Argon Microwave Research Articles

Spectroscopic Study of an Expanded Argon Microwave (2.45 GHz) Plasma at Atmospheric Pressure in a Helium Environment

In the present work, an argon microwave (2.45 GHz) plasma flame created at the end of a surface-wave-sustained discharge column in a helium environment has been experimentally studied. This is a plasma with new possibilities because under some experimental conditions it expands, being less contracted than the plasma flame created in open air. The new expanded discharge could offer additional advantages for applications in which larger extensions of plasma were required. The expansion phenomenon of this plasma flame was studied under different experimental conditions. In every case, the characteristic parameters of this expanded plasma such as electron density, electron and gas temperatures, or density population of excited atomic levels were measured by using optical emission spectroscopic techniques. From these results, the main advantages of this plasma source were pointed out.

Filamentation in argon microwave plasma at atmospheric pressure

Filamentation in an argon plasma is studied using a microwave cavity at atmospheric pressure. We show that the size and gas temperature of the filaments increase with the power absorbed by the plasma. The appearance of an additional filament occurs at specific values of the absorbed power. Each new filament appears with a smaller diameter than that of its parent filament but the sum of the diameters of all filaments evolves linearly with the absorbed power. A secondary filament emerges from a set of microfilaments created by a perturbation of the electric field (a slight increase in the incident power above a threshold value). This perturbation occurs over a larger radius than that of the parent filament. By resorting to modeling, we found that the filamentation process involves either a decrease in the effective frequency for momentum-transfer collisions, i.e., a lower electron temperature, or an increase in the electron density. We could show that a small change in the relative positions occupied by two filaments in the microwave cavity requires a strong variation in the electron temperature.

Optical diagnostics of a low power—low gas flow rates atmospheric-pressure argon plasma created by a microwave plasma torch

We employ a suite of optical techniques, namely, visual imaging, optical emission spectroscopy and cavity ringdown spectroscopy (CRDS), to characterize a low power, low gas flow rates, atmospheric-pressure argon microwave induced plasma. The plasma is created by a microwave plasma torch, which is excited by a 2.45 GHz microwave with powers ranging from 60 to 120 W. A series of plasma images captured in a time-resolution range of as fine as 10 µs shows that the converging point is actually a time-averaged visual effect and the converging point does not exist when the plasma is visualized under high time resolution, e.g. <2 ms. Simulations of the emission spectra of OH, N2 and in the range 200–450 nm enable the plasma electronic excitation temperature (Texc) to be determined at 8000–9000 K, while the vibrational temperature (Tv), the rotational temperature (Tr) and the gas temperature (Tg) at different locations along the axis of the plasma column are all determined to be in the range 1800–2200 K. Thermal equilibrium properties of the plasma are discussed. OH radical concentrations along the plasma column axis are measured by CRDS and the concentrations are in the range 1.6 × 1013–3.0 × 1014 cm−3 with the highest density at the tail of the plasma column. The upper limit of electron density ne is estimated to be 5.0 × 1014 cm−3 from the Lorentzian component of the broadened lineshape obtained by ringdown spectral scans of the rovibrational line S21 of the OH A–X (0–0) band.

Abatement of perfluorocompounds with microwave plasma in atmospheric pressure environment

Perfluorocompounds emitted by the semiconductor industry are global warming gases. These gases need to be removed efficiently because of their strong absorption of infrared radiation and long atmospheric lifetimes which cause the global warming effect. In this study, microwave argon plasma operating at atmospheric pressure was investigated experimentally for various operating conditions including microwave power, total gas flow rate, initial concentration, and additive gas. The mechanisms of perfluorocompounds decomposition were studied by the plasma emission spectrum. Under the optimum condition, the destruction and removal efficiency of CF 4 could reach up to 98.4%. The emission spectrum analysis indicated that the existence of the O or OH radicals could enhance the CF 4 decomposition by adding suitable volume of O 2 or H 2O. The mechanisms of CF 4 decomposition are that the electron, O and OH radicals all associated with CF 4 conversion, it has the sequence that enough effective electrons reacted with CF 4 to form CF i radicals, O and OH radicals further reacted with CF i radicals to convert CF 4 into CO 2 and HF.

Argon Microwave Discharges Sustained at Atmospheric Pressure: Suppression of Plasma Filaments with Molecular Gases

Argon Microwave Discharges Sustained at Atmospheric Pressure: Suppression of Plasma Filaments with Molecular Gases

Ozone-stimulated emission due to atomic oxygen population inversions in an argon microwave plasma torch

It is shown that, in a microwave torch discharge in an argon jet injected into an oxygen atmosphere at normal pressure, quasi-resonant energy transfer from metastable argon atoms to molecules of oxygen and ozone generated in the torch shell and, then, to oxygen atoms produced via the dissociation of molecular oxygen and ozone leads to the inverse population of metastable levels of atomic oxygen. As a result, the excited atomic oxygen with population inversions becomes a gain medium for lasing at wavelengths of 844.6 and 777.3 nm (the 33P–33S and 35P–35S transitions). It is shown that an increase in the ozone density is accompanied by an increase in both the lasing efficiency at these wavelength and the emission intensity of the plasma-forming argon at a wavelength of 811.15 nm (the 2P04s–2P04p transition). When the torch operates unstably, the production of singlet oxygen suppresses ozone generation; as a result, the lasing effect at these wavelengths disappears.

Functionalization of multi-walled carbon nanotubes (MWCNTs) with nitrogen plasma for photovoltaic device application

Abstract Multi-walled carbon nanotubes (MWCNTs) placed under nitrogen (N 2 ) and argon (Ar) microwave plasma in order to functionalize covalently their side walls with nitrogen containing groups. X-ray photoelectron spectroscopy (XPS) study shows surface modification of the MWCNTs with imine, amine, nitride and amide groups grafted on the side walls. Due to the functional groups, homogenous distribution of MWCNTs in solvent could be obtained. For photovoltaic device fabrication MWCNTs film was casted over n-Si wafer and poly(3-octylthiophene) solution was infiltered. Devices with functionalized MWCNTs show short circuit current density ( J sc ), open circuit voltage ( V oc ), fill factor (FF) and power conversion efficiency ( η ) as 1.8 mA/cm 2 , 0.20 V, 24% and 0.086%, respectively. In the composite film functionalized MWCNTs facilitate photo induced charge separation and efficient holes transportation, suppressing recombination of photo generated charges.

Characterization of high density matrix microwave argon plasmas by laser absorption and electric probe diagnostics

Microwave plasma sources distributed on a planar matrix configuration can produce uniform bi-dimensional plasmas free from magnetic field in the 100 Pa pressure range. In argon, such uniform sheets of plasma have been obtained with ion densities in the range of 1012 to 1013 cm−3 with microwave power ranging from 0.4 to 2 kW. The electrical characterization of the plasma has been investigated using a cylindrical Langmuir probe. A first feature concerns the plasma potential that exhibits quite high values due to the large increase in the electron temperature towards the source plane where the microwave electric field is applied. Secondly, the decrease in the electron temperature observed when increasing the microwave power can be justified by the apparition of multi-step ionization mechanisms via metastable and higher excited states of Ar atom. The concentration and temperature of Ar(3P2) metastables have been measured by laser diode absorption spectroscopy. The results indicate that the presence of Ar(3P2) metastables is significant at 2 cm from the source plane with concentration and temperature values varying from 1010 to 1011 cm−3 and from 500 K to 1300 K, respectively, as functions of argon pressure and microwave power. An analytical model using a few simplifying assumptions provides a plasma picture in good agreement with the experimental results.

Using the van der Waals broadening of the spectral atomic lines to measure the gas temperature of an argon microwave plasma at atmospheric pressure

The ro-vibrational emission spectra of the molecular species are usually used to measure the gas temperature of a discharge at atmospheric pressure. However, under some experimental conditions, it is difficult to detect them. In order to overcome this difficulty and obtain the temperature, there are methods based on the relation between the gas temperature and the van der Waals broadening of argon atomic spectral lines with a Stark contribution negligible. In this work, we propose a method based on this relation but for lines with a Stark broadening comparable with the van der Waals one.

Diagnostic study on the electron density distribution of microwave plasma jet in vacuum environment

In order to diagnose precisely the electron number density of microwave plasma jet in vacuum environment, the integrative probe whose function is the same as that of emissive and Langmiur ones was applied to measure the plasma space potential and its current and voltage property when the probe is charged by the electric power of emissive probe and scanning electric power separately. According to the plasma space potential, saturated current on the current-voltage curve of plasma can be determined, which can be used to estimate the number density of electrons. The experimental results show that the number density of electrons in microwave argon plasma jet in vacuum environment is 1×1016—7.2×1016/m3, when the vacuum pressure is 3.2 and 5.4 Pa, the microwave output power is under 60 W and gas mass flow rate is in the range of 42—106 mg/s.

Study of Spectral Character of Alkali Metals Using Microwave Plasma Torch Simultaneous Spectrometer

A microwave plasma torch (MPT) simultaneous spectrometer was used to study the spectral character and the matrix effect on alkali metal ions in solution. The main parameters were optimized. The microwave forward power was 100 W. The argon flow rate that was used to sustain the Ar-MPT included the flow rate of carrier gas and the flow rate of support gas, which were 0.8 and 1.0 L/min, respectively. The HC1 concentration in the solution was 0.02 mol/L. The observation height was 9.0 mm. The detection limits of Li, Na, K, Rb, and Cs were 0.0003, 0.0004, 0.009, 0.07 and 2.4 mg/L, respectively, and the results obtained by the Ar-MPT were compared with those obtained by argon inductively coupled plasma(Ar-ICP) and argon microwave induced plasma(Ar-MIP). The interference effects of several matrix elements were also studied.

Treatment of Immobilized Collagen on Poly(tetrafluoroethylene) Nanoporous Membrane with Plasma

In this work we treated type I collagen immobilized on different nanoporous membranes with microwave (MW) argon plasma. Hydrophobic and hydrophilic nanoporous substrates of poly(tetrafluoroethylene), with thickness varying from 35 to 70 µm and a 100 nm pore size, were employed as support for collagen immobilization. On the hydrophilic nanoporous membrane, after the MW plasma treatment, the immobilized collagen changed its morphology and showed a tendency to self-assemble in quasi-regular forms as microellipsoids. The presence of collagen immobilized on the nanoporous membrane after the MW plasma treatment was analyzed by detecting in the Raman spectrum an α-helix form, NH deformation vibration, amide II band at 1550 cm-1, a characteristic group frequency of the collagen macromolecule.

Studies on Excitation and Rotational Temperatures of an Oxygen-shielded Argon Microwave Plasma Torch Source

Excitation( T exc ) and rotation( T rot ) temperatures were determined under different conditions for an oxygen-shielded argon microwave plasmsa torch source(OS-Ar-MPT). The T exc value, which was shown to be between 4300 and 5250 K under different operating conditions, was calculated from the slope of the Boltzmann plot with Fe as the thermometric species. The T rot value, which was in the range of 2100–2500 K, was measured with OH molecular spectra. The influences of microwave power, flow rates of the support gas, carrier gas, and shielding gas, as well as the observation height on T exc and T rot were investigated and discussed. The detailed results of T exc and T rot provided a better understanding of the performance of an OS-ArMPT as a source for atomic emission spectrometry.

Modelling of microwave sustained capillary plasma columns at atmospheric pressure

In this work we present a model of argon microwave sustained discharge at high pressure (1 atm), which includes two self-consistently linked parts - electrodynamic and kinetic ones. The model is based on a steady-state Boltzmann equation in an effective field approximation coupled with a collisional-radiative model for high-pressure argon discharge numerically solved together with Maxwell's equation for an azimuthally symmetric TM surface wave and wave energy balance equation. It is applied for the purpose of theoretical description of the discharge in a stationary state. The phase diagram, the electron energy distribution function as well as the dependences of the electron and heavy particles densities and the mean input power per electron on the electron number density and wave number are presented.

On the use of the H α spectral line to determine the electron density in a microwave (2.45 GHz) plasma torch at atmospheric pressure

The electron density of an argon microwave (2.45 GHz) plasma flame generated at atmospheric pressure has been determined by using the Stark broadening of the experimentally measured H α line emitted by the discharge. The H β line was not observable under the experimental conditions of this discharge. Two methods have been employed to obtain the electron density from the Stark broadening of the H α line. The first used the Gigosos–Cardeñoso computational model that considers the strong broadening of the H α line by ionic dynamics. Alternatively, a second method based on a calibration of Stark broadenings of H α and H β lines offered a simpler way to obtain the electron density.

Influence of indium tin oxide treatment using UV–ozone and argon plasma on the photovoltaic parameters of devices based on organic discotic materials

AbstractRecently, we reported that the open circuit voltage, V0C, in two‐layer organic solar cells depends on the indium tin oxide (ITO) treatment. However, the V0C variation details were not clearly understood. The study of the electronic structure at the ITO/organic interface was carried out by using the Kelvin probe method. The results obtained show a strong dependence of the organic vacuum level on the ITO work function, which, in turn, depends on the anode treatment. An abrupt variation of the vacuum level was observed after deposition of a few organic monolayers, which could be attributed to the presence of dipoles at the interface. We demonstrate that the shift magnitude depends on the nature and duration of the ITO treatment. To this end, two different ITO treatments were used. The first one, based on UV–ozone exposure, is known to increase the ITO work function, WITO. The second of these uses a microwave argon plasma generated by a repartee cyclotron excitation. This was adapted for decreasing the WITO value. An investigation on the origin of these variations (‘up and down’) is presented in this study. Copyright © 2005 Society of Chemical Industry

Influence of the excited states on the electron-energy distribution function in low-pressure microwave argon plasmas

In this work the influence of the excited states on the electron-energy distribution function has been determined for an argon microwave discharge at low pressure. A collisional-radiative model of argon has been developed taking into account the most recent experimental and theoretical values of argon-electron-impact excitation cross sections. The model has been solved along with the electron Boltzmann equation in order to study the influence of the inelastic collisions from the argon excited states on the electron-energy distribution function. Results show that under certain conditions the excited states can play an important role in determining the shape of the distribution function and the mean kinetic energy of the electrons, deplecting the high-energy tail due to inelastic processes from the excited states, especially from the 4s excited configuration. It has been found that from the populations of the excited states an excitation temperature can be defined. This excitation temperature, which can be experimentally determined by optical emission spectroscopy, is lower than the electron kinetic temperature obtained from the electron-energy distribution function.

Role of dissociative recombination in the excitation kinetics of an argon microwave plasma at atmospheric pressure

A collisional radiative model was developed in order to investigate the influence of dissociative recombination on the Saha–Boltzmann plasma equilibrium. As the dissociative recombination products are not well known, their relative importance was tested through comparison with the distribution of line intensities obtained in a microwave argon discharge produced at atmospheric pressure by a surface wave. It was found that the main dissociation products are the ground state and the 4s levels, the 5p and upper levels playing a negligible role. Because the higher levels are only weakly affected by dissociative recombination, they remain in partial local thermodynamic equilibrium. Therefore, the excitation temperature determined from these levels adequately describes the electron temperature. The model well reproduces experimental measurements of excitation temperature, rotational temperature, electron density, and absolute populations of the excited levels.

Plasma Polymerization of Rhodamine 6G Thin Films

This paper reports the first preliminary results about the direct plasma polymerization of rhodamine thin films at room temperature. These films are coloured, fluorescent, well adhered to the substrate, mechanically tough and insoluble in water. The layers are obtained by sublimating the dye molecule in a remote electron cyclotron resonance microwave argon plasma operating at low pressure and power. Results about the characterization of the films and their optical properties are discussed.

Self-absorbing method to measure the population of the metastable levels in an argon microwave plasma at atmospheric pressure

Metastable atoms play an important role in the kinetics of plasmas. A self-absorbing method has been used to determine the population density of Ar( 3 P 0 ) and Ar( 3 P 2 ) atomic metastable levels and Ar( 1 P 1 ) and Ar( 3 P 1 ) atomic resonant levels in an argon microwave discharge sustained by a surface wave at atmospheric pressure. Under the operative conditions investigated, the concentrations of these levels ranged from 10 10 −10 12 cm −3 , being in agreement with those reported in the literature, which seems to indicate that this method could be used for this calculation.