Low-power Plasma Research Articles

Hardness and Young's modulus evolution of low-power plasma sprayed Inconel 625 coatings exposed to high temperatures

The use of renewable energy sources has been increasing in recent years as it aims to balance the production of fossil fuels by 2050. Among the various alternatives, concentrated solar power plants are considered the most feasible due to their capability of storing energy. Ongoing research is conducted to enhance the performance of third-generation plants by achieving higher temperatures. It makes necessary to explore new materials. This research is focused on concentrated solar power plants with central tower receivers, for which coatings used nowadays do not withstand the new requirements. For this reason, an alternative plasma sprayed Inconel 625 coating has been proposed. This study confidently presents an analysis of the high temperature exposure effects on the coating's mechanical properties at two temperatures, 520 and 800 °C. The study focuses on the Young's modulus and hardness, and the results demonstrate a significant improvement in these properties due to the formation of secondary phases. Coating hardness increased gradually from 4.12 GPa to 5.3 GPa during exposition at 520 °C. In contrast, the increment was attained quickly during the first 24 h exposure at 800 °C, reaching 4.5 GPa, and then maintained for all times studied. The microstructure was characterized using transmission electron microscopy, which identified the presence of carbides and intermetallic phases. The application of these coatings will significantly enhance the performance of solar receivers due to their superior properties compared to the currently available Pyromark coatings.

Reliable plasmonic biosensing with atmospheric pressure dielectric barrier discharge oxygen plasma treated polydimethylsiloxane microfluidic channels

Polydimethylsiloxane (PDMS) has emerged as a popular choice of material for many microfluidic and flexible sensing devices despite its inherent hydrophobic nature. Here, we report on the use of atmospheric pressure dielectric barrier discharge (APDBD) oxygen (O2) plasma in the development of hydrophilic and protein repulsive PDMS microchannels for plasmonic sensing application. The effect of plasma treatment on the wettability, surface energy and hydrophilicity retention capacity of PDMS was determined using contact angle measurements. The PDMS sample exposed to low-power DBD O2 plasma for 6 min demonstrated lowest contact angle of 35.15˚, surface energy of 62.83 mN/m and hydrophilicity retention capacity of more than 50 days in Phosphate Buffered Saline (PBS). The treatment of PDMS with plasma induces surface hydrophilicity due to the introduction of polar functional groups as evinced by Fourier Transform Infrared (FTIR) analysis without compromising the bulk structure and optical properties of PDMS which were confirmed by X-Ray Diffraction (XRD) and Ultraviolet-visible (UV-Vis) Spectroscopic measurements. The plasma treated PDMS was used in the construction of a microfluidic Surface Plasmon Resonance (SPR) biosensor which demonstrated very low detection limits of 7.13 ng/ml, 5.91 ng/ml and 1.47 ng/ml and high sensitivities of 16.8˚/(µg/ml), 13.5˚/(µg/ml) and 16.65˚/(µg/ml) against anti-Human Immunoglobulin-G protein raised in mouse, goat and rabbit respectively. The obtained results infer that APDBD O2 plasma is a promising technique to render PDMS hydrophilic suited for reliable microfluidic based plasmonic biosensing applications.

Surface adhesion enhancement of anodized A5052 aluminum alloy with low-power atmospheric pressure plasma jets in order to recover wettability

Surface adhesion enhancement of anodized A5052 aluminum alloy with low-power atmospheric pressure plasma jets in order to recover wettability

Sputtering fabrication of isolated W nanocolumns: A possible alternative as plasma facing material for nuclear fusion reactors

Isolated tungsten nanocolumns (W-NCs) have been reported to exhibit a higher radiation resistance than coarse grained W samples, under radiation conditions similar to those that plasma facing materials would face in both magnetic and inertial confinement nuclear fusion approaches (MCF and ICF, respectively). This is so, because their ability to release He via the free surfaces and, the strong reduction of the sputtering yield under KeV Ar and D irradiation as well as, flattening of its angular dependence. The latter is very important for the divertor location in MCF.In this work, we investigate the capabilities of sputtering (an easy control, environmentally friendly, versatile, scalable and low-cost technique) to fabricate isolated W nanocolumns. We study the influence of sputtering parameters (plasma power and deposition angle) on the morphology, density and microstructure of the deposited coatings. Results show that stable α-phase 3D isolated W-NCs are produced at low plasma power (<100 W) and high deposition angles (θ ≥ 75°).

Effect of Ti3SiC2 concentration on corrosion resistance and ICR in bipolar plates composite ceramic coatings

Ti3SiC2, a MAX-phase ceramic, amalgamates metallic and ceramic traits, delivering exceptional electrical conductivity and corrosion resistance. In this research, Ti3SiC2 composite coatings were applied to 316 L stainless steel via low-power atmospheric plasma spraying (APS), aiming to bolster the electrical and corrosion resistance attributes of bipolar plates (BPPs). A power input of 15 kW notably enhanced coating density, yielding a Ti3SiC2 concentration of 19.2 wt% in the coating. Extremes in the spraying power led to either diminished deposition efficiency or a reduction of Ti3SiC2 mass fraction below 5 wt%. Tafel curves demonstrated that specimens with elevated Ti3SiC2 mass fractions exhibited robust corrosion resistance, characterized by a self-corrosion potential of −162.5 mV and a self-corrosion current density of 1.7217 × 10−6 A·cm−2. Moreover, the interfacial contact resistance (ICR) between the coating and the gas diffusion layer was remarkably low (down to 5.49 mΩ·cm−2), indicating enhanced surface electron transfer with increasing Ti3SiC2 mass fractions.

Characterization of a Glow Discharge in a Tripped Hypersonic Boundary Layer

A direct current glow discharge plasma was generated on a canonical 2.75° half-angle wedge test article. Experiments were conducted in the Texas A&M University Actively Controlled Expansion Tunnel at M=5.7 and Re=6×106/m. The effects of Reynolds number, polarity, and upstream perturbation were all independently studied via imaging, power measurements, and optical emission spectroscopy (OES). These measurements are the first to be conducted in a tripped hypersonic boundary layer and allow a deeper understanding of the interplay between the plasma and tripped flow. The plasma, formally characterized as a normal glow discharge, had negligible Joule and cathode heating effects on the boundary layer. Analogously, the installation of trips upstream of the electrodes changed only the appearance of the plasma, creating periodic streaks corresponding to the wakes and vortices produced by each trip but not altering the power across the electrodes. The OES indicates generation of nitric oxide (NO) in both the positive column and, mainly, at the cathode at the relatively low plasma power of ∼47W.

Suppressing substrate oxidation during plasma-enhanced atomic layer deposition on semiconductor surfaces

Plasma-enhanced atomic layer deposition (PE-ALD) is widely employed in microelectronics, energy, and sensing applications. Typically, PE-ALD processes for metal oxides utilize remote inductively coupled plasmas operated at powers of &amp;gt;200 W, ensuring a sufficient flux of oxygen radicals to the growth surface. However, this approach often leads to significant oxidation of chemically sensitive substrates, including most technological semiconductors. Here, we demonstrate that plasma powers as low as 5 W can effectively suppress substrate oxidation while maintaining the structural, optical, and electronic quality of the films. Specifically, we investigate the growth of titanium oxide (TiOx) using two commonly used metalorganic precursors, titanium isopropoxide and tetrakis(dimethylamino)titanium. Films deposited with 5 and 300 W oxygen plasma power are nearly indiscernible from one another, exhibiting significantly lower defect concentrations than those obtained from thermal ALD with H2O. The low plasma power process preserves desired physical characteristics of PE-ALD films, including large optical constants (n &amp;gt; 2.45 at 589 nm), negligible defect-induced sub-bandgap optical absorption (α &amp;lt; 102 cm−1), and high electrical resistivity (&amp;gt;105 Ω cm). Similar behavior, including suppressed interface oxidation and low defect content, is observed on both Si and InP substrates. As an example application of this approach, the assessment of InP/TiOx photocathodes and Si/TiOx photoanodes reveals a significant improvement in the photocurrent onset potential in both cases, enabled by suppressed substrate oxidation during low power PE-ALD. Overall, low power PE-ALD represents a generally applicable strategy for producing high quality metal oxide thin films while minimizing detrimental substrate reactions.

A novel method for supersonic plasma measurement using a double-jacketed enthalpy probe

A novel method to characterize a supersonic plasma jet using a double-jacketed enthalpy probe is presented and applied to Ar supersonic plasma jets generated by a plasma torch operated at an input power level of 5.7 kW and a chamber pressure of 2.3 kPa. The basis of this method is to measure total stagnation pressure, total enthalpy, and static pressure at the backside of a shock wave formed in front of the probe with a single insertion of the probe. Once these three variables are known, normal shock relations before and after the shock wave can disclose information on static pressures, Mach numbers, temperatures, and velocities of the supersonic plasma jet under a calorically perfect gas assumption. For example, measurement experiments carried out with the proposed probe revealed that static pressure of Ar supersonic plasma jet oscillated around the chamber pressure of 2.3 kPa in a range of 1–5 kPa along the jet axis, clearly showing an aerodynamic non-equilibrium. Corresponding to the behaviors of static pressures, Mach numbers also oscillated in the range of 1.1–3.5 along the jet axis. In addition, oscillation patterns of static pressures and Mach numbers agreed well with those of compression and expansion wave zones observed in the photograph of an over-expanded Ar supersonic plasma jet. Although relatively large errors were accompanied due to a low input power level, plasma temperatures and velocities were measured to be decreasing and increasing, respectively, in the expansion wave zone while opposite behaviors were observed in the compression wave zone.

Experimental investigation of the plasma-assisted spray combustion of methanol/water mixtures

To achieve the goal of net zero by 2050, carbon dioxide emissions must be reduced using carbon–neutral fuels, and methanol is a feasible choice for gas turbines, IC engines, and furnaces. Methanol can be prepared by bio-process or thermal catalytic processes, but the crude product contains much water. Crude methanol must be dehydrated into high-grade methanol to enable its use as fuel. The dehydration process is the most energy-intensive step in methanol production. Therefore, this study investigated the feasibility of adding different proportions of water to methanol as a fuel for plasma-assisted spray combustion by using low-power gliding arc plasma. Based on the current sprayer setup, using plasma to sustain water-content methanol is more energy-efficient than refining it. The results delineate that plasma can sustain the combustion of methanol in a spray, even when the methanol contains 60 % water. The length and lift-off height of the flame are related to the water content of the fuel. To illustrate this distinguishing phenomenon, this study used CH and OH fluorescence to conduct a more in-depth analysis. The distribution of CH* radicals indicated that the gliding arc plasma enhanced the flame heat release rate, which may be why the flammability limit extended to greater proportions of water with methanol. It's fascinating to observe that blended fuel with higher water content can result in higher OH chemiluminescence signals. This suggests that the dissociation of water vapor, caused by the thermal effect of the gliding arc, plays a crucial role at the flame base locations. In addition, the flammability limits, emissions, and combustion efficiency of methanol/water spray combustion with and without plasma assistance were all examined.

Plasma power effect on crystallinity and density of AlN films deposited by plasma enhanced atomic layer deposition

Aluminum nitride (AlN) film is a promising material which is used in various fields. In this study, AlN films with different plasma powers were grown by remote plasma atomic layer deposition. Saturation experiments have been applied in the plasma power between 1000 and 3000 W. The influence of plasma power on preferential orientation, chemical, optical, and electrical properties of AlN films are investigated. AlN films displayed multiphase hexagonal wurtzite crystal structure with (002) preferential orientation for higher plasma power, while the predominant orientation shifted toward (100) at lower plasma power. The optical emission spectroscopy analyses show that NH and NH2 radicals conduce to the deposition of AlN films and H radicals selectively dissociate Al–OH bonds which were on AlN film surface and etch deposition films. Atomic force microscopy measurements show that the 1500 W prepared AlN film with smallest surface roughness may be related to the relatively smaller concomitant crystal grains of (100) and (002). X-ray photoelectron spectroscopy investigation presents that oxygen content decreases as the plasma power increases. The obtained maximum value of dielectric constant and breakdown electrical field of AlN film deposited at 3000 W is 8.23 and 5.42 MV/cm, respectively.

Minimally destructive laser-induced breakdown spectroscopy of brass assisted by a low-power atmospheric pressure plasma jet

Minimizing sample damage is crucial in laser-induced breakdown spectroscopy (LIBS) for applications involving valuable samples and elemental mapping. In this study, we introduced a low-power atmospheric pressure plasma jet (APPJ) to reduce sample damage by obtaining LIBS signals at significantly lower laser fluences. The proposed technique, APPJ-assisted LIBS (APPJ-LIBS), utilized an argon APPJ to provide seed electrons and enhance the excitation. The APPJ was generated by a 10 kHz alternating current power supply and made contact with the surface of a brass sample at a 30° angle. An infrared nanosecond Nd:YAG laser was focused onto the contacting zone, allowing the resulting laser-induced plasma to evolve within the surrounding APPJ and produce optical emission. The optimized APPJ-LIBS system reduced the laser fluence threshold for spectral detection of the brass sample by 97 %, from 1.43 J/cm2 to 0.05 J/cm2, which represented the lowest laser fluence threshold reported in LIBS studies on copper-based materials. Micrographs of the sample surface showed no visible damage after the APPJ-LIBS measurement at a near-threshold laser fluence and an APPJ input power as low as 6.0 W. Furthermore, gated images showed the plasma evolution in APPJ-LIBS and confirmed the excitation capability of the APPJ for the laser-ablated materials.

Thermoacoustic stabilization of a sequential combustor with ultra-low-power nanosecond repetitively pulsed discharges

This study demonstrates the stabilization of a sequential combustor with Nanosecond Repetitively Pulsed Discharges (NRPD). Sequential combustors offer advantages such as enhanced fuel flexibility and broader operational range compared to the conventional combustors. However, thermoacoustic instabilities limit their potential. While passive control strategies like Helmholtz dampers have been utilized, active control methods have been hindered by the lack of robust actuators for harsh conditions with sufficient control authority. This study demonstrates successful suppression of instabilities using NRPD in a lab-scale atmospheric sequential combustor, even at low plasma power (1.1 W, about 1.5×10−3 percent of thermal power of 73.4 kW). We also examine the effect of pulse repetition frequency and plasma generator voltage on NO emissions and the sequential flame topology. Notably, higher plasma power can further enhance suppression, albeit with a slight increase in NO emissions. However, the highest plasma power in our study (81 W, 1.1×10−1 percent of flame thermal power) shows a slight improvement in acoustic suppression while significantly elevating NO emissions. Intriguingly, specific plasma parameter combinations can excite another acoustic mode, necessitating further exploration for optimized control. This pioneering study highlights the potential of ultra-low-power plasma-based thermoacoustic control in sequential combustors, paving the way for enhanced stability and performance.

Azimuthal ion movement in HiPIMS plasmas—Part II: lateral growth fluxes

The transport of sputtered species from the target of a magnetron plasma to a collecting surface at the circumference of the plasma is analyzed using a particle tracer technique. A small chromium insert at the racetrack position inside a titanium target is used as the source of tracer particles, which are redeposited on the collecting surface. The azimuthal velocity of the ions along the racetrack above the target is determined from the Doppler shift of the optical emission lines of titanium and chromium. The trajectories are reconstructed from an analysis of the transport physics leading to the measured deposition profiles. It is shown that a simple direct line-of-sight re-deposition model can explain the data for low-power plasmas (direct current magnetron sputtering) and for pulsed high-power impulse magnetron plasmas (HiPIMS) by using the Thompson velocity distribution from the sputtering process as starting condition. In the case of a HiPIMS plasma, the drag force exerted on the ions and neutrals by the electron Hall current has to be included causing an azimuthal displacement in direction. Nevertheless, the Thompson sputter distribution remains preserved for 50% of the re-deposited growth flux. The implications for the understanding of transport processes in magnetron plasmas are discussed.

Highly effective CO2 splitting in a plasma-assisted membrane reactor

Membrane reactors offer a promising approach to converting CO2 into chemicals, fuels, and value-added products. However, challenges remain in its high energy input and deactivation of the catalyst. Here, we report a breakthrough strategy that uses dielectric barrier discharge (DBD) plasma to enhance the CO2 splitting in a perovskite-based La0.6Sr0.4Co0.5Fe0.5O3-δ (LSCF) membrane reactor where a traditional catalyst is not required however instead relies on the highly reactive species generated by the CO2 plasma. The CO2 conversion, physical and chemical evolution of membranes at different temperatures, CO2 plasma power, and purging gas were systematically investigated. The maximum CO2 conversion was achieved at 800 °C and 25 W while reaching 10.6%, 20.0%, and 28.0% via helium, complete oxidation of methane, and partial oxidation of methane purging on the permeate side, respectively. The experimental results obtained under low plasma power consumption suggest that the plasma-assisted membrane reactor strategy has the potential to be energy-efficient and sustainable, particularly when combined with renewable energy sources.

Effect of radial scaling down on the performance of low-power external discharge plasma thrusters

The external discharge plasma thruster removes the annular channel of the traditional Hall thruster, allowing the ionization region to appear outside the thruster, which is expected to reduce the plasma-wall interaction and extend the thruster lifetime. Due to its simpler structure and lighter weight, the external discharge plasma thruster is expected to be scaled down to lower power levels. In this work, the effect of radial scaling down on the performance of low-power external discharge plasma thrusters was experimentally investigated by comparing the discharge characteristics, thrust performance, beam characteristics, and spectral characteristics of thrusters with two different anode diameters of 15 and 30 mm. The 30 mm thruster has thrust of 78–235 mN, specific impulse of 566–1071 s, and anode efficiency of 11.8–23.4% at 78–235 W anode power. Compared with the 30 mm thruster, the anode power and thrust of the 15 mm thruster were decreased by approximately half. Plume diagnostic results show that the 15 mm thruster had a higher current utilization, higher ion peak energy and more active ionization due to better electron confinement. However, the propellant utilization of the 15 mm thruster was lower because of the shortened ionization region length.

Characterisation of thin α-Al2O3 tribo-coating deposited by low-power gas tunnel plasma spray

This study used a unique, low-power (2.8 kW) gas tunnel plasma spray and γ-Al2O3 feedstock powder to deposit a thin Al2O3 coating (<2 µm) on mild steel substrate. By optimising the plasma gas flow rate, powder feed rate, spraying time, and distance, a dense and homogeneous Al2O3 coating was obtained at a very high deposition rate (150 nm/s). During plasma coating, the high energy density plasma transforms the γ-Al2O3 powder into a highly crystalline α-Al2O3 as the predominant microstructure of the coating. The performance of the Al2O3 coating on mild steel was then evaluated preliminary using a linear sliding wear test against a chrome-steel ball, with the results indicating an 18–26% reduction in wear when compared to the uncoated substrate.

Optical, surface, and structural studies of InN thin films grown on sapphire by molecular beam epitaxy

A series of indium nitride (InN) thin films have been grown on sapphire substrates by molecular beam epitaxy (MBE) technology under different growth conditions of temperature and plasma power. Their structural, surface, and optical properties are studied by a variety of techniques of scanning electron microscopy, Hall effect, x-ray diffraction, photoluminescence (PL), Raman scattering, x-ray photoelectron spectroscopy (XPS), synchrotron radiation x-ray absorption near edge structure (XANES), and so on. The lower carrier concentration in InN can be obtained with a higher MBE growth temperature and a lower plasma power. As the plasma power increases, the PL peak energy is observed to shift toward the higher energy side and the Raman E2 (high) and A1 (LO) modes are shifted to the lower frequency. The residual compressive strain in epitaxial InN is relaxed. The lower plasma power and the higher growth temperature are preferred for the MBE growth of high-quality InN films. The influencing factors on the InN PL peak and band gap Eg have been revealed. It is evidenced that the InN PL peak and Eg can be shifted from high down to ∼0.65 eV with the carrier concentration down to low E19 cm−3 and the plasma power down to ∼80 W. Both the XPS and N K-edge XANES revealed the antisite defect of N on the In site, NIn. The XANES In L-edge measurements on the In L3-edge of InN films with various carrier concentrations has indicated the fourfold InN intermediate crystal structures. These obtained results are significant and useful to deepen the understanding and promote further investigation in InN and III-N materials.

Physical Properties of a Low-Power Helicon Source Operating on a High-Frequency Discharge with a Capacitive Component

The results of an experimental study of a low-power RF plasma source placed in a longitudinal magnetic field (helicon thruster), when it operates on a capacitive RF discharge and inductive RF discharges with a capacitive component, are presented. A significant dependence of the characteristics of the ion and electron fluxes of the source on the induction of a constant magnetic field is shown. The fundamental applicability of capacitive RF discharge as a working process in the studied plasma source is demonstrated. It is shown that the increase in the average energy of ions in the flow at the outlet of the source with the appearance of the capacitive component of the discharge is slight.

1,4-Bis(trimethylsilyl)piperazine—Thermal Properties and Application as CVD Precursor

We report an investigation into 1,4-Bis-N,N-(trimethylsilyl)piperazine (BTMSP) as a novel precursor for the synthesis of silicon carbonitride films by chemical vapor deposition (CVD). The thermal stability, temperature dependence of vapor pressure and thermodynamic constants of the evaporation process of BTMSP were determined by static tensimetry with a glass membrane zero manometer. The transformation of the compound in low-power (25 W) plasma conditions was investigated by optical emission spectroscopy. It was shown that BTMSP undergoes destruction, accompanied by H and CH elimination and CN formation. SiCN(H) films were deposited in a hot-wall plasma-enhanced CVD reactor. The optical properties of the films were studied by spectral ellipsometry (refractive index: 1.5–2.2; absorption coefficient: 0–0.12) and UV–Vis spectroscopy (transmittance: up to 95%; optical bandgap: 1.6–4.9 eV). Information on the aging behavior of the films is also provided. The transformation of the films occurred through water adsorption and the formation of Si–O bonds with the degradation of Si–H, N–H and Si–CHx–Si bonds.

Development and tests of a thrust stand with an in-situ null position adjustment and calibration method for low power plasma thrusters

A growing number of space missions use electric propulsion systems due to their higher specific impulse and greater efficiency compared to chemical propulsion systems. Because they are able to generate relatively low thrust values, conventional thrust measurement mechanisms used for chemical propulsion systems can not be used for electric propulsion systems. Thus, millinewton level thrust measurement systems are needed to be developed for measuring the low-level thrust of these types of thrusters. At the Bogazici University Space Technologies Laboratory (BUSTLab), a double inverted pendulum type thrust stand with a changeable thrust measurement range between 6 mN – 300 mN was designed, built and tested. The measurement resolution of this thrust stand can be as low as 100 μN level and it can be adjusted by changing the flexure stiffness and the mass of a counterweight. This study investigates the BUSTLab thrust measurement system and its key design points, with a particular focus on its in-situ null position adjustment and calibration process, and methods for mitigating external perturbations during thrust measurements.