Plasma Electron Temperature Research Articles

64‐4: ECR Plasma Source for Copper Thin Film Dry Etching

Dry etching process of thin copper films using high electron temperature ECR (electron cyclotron resonance) plasma source is developed. With ECR source and RIE (reactive ion etching) mode, etching rate of 175 nm/min is achieved. Dry etching is performed under high electron temperature plasma source with low temperature substrate and employing a reactive ion etching mode. To compensate the large area etching uniformity, scanning low temperature susceptor is adopted. Rectangular‐type microwave slot antenna (ReSLAN) is used to generate ECR plasma.

Spectroscopic measurement of atmospheric-pressure non-equilibrium Ar plasma using continuum and line spectra

A robust method for determining the electron temperature and density of atmospheric-pressure non-equilibrium argon plasmas is reported. The methodology is based on the analysis of the continuum and line spectra of the plasma. Assuming that the electron energy distribution function (EEDF) is expressed as a two-temperature generalized EEDF (GEEDF), the gamma value of the GEEDF is determined through a grid search of the continuum spectrum analysis given by the bremsstrahlung process, which minimizes the mean-squared logarithmic error (MSLE). In addition, the relationship between the gamma value and the electron temperature and density is determined. Utilizing this relationship, the electron temperature and density are determined by minimizing the MSLE between the excited-state densities obtained from the line spectrum analysis and numerically calculated using the collisional-radiative model. This methodology yielded results that satisfied both continuum and line spectrum analyses. In addition, the same analysis was conducted either by continuum spectrum analysis or by line spectrum alone to compare the results.

Effect of single and double pulse laser-induced breakdown spectroscopy towards steel alloy in different gaseous media

In recent years, laser-induced breakdown spectroscopy (LIBS) technique showed its promising for material analysis, quality control, forensic science, and environmental safety monitoring. Besides, due to its rapid measurement capability and minimal sample-preparation requirements, it is a widely recognized elemental analysis approach used in a variety of study domains. The current work compares spatially resolved single (SP) and double pulse (DP), especially orthogonal DP, setups for LIBS to examine and enhance the limit of detection (LOD) in duplex stainless steels alloy. Using the Boltzmann plot method and the Stark broadening mechanism, the electron temperature and density of local arc plasma are highlighted due to single pulse and orthogonal pre-pulse double pulse configurations. With delay time, the circumstances of arc plasma's local thermodynamic equilibrium (LTE) of emission spectral lines are investigated. The experimental results show that there are significant increases in the spectral intensities of the Fe lines in double pulse LIBS under Ar-gas compared to those under He-gas. Internal standardization was used to create calibration curves for the spectral lines of Cr, Cu, and Mn in the alloy sample for the both studied media. It demonstrated that argon outperforms helium in determining the elemental composition of steel alloys. Furthermore, LOD for SP-LIBS and DP-LIBS in both media were calculated, which showed a higher detection LOD for DP-LIBS in the presence of Ar-gas compared to that in He-gas.

Highly efficient electric-thermal conversion of Silver/PVP composites for micro initiators by direct ink writing

Traditional film initiator fabrication techniques were limited by material and process constraints, resulting in restricted ignition capability, durability issues, and complexity in manufacturing. In this study, Metal/polymer composite materials were applied in film initiators in order to enhance the mechanical properties, longevity, and thermal attributes. Silver/polyvinylpyrrolidone composite film bridge (SPB) initiators were fabricated by direct ink writing (DIW). By adjusting the silver loading level and sintering temperature in the Ag nanoparticles/polyvinylpyrrolidone (Ag NPs/PVP) ink formulation, precise control over the structure and resistivity of the SPB was achieved. Compared to single silver film bridge (SFB) initiators prepared by magnetron sputtering (MS), SPBs demonstrated superior heating performance, higher current carrying capacity, and energy utilization under constant current excitation. In capacitor discharge tests, SPBs exhibited superior electric explosion characteristics and plasma properties, with a 25.53% higher energy utilization efficiency compared to SFBs. The peak plasma electron temperature of SPBs reached 7610 K, which was 1065 K higher than that of SFBs. This makes Silver/polyvinylpyrrolidone composite highly promising practical alternatives for high-efficiency, stable, and reliable ignition processes, with potential widespread applications in the aerospace field.

Modelling of plasma discharge in a filament negative ion source

Most of the currently operating Negative ion Neutral Beam Injectors (N-NBIs) exploit filament powered sources for the generation of beam ions. Being widely used in fusion experiments, the filament arc technology has been thoroughly investigated and optimized over the years, allowing to achieve excellent performances in terms of extracted beam optics. The source geometry, the magnetic field topology and the arc power strongly influence both the plasma discharge and the background gas properties and, consequently, the beam features. In this framework, this contribution describes a numerical investigation of the plasma properties in a filament-powered negative ion source, performed by means of a 2D3V Particle In Cell-Monte Carlo Collisions (PIC-MCC) code. Specifically, we discuss plasma formation by the thermionic electrons emitted by the filaments, investigating their interaction with the background gas. We also study the plasma diffusion through the magnetic filter field and how the latter modifies plasma density, electron temperature and plasma potential along the axial direction when approaching the plasma facing electrode.

Effect of antenna helicity on discharge characteristics of helicon plasma under a divergent magnetic field

The characteristics of the blue core phenomenon observed in a divergent magnetic field helicon plasma are investigated using two different helical antennas, namely right-handed and left-handed helical antennas. The mode transition, discharge image, spatial profiles of plasma density and electron temperature are diagnosed using a Langmuir probe, a Nikon D90 camera, an intensified charge-coupled device camera and an optical emission spectrometer, respectively. The results demonstrated that the blue core phenomenon appeared in the upstream region of the discharge tube at a fixed magnetic field under both helical antennas. However, it is more likely to appear in a right-handed helical antenna, in which the plasma density and ionization rate of the helicon plasma are higher. The spatial profiles of the plasma density and electron temperature are also different in both axial and radial directions for these two kinds of helical antenna. The wavelength calculated based on the dispersion relation of the bounded whistler wave is consistent with the order of magnitude of plasma length. It is proved that the helicon plasma is part of the wave mode discharge mechanism.

Correction of self-absorption effect in laser-induced breakdown spectroscopy based on temperature iteration

Laser-induced breakdown spectroscopy (LIBS) is an ideal real-time on-line method for the detection of minor elements in alloy steel, but it needs to solve the undesired self-absorption effect in plasma. Since the plasma electron temperature (T), radiation particle number density and absorption path length (Nl) determine the degree of self-absorption and affect the corrected spectral line intensity, a new temperature iterative self-absorption correction method based on the plasma thermal equilibrium radiation model is proposed to continuously calculate and correct these two parameters. Compared with generally applied self-absorption correction methods, this method has obvious advantages of simple programming, high computational efficiency, and independence of the availability or accuracy of Stark broadening coefficients. The quantitative analysis results of Cu show that the linearity of calibration curves and the measurement accuracy of elemental content are significantly improved with the self-absorption correction. In addition, this method can directly obtain the accurate radiation particle number density and absorption path length, which benefits the plasma diagnostics and quantitative analysis.

Layer-by-layer structured nanocomposite deposits from plasma-synthesized organosilicon nanoparticles and organosilicon nanoparticles decorated with Ag nanoparticles by taking advantage of cyclic nanoparticle formation in Ar/HMDSO reactive plasmas

Rational engineering of thin nanocomposite layers, deposited in reactive plasmas, requires knowledge on the plasma behavior in order to produce multifunctional deposits with tailored properties (structural, optical, electrical, etc.) This work presents an experimental study of nanoparticles synthesized in the plasma gas-phase and their subsequent use as building-blocks to form layer-by-layer nanostructures. The experiment is performed in a plasma process that successfully combines plasma polymerization of an organosilicon molecular precursor (hexamethyldisiloxane, HMDSO) and sputtering of a metallic (silver) target. Pulsed injection of the precursor is found to promote cyclic nanoparticle formation in Ar/HMDSO reactive plasmas. The plasma electron temperature is found to vary in the range 1.6—2.2 eV as derived from time-resolved optical emission spectroscopy of the plasma energetic conditions. This diagnostic method is also shown to provide a reliable tool for online monitoring of the nanoparticle synthesis process. Two types of layer-by-layer structured nanocomposites can be obtained depending on the type of nanoparticles synthesized: (i) organosilicon nanoparticles of size less than 100 nm in all studied plasma conditions for a large quantity of injected HMDSO and (ii) raspberry-like nanoparticles of size less than 150 nm when the quantity of injected HMDSO is reduced. The organosilicon nanoparticle growth follows a polydimethylsiloxane (PDMS)-like oligomerization scheme in which the R2-Si(-O)2 silicon bond tends towards the formation of polymeric structure in a R3-Si(-O)1 silicon chemical environment, containing Si-(CH2)-Si type bridges that are involved in cross-linking. The elemental composition of the raspberry-like nanoparticles is similar to that of the organosilicon nanoparticles, supplemented by the Ag component. The decorating silver nanoparticles are ∼15 nm of size, round in shape and polycrystalline. There is no evidence for silver oxides in the nanostructures. The Si-O-Ag bridges, revealed by infrared spectroscopy, suggest the presence of junction sites between the metallic and the organosilicon parts of the raspberry-like nanoparticles. The silver nanoparticles are found to decorate the organosilicon nanoparticles to form the raspberry-like nanoparticles in the plasma gas-phase, before being deposited. This reveals a very interesting phenomenon of simultaneous growth of the silver- and organosilicon-parts in the plasma without mixing during the nucleation phase.

Effect of Femtosecond Ultraviolet and Infrared Laser Wavelength on Plasma Characteristics of Metals, Ceramics and Glass Samples Using Femtosecond Laser-Induced Breakdown Spectroscopy.

In this work, we present studies on the effect of laser wavelengths on the laser-induced plasma characterization using a femtosecond (fs) ytterbium-doped potassium-gadolinium tungstate (Yb:KGW) laser. Plasma plumes of copper, steel, ceramics, and glass samples were induced using a multiple shot of 200 fs laser pulses with 1030 nm and 343 nm wavelengths at fixed laser fluence () and analyzed using the laser-induced breakdown spectroscopy (LIBS) technique. Time-resolved fs-LIBS measurements were performed on the same set of samples and under the same experimental conditions. For the calculation of plasma parameters, the set of spectral lines of Cu(I) (for copper sample), Fe(I) (for steel sample), and Ca(I), K(I) (for glass and ceramics samples) were observed. The plasma electron temperature and density were evaluated from the Boltzmann plots and Stark-broadening profiles of the plasma spectral lines, assuming the local thermodynamic equilibrium condition. Time-resolved plasma temperature and electron density for fs-LIBS using ultraviolet (UV) and infrared (IR) laser wavelengths were analyzed and no significant dependence on fs laser wavelength was observed for any of the samples. However, for all samples the signal-to-noise ratio (SNR) significantly increased using UV laser radiation: copper (), steel (), glass (), and ceramics (). Therefore, by using a fs UV laser wavelength for laser-induced breakdown spectroscopy experiments, for certain materials the SNR and at the same time the limit of detection can be significantly enhanced.

Impact of ambient temperature on the filter polychromators performance and accuracy of thomson scattering diagnostics

Thomson scattering is one of the most important diagnostic methods for measuring plasma electron temperature (Te) and electron density (ne). In the diagnostic system, the polychromator is often used to analyze the spectral broadening and intensity of the detected scattered light. The performance of the avalanche photodiode (APD) used in the polychromator is greatly affected by the ambient temperature. The change of ambient temperature will seriously affect the accuracy of Thomson scattering diagnosis. Through experimental analysis, when the ambient temperature increases, the gain of APD will be significantly reduced, resulting in a significant deviation in electron density measurement. Taking the system response at an ambient temperature of 24.1 °C as reference, the deviation of electron density measurement varies from 43% to −16%, with the ambient temperature from 16.6 °C to 29.9 °C. However, the change of ambient temperature has little impact on the measurement of electron temperature. Detailed test of the polychromator shows that the estimated deviation of the electron temperature is within 3%. Due to the change of ambient temperature, the response of the detectors in each channel of the polychromator is inconsistent, which will cause random errors. The influence on electronic temperature calculation is analyzed by numerical simulation.

A field programmable gate array based Langmuir probe system for measurement of plasma parameters at 500kHz in a high-power impulse magnetron sputtering plasma.

By utilizing Field Programmable Gate Arrays in a configuration similar to that of the Mirror Langmuir Probe, it is possible to bias a single probe at three precise voltages in sequence. These voltages can be dynamically adjusted in real-time based on the measured plasma electron temperature to ensure the transition region is always sampled. The first results have been obtained by employing this method and have generated real-time outputs of electron temperature, ion saturation current, and floating potential on a low temperature pulsed-DC magnetron at 500kHz. These results are in good agreement with the analysis of a conventionally swept Langmuir probe. This probe is designed with the intention of being implemented on MAST-U to aid in the study of exhaust physics and enable further investigation into filamentary behavior.

Modeling and experimental comparison of pulsed-DC driven low-pressure plasma discharge in a metal tube

High-voltage pulsed-DC can be used to deposit films on the inner surfaces of tubes and pipes. However, the characteristics of the plasma discharge in the tubes and mechanisms of film deposition are not well understood. In this study, a discharge is formed in a metal tube inserted with a coaxial anode by microsecond (μs) pulsed power to explore the influence of the pulse parameters on the plasma characteristics, including the temporal and spatial evolution near the tube walls experimentally and by simulation. The discharge waveform is monitored by a voltage-current probe to analyze the impact of the electrical characteristics on the plasma. The plasma properties are diagnosed by a Langmuir probe and numerically calculated by the fluid model. The source voltage and current jointly influence the plasma density and electron temperature, and secondary electron emission by energetic ion bombardment affects not only the distribution of electron density measured by the probe, but also the temporal distribution during the pulse-on and pulse-off time. The electron temperature varies conversely with the density from the plasma zone to the cathode suggesting the typical glow discharge in the pulsed-DC tube. Secondary electron emission is created at a higher discharge frequency, and a sustained plasma between pulse cycles appears to be produced at a higher frequency. The results impart information about the pulsed-DC driven plasma discharge at low pressure as well as the role energetic ions play on the cathode and elucidate the mechanisms of plasma deposition on the interior tube wall.

Influence of the argon admixture on the reactive oxide species formation inside an atmospheric pressure oxygen plasma jet

In this work, a new atmospheric pressure plasma generated in a wire-to-multiwire dielectric barrier discharge on pure oxygen is introduced. This special geometry of 13 wires (one central wire and 12 ones on the external tube) is feeding by a radio frequency (RF) power (13.56 MHz, 1 kW) and produces a stable discharge. The capacity of this device to produce oxygen reactive species and the influence of Ar gas mixture (1–3%) on this production are investigated. The main characteristics of this DBD plasma are measured using optical emission spectroscopy techniques. The rotational, vibrational, and excitation temperatures along with the electron density are determined from OH (A2Σ → X2Π) band and the Stark broadening of the hydrogen atomic line at 486.1 nm, respectively. The temporal evolution and spatial distribution of charged and reactive species in this plasma are also numerically studied by a Global scheme and a two-dimension fluid model based on drift–diffusion approximation. A kinetic dominated by electron collisions is obtained for this plasma. The generation and movement of electrons, positive and negative ions in the wire-to-multiwire configuration are analyzed and discussed according to changes the electric field and plasma frequency. It is shown that the density of both charged and reactive species increases by adding a small amount of argon to the oxygen plasma while the electron temperature reduces in this configuration. A high level of agreement is observed between the experimental and simulation results for the electron density and temperature in this DBD plasma.

Anomalous hot electron generation via stimulated Raman scattering in plasma with up-ramp density profiles

We investigate the evolution and propagation of the electron plasma waves (EPWs) excited by stimulated Raman scattering (SRS) in the inhomogeneous plasma theoretically and numerically with particle-in-cell (PIC) simulations. A theoretical model of EPWs in inhomogeneous plasmas is presented, which shows that the evolution of the EPW wavenumber is mainly related to the plasma density profile rather than the plasma electron temperature, in agreement with PIC simulations. When the density gradient is positive along the propagation direction of an EPW, its wavenumber decreases with time and consequently its phase velocity increases continuously, causing the trapped electrons to be accelerated to anomalous high energy. Furthermore, it is found that the Langmuir decay instability tends to reduce the levels of SRS saturation and electron acceleration and produce hot electrons in the opposite direction. This work provides a new understanding of electron heating due to SRS excitation.

Comparison of Electron Densities and Temperatures in Helium and Argon Nonthermal Atmospheric-Pressure Plasmas by Continuum Spectral Analysis

Comparison of Electron Densities and Temperatures in Helium and Argon Nonthermal Atmospheric-Pressure Plasmas by Continuum Spectral Analysis

Better Understanding of Hydrogen Pellet Ablation Cloud Spectra through the Occupation Probability Formalism in LHD

We have recently incorporated the occupation probability formalism (OPF) in the simulation model [C. Stehlé and S. Jacquemot, Astron. Astrophys. 271, 348 (1993)] to have a smooth transition from discrete lines to continuum spectrum in the wavelength range near the Balmer series limit. We have analyzed spectra measured for the hydrogen pellet ablation cloud in the Large Helical Device with the revised model, and have found that the electron density in the ablation cloud has a close correlation with the electron temperature of the background plasma. This type of correlation is first confirmed in the present analysis and should give a new insight in the simulation studies of pellet ablation for the magnetically confined fusion plasma.

Turbulence simulations with BOUT++ by using SOLPS grids for SOLPS/BOUT++ coupling

AbstractThe coupling of transport code SOLPS with the turbulence code BOUT++ was reported in Reference [D. R. Zhang et al., Phys. Plasmas 26, 012508 (2019)], while the grids of SOLPS and BOUT++ are not completely consistent with each other, especially in the divertor region. In the present work, a method of replacing the grids of BOUT++ with the grids of SOLPS is proposed to make the simulation region fully consistent with each other for the SOLPS/BOUT++ coupling. A SOLPS grid file is generated with an MHD equilibrium and used in BOUT++ code to simulate the profiles of plasma density, ion temperature, and electron temperature with the six‐field two‐fluid model. The profiles of the main plasma parameters simulated with the SOLPS grids are similar with the profiles simulated with the BOUT++ grids at the midplane, while the profiles are deformed compared with the profiles simulated with the BOUT++ grids at the outer divertor target because of the differences of the distributions of SOLPS grids and BOUT++ grids in the divertor region. The radial particle transport coefficient and heat transport coefficients are also calculated by using the BOUT++ code with the two grids, and the comparisons of the radial particle transport coefficient and heat transport coefficients simulated with the two grids at the midplane and outer divertor target plate are discussed.

Investigation of the temperature of electrons in a glow discharge plasma at direct current Ar and Ar/C2H2

This paper presents the results of the study of the electron temperature in argon and argon-acetylene plasma of DC glow discharge. The optical-emission method was used to determine the main parameter of the complex plasma. The dependence of the electron temperature on the operating pressure, voltage, and discharge time was determined from the intensity of spectral lines. The source voltage was varied from 1 kV to 1.5 kV, and the pressure was maintained between 0.1-1 torr. As a time-dependent function, the electron temperature was calculated every 20 seconds during a 200-second discharge. The results showed that in argon plasma, as the pressure increases, the electron temperature decreases up to a pressure value of 0.4 torr, subsequent increase leads to an increase in temperature. Also, with the increase in source voltage, a decrease in electron temperature within the error limits is observed. In addition, in dust plasma (PECVD in Ar-C2H2), the electron temperature as a function of pressure and source voltage showed a trend similar to that observed in argon plasma. However, the electron temperature in dust plasma increases as a function of time at the initial moment, after which it decreases sharply with time.

Quantitative analysis method of laser-induced breakdown spectroscopy based on temperature iterative correction of self-absorption effect

Laser-induced breakdown spectroscopy (LIBS) is an ideal real-time on-line method of detecting minor elements in alloys. However, in the case of laser-produced high-density plasma, the self-absorption is usually an undesired effect because it not only reduces the true line intensity, leading the line intensity to become nonlinear with the increase of emitting species content, but also affects the characterization parameters of the plasma, and finally affects the accuracy of quantitative analysis. Since the plasma electron temperature <inline-formula><tex-math id="Z-20240228161235">\begin{document}$(T)$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20231541_Z-20240228161235.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20231541_Z-20240228161235.png"/></alternatives></inline-formula>, radiation particle number density and absorption path length (<i>Nl</i> ) determine the degree of self-absorption and affect the corrected spectral line intensity, a new self-absorption correction method is proposed based on temperature iteration. The initial <i>T</i> is obtained by using this method through spectral line intensity, and the self-absorption coefficient SA is calculated based on the initial <i>Nl</i> parameter to correct the spectral line intensity. Then a new <i>T</i> is obtained from the new spectral line intensity and the new SA is calculated to further correct the spectral line intensity. Through continuous calculation and correction of these two parameters, self-absorption correction is finally achieved. The experimental results of alloy steel samples show that the linearity of Boltzmann plot is increased from 0.867 without self-absorption correction to 0.974 with self-absorption correction, and the linear correlation coefficient <i>R</i><sup>2</sup> of the single variable calibration curve for Mn element increases from 0.971 to 0.997. The relative error of elemental content measurement is improved from 4.32% without self-absorption correction to 1.23% with self-absorption correction. Compared with the commonly applied self-absorption correction methods, this method has obvious advantages of simpler programming, higher computation efficiency, and its independence of the availability or accuracy of Stark broadening coefficients. Moreover, this method can directly obtain the radiation particle number density and absorption path length, which is beneficial to the diagnosis and quantitative analysis of plasma.

Development of the Langmuir probe under q-distribution for NCST

The Langmuir probe is one of the important diagnostic methods for measuring the edge plasma parameters of tokamak. A quadruple Langmuir probe (QLP) system was designed and built on the NanChang Spherical tokamak (NCST). The nonextensive single Langmuir probe (NSLP) theory [Qiu et al., Phys. Rev. E 101, 043206 (2020)] is extended to the nonextensive QLP (NQLP) theory, and then the electron temperature and electron number density of the edge plasma in NCST are obtained. The results show that the differences between the edge plasma parameters (electron temperature and number density) under the nonextensive statistics and those under the Maxwellian distribution are more than 50%, which indicates that the nonextensive parameters have an important influence on the actual measurement of QLP.