Increasing Plasma Treatment Time Research Articles

Argon Plasma Jet-Treated Poly (Vinyl Alcohol)/Chitosan and PEG 400 Plus Mangifera indica Leaf Extract for Electrospun Nanofiber Membranes: In Vitro Study.

The wound-healing process can be disrupted at any stage due to various internal and external factors. The inflammatory stage of the process plays a vital role in determining the outcome of the wound. Prolonged inflammation due to bacterial infection can lead to tissue damage, slow healing, and complications. Wound dressings made using materials such as poly (vinyl alcohol) (PVA), chitosan (CS), and poly (ethylene glycol) (PEG) with Mangifera extract (ME) added can help reduce infection and inflammation, creating a conducive environment for faster healing. However, creating the electrospun membrane is challenging due to balancing various forces such as rheological behavior, conductivity, and surface tension. To improve the electrospinnability of the polymer solution, an atmospheric pressure plasma jet can induce chemistry in the solution and increase the polarity of the solvent. Thus, this research aims to investigate the effect of plasma treatment on PVA, CS, and PEG polymer solutions and fabricate ME wound dressing via electrospinning. The results indicated that increasing plasma treatment time increased the viscosity of the polymer solution, from 269 mPa∙to 331 mPa∙s after 60 min, and led to an increase in conductivity from 298 mS/cm to 330 mS/cm and an increase in nanofiber diameter from 90 ± 40 nm to 109 ± 49 nm. Incorporating 1% mangiferin extract into an electrospun nanofiber membrane has been found to increase the inhibition rates of Escherichia coli and Staphylococcus aureus by 29.2% and 61.2%, respectively. Additionally, the fiber diameter decreases when compared with the electrospun nanofiber membrane without ME. Our findings demonstrate that electrospun nanofiber membrane with ME has anti-infective properties and can promote faster wound healing.

Stretchable silver electrodes adopting double stress release design directly deposited on an eco-flex substrate

In this paper, stretchable electrodes adopting a double stress release structure were fabricated and characterized on eco-flex substrates. First, the correlation between mechanical properties applying surface plasma treatment and stretching capability of stretchable silver electrodes directly deposited on eco-flex substrate was studied. The Young’s modulus values of the substrate and metal were extracted using the force-distance relation via atomic force microscopy employing Johnson–Kendall–Roberts model. It was found that, as the Young’s modulus increased with the increase of plasma treatment time, the stretching capability first improved; then, samples showed no improvement over long plasma treatment time. This indicates that there is an optimum plasma treatment time to simultaneously achieve high stretching capability and low initial resistance. Using the optimum time, stretchable silver electrodes adopting double stress release structure along lateral and vertical directions were fabricated and the high stretching capability of the silver electrodes was achieved up to tensile strain of about 160%, as was high stability of up to 1000 times the multi-cycling strain.

Plasma-Initiated Grafting of Bioactive Peptide onto Nano-CuO/Tencel Membrane.

A bioactive peptide has been successfully grafted onto nano-CuO impregnated Tencel membranes by a simple and rapid method involving a series of textile processes, and an atmospheric argon plasma treatment that requires no additional solvent or emulsifier. Surface morphology shows an apparent change from smooth, slightly roughened, and stripped with increasing plasma treatment time. The FT-IR characteristic peaks confirm the presence of the CuO nanoparticle and peptide on the extremely hydrophilic Tencel membranes that exhibit a zero-degree contact angle. Prepared nano-CuO/Tencel membranes with 90 s plasma treatment time exhibit excellent antimicrobial activity against E. coli and S. aureus, and promote fibroblast cell viability with the assistance of a grafted bioactive peptide layer on the membrane surface.

Photoluminescence quenching of CVD grown WS2 monolayers treated with low-power Ar plasma

Defect engineering in two-dimensional materials is of high importance to improve a specific property of such materials. By introducing defects directly in the lattice, by means of ion doping or vacancies, it is possible to optimize the structure for a target application, such as high-performance batteries, catalysis, or optoelectronics. Herein, monolayer WS2 was synthesized by chemical vapor deposition and was subsequently subjected to Ar plasma treatment. The changes in properties were monitored using Raman spectroscopy, photoluminescence (PL) spectroscopy, X-ray photoelectron spectroscopy, and atomic force microscopy. The influence of defects resulted in a variation in the intensity of the PL signal, as well as a progressive redshift owing to an increase in the defect density with increasing plasma treatment time, and through the analysis of the PL and Raman spectra one can quantify the evolution of defects in the WS2 monolayers due to the treatment.

Effect of plasma treatment parameters on the interfacial joining strength of overmolded hybrid fiber reinforced thermoplastic composites

AbstractIn this study, hybrid fiber reinforced thermoplastic composites (hybrid thermoplastic composites) with high interfacial joining strength were fabricated using a plasma treatment strategy and injection overmolding technique. A series of experimental investigations were carried out to ascertain the effects of various plasma treatments on the interfacial joining strength of the overmolded hybrid composites. Test results reveal that compared with the untreated continuous fiber reinforced thermoplastic (CFRT) substrates, the surface roughness of the CFRT substrates treated by plasma with air for the 10 min–160 W set‐up increases by 28.7%, the contact angle decreases by 50.5%, the silicon and fluorine are effectively removed, and the content of polar functional group increases remarkably, which bring about the increase of 24.76% of the interfacial shear strength of the overmolded hybrid composites. Further increase of plasma treatment time does not contribute to increase the interfacial shear strength of the overmolded hybrid composites. The interfacial shear strength at 60 W is 6.38% higher than that at 160 W, which is ascribed to the increase of the oxygen‐containing functional group content. Compared with the air and nitrogen plasma treatment, the interfacial shear strength of the overmolded hybrid composites after oxygen plasma treatment reaches the maximum value.

Plasma-assisted ITO sol coating for optimizing the optoelectronic properties of ITO glass

The argon atmospheric pressure plasma treatment is combined with the conventional sol-gel dip-coating process for fabricating ITO thin films to improve the electrical property of the ITO glass. The increase of the surface free energy of the ITO layer by plasma treatment improves the adhesion of the pre-annealed ITO layer, thereby increasing the thickness of the ITO film without significantly losing the light transmittance. While increasing the plasma treatment time up to 240 s, both the thickness and surface free energy of the ITO layer are increased, and the sheet resistance of the thin film is rapidly decreased. The ITO layer plasma-treated for 240 s with the thickness of 360 nm exhibits the lowest sheet resistance of 126.5 Ω/sq and the highest surface free energy of 79.45 mJ/m2. However, the increase of the plasma treatment time over 240 s do not affect the increase of film thickness, but the increase of sheet resistance. X-ray photoelectron spectroscopy depth profile reveals the decrease of the level of the oxygen vacancies with increasing plasma treatment time over 240 s. It results from the diffusion of oxygen from the surface into the bulk and explains the increase of the sheet resistance.

Effect of inkjet-printed flexible dielectric barrier discharge plasma on reduction of pathogen and quality changes on sliced cheese

The objective of this study was to investigate pathogen reduction and quality changes in sliced cheddar cheese treated with inkjet-printed flexible dielectric barrier discharge (FXDBD) plasma. The samples were treated with plasma for 0, 5, 10, 15, and 20 min. The surviving populations of Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes were significantly reduced by 2.65, 2.80, and 2.03 log CFU/g, respectively, after 20 min. The main reactive species that could be involved in bacterial inactivation were ozone (O3) and nitrogen oxides (NOx), which were produced at concentrations of 298.19 and 28.08 ppm, respectively, after 20 min plasma treatment. The pH of the plasma-treated sample was lower than that in the control group (P < 0.05), whereas there was no significant difference among treatment times. With increasing plasma treatment time, the L* value decreased, while the b*, total color difference, and 2-thiobarbituric acid reactive substances values increased (P < 0.05) while the redness (a*) value remained unchanged. These results indicate that inkjet-printed FXDBD plasma can effectively inactivate pathogens in cheese; however, it causes an increase in lipid oxidation. Plasma treatment with newly developed inkjet-printed FXDBD showed improved microbiological safety with minimal effects to the physicochemical quality of cheese.

Energy distribution of interface states generated by oxygen plasma treatment for control of threshold voltage in pentacene thin-film transistors

Pentacene metal-oxide-semiconductor (MOS) capacitors with a SiO2 dielectric treated by oxygen plasma have been studied by capacitance-voltage (C-V) measurements to investigate the energy distribution of the interface states. Oxygen plasma treatment, which is used for control of the threshold voltage in pentacene thin-film transistors, shifted the C-V curves of pentacene MOS capacitors to a positive gate voltage as well as the transfer curves of pentacene thin-film transistors (TFTs). The shift is explained by electrons captured at interface states generated by oxygen plasma treatment. The interface states capturing the electrons are expected to locate at low energy levels. The energy distribution of the interface states locating at middle or high energy levels was extracted by a method equivalent to the Terman method. By use of the method in two steps, the interface state densities distributed at middle and high energy levels (D M and D H) were separately obtained. D M and D H were of the order of 1010–1012 cm−2 eV−1, and increased with an increase in plasma treatment time.

Enhancement of antibacterial and wettability performances of polyvinyl alcohol/chitosan film using non-thermal atmospheric pressure plasma

The surface of polyvinyl alcohol/chitosan (PVA/Cs) films was modified utilizing facing-dielectric barrier discharge argon plasma driven by alternating current in an atmospheric pressure condition. The surface properties of the films were analyzed using the scanning electron microscope, water contact angle, X-ray photoelectron spectroscopy, and atomic force microscope. The surface energy and corresponding components were evaluated by the Owens–Wendt technique. Additionally, the antibacterial properties of samples were studied using the plate counting method against Escherichia coli and Staphylococcus aureus. After the plasma treatment, a new oxygen-containing hydrophilic group was introduced, and the surface roughness of the film significantly increased. The wettability of PVA/Cs films improved owing to a new polar OCO functional group and increased surface roughness. With increasing plasma treatment time, up to 10 min, more significant antibacterial efficiency of the films against E. coli (98%) and S. aureus (96%) was observed. The results demonstrate that the increased surface wettability of PVA/Cs films enhanced their antibacterial efficiency against the two microscopic organisms. Additionally, the plasma treatment enabled the strong hydrogen bonds formed between the two polymer chains of the film, resulting in slightly increased of elastic and plastic behaviors.

Low‐Damaged Layer‐by‐Layer Etching of Large‐Area Molybdenum Disulfide Films via Mild Plasma Treatment

AbstractControlling the number of layers of 2D transition metal dichalcogenide (TMDC) film is indispensable for optoelectronic applications because of their layer‐dependent optical features. However, most of methodologies on controlling TMDC layers induce undesirable defect formation and are performed on TMDC flakes, obtained from mechanical exfoliation. These limitations make practical TMDC‐based optoelectronic applications more difficult. Herein, layer‐by‐layer etching methodology of molybdenum disulfide (MoS2) films is developed using mild sulfur hexafluoride (SF6) plasma treatment. It is confirmed that the number of layers is successfully controlled from trilayer to monolayer by increasing plasma treatment time, while preserving overall film quality. Such low‐damaged layer‐by‐layer etching is attributed to this mild plasma etching system to only introduce the chemical reaction between ionized fluorine and MoS2, without physical damage to MoS2. Electrical properties of layer‐controlled MoS2 devices are also investigated, achieving comparatively high field‐effect mobilities of 16.2, 8.84, and 2.87 cm2 V−1 s−1 for tri‐, bi‐, and monolayer MoS2, respectively. This finding provides the possibility of realizing layer‐by‐layer engineering of 2D TMDCs.

Ar plasma treatment on ZnO–SnO2 heterojunction nanofibers and its enhancement mechanism of hydrogen gas sensing

In this study, ZnO–SnO2 heterojunction nanofibers were fabricated using electrospinning and treated by Ar plasma. The post treatment demonstrated the ability to regulate adsorbed oxygen of nanofibers and thus affecting the gas sensing performance. The results revealed that the gas sensing performances increased with the increase of plasma treatment time at first, then showed a downward trend. The setting for the best H2 gas performance was 20 min of plasma treatment, under which the response of the sample was 80% higher and the response time was two thirds shorter than those of the untreated sample. The explanation can be that appropriate plasma treatment can increase the oxygen vacancy on the surface of heterojunction nanofibers as well as the resistance modulation range in the air; however, excessive plasma treatment can result in the reduction of the resistance modulation range in the air by reducing the metal oxide to metal.

Cold Atmospheric Pressure Argon Plasma Jet Assisted Degradation of Malachite Green (MG) Aqueous Solution

The oxidative degradation of cold atmospheric pressure plasma assisted degradation of malachite Green (MG) was investigated in this study. Cold atmospheric pressure plasma assisted MG degradation process was carried out as a function various plasma treatment time (05, 10, and 15 mins). The % of degradation and presence carbon content in the plasma treated MG was examined by UV-Visible spectroscopy (UV-Vis) and total organic carbon (TOC) analyzer. Optical emission spectrometer was used to identify formation of various reactive species during in situ plasma treatment. The higher degradation percentage of 90% was obtained after plasma treatment time of 15 min and value of TOC also found to decreased significantly with increasing plasma treatment time. Toxicity of the plasma-treated MG aqueous solution samples was also examined by Staphylococcus aureus (S.aureus) bacteria.

Reduced Turn-On Voltage and Boosted Mobility in Monolayer WS2 Transistors by Mild Ar+ Plasma Treatment.

Monolayer two-dimensional transition-metal dichalcogenides, such as tungsten disulfide (WS2), are regarded as promising candidates for optoelectronic and electronic applications. Although theoretical calculations have predicted outstanding electronic properties of WS2, the performance of WS2-based electronic devices is still limited by the relatively high Schottky barrier and low carrier mobility. In this work, low-energy argon (Ar+) plasma treatment was used as a nondestructive preconditioning technique to tailor the electrical properties of the WS2 monolayer grown by chemical vapor deposition. Photoluminescence and Raman spectroscopy were used to monitor the modified optical properties of WS2 with increasing plasma treatment time. An improved electrical conductivity was observed after a short-time plasma treatment. The physical mechanism was further revealed by a comparative study between top-electrode and bottom-electrode devices and simulation based on the density functional theory. It is concluded that mild Ar+ plasma treatment can effectively lower the Schottky barrier height and the effective mass of carriers, which reduces the turn-on voltage and enhances the mobility, respectively. However, if the processing time is too long, the WS2 lattice structure will be destroyed. This work has provided an effective method for manipulating the Schottky barrier and mobility of monolayer WS2 transistors and paves the way for developing high-performance electronic devices based on 2D semiconductors.

Influence of the Plasma of Pd–Ce/Porous Biomass Carbons Catalysts on the Surface Texture with Enhance Catalytic Activity Toward CO Oxidation

The porous biomass carbons (PBCs) as catalyst supports were synthesized by simple hydrothermal and carbonization method, and the surface property of PBCs were designed by plasma treatment technology. The Pd and Ce loaded TPBCs (PBCs were treated with plasma) supports were evaluated for their catalytic activity in the CO oxidation reaction. The Pd–Ce/TPBCs-20 catalyst (Conditions: CO concentration: 1 vol%, Total flow rate: 50 mL min−1, Moisture: 4 vol%) exhibited the highest catalytic activity, and the complete conversion temperature (T100) was about 20 °C for CO catalytic oxidation. Moreover, the Pd–Ce/TPBCs-20 catalyst behaved an excellent stability with the CO conversion rate in the presence of moisture, remaining higher than 90% after 24 h on stream at 20 °C. Raman, XPS, H2-TPR and O2-TPD analysis revealed that the surface oxygen-containing functional groups and defect concentration will increase with increasing plasma treatment time, which could improved Pd and Ce diffusion and Pd–O–Ce bonding interactions, resulting in increased CO catalytic activity. In addition, chitosan as the raw material for the synthesis of PBCs support, is low-cost and easy to be obtained from nature. Therefore, the Pd–Ce/TPBCs catalysts have great potential for catalytic removal of CO in practical application.

Tunable resistivity in ink-jet printed electrical structures on paper by plasma conversion of particle-free, stabilizer-free silver inks

Printable metal inks are typically composed of premade nanoparticles that require postdeposition thermal sintering to produce crystalline, electrically conductive features. In this paper, it is shown that particle-free Ag inks made from simple, water-soluble metal salts such as silver nitrate can be ink-jet printed and converted into electrical features with tunable resistivity at low temperature (&amp;lt;100 °C) by exposure to a pure argon plasma. X-ray diffraction confirms that the converted inks are crystalline, and four-point probe electrical measurements show that the sheet resistances are a function of the pressure and power in the plasma. From cross-sectional scanning electron microscopy analysis, it is found that the morphology of the converted silver layer becomes increasingly dense with increasing plasma treatment time, which explains the measured changes in sheet resistance, and that the thickness of the layer is ∼1.5 μm, which yields a minimum resistivity of ∼6 × 10−8 Ω m, approximately 3.8 times higher than bulk resistivity of silver. Interestingly, the resistivity can be varied over a span of 6 orders of magnitude which allows resistor–capacitor filter devices to be fabricated exhibiting varying cut-off frequencies from a single material and geometry.

Plasma polymerized bioceramics for drug delivery: Do surface changes alter biological behaviour?

One of the treatments for recurrent or complicated osteomyelitis is by local antibiotherapy mediated by suitable bone grafts. β–Tricalcium Phosphate (β–TCP) bioceramic is a resorbable bone graft. Its microporosity allows for incorporation of drugs, but a too fast release is often obtained. Complex strategies have been explored to obtain controlled drug release. In this work, plasma polymerization of a biocompatible polymer was investigated on β-TCP. Polyethyleneglycol (PEG)-like polymer coatings of different thickness were deposited on microporous β-TCP loaded with antibiotics. A highly hydrophobic surface was obtained despite the hydrophilicity of the PEG-like layer produced, which was associated to the roughness of the β-TCP substrate. The bioceramics nevertheless retained their suitable biological behavior with regard to human osteoblast cells. The microbiological activity of the antibiotics was preserved, and the coatings reduced the total amount of drug released as a function of the increasing plasma treatment time.

Structural and Optical properties of Multiwalled Carbon Nanotubes Modified by DBD Plasma at Atmospheric Pressure

Structure, chemical, and physical properties of Multiwalled Carbon Nanotubes (MWCNTs) after modification by dielectric barrier discharge (DBD) at atmospheric pressure is investigated using Transmission Electron Microscopy (TEM), Raman and Uv-vis-NIR spectroscopy. Effects of plasma treatment time on MWCNTs are analyzed. TEM result shows that during the short period of plasma treatment time of 5 minutes, the tube surface experienced a few damages. With increase in plasma treatment time, the tube surface is damaged to a certain extent. Intensity ratio, ID/IG through Raman analysis shows a good agreement with TEM. The values of ID/IG of the modified MWCNTs are larger than those of pristine MWCNTs. An increase of ID/IG indicates that considerable defects are produced on the surfaces of MWCNTs. The treated MWCNTs has energy band gap compared to zero band gap of untreated MWCNTs. It is believed that the defect site of MWCNTs can modify the electronics properties of MWCNTs from being metallic to semiconducting structure, which is applicable for almost all electronics device applications.

Application of pentacene thin-film transistors with controlled threshold voltages to enhancement/depletion inverters

Oxygen plasma treatment has been carried out to control the threshold voltage in organic thin-film transistors (TFTs) having a SiO2 gate dielectric prepared by rf sputtering. The threshold voltage linearly changed in the range of −3.7 to 3.1 V with the increase in plasma treatment time. Although the amount of change is smaller than that for organic TFTs having thermally grown SiO2, the tendency of the change was similar to that for thermally grown SiO2. To realize different plasma treatment times on the same substrate, a certain region on the SiO2 surface was selected using a shadow mask, and was treated with oxygen plasma. Using the process, organic TFTs with negative threshold voltages and those with positive threshold voltages were fabricated on the same substrate. As a result, enhancement/depletion inverters consisting of the organic TFTs operated at supply voltages of 5 to 15 V.

Study of H2/N2Mixture Plasma Treatment on the AISI 1045

In the present work, we analyzed the effect of the plasma treatment of 80% H2/20% N2 mixture plasma over the AISI 1045 steel. To produce the plasma, an AC discharge of 0.1 A at 350 V was produced at a total pressure of 3.0 Torr. The mixture plasma was analyzed using optical emission spectroscopy (OES), in the wavelength range of 200 to 1100 nm. The principal species observed in the plasma were NH, N2, N2+, H2, and Hα. The electron temperature and ion density have been measured using a double Langmuir probe. The samples of steel were treated by plasma at different discharge times, between 3 and 12 h, at the same pressure and AC parameters (0.1 A and 350 V). The treated samples were characterized using X-ray analysis, finding the phases gamma and epsilon of iron nitride. The thickness of the nitrided layers was measured using a scanning electron microscope (SEM). From the images obtained, it is possible to appreciate the interphase between the nitrided layer and the steel matrix. The relationship between the morphology of the surface of nitrided steel and the wetting was analyzed by measuring the contact angle between the surface and a drop of 5 μL of distilled water. The contact angle of the drop increased with the increase of plasma treatment time. The control sample without treatment presented a smaller angle, and after the treatment the surfaces of the steel became hydrophobic. This may be related to the morphology change of the steel surface produced by plasma treatment.

One-pot preparation of Pd nanoparticles supported on graphene from Pd electrodes by discharge plasma in graphene suspension and its catalytic activity for hydrogenation of nitrobenzene

We developed a one-pot preparation method of Pd nanoparticles (NPs) supported on graphene (Pd/G) by using Pd electrode plasma treatment of aqueous KCl solution containing graphene. It was found that Pd NPs were formed from the Pd electrodes during the plasma treatment and they were supported on graphene. The number of Pd NPs on graphene increased with increasing plasma treatment time, but the size of the Pd NPs was almost the same among different plasma treatment time. From the results of FT-IR and Raman spectra of the products, the formation of CO and defect on graphene were confirmed. The prepared Pd/G showed a superior catalytic activity for the hydrogenation of nitrobenzene to aniline to Pd NPs on α-Al2O3, which was prepared by the same plasma method in the presence α -Al2O3 instead of graphene.