Plasma Jet Systems Research Articles

AI-powered precursor quantification in atmospheric pressure plasma jet thin film deposition via optical emission spectroscopy

Abstract This study explores the feasibility of using Optical Emission Spectroscopy (OES) for in situ monitoring of Atmospheric Pressure Plasma Jet systems in the deposition of thin films. We identify process parameters to control film properties by machine learning for data analysis. In experiments, the depth of the carrier gas inlet pipe (pipe depth) is a crucial controllable variable that directly affects the amount of precursor, influencing the film’s thickness, sheet resistance, and resistivity. We collected 96 000 spectra while preparing 12 film samples, subsequently measured the properties of the samples, and analyzed the spectral data using Principal Component Analysis (PCA) and seven supervised machine learning models. A high correlation was found between spectral features and film thickness. We divided the spectral data in a single process based on processing time into the first third (F-third) and the last third (L-third). Using the F-third data, the PCA plot clearly indicated a significant difference between the two pipe depths, achieving a mean recognition accuracy of 95.1% with machine learning models. In contrast, using the L-third data, the PCA plot showed a high degree of overlap between the two pipe depths, resulting in a considerable decline in recognition performance. Overall, it is challenging to distinguish the spectra visually due to variations in precursor amounts and dynamic fluctuations in the OES signals, even after averaging. Nonetheless, through the successful application of machine learning, we demonstrated an effective spectral recognition system for monitoring pipe depth, which aids in the timely control of film properties.

The Impact of Argon Flow Rates on Plasma Behavior in Plasma Jet Systems for Medical Applications

This research presents a thorough spectroscopic investigation of atmospheric- plasma generated by a plasma jet. The study examines the plasma behavior under varying flow rates of argon gas. A primary objective is to identify the optimal flow rate that facilitates the application of the generated plasma in sterilization and bacterial eradication operations. The findings establish a correlation between argon flow and critical plasma parameters, specifically noting variations in electron temperature (Te) & electron number density (ne). Crucially, the study demonstrates that lower argon flow rates are more effective in generating active species such as hydroxyl and NO reactive species. The results of this investigation hold significant promise for advancing our comprehension of plasma jet technology's utility in sterilization or medical treatment processes, emphasizing the importance of gas flow optimization for these applications.

Analysis of Hazy Ga- and Zr-Co-Doped Zinc Oxide Films Prepared with Atmospheric Pressure Plasma Jet Systems.

Co-doped ZnO thin films have attracted much attention in the field of transparent conductive oxides (TCOs) in solar cells, displays, and other transparent electronics. Unlike conventional single-doped ZnO, co-doped ZnO utilizes two different dopant elements, offering enhanced electrical properties and more controllable optical properties, including transmittance and haze; however, most previous studies focused on the electrical properties, with less attention paid to obtaining high haze using co-doping. Here, we prepare high-haze Ga- and Zr-co-doped ZnO (GZO:Zr or ZGZO) using atmospheric pressure plasma jet (APPJ) systems. We conduct a detailed analysis to examine the interplay between Zr concentrations and film properties. UV-Vis spectroscopy shows a remarkable haze factor increase of 7.19% to 34.8% (+384%) for the films prepared with 2 at% Zr and 8 at% Ga precursor concentrations. EDS analysis reveals Zr accumulation on larger and smaller particles, while SIMS links particle abundance to impurity uptake and altered electrical properties. XPS identifies Zr mainly as ZrO2 because of lattice stress from Zr doping, forming clusters at lattice boundaries and corroborating the SEM findings. Our work presents a new way to fabricate Ga- and Zr-co-doped ZnO for applications that require low electrical resistivity, high visible transparency, and high haze.

Extraction yield and biological activity of phycobiliproteins from Porphyridium purpureum using atmospheric cold plasma discharge and jet systems

Phycobiliproteins (PBPs) extracted from Porphyridium purpureum (P.p) have bioactive properties and are widely used as ingredients in nutraceutical and food applications. This study investigated the use of two cold plasma systems, namely cold plasma discharge system (CPDS) and cold plasma jet system (CPJS), for the aqueous extraction of PBPs from P. p. Three types of PBPs, namely phycoerythrin (PE), phycocyanin (PC) and allophycocyanin (APC) were identified in the crude extracts obtained. The highest PBPs extraction yield (11.31 ± 1.02 mg/g DW P. p) was obtained from CPDS treated samples at 25 kV using N2 for 9 min. CPDS treatments were also shown to be more effective than CPJS treatments in increasing antioxidant activities of the PBPs crude extracts obtained. PBPs crude extracts obtained using CPDS (25 kV; 6 min; N2) had the highest DPPH (69.44 ± 0.10%) and FRAP (207.34 ± 12.96 μmol/L) antioxidant activities observed. PBPs obtained from samples treated with CPDS (25 kV; 9 min; N2) exhibited the highest cytotoxicity potential in Caco-2 human colorectal adenocarcinoma cell lines. This study demonstrates that cold plasma treatments increase the extraction yield of PBPs obtained from P. p and also enhance antioxidant and cytotoxic properties of the PBP crude extracts. However, an increase in treatment time beyond 6 min for both plasma systems was shown to reduce the level of antioxidant activity in PBPs.

A boundary value problem of heat transfer within DBD-based plasma jet setups.

We claim an analytical solution for the thermal boundary value problem that arises in DBD-based plasma jet systems as a preliminary and consistent approach to a simplified geometry. This approach involves the outline of a coaxial plasma jet reactor and the consideration of the heat transfer to the reactor solids, namely, the dielectric barrier and the grounded electrode. The non-homogeneous initial and boundary value thermal problem is solved analytically, while a simple cut-off technique is applied to deal with the appearance of infinite series relationships, being the outcome of merging dual expressions. The results are also implemented numerically, supporting the analytical solution, while a Finite Integration Technique (FIT) is used for the validation. Both the analytical and numerical data reveal the temperature pattern at the cross-section of the solids in perfect agreement. This analytical approach could be of importance for the optimization of plasma jet systems employed in tailored applications where temperature-sensitive materials are involved, like in plasma biomedicine.

Design and Construction of a New Plasma Applicator for the Improved Disinfection and Activation of Large Surfaces

This paper describes the design and operation of a low-cost plasma applicator based on a patented, swirled-type dielectric barrier discharge configuration with a treatment width up to 300 mm. Differences from earlier plasma applicators include: blown cylindrical dielectric barrier discharge, combining the functional properties of the plasma jet systems, arc and corona discharge blown in a single type of universal applicator, and the possibility of treating large areas of samples with cold plasma generated in a certain type of specific process gas mixture chosen according to the type of desired effect. We tested the effect of the plasma on a few materials such as cotton and linen fabrics, glass wafers and printing cardboard, proving that the generated plasma can easily make hydrophilic or hydrophobic surfaces. We also tried the plasma’s sterilizing effect on Escherichia coli (E. coli) bacteria. The results suggest that our plasma system can be successfully applied to medical and biological fields as well, where the removal of bacteria and their fragments is required.

Nanoscale plasma-activated aerosol generation for in situ surface pathogen disinfection

Plasma treatment constitutes an efficient method for chemical-free disinfection. A spray-based system for dispensing plasma-activated aerosols onto surfaces would facilitate disinfection of complex and/or hidden surfaces inaccessible to direct line-of-sight (for example, UV) methods. The complexity and size of current plasma generators (for example, plasma jet and cometary plasma systems)—which prohibit portable operation, together with the short plasma lifetimes, necessitate a miniaturized in situ technique in which a source can be simultaneously activated and administered on-demand onto surfaces. Here, we demonstrate this possibility by combining two nanoscale technologies for plasma and aerosol generation into an integrated device that is sufficiently small and lightweight. Plasma is generated on a carpet of zinc oxide nanorods comprising a nanoneedle ensemble, which when raised to a high electric potential, constitutes a massive point charge array with near-singular electric fields to effect atmospheric breakdown. The plasma is then used to activate water transported through an underlying capillary wick, that is subsequently aerosolized under MHz-order surface acoustic waves. We show that the system, besides being amenable to miniaturization and hence integration into a chipscale device, leads to a considerable improvement in plasma-activation over its macroscale cometary discharge predecessor, with up to 20% and 127% higher hydrogen peroxide and nitrite ion concentrations that are respectively generated in the plasma-activated aerosols. This, in turn, leads to a 67% reduction in the disinfection time to achieve 95% bacterial load reduction, therefore demonstrating the potential of the technology as an efficient portable platform for on-demand field-use surface disinfection.

(Invited) Stabilizing Effect of Impinging Plasma Jet on the Water Surface

Year by year, plasma processing with atmospheric pressure plasma jets is increasingly gaining attention and diversifying into various scientific and industrial fields; plasma jet systems have the merit of being able to release plasma into target liquids or solids. Thus, naturally, part of plasma jet research has directed towards investigating interfacial phenomenon between plasma–liquid or –solid and understanding underlying principles thereof. Since impinging plasma jet on the liquid surface has been considered as a basis of plasma jet processing, for example, active efforts to assess the transport of electrons and other reactive species from plasma to liquid have been made. However, despite its scientific and practical significance, surprisingly little attention has been given to the stabilizing effect of plasma jets on plasma–liquid interfaces thus far. In this contribution, we demonstrate the stabilization of liquid instabilities by weakly ionized gas for the case of a helium gas jet impinging on water, which profoundly affects the water free surface. Special attention is given to the interfacial dynamics relevant to electrohydrodynamic (EHD) gas flow, so-called electric wind, induced by the momentum transfer from accelerated charged particles to neutral gas under a strong electric field. A plasma jet consisting of periodic pulsed ionization waves, called plasma bullets, exerts more force via electrohydrodynamic flow on the water surface than a neutral gas jet alone, resulting in cavity expansion without destabilization. Furthermore, both the bidirectional EHD gas flow and parallel electric field to the gas–water interface caused by plasma interacting ‘in the cavity’ render the surface more stable. This case study demonstrates the dynamics of liquids subjected to a plasma-induced force, offering new insights into physical processes and revealing an interdependence between weakly ionized gases and deformable dielectric matter, including plasma–water systems, and their potential stabilization.

Impact of plasma jet geometry on residence times of radical species

Numerous electrode geometries and power supplies, both commercial and in-house, have been employed for the generation of low-temperature atmospheric plasma jets. In this work, the development and operation of a 12 jet nonthermal atmospheric plasma system is presented. The study is based on optical spectroscopy as a diagnostic method due to its nonintrusive nature. A key focus of this study was the material selection (conductive and nonconductive), with several polymers screened for the jet design leading to polyacetal as the choice material. Their results are compared with other atmospheric plasma jet systems. The results show a significant increase in residence time and the spatial homogeneity for ambient air's main species, including: OH, O I, O2, O3, N2, and N2+. Their densities are studied with respect to treatment time, distance, duty cycle, and discharge frequency, as well as the jets' carrier gas chemistries (argon and helium). For their plasma jet system, the bulk of the chemical reactions occur in the surrounding atmosphere and not in the jet nozzle, which is different from most other plasma jet systems. The electron energy distribution function, for the given chemistries, is also reported.

Plasma Apparatuses for Biomedical Applications

Plasma-jet systems and plasma devices of dielectric barrier discharge (DBD) are introduced for biomedical applications. To achieve the purpose of being safe and user friendly, these devices have been developed to avoid electric shock and thermal damage. These types of plasma equipment operate with a sinusoidal voltage of kilovolts at a low frequency of several tens of kilohertz. The plasma jets have been developed with the specific ground-electrode structures according to the various gases in use, such as inert gases, molecular gases, or mixture gases, and air. The Ar-plasma jet with the external ground electrode is operated in a low current of 1–2 mA with the voltage of 1–2 kV. The stable air-jet plasma/plume exiting from a small hole at the cold metal-cap nozzle of the ground electrode can be obtained in a low current of 0.5–1 mA for safety with the voltage of 5–10 kV. Both types of ground electrode, the external electrode and the metal-cap electrode, are applicable to the plasma jets of molecular or mixture gases. The devices for DBD plasmas are shown to be the new advents of plasma stamp, plasma stick, plasma comb, and plasma roller, which operate with the voltage of 2–3 kV.

Importance of Plasma Thermal Energy Transfer for Plasma Jet Systems

Atmospheric pressure plasma systems are routinely used to treat the surfaces of thermally sensitive materials. There are wide ranges of commercial plasma jet systems available, and for the end user, it can be difficult to directly compare the power outputs of these sources. This paper evaluates the use of a thermal imaging technique in order to provide a semiquantitative evaluation of energy output from plasma jets. The evaluation involved a comparison of the thermal energy transfer obtained from three commercially available atmospheric pressure plasma jet systems: 1) PlasmaTreat's Openair; 2) Dow Corning's PlasmaStream; and 3) SurFx's Atomflo.

OH radicals distribution in an Ar-H2O atmospheric plasma jet

Recently, plasma jet systems found numerous applications in the field of biomedicine and treatment of temperature-sensitive materials. OH radicals are one of the main active species produced by these plasmas. Present study deals with the investigation of RF atmospheric pressure plasma jet in terms of OH radicals production by admixture of H2O into argon used as a feed gas. Generation of OH radicals is studied by laser-induced fluorescence spectroscopy. The excitation dynamics of OH radicals induced by the laser photons is studied by time-resolved spectroscopy. It is shown that vibrational and rotational energy transfer processes, which are sensitive to the surrounding species, can lead to the complication in the OH radicals diagnostics at high pressure and have to be considered during experiments. The axial and radial 2D maps of absolute densities of hydroxyl radicals at different water contents are obtained. The highest density of 1.15 × 1020 m−3 is measured in the plasma core for the case of 0.3% H2O. In the x–y-plane, the OH density steeply decreases within a range of ±2 mm from its maximum value down to 1018 m−3. The effect of H2O addition on the generation of OH radicals is investigated and discussed.

Novel low temperature atmospheric pressure plasma jet systems for silicon dioxide and poly-ethylene thin film deposition

In this study, both low-density plasma quartz tube (QT) and high-density plasma metallic tube (MT) jet-electrodes with pulsed-type alternating-voltage (AC) generator were used to investigate the influences of the process parameters and electrode types on the microstructures and the corrosion behaviors of silicon dioxide (SiO 2) or poly-ethylene (PE, (CH 2CH 2)n ) thin films. Tetraethoxysilane (TEOS) and ethylene (C 2H 4) were used as precursors for SiO 2 and PE thin film deposition. The TEOS precursor was vaporized by an ultrasonic oscillator and introduced into the AP plasma systems by argon (Ar) carrier gas. The main plasma working gas was Ar gas mixed with or without oxygen gas. The pulsed-type AC generator, with a frequency of 30 kHz, a voltage of 10 kV and a wattage of 300 W, was used to deposit SiO 2 and PE thin films on the silicon and AISI 1005 low carbon steel substrates at the room temperature, respectively. The high-density plasma MT jet-electrode with an Ar gas flow rate of 6 slm, a precursor flow rate of 40 sccm and an oxygen flow rate of 40 sccm revealed optimal plasma dissociation and chemical reaction efficiencies to synthesize effective atomic stoichiometry of SiO 2 (in-organic films) thin films. However, the low-density plasma QT jet-electrode with an Ar gas flow rate of 6 slm and an ethylene flow rate of 15 sccm appeared optimal plasma-induced polymerization efficiency to exhibit reasonable atomic stoichiometry of PE (organic films) thin films. Moreover, the optimal SiO 2 thin films deposited by MT jet-electrode possessed better corrosion resistant integrity than the optimal PE thin films synthesized by QT jet-electrode. It was also found that SiO 2 and PE thin films synthesized by the AP plasma method possess effective corrosion barrier characteristics like other deposition techniques.

Langmuir probe diagnostics of a plasma jet system

Eighty years have passed since Langmuir's first use of the word ‘plasma’ for describing ionized media. On this occasion we would like to present selected recent results on the application of Langmuir probes to diagnose plasma jet systems. To demonstrate the versatility of the Langmuir probe method we give examples of measurements of the spatial distribution of the plasma parameters as well as their temporal dependence in cases when the plasma jet system operates in a pulsed regime. A part of this paper is devoted to introducing the Langmuir probe technique, especially with regard to its application under conditions when collisions between the charged and neutral particles in the probe sheath cannot be neglected and when the electron energy distribution function in plasma cannot be approximated by a Maxwellian one. In the experimental part we present Langmuir probe measurement of low-pressure and atmospheric-pressure plasma jet systems that are currently used for experiments with deposition of materials with special properties.Most of the experimental results presented in this paper are original data. However, in order to fill in the picture we have used in the case of a barrier-torch discharge three figures that have already been published.

Probe diagnostics of the RF barrier-torch discharge at atmospheric pressure

Abstract Accurate control of plasma microparameters at the position of the substrate is crucial factor in applications of the barrier-torch plasma source for technological purposes. We present measurements of the electron temperature T e in the RF barrier-torch discharge by means of the planar RF-compensated Langmuir probe. The probe was mounted at the substrate position. The error caused by collisions of charged particles with neutrals in the space-charge sheath around the probe (collision probe working regime) at atmospheric pressure is discussed. In order to minimize this error the single probe technique was used to acquire the probe data, which were then recalculated to get the double probe characteristic. From this the electron temperature T e has been obtained in usual manner. The T e was measured at the position of the substrate in the single- and multi-torch barrier atmospheric plasma-jet systems. Using He as a working gas T e was found to be in the interval T e =2.7–6 eV depending on the applied RF power and system configuration. The neutral gas temperature has been measured by optical diagnostics and found to be 400–800 K. The plasma of the RF barrier-torch discharge is therefore strongly non-isothermal even at such high operation pressure.

Investigation of the rf and dc hollow cathode plasma-jet sputtering systems for the deposition of silicon thin films

Both rf and dc hollow cathode plasma-jet sputtering systems have been investigated for thin film semiconductor deposition. These systems were studied as a modification of the well-known rf hollow cathode plasma jet system. The aim of this modification was to provide low temperature deposition of semiconductor silicon and silicon-based alloys as thin films with these plasma jet systems. As a first step, the deposition of an already well explored, hydrogenated amorphous silicon material, a-Si:H, was chosen for experimentation. Plasma erosion of single crystal silicon nozzles in an Ar and H 2 working gas mixture was utilized for this purpose. A comparison of both dc and rf hollow cathode plasma jets has been made and correlated to the a-Si:H thin film properties. As a preliminary result, large differences between the properties of a-Si:H thin films deposited using dc and rf plasmas have been found. Monohydride Si:H composition was found for a-Si:H films fabricated using the dc plasma jet system under certain experimental conditions. However, predominantly di-hydride and multi-hydride structures and strong oxidization were found for the a-Si:H films deposited using rf plasma excitation. The sputtering efficiencies of both the rf and dc jet sources for silicon films have been found to be similar.

Production and characterization of d.c. and h.f. plasma jet diamond films

Diamond films have been achieved, on molybdenum substrates, with two chemical vapour deposition techniques: d.c. and h.f. plasma jet systems. Gas mixtures with methane, hydrogen and CO 2 have been used. The d.c. plasma system gave the highest growth rate (400 μm h −1) when oxygen was added to the reactant gases. Feasibility attempts were conducted with the h.f. system. The growth rate obtained, in this case, was 50–60 μm h −1. The films were characterized by different methods such as X-ray diffraction, scanning electron microscopy, electron microprobe analysis, secondary-ion mass spectrometry and Raman spectrometry.