predominating diamond phase can be produced. The properties of the deposited carbon films were studied as a function of experimental conditions by a number of complementary techniques. The composition of the films was assessed by electron spectroscopy and the elastic recoil detection method; the morphology and structure of the films were investigated by high-resolution scanning and transmission electron microscopy (HR TEM and HR SEM). Particular attention was paid to the studies of chemical bonding of the deposited materials. For this purpose, the near-edge X-ray absorption fine structure (NEXAFS) and X-ray photoelectron spectroscopy and electron energy loss spectroscopy (EELS) techniques were used. The average film density was measured by Rutherford backscattering spectrometry. Electron diffraction, NEXAFS and EELS measurements render unambiguous evidence of diamond phase formation by the DC-glow discharge process. The nano-size dimensions of the deposited material were determined from both HR-SEM and -TEM measurements. The critical role of substrate temperature for the formation of nano-diamond particles was established based on the spectroscopic and microscopic results. Hydrogen adsorption/desorption appears to be a critical factor in this process.

Investigation of the velocity fluctuation spectrum of a vortex flow of vibrationally excited molecular gas in a glow discharge

The flow velocity fluctuations in a gas laser are measured under non-self-maintained glow discharge conditions. Spectra of the pulsating velocity signal on the frequency interval up to 2 kHz and the time dependence of the signal under glow and neutral flow conditions for pure nitrogen, a mixture of nitrogen and helium, and a trial CO2-N2-He mixture are obtained. Deformation (due to the action of the discharge) of the spectra of the transverse velocity component in the wake of a right circular cylinder is observed. In order to analyze the data obtained a model of the dynamic response of the pulsating velocity is constructed and a model of the Karman vortex street behind a body is generalized with allowance for variations of the oscillation phase in the street.

Improvement of titanium alloy for biomedical applications by nitriding and carbonitriding processes under glow discharge conditions.

Although titanium alloys are used in medicine, they present low wear resistance. In this paper we present the results of studies on surface layers produced by nitriding at three different temperatures, and by carbonitriding under glow discharge conditions in order to improve wear resistance, hardness, and to modulate microstructure and chemical composition of surface layers. A cell culture model using human fibroblasts was chosen to study the effect of such treatments on the cytocompatibility of these materials. The results showed that nitrided and carbonitrided surface layers were cytocompatible. Modulation of surface microstructure by temperature in the nitriding process and chemical composition of surface layers by carbonitriding led to differences in cellular behaviour. Cell proliferation appeared to be slightly reduced from the 6th day of culture on nitrided surfaces produced at 730 degrees C and 1000 degrees C, however after 12 days of culture, the best growth was on surface layers produced at 850 degrees C. The best viability was observed on the carbonitrided layer. The orientation and shape of the cells corresponded to surface topography. Nitriding and carbonitriding under glow discharge conditions may constitute interesting techniques allowing the formation of surface layers on parts with sophisticated shapes. They may also permit modulating surface topography in a way improving the features of titanium alloys for various applications in medicine.

D.C. glow discharge in a gas under lowered pressure in ion nitriding of Armco iron

For many years a d.c. glow discharge under lowered pressure in nitrogen or nitrogen and hydrogen atmospheres has been applied in the nitriding processes. Presently, there are two major proposals regarding the basic reaction mechanism of ion nitriding. The first model, mainly developed for ferrous alloys, assumes the formation of high iron nitrides (FeN and Fe2N) in the plasma, results from the reaction between active nitrogen ions and sputtered iron atoms [1, 2]. After condensation on the cathode surface, these nitrides decompose to lower iron nitrides and release free nitrogen that diffuses into the substrate. Diffusion is accelerated by the existence of this strong source. The second model proposes that ionic bombardment introduces vacancies and vacancy clusters and therefore increases nitrogen diffusion [3, 4]. The energy of particles in conventional ion nitriding is sufficient to produce a defect layer a few atomic layers thick that can act as a source for vacancies and interstitials. Even though most of these defects will be annihilated at the surface, a number of them will have the chance to migrate into the interior of the material and thus enhance the diffusion rate. It is apparent that, in either one of the above models, the number of ions in the plasma and their energy play an important or dominant role in the nitriding process. In this paper research results will be presented showing that under plasma d.c. glow discharge conditions a nitriding process occurs not only on the cathode, but also on the anode and substrates with plasma potential (isolated from the cathode and the anode) if only they reach the proper temperature. The temperature necessary for the nitriding process on the anode could be obtained in the apparatus for glow discharge treatment with the hot anode. In the apparatus the anode is additionally heated e.g. in a resistance furnace. In the Fig. 1 the schematic diagram of the hot anode apparatus used for glow discharge treatment is shown [5]. The apparatus design allows for realization of the thermochemical treatment of plasma in various regions of a d.c. glow discharge. The substrates placed directly at the cathode or at the anode have respectively the temperature and the potential of the cathode or the anode. The substrates, which during the treatment are to have the plasma potential, are placed at the insulator with ceramic labyrinth (Fig. 2) [6]. When the insulator is placed at the cathode, the treated substrate has the cathode temperature, though it is isolated from the cathode. When the insulator is placed at the anode, the treated substrate has the anode temperature and is also isolated from the anode. Samples of Armco iron (0.05% C) were exposed to nitriding processes in various regions of a d.c. glow discharge using the hot anode apparatus (Fig. 1). Parameters of the nitriding process are given in Table I. Tests of the phase composition of nitrided layers were carried out in X-ray diffractometer using CuKα radiation. Metallographic tests were conducted on perpendicular microsections using the optical microscope. In Table II results are listed of the phase analysis and metallographic test carried out on Armco iron substrates exposed to nitriding in various regions of a d.c.

Hydrogenated Microcrystalline Silicon: From Material to Solar Cells

ABSTRACTUndoped hydrogenated microcrystalline silicon (νc-Si:H) layers and solar cells have been deposited by plasma-enhanced chemical vapour at low temperature and at different values of VHF plasma power and silane to hydrogen dilution ratios. Transport and defect density measurements on layers suggest that structural properties (e.g. crystallite shape and size) only marginally influence the electronic transport properties. The latter are influenced strongly by the Fermi level, which depends on the oxygen impurity content. Furthermore, they are best described by the quality parameter ν0τ0 (deduced from photoconductivity and ambipolar diffusion length). Cell efficiency correlates better with νoτ0 than with the defect density as determined from subbandgap absorption. Anisotropy of the transport properties in some νc-Si:H is also demonstrated but does not seem to play a major role in νc-Si:H cells deposited at high rates under VHF glow discharge conditions.

Surface modification of poly(tetrafluoroethylene) films by plasma polymerization of glycidyl methacrylate and its relevance to the electroless deposition of copper

Surface modification of poly(tetrafluoroethylene) films by plasma polymerization and deposition of glycidyl methacrylate (GMA) was carried out. The effects of glow-discharge conditions on the chemical structure and composition of the deposited GMA polymer were analyzed by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy. XPS and FTIR results revealed that the epoxide groups in the plasma-polymerized GMA (pp-GMA) layer had been preserved to various extents, depending on the plasma deposition conditions. The morphology of the modified PTFE surface was investigated by atomic force microscopy (AFM). The pp-GMA film with well-preserved epoxide groups was used as an adhesion promotion layer to enhance the adhesion of the electrolessly deposited copper on the PTFE film. The T-peel adhesion test results showed that the adhesion strength between the electrolessly deposited copper and the pp-GMA-modified PTFE (pp-GMA-PTFE) film was much higher than that between the electrolessly deposited copper and the pristine or the Ar plasma-treated PTFE film. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3498–3509, 2000

Characteristics of a 40.68-MHz radio frequency boosted low power glow discharge lamp

In order to perform precise depth profiling of conducting solid sample, a DC glow discharge lamp is often operated under low power conditions. Since a DC glow discharge at low power conditions gives low excitation, an additional boosting method having no influence on the cathodic sputtering (sampling process) is needed to obtain an emission intensity enough for precise depth profiling. When the frequency of a radio frequency (RF) discharge increases, the DC bias voltage decreases, yielding less sputtering. At 40.68 MHz, almost no sputtering occurs. When a DC discharge and such a 40.68-MHz RF discharge are combined, sputtering and excitation can be controlled independently. It is found (by selecting only the RF-excited spectra using a modulation technique) that higher excitation and emission (at least for excited levels below 15 eV) occur due to the RF-power, compared to a pure DC discharge at low power conditions. Since emission signal from the DC glow discharge can be eliminated by using modulation technique, interpretation of spectral intensity–time relationship is simple, regardless of DC glow discharge conditions for cathodic sputtering. Such a characteristic is advantageous in a precise profiling.

Properties of multicomponent layers produced on high speed steel by combined nitriding and PACVD methods under glow discharge conditions

A prospective line in the development of thermo-chemical treatments under glow discharge conditions is to work out new techniques of producing multicomponent layers such as e.g. combined plasma nitriding and PACVD technique with the use of organic compounds. These layers permit widening the application range of treated parts since they improve their useful properties. The paper specifies the conditions under which the composite layers of the nitrided - Ti(NCO) type can be produced on high speed steel using a gaseous atmosphere of the organic titanium compound Ti(OC 3 H 7 ) 4 nitrogen and hydrogen and discusses the influence of the carbon and oxygen contents in the Ti(N x C y O z ) layer on its properties such as hardness and wear resistance. The composite layers of the nitrided-Ti(NCO) type have a good resistance to frictional wear. The chemical composition of these layers can be controlled. This new processes can be performed during a sole technological operation in a conventional equipment designed for glow discharge assisted techniques.

Properties of the surface layers on titanium alloy and their biocompatibility in in vitro tests

Recently, it has been suggested that the future designs of implants and endoprothesis should be focused on the use of a new generation of biocompatible, corrosion and wear resistant materials or materials currently used but modified by surface engineering processes. The aim of the study was to investigate the features of titanium oxide and titanium nitride layers produced on titanium alloy by plasma nitriding and oxidizing under glow discharge conditions and their biocompatibility in in vitro tests. The plasma nitriding and oxidizing techniques essentially improved the properties of titanium alloys. Their microstructure and the results of hardness, wear and corrosion resistance tests are presented. In the investigations of the cellular responses of human fibroblast cells to these layers, three aspects were considered: the number of growing cells, their morphological features and their biological corrosion resistance. Nitriding and oxidizing under glow discharge conditions have provided new possibilities of producing non-toxic, human fibroblast-compatible surface layers on parts made of titanium alloys with sophisticated shapes. Uniform surface layers having a controlled microstructure and phase composition can contribute to the opening of a wider application range of titanium alloys as biomaterials.

High field breakdown of narrow quasi uniform field gaps in vacuum

The challenge in vacuum microelectronic device design is to be able to stress a given micrometric gap to relatively high voltages without threat of a breakdown, which, in effect could destroy the device. In order to obtain basic vacuum insulation data related to the regime of vacuum microelectronics, the prebreakdown and breakdown characteristics of narrow gaps in the range of 3–25 μm were extensively investigated. The observed prebreakdown current was related to field emission from atomic scale microprotrusions or planar emission sites; the emission from these sites eventually produces breakdown. A single spark breakdown caused damage to both the anode and cathode. The dc glow discharge conditioning in air improved the insulation capability of narrow gaps (3–25 μm) significantly. The breakdown strength of a 5 μm gap after conditioning was as high as 5×108 V/m, which is the highest value reported in literature for broad area electrodes. It is shown that the electric field evaporation of metal ions from the electrode surface at an electric field E≅1010 V/m is able to instigate breakdown of the gap even under high vacuum conditions. Electric field evaporation can occur both at the cathode and anode surfaces to create the breakdown conditions. The breakdown data obtained in the micrometric gap regime is very valuable in the design of field emission displays and other vacuum microelectronic devices.

Dependence of surface oxidation on hydrogen absorption and desorption behaviors of Ti–6Al–4V alloy

The hydrogen absorption and desorption behaviors of surface oxidized and degassed Ti–6Al–4V alloys under a condition of hydrogen pressure near to the pressure during glow discharge conditioning in reactor were evaluated by thermal desorption spectroscopy (TDS). The equilibrium hydrogen concentration, C eq, of degassed Ti–6Al–4V alloy decreased with increase of temperature. The C eq was about half of that of pure Ti in the temperature region of 673–873 K. The desorption peak of degassed Ti–6Al–4V alloy appeared at the temperature of 790 K. The peak temperature was almost the same even when the absorption amount changed. The absorption amount, C ab, of surface oxidized alloy largely decreased with the increase of atomic ratio (O/Ti) on the top surface and the thickness of the oxide layer when adsorption time was 1 h. In addition, the desorption peak shifted to a higher temperature region with the increase of O/Ti ratio. In the surface oxidized Ti–6Al–4V alloy with an oxide layer of about 10 nm, the C ab was two orders of magnitude smaller than that of the degassed sample when the absorption temperature and time were kept at lower than 650 K and 1 h, respectively. However, the C ab of surface oxidized alloy became comparable with that of degassed sample when the absorption temperature was higher than 800 K because the oxide layer disappeared in the higher temperature region.