Glow Discharge Reactor Research Articles

Temperature Dependence of AC Electrical Conduction in Plasma Polymerized Pyrrole-N,N,3,5 Tetramethylaniline Bilayer Composite Thin Films

The temperature dependence of alternating current (ac) electrical conduction in Plasma Polymerized Pyrrole-N,N,3,5 tetramethylaniline (PPPy-PPTMA) bilayer composite thin films have been discussed in this article. The thin films were deposited by using a parallel plate capacitively coupled glow discharge reactor. To study the temperature dependence of ac electrical conduction the variation of dielectric constant (<i>ε</i>′), the dielectric loss factor (<i>ε</i>"), and the ac conductivity (<i>σ_ac</i>) of the thin films were investigated in the frequency range 100 Hz to 10 MHz and in the temperature range 298K to 398K. The decrease of dielectric constant <i>ε</i>′ with increasing frequency was observed and was attributed to the dielectric relaxation process. The dielectric constant, however, is observed to be increased with temperature in all frequency regions which is due to greater freedom of movement of dipole molecular chain in polymer films at high temperature. The variation of dielectric loss factor <i>ε</i>" with frequency showed a loss minimum then rises to a sharp peak which was also attributed to the relaxation phenomena of polymer. It is, however, observed that the loss peaks have shifted towards the higher frequency side with the increase of temperature which is usually attributed to dipolar orientation. The dielectric loss factor is also observed to be increased with temperature in all frequency regions. At lower frequencies the increase of loss factor with temperature was attributed to the effective chain motion of polymer and at high frequencies this increase might indicate the orientational polarization due to chain motion in bilayer film. The linear behavior of the ac conductivity <i>σ_ac</i> with the frequency and the observed weak temperature dependence of <i>σ_ac</i> led to interpret the ac conduction mechanism as the hopping between localized states at the Fermi level.

Effect of Argon on Decomposition in Micro-Slit Sustained Glow Discharge Reactor

The microdischarge decomposition devices have the advantages of a simple structure and low energy consumption and thus have a very promising future in in-situ resource utilization technology for Mars missions. It was found that the addition of Ar increased the conversion rate of in a micro-slit sustained glow discharge reactor. The experimental results showed that the breakdown voltage of Ar was significantly lower than that of in the micro-slit discharge, which indicated that the discharge breakdown channel was more likely to be generated. Thus, the addition of Ar to resulted in a lower breakdown voltage, and the discharge energy could be more distributed for decomposition. Spectral intensity analyses showed that, for mixture discharges, the presence of high-energy Ar excited states was clearly observed. With increasing discharge voltage, an increase in the light intensity of active components such as , O, and CO was observed. Combined with the discharge parameters and spectral characterization, it can be concluded that the metastable species of Ar exist and accumulate during the discharge, which contributes to the conversion of .

Comparative Study on the Direct Current Electrical Conduction in Monolayer and Bilayer Plasma Polymerized Thin Films

A comparative study on the nature of direct current electrical conduction in the monolayer and bilayer plasma polymerized thin films has been discussed in this article. The plasma polymerized pyrrole (PPPy) monolayer, plasma polymerized N,N,3,5-tetramethylaniline (PPTMA) monolayer and plasma polymerized pyrrole-N,N,3,5-tetramethylaniline (PPPy-PPTMA) bilayer thin films were deposited at room temperature onto glass substrates by using a parallel plate capacitively coupled glow discharge reactor. The current density-voltage (J-V) characteristics and the conductivity-voltage (σ-V) characteristics have been studied to analyze the direct current conduction mechanism in PPPy, PPTMA monolayer and PPPy-PPTMA bilayer thin films. The observed results have been presented in this paper. The J-V and σ-V characteristics of PPPy and PPTMA monolayer thin films of different thicknesses indicated an increase in electrical conduction and also an increase in conductivity in the films of lower thicknesses. It is also observed that PPTMA thin films are more conductive than that of PPPy thin films. As a result the PPPy-PPTMA bilayer thin films of different thicknesses and different deposition time ratios indicated an increase in conductivity as the proportion of PPTMA is increased in the films. In addition to that, from the J-V and σ-V characteristics of PPPy, PPTMA and PPPy-PPTMA thin films of same thickness, it is observed that the current conduction and the conductivity in the bilayer thin films is less compared to the monolayer thin films. This unusual result has been explained by studying ideal and real bilayer thin films. It is also seen that in the low voltage region, the current conduction obeys Ohm’s law while the charge transport phenomenon appears to be the space charge limited conduction (SCLC) in the higher voltage regions.

Morphological changes and kinetic assessment of Cu2O powder reduction by non-thermal hydrogen plasma

Non-thermal hydrogen plasma is a novel reducing medium that can yield H2 derived species capable of improving the reduction efficiency of metallic oxides when compared to a conventional reduction by hydrogen gas. To analyze the morphological changes of the samples and evaluate the impact of the plasma hydrogen species on the kinetic process, this work performed Cu2O powder reduction by non-thermal hydrogen plasma and compared it to hydrogen gas reduction at the same experimental conditions. The experiments were conducted in a pulsed direct current glow discharge reactor at pressure of 533 Pa, varying temperatures between 250°C and 400°C and reduction time intervals from 5 to 120 min. The results show that hydrogen plasma reduction is a faster process, reaching a higher degree of metallization of the Cu2O powder than hydrogen gas process in any reduction condition. Hydrogen plasma promotes a higher sintering degree of the newly formed porous copper particulates than hydrogen gas processing. The kinetic assessment of experimental data shows that plasma process kinetics are best-fitted to Prout-Tompkins’ nucleation model at temperature range from 300°C to 400°C, and to Jander's diffusion model at 250°C. On the other hand, gas process kinetics are best adjusted to Prout-Tompkins’ and JMAEK's models at 400°C and 350°C, respectively. The calculated apparent activation energy of plasma reduction is 19.06 kJ/mol at temperature range of 300°C – 400°C; whilst for gas reduction is 73.79 kJ/mol at temperature range of 350°C–400°C.

Development of a Swirl‐Induced Rotating Glow Discharge Reactor for CO2 Conversion: Fluid Dynamics and Discharge Dynamics Studies

Herein, CO2 conversion is conducted in a newly developed swirl flow–induced rotating glow discharge reactor. The swirl injector is designed to produce forward vortex by eight inclined guided vanes. A glow‐type rotating discharge is formed between two electrodes of constant height. The discharge and fluid dynamics studies reveal that the magnitude of tangential velocity and secondary vortex formation affects the rotational frequency of the discharge. It is also found that the anchoring point of the plasma column root is greatly influenced by the increased pressure gradient, especially in the turbulent regime. The conversion of CO2 as a function of flow rate is found to increase in the laminar regime and decrease in the turbulent regime. With increasing specific energy input from 0.25 to 3.4 kJ L−1, there is a rise in conversion from 1.2% to 4.6%, which indicates the high residence time and high energy deposition to lesser number of CO2 molecules. Higher energy efficiencies (54.9–63.7%) at turbulent flow rates show that this swirl design enhances the distribution of electron energy to incoming fresh molecules by formation of circulation zones and turbulence.

High efficiency CO2-splitting in atmospheric pressure glow discharge

Carbon Dioxide (CO2) utilization provides a valuable source of carbon for the sustainable production of fuels and chemicals. The splitting of CO2 can be performed in plasmas. It is highly endothermal, making energy efficiency an important design criterion. This paper presents a glow discharge reactor and appropriate power supply with low complexity and high efficiency, which can ignite and sustain a stable atmospheric pressure discharge of up to 20 mm length in a CO2 atmosphere. Glow-to-arc transition, which usually prohibits glow discharge operation at high pressures, is suppressed, leading to high overall efficiency. The maximum efficiency for the driver circuit was measured as 79 %. The reactor utilizes a permanent magnetic field to achieve a large and uniform discharge volume. High power densities of up to 100 W cm-3 and low electric field of less than 100 Vmm-1 in the bulk plasma were achieved, both of which are important criteria for efficient splitting of CO2. Efficiency measurements for the splitting of CO2 were performed and revealed a system energy efficiency of up to 22 %. Maximum conversion reached was 20 % at 14.4 % energy efficiency. This indicates that the presented technology is competitive with other approaches. Ways to further improve the system are presented and discussed.

Alternating Current Electrical Characterization of Plasma Polymerized Pyrrole Thin Films

The alternating current (ac) electrical characterization of plasma polymerized pyrrole (PPPy) thin films have been discussed in this article. A parallel plate capacitively coupled glow discharge reactor was used to deposit PPPy thin films. To study the ac electrical conduction in the thin film, the variation of ac conductivity and dielectric constant of different thicknesses were investigated as the function of frequency and temperature. The observed frequency dependence of the ac conductivity is attributed to relaxations caused by the motion of electrons, which could be involved to hopping or tunneling between equilibrium sites. It is also concluded that, the ac conduction mechanism in PPPy thin films shows the correlated barrier hopping (CBH) model. The strong dependence of conductivity on frequency and the low activation energies of the carriers are also an indication of a hopping conduction mechanism at low temperatures. At high temperatures it may be due to the movements of thermally excited carriers from energy levels within the band gap. In conductivity vs temperature study a weak dependence of σac on temperature is observed which interprets the ac conduction mechanism as the hopping between localized states at the Fermi level. The observed frequency dependence of the dielectric constant in this study is attributed to the interfacial or space charge polarization and to the orientational polarization of molecular chains. On the other hand, the strong temperature dependence of dielectric constant at higher temperature and lower frequencies is attributed to the thermally activated electron hopping mechanism.

Understanding the dielectric and electrical transport behaviors of plasma polymerized diethanolamine thin films under alternating electric field

A capacitively coupled parallel plate glow discharge reactor has been utilized to develop plasma polymerized diethanolamine (PPDEOA) thin films to look into the alternating current (AC) features of PPDEOA thin films. It is observed that the dielectric constant, ɛ′ in PPDEOA thin films enhances by declining the frequency and that increases with increasing temperature. The AC electrical conductivity, σac is frequency dependent. The frequency exponent, s values are found to be 0.32 to 1.0 and 1.0 to 1.8 in the lower (102–103 Hz) and higher (>103 Hz) frequencies, respectively. These suggest the presence of hopping conduction in the lower frequency region and other mechanisms in the higher frequency region. The activation energies are derived to be 0.03 to 0.28 eV illustrating the less effect of temperature on them. The real part, M´ and imaginary part, M ̋ of electric modulus vary with frequency. The frequency dependent loss tangent, tanδ is obtained. The ɛ′, σac , and tanδ deviate by the virtue of film thicknesses.

Experimental Study of CO2 Decomposition in a DC Micro-slit Sustained Glow Discharge Reactor

Carbon dioxide decomposition in a micro-slit sustained glow discharge reactor operated at low pressure of 8 Torr was studied experimentally. A specially designed reactor with a micro-slit configuration, combined with a third electrode that allows the extraction of electrons from the micro-slit discharge, was used to extend the glow discharge volume of the micro-slit discharge. It is found that, with the increase of the applied voltage of the third electrode, both the conversion fraction and energy efficiency of CO2 decomposition increase. The three-electrode structure was also extended to parallel operation to investigate the effects of applied voltage, flow rate, and number of parallel units on the conversion fraction and energy efficiency of CO2 decomposition. A maximum energy efficiency of 7.2% was achieved at a flow rate of 30 ml/min and power of 2.1 W for a single discharge unit, while for three discharges units connected in parallel, the maximum conversion fraction was 26.2% at a flow rate of 2 ml/min and power of 6.6 W. The results demonstrate the feasibility of parallel operation of the three-electrode micro-slit discharges, and increasing the number of parallel discharges increases both energy efficiency and conversion fraction at high flow rates. A better understanding of the physical and chemical kinetic processes will lead to optimization of future reactors to improve conversion and energy efficiency.

THERMAL AND AC ELECTRICAL PROPERTIES OF THIN FILMS PREPARED FROM n-BUTYL METHACRYLATE BY A CAPACITIVELY COUPLED PLASMA REACTOR

Plasma-polymerized thin films of n-butyl methacrylate (PPnBMA) have been deposited on to glass substrate in an aluminium/PPnBMA/aluminium configuration by a capacitively coupled glow discharge reactor. The field emission scanning electron microscope and atomic force microscope images of PPnBMA thin films showed a flat, uniform and continuous surface. With increasing deposition time the root mean square roughness of the PPnBMA thin films increases. The differential thermal analysis and thermogravimetric analysis demonstrated that PPnBMA was thermally stable up to about 476 and 500[Formula: see text]K in air and N2 environments, respectively. The alternating current (AC) electrical conductivity ([Formula: see text]) and dielectric properties of the PPnBMA thin films of thickness 120[Formula: see text]nm were investigated in the frequency region from 102–106[Formula: see text]Hz at various temperatures. It was found that the mechanism dependable for the conduction process in PPnBMA is hopping. The trend of dielectric constant ascends with ascending temperature and descends with frequency. The dielectric loss tangent is seen to increase with frequency and attains a maximum loss peak at around 105[Formula: see text]Hz and above this frequency it decreases. The plot of relaxation time against the reciprocal of absolute temperature for PPnBMA thin film yields the activation energy for dielectric relaxation at 0.05[Formula: see text]eV. Cole–Cole plot exhibits little distorted semicircle which also indicates nearly Debye type relaxation process in this film.

Atmospheric pressure glow discharge for CO2 conversion: Model-based exploration of the optimum reactor configuration

We investigate the performance of an atmospheric pressure glow discharge (APGD) reactor for CO2 conversion in three different configurations, through experiments and simulations. The first (basic) configuration utilizes the well-known pin-to-plate design, which offers a limited conversion. The second configuration improves the reactor performance by employing a vortex-flow generator. The third, “confined” configuration is a complete re-design of the reactor, which encloses the discharge in a limited volume, significantly surpassing the conversion rate of the other two designs. The plasma properties are investigated using an advanced plasma model.

Carrier transport behavior in as-deposited and iodine-doped plasma polymerized 2, 6-diethylaniline thin films

The temperature dependent electrical carrier transport properties of as-deposited and iodine-doped plasma polymerized 2, 6-diethylaniline (PPDEA) thin films of different thicknesses prepared using a capacitively coupled glow discharge reactor at room temperature were investigated. The FTIR analyses show that iodine doping process occurred at the quinoid units in the polyaniline backbone of PPDEA. The activation energy (ΔE) of both types of PPDEA thin films suggests hopping type conduction of carriers between the localized states at temperatures ranging from 298 K to 423 K. The ΔE in the higher temperature region suggests a thermally activated charge carrier transition mechanism in the energy band gap. The ΔE of as-deposited PPDEA thin films is higher for the applied voltages of 5 and 15 V as compared to those for the iodine-doped ones. The lower value of ∆E of iodine-doped PPDEA thin films indicates formation of charge-transfer-complex.

Thickness dependence of ac electrical conductivity and dielectric behavior of plasma polymerized 1, 1, 3, 3–tetramethoxypropane thin films

AC electrical conductivity (σac), dielectric constant (ɛ′), and dielectric loss tangent (tan δ) of plasma polymerized 1, 1, 3, 3‐tetramethoxy‐propane (PPTMP) thin films of thicknesses 100, 150, and 200 nm prepared by plasma polymerization technique using a capacitively coupled glow discharge reactor have been investigated in the frequency range of 30–106 Hz. It is observed that σac increases as frequency increases with a higher slope in the medium frequency (&lt;105Hz) region in the PPTMP thin films of three thicknesses. These observations suggest that the conduction may be dominated by hopping of carriers between the localized states. The general trend of ɛ′ is to increase with increasing thickness, ɛ′ remains independent of frequency upto about 104Hz and then falls rapidly. The dependence of tanδ with frequency for PPTMP thin films of different thicknesses showed small relaxation peak at the very low frequencies (&lt;102Hz) and then it decreases slightly with a broad minimum at 103 Hz and again increases. Cole–Cole plot reveals that Debye type of mechanism is operative in the experimental frequency range. POLYM. ENG. SCI., 58:1342–1345, 2018. © 2017 Society of Plastics Engineers

Structural, morphological, compositional and optical studies of plasma polymerized 2-furaldehyde amorphous thin films

Plasma synthesized 2-furaldehyde (PPFDH) amorphous polymer thin films of varying thicknesses were prepared in optimum conditions by a capacitively coupled parallel plate glow discharge reactor at room temperature. The structure, morphology, composition and optical properties of deposited PPFDH thin films have been investigated using X-Ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Scanning electron microscopy (SEM), Energy dispersive X-Ray spectroscopy (EDS), as well as Ultraviolet–visible (UV–vis) absorption spectroscopy. XRD results confirmed the amorphous nature of the films. The smooth and uniform nature of the PPFDH thin films were observed by SEM images. FTIR analyses of monomer FDH and PPFDH thin films show that structural rearrangement has occurred due to the synthesis process taking place in the chemical structure. IR stretching bands obtained from DFT calculations of the optimized structures of monomer and polymer of 2-furaldehyde are in good agreement with the experimental results. UV–vis absorption spectra in transmittance as well as reflectance mode was utilized to compute absorption coefficient, allowed direct and indirect transition energy gaps, band edge sharpness, Urbach energy, steepness parameter, extinction coefficient, and dispersion and oscillator energy. The oscillator strength, moments of optical spectra, refractive index at infinite wavelength, high frequency dielectric constant, average oscilator strength, complex refractive index, dissipation factor, optical conductivity and skin depth were also determined by using measured UV–vis transmittance and reflectance spectra.

Thiol surface functionalization via continuous phase plasma polymerization of allyl mercaptan, with subsequent maleimide‐linked conjugation of collagen

Thiol groups can undergo a large variety of chemical reactions and are used in solution phase to conjugate many bioactive molecules. Previous research on solid substrates with continuous phase glow discharge polymerization of thiol-containing monomers may have been compromised by oxidation. Thiol surface functionalization via glow discharge polymerization has been reported as requiring pulsing. Herein, continuous phase glow discharge polymerization of allyl mercaptan (2-propene-1-thiol) was used to generate significant densities of thiol groups on a mixed macrodiol polyurethane and tantalum. Three general classes of chemistry are used to conjugate proteins to thiol groups, with maleimide linkers being used most commonly. Here the pH specificity of maleimide reactions was used effectively to conjugate surface-bound thiol groups to amine groups in collagen. XPS demonstrated surface-bound thiol groups without evidence of oxidation, along with the subsequent presence of maleimide and collagen. Glow discharge reactor parameters were optimized by testing the resistance of bound collagen to degradation by 8 M urea. The nature of the chemical bonding of collagen to surface thiol groups was effectively assessed by colorimetric assay (ELISA) of residual collagen after incubation in 8 M urea over 8days and after incubation with keratinocytes over 15days. The facile creation of useable solid-supported thiol groups via continuous phase glow discharge polymerization of allyl mercaptan opens a route for attaching a vast array of bioactive molecules. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 1940-1948, 2017.

Tuning the Surface Properties of Oxygen-Rich and Nitrogen-Rich Plasma Polymers: Functional Groups and Surface Charge

Controlling the concentration and nature of functional groups in plasma polymer films by adjusting the flow ratio of constituent precursor gases can be exploited to tune the surface charge of the resulting coating. Plasma polymer films containing various concentrations of nitrogen and oxygen functional groups were deposited in a low-pressure capacitively-coupled glow discharge reactor by plasma polymerization of binary gas mixtures of a hydrocarbon (ethylene or butadiene) and a heteroatom source gas (ammonia and/or carbon dioxide). Increasing the flow ratio of heteroatom to hydrocarbon gases increased the concentration of bonded nitrogen or oxygen, including that of primary amine or carboxylic groups as determined by X-ray photoelectron spectroscopy and chemical derivatization procedures. The zeta potential of samples was measured using an electro-kinetic analyser in a diluted sodium chloride solution. The deposition parameters controlled the composition of the coatings, allowing to tune the surface charge to either positive (ammonia based films)—or negatively (carbon dioxide base films) values at physiological pH.

Effects of Oxygen Plasma Treatment on the Wettability of Polypropylene Fabrics

The objective of this study is to give PP(polypropylene) fabric a good affinity for water. Oxygen plasma was treated to PP fabrics in a commercial glow discharge reactor with different RF power, discharge pressure, and reaction time. The PP fiber surfaces were characterized by the measurement of contact angle and ESCA. A JEOL scanning electron microscope was used to observe the surface morphology of fibers. The spontaneous water uptake amount of PP fabrics was determined by the demand wettability test. To determine the effect of aging on the surface properties of <TEX>$O_2$</TEX> plasma treated PP, all the above measurements of the samples were carried out after 1, 7, 30, 60, and 150 days. The results are as follows. The PP fiber surfaces treated by <TEX>$O_2$</TEX> plasma treatment have a chemical composition that consisted of various oxygen containing polar groups. Consequently, the contact angles of the treated PP fibers decreased, which improved the water uptake rate of PP fabrics. Surface roughness of the treated PP affected the fabric wettabiity as well. Wettability of the treated PP decreased and leveled off with aging. The <TEX>$O_2$</TEX> plasma treatment is a simple and effective method to increase the water uptake rate of PP fabrics.

Effect of self-bias voltage on the wettability, chemical functionality and nanomechanical properties of hexamethyldisiloxane films

Copper and silicon substrates were coated by chemical vapor deposition using hexamethyldisiloxane (HMDSO) as the precursor gas. Substrates were placed both at the anode and cathode of a glow discharge reactor, and films were deposited using different self-bias voltages. This study focuses on comparing the differences between the hydrophilicity, polymeric character, chemical structure and nanomechanical properties of HMDSO films produced at the cathode and anode of the reactor at different self-bias voltages. Fourier transform infrared spectroscopy and Raman confocal spectroscopy indicated a significant increase in the content of organic groups when films were deposited at the anode. Analyzing the nanomechanical properties of the cathode and anode films indicated that the penetration depth was higher for samples prepared at the cathode (lower hardness) compared with the samples produced at the anode. The measured contact angles indicated that all samples became hydrophobic with water contact angles close to 100°; however, a different lyophobic character was observed when diiodomethane was used. Films produced at the anode with diiodomethane exhibited higher contact angles than did films produced at the cathode.

Alternating Current Electrical Properties of Thin Films of Plasma Polymerized 1, 1, 3, 3‐Tetramethoxypropane

ABSTRACTPlasma‐polymerized 1, 1, 3, 3‐tetramethoxy‐propane (PPTMP) thin films are prepared by using a capacitively coupled glow discharge reactor. The dielectric constant and the alternating current (AC) electrical conductivity of the PPTMP thin films are investigated in the frequency range from 30 to 104 Hz, and in the temperature range from 298 to 423 K. The AC electrical conduction mechanism in the PPTMP thin films is observed to be dominated by hopping of carriers between localized states. The trend of dielectric constant is to decrease slowly with the increasing frequency. The dielectric constant is weakly dependent on temperature (T). The dielectric loss tangent, tanδ decreases slightly with a broad minimum around 103 Hz and again increases with increasing frequency. © 2013 Wiley Periodicals, Inc. Adv Polym Technol 2014, 33, 21394; View this article online at wileyonlinelibrary.com. DOI 10.1002/adv.21394

Reduction of Cr(VI) in aqueous solution with DC diaphragm glow discharge

This paper investigated the reduction of Cr(VI) in aqueous solution with direct current diaphragm glow discharge (DGD). The glow discharge sustained around the hole on a quartz tube which divided the electrolyte cell into two parts. The reduction efficiencies of Cr(VI) under different applied voltages, initial conductivities, hole diameters, hole numbers, initial pH values and initial concentrations were systematically studied. The results showed that the reduction efficiency of Cr(VI) increased with the increase of applied voltage, initial conductivity, hole diameter and hole number. The different initial pH values showed less effects on the reduction of Cr(VI). The reduction efficiency decreased with the increasing initial concentration. In addition, the simultaneous reduction of Cr(VI) and decolorization of acid orange (AO) with DGD were also fulfilled. Furthermore, the energy efficiency for Cr(VI) reduction with DGD was calculated and compared with those in photocatalysis and other glow discharge reactor.