Gas Mixture Ratio Research Articles

Fabrication and characterization of photo- and plasma-chemically deposited thiol-terminated films for biomedical applications

Event Abstract Back to Event Fabrication and characterization of photo- and plasma-chemically deposited thiol-terminated films for biomedical applications Evelyne Kasparek1, Jason R Tavares2, Michael R Wertheimer3 and Pierre-Luc Girard-Lauriault1 1 McGill University, Plasma Processing Lab, Department of Chemical Engineering, Canada 2 École Polytechnique de Montréal, Department of Chemical Engineering, Canada 3 École Polytechnique de Montréal, Department of Engineering Physics, Canada Introduction: The performance of synthetic polymers, including applications in biomedical fields, can be improved by modifying their surface properties. Polymer surfaces generally have low chemical reactivity,are not capable of forming adhesive bonds, and poorly-wetting. Among different modified surfaces, thiol (SH)-terminated ones have been progressively gaining interest over the past years[1]. They have been shown useful for many applications, such as promoting adhesion of gold layers and nanoparticles, and for immobilizing biomolecules. An important advantage of using SH-terminated surfaces for biomolecule immobilization is the possible covalent attachment of these molecules via thiol-ene click chemistry, superior to electrostatic attachment[2]. Materials and Methods: In this work, thin organic films incorporating sulfur (S)-bearing functional groups have been prepared by “co-polymerizing” gas mixtures of ethylene (C2H4) or butadiene (C4H6), as hydrocarbon source, with H2S, as source of bound S in the coatings. This has been accomplished by either (i) vacuum-ultraviolet (VUV) irradiation of the reagent gas mixtures at reduced pressure with near-monochromatic radiation from a Kr lamp (λ = 123.6 nm); or (ii) by low-pressure r.f. plasma-assisted chemical vapor deposition (PACVD). The different films were prepared with gas mixture ratios, R (e.g. FH2S/FC4H6), ranging from 0 to 1.5. The polymer-like coatings resulting from photo-chemical or plasma reactions are respectively designated ‘‘UV-PB/E:S’’ (for ‘‘ultraviolet- polymerized sulfurized butadiene/ethylene’’), or L-PPB/E:S (for ‘‘low-pressure plasma-polymerized, sulfurized butadiene/ethylene’’). All deposits were characterized by X-ray photoelectron spectroscopy (XPS) before and after chemical derivatization with N-ethylmaleimide, which serves to quantify the thiol concentrations, [SH], on the surfaces. The stability of the coatings was measured as loss of thickness in water after 24h of immersion. Results and Discussion: XPS survey spectra of the deposited films at different R values reveal important amounts of bonded sulfur, the concentration, [S], being found to increase with rising R, namely 2 ≤ [S] ≤ 48 at. % (Figure 1). This analysis also shows that both deposition methods, plasma and VUV, influence [S] in quite similar ways. After derivatization with N-ethylmaleimide, some differences between the two film types can be observed: plasma-polymers show higher [SH] values, up to 3 %. After immersing the films in toluene for 24h, no significant differences in [S] were observed, indicating that the remaining S content in the films is not inorganic, but otherwise- bonded organic sulfur. The stability in aqueous media of all investigated coatings is a key requirement when used in biomedical applications: after immersion in water for 24h, all remained of essentially unchanged thickness. Figure 1 Surface-near sulfur concentrations, [S] (in at.- %), of a) L-PPB:S (squares, 20 W) and UV-PB:S (circles, KrL); b) L-PPE:S (squares, 20 W) and UV-PE:S (circles, KrL), both as a function of gas mixture ratio, R. Conclusion: To our knowledge, we are for the first time, demonstrating thiol-terminated surfaces by “co-polymerizing” mixtures of a hydrocarbon and H2S, by both vacuum-ultraviolet photo-CVD and low-pressure r.f. PACVD. All of the obtained deposits show significant [S] values, whereof a satisfactory portion is bonded in the form of thiols. These SH-terminated surfaces show good stability in aqueous media, a characteristic that is essential for biomedical applications. The authors would like to acknowledge McGill Engineering Doctoral Award (MEDA), Fonds de recherche du Québec (FQRNT) and Natural Sciences and Engineering Research Council of Canada (NSERC) for the funding

Selective Boron Elimination from B2H6–SiH4 Gas Mixtures for Purifying Si

A boron elimination method based on the difference in the pyrolysis temperatures of SiH4 and B2H6 is proposed for purifying metallurgical grade Si feedstock for photovoltaic applications through direct hydrogenation using high-pressure hydrogen plasma. A simple kinetic model is constructed to estimate the proposed boron elimination filter performance. The filter performance is experimentally evaluated. It is confirmed that there is a significant temperature difference between the B2H6 and SiH4 transmission behavior through the filter. However, when SiH4 and B2H6 gases are simultaneously supplied to the filter at the same flow rate of a few standard cubic centimeters per minute, the SiH4 transmission curve is affected by B2H6 and almost overlaps with the B2H6 curve. In contrast, by decreasing the B2H6 flow rate to one thousandth the SiH4 flow rate, B2H6 co-supply has little influence on the SiH4 transmission curve. The type of carrier gas (H2 and He) also affects the transmission curve. With increasing filter temperature, the B elimination effect of the filter becomes greater. The B concentration in Si films prepared by a single elimination process can be reduced to about 1/3000 of the value estimated from the concentration ratio in the unfiltered gas mixture.

Analysis of the Sensitivity of K-Type Molecular Sieve-Deposited MWNTs for the Detection of SF₆ Decomposition Gases under Partial Discharge.

Sulfur hexafluoride (SF6) is widely utilized in gas-insulated switchgear (GIS). However, part of SF6 decomposes into different components under partial discharge (PD) conditions. Previous research has shown that the gas responses of intrinsic and 4 Å-type molecular sieve-deposited multi-wall carbon nanotubes (MWNTs) to SOF2 and SO2F2, two important decomposition components of SF6, are not obvious. In this study, a K-type molecular sieve-deposited MWNTs sensor was developed. Its gas response characteristics and the influence of the mixture ratios of gases on the gas-sensing properties were studied. The results showed that, for sensors with gas mixture ratios of 5:1, 10:1, and 20:1, the resistance change rate increased by nearly 13.0% after SOF2 adsorption, almost 10 times that of MWNTs sensors, while the sensors’ resistance change rate with a mixture ratio of 10:1 reached 17.3% after SO2F2 adsorption, nearly nine times that of intrinsic MWNT sensors. Besides, a good linear relationship was observed between concentration of decomposition components and the resistance change rate of sensors.

Large-area MoS2 grown using H2S as the sulphur source

We report on the growth of molybdenum disulphide (MoS2) using H2S as a gas-phase sulfur precursor that allows controlling the domain growth direction of domains in both vertical (perpendicular to the substrate plane) and horizontal (within the substrate plane), depending on the H2S:H2 ratio in the reaction gas mixture and temperature at which they are introduced during growth. Optical and atomic force microscopy measurements on horizontal MoS2 demonstrate the formation of monolayer triangular-shape domains that merge into a continuous film. Scanning transmission electron microscopy of monolayer MoS2 shows a regular atomic structure with a hexagonal symmetry. Raman and photoluminescence spectra confirm the monolayer thickness of the material. Field-effect transistors fabricated on MoS2 domains that are transferred onto Si/SiO2 substrates show a mobility similar to previously reported exfoliated and chemical vapor deposition-grown materials.

A comparative study of capacitively coupled HBr/He, HBr/Ar plasmas for etching applications: Numerical investigation by fluid model

Fluid model has been applied to perform a comparative study of hydrogen bromide (HBr)/He and HBr/Ar capacitively coupled plasma discharges that are being used for anisotropic etching process. This model has been used to identify the most dominant species in HBr based plasmas. Our simulation results show that the neutral species like H and Br, which are the key player in chemical etching, have bell shape distribution, while ions like HBr+, Br+, which play a dominant rule in the physical etching, have double humped distribution and show peaks near electrodes. It was found that the dilution of HBr by Ar and/or He results in an increase in electron density and electron temperature, which results in more ionization and dissociation and hence higher densities of neutral and charged species can be achieved. The ratio of positive ion flux to the neutral flux increases with an increase in additive gas fraction. Compare to HBr/He plasma, the HBr/Ar plasma shows a maximum change in the ion density and flux and hence the etching rate can be considered in the ion-assisted and in the ion-flux etch regime in HBr/Ar discharge. The densities of electron and other dominant species in HBr/Ar plasma are higher than those of HBr/He plasma. The densities and fluxes of the active neutrals and positive ions for etching and subsequently chemical etching versus physical sputtering in HBr/Ar and HBr/He plasmas discharge can be controlled by tuning gas mixture ratio and the desire etching can be achieved.

Self-absorption-calibrated vacuum ultraviolet absorption spectroscopy for absolute oxygen atomic density measurement

Using a compact microwave plasma light source, a self-absorption-calibrated vacuum ultraviolet absorption spectroscopy (VUVAS) method was developed based on resonance escape factor theory and numerical analysis of the emission profile using Specair. After theoretical calibration of the self-absorption effect for two adjacent oxygen lines at 130.22 nm and 130.49 nm emitted from the light source, absolute oxygen atomic densities were measured for different N2/O2 gas mixture ratios in surface-wave plasmas. The oxygen atomic densities obtained for the two light probes were fairly close, supporting good reliability of the proposed self-absorption-calibrated VUVAS method. It is expected from the present results that the proposed method will extend the range of application of the VUVAS method in industrial plasma processing.

Experimental Investigation of Carbon Deposition on a Ni/YSZ Anode of Solid Oxide Fuel Cell

The carbon depositions on a Ni/YSZ anode of solid oxide fuel cell (SOFC) with different gas ratios of CH4+H2 and CO+CO2 gas mixtures were experimentally studied. The carbon deposition rates for methane cracking and CO disproportionation were acquired at temperatures from 873K to 1073K. The kinetic models of the methane cracking and CO disproportionation reactions were verified by the experimental data. The results show that both the reactions of methane cracking and CO disproportionation are not solely related with the temperature or the gas mixture ratios. A kinetic model based on the elementary steps suggested by Alstrup fits well to the experimental data of methane cracking at the temperature range of 873-1073K. By assuming C-O bond cleavage as the rate-limiting step, a kinetic model of carbon deposition was derived for the CO disproportionation reaction and it is well fit to the experiments at temperature 973-1073K. The experimental results also show that the carbon deposition in the SOFCs is mainly due to the methane cracking reaction. Comparatively, the carbon deposition from CO disproportionation reaction is negligible.

Separation of Methane/Ethylene Gas Mixtures Using Wet ZIF-8

The separation of methane/ethylene gas mixtures by the adsorption–hydration method was investigated by using a wet zeolitic imidazolate framework (ZIF) microporous material, ZIF-8. The influences of the initial gas–solid ratio (the volume ratio of gas mixture to ZIF-8) and water content of wet ZIF-8 on the separation performance were studied systematically at 274.15 K. The experimental results show that gas–solid ratio of ca. 310 and water content of ca. 38.50 wt % are the suitable conditions for the separation of methane/ethylene mixture with wet ZIF-8 on the premise of hydrate formation. When water content of wet ZIF-8 is 38.50 wt % and the gas–solid ratio is 297, the mole fraction of ethylene in gas phase decreases from 30.91% to 14.44%, the selectivity coefficient reaches 5.57, and the adsorption quantity of ethylene reaches 3.37 mmol/g after one stage of the adsorption–hydration process. Compared with a single adsorption method or hydration method, methane/ethylene gas mixtures can be further separat...

Oxygen atomic density measured with a self-absorption calibrated vacuum ultraviolet absorption spectroscopy and its effect on spore etching in N2/O2 surface-wave plasma

A compact microwave plasma light source for vacuum ultraviolet absorption spectroscopy (VUVAS) technique was developed to measure the absolute oxygen atomic density in N2/O2 gas mixture surface-wave plasma. With self-absorption calibrated VUVAS technique based on the theory of resonance escape factor, the absolute oxygen atomic densities were consistently analyzed using two adjacent oxygen atom emissions at 130.22 and 130.49 nm for different N2/O2 gas mixture ratios in surface-wave plasma (SWP). Results of the absolute oxygen atomic densities clearly indicate a strong correlation with previously observed etching results of spore-forming microorganisms under the same N2/O2 SWP discharge conditions.

Surface characteristics and cell-adhesion performance of titanium treated with direct-current gas plasma comprising nitrogen and oxygen

In this study, we attempted to form titanium oxynitride (TiOxNy) layers on titanium (Ti) surfaces using direct-current (DC) plasmas generated from gas mixture comprising hydrogen, nitrogen, and oxygen. Additionally, the effect of gas mixture ratio on the surface characteristics and cell-adhesion performance was investigated. Scanning probe microscopy (SPM) images showed that the plasma-treated surfaces were slightly rougher than untreated Ti surfaces, owing to the formation of new layers. Chemical state analysis using X-ray photoelectron spectroscopy (XPS) revealed that the layers were comprised TiOxNy, titanium nitride (TiN), and titanium dioxide (TiO2); the concentrations of TiOxNy and TiN decreased and that of TiO2 increased with an increase in the amount of oxygen in the gas. An increase in the amount of oxygen gas did not affect the layer thickness, which was approximately 25nm. Furthermore, no differences in cell morphology and cell-adhesion performance were found between the specimens treated with various plasma gases. This is probably because the treatment insufficiently improved the hydrophilicity. Layers composed of TiOxNy, TiN, and TiO2 were formed using the DC plasma treatment; however, the layers did not improve the cell-adhesion at an initial stage after the seeding.

Nitrogen‐Rich Plasma Polymer Coatings for Biomedical Applications: Stability, Mechanical Properties and Adhesion Under Dry and Wet Conditions

Plasma polymerized coatings (PP) are increasingly used for biomedical applications in contact with body fluids. We optimized and studied the stability, mechanical properties, and adhesion in air and aqueous media of amine (NH2)‐rich PP in low‐pressure r.f. plasma from [NH3/C2H4] mixtures (L‐PPE:N). Quartz crystal microbalance with dissipation monitoring (QCM‐D) revealed partial dissolution or water‐uptake (swelling) in real‐time in various solutions, which helped identify the best gas mixture ratio for compromise between stability and high concentration of (NH2) groups. Nanoindention revealed strong decrease of Young's modulus and hardness in water. Finally, a Cross‐Hatch peel test was used to optimize L‐PPE:N adhesion on poly(tetrafluoroethylene) (PTFE): plasma pre‐treatment prevented both dry and wet delamination.

Simultaneous dissociation of CO2 and H2O to syngas in a surface-wave microwave discharge

In this research, conversion of carbon dioxide and water vapor into value-added chemicals has been investigated in a pulsed surfacewave sustained microwave discharge operating under different conditions. Formation of syngas (CO/H2) was observed. The influence of the gas mixture ratio, the specific energy input (SEI), Espec, and the feed flow rate on H2 and CO production, was studied. It is found that syngas with a ratio close to 1 can be produced when CO2 – H2O ratio in the gas mixture is 50:50. The optimum SEI for H2 and CO formation for this gas mixture ratio is 1.6 eV/mol. Experiments carried out with Ar/H2O showed that the presence of CO2 supports the H2 formation at low SEI. Increasing the feed flow rate, i.e. reducing the residence time, hinders the H2 yield while the CO yield initially decreases and reaches a stable level. The highest energy conversion efficiency is calculated to be at low SEI and low flow rate. Optical emission spectroscopy measurements show that comparatively high dissociation rates correspond to low gas temperatures.

Corrosion Resistance of Plasma Nitrided Structural Steels

Plasma nitriding technology, based on plasma assisted nitrogen diffusion into the steel surface, mostly used for improvement of wear resistance and fatigue strength is well known. Additional benefit of plasma nitriding is heat and corrosion resistance improvement. This study is focused on evaluation of corrosion resistance of plasma nitrided structural steels under several nitriding conditions. Experiments were performed on structural steels CSN 41 2050 (C45E), CSN 41 4220 (16MnCr5) and CSN 41 5230 (DIN 1.7361). Selected structural steels were manufactured for experimental specimens (size of 80x50x4 mm), heat-treated and plasma nitrided under following conditions: T = 500 °C, process duration t = 10 and 20 h, p = 280 Pa, U = 510 V and variable gas mixture ratio of 3H2:1N2 [l/h] and 1H2:3N2 [l/h] for different compound layer phase composition. Corrosion tests were performed in the Liebisch GmbH & Co (S 400 M-TR) corrosion chamber in the mist of neutral sodium chloride dilution (NSS method), evaluated and documented in accordance to ISO 9227 standard and results compared to different plasma nitriding conditions. Under different plasma nitriding conditions were different nitride layer characteristics obtained. Nitride layers were by surface hardness (HV), metallographic testing and microhardness testing (HV0,05) classified. Using the microhardness testing were different values of microhardness and nitride layer depth detected. Metallographic testing and additional concentration profiles measuring (using GDOES method) displayed different compound layers thickness, which tends to be a significant factor to corrosion resistance of plasma nitrided structural steels.

The Effect of Plasma Nitriding Process on the Change of Dynamic Parameters of Steel DIN 1654/4

This article describes the effect of selected parameters of plasma nitriding on the change of dynamic parameters of steel DIN 1654/4. Plasma nitriding is currently used in a wide range of technical applications such as a final operation to improve the mechanical properties of components. This experimental investigation is devoted to the analysis of the influence of plasma nitriding on the notch toughness of structural steel DIN 1654/4 (CSN 41 2042.4). The test of the dynamic fracture behaviour of structural steel was carried out using by instrumental Charpy hammer on the plasma nitrided specimens with V and U notch, manufactured according to standard CSN ISO 148-1. The plasma nitriding was implemented at 500 (°C), process duration t = 10 and 20 (h) and variable gas mixture ratio of 24H2: 8N2 (l/h) and 8H2: 24N2 (l/h). The test results showed that nitrided steel has become more brittle. However, it was found that for different gas composition, the notch toughness has behaved quite diversely. The values of notch toughness of steel in case of gas ratio 8H2: 24N2 (l/h) were decreased but for gas ratio 24H2: 8N2 (l/h), with extension of time, the notch toughness was slightly increased.

100 kHz Bandwidth Ultrasonic Recording System

We have developed a complete 100 kHz ultrasonic recording system. The primary components of the system are a SensComp Series 600 Instrument Grade Electrostatic Transducer, custom printed circuit board (PCB), wide-bandwidth instrumentation amplifier, linear-phase filter, fully differential 16-bit analog to digital converter (ADC) sampling at 840 kHz, 168 MHz STM32F4 32-bit microcontroller, and a direct 100 Mbps Ethernet connection. A host computer running a custom application written in C++ provides a unified computer interface that allows the user to control all aspects of the system and provides a real time spectrogram. The system is designed for general use but has been initially used to study the ultrasonic vocalizations of rodents. We demonstrate the system by recording a well-established call made by Long-Evans rats termed 50-kHz vocalizations. The system was also designed with possible physical measurements in mind, e.g., distance, temperature, humidity, and gas mixture ratios.

Rapid Formation of Transparent Superhydrophobic Film on Glasses by He/CH4/C4F8Plasma Deposition at Atmospheric Pressure

A transparent superhydrophobic surface on glass is prepared by a rapid single-step method using a He, CH4, C4F8 mixture plasma at atmospheric pressure. Water droplet contact angles and surface properties are investigated to analyze both chemical and physical characteristics of the plasma treated surfaces. As the C4F8 gas flow rate is increased in the He/CH4 plasma, both advancing, and receding water contact angles are increased, while UV-visible transmittance is degraded. By optimizing the gas mixture ratio, we find rapid deposition conditions for superhydrophobic formation without losing the visible to near-infrared transparency of the glass. The chemical and physical mechanism responsible for hydrophobicity is also discussed through the investigation of chemical composition and surface morphology.

RETRACTED: Growth of boron-doped diamond nanoclusters using the HFCVD technique

Boron-doped diamond nanocrystals were grown on Si wafers through introduction of the gas mixture of B2O3 dissolved in ethanol and hydrogen by a hot filament chemical vapor deposition (HFCVD) technique. Boron level in diamond films were controlled in the range from 100 to 500 ppm by adjusting the B/C ratios of gas mixtures in order to synthesize and improve the conductivity and quality of HFCVD diamond films with cluster size of nanometer. To investigate the effect of different boron percentage in the chamber on deposited films, Raman spectroscopy, field emission scanning electron microscopy and four point probe techniques were applied to characterize the properties of diamond films. Experimental results indicated that higher boron incorporation in the diamond films introduced bigger crystal clusters, better crystal quality and smaller film resistivity when the level of boron increased from 100 to 300 ppm, while they showed an opposite trend with a further increase of boron level from 300 to 500 ppm. However, in any case the higher boron-doping level led to a decrease of the non-diamond phase in the nanodiamond films.

A bubble-based microfluidic gas sensor for gas chromatographs

We report a new proof-of-concept bubble-based gas sensor for a gas chromatography system, which utilizes the unique relationship between the diameters of the produced bubbles with the gas types and mixture ratios as a sensing element. The bubble-based gas sensor consists of gas and liquid channels as well as a nozzle to produce gas bubbles through a micro-structure. It utilizes custom-developed software and an optical camera to statistically analyze the diameters of the produced bubbles in flow. The fabricated gas sensor showed that five types of gases (CO2, He, H2, N2, and CH4) produced (1) unique volumes of 0.44, 0.74, 1.03, 1.28, and 1.42 nL (0%, 68%, 134%, 191%, and 223% higher than that of CO2) and (2) characteristic linear expansion coefficients (slope) of 1.38, 2.93, 3.45, 5.06, and 5.44 nL/(kPa (μL s(-1))(-1)). The gas sensor also demonstrated that (3) different gas mixture ratios of CO2 : N2 (100 : 0, 80 : 20, 50 : 50, 20 : 80 and 0 : 100) generated characteristic bubble diameters of 48.95, 77.99, 71.00, 78.53 and 99.50 μm, resulting in a linear coefficient of 10.26 μm (μL s(-1))(-1). It (4) successfully identified an injection (0.01 μL) of pentane (C5) into a continuous carrier gas stream of helium (He) by monitoring bubble diameters and creating a chromatogram and demonstrated (5) the output stability within only 5.60% variation in 67 tests over a month.

DEPOSITION CARBON NANOSTRUCTURES BY SURFATRON GENERATED DISCHARGE

Carbon nanostructures were deposited by surface wave discharge using various Ar/CH<sub>4</sub>/ CO<sub>2</sub> gas mixture ratios. The morphology was controlled by adjusting of gas concentration and was investigated by scanning electron microscopy (SEM). Also, the influence of the low temperature plasma treatment and process time on the wettability of the diamond films has been studied. The results indicate that for hydrogen termination of diamond surface indicate that the temperature as low as 400°C and treatment time of 15 min is sufficient to attain the p-type surface conductivity of diamond.

FCAW를 이용한 SM45C의 혼합가스비율에 따른 전류파형 및 용접특성 연구

This study, analyzed the waveform and mechanical properties of flux cored arc Welding on SM45C. <TEX>$CO_2$</TEX> 10% + Ar 90% shows the lowest standard deviation and shunt ratio at which the arc was most stable. <TEX>$CO_2$</TEX> 10% + Ar 90% is equal to <TEX>$CO_2$</TEX> 20% + Ar 80%. therefore, <TEX>$CO_2$</TEX> 20% + Ar 80% is the best of mixture gases. The hardness test result for the gas mixture ratio of <TEX>$CO_2$</TEX> 10% + Ar 90% was HV 249.7 which is the highest measured value. According to tensile test results, the tensile strength increased with increasing Ar in the mixture gas. This was because of the inertness of the argon, which does not combine with other elements, causing <TEX>$CO_2$</TEX> to combine with pearlite and ferrite and decreasing the maximum tensile strength. Microstructural examination results show that with increasing Ar, ferrite generation decreases while the mild microstructure increases which influences the hardness.