Low Pressure Plasma Processing Research Articles

Investigating the effect of combined radiofrequency cold plasma (RF-CP) treatment on techno-functional attributes of Cashewnut

In the realm of food safety, dried foods often find themselves on the favourable side of the risk spectrum, enjoying the reputation of being relatively safer. However, dried food products are reportedly contaminated by microorganism beyond permissible limits, thus, depleting their quality, shelf-life, etc. and pose a threat to the consumers. This study aims to explore the effect of radiofrequency low-pressure cold plasma (RF-CP) processing on cashew nuts, using four gas combinations: Nitrogen (N2), Argon (Ar), N2+O2, and Ar+O2. Dried cashew nut kernels underwent RF-CP treatment at six different power options (60, 90, 120, 150, 180, and 210 W), at four distinct time (5, 10, 15, and 20 min). Following the treatment, the samples underwent proximate analysis, microbial load reduction, sensory analysis, peroxide value, and texture analysis. The findings exhibited a direct relationship between plasma power and treatment duration, indicating that an escalation in both parameters induced proportional enhancement in the reduction rate of microbes, with a maximum reduction of over 99% in total plate count, yeast and mould count at 120 W for 20 min and 150 W for 15 min for N2+O2 and Ar+O2 gas combinations, respectively. No statistically significant difference was observed in the sensory, nutritional, and peroxide value between the treated and untreated samples (p > 0.05). However, the moisture content of treated sample decreased, and firmness increased with an increase of power and RF-CP exposure time. This research demonstrates the feasibility of using RF-CP to decontaminate cashews by inactivating microbes, extending shelf life, and altering surface properties, which may enhance texture and appearance. However, it may also induce oxidative changes in lipids and proteins, potentially affecting flavor, nutritional quality, and allergenicity. It is an emerging and alternative to high-temperature processing for disinfecting products like nuts, spices, aromatic plants, and other delicate and luxurious foods.

Time-resolved analysis of Ar metastable and electron populations in low-pressure misty plasma processes using optical emission spectroscopy

Misty plasmas have recently emerged as a promising tool for nanocomposite thin films deposition. However, aerosol-plasma interactions remain poorly documented, especially at low working pressure. In this work, optical emission spectroscopy is used to probe the temporal evolution of three fundamental plasma parameters during pulsed liquid injection in an inductively coupled argon plasma at low-pressure. Time-resolved values of metastable argon density, electron temperature, and electron density are determined from radiation trapping analysis and particle balance equations of selected argon 1s and 2p levels. Pulsed liquid injection is found to induce a sudden drop in metastable density and electron temperature, and an increase in electron density. These results are attributed to the lower ionization thresholds of the injected molecular species compared to the one of argon. In addition, upstream liquid temperature is found to affect the transitory kinetics for non-volatile solvents more than volatile ones, in accordance with a previously reported flash boiling atomization mechanism.

About the Data Analysis of Optical Emission Spectra of Reactive Ion Etching Processes—The Method of Spectral Redundancy Reduction

In this study, we present the Method of Spectral Redundancy Reduction (MSRR) for analyzing OES (optical emission spectroscopy) data of dry etching processes based on the principles of spectral clustering. To achieve this, the OES data are transformed into abstract graph matrices whose associated eigenvectors directly indicate anomalies in the data set. We developed an approach that allows for the reduction in temporally resolved optical emission spectra from plasma structuring processes in such a way that individual emission lines can be algorithmically detected, which exhibit a temporal behavior different from the collective behavior of the temporally resolved overall spectrum. The proportion of emission lines that behave consistently throughout the entire process duration is not considered. Our work may find applications in which OES is used as a process-monitoring technique, especially for low-pressure plasma processing. The major benefit of the developed method is that the scale of the original data is kept, making physical interpretations possible despite data reductions.

Nanoparticles synthesis in microwave plasmas: peculiarities and comprehensive insight

Low-pressure plasma processes are routinely used to grow, functionalize or etch materials, and thanks to some of its unique attributes, plasma has become a major player for some applications such as microelectronics. Plasma processes are however still at a research level when it comes to the synthesis and functionalization of nanoparticles. Yet plasma processes can offer a particularly suitable solution to produce nanoparticles having very peculiar features since they enable to: (i) reach particle with a variety of chemical compositions, (ii) tune the size and density of the particle cloud by acting on the transport dynamics of neutral or charged particles through a convenient setting of the thermal gradients or the electric field topology in the reactor chamber and (iii) manipulate nanoparticles and deposit them directly onto a substrate, or codeposit them along with a continuous film to produce nanocomposites or (iv) use them as a template to produce 1D materials. In this article, we present an experimental investigation of nanoparticles synthesis and dynamics in low-pressure microwave plasmas by combining time-resolved and in-situ laser extinction and scattering diagnostics, QCL absorption spectroscopy, mass spectrometry, optical emission spectroscopy and SEM along with a particle transport model. We showed for the first time the thermophoresis-driven dynamic of particle cloud in electrodless microwave plasmas. We showed that this effect is linked to particular fluctuations in the plasma composition and results in the formation of a void region in the bulk of the plasma surrounded by a particle cloud in the peripherical post-discharge. We also reveals and analyze the kinetics of precursor dissociation and molecular growth that result in the observed nanoparticle nucleation.

Dual low pressure plasma process for SiCN:H thin films deposition: A comparative study

SiCN:H thin films have large possibilities of applications due to their versatile chemical and physical properties. Plasma Assisted Chemical Vapor Deposition (PACVD) process is widely used for SiCN:H deposition. Here we discuss on the potentialities of dual Electron Cyclotron Resonance (ECR) and Radio Frequency Magnetron Sputtering (rf MS) plasmas coupling for SiCN:H deposition in Ar/N2/Si(CH3)4 gas mixture. The study is carried out by varying the autopolarisation voltage Vbias of the silicon target. ECR plasma gives low deposition growth rate about 50 nm/h. The films are transparent. SiCN nanopillars with high aspect ratio are obtained. Rf MS plasma gives high deposition growth rate up to 2200 nm/h. The films are opaque in the near UV and transparent in the visible depending on their thickness. The optical index at 630 nm is 1.95, the Tauc's band gap is 3.0 eV and do not change with Vbias. Dual ECR/rf MS plasma gives high deposition growth rate up to 2300 nm/h. The films are transparent. The optical index varies between 1.7 and 2.05 at 630 nm and the Tauc's band gap decreases linearly between 4.75 and 3.4 eV with Vbias. Dual ECR/rf MS plasma coupling is a very promising PACVD process for thin films deposition.

Effects of Different Cooking Methods on Glycemic Index, Physicochemical Indexes, and Digestive Characteristics of Two Kinds of Rice

Diets including rice and rice-cooking methods influence digestive processes and blood glucose control. In this research, the effects of three different treatments (high-temperature and low-pressure plasma cooking, high-temperature cooking at atmospheric pressure (traditional method), and high-temperature cooking at high pressure) on the texture, color, molecular structure, infrared spectrum, microstructure, debranching enzyme activity, amylopectin content, glycemic index (GI), and in vitro starch digestibility of two rice varieties were studied. The results showed that the hardness, elasticity, viscosity, and chewability of rice after the high-temperature and low-pressure plasma treatment had no obvious changes compared with the traditional cooking method. A SEM analysis showed that the physical properties of the hydrophilicity on the surface of the rice increased after the high-temperature and low-pressure plasma treatment; the debranching enzyme activity reached 3.88 U/g (Xiantao rice) and 3.81 U/g (Heyuan rice), respectively, the amylose content of raw rice reached 68.77 mg/mL (Xiantao rice) and 64.92 mg/mL (Heyuan rice), which increased by 43.31 mg/mL and 39.46 mg/mL, respectively, and the GI was within the medium glycemic index of 56–69. The resistant starch in the Heyuan and Xiantao rice varieties amounted to 88.60 ± 3.10% and 89.40 ± 3.58%, respectively, after the high-temperature and low-pressure plasma processing method. The results showed positive effects and application potential for the cooking method in respect of diabetic consumers.

Enhanced electrochemical performance of low-pressure-plasma-treated paper-based fluidic aluminum-air battery

This study investigates the effect of low-pressure plasma (LPP) processing of a graphite foil as the cathode of a paper-based fluidic Al-air battery. A 10-s plasma treated battery exhibited better discharge performance in terms of the current density, power density, and energy density compared with an untreated battery. Scanning electron microscopy, x-ray photoelectron spectroscopy, and water contact angle measurements were used to investigate the difference in the surface properties of the graphite foil before and after LPP modification. Further, linear sweep voltammetry, constant current discharge measurement, and electrochemical impedance spectroscopy analysis were used to demonstrate the enhancement in discharge performance.

Kinetics driving nanocomposite thin-film deposition in low-pressure misty plasma processes

Mist-assisted methods have recently attracted much attention for plasma deposition in high-quality (multi)functional thin films. However, very little is known on plasma interactions with misted colloidal solutions and their role in plasma process kinetics. Time-resolved optical diagnostics have been carried out to study the deposition of TiO2–SiO2 nanocomposite thin films in low-pressure oxygen-argon plasmas with organosilicon precursors and TiO2 suspensions. Each pulsed injection of the dispersion was followed by a pressure rise due to solvent evaporation. This caused a significant reduction in the electron temperature and density, which mitigated matrix precursor fragmentation and SiO2 deposition as TiO2 nanoparticles were supplied to the film. Comparing injections with and without nanoparticles, misty plasma effects were dominated by plasma droplets rather than plasma-nanoparticle interactions. Successive matrix-rich and nanoparticle-rich deposition steps were confirmed by in situ spectroscopic ellipsometry.

(Invited) Atmospheric Pressure Plasma Treatment of Materials

Technologies based on the use of non-equilibrium plasmas have become virtually irreplaceable in diverse application fields. These range from modification/functionalization of surfaces of medical implants, production of functional thin films or nanostructured materials, light generation, environmental remediation, ozone generation or sterilization/decontamination of surfaces. However, there is a clear trend in the last few decades to substitute low-pressure plasma systems with the ones operated at atmospheric pressure. The interest in atmospheric pressure plasmas is stimulated not only by the decrease in equipment costs by avoiding expensive pumping systems of conventional low-pressure plasma devices but also by the possibility to process objects non-compatible with vacuum conditions. The latter triggered off rapid development of brand new scientific fields – plasma medicine and plasma agriculture.In this work, we briefly review the main operational principles of atmospheric pressure plasma sources, as well as the advantages/drawbacks of atmospheric plasma for a better understanding of the capabilities and limitations of the atmospheric plasma processing technology compared with conventional low-pressure plasma processing technologies. Subsequently, the possible use of two common atmospheric pressure plasma systems - dielectric barrier discharges and atmospheric pressure jets - will be demonstrated on the selected examples. The main emphasis will be given to the issues connected with the control of the wetting/drying/condensation of liquids on plasma-treated polymers, use of plasma pre-treatment on metallization of surfaces or their improved biocompatibility, application of atmospheric pressure plasma for deposition of nanostructured thin films, treatment of seeds with an aim to improve their germination, and last, but not least, the attention will also be devoted to the removal of organic deposits/contaminants, including pathogens, from different types of surfaces.

Surface-Active Plasma-Polymerized Nanoparticles for Multifunctional Diagnostic, Targeting, and Therapeutic Probes

Surface-functionalized polymeric nanoparticles have advanced the field of nanomedicine as promising constructs for targeted delivery of molecular cargo as well as diagnostics and therapeutics. Conventionally, the functionalization of polymeric nanoparticles incorporates tedious wet chemical methods that require complex, multistep protocols. Surface-active plasma-polymerized nanoparticles (PPNs) produced by a dry, low-pressure plasma process can be easily functionalized with multiple ligands in a simple step. However, plasma polymerization remains limited by the challenge of efficient collection of PPNs from low-pressure plasma reactors. Here, we demonstrate a simple method to overcome this limitation by delaying the inflow of the polymer-forming precursor gas, acetylene, into a nitrogen and argon plasma discharge. We provide evidence that this cutting-edge development in the plasma polymerization method drastically enhances the collection yield of nanoparticles by 2.5-fold, compared to the simultaneous inflow of the gases. COMSOL Multiphysics simulations support our experimental data and provide insights into the role of pressure gradients in regulating the forces controlling the collection of the particles. Surface characterization data revealed that changing the sequence of the precursor gas inflow had no significant effect on the physicochemical properties of the nanoparticles, as critically important for theranostic applications. A model, green fluorescent protein, was successfully conjugated to the surface of the PPNs via a reagent-free, one-step incubation process that immobilized the biomolecule while retaining its biological activity. Cytotoxicity of the particles was assessed by a lactate dehydrogenase (LDH) assay at concentrations of up to 5 × 105 nanoparticles per cell. Despite their high concentrations, the nanoparticles were remarkably well tolerated by the cells, demonstrating their superb potential for in vivo cellular uptake. This study advances previous research on plasma-polymerized nanoparticles, introducing a low-waste synthesis method that achieves higher yields. This sustainable technology has important implications for the production of multifunctional nanoparticles for drug delivery, tumor targeting, and medical imaging.

Hybrid Thermoset-Thermoplastic Structures: An in-depth study on plasma pretreated continuous fiber-reinforced epoxy specimens

Hybrid thermoset-thermoplastic structures can be manufactured by using a 3d robot-based filament winding process, low-pressure plasma and thermoplastic injection molding. This newly hybrid concept is only possible, when a strong interface is created between the two different polymer systems. Low-pressure plasma has the ability to expose the carbon fibers of a cured continuous carbon fiber reinforced epoxy (CFRP) structure so that a direct load transfer between the two polymers via the continuous fibers is possible. It also improves the bonding of short glass fiber reinforced polyamide (PA6GF30) to these carbon fiber epoxy structures. It is possible to create load path optimized structural hybrid components in a highly automated manner with this discovery. Therefore, different low-pressure plasma processes, plasma gases, plasma durations and a robot-based specimen production are investigated.

Effect of low-pressure cold plasma processing on decontamination and quality attributes of Saffron (Crocussativus L.).

This study investigated the microbial decontamination of saffron using the low‐pressure cold plasma (LPCP) technology. Therefore, other quality characteristics of saffron that create the color, taste, and aroma have also been studied. The highest microbial log reduction was observed at 110 W for 30 min. Total viable count (TVC), coliforms, molds, and yeasts log reduction were equal to 3.52, 4.62, 2.38, and 4.12 log CFU (colony‐forming units)/g, respectively. The lowest decimal reduction times (D‐values) were observed at 110 W, which were 9.01, 3.29, 4.17, and 8.93 min for TVC, coliforms, molds, and yeasts. LPCP treatment caused a significant increase in the product's color parameters (L*, a*, b*, ΔE, chroma, and hue angle). The results indicated that the LPCP darkened the treated stigma's color. Also, it reduced picrocrocin, safranal, and crocin in treated samples compared to the untreated control sample (p < .05). However, after examining these metabolites and comparing them with saffron‐related ISO standards, all treated and control samples were good.

Low-pressure plasma process for the dry synthesis of cactus-like Au-TiO2 nanocatalysts for toluene degradation

The development of environment-friendly, low-cost and efficient catalyst preparation processes has always been a major issue in the field of catalysis. Wet chemistry methods are often used but these techniques are not sustainable, as post waste solution treatment remains an important drawback. Here an innovative dry low-pressure plasma process for metal nanoparticles supported nanocatalysts preparation is reported. The solid metal and oxide support precursors are physically mixed and then exposed to a radiofrequency Ar/N2 plasma discharge, leading to the precursor degradation and the subsequent nanoparticles generation, without pre- or post- preparation steps. The metal nanoparticle loading and the particle size of metal and oxide support can be easily tuned by changing the ratio of the precursor materials, making the process simple, versatile, highly efficient, and scalable. As a proof of concept, gold nanoparticles (Au NPs) supported on titanium dioxide (TiO2) were prepared and tested as nanocatalysts for toluene (C7H8) degradation at temperatures ranging from 25 to 450 °C. Up to 100% of C7H8 conversion into CO2 was achieved over the Au-TiO2 nanocatalysts, demonstrating that this dry method is a very efficient way to prepare highly active nanocatalysts.

Für den weitesten Weg: Schichten im All

SummaryFor the Longest Way: Thin Films in SpaceThin films for space application have to operate under extreme conditions, reworks or replacement of components in general is not possible. The main challenges are extreme temperatures, bombardment by energetic particles (ionizing radiation) and sometimes mechanical stress. The „toolbox“ of deposition processes ranges from Atomic Layer Deposition to low pressure plasma processes to electroplating.Due to its low specific weight carbon fibre reinforced plastic (CFRP) is an often used construction material for space applications. The uniform deposition of copper on CFRP waveguides for the RADAR antennas of the Sentinel satellites has been an impressive demonstration for the generation of functional surfaces on complex shaped 3D substrates by electrochemical processes. Sometimes optimal solutions require hybrid processes. A heat reflector on components for the BepiColombo mission investigating the Hermean environment has been realized by a combination of sputtering and electroplating.Systems in space often have to observe with high precision and therefore need „eagle eyes“. The continuous development of magnetron sputter technology during the past 10 years has enabled the deposition of optical interference systems with hundreds of individual layers and thickness precision in the ± 0,15 % range. As examples a beam splitter and a band pass filter for space missions are presented.

Optimization of a low pressure plasma process for fabrication of a Drug Delivery System (DDS) for cancer treatment.

A low pressure ICP plasma setup was utilized to deposit thin organic barrier coatings on various substrates to fabricate DDS with encapsulated Carboplatin as a drug and Methylene Blue as a drug model. Choice of the substrates and optimal plasma parameters were discussed for the fabrication of DDS with required characteristics. Prepared thin films were analysed by FTIR, SEM, and the barrier properties were studied by measuring drug concentration released into the medium by UV-VIS and ICP-MS techniques.

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.

Introduction of a New Baffle-Plate Concept to Control the Gas Flow Behavior in a Large Volume PECVD Chamber

Achieving a reasonable homogeneity of the coating deposition rate within a low-pressure plasma process is a challenge, especially in large volume chambers. The local gas flow behavior is one key parameter in the coating deposition. Basically, with the exception of the product geometry and the electrode design, there are two main influences on the gas flow distribution inside a large volume chamber: 1) gas feed-in system and 2) gas exhaustion system. This work focuses on the gas exhaustion system with the aim to reduce its influence on the gas flow behavior inside a large plasma coater. In this sense, a solution with a perforated plate, named “Baffle-Plate”, is created. Thereby relevant construction parameters are identified and investigated to understand their influence in respect to the homogeneity of the gas exhaustion. Number of holes, hole diameter, distance of the Baffle-Plate to the top of the chamber, gas flow and chamber volume are evaluated parameters. Computational fluid dynamics (CFD) simulations are used as a tool to determine velocity and pressure distribution inside the PECVD-chamber and, consequently, to evaluate the layout parameters of the Baffle-Plate. Additionally, practical coating experiments with and without the Baffle-Plate installed are performed. The results show a correlation between the gas flow distribution and the homogeneity of the coating deposition rate. With these results construction guidelines have been formulated. Hence in future developments correct technical layouts of the Baffle-Plate can be applied, easily.

Low Pressure Plasma Processing of Collagen Membranes for Anti-Cancer Drug Delivery

For targeting the cancer cells, a low pressure ICP reactor was utilised to fabricate a drug delivery system. On the surface of biocompatible collagen membranes, thin plasma polymer coatings were deposited to encapsulate an anticancer drug carboplatin and impart different biologically active functionalities. The characteristics of the deposited films were analysed by FTIR and XPS and the overall functionalities were tested by in vitro and in vivo experiments on the cancer cells lines on the cancer nodules respectively. Preliminary results of fabricated drug delivery systems showed the inhibition of cancer cell proliferation in vitro as well as tumour growth in mice models by 2.8 folds in mass compared to the control case

Influence of surface activated carbon nano fibres on mechanical properties of poly ether ketone (PEK)

This investigation highlights different surface functionalization processes of Carbon Nano Fibres (CNF’s) and their effects on mechanical properties of Polyetherketone (PEK) nano composite. Surfaces of CNF’s were modified by low pressure plasma process. There is a significant change in physico-chemical characteristics of CNF’s after low plasma treatment as evident from Transmission Electron Microscopy (TEM) and Fourier Transform infrared Spectroscopic (FTIR) studies. Significant modification in surface morphology and oxygen functionalities are observed as a result of surface modification. There is a significant increase in mechanical properties of high performance polymeric nano composites when surface functionalized CNF’s are dispersed in polymeric matrix.

Grafting of N‐moieties onto octa‐methyl polyhedral oligomeric silsesquioxane microstructures by sequential continuous wave and pulsed plasma

A functionalization of microstructures of polyhedral oligomeric silsesquioxane (POSS) to obtain substrates contain N‐moieties, with a probable high selectivity of primary mines is demonstrated for the first time in a low pressure plasma process through a sequential continuous wave plus pulsed mode (CW + P). Selective grafting of N‐moieties was performed across octa‐methyl POSS micro‐powder by substituting hydrogen atoms of the terminal methyl groups during nitrogen/hydrogen (N2/H2) gases plasma. As opposed to wet chemical functionalization approaches, the plasma method does not require reactive chemicals and is environmentally friendly. The results demonstrate the efficiency of the treatment (N/Si) reaches 7.1% with an indication of high NH2 selectivity (NH2/N). The amount of primary amines is determined from XPS data after 4‐(trifluoromethyl) benzaldehyde (TFBA) chemical derivatization.