Radio Frequency Oxygen Plasma Research Articles

Germination and Growth of Plasma-Treated Maize Seeds Planted in Fields and Exposed to Realistic Environmental Conditions.

In this study, we applied an inductively coupled, radio frequency oxygen plasma to maize seeds and investigated its effects on seedling emergence, plant number at tasseling, and crop yield of maize in realistic field conditions. Maize seeds of seven different hybrids were treated over two harvest years. In addition to plasma-treated seeds, a control sample, fungicide-treated seeds, an eco-layer, and a plasma and eco-layer combination, were planted. Seedling emergence, plant number at tasseling (plants/m2), and yield (kg/ha), were recorded. In the first harvest year, results were negatively affected by the presence of an insect pest. In the second harvest year, plant number and yield results were more uniform. In both years, for two and three hybrids, respectively, the highest yield arose from plants from plasma-treated seeds, but the differences were only partially significant. Considering our results, plasma treatment of maize seeds appears to have a positive effect on the yield of the plant.

An Experimental Anodized Titanium Surface for Transgingival Dental Implant Elements-Preliminary Report.

The characteristics such as microtopography, physical and chemical properties influence the behavior of an implant in a soft tissue. Anodization-as a potent method of titanium alloy surface modification-of the transgingival abutment or healing screw, has achieved some improvement. One of the possible surface treatment method is low-pressure radiofrequency oxygen plasma treatment. The aim of the study was to evaluate the chemical properties and cytocompatibility of the experimental surface. Titanium discs made of grade-23 titanium alloy (Ti-6Al-4V) anodized (A sample) with different voltage parameters (28, 67, 78, and 98 V) were included in the study. Half of the samples regarded as the "S" group were additionally treated with low-pressure radiofrequency oxygen plasma treatment. The surfaces were characterized using scanning electron microscopy, X-ray spectroscopy and Raman spectroscopy, and electrochemically investigated via a corrosion test. Furthermore, two cell lines were used, including the CHO-compatible reference line and a primary human fibroblast line for the MTT assay; direct (contact) cytotoxicity of the materials was tested with the cells, and the growth of fibroblasts on the surfaces of the different materials was tested. The morphology of the "S"-treated samples did not differ from the morphology of only-anodized samples. However, the oxygen concentration on the surface in that group slightly increased by about 1% as a result of post-trial treatment. The highest corrosion resistance was observed for both A-78 V and S-78 V samples. The cytotoxicity assay revealed no changes in cell morphology or vitality. The MTT test proved comparable culture viability among all groups; however, the "S" samples showed statistically significantly higher fibroblast proliferation and adhesion scores compared to the "A" samples. Through the in vitro study, the low-pressure radiofrequency oxygen plasma treatment of the anodized Ti-6Al-4V alloy presented itself as an auspicious option in the field of transgingival element surface modification of implants.

Effect of Oxygen Plasma Treatment on Wheat Emergence and Yield in the Field.

This paper investigates the effects of an inductively coupled, radio frequency oxygen plasma on the plant emergence and crop yield of wheat in field growth conditions. Wheat seeds of eight different cultivars were plasma-treated using conditions selected based on preliminary experiments. Additionally, a control sample, as well as seeds treated with fungicide, an eco-layer, or a plasma + eco-layer combination, were planted in parallel. Four cultivars per harvest year were used. Plant emergence (plants/m2) and yield (kg/ha) were followed. There was little variation among the control and the various treatments regarding plant emergence. Regarding yield, there were statistically significant differences, but no discernible trend was seen when comparing the individual treatments. In the case of several cultivars, plasma-treated seeds performed as well as the control, but there was a significant increase in yield only in the case of cultivar 88.5 R. In several cases, yield of plants for plasma-treated seeds was also lower than the control. Our results demonstrate that the response of wheat yield to plasma treatment, as well as to other seed treatments, differs depending on the wheat cultivar.

The Influence of Glow and Afterglow Cold Plasma Treatment on Biochemistry, Morphology, and Physiology of Wheat Seeds.

Cold plasma (CP) technology is a technique used to change chemical and morphological characteristics of the surface of various materials. It is a newly emerging technology in agriculture used for seed treatment with the potential of improving seed germination and yield of crops. Wheat seeds were treated with glow (direct) or afterglow (indirect) low-pressure radio-frequency oxygen plasma. Chemical characteristics of the seed surface were evaluated by XPS and FTIR analysis, changes in the morphology of the seed pericarp were analysed by SEM and AFM, and physiological characteristics of the seedlings were determined by germination tests, growth studies, and the evaluation of α-amylase activity. Changes in seed wettability were also studied, mainly in correlation with functionalization of the seed surface and oxidation of lipid molecules. Only prolonged direct CP treatment resulted in altered morphology of the seed pericarp and increased its roughness. The degree of functionalization is more evident in direct compared to indirect CP treatment. CP treatment slowed the germination of seedlings, decreased the activity of α-amylase in seeds after imbibition, and affected the root system of seedlings.

Surface Modifications of Wheat Cultivar Bologna upon Treatment with Non-Equilibrium Gaseous Plasma.

Seeds of wheat cultivar Bologna were treated with a low-pressure, inductively coupled, radio frequency oxygen plasma. E-mode and H-mode plasma at the real powers of 25 and 275 W, respectively, was used at treatment times of 0.1–300 s. Plasma affected seed surface chemistry, determined by XPS, and surface topography, visualized by SEM. The combined effects of functionalization and etching modified seed surface wettability. The water contact angle (WCA) exponentially decreased with treatment time and correlated with the product of discharge power and treatment time well. Super-hydrophilicity was seen at a few 1000 Ws, and the necessary condition was over 35 at.% of surface oxygen. Wettability also correlated well with O-atom dose, where super-hydrophilicity was seen at 1024–1025 m−2. A relatively high germination percentage was seen, up to 1000 Ws (O-atom dose 1023–1024 m−2), while seed viability remained unaffected only up to about 100 Ws. Extensively long treatments decreased germination percentage and viability.

Wettability and Water Uptake Improvement in Plasma-Treated Alfalfa Seeds

The cultivation of alfalfa (Medicago sativa L.), a forage crop grown worldwide, is negatively affected by hard seed presence. We show that treatment of alfalfa seeds with an inductively coupled radio frequency oxygen plasma improves their surface hydrophilicity, as determined by water contact angle (WCA) measurements and water uptake. Furthermore, we see that these effects are mediated by functionalization and etching of the alfalfa seed surface. Surface chemistry is analyzed by X-ray photoelectron spectroscopy (XPS), while morphology is viewed using scanning electron microscopy (SEM). Plasma produces effective alfalfa seed hydrophilization with a variety of treatment parameters. With its potential for fine-tuning, plasma modification of seed wettability shows promise for introduction into agricultural practice.

Modulation of interfacial interactions toward strong and tough cellulose nanofiber-based transparent thin films with antifogging feature

Cross-linking is often performed to overcome the weak mechanical properties of native polymer films in order to expand their functional properties and applications. While this approach offers enhanced strength to the film, the film also suffers from low flexibility, low toughness and high brittleness. However, in view of the growing demand for strong and tough transparent thin films, this article reported our study to develop films made from cellulose nanofiber (CNF) via tailoring the interfacial bonding interactions through the application of glycerol (Gly) and glutaraldehyde (GA), which functioned as a plasticizer and cross-linking agent, respectively. Among the prepared films, the 10GA-8Gly-CNF film exhibited the best results with regard to the enhancement in the tensile strength (21.1%), Young's modulus (10.6%), elongation at break (100%) and toughness (32.7%), as compared to the native CNF film. Importantly, treating the surface of the film to radiofrequency oxygen plasma endowed the film with antifogging property, without compromising the optical clarity.

Multivariate Correlation Analysis of the Electroconductive Textiles Obtained Using Functionalization by Radio-Frequency Oxygen Plasma Treatments.

This paper presents a study concerning the preliminary treatments in radiofrequency (RF)oxygen (O2) plasma used to obtain a hydrophilic effect on raw cotton fabrics followed by electroconductive thin film deposition to obtain electroconductive textile surfaces. In addition, this study presents a multivariate correlation analysis of experimental parameters. The treatment using RF plasma O2 aimed to increase the hydrophilic character of the raw fabric and adherence of paste-based polymeric on polyvinyl alcohol (PVA) matrix and nickel (Ni), silver (Ag) or copper (Cu) microparticles. The purpose of the research was to develop electroconductive textiles for flexible electrodes, smart materials using a clean technology such as radiofrequency (RF) plasma O2 to obtain a hydrophilic surface with zero wastewater and reduced chemicals and carbon footprint. To achieve the foreseen results, we used advanced functionalization technologies such as RF plasma O2, followed by scraping a thin film of conductive paste-based Ni, Ag or Cu microparticles, and multivariate correlation methods to observe the dependence between parameters involved (dependent and independent variables). Overall, the fabrics treated in plasma with O2 using a kHz or MHz generator and power 100–200 W present an excellent hydrophilic character obtained in 3 min. After RF O2 plasma functionalization, a thin film based on polymeric matrix PVA and Ni microparticles have been deposited on the fabric surface to obtain electroconductive materials.

Probing negative ions and electrons in the afterglow of a low-pressure oxygen radiofrequency plasma using laser-induced photodetachment

This paper reports on the further development and improvement of time-resolved laser-induced photodetachment in concert with microwave cavity resonance spectroscopy. The method is applied to measure—with microsecond time resolution—the decaying density of negative oxygen ions (O−, O, and O) and that of free electrons in the afterglow of a pulsed capacitively coupled radiofrequency-driven oxygen plasma. The afterglow behavior of the electrons shows a significant dependence on the gas pressure between 3 Pa and 6 Pa. For a pressure of 3 Pa, at which the plasma is in the so-called γ-mode, the decay of the negative ion density is slower than that of the electron density, eventually leading to the occurrence of a negative-ion-positive-ion plasma. At a slightly elevated pressure of 6 Pa (and higher), the plasma transits into the so-called α-mode, in which a short period of increased electron density is detected just after switching off the plasma. In the α-mode, the negative ion and electron densities decay within similar timescales, leading to the trapping of negative ions. In this pressure range, the decay of the additional electron density released by the photodetachment of negative ions occurs according to two distinct timescales. However, for increasingly elevated pressures above 10 Pa, the photodetachment signal is characterized by decay with an undershoot, which may indicate a temporary local disturbance of the plasma’s quasi-neutrality in the volume irradiated by the laser beam.

Response of Two Different Wheat Varieties to Glow and Afterglow Oxygen Plasma.

Cold plasma technology has received significant attention in agriculture due to its effect on the seeds and plants of important cultivars, such as wheat. Due to climate change, wherein increasing temperatures and droughts are frequent, it is important to consider novel approaches to agricultural production. As increased dormancy levels in wheat are correlated with high temperatures and drought, improving the germination and root growth of wheat seeds could offer new possibilities for seed sowing. The main objective of this study was to evaluate the influence of direct (glow) and indirect (afterglow) radio-frequency (RF) oxygen plasma treatments on the germination of two winter wheat varieties: Apache and Bezostaya 1. The influence of plasma treatment on seed surface morphology was studied using scanning electron microscopy, and it was observed that direct plasma treatment resulted in a high etching and nanostructuring of the seed surface. The effect of plasma treatment on germination was evaluated by measuring the germination rate, counting the number of roots and the length of the root system, and the fresh weight of seedlings. The results of this study indicate that the response of seeds to direct and indirect plasma treatment may be variety-dependent, as differences between the two wheat varieties were observed.

Bio-composites from banana tree fibers ambient with multi-walled carbon nanotubes: manufacturing and properties

A biodegradable composite fibers have been fabricated from easily available banana tree fibers (BTFs) using a simple dip-drying technique, where carbon nanotubes (CNTs) are used as reinforcing agent. A safe radio frequency oxygen plasma processing method is used to functionalize the surface of the CNTs with hydrophilic oxygen-containing group. The fibers are chemically treated with NaOH followed by oxygen plasma treatment to increase the heat conduction between the fibers in thermal contact. The implications of incorporating CNTs in the BTFs are observed by studying the surface morphology, structural, thermal, electrical and mechanical properties. The homogeneous CNT coverage on the BTFs surface is featured by the scanning electron micrographs of the CNT/treated BTF. The crystallinity index is exposed through X-ray diffraction analysis, which indicates the crystalline feature of the nanocomposites. The surface modification by CNT treatment has improved the thermal stability and flame retardancy of BTFs. A gradual decrease of resistivity of these composite fibers is observed from 5.69 to 0.0021 Ω m by increasing the number of dip-drying cycle of BTFs in the CNTs solution. The electrical conductivity of the CNT/treated BTF becomes 163.75 S/m under the applied voltage of 100 V. The developed composite fibers exhibit an increase in the mechanical strength with the CNT coating. Therefore, the developed CNT-reinforced composite fibers affirm its aptitude as reliable reinforcement in electronic devices and as conductive fillers in composites industries.

Carbon Nanotube Reinforced Natural Fibers for Biodegradable Nanocomposites

Natural fiber-reinforced nanocomposites (NFRCs) are proved as the best alternative for synthetic composites in view of cost and environmental effects. NFRCs have been produced from agro-waste such as banana tree fiber (BFs), because of BF are strong, light-weight, have smaller elongation. To improve the quality of BF, multiwall carbon nanotubes (MWCNTs) are used as reinforcing filler, which are functionalized by an ecofriendly radio frequency oxygen plasma processing method. cellulose nano-crystals (CNC) is extracted from BFs by double hydrolysis process and a simple dip-drying technique has been used to produce NFRCs. Field emission scanning electron micrographs and transmission electron microscopy conform the well dispersion of MWCNTs in the BF matrix. Thermal stability and mechanical strength of the NFRCs are improved owing to the incorporation of MWCNTs. Functional groups in the BFs, CNC and NFRCs are investigated by Fourier transform infrared spectroscopy. The current density of the sample is increased 1000 times and conductivity increases up to 17 Sm−1, which increases with temperature. Therefore, these light-weight biodegradable NFRCs encourage its ability as cost effective industrial conductive composite as usable in electronic devices.

Carbon Nanotube Reinforced Natural Fibers for Biodegradable Nanocomposites

Natural fiber-reinforced nanocomposites (NFRCs) are proved as the best alternative for synthetic composites in view of cost and environmental effects. NFRCs have been produced from agro-waste such as banana tree fiber (BFs), because BF are strong, light-weight, and have smaller elongation. To improve the quality of BF, multiwall carbon nanotubes (MWCNTs) are used as reinforcing filler. MWCNTs are functionalized by an ecofriendly radio frequency oxygen plasma processing method. Cellulose nano-crystals (CNC) are extracted from BFs by double hydrolysis process and a simple dip-drying technique has been used to produce NFRCs. Field emission scanning electron micrographs and transmission electron microscopy conform the well functionalization of MWCNTs and also ensure homogeneous incorporation in the BF matrix. The composites continue thermally stable corresponding to BFs. Mechanical strength of the NFRCs are improved owing to the incorporation of MWCNTs. Functional groups in the BFs, CNC and NFRCs are investigated by Fourier transform infrared spectroscopy. The current density of the sample is increased 1000 times than the raw fibers and conductivity increases up to 17 Sm^-1, which increases with temperature under the applied voltage 100 V and shows the linier characterization. Therefore, these light-weight biodegradable NFRCs encourage its ability as cost effective industrial conductive composite as usable in electronic devices.

Plasma-induced grafting of polyaniline on polyester fabric for gas sensing application

In this work, we have grafted Polyaniline (PANI) on polyester fabric by Chemical oxidative polymerization of aniline monomer using Ammonium per sulphate (APS) as oxidant and Sodium salt of dodecyl benzene sulfonic acid (DBSA) as a co-dopant. For better deposition and adhesion of PANI on the surface of polyester fabric, low-pressure radio frequency (RF) oxygen (O2) plasma treatment is applied to the fabric prior to grafting of PANI. Characterization of conducting fabrics is done using ATR-FTIR Spectroscopy, Scanning electron microscopy (SEM), Contact angle measurement, X-ray Photoelectron spectroscopy (XPS) and Sheet resistance measurement. It is observed that O2 plasma treatment enhances uniformity of grafting, conductivity and gives strong interfacial bonding of PANI on the surface of polyester fabric. O2 plasma-treated fabrics followed by grafting with PANI was then investigated for detection of ammonia gas.

Oxidation of Au/Ag films by oxygen plasma: phase separation and generation of nanoporosity.

The oxidation of Au/Ag alloy thin films using radio-frequency oxygen plasma was studied in this work. It was demonstrated that there is a phase separation occurring between silver and gold. In addition, it was shown that the preferential oxidation of silver resulted in a solid-state diffusion of silver toward the surface where it oxidized and formed nanoporous microspheres. The gold phase remaining in the film exhibited nanoporosity due to the injected vacancies at the metal/silver oxide interface. Based on the scanning transmission electron microscopy analysis coupled with energy dispersive X-ray mapping a mechanism was proposed based on solid-state diffusion and the Kirkendall effect to explain the different steps occurring during the oxidation process.

Plasma-Assisted Grafting of PPY on Polyester Fabric as Gas Transducer

In this study, we have grafted polypyrrole (PPY) on polyester fabrics by chemical oxidative polymerization of pyrrole using ferric chloride (FeCl3) as oxidant and sodium dodecyl benzene sulfonate as a dopant. Polyester fabric treated with radio frequency oxygen plasma prior to grafting of PPY showed better deposition and adhesion. Characterization of both untreated and plasma-treated conducting fabrics was done using ATR-FTIR, XPS, SEM, contact angle, and sheet resistance measurement. It was found that higher amount of PPY with uniform grafting, better conductivity, and strong interfacial bonding of PPY on the surface of polyester fabric was accomplished by oxygen plasma treatment. Such oxygen plasma pretreated PPY grafted polyester fabrics were then tested for detection of ammonia gas.

Reduction of unintentional Si doping in β-Ga2O3 grown via plasma-assisted molecular beam epitaxy

The authors investigate unintentional Si doping in β-Ga2O3 thin films grown via plasma-assisted molecular beam epitaxy. By identifying the Si dopant cell and the radio frequency oxygen plasma source as the two major sources of unintentional Si present in the growth chamber, adjustments to the parameters controlling these sources allow for the reduction of unintentional Si doping in β-Ga2O3 films by over two orders of magnitude. Decreasing the temperature of the Si dopant cell when idle reduces the unintentional doping from 2 × 1018 to 3 × 1017 cm−3. Furthermore, decreasing the oxygen plasma power from 300 to 250 and to 200 W results in the reduction of the unintentional Si doping from 3 × 1017 to 1 × 1016 cm−3. The reduction in unintentional Si doping concentration allows for low doping density in the drift region of β-Ga2O3 devices to design for high breakdown voltage via plasma-assisted molecular beam epitaxy.

Electron power absorption in low pressure capacitively coupled electronegative oxygen radio frequency plasmas

A thorough understanding of the energy transfer mechanism from the electric field to electrons is of utmost importance for optimisation and control of different plasma sources and processes. This mechanism, called electron power absorption, involves complex electron dynamics in electronegative capacitively coupled plasmas (CCPs) at low pressures, that are still not fully understood. Therefore, we present a spatio-temporally resolved analysis of electron power absorption in low pressure oxygen CCPs based on the momentum balance equation derived from the Boltzmann equation. Data are obtained from 1d3v particle-in-cell/Monte Carlo Collision simulations. In contrast to conventional theoretical models, which predict ‘stochastic/collisionless heating’ to be important at low pressure, we observe the dominance of Ohmic power absorption. In addition, there is an attenuation of ambipolar power absorption at low pressures due to the strong electronegativity, and the presence of electropositive edge regions in the discharge, which cause a high degree of temporal symmetry of the electron temperature within the RF period.

Effect of Oxygen Plasma on Sprout and Root Growth, Surface Morphology and Yield of Garlic.

Depending on the climate, garlic can be planted either in the fall or spring for a harvest in the summer, but spring planting might require the strengthening of the plant by external techniques. We have used low pressure, inductively coupled, radio frequency oxygen plasma for the treatment of peeled garlic cloves of a spring-planted Slovenian autochthonous cultivar. The aim of the study was to assess the effects of plasma treatment on garlic clove shoot and root growth and, ultimately, the yield. The roles of surface chemistry, surface morphology, and water uptake in these effects were also evaluated. The plasma treatment of cloves induced increases in water uptake. The increases were explained by changes in surface morphology that were determined by using scanning electron microscopy (SEM) and atomic force microscopy (AFM). Nanostructured epicuticular wax structures appeared at the cuticle surface. The optimal treatment parameters accelerated root growth, but not shoot growth, in a laboratory setting. After growth in the field, the trends indicated that plant height and dried bulb mass increase, but the improvements were not statistically significant.

Surface Modification and Aging of Polyacrylonitrile Butadiene Styrene Polymer Induced by Treatment in RF Oxygen Plasma

Polyacrylonitrile butadiene styrene (ABS) was treated in a radio frequency oxygen plasma created at various powers in two discharge modes (E-mode and H-mode). After plasma treatment, which lasted for 2 s, the samples were analyzed using X-ray photoelectron spectroscopy, atomic force microscopy, and contact angle measurements, whereas plasma was characterized by an optical emission spectroscopy. The E-mode allowed for gentle functionalization, whereas the H-mode also for extensive etching. The water contact angle (WCA) dropped to approximately 20° even for the lowest power of 50 W (E-mode) and remained unchanged up to approximately 600 W (H-mode) when it started increasing slightly. Contradictory, the oxygen concentration on the surface was a few at% higher in the H-mode. Furthermore, a removal of the original CN groups in ABS surface layer was observed after treatment in the H-mode, indicating intense surface etching and degradation. All samples exhibited rapid hydrophobic recovery because the WCA increased up to 27° and 42° in one day for E-mode and H-mode, respectively. The recovery was slower when samples were stored in a fridge.