Pulsed Plasma Process Research Articles

Effect of free radicals on rheological properties, antioxidant activity, and molecular conformation of chitosan under solution pulsed plasma process based on radical scavengers

Radical scavengers were employed to evaluate the influence of various active species (•OH, •O, and H2O2) on the rheological properties, antioxidant activity, and molecular conformation of chitosan under solution plasma process (SPP) degradation. ESR analysis showed that •OH and •O radicals played important roles in SPP degradation. The results of rheological properties and antioxidant activity indicated that the •OH scavenger (tert-butanol), •O scavenger (1, 4-benzoquinone), and H2O2 scavenger (MnO2) remarkably inhibited the decrease of G' and G" of the degraded chitosan, the formation of gel structure, and the increase of antioxidant activity. The analysis of molecular conformation of the chitosan by particle size analysis, atomic force microscopy (AFM), and high performance size exclusion chromatography coupled with multi-angle laser light scattering (HPSEC-MALLS) revealed that the decrease of particle size, molecular aggregation, and molecular weight of chitosan was inhibited after the addition of radical scavengers. An evident effect of radical scavengers on the hard sphere conformation of chitosan was observed. It was found that the above effects were strongly dependent on the scavenger concentration. These results proved that •OH, •O, and H2O2 played important roles in SPP treatment. For the rheological properties and molecular conformation, H2O2 exhibited the greatest impact. For the antioxidant activity and molecular weight, •OH presented the biggest influence. Besides, •O expressed the weakest effect. This study will be beneficial to reveal the action mechanisms of SPP technology to the degradation of chitosan.

Evaluation of Methods for Superhard Material Processing to Ensure Wear Resistance of Finished Structures

New alloys and their processing methods to increase hardness and wear resistance are constantly being searched. After frictional wear and water suspension testing at various exposure angles, the impact of various composite processing techniques (laser, pulsed plasma, and freezing at −192 °C with varying exposure times from 16 to 24 h in increments of 2 h) on the strength and elasticity of the Ti(0.75)-Al2O3(0.05)-WC(0.2) alloy was investigated. The preservation of qualities after the wear test, particularly after friction, was found to be improved by the laser’s and the pulses’ effects. In comparison to laser processing, pulsed plasma processing increased the material’s hardness, elasticity, compressive strength, and tensile strength for practically all experimental types. The alloy’s tensile strength was at its peak (3.8%), following laser processing, and fell by a maximum of 0.383% when the suspension was used at the highest angle. The attribute that underwent the most beneficial change as a result of pulsed plasma processing was elasticity. This sort of processing produced a final value of 1,482 MPa. Wear-insensitive tests revealed a considerable degradation of the test material’s characteristics. The alloy’s hardness was raised by cryogenic processing. Under exposure to negative temperatures for 24 h, the highest value was attained.

Effect of solution pulsed plasma process on the degradation and physicochemical properties of pectin

Pectin was degraded by solution pulsed plasma (SPP). The impacts of discharge voltage and the distance between the electrodes on pectin degradation and its steady shear flow behavior and characterization were investigated. The results showed that the influence of the discharge voltage was higher than that of the distance between the electrodes. The stronger discharge voltage and the narrower distance between the electrodes presented the lower intrinsic viscosity, the greater shear-thinning capacities, and the stronger viscoelastic behavior. FT-IR and 1H NMR analysis demonstrated that SPP treatment did not damage the main structure of pectin. XRD, SEM and HPSEC-MALL analysis revealed that the crystallinity, Mw and <S2>z1/2 of pectin gradually decreased with the increasing discharge voltage and decreasing the distance between the electrodes. The depolymerized pectin molecules exhibited a hard sphere conformation in the aqueous solution. A higher degradation effect had a greater influence on the conformation of pectin.

Influence of Emerging Technologies on the Utilization of Plant Proteins.

Protein from plant sources is claimed alternatives to animal sources in the human diet. Suitable protein sources need high protein digestibility and amino acid bioavailability. In terms of protein functionality and food applications, they also need high-quality attributes, such as solubility, gelling, water- and oil-holding capacities, emulsifying, and foaming. Thermal processing can improve the nutritional quality of plants with some disadvantages, like reducing the assimilation of micronutrients (vitamins and minerals). Emerging technologies—such as ultrasound, high-pressure, ohmic heating, microwave, pulsed electric field, cold plasma, and enzymatic processes—can overcome those disadvantages. Recent studies demonstrate their enormous potential to improve protein techno-functional properties, protein quality, and decrease protein allergenicity. However, the literature lacks a broader evaluation, including protein digestibility, industrial-scale optimization, and exploring applications to these alternative protein sources.

Surface Improvement of Low Carbon Steels (St37) by Duplex Treatments

The aim of this work was seen to effect to duplex treatment on steel surface. Firstly, arc spray and secondly pulse plasma treatment were applied to sample surface. The influence of these duplex process and process parameters want to see on surface. Swm Inox 446-TW wire was used in arc spray process. Then the pulse plasma process was applied to surface. The different distances and number of pulse were used as the pulse plasma treatment. After duplex treatments, the samples were characterized by using OM (optical micrograph), scanning electron microscopy (SEM-EDS). X-ray diffractometer (XRD) analyses and microhardness tests were applied. The surface roughness of samples was measured with 3D-roughness device. The microhardness values of treated surfaces are about four times higher than that of un-treated surfaces. After duplex treatments, the improved performance of surface the St 37 steel was presented.

A review on novel non‐thermal food processing techniques for mycotoxin reduction

AbstractThe overarching challenges of mycotoxin contamination in food necessitate the development of strategies to be implemented to combat their effects thereof. Common processing techniques have been utilised but do not necessarily meet the desired efficacy. This review appraises studies on novel non‐thermal food processing techniques, particularly high pressure processing, pulsed electric filed, cold plasma and ultrasound processing for the decontamination of mycotoxins in food. Although available studies on these techniques have suggested a reduction of mycotoxins and in some instances, complete decontamination of mycotoxins was also reported. The mechanisms by which reduction/elimination occurs include through decomposition of toxins after collision with ions/electrons leading to cleavage of bonds, structural degradation of the mycotoxins structure and cleavage of functional groups. Additional studies into the toxicity of degraded products and the composition of the food products are still required to ensure a more widespread adoption of these techniques to enhance food safety.

Effects of O2 addition on in-plasma photo-assisted etching of Si with chlorine

Addition of oxygen was used to control the in-plasma photo-assisted etching (PAE) of p-type Si(100) and poly-Si in a high density, inductively coupled, Faraday-shielded, Ar/Cl2 (225/25 SCCM), 60 mTorr plasma. After etching, samples were transferred under vacuum to an UHV x-ray photoelectron spectroscopy chamber for surface analysis. Samples etched under PAE conditions (ion energies below the ion-assisted etching, IAE, threshold) had a thicker surface oxide and lower [Cl] surface concentration, when compared to samples etched under IAE conditions (ion energies above the IAE threshold). PAE was found not to be affected by 0.1 or 0.25 SCCM O2 addition, while etching stopped with more than 0.5 SCCM O2 addition. IAE with RF power on the sample stage, resulting in −65 V self-bias, was not affected by up to 2 SCCM of oxygen addition but decreased rapidly when more than 5 SCCM O2 was added to the plasma. These results imply that PAE may be completely suppressed, while IAE occurs unobstructed. The implications of these findings are discussed in view of applications involving continuous wave and pulsed-plasma processes.

Surface properties of AISI 4140 steel modified by pulse plasma technique

The pulse plasma process is a kind of surface modification technique. In this study, the microstructure and mechanical properties of pulse plasma-treated AISI 4140 steel were studied. Four different sample-plasma gun nozzle distances and three different pulses were chosen for the surface modification at a constant battery capacity of 800 mf. The samples were subjected to optical microscope, SEM and EDS analyses, microhardness testing and X-ray diffraction (XRD) analysis. The columnar and fine grained structures were formed in modified layer. New and hard phases were formed on the modified layer. Hence, the hardness increased five times after pulse plasma treatment. The amount of wear for all specimens was evaluated by using the reciprocating wear (linear wear test machine) test with a 0.15 m/s constant sliding speed under 5, 7, and 9 N loads along a 200 m sliding distance. A WC ball (with 6 mm diameter) was used in this test. The friction coefficient and wear rate were changed in accordance with the applied load. The friction coefficient values decreased and the wear resistance increased in the surface-modified specimens compared to the non-modified ones. The wear rate and the friction coefficient were changed with the wear debris and load. The debris was increased by the resistance to wear of surface. The worn surfaces of the specimens were studied by using atomic force microscopy (AFM), scanning electron microscopy (SEM) and electron dispersive spectroscopy (EDS). The abrasive wear was shown on worn surface.

Texture Modification Technologies and Their Opportunities for the Production of Dysphagia Foods: A Review.

Dysphagia or swallowing difficulty is a common morbidity experienced by those who have suffered a stroke or those undergone such treatments as head and neck surgeries. Dysphagic patients require special foods that are easier to swallow. Various technologies, including high-pressure processing, high-hydrodynamic pressure processing, pulsed electric field treatment, plasma processing, ultrasound-assisted processing, and irradiation have been applied to modify food texture to make it more suitable for such patients. This review surveys the applications of these technologies for food texture modification of products made of meat, rice, starch, and carbohydrates, as well as fruits and vegetables. The review also attempts to categorize, via the use of such key characteristics as hardness and viscosity, texture-modified foods into various dysphagia diet levels. Current and future trends of dysphagia food production, including the use of three-dimensional food printing to reduce the design and fabrication time, to enhance the sensory characteristics, as well as to create visually attractive foods, are also mentioned.

Atmospheric Aerosol Assisted Pulsed Plasma Polymerization: An Environmentally Friendly Technique for Tunable Catechol-Bearing Thin Films.

In this work, an atmospheric aerosol assisted pulsed plasma process is reported as an environmentally friendly technique for the preparation of tunable catechol-bearing thin films under solvent and catalyst free conditions. The approach relies on the direct injection of dopamine acrylamide dissolved in 2-hydroxyethylmethacrylate as comonomer into the plasma zone. By adjusting the pulsing of the electrical discharge, the reactive plasma process can be alternatively switch ON (tON) and OFF (tOFF) during different periods of time, thus allowing a facile and fine tuning of the catechol density, morphology and deposition rate of the coating. An optimal tON/tOFF ratio is established, that permits maximizing the catechol content in the deposited film. Finally, a diagram, based on the average energy input into the process, is proposed allowing for easy custom synthesis of layers with specific chemical and physical properties, thus highlighting the utility of the developed dry plasma route.

Low-k dielectric etch challenges at the 7 nm logic node and beyond: Continuous-wave versus quasiatomic layer plasma etching performance review

For logic nodes of 7 nm and beyond, back-end-of-line (BEOL) trench patterns have a critical pitch of less than 40 nm, directly affecting the plasma etch process window of the dual damascene etch process. Feature size dependent etch depth (reactive ion etch, RIE lag), hard mask selectivity, and ultra-low-k (ULK) damage have become significant challenges that must be overcome in order to meet target device performance. Recently, atomic layer etching has been used to widen the plasma etch process window in terms of selectivity and process control [S. Sherpa, P. L. F. Ventzek, and A. Ranjan, J. Vac. Sci. Technol. A 35, 05C310 (2017); T. Tsutsumi, H. Kondo, M. Hori, M. Zaitsu, A. Kobayashi, T. Nozawa, and N. Kobayashi, J. Vac. Sci. Technol. A 35, 01A103 (2017)]. In this work, the impact of a quasiatomic layer etch (QALE) process, a conventional continuous wave plasma, and a pulsed plasma process on ULK materials were investigated to determine the benefits of an ALE process approach for BEOL etching. Both blanket ULK film and patterned ULK samples were used for this study. The ULK etch damage from each process was characterized using Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy on three different ULK films. From patterned samples, it was determined that QALE could be used to successfully suppress RIE lag in low-k materials at advanced pitches, while keeping low-k damage to a minimum. In addition, the QALE technique showed improved hard mask selectivity and resulted in lower line edge pattern roughness. Based on this study, the authors concluded that QALE is a powerful plasma etch method to overcome BEOL etch challenges at advanced pitches.

Focus on software, data acquisition, and instrumentation

Focus on software, data acquisition, and instrumentation

Application of Cold Plasma Technology in Quality Preservation of Fresh Fig Fruit (Siyah): A Feasibility Study

Fig (Ficus carica L.) is a perishable fruit and it needs to use new techniques in order to increase shelf life of this product. In present study, atmospheric cold plasma as a non-thermal treatment was utilized for preserving fresh fig quality. Dielectric barrier discharge plasma was applied to fruits in two steps. Durations of first treatments were 1 and 5 minutes. Based on this step results, main experiments were conducted for 30, 90 and 180s and cold plasma was applied to packed and unpacked fig samples. Quality was sensory evaluated in terms of color, texture, odor, appearance and overall acceptance. Firmness, color indices (L*, a* and b*),, total soluble solids and pH were also determined. Subjective measurements showed significant shelf life improvement of treated figs compared to control samples while objective quality attributes were not changed except pH and a* which are not undesired. Direct application of plasma for 90 s and in-package treatment for 30 s were suggested for further investigation and considering the practical aspects, pulsed plasma processing of packed figs for 30 s is recommended. It is concluded that atmospheric cold plasma has a potential for prolonging the shelf life of fresh fig fruits.

A model for etching of three-dimensional high aspect ratio silicon structures in pulsed inductively coupled plasmas

A coupled plasma—feature scale model is employed to investigate the etching of high aspect ratio (HAR) silicon (Si) structures using a cyclic multi-step pulsed plasma process in an inductively coupled plasma (ICP) reactor. This process sequence includes an oxidation step to help protect the Si sidewalls, a main Si etch step where the ion energy and angular distribution (IEAD) and ion/neutral flux ratio are controlled through power pulsing, and a clean step prior to repeating the multi-step process. Two-dimensional plasma models are used to compute the IEAD as well as the fluxes of relevant ions and neutral radicals at the wafer. These plasma models are coupled to a three-dimensional feature scale model, where multiple cycles of the three-step etch sequence are simulated. The paper focuses on evaluation of several pulsing modes during the main Si etch step including separate pulsing of the ICP source or RF bias power, and their synchronized pulsing (with phase control). Process performance has been quantitatively evaluated by examining etch rates for Si and the SiO2-like mask, Si/mask etch selectivity, and CDs within the HAR features. When only the RF bias power is pulsed, Si and mask etch rates scale with pulse duty cycle (DC). As a result, if Si is etched to the same depth, the HAR trenches are wider at higher DCs due to less total oxidation time and less protection of the sidewalls. ICP source power pulsing provides higher Si etch rate because of RF bias power being on continuously, but suffers from poor mask selectivity. Synchronized pulsing of both the ICP source and RF bias powers in conjunction with phase control provides additional flexibility in modulating the IEAD and the ion/neutral flux ratio. RF bias pulsing and in-phase synchronized pulsing yield the best selectivity for the conditions explored.

Catalytic Nanotruss Structures Realized by Magnetic Self-Assembly in Pulsed Plasma.

Tunable nanostructures that feature a high surface area are firmly attached to a conducting substrate and can be fabricated efficiently over significant areas, which are of interest for a wide variety of applications in, for instance, energy storage and catalysis. We present a novel approach to fabricate Fe nanoparticles using a pulsed-plasma process and their subsequent guidance and self-organization into well-defined nanostructures on a substrate of choice by the use of an external magnetic field. A systematic analysis and study of the growth procedure demonstrate that nondesired nanoparticle agglomeration in the plasma phase is hindered by electrostatic repulsion, that a polydisperse nanoparticle distribution is a consequence of the magnetic collection, and that the formation of highly networked nanotruss structures is a direct result of the polydisperse nanoparticle distribution. The nanoparticles in the nanotruss are strongly connected, and their outer surfaces are covered with a 2 nm layer of iron oxide. A 10 μm thick nanotruss structure was grown on a lightweight, flexible and conducting carbon-paper substrate, which enabled the efficient production of H2 gas from water splitting at a low overpotential of 210 mV and at a current density of 10 mA/cm2.

Correlation of the Debye sheath thickness and (Cr,Al)N coating properties for HPPMS, dcMS, CAE and PCAE processes

Physical vapor deposited (PVD) coatings are widely-used in tool and component applications, where the predominant aims are the enhancement of the lifetime and an improvement of the economic efficiency. The achievement of these aims amongst others strongly depends on a homogeneous distribution of the coating properties with respect to the entire functional surface, in particular on complex-shaped tools. In order to obtain a sufficient coating homogeneity, pulsed high power plasma processes such as the high power pulsed magnetron sputtering (HPPMS) or the pulsed cathodic arc evaporation (PCAE) has to be chosen. In order to characterize the influence of both technologies on the coating homogeneity, the Debye sheath thickness sD at the substrate side was determined, which is expected to strongly correlate with the coating homogeneity on complex surfaces, since it is a measure for the shielding of charged coating atoms. Measurements with varying pulse parameters were performed. In addition, as reference a direct current magnetron sputtering (dcMS) and cathodic arc evaporation (CAE) process were conducted, respectively. As it is widely used as protective coating for tools in many applications, the coating system (Cr,Al)N was chosen. In the first step, the Debye sheath thickness was determined by means of Langmuir probe. A Debye sheath thickness from sD=430μm to sD=48μm was found for the different processes and parameters. In the second step, the (Cr,Al)N coatings were deposited with selected process parameters on structured tungsten carbide substrates. The coating morphology, coating thickness, surface roughness and chemical composition were observed to be more homogeneous for processes with a lower Debye sheath thickness. The best results were obtained for the HPPMS and PCAE technology. In summary, processes and parameters were identified which can be used for the coating of complex structured tools.

Effect of Heat Treatment and Pulse Plasma Process on Surface Properties of Steels

Effect of Heat Treatment and Pulse Plasma Process on Surface Properties of Steels

Kinetic analysis of soil contained pyrene oxidation by a pulsed discharge plasma process**Supported by National Natural Science Foundation of China (No. 21207052).

A pulsed discharge plasma (PDP) reactor with net anode and net cathode was established for investigating the pyrene degradation in soil under different pulse peak voltage, air flow rate, pyrene content in soil, initial pH value and initial water content of the soil. Pyrene oxidation within the 60 min discharge time was fitting according to the pseudo-first order equation and the corresponding reaction kinetics constants (k values) were calculated. The obtained results show that pyrene oxidation under all the different reaction conditions obeyed the pseudo-first order equation well. Higher pulsed peak voltage and appropriate air flow rate were in favor of the increase of reaction rate of pyrene oxidation. A higher k value could be achieved in the lower initial pyrene content (the value was 100 mg kg−1). The k value of pyrene oxidation in the case of pH = 4 was 11.2 times higher than the value obtained under the condition of pH = 9, while the initial water content of the soil also has a large effect on the oxidation rate of pyrene due to the effect of PDP.

Quasi-atomic layer etching of silicon nitride

Atomic layer etching (ALE) is a promising technique that can solve the challenges associated with continuous or pulsed plasma processes—trade-offs between selectivity, profile, and aspect ratio dependent etching. Compared to silicon, oxide, and other materials, atomic layer etching of silicon nitride has not been extensively reported. In this paper, the authors demonstrate the self-limited etching of silicon nitride in a commercial plasma etch chamber. The process discussed in this paper consists of two sequential steps—surface modification in hydrogen plasma followed by the removal of modified layers in fluorinated plasma. In addition to the ALE characteristics, the authors also demonstrate that the process is anisotropic and the selectivity to oxide is &amp;gt;100. Although the saturated etch rate of one monolayer per cycle could not be attained, self-limited etching of silicon nitride still enables us to incorporate the benefits of atomic layer etching such as an absence of isodense bias and an extremely high selectivity to oxide into practical etch applications.

Roughness generation during Si etching in Cl2 pulsed plasma

Pulsed plasmas are promising candidates to go beyond limitations of continuous waves' plasma. However, their interaction with surfaces remains poorly understood. The authors investigated the silicon etching mechanism in inductively coupled plasma (ICP) Cl2 operated either in an ICP-pulsed mode or in a bias-pulsed mode (in which only the bias power is pulsed). The authors observed systematically the development of an important surface roughness at a low duty cycle. By using plasma diagnostics, they show that the roughness is correlated to an anomalously large (Cl atoms flux)/(energetic ion flux) ratio in the pulsed mode. The rational is that the Cl atom flux is not modulated on the timescale of the plasma pulses although the ion fluxes and energy are modulated. As a result, a very strong surface chlorination occurs during the OFF period when the surface is not exposed to energetic ions. Therefore, each energetic ion in the ON period will bombard a heavily chlorinated silicon surface, leading to anomalously high etching yield. In the ICP pulsed mode (in which the ion energy is high), the authors report yields as high as 40, which mean that each individual ion impacts will generate a “crater” of about 2 nm depth at the surface. Since the ion flux is very small in the pulsed ICP mode, this process is stochastic and is responsible for the roughness initiation. The roughness expansion can then be attributed partly to the ion channeling effect and is probably enhanced by the formation of a SiClx reactive layer with nonhomogeneous thickness over the topography of the surface. This phenomenon could be a serious limitation of pulsed plasma processes.