Rf Glow Discharge Research Articles

On the control of thin film growth by angular reflectometry near the brewster angle

The method of angular reflectometry is used to analyze the formation dynamics of layered structures on transparent substrates. This method is highly sensitive to changes in the parameters of a film structure at the early stage of formation thereof. It is based on the angular dependence of the reflected signal intensity near the Brewster angle and is almost independent of the state of the measuring facility. Experimental data obtained for multiferroic thin films on an isotropic crystalline Al2O3(001) substrate are presented. The films on the Al2O3(001) substrate are obtained by sputtering a Bi0.95Nd0.05FeO3 target for 5–600 s in an rf glow discharge initiated in oxygen.

Spatial distributions of gas composition in rf glow discharge plasmas measured using a quartz sensor

A quartz sensor can detect changes in gas composition caused by plasma because the quartz sensor output depends on the total pressure, viscosity, and molecular weight of the gas. This simple mode of quartz sensor measurement was used to obtain spatial distributions of the gas composition changes in the plasmas between a chamber inner wall and a plasma electrode. These spatial distributions reflect gas phase reactions in the plasmas. For that reason, they are helpful to elucidate the reaction mechanisms occurring in the plasmas. Applying such quartz sensor measurements for hydrogen and argon–hydrogen plasmas, we found that the spatial distributions of the gas composition change, as measured using a quartz sensor, depend on source gases. The positions at which the quartz sensor output show the maximum gas composition change for hydrogen and argon–hydrogen plasmas were at the chamber inner wall and near the edge of the plasma electrodes that are the closest positions to the plasma glow. These results show that the gas composition change detected using the quartz sensor resulted from degassing from the chamber inner wall and the plasma electrodes.

Influence of molybdate species on the tartaric acid/sulphuric acid anodic films grown on AA2024 T3 aerospace alloy

AA2024 T3 alloy specimens have been anodised in tartaric acid/sulphuric media and tartaric acid/sulphuric media containing sodium molybdate; molybdate species were added to the anodising bath to enhance further the protection provided by the porous anodic film developed over the macroscopic alloy surface. Morphological characterisation of the anodic films formed in both electrolytes was undertaken using scanning electron and transmission electron microscopies; the chemical compositions of the films were determined by Rutherford backscattering spectroscopy that was complemented by elemental depth profiling using rf-glow discharge optical emission spectrometry. The electrochemical behaviour was evaluated using potentiodynamic polarisations and electrochemical impedance spectroscopy; the corrosion performance was examined after salt spray testing. The porous anodic film morphology was little influenced by the addition of molybdate salt, although thinner films were generated in its presence. Chemical composition of the anodic film was roughly similar; however, addition of sodium molybdate in the anodizing bath resulted in residues of molybdate species in the porous skeleton and improved corrosion resistance measured by electrochemical techniques that was confirmed by salt spray testing.

Stabilized aqueous dispersion of multi-walled carbon nanotubes obtained by RF glow-discharge treatment

This article reports a method for surface modification of multi-walled carbon nanotubes (MWNTs) using a low-pressure capacitively coupled RF glow-discharge. Ar/C2H6 and Ar/C2H6/O2 gaseous mixtures were used to produce non-polar (np-) and polar (p-) coatings, respectively, onto MWNTs. After 5 min of plasma treatment at 20 W and 20 torr, strongly hydrophobic and non-electrically conductive np-MWNTs were produced. The p-MWNTs were strongly hydrophilic and showed no measurable hydrophobic recovery 2 weeks after treatment. Aqueous suspensions of p-MWNTs remained stable and free of agglomerates after being boiled. The ζ-potential of p-MWNT nanofluids was −40.3 mV, indicating a highly stable dispersion.

H2/NH3 Plasma‐Grafting of PEEK‐WC‐PU Membrane to Improve their cyto‐Compatibility with Hepatocytes

AbstractPlasma treatments in H2 and NH3 RF (13.56 MHz) glow discharges have been used for modifying the surface of PEEK‐WC‐PU membranes. Water contact angle (WCA) and X‐Ray photoelectron spectroscopy (XPS) analyses were performed to study the compositional changes of PEEK‐WC‐PU membranes after grafting. Cell culture experiments with human hepatocytes clearly show that grafting N‐containing groups improves the cyto‐compatibility of the membranes.

Plasma deposition of organosilicon polymer thin films with embedded nanosilver for prevention of microbial adhesion

Composite thin films (∼170 nm) containing silver nanoclusters embedded in an organosilicon matrix were deposited by PE-CVD onto stainless steel in order to prevent microbial adhesion. The process originality relies on a dual strategy combining silver sputtering and simultaneous plasma polymerization in argon–hexamethyldisiloxane (HMDSO) plasma, using an asymmetrical RF glow discharge. The metal content in the film was controlled by varying the HMDSO flow rate. Investigation of the physico-chemical properties of the obtained films was conducted by X-ray photoelectron spectroscopy and transmission FTIR spectroscopy. Plasma-mediated coatings were composed of C, O, Si and Ag which was predominantly under metallic form, as indicated by XPS analysis. The presence of Si–H, Si–O–Si, Si–(CH) n –Si and C–H groups was established by FTIR. The yeast Saccharomyces cerevisiae was selected as the model for eukaryotic microorganisms. The maximal anti-adhesive efficiency was achieved for the organosilicon matrix alone. When nanosilver was incorporated into the organic matrix, the efficiency was reduced, especially for high metal contents. Silver antimicrobial property was assumed to be related to Ag + progressive release from the embedded nanoparticles into the surrounding medium. This release was confirmed by ICP-MS measurements. Moreover, silver-containing film antifungal activity was observed towards sessile cells.

NMR Study of Polyethylene‐Like Plasma Polymer Films

AbstractThermal decomposition (“evaporation”) of polyethylene (PE) was performed with or without an activation of volatile fragments in an rf glow discharge. Study of the deposition process via quadrupole mass spectrometry showed the presence of hydrocarbon fragments up to 100 amu. Properties of the resulting films were investigated by means of FTIR, XPS, and NMR spectroscopy. These analyses showed that the activation of polymeric fragments in plasma enhances cross‐linking and the films become hydrocarbon plasma polymers. However, these plasma polymers resemble much more the original PE. In addition, NMR technique enabled to assess the ratio of crystalline and amorphous phases in the films.

Feasibility study of the sterilization of pork and human skin surfaces by atmospheric pressure plasmas

Atmospheric pressure radio frequency (rf) glow discharge characteristics were studied aiming for the plasma treatment of living tissues such as pork and human skin. Electrical and optical measurements of the plasma gave reasonable values at low current of 4 mA and gas temperature of 60 °C at 100 W. The colorimetric measurement of the treated pork sample demonstrated negligible thermal effect from the plasma. In addition, the sterilization efficiency of Escherichia coli inoculated on pork surface was comparable with that of a conventional UV sterilizer. The experimental results promise that the atmospheric pressure rf plasma can be safely applied to human skin treatment without electrical and thermal damage.

Measurement of voltage and current in continuous and pulsed rf and dc glow discharges

Electrical measurements are an important tool for the characterisation of glow discharges and have proved to be useful for a variety of needs in fundamental studies and as control parameter. Therefore, extensive hardware developments and studies of current-voltage (I-U) characteristics in continuous and pulsed, dc and rf modes have been made [1] and will be presented together with new results.In continuous dc mode, the I-U curves are non-linear and may be characterised by a threshold voltage U0 and saturation current Imax (both cathode material and pressure dependent). On the other hand P-U curves are to a large extent linear and very similar in the continuous rf mode [2]. The ionic part of time resolved I-U curves of rf discharges however shows almost a linear behaviour and the capacitive component is small. This led to the assumption that gas heating is responsible for the non-linearity between I and U in continuous dc discharges. Consistent with this assumption, a dependence of the I-U curves of pulsed discharges on the duty cycle was found. The comparison of the curves with those at low duty cycle (cold) led to a rough estimation of the gas temperature.Further investigation and cooperation with modelling groups is needed and planned to explain these results.

Numerical Study on Characteristics of Argon Radio-Frequency Glow Discharge with Varying gas Pressure

A one-dimensional fluid simulation on argon rf glow discharge with varying linearly gas pressure from 1 Torr to 100Torr is performed. The model based on mass conservation equations for electron and ion under diffusion and mobility approximation, and the electron energy conservation equation is solved numerically by finite volume method. The numerical results show that a uniform plasma with high density can be obtained from rf glow discharge with varying gas pressure, and the density of plasma becomes higher as the gas pressure varies from 1 Torr to 100 Torr. It is also shown that in the range of the gas pressure from 1 Torr to 100 Torr with the slower rate of varying gas pressure, higher density of plasma can be obtained.

Emitting a-SiOx(Er) films and a-SiOx(Er)/a-Si:H microcavities doped with Er by remote magnetron sputtering technique

We have developed the technique of growing amorphousa-SiOx(Er) filmsand a-SiOx(Er)/a-Si:H multilayer structures based on spatially separating the processes of the decompositionof an oxygen–silane gas mixture in an rf glow discharge plasma and remote magnetronsputtering of an Er target. This approach allows us to control independently the filmdeposition rate, the Er-ion concentration and its depth distribution in the film. Time-resolvedphotoluminescence measurements have shown that films and planar microcavities with anEr-doped active layer exhibit internal quantum efficiency for Er ion emission of∼75%. The method that we suggest is a way of producing effectively emitting microcavitystructures, in which the distribution profile of emission centers coincides with that of theelectromagnetic field in individual layers of the structure.

Nanocrystalline silicon prepared at high growth rate using helium dilution

Growth and optimization of the nanocrystalline silicon (nc-Si: H) films have been studied by varying the electrical power applied to the helium diluted silane plasma in RF glow discharge. Wide optical gap and conducting intrinsic nanocrystalline silicon network of controlled crystalline volume fraction and oriented crystallographic lattice planes have been obtained at a reasonably high growth rate from helium diluted silane plasma, without using hydrogen. Improving crystallinity in the network comprising ∼ 10 nm Si-nanocrystallites and contributing optical gap widening, conductivity ascending and that obtained during simultaneous escalation of the deposition rate, promises significant technological impact.

Influence of Mixed Field Radiation and Gamma Radiation on Nano Adhesive Bonding of HP Polymer

In this investigation, attempts are made to fabricate high performance polymer such as polybenzimidazole (PBI) (service temperature ranges from -260°C to +500°C) by nano silicate epoxy adhesive and to see its performance under space radiation. The polybenzimidazole sheets are fabricated by high performance nano adhesive i.e., by dispersing silicate nano powder into the ultra high temperature resistant epoxy adhesive (DURALCO 4703, the service temperature of the adhesive is -260°C to +350°C) with 2 to 20% weight ratios with the matrix adhesive. Prior to fabrication of polybenzimidazole sheet, the surface of the polybenzimidazole is ultrasonically cleaned by acetone followed by its modification through low-pressure plasma by using 13.56 MHz RF Glow Discharge with 30, 60, 120, 240 and 480 seconds at 100 W of power using nitrogen as process gas. It is observed that polar component of surface energy leading to total surface energy of the polymer increases with exposure time of low pressure plasma up to 120 seconds and then it saturates. Nano adhesive bonding of high performance polymer is exposed to two types of radiations (i) mixed field radiation for 24 hours at a dose rate of 37kGy/hr in the pool of a SLOWPOKE-2 (safe low power critical experiment) nuclear reactor and (ii) Co-60 irradiation with 100 % gamma radiation at a dose rate of 4 kGy/hr for 60 hours. Tensile lap shear strength reveals that when the polymer surface is modified by low pressure plasma, joint strength increases from 1 MPa to 13 MPa and increases further up to 23 MPa when the polymer is fabricated by nano silicate epoxy adhesive with increasing weight ratios of silicate nano powder up to 10% and then it deteriorates with the increasing weight ratio of silicate nano powder. When this nano silicate epoxy adhesive joint is exposed to high-energy radiation of mixed field, there is a further considerable increase in joint strength up to 30 MPa. However, when the nano silicate epoxy adhesive joint is exposed to 100 % gamma rays condition, joint strength deteriorates. Therefore, this is possible that mixed field radiation; basically increase the crosslink density of the adhesive resulting in increase in adhesive joint strength and in the second case: gamma radiation is detrimental and which could essentially makes chain scission to the basic adhesive and resulting in significant deterioration of joint strength. Finally, to understand the behaviour of nano silicate epoxy adhesive bonding of Polybenzimidazole, the fractured surfaces of the joints are examined by scanning electron microscope.

Development of functional sportswear for controlling moisture and odor prepared by atmospheric pressure nonthermal plasma graft polymerization induced by RF glow discharge

When atmospheric pressure nonthermal plasma (APNTP) is first applied followed by graft polymerization of hydrophilic monomers on the surface of cloth, the cross-section of the cloth acquires functionally graded hydrophilicity and controls moisture and offensive odor simultaneously. The objective of this study is to develop a functional and comfortable sportswear surface, which is treated with this APNTP process. The apparatus of glow discharge graft polymerization for the treatment of textiles was improved to directly treat commercial sportswear the surface of which is naturally hydrophobic. In this apparatus, acrylic acid can be polymerized on the surface by the APNTP. A high performance in controlling moisture and odor was observed in the one-side treated cloth and sportswear. It was possible to expel human sweat to the outside environment effectively by using functional sportswear that is hydrophilic on the outer side and hydrophobic on the inner side.

Modeling characteristics of nonequilibrium processes during breakdown of capacitive rf argon glow discharge

A self-consistent, diffusion-drift approximated fluid model including ion and electron continuity equations and an electron energy equation is presented for simulating the nonequilibrium characteristics during breakdown of argon rf glow discharge. The nonlinear partial differential equations of the model are solved numerically by using a so-called finite volume method. The numerical results indicate that there exist two different phases on the breakdown curves, i.e., the low p⋅d phase and high p⋅d phase. The breakdown voltage, analyzed for three different gaps, varies little in low p⋅d phase while in the high p⋅d phase, it increases linearly with pressure increase. Time evolution of Ohmic heating and energy loss during breakdown are presented in detail. Analysis yields that the heating mechanisms are the dominant factors in breakdown. Moreover, the steady discharge characteristics are also studied specifically under breakdown voltage of 10Torr. The charged particle densities are on the order of 1015∕m3 and the electron energy has two characteristic values at different rf phases.

Growth mechanism of microcrystalline and polymorphous silicon film with pure silane source gas

Microcrystalline, polymorphous and amorphous silicon films were deposited in a standard radio frequency (rf) plasma enhanced chemical vapour deposition system at a high growth rate by using pure silane as source gas. The influence of thermal gradient variation on the growth model of the hydrogenated silicon film was investigated. The structure and optical properties of these silicon samples were characterized by Raman spectroscopy, spectroscopic ellipsometry and Fourier transform infrared spectrometry. The phase state at the boundary of the deposited silicon films was analysed using ion drag and plasma-induced thermophoresis on particles in a rf glow discharge. The results showed that control of the thermal gradient allows a switch from polymorphous to microcrystalline silicon growth. The crystalline volume fraction increases with increasing film thickness, and this demonstrates that there is a crystalline gradient between the surface and the bottom of the microcrystalline silicon film.

Plasma Deposition of Silver Nanoparticles onto Stainless Steel for the Prevention of Fungal Biofilms: A Case Study on Saccharomyces cerevisiae

AbstractA silver nanoparticle composite film was deposited onto stainless steel to reduce the adhesion strength of the model yeast S. cerevisiae. Deposition was carried out under cold‐plasma conditions, combining RF glow discharge and silver sputtering. Shear‐flow‐induced detachment experiments demonstrated the film's anti‐adhesive properties. However, the surface tended to undergo some chemical changes after use, such an increase in hydrophilicity. XPS analysis confirmed the presence of metallic silver for the native plasma‐modified surface and revealed silver oxidation after use. The silver content was also lowered, due to the progressive release of ionic silver from the composite into the medium.magnified image

Properties of light-induced degradation and the electronic properties of nanocrystalline silicon solar cells grown under functionally graded hydrogen dilutions

The electronic properties of hydrogenated nanocrystalline silicon (nc-Si:H) were studied using drive-level capacitance profiling (DLCP) to obtain defect density profiles as well as transient photocapacitance (TPC) and transient photocurrent (TPI) spectroscopies to study the spectra of defect related optical transitions. These measurements were performed on a series of n–i–p solar cell devices with intrinsic layer thickness of roughly 1μm. The nc-Si:H intrinsic layers were deposited using RF or MVHF glow discharge with various hydrogen dilution profiles predominantly on specular stainless steel substrates (SS/n+/i nc-Si:H/p+/ITO), but also on textured back reflectors (SS/Ag/ZnO/n+/i nc-Si:H/p+/ITO) in some cases. Crystallite fractions were estimated using Raman spectroscopy. The electronic properties determined by our measurements could be correlated with variations in structural device parameters and with the degree of hydrogen dilution profiling during growth. We also found, depending on the growth conditions, that the devices exhibited markedly different behaviors after prolonged light exposure (100h using light at 610nm and 500mW/cm2 intensity). We discuss one specific microscopic mechanism that may be responsible for the light-induced changes that we have observed.

Ultra-high performance of DLC-coated Si 3N 4 rings for mechanical seals

Silicon nitride (Si 3N 4)-based ceramics are useful materials for tribological purposes due to their superior mechanical properties. One of their applications is as mechanical face seals. However, Si 3N 4 rings failed as self-mated systems, leading to fluid leakage and catastrophic failure under high-sealing loads. In order to improve the tribological behaviour and to provide efficient full-sealing conditions, the coating of the Si 3N 4 surfaces with a solid lubricating diamond-like carbon (DLC) film is here proposed. Plasma-enhanced chemical vapour deposition (PECVD) DLC coatings with approx. thickness of 1.5 μm were deposited on Si 3N 4 rings by conventional RF glow discharge taking only pure methane or a 95:5 methane/silane mixture, under an applied self-bias voltage of −800 V. After 419 h of continuous work (4300 km), the self-mated pure DLC ring-on-ring tribosystem proved its outstanding performance in sealing of 2 bar of internal pressure of water, at 4 m s −1, in the range 0.48–1 kN of applied normal load, without any signs of surface damage and a super low-friction coefficient value less than 0.001. The Si-DLC coatings have a slightly worse performance, with a running-in period and a steady-state friction coefficient of about 0.02.

Pulsed radiofrequency glow discharge time of flight mass spectrometer for the direct analysis of bulk and thin coated glasses

Direct solid analysis of bulk and thin coated glasses by pulsed radiofrequency (rf) glow discharge time-of-flight mass spectrometry (GD-TOFMS) is investigated. Modulated low pressure plasma created by pulsed-rf-GD has been coupled to a fast TOFMS in order to obtain complete mass spectra information from the different GD pulse domains (pre-peak, plateau and afterglow). In particular, it was observed that the analytes show the highest atomic ion signals in the afterglow region some hundred microseconds after the maximum of the Ar ion signal. However, it should be highlighted that the analyte ions exhibited their peak maxima at different delay times, depending on the element, after the end of the GD pulse. Such ion signal delays have been measured for different selected isotopes, covering a mass spectrum from light to heavy isotopes at different conditions of pressure and applied power. The results showed that ion signal delays are influenced by both the isotope mass and the pressure of the GD. Furthermore, GD operating conditions (pressure and applied power) were optimised in terms of sensitivity, using a bulk glass certified reference material (NIST 1411). The best analytical performance was observed at low pressure (150–200 Pa) and high applied power (135 W). Moreover, different pulse GD duty cycles (relationship between pulse duration and pulse period) were investigated. An optimum value of 50–65% duty-cycle was selected considering the signal stability and the signal intensity.