Single Langmuir Probe Research Articles

Measurement of the electron energy distribution function in CO2 inductively coupled plasma

CO2 inductively coupled plasmas (ICPs) were generated using a radio frequency power of 13.56 MHz at 100 mTorr. Electron energy distribution functions (EEDFs) were measured using a single Langmuir probe, and various plasma parameters such as the electron density and electron temperature were obtained from the measured EEDFs. EEDFs with multislope structures are obtained. However, changes in the gas composition in the ICP were observed via optical emission spectroscopy. The electron density barely increases when a sudden change in the gas composition occurs. The E to H mode transition occurs at a stationary gas composition as the absorbed power increases. The EEDFs of CO2 plasma, CO plasma, and O2 plasma were calculated using BOLSIG+, which is a two term Boltzmann solver [G. Hagelaar and L. Pitchford, Plasma Sources Sci. Technol. 14(4), 722 (2005)]. The measured EEDF is closest to the EEDF of the CO plasma.

Langmuir probe in magnetized plasma: Determination of the electron diffusion parameter and of the electron energy distribution function

AbstractThis work is devoted to a new method used to determine the electron diffusion parameter and the electron energy distribution function (EEDF) in magnetized plasma, by means of a Langmuir single probe. This method is only based on calculations performed on experimental data, no model is used and results do not depend on the accuracy of the different hypothesis, the probe orientation within the plasma, the magnetic field intensity, the diffusion coefficient, the mean free path or the potential profile through the sheath. We test the method and show its efficiency with experiments performed in hydrogen magnetized microwave plasma, using magnetic field intensity up to 0.12 T. The results are compared with those obtained using classical methods based on models and hypothesis reported in the literature.

Packet-Pulse Dual Magnetron Sputtering

The paper presents the results of experimental study of the discharge formed by a dual (DU) magnetron sputtering system (MSS) with aluminum targets in the mode of packet-pulse magnetron sputtering of high power (called deep oscillation magnetron sputtering (DOMS) in foreign literature). A special feature of the discharge in the DOMS mode is the use of unipolar sequence of micropulses with short durations and high powers that form macropulse duration 1000–3000 μs. This mode of sputtering was previously used only in single MSS. In this paper, the DOMS mode is first investigated with a dual magnetron sputtering system. The main plasma parameters are measured using triple and single Langmuir probes. Dependences of plasma parameters on the parameters of the pulsed discharge power supply: voltage and current amplitudes, current density, and power density on the target surface are established. The results of experiments show that the use of the dual packet-pulse magnetron sputtering can significantly increase the plasma density and the ion current density on the substrate in comparison with the traditional DC and MF modes of magnetron sputtering. The ratio of the ion flux density to the flux density of neutral atoms, characterizing the degree of ion bombardment of the growing coating in the DU DOMS mode, reached a value of 28, whereas in the DC mode it was 0.8.

Measurement of plasma parameters in an electron source with a plasma cathode based on a low-pressure arc discharge

In the electron source with a grid plasma cathode based on a low-pressure arc discharge, the parameters of the emission plasma were investigated depending on the different conditions of its generation (type of gas, operating pressure, discharge current amplitude, resistance in the hollow anode circuit of a plasma emitter). For this purpose, a single cylindrical Langmuir probe was used. To measure the current-voltage characteristics of the probe, taking into account the features of the functioning of the electron source (galvanic isolation from high accelerating voltage, the use of high-voltage cables with high parasitic parameters, etc.), an automated measurement circuit was used, allowing for a relatively short time to collect high statistics of experimental data (depending on the frequency the impulses of the discharge current and their total number). To eliminate the influence of the parasitic parameters of the circuit, the measurement circuit was located in the maximum proximity to the generation space of the emission plasma (in a vacuum chamber), which significantly increased the accuracy of the experimental data obtained.

Physical and mechanical properties of surface modified poly ethylene terephthalate films through low pressure plasma and ultra-violet light

The present work focussed on the effect of UV light radiation and Direct current glow Discharge Plasma (DC) on Polyethylene Terephthalate (PET) surface for food packaging applications. The PET was treated by three different plasma such as air, argon, and oxygen with a treatment time of 5–25 min and pressure kept as 3 Pa. The PET film was exposed by UV radiation using the wavelength between 200–400 nm UV light Lamp with a treatment time of 5–25 min. And also we measured the electron temperature (Te) and electron density (Ne) of the three different plasmas by Single Langmuir probe method. The surface properties of UV light radiated and plasma treated PET films were characterized by static contact angle, x-ray diffraction, Optical analysis (UV–vis), ATR-FTIR, Structural analysis (AFM)) and the results were compared. We observed that the bulk properties of the treated materials remained unchanged. This was confirmed by x-ray diffraction results. The new polar functional groups were also detected on the treated films by FTIR spectrum analysis. The surface roughness was calculated from AFM analysis for both untreated and treated PET films. The oxygen plasma treated sample showed higher roughness, which indicated that a large amount of oxygen containing polar groups appeared on the surface of the PET film. The obtained results reveal that the plasma treated PET films were more effective than the Ultra-violet (UV) light radiated film.

Registration of an ICP Plasma CV Dependences under Various Pressures in the Plasma-Chemical Deep Etching System

The Langmuir probe plasma parameters diagnostics method was studied based on the ICP plasma chemical processing system. Single Langmuir probe with high-frequency compensation system and the special electrical circuit was designed and constructed. CV dependences in various working pressures were registered.

Local Ion Nitriding of Martensitic Structural Steel in Plasma of Glow Discharge with Hollow Cathode

A probe study of glow discharge plasma is carried out according to the technique of a single cylindrical Langmuir probe at a pressure of 60 Pa in a gas mixture of 70% Ar + 30% N2. The distribution of density of charged particles in a cavity formed by a technological screen to create a hollow cathode effect and by the treated surface of the material is obtained. It is established that the hollow cathode effect leads to increasing ion concentration near the cathode surface during ion nitriding in a glow discharge. The maximum ion concentration in the center of a cathode cavity is ni = 3.5 × 1016 m–3. Effects of the local ion nitriding in the plasma of glow discharge with a hollow cathode as well as the duration of the plasma treatment process on the microhardness and structure of diffusion layer of martensitic structural steel at the temperature of 550°C are studied. The process of diffusion saturation for martensitic steel local ion nitriding is found to be described by an inverse parabolic law. It is proved that smoothing of microhardness distribution through the hardened case rises with the rise of duration of nitriding in plasma of glow discharge with hollow cathode. Three zones are formed in the steel surface as a result of the local ion nitriding: plasma modified zone, transition zone, and unmodified zone. The thickness of the diffusion layer in the zone modified with plasma of glow discharge with hollow cathode effect is two times greater than that in the zone modified without hollow cathode effect.

Investigation of Plasma Parameters During Mode Transition in Magnetic-Pole-Enhanced- Inductively Coupled Neon Plasma

Magnetic-pole-enhanced inductively coupled plasmas (MaPE-ICPs), in comparison with the conventional ICPs, operate in two modes (E and H) dependent upon the power coupling mechanisms, i.e., a low-power capacitive coupling mode (E-mode) and a comparatively high-power inductive coupling mode (H-mode). In this paper, the key plasma parameters during the E–H transition are investigated in neon MaPE-ICP for numerous applied powers (5–100 W) and gas pressures (1–100 Pa). The electron density and electron energy probability functions (EEPFs) are measured by means of a single Langmuir probe (LP). The electron temperature is evaluated by employing an LP, a Boltzmann plot (BP), and the modified BP methods. It is observed that the electron density enhances, whereas the electron temperature reduces with applied RF power and pressure of the feed gas in both the modes of the discharge. In E-mode, the measured EEPFs evolve from the bi-Maxwellian behavior to Druyvesteyn-like distributions with an increase in pressure due to the transition in electron heating mode with pressure. However, the higher electron–electron collision frequency forces the EEPFs to become Maxwellian in the H-mode of the discharge.

Characterization of Arc Plasma by Movable Single and Double Langmuir Probes

In this work, plasma is produced by arc discharge between two copper electrodes and is characterized by a movable single probe and a double Langmuir probe. The movable Langmuir single-probe technique has a reference point since it is biased with reference to one of the electrodes of the plasma-producing system. In some situations such as radio-frequency discharges, no reference point is available to bias the movable single probe. In the double-probe method, each probe is biased with respect to each other and allowed to move through the arc plasma. Depending on the magnitude of the biasing potential, charges are collected by the probes, and the probe current flowing to the circuit is calculated. After that, we obtain the electron temperature and plasma density of the arc plasma. By using the double-probe method, the value of the plasma density is more precise than with the single-probe method. Hence, the double-probe method is more appropriate than the single-probe method.

Electrical Characteristics of Capacitive Coupled Radio Frequency Discharges in Argon and Hydrogen

A symmetric radio frequency (RF) (13.56 MHz) electrode discharge system with different geometry has been investigated at low pressure. All electrical properties of symmetric capacitive RF discharge in pure argon (Ar) and pure hydrogen (H2) have been obtained from the current and voltage waveforms. Here, the changes of voltage and current were investigated according to external electrical discharge parameters. The electron densities of these discharges were measured with a single Langmuir probe. A homogeneous model of capacitive coupled RF (CCRF) discharge was used to determine the electrical properties of a parallel-plate RF discharge system and their dependences on the input RF power and gas pressure .

Pathways in the molecular fragmentation for the C2H5OH/He electrical discharge

ABSTRACTThis study focuses on the glow discharge generated with a gases mixture of Ethanol (C2H5OH) and Helium (He), at different concentrations maintained at a total pressure of 2.0 Torr. We used optical emission spectroscopy (OES) to analyze the discharge mixture at different concentrations of Helium. Single Langmuir probe data was used to determine the Electron Energy Distribution Function (EEDF). For the total C2H5OH/He mixture plasma concentrations, the EEDF has a Maxwellian distribution function. A decrease in He concentration results in significant changes in the EEDF, this behavior is related to the increase in the C2H5OH percentage must increase the energy loses of the electrons in the inelastic collision with C2H5OH producing a significant change in the EEDF, therefore, the EEDF pattern results in an increase of electron–molecule reaction rates. The rise in electron temperature for increasing Helium percentage is explained by the decreasing electron energy loss in the inelastic collisions with C2H5OH molecule. It observes a decrease of electron density ne as a function of the Helium percentage, which can be related to the ratio between ionization cross sections of Helium and C2H6O molecule. The active species are generated in the electron-molecule processes, which are associated with electron impact dissociation of C2H5OH and Helium electronic impact excitation in the gas phase. The emission optical spectra (OES) show changes in the intensity of the most important peaks of the plasma mixture, which indicates the dependence in the formation of the plasma as a function of the percentage of the gases. The changes in the intensities of the same observed species are due to different processes of excitation and ionization energies of the system, in addition to the increase of He metastable states He I. Hydrogen is the main product obtained from the decomposition of C2H5OH.

Experimental Study of Ethanol and Helium Mixture Glow Discharge

This paper focuses on the study of a glow discharge generated from a mixture of ethanol (C 2 H 6 O) and helium (He). Plasma was generated at different concentrations of C 2 H 6 O and He gases maintained at a total pressure of 2 torr. We used optical emission spectroscopy (OES) to analyze the discharge mixture at different concentrations of He. The species identified by the OES technique correspond to O 2 , CO + , CO, H β , H α , and He. A single Langmuir probe was used to obtain the electron temperature (Te) and electron density (ne). Te was found to be below 1.2 eV and ne in the order of 1010 particles per cm 3 .

Langmuir probe and optical diagnostics of stratified glow discharge in a magnetic field

The article presents the preliminary results of an experimental study of the characteristics of a DC stratified glow discharge plasma in an external magnetic field. Single Langmuir probe and emissive spectrometer are used as diagnostic tools for the estimation of various plasma parameters. The main plasma parameters, such as electron temperature, density and floating potential were determined from the voltage- current (VI) characteristics of the probe in the stratified glow discharge plasmas for different magnetic field values. Increasing the value of the magnetic field leads to an increase in the concentration of plasma particles and a decrease in the temperature of electrons. Also by the optical emission spectroscopic (OES) method it was found that the intensity of spectral lines of the stratified glow discharge increases with an increase value of magnetic field. A simple interpretation was made to explain our results according to the work of Bickerton&Engel [21].

Effect of electrode separation in magnetron DC plasma sputtering on grain size of gold coated samples

In this work, an experimental research on a low voltage DC magnetron plasma sputtering (0-650) volt is used for coating gold on a glass substrate at a constant pressure of argon gas 0.2 mbar and deposition time of 30 seconds. We focused on the effects of operating conditions for the system such as, electrode separation and sputtering current on coated samples under the influence of magnetic flux. Electron temperature and electrons and ions densities are determined by a cylindrical single Langmuir probe. The results show the sensitivity of electrode separation lead to change the plasma parameters. Furthermore, the surface morphology of gold coated samples at different electrode separation and sputtering current were studied by atomic force microscopy (AFM). The AFM analysis showed that the variation of average grain diameter and average grain height is nonlinear with a minimum value of average grain diameter 90 nm at electrode separation of 4 cm and 30 mA sputtering current.

Measurement of Plasma Density in Brass Arc Plasma at Atmospheric Pressure Using a Langmuir Single Probe

Measurement of Plasma Density in Brass Arc Plasma at Atmospheric Pressure Using a Langmuir Single Probe

Plasma beam structure diagnostics in krypton Hall thruster

AbstractKrypton Large Impulse Thruster (KLIMT) project was aimed at incremental development and optimization of a 0.5 kW-class plasma Hall Effect Thruster in which, as a propellant, krypton could be used. The final thermally stable version of the thruster (the third one) was tested in the Plasma Propulsion Satellites (PlaNS) laboratory in the Institute of Plasma Physics and Laser Microfusion (IPPLM) in Warsaw as well as in the European Space Agency (ESA) propulsion laboratory in the European Space Research and Technology Centre (ESTEC).During final measurement campaign, a wide spectrum of parameters was tested. The plasma potential, electron temperature, electron concentration, and electron energy probability function in the far-field plume of the thruster were measured with a single cylindrical Langmuir probe. Faraday probes were used for recording local values of ion current. Using several collectors in different locations and moving them on the surface of a sphere, the angular distribution of the expelled particles was reconstructed which was a local measure of beam divergence. Angular distribution of ion flux as measured with a central Faraday probe was parameterized with krypton mass flow rate, voltage, coil current ratio, and the cathode mass flow rate. Beam divergence measurements with Faraday probes as well as plasma parameters derived from Langmuir probe seem to be consistent with our understanding of the operating envelope. Obtained results will serve as a baseline in the design of plasma beam structure diagnostics system for the PlaNS laboratory.

Experimental Studies on Low-Pressure Plane-Parallel Hollow Cathode Discharges

Hollow cathode discharge (HCD) is widely used in material processing and plasma emission spectroscopy due to several advantages over other plasma sources. Basically, the HCD consists of a cathode with a hollow structure (cavity, hole, or parallel faces) and an anode of arbitrary shape. In this investigation, experimental studies on low-pressure plane-parallel HCD operated at different process conditions are reported. Herein, we investigate the dependence of the discharge current on the product of the gas pressure and inter-cathode distance (pD). In addition, the electron temperature and density were inferred from the current-voltage characteristics of a single cylindrical Langmuir probe positioned between the cathodes, on the discharge axis. The measurements were carried out at different gas pressures, magnetic field intensities, working gases, inter-cathode distances, cathode materials, and discharge voltages. The results showed that, at different gas pressures, the maximum discharge current (Id,max) is not only a function of the product pD, but also of the pressure itself. Application of a uniform longitudinal magnetic field improved plasma confinement between cathodes, leading to a substantial increase in Id,max in most of the situations considered in this study. However, for oxygen discharge, a strong discharge current reduction after the application of the magnetic field was observed. In relation to the Langmuir probe studies, it was observed that the uniform longitudinal magnetic field reduced the electron temperature, but this behavior depends strictly on pD. The typical values of electron density and electron temperature in the case of the nitrogen discharge were ne = 1017 m−3 and Te = 2.5 eV, respectively. Finally, our experiments showed that the pD range for hollow cathode effects was between 0.2–5 Pa m.

Validation of double Langmuir probe in-orbit performance onboard a nano-satellite

Many plasma measurement systems have been proposed and used onboard different satellites to characterize space plasma. Most of these systems employed the technique of Langmuir probes either using the single or double probes methods. Recent growth of lean satellites has positioned it on advantage to be used for space science missions using Langmuir probes because of its simplicity and convenience. However, single Langmuir probes are not appropriate to be used on lean satellites because of their limited conducting area which leads to spacecraft charging and drift of the instrument's electrical ground during measurement. Double Langmuir probes technique can overcome this limitation, as a measurement reference in relation to the spacecraft is not required. A double Langmuir probe measurement system was designed and developed at Kyushu Institute of Technology for HORYU-IV satellite, which is a 10 kg, 30 cm cubic class lean satellite launched into Low Earth Orbit on 17th February 2016. This paper presents the on-orbit performance and validation of the double Langmuir probe measurement using actual on-orbit measured data and computer simulations.

The influence of oxygen ratio on the plasma parameters of argon RF inductively coupled discharge

In this paper, the RF-coupled plasma characteristics of argon and oxygen mixed gases were analyzed by emission spectra and Langmuir single probes. The experimental pressure was kept at 0.63 Pa, and the electron temperature and electron density were measured by Boltzmann curve method and Langmuir single probe respectively under different oxygen ratio. The results demonstrate that increasing the oxygen content reduces the plasma electron density, and the plasma will change from E mode to H mode when the discharge power increase from 350 W to 400 W if the discharge gas is pure argon or oxygen ratio is low, but the plasma is in a single E-mode at relatively high oxygen ratios. When the power reaches 450 W, the plasma becomes unstable and the state of plasma will change no matter what mode it is (H mode or E mode). In addition, as the oxygen ratio increases, there is a good agreement between the plasma electron density and the argon 738.74 nm line intensity. However, the electron temperature will decrease in H mode.

Diagnostics of microwave assisted electron cyclotron resonance plasma source for surface modification of nylon 6

Looking at the increasing scope of plasma processing of materials surface, here we present the development and diagnostics of a microwave assisted Electron Cyclotron Resonance (ECR) plasma system suitable for surface modification of polymers. Prior to the surface-treatment, a detailed diagnostic mapping of the plasma parameters throughout the reactor chamber was carried out by using single and double Langmuir probe measurements in Ar plasma. Conventional analysis of I-V curves as well as the elucidation form of the Electron Energy Distribution Function (EEDF) has become the source of calibration of plasma parameters in the reaction chamber. The high energy tail in the EEDF of electron temperature is seen to extend beyond 60 eV, at much larger distances from the ECR zone. This proves the suitability of the rector for plasma processing, since the electron energy is much beyond the threshold energy of bond breaking in most of the polymers. Nylon 6 is used as a representative candidate for surface processing in the presence of Ar, H2 + N2, and O2 plasma, treated at different locations inside the plasma chamber. In a typical case, the work of adhesion is seen to almost get doubled when treated with oxygen plasma. Morphology of the plasma treated surface and its hydrophilicity are discussed in view of the variation in electron density and electron temperature at these locations. Nano-protrusions arising from plasma treatment are set to be responsible for the hydrophobicity. Chemical sputtering and physical sputtering are seen to influence the surface morphology on account of sufficient electron energies and increased plasma potential.