Radio Frequency Inductively Coupled Plasma Research Articles

Fast and High-Throughput Synthesis of Medium- and High-Entropy Alloys Using Radio Frequency Inductively Coupled Plasma

Multi-principal element alloys, or medium- and high-entropy alloys (MEAs and HEAs), hold great potential for numerous structural and functional applications, yet the synthesis of such alloys out of a vast composition space is a daunting task. Here, we report a radio frequency inductively coupled plasma (RF-ICP) method for preparing bulk MEAs and HEAs in a rapid and high-throughput fashion. Typical MEAs and HEAs are successfully synthesized within 40 s per alloy, thereby greatly improving the fabrication efficiency and throughput. This method provides a new opportunity to accelerate the discovery of new complex alloys for a broad range of applications.

MICROSTRUCTURE AND MICROHARDNESS EVALUATION FOR NiCrAlY MATERIALS MANUFACTURED BY SPARK PLASMA SINTERING AND PLASMA SPRAYING

NiCrAlY deposited by different thermal spraying methods is commonly used as the bond coat material in thermal barrier coatings (TBCs). In the present study, two experimental coatings were deposited by hybrid water stabilized plasma (WSP-H) and radio frequency inductively coupled plasma (RF-ICP) using the same feedstock powder. Spark plasma sintering (SPS) was used to manufacture a compact NiCrAlY from the same feedstock powder as a reference material. Microstructure, internal oxidation, phase characterization and quantification of the mechanical behaviour in terms of microhardness were studied. The investigations clearly showed microstructural and mechanical differences between the NiCrAlY samples manufactured by different plasma technologies. The results confirmed that SPS and RF-ICP provide dense structures with no oxides due to the fabrication under protective atmosphere and similar mechanical properties. Thus, RF-ICP may be used for deposition of very dense coatings with microstructure and hardness comparable to compacted materials prepared by SPS.

Conversion of CO2 by non- thermal inductively-coupled plasma catalysis

CO2 decomposition is a very strongly endothermic reaction where very high temperatures are required to thermally dissociate CO2. Radio frequency inductively-coupled plasma enables to selectively activate and dissociate CO2 at room temperature. Tuning the flow rate and the frequency of the radio frequency inductively-coupled plasma gives high yields of CO under mild conditions. Finally the discovery of a plasma catalytic effect has been demonstrated for CO2 dissociation that shows a significant increase of the CO yield by metallic meshes. The metallic meshes become catalysts under exposure to plasma to activate the recombination reaction of atomic O to yield O2, thereby reducing the reaction to convert CO back to CO2. Inductively-coupled hybrid plasma catalysis allows access to study and to utilize high CO2 conversion in a non-thermal plasma regime. This advance offers opportunities to investigate the possibility to use radio frequency inductively-coupled plasma to store superfluous renewable electricity into high-valuable CO in time where the price of renewable electricity is plunging.

Dry Reforming of Methane under Mild Conditions Using Radio Frequency Plasma

Dry reforming of methane (DRM) is a challenging process wherein methane reacts with CO2 to give syngas. This reaction is strongly endothermic, typically requiring temperatures higher than 500 °C. Catalysts can be used, but the high temperatures (which are a thermodynamic requirement) often lead to catalyst deactivation. Herein, the reaction from another conceptual direction is approached, using low‐power radio frequency inductively coupled plasma (RF‐ICP). It is demonstrated that this system can give high conversions of methane and CO2 at near‐ambient temperatures. Importantly, the energy costs in this system are considerably lower compared with other plasma‐driven DRM processes. Furthermore, it is shown that the yield of hydrogen can be increased by minimizing the C2 compound formation. The factors that govern the DRM process and discuss Hα emission and its influence on H atom recycling in the process are examined.

An Inductively-Coupled Plasma Electrothermal Radiofrequency Thruster

The “cubesat” form factor has been adopted as the defacto standard for a cost effective and modular, nano-satellite platform. Many commercial options exist for nearly all components re- quired to build such satellite; however, there is a limited range of thruster options that suit the power and size restrictions of a cubesat. Based on the prior work on the “Pocket Rocket” electro- thermal capacitively-coupled radiofrequency (RF) plasma thruster operating at 13.56 MHz, a new design is proposed which is based on an inductively-coupled radiofrequency plasma system operat- ing at 40.68 MHz. The new thruster design, which includes a compact and efficient radiofrequency matching network adjacent to the plasma cavity is presented, together with the first direct thrust measurements using argon as the propellant with the thruster immersed in vacuum and attached to a calibrated thrust balance. These initial results of the unoptimised first prototype indicate an up to 40% instantaneous thrust gain from the plasma compared to the cold gas thrust: typical total thrust at 100 SCCM of argon and 50 W RF power is ∼ 1.1 mN.

Numerical Analysis of Radio-Frequency Inductively Coupled Plasma Spheroidization of Titanium Metal Powder Under Single Particle and Dense Loading Conditions

In order to allow more practical prediction of RF (radio-frequency)–ICP (inductively coupled plasma) spheroidization results of titanium metal powder, numerical analyses under single particle and dense loading conditions were carried out and the results were compared. First, both of the numerical results for Ar inductively coupled plasma with the power level of 30 kW revealed that the injected particles can experience not only spheroidization by melting, but also size reduction by evaporation. In addition, this size reduction was found to strongly depend on the initial sizes of the injected particles, due to the relatively short heating time. For example, the 100 µm Ti particles were computed to hardly experience size reduction by evaporation regardless of feeding rates. However, relatively small Ti particles < 100 µm can be rapidly heated up to boiling points during the short flight of plasma, resulting in the size reduction by the surface evaporation. In particular, numerical results under dense loading condition showed that the final sizes of these small Ti particles can be changed depending on the feeding rate. For example, a single 60 µm Ti particle was calculated to be a 51 µm spherical Ti particle due to the excessive heating. However, with the increase of feeding rate up to 1.0 kg/h, the final sizes of the as-treated Ti powder could be improved to 55 µm due to the plasma temperatures decreasing through complicated plasma–particle interactions. By predicting the relationships between the feeding rates and the initial diameters of Ti powders at a given plasma power level, numerical modellings under single particle and dense loading conditions can help in optimizing the RF–ICP spheroidization process of titanium metal powder.

Numerical Simulation of Crystalline Silicon Heterojunction Solar Cells with Different p-Type a-SiOx Window Layer

In this study, p-type amorphous silicon oxide (a-SiOx) films are deposited using a radio-frequency inductively-coupled plasma chemical vapor deposition system. Effects of the CO2 gas flow rate on film properties and crystalline silicon heterojunction (HJ) solar cell performance are investigated. The experimental results show that the band gap of the a-SiOx film can reach 2.1 eV at CO2 flow rate of 10 standard cubic centimeters per minute (sccm), but the conductivity of the film deteriorates. In the device simulation, the transparent conducting oxide and contact resistance are not taken into account. The electrodes are assumed to be perfectly conductive and transparent. The simulation result shows that there is a tradeoff between the increase in the band gap and the reduction in conductivity at increasing CO2 flow rate, and the balance occurs at the flow rate of six sccm, corresponding to a band gap of 1.95 eV, an oxygen content of 34%, and a conductivity of 3.3 S/cm. The best simulated conversion efficiency is 25.58%, with an open-circuit voltage of 741 mV, a short-circuit current density of 42.3 mA/cm2, and a fill factor of 0.816%.

A Novel ICP Torch with Conical Geometry

This paper presents the development of a novel radio-frequency inductively coupled plasma (RF-ICP) torch. Computer simulations and experiments were employed to investigate the underlying phenomena which led to improved excitation temperature, electron density, robustness, and multielement detection limits of a new analytical ICP torch. Due to its conical geometry, compared to conventional torches, the new torch consumes 50–70% less argon and power. Additionally, the new torch has higher power density, better plasma stability, and better resistance against extinguishing factors. A comparison of time-lapse images of conventional and conical torches shows an enhancement in the plasma ignition process for the new torch. In agreement with simulations, spectroscopic measurements demonstrate that the new torch offers 1200 K higher excitation temperature compared to the conventional torch for the same power input. These improvements result in faster ionization/excitation of the sample particles as shown by the simulation results. In combination with improved particle trajectories inside plasma, this feature is expected to allow higher rates of analysis in single-particle ICP-mass spectrometry with improved sensitivity and accuracy.

Numerical analysis of effects of ion-neutral collision processes on RF ICP discharge

The discharge process of a radiofrequency (RF) inductively coupled plasma (ICP) has been modeled by an ElectroMagnetic Particle-in-Cell Monte Carlo Collision method (EM PIC-MCC). Although the simulation had been performed by our previous model to investigate the discharge mode transition of the RF ICP from a kinetic point of view, the model neglected the collision processes of ions (H+ and H2+) with neutral particles. In this study, the RF ICP discharge process has been investigated by the latest version of the model which takes the ion-neutral collision processes into account. The basic characteristics of the discharge mode transition provided by the previous model have been verified by the comparison between the previous and present results. As for the H-mode discharge regime, on the other hand, the ion-neutral collisions play an important role in evaluating the growth of the plasma. Also, the effect of the ion-neutral collisions on the kinetic feature of the plasma has been investigated, which has highlighted the importance of kinetic perspective for modeling the RF ICP discharge.

Disinfection Performance against Salmonella Typhi in Water by Radio Frequency Inductive Couple Plasma System

The disinfection performance of the radio frequency inductively coupled plasma (RFICP) system against Salmonella Typhi in water was examined using continuous flow experiments. The evaluation was based on disinfection efficiency, death rate constant, disinfection yield, and energy consumption. For all experiments the electromagnetic flux generated in the plasma reactor varied from 4 to 6 W/cm2. The disinfection efficiency and death rate constant of Salmonella Typhi decreased with the increase of the initial number of Salmonella Typhi bacteria. The disinfection yield increased from 784 to 1889 CFU/KWh and the energy consumption decreased from 0.28 to 0.07 KWh/L with the flowrate increasing from 5 to 20 mL/minute. The flowrate is an important parameter in predicting disinfection performance against pathogenic bacteria in water to design drinking water treatment plants.

The Effect of Radio Frequency Plasma Nitriding on Biocompatibility of Nickel-Titanium Shape Memory Alloys

Nickel-titanium (Ni-Ti) shape memory alloys (SMAs) are attractive materials for orthopedic and dental implants, due to its two intrinsic properties including shape memory effect (SME) and superelasticity (SE), which may not be found in other commonly- used surgical metals. Possible Ni ion release, however, hampers their medical applications, particularly in orthopedic implants where fretting is always expected at the articulating surface. Inductively coupled radio frequency plasma (ICRFP) was employed to alter the surface of equiatomic Ni-Ti discs in order to create a barrier to out-diffusion of Ni ions from the bulk material. The ICRFP experiments were carried out with nitrogen, which promoted the formation of a titanium nitride layer on the surface of the Ni-Ti samples. The present paper explores the biocompatibility and performance of the ICRFP treated and untreated Ni-Ti samples. The results confirm that nitrogen plasma modified Ni-Ti alloys are potentially suitable materials for orthopedics without inducing harmful biological effects.

Low temperature deposition of a-SiC:H thin films applying a dual plasma source process

The utilization of silicon carbide (SiC) thin films is of great interest whenever a high robustness is requested for MEMS/NEMS-based devices, which are operated in harsh environments beyond the applicability of standard silicon technology. Hydrogenated amorphous SiC (a-SiC:H) is especially attractive for these scenarios, as it can be deposited at temperatures lower than 400°C while still being beneficial for enhanced device performance. Furthermore, the thin film properties can be tailored to a great extent during synthesis or via post-deposition annealing. This study reports on the deposition of a-SiC:H thin films at a substrate temperature of 250°C applying a dual plasma process by superimposing a radio frequency (RF) plasma which excites the substrate table to an inductively-coupled RF plasma. This auxiliary plasma source has a huge impact on the resulting thin film properties due to the interaction of various opposing processes during film growth. To understand these processes, the layer composition was determined using time-of-flight elastic recoil detection analyses, Fourier transform infrared spectroscopy and by mass effusion measurements up to 1000°C, thus revealing changes in chemical composition, but also the power dependent incorporation of gaseous species from the plasma. This, for example, allows modification of the residual stress ranging from nearly stress free to highly compressively stressed layers of more than −2GPa, Young's modulus values ranging from about 168GPa down to 48GPa, but also greatly affects the surface topography which can be adjusted to a very low root mean squared roughness of less than 0.1nm.

Estimation Using an Enhancement Factor on Non Local Thermodynamic Equilibrium Behavior of High-lying Energy Levels of Neutral Atom in Argon Radio-Frequency Inductively-Coupled Plasma.

This paper describes a plasma-diagnostic method using an enhancement factor on the Boltzmann distribution among emission lines of iron atom in an argon radio-frequency inductively-coupled plasma (ICP). It indicated that Boltzmann plots of the atomic lines having lower excitation energies (3.4 to 4.8 eV) were well fitted on a straight line while those having more than 5.5 eV deviated upwards from a linear relationship. This observation could be explained by the fact that ICP is not in a complete thermodynamic equilibrium between direct excitation to energy levels of iron atom, ionization of iron atom, and radiative decay processes to the ground state. Especially, the recombination of iron ion with captured electron should accompany cascade de-excitations between closely-spaced excited levels just below the ionization limit, the rates of which become slower as a whole; as a result, these high-lying levels might be more populated than the low-lying levels as if a different LTE condition coexists on the high energy side. This overpopulation could be quantitatively estimated using an enhancement factor (EF), which was a ratio of the observed intensity to the expected value extrapolated from the normal distribution on the low energy side. The EFs were generally small (less than 3); therefore, the cascade de-excitation process would slightly contribute to the population of these excited levels. It could be considered from variations of the EF that the overpopulation proceeded to a larger extent at lower radio-frequency forward powers, at higher flow rates of the carrier gas, or at higher observation heights. The reason for this is that the kinetic energy of energetic particles, such as electrons, becomes reduced under all of these plasma conditions, thus enabling the high-lying levels to be more populated by cascade de-excitation processes from iron ion rather than by collisional excitation processes with the energetic particles. A similar Boltzmann analysis using the EF was also carried out in emission lines of nickel atom, which confirmed the conclusion concerning the atomic lines of iron.

Comparative study on contribution of charge-transfer collision to excitations of iron ion between argon radio-frequency inductively-coupled plasma and nitrogen microwave induced plasma

This paper describes an ionization/excitation phenomenon of singly-ionized iron occurring in an Okamoto-cavity microwave induced plasma (MIP) as well as an argon radio-frequency inductively-coupled plasma (ICP), by comparing the Boltzmann distribution among iron ionic lines (Fe II) having a wide range of the excitation energy from 4.76 to 9.01eV. It indicated in both the plasmas that plots of Fe II lines having lower excitation energies (4.76 to 5.88eV) were fitted on each linear relationship, implying that their excitations were caused by a dominant thermal process such as collision with energetic electron. However, Fe II lines having higher excitation energies (more than 7.55eV) had a different behavior from each other. In the ICP, Boltzmann plots of Fe II lines assigned to the higher excited levels also followed the normal Boltzmann relationship among the low-lying excited levels, even including a deviation from it in particular excited levels having an excitation energy of ca. 7.8eV. This deviation can be attributed to a charge-transfer collision with argon ion, which results in the overpopulation of these excited levels, but the contribution is small. On the other hand, the distribution of the high-lying excited levels was non-thermal in the Okamoto-cavity MIP, which did not follow the normal Boltzmann relationship among the low-lying excited levels. A probable reason for the non-thermal characteristics in the MIP is that a charge-transfer collision with nitrogen molecule ion having many vibrational/rotational levels could work for populating the 3d64p (3d54s4p) excited levels of iron ion broadly over an energy range of 7.6–9.0eV, while collisional excitation by energetic electron would occur insufficiently to excite these high-energy levels.

Low Temperature Nitriding of 304 Austenitic Stainless Steel Using RF-ICP Method: the Role of Ion Beam Flux Density

The significant role of ion beam flux during nitriding 304 austenitic stainless steel has been investigated by using a radio frequency inductively-coupled plasma reactor into which a sample with negative bias voltage was inserted. A milliammeter is used to detect the current of ions which collide with the sample and optical emission spectroscopy is used to discern the reactive species included in the nitrogen plasma. The nitriding efficiency is indicated by X-ray diffraction and the microhardness test. The reported data reveal that the ion beam flux density as well as the deposition pressure, bias voltage and time can strongly affect the nitriding of stainless steel via the expanded multiphase microstructure inside the nitrided layer. The increase in the density of ion flux results in an ascent in the intensity of the expanded peak and a simultaneous decline in the intensity of the γ austenite peak. The evolution trend of ion beam flux density is described as a function of the operating pressure and the bias voltage. The maximum ion flux density has been achieved at 10 Pa pressure and −500 V bias voltage. A reasonable nitriding region has been, consequently, suggested after comparing this work with previously reported results.

Ground state bromine atom density measurements by two-photon absorption laser-induced fluorescence

Ground state bromine atom detection by two-photon absorption laser-induced fluorescence (TALIF) is demonstrated. The bromine atoms are excited by two-photon absorption at 252.594 nm to the state and detected by 635.25 nm fluorescence to the (5s) 4P5/2 state. The atoms are generated in a radio-frequency inductively-coupled plasma in pure HBr. The excitation laser also causes some photodissociation of HBr molecules, but this can be minimized by not focussing the laser beam, still giving adequate signal levels. We determined the natural lifetime of the emitting state, and the rate constant for quenching of this state by collision with HBr molecules, .

Comparative study on the emission spectrometric determination of manganese using nitrogen-oxygen Okamoto-cavity microwave induced plasma and argon radio-frequency inductively-coupled plasma

Microwave-induced plasma optical emission spectrometry (MIP-OES) using Okamoto-cavity was investigated in the determination of manganese, in comparison with argon radio-frequency inductively-coupled plasma (ICP)-OES. An important point of this study is that, in the Okamoto-cavity MIP, the emission intensity of particular atomic emission lines is much elevated by adding oxygen of ca. 10% to the nitrogen matrix plasma gas. Intensity variations in emission lines of manganese atom as well as the ion and in a band head of nitrogen molecule were observed, when oxygen was added to the nitrogen plasma, indicating that the emission intensity of the atomic lines was drastically elevated while the intensities of the ionic lines and the nitrogen band head decreased in a similar manner. This observation can be explained by the fact that the nitrogen excited species, contributing to the transition of the band head, are consumed through collisions with oxygen molecules to cause their dissociation, and eventually manganese atoms in the nitrogen–oxygen plasma would be less ionized than in the pure nitrogen plasma, because the ionization of manganese is also caused by collisions with the nitrogen excited species. Optimization of the measuring parameters in the Okamoto-cavity MIP-OES was conducted for the determination of manganese; as a result, the Mn I 403.076-nm line was recommended as the analytical line in the nitrogen-oxygen mixed gas MIP, while the most intense ionic line, Mn II 257.065nm, should be employed in the argon ICP. Their detection limits were of the same order, implying that the Okamoto-cavity MIP had as good analytical performance as the conventional ICP.

Surface Modification of Graphite-Encapsulated Iron Compound Magnetic Nanoparticles by Radio Frequency Inductively-Coupled Plasma for Biomolecules Immobilization

We proposed the graphite-encapsulated iron compound magnetic nanoparticles as a candidate of nanomater ial due to their potential properties on physical, chemical an d biological fields. This study was performed in th ree steps, starting from the nanoparticle fabrication, nanoparticle sur face modification by plasma treatment, leading to b iomolecules immobilization for testing the treated nanoparticle s capabilities. After the plasma treatment, the sur face of the outmost graphene layer is successfully covered by nitrogen- containing groups definitively assigned by XPS spec tra and the STEM-EDS elemental mapping. The nitrogen-containing groups formed during the post-treatment plasma sel ectively attached on the outmost of graphene layer. The inne r structure of inner graphene layer and the iron co re are still found in stable condition which means that the applied pl asma condition allows the efficient covalent functi onalization of nitrogen-containing group to the surface particles without give any destruction. The results shows the highest values of N/C atomic ratio of 5.4% is obtained by applying 10 min of Ar plasma pre-treatment and 2 min of NH 3 plasma posttreatment conducted in RF power of 80W and gas pressure of 50 Pa. Finally, in the biomolecules section , it is found that the primary amino groups grafted after Ar plasma pr e-treatment followed by NH 3 plasma post-treatment appeared to play an important role in dextran immobilization. T he primary amines provide a high selective reaction between aldehyde group of oxidized dextran and amino groups of treated nanoparticles, hence the covalent immob ilization was successfully achieved. The dextran immobilization was confirmed by XPS and HR-TEM analysis followed by amino group derivatization using TFBA. The deconvoluted peak at ~398.6 eV (C=N) (as an evidence for Schiff-b ase linkages between dextran and amino groups on the treated nanoparticles) increased with the increasing of the de xtran concentration. This result is consistent with the d ecrease of free amino group percentage remaining on the nanoparticles surfaces which was evidenced when the dextran concentration increased. High magnification images obtai ned by HRTEM allowed the visual observations of the differen ces between surface morphology of nanoparticles before and after dextran immobilization .

Analysis of rapid increase in the plasma density during the ramp-up phase in a radio frequency negative ion source by large-scale particle simulation

Numerical simulations become useful for the developing RF-ICP (Radio Frequency Inductively Coupled Plasma) negative ion sources. We are developing and parallelizing a two-dimensional three velocity electromagnetic Particle-In-Cell code. The result shows rapid increase in the electron density during the density ramp-up phase. A radial electric field due to the space charge is produced with increase in the electron density and the electron transport in the radial direction is suppressed. As a result, electrons stay for a long period in the region where the inductive electric field is strong, and this leads efficient electron acceleration and a rapid increasing of the electron density.

P-Type zinc oxide films grown by infrared-light-assisted pulsed laser deposition

In this paper, ZnO films were grown on sapphire (0001) substrates by infrared-light-assisted pulsed-laser deposition (IRA-PLD). In addition, a nitrogen-plasma-assisted (PA-N) system was utilized for effectively doping the acceptor by radio frequency induction coupled plasma (RF-ICP). The effect of IRA-PLD and PA-N systems was investigated by studying the difference in substrate temperature with and without plasma assistance. We found that ZnO films exhibit no exciton emission with PA-N at a high temperature and that an increase in the substrate temperature yields ZnO films with a (002) and c-axis preferred orientation in a nitrogen (N2) gas atmosphere. ZnO films are changed from n-type to p-type at a substrate temperature of 673 K by IRA-PLD with an N2 background atmosphere.