Plasma Process Parameters Research Articles

Critical investigation on Cu-O bonding configuration variation in copper-oxide thin films for low-cost solar cell applications

The present work provides a detailed investigation on how Copper-Oxygen bonding configuration varies with the plasma processing parameters. XRD, FTIR, XPS and Raman spectroscopy is extensively used to identify and study the phases and phase changes in the films. The Copper-Oxygen bonding configuration was altered by varying the RF power and substrate temperature. We studied the combined effect of both RF power and substrate temperature on the Cu-O bonding configuration, which in turn affects the optical and electrical properties, which are essential to understand before the device fabrication. Films were deposited with 40, 60 and 80 W of RF power at the different growth temperatures such as RT(room temperature), 200 °C and 400 °C. Even the RT deposited films were found to be exhibiting the crystalline nature to the maximum extent. We observed a wide range of variation in the Cu-O bonding configurations with the RF power and growth temperature. Films deposited at 80 W are leaning towards Cu2O phase, whereas films deposited with 40 W is close to CuO phase. Also it is found that, for a fixed power, the films deposited at high substrate temperature are leaning towards Cu2O Phase.

Investigation of CO2 Splitting Process Under Atmospheric Pressure Using Multi-electrode Cylindrical DBD Plasma Reactor

In this paper, the CO2 splitting process was performed under atmospheric pressure in a multi-electrode cylindrical dielectric barrier discharge (DBD) plasma reactor. The influence of the plasma processing parameters including discharge voltage, discharge length and gas flow rate was investigated. Besides, the effect of the similar specific energy input (SEI) values obtained using different plasma powers and gas flow rates was studied. The experimental results indicated that the CO2 conversion and energy efficiency increased along with the increased discharge length due to the increased residence time and the enhanced electric field. The increase of the applied voltage and hence the plasma power or the decrease of the gas flow rate generated enhanced effect on CO2 conversion while negative influence on energy efficiency. In addition, by comparing the energy efficiency at similar SEI values obtained with different discharge powers and gas flow rates, it was found that the gas flow rate played a more important role in CO2 conversion. The proposed multi-electrode plasma reactor led to the highest CO2 conversion of 18.50% and maximum energy efficiency of 12.83%. Compared with other types of cylindrical DBD plasma reactors, the multi-electrode design proposed in this work can give a similar CO2 conversion and higher energy efficiency. The multi-electrode design can enhance the local electric field at the electrode edges, leading to the enhanced corona discharge and the generation of more micro-discharges, which is considered to be responsible for enhanced CO2 conversion process.

Smart adhesion by surface treatment experimental and theoretical insights

To investigate how plasma treatment affected the surface structure and adhesion to polypropylene matrix and unsaturated polyester matrix, green abaca fibers were treated by low temperature plasma under different plasma processing parameters including treatment time, output power, and working gas. Abaca fibers were characterized by atomic force microscope, X-ray photoelectron spectroscopy, contact angle and interfacial shear strength. The results of contact angle and interfacial shear strength were consistent with the changes in surface roughness and the atomic ratio of the plasma treated abaca fibers with treatment time, output power, and working gas. It was concluded that the surface roughness and atomic ratio played a major role in the adhesion improvement of the plasma treated abaca fibers to polypropylene matrix and unsaturated polyester matrix due to the mechanical interlocking and chemical bonding, respectively. The geometrical potential theory was adopted to elucidate the mechanism of the adhesion property.

Simple Fabrication of Superhydrophobic Surfaces Using Atmospheric-Pressure Plasma

Nature-inspired superhydrophobic surfaces have received immense industrial and academic interest due to their non-wettability and self-cleaning properties. To fabricate superhydrophobic silicone rubber surfaces, a simple, environmentally friendly atmospheric-pressure plasma treatment was applied. The effect of diverse plasma processing parameters on the final wettability behavior of the substrates, including plasma power, plasma frequency, number of passes, plasma jet speed, plasma cycle time and distance between the nuzzle outlet and substrate, were analyzed by means of design of experiments (DoE). Surface chemical characterization illustrated the influence of plasma treatment on the chemical composition of the produced silicone rubber. Furthermore, the presence of microstructures as well as the chemical composition of the surface was confirmed using scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy analysis.

Chocolate milk drink processed by cold plasma technology: Physical characteristics, thermal behavior and microstructure

The present study aimed to evaluate the effect of cold plasma processing parameters (time and flow rate) on the physical (rheological parameters and particle size), microstructure (optical microscopy) and thermal properties (differential scanning calorimetry) of chocolate milk drinks. The beverages treated by cold plasma presented particles with increased size and had higher consistency and altered melting profile (lower temperature and bound water and higher enthalpy) than the pasteurized product, suggesting denaturation processes and formation of protein aggregates. More severe conditions resulted in beverages with particles of larger surface areas ([D 3,2]) and volume diameters ([D4,3]), resulting in higher consistency. Intermediate processing conditions resulted in products with characteristics more similar to the pasteurized beverages. The results indicate that the beverages submitted to cold plasma and pasteurization have different physical characteristics, melting profile and microstructure. Chocolate milk drinks with different characteristics could be obtained varying the cold plasma process parameters.

Processing chocolate milk drink by low-pressure cold plasma technology

This study aimed to evaluate the effect of the process time (5, 10, and 15 min) and flow rate (10, 20, and 30 mL/min) of cold plasma technology on physio-chemical characteristics (pH), bioactive compounds (DPPD, Total Phenolic Compounds, ACE-inhibitory activity values), fatty acid composition, and volatile compounds profile of chocolate milk drink. The mild (lower flow rate and process time) and more severe (higher flow rate and process time) conditions led to a reduction of the bioactive compounds (total phenolic compounds and ACE-inhibitory activity), changes in fatty acid composition (increased saturated fatty acid and decreased monounsaturated fatty acid and polyunsaturated fatty acid), less favorable health indices (higher atherogenic, thrombogenic and hypercholesterolemic saturated fatty acids and lower desired fatty acids), and lower number of volatile compounds. In contrast, in intermediate cold plasma conditions, an adequate concentration of bioactive compounds, fatty acid composition, and health indices, and increased number of volatile compounds (ketones, esters, and lactones) were observed. Overall, cold plasma technology has proven to be an interesting alternative to chocolate milk drinks, being of paramount importance the study of the cold plasma process parameters.

Influence of different low-pressure plasma process parameters on shear bond strength between veneering composites and PEEK materials

ObjectiveThe aim of this study was to evaluate the impact of oxygen and argon/oxygen low-pressure plasma on the shear bond strength (SBS) between dental PEEK compounds and veneering composites as a function of plasma process time. MethodsOf an unfilled PEEK (“Juvora”) and two pigment powder filled PEEK compounds (“DC4420”, “DC4450”), 273 rectangular plates were prepared and polished up to 1200 grit. Afterwards the samples were sandblasted and randomly assigned to five different surface pre-treatment groups (1. No plasma (control); 2. O2 plasma for 3min; 3. O2 plasma for 35min; 4. Ar/O2 plasma for 3min; 5. Ar/O2 plasma for 35min). Surface roughness and water contact angles were recorded using three samples of each PEEK compound for each of the plasma treatment groups. An adhesive (visio.link, Bredent GmbH & Co KG, Senden, Germany) was applied onto the specimen surfaces and light cured. A mold was used to shape three different veneering composites (a) Vita VM LC, “Vita” (Vita Zahnfabrik, Bad Säckingen, Germany); (b) GC GRADIA, “Gradia” (GC Europe, Leuven, Belgium); (c) GC GRADIA DIRECT Flo, “Gradia Flo” (GC Europe, Leuven, Belgium)) into a cylindrical form on the sample surface before light curing. SBS was measured using a universal testing machine after 24h of incubation in distilled water at 37°C. ResultsThe two pigment filled PEEK compounds treated with O2 plasma and veneered with Gradia Flo showed the highest SBS values (34.92±6.55MPa and 34.2±1.87MPa) followed by the combination of the unfilled PEEK material with Gradia Flo (29.57±3.71MPa). The SBS values of the samples veneered with Gradia were lower, but not significantly so. The SBS values of the specimens with Vita were for the most part associated with significantly lower results. SignificanceA low-pressure plasma process using oxygen plasma for a duration of 35min, preceded by sandblasting, seems to be the most effective in increasing shear bond strength between veneering composites and PEEK materials.

Nano-Thick Amorphous Oxide Layer Produced by Plasma on Type 316L Stainless Steel for Improved Corrosion Resistance Under Plastic Deformation

Localized corrosion constitutes a major concern in medical devices made of stainless steel. The conventional approach to circumvent such a problem is to convert the surface polycrystalline microstructure of the native oxide layer to an amorphous oxide layer, a few micrometers thick. This process cannot, however, be used for devices such as stents that undergo plastic deformation during their implantation, especially those used in vascular surgery for the treatment of cardiac, neurological, and peripheral vessels. This work explores the feasibility of producing a nano-thick plastic-deformation resistant amorphous oxide layer by plasma-based surface modifications. By varying the plasma process parameters, oxide layers with different features were produced and their properties were investigated before and after clinically-relevant plastic deformation. These properties and the related corrosion mechanisms were mainly evaluated using the electrochemical methods of open-circuit potential, cyclic potentiodynamic polarization, and electrochemical impedance spectroscopy. Results showed that, under optimal conditions, the resistance to corrosion and to the permeation of ions in a phosphate buffered saline, even after deformation, was significantly enhanced.

Optimization of cold plasma process parameters for organosilicon films deposition on carbon steel: Study of the surface pretreatment effect on corrosion protection performance in 3 wt% NaCl medium

Organosilicon films were deposited on carbon steel using plasma enhanced chemical vapour deposition (PECVD) process prepared from cold plasma polymerization of 1,1,3,3-tetramethyldisiloxane (TMDSO). The experimental design technique allowed determining the optimal conditions of the plasma process. The effect of different surface pretreatments was investigated using amorphous phosphatation, argon (Ar) and nitrogen (N2) plasma. Coatings showing a hydrophobic character and good adhesion were obtained. Several surface characterization techniques using Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), contact angle, cross-cut and surface profilometry were used. The protection efficiency against corrosion of the deposited films has been demonstrated by coupling different electrochemical techniques such as open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS) in 3 wt% NaCl solution. The organosilicon coatings showed good barrier against corrosion even after long immersion time in the aggressive environment, especially when N2 plasma pretreatment is performed.

Maskless Surface Modification of Polyurethane Films by an Atmospheric Pressure He/O₂ Plasma Microjet for Gelatin Immobilization.

A localized maskless modification method of polyurethane (PU) films through an atmospheric pressure He/O2 plasma microjet (APPμJ) was proposed. The APPμJ system combines an atmospheric pressure plasma jet (APPJ) with a microfabricated silicon micronozzle with dimension of 30 μm, which has advantages of simple structure and low cost. The possibility of APPμJ in functionalizing PU films with hydroxyl (–OH) groups and covalent grafting of gelatin for improving its biocompatibility was demonstrated. The morphologies and chemical compositions of the modified surface were analyzed by scanning electronic microscopy (SEM), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The fluorescent images show the modified surface can be divided into four areas with different fluorescence intensity from the center to the outside domain. The distribution of the rings could be controlled by plasma process parameters, such as the treatment time and the flow rate of O2. When the treatment time is 4 to 5 min with the oxygen percentage of 0.6%, the PU film can be effectively local functionalized with the diameter of 170 μm. In addition, the modification mechanism of PU films by the APPμJ is investigated. The localized polymer modified by APPμJ has potential applications in the field of tissue engineering.

Surface Treatment of PEOT/PBT (55/45) with a Dielectric Barrier Discharge in Air, Helium, Argon and Nitrogen at Medium Pressure.

This work describes the surface modification of 300PEO-PEOT/PBT 55/45 thin films using a medium pressure dielectric barrier discharge system operated in argon, helium, nitrogen or dry air to improve cell-surface interactions of this established biomaterial. The first part of the paper describes the optimization of the plasma processing parameters using water contact angle goniometry. The optimized samples are then characterized for changes in surface topography and surface chemical composition using atomic force microscopy (AFM) and X-ray fluorescence spectroscopy (XPS) respectively. For all plasma treatments, a pronounced increase in surface wettability was observed, of which the extent is dependent on the used plasma discharge gas. Except for dry air, only minor changes in surface topography were noted, while XPS confirmed that the changes in wettability were mainly chemical in nature with the incorporation of 5–10% of extra oxygen as a variety of polar groups. Similarly, for the nitrogen plasma, 3.8% of nitrogen polar groups were additionally incorporated. Human foreskin fibroblast (HFF) in vitro analysis showed that within the first 24 h after cell seeding, the effects on cell-surface interactivity were highly dependent on the used discharge gas, nitrogen plasma treatment being the most efficient. Differences between untreated and plasma-treated samples were less pronounced compared to other biodegradable materials, but a positive influence on cell adhesion and proliferation was still observed.

Fabrication of amorphous silica nanowires via oxygen plasma treatment of polymers on silicon

We demonstrate a facile non-catalytic method of fabricating silica nanowires at room temperature. Different polymers including photoresists, parylene C and polystyrene are patterned into pedestals on the silicon substrates. The silica nanowires are obtained via the oxygen plasma treatment on those pedestals. Compared to traditional strategies of silica nanowire fabrication, this method is much simpler and low-cost. Through designing the proper initial patterns and plasma process parameters, the method can be used to fabricate various regiment nano-scale silica structure arrays in any laboratory with a regular oxygen-plasma-based cleaner or reactive-ion-etching equipment.

Rapid and selective surface functionalization of the membrane for high efficiency oil-water separation via an atmospheric pressure plasma process

Oil-water separation is a worldwide challenge because of the increasing production of industrial oily wastewater and frequent oil spills. The growing environmental and economic demands emphasize the need to develop effective solutions to separate oil and water. Recently, oil-water separation methods were developed by tuning the wettability of membranes via surface functionalization. However, the industrialization of such methods remains challenging due to the easy-fouling, high cost and complex fabrication. Herein, a simple and rapid pathway to separate oil from oil-water mixtures is reported using plasma surface functionalization in an open-air environment. The fine tuning and study of the plasma process parameters enables the selective functionalization of each side of the membranes which led respectively to a superhydrophobic-superoleophilic and superhydrophobic-oleophobic sides. The successful separation, without any external force, of a 50 mL oil-water solution in 6 minutes was achieved. This work paves the way for an efficient, low cost and easily upscalable method for oil-water separation due to the high versatility of the atmospheric pressure plasma processes.

Spectroscopic investigation of a dielectric barrier discharge in modified atmosphere packaging

Diagnostics of a dielectric barrier discharge (DBD), in a sealed package (with and without meat) filled with gas mixtures of oxygen and carbon-dioxide (O2 –CO2 ), is reported. The generation and evaluation of the plasma chemistry induced within the confines of the sealed package is studied. The plasma discharges were analyzed by optical emission spectroscopy (OES) and optical absorption spectroscopy (OAS) over a range of plasma process parameters. The study includes a detailed experimental investigation of the spatial and temporal spectroscopic data and links them with plasma kinetics. The results from the spectral radiation from package provide information about the electron energy distribution function. The experimental data indicates that the humidity level in the package with and without meat is unchanged, and that the gas temperature was not significantly modified. Oxygen and nitrogen radicals (trapped gas atmosphere and modified atmosphere) are increased in the package containing meat; at the same time there is no evidence of the presence of carbon monoxide molecules. The role of the nitrogen molecule in the quenching of O2 and CO2 molecules is also evaluated.

Tailoring terpenoid plasma polymer properties by controlling the substrate temperature during PECVD

ABSTRACTPolymers derived from natural, minimally‐processed materials have recently emerged as a more sustainable alternative to synthetic polymers, with promising applications in biocompatible and biodegradable devices. Plasma‐enhanced deposition is well‐suited to one‐step, fast, and efficient synthesis of highly crosslinked inert polymers directly from natural resources, however, fabrication of biologically active polymers remains a challenge. Plasma processing parameters influence the properties such as surface energy, roughness, morphology, and chemical composition of deposited polymers and thus their final applications. This article reports on the important role of substrate temperature (TS) in the chemical composition, wettability, refractive index, and crosslinking density of plasma polymers derived from terpenoids. Experiments are conducted as a function of deposition power Pd, and substrate temperature, TS. TS varied from 40 to 280 °C and is externally controlled. Atomic force microscopy analysis reveals the change in deposition mechanism attributed to shadowing effect at higher TS and Pd. Increase in band gap (Eg) with high Ts deposition for terpenoid based plasma polymers is observed. Swelling behavior analyzed by in situ ellipsometry affirms the enhanced crosslink density with increasing deposition rate. Fourier transform infrared analysis exhibits the formation of additional chemical moieties with increasing TS. Increase in deposition rate with increasing TS at higher Pd supports the theory of direct incorporation of depositing particles as dominant mechanism of plasma polymerization in this study. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45771.

Plasma–surface interaction at atmospheric pressure: A case study of polystyrene etching and surface modification by Ar/O2 plasma jet

In this paper, the authors studied atmospheric pressure plasma–surface interactions using a well-characterized radio-frequency Ar/O2 plasma jet with polystyrene (PS) polymer films in controlled gas environments as a model system. A number of plasma processing parameters, such as the treatment distance, environmental gas composition, and substrate temperature, were investigated by evaluating both the changes in the thickness and the surface chemical composition of PS after treatment. The authors found that the polymer average etch rate decayed exponentially with the nozzle–surface distance, whereas the surface oxygen composition increased to a maximum and then decreased. Both the exponential decay constant and the oxidation maximum depended on the composition of the gaseous environment which introduced changes in the density of reactive species. The authors previously reported a linear relationship between measured average etch rates and estimated atomic O flux based on measured gas phase atomic O density. In this work, the authors provided additional insights into the kinetics of surface reaction processes. The authors measured the substrate temperature dependence of the PS etch rate and found that the apparent activation energy (Ea) of the PS etching reaction was in the range of 0.10–0.13 eV. Higher values were obtained with a greater nozzle-to-surface distance. This relatively low Ea value suggests that additional energetic plasma species might be involved in the etching reactions, which is also consistent with the different behavior of etching and surface oxidation modification reactions at the polymer surface as the treatment distance is varied.

Conversion of CO2 in a cylindrical dielectric barrier discharge reactor: Effects of plasma processing parameters and reactor design

Direct conversion of CO2 into CO and O2 was carried out in a cylindrical dielectric barrier discharge (DBD) reactor at atmospheric pressure and low temperatures. The influence of plasma processing parameters (e.g. discharge frequency, CO2 flow rate, discharge power, discharge length, discharge gap, and dielectric material’s thickness) on the plasma CO2 conversion and energy efficiency of the process was investigated. The major products of this reaction were CO and O2, which suggests the stoichiometric conversion of CO2 into CO and O2 was achieved. The results indicate that discharge frequency has a negligible influence on the conversion of CO2 at a constant discharge power. Increasing discharge power or decreasing feed flow rate enhanced CO2 conversion but lowered the energy efficiency when all other parameters were kept constant. In addition, decreasing the discharge gap and the dielectric material’s thickness, or enlarging the discharge length, increased both conversion of CO2 and process efficiency. Two regression models for the plasma process were developed to elucidate the relative significance of these plasma processing parameters on the plasma conversion of CO2. It was found that the flow rate of CO2 and discharge power play the most important role in CO2 conversion, while the energy efficiency is most significantly influenced by the discharge power. Modification of the plasma design was explored by using different inner and outer electrodes in the DBD system. The combination of the Al foil outer electrode with the stainless steel (SS) screw-type inner electrode showed an enhanced CO2 conversion and energy efficiency compared to other electrode forms, leading to the maximum CO2 conversion of 27.2% and maximum energy efficiency of 10.4% in this work. The use of the SS screw-type inner electrode could lead to an enhanced local electric field near the sharp edge of the electrode, while the use of Al foil as an outer electrode could enlarge the effectiveness of discharge area compared to the mesh electrode. Both effects contributed to the enhanced efficiency of the plasma CO2 conversion.

Cleaning of magnetic nanoparticle surfaces via cold plasmas treatments

We report surface cleaning of magnetic nanoparticles (SmCo5 nanochips and CoFe2O4 nanoparticles) by using cold plasma. SmCo5 nanochips and CoFe2O4 nanoparticles, coated with surfactants (oleic acid and oleylamine, respectively) on their surfaces, were treated in cold plasmas generated in argon, hydrogen or oxygen atmospheres. The plasmas were generated using a capacitively coupled pulsed radio frequency discharge. Surface cleaning of nanoparticles was monitored by measurement of the reduction of surface carbon content as functions of plasma processing parameters and treatment times. EDX and XPS analyses of the nanoparticles, obtained after the plasma treatment, revealed significant reduction of carbon content was achieved via plasma treatment. The SmCo5 nanochips and CoFe2O4 nanoparticles treated in an argon plasma revealed reduction of atomic carbon content by more than 54 and 40 in atomic percentage, compared with the untreated nanoparticles while the morphology, crystal structures and magnetic properties are retained upon the treatments.

Stability of maleic anhydride plasma polymer film to water drop evaporation

Previous work revealed the possibility of controlling the nanostructuration of maleic anhydride plasma polymer (MAPP) by adjusting the plasma process parameters or adding cellulose nanocrystals (CNCs) previously on the substrate. This work aimed to evaluate the stability of MAPP coating to water drop evaporation. The evaporation process was followed by optical microscopy and the effects of substrate surface chemistry and presence of CNCs were investigated. The presence of CNCs affected not only the MAPP adhesion under wet condition, leading to an impressive morphological reconstruction of MAPP coating, but also the evaporation kinetics. Therefore, this work exhibits a simple way to obtain functional surface patterns by changing the coating wet adhesion and opens new opportunities for the utilization of CNCs.

Spectroscopic and Langmuir probe measurements of Ar-N2 mixture plasma in magnetic pole enhanced ICP source

Over the last decade, the plasma sources based on electromagnetic power absorption mechanisms have emerged for large scale semiconductor manufacturing. For this purpose inductively coupled plasmas (ICPs), helicons, electron cyclotron resonance (ECR) etc have been widely explored. Recently, new designs of ICPs have been proposed for the improvement of plasma processing reactors including ICPs enhanced by a ferromagnetic core and ICPs with multiple antennas for a uniform spread of plasma over a large processing area. Present paper deals with variation in plasma processing parameters of a low pressure Ar-N2 inductively coupled plasma source with magnetic pole enhancement (MaPE-ICP). Optical emission spectroscopy (OES) and an RF compensated Langmuir probe are employed to examine the trends of parameters including the electron density, electron temperature and electron energy probability functions (EEPFs). Moreover, Ar metastable fractions are also calculated from line ratio method using optical emission intensities of the Ar spectral lines. The variation in emission intensities of the selected lines and in metastable fractions can be related with electron densities in various parts of the EEPFs. Furthermore, at low RF powers the evolution in EEPFs from ‘bi-Maxwellian’ to ‘Maxwellian’ distribution with increasing Ar concentration in the mixture is also observed. The dissociation fraction of N2 determined by ‘advanced actinometry’ technique, based on Trace rare gas-actinometry (TRG-actinometry), is also reported. It is found that dissociation fraction increases with Ar concentration in the discharge as well as RF power and filling gas pressure.