Radio Frequency Discharge In Oxygen Research Articles

Validation of THz absorption spectroscopy by a comparison with ps-TALIF measurements of atomic oxygen densities

Terahertz (THz) absorption spectroscopy has recently been developed as a diagnostic technique for measuring absolute ground-state atomic oxygen densities in plasmas. To demonstrate the validity of this approach, we present in this Letter a benchmark against a more established method. Atomic oxygen densities were measured with THz absorption spectroscopy and compared to those obtained from picosecond (ps) two-photon absorption laser induced fluorescence (TALIF) measurements on the same capacitively coupled radio frequency oxygen discharge. Similar changes in the atomic oxygen density were observed with both diagnostics when varying the applied power (20–100 W) and the gas pressure (0.7–1.3 mbar). Quantitatively, the results are in good agreement as well, especially when considering the total margin of error of the two diagnostics. For example, for a gas pressure of 1.3 mbar and an applied power of 30 W, atomic oxygen densities measured with THz absorption spectroscopy and TALIF were (7.0 ± 1.7)×1014 cm−3 and (5.3 ± 3.2)×1014 cm−3, respectively. This shows that THz absorption spectroscopy is an accurate technique that can be reliably used for real-world applications to determine atomic oxygen densities in plasmas.

Terahertz absorption spectroscopy for measuring atomic oxygen densities in plasmas

This paper describes the first implementation of terahertz (THz) quantum cascade lasers for high-resolution absorption spectroscopy on plasmas. Absolute densities of ground state atomic oxygen were directly obtained by using the fine structure transition at approximately 4.75 THz. Measurements were performed on a low-pressure capacitively coupled radio frequency oxygen discharge. The detection limit in this arrangement was found to be cm−3, while the measurement accuracy was within 5%, as demonstrated by reference measurements of a well-defined ammonia transition. The results show that the presented method is well suited to measure atomic oxygen densities, and it closes the THz gap for quantitative atomic density measurements in harsh environments such as plasmas.

Influence of magnetic filter position on negative ion density in oxygen RF discharge

In this study, the influence of the position of a magnetic filter on electron temperature and hence on the negative ion density in helicon oxygen discharge is investigated. This study is performed with the view to improve negative ion density in radio frequency (RF) plasma. RF plasma is produced in the source region of Helicon Plasma Source (HeliPS) and the variation of electron temperature, density, and negative ion density in case of oxygen discharge is studied to determine the optimum position of the magnetic filter relative to the position of the antenna where RF power is applied. It is observed that the RF field can penetrate beyond the magnetic filter and cause additional ionization in the expansion chamber and thereby produce high energy electrons and decrease the negative ion density. Therefore, the position of the magnetic filter should be sufficiently away from the location of the antenna as it influences the formation of negative ions.

Global model study of plasma parameter variation in helicon plasma source in oxygen discharge

In this work, different plasma parameters, such as electron density, temperature, and negative ion density are measured in both the source and expansion chamber of the Helicon Plasma Source (HeliPS) in a radio frequency (RF) oxygen discharge of 13.56 MHz and are compared with the values obtained numerically using the volume-averaged global model. For this purpose, the global model of RF oxygen discharge suitable for the HeliPS having two chambers (source and expansion) together with the electromagnet in the source chamber and the magnetic cage in the expansion chamber to reduce the radial loss of plasma is developed using the particle and power balance equations. In this model, the radial confinement by the axial field of the electromagnet in the source chamber and the confinement in the expansion chamber by the cusped field of the magnetic cage is incorporated. Studies on the charged particle dynamics by both the model and the experiment show comparable values of the variation of species density and electron temperature with RF power and working pressure as well as with the applied magnetic field of the electromagnet in the source chamber.

Separators for alkaline water electrolysis prepared by plasma-initiated grafting of acrylic acid on microporous polypropylene membranes

Highly hydrophilic separators for alkaline water electrolysis were prepared by plasma-initiated grafting of acrylic acid on porous polypropylene (PP) membranes. The membranes were activated in a low-pressure radio-frequency discharge in oxygen and subsequently graft polymerization of acrylic acid was performed in aqueous solution. The membranes were characterized by gravimetric grafting degree (GD), SEM, FTIR, critical wetting surface tension (CWST) test, mechanical strength, and electrolytic conductivity. Moreover, the membranes were applied as separators in alkaline electrolysis cell, and content of hydrogen in the produced oxygen was measured to determine membrane permeability to hydrogen dissolved in the electrolyte. It was observed that increasing GD improves performance of membranes as separators in alkaline electrolysis, although the particular effects on the electrolytic conductivity and hydrogen permeability strongly depend on structure the of initial PP substrate. Ageing test conducted in 30 wt% KOH at 60 °C revealed that although considerable degrafting took place at beginning of the test, the remaining polyacrylic acid provided highly hydrophilic character to membrane for 7000 h of the test.

Application of RF discharge in oxygen to create highly oxidized metal layers

ABSTRACTThe radio frequency (RF) discharge in an oxygen atmosphere was used to produce metal oxide films. The high efficiency of the RF discharge technique for metal oxidation at room temperature was demonstrated for gold, silver and copper foils. Oxide films up to 10 nm in thickness were obtained. The produced oxide films were studied by X-ray photoelectron spectroscopy (XPS). The XPS data showed the formation of oxidised species: Cu2+, Ag1+ and Au3+. Analysis of the oxygen species was performed using O1s spectra. For copper and silver foils, the formation of additional oxygen species apart from oxygen in the structure of oxides was shown. The reaction probability toward oxidation of carbon monoxide (CO) was estimated for all oxidised layers. It was established that gold and silver oxide films interacted with CO at room temperature, while cupric oxide showed high activity at temperature >353 K.

Anodization of titanium in radio frequency oxygen discharge — Microstructure, kinetics & transport mechanism

Plasma anodization in oxygen discharges is a prominent technique in semiconductor processing, allowing nearly defect-free oxidation at low temperatures. Here we apply inductively coupled radio frequency oxygen plasma anodization to titanium and study the effect of temperature and dc bias potential on the oxide film morphology. To achieve a detailed understanding of the growth process, the oxide crystal phase is characterized by Raman spectroscopy and the orientation between the oxide film and the substrate is determined by TEM. The constant voltage oxidation kinetics is modelled and growth experiments with inert markers allow to identify the ionic species controlling the growth rate. Plasma anodization experiments in combination with SIMS depth profiling of the interface region add to these experiments and prove that oxygen is the mobile species in the titania layer. The applied kinetic model allowed the determination of the activation energy for ionic transport with values of 1.31eV at 200°C and 1.58eV at 400°C and 550°C. As oxygen ion transport is likely responsible for film growth, the observed surface morphologies were most likely formed by oxygen ion sputtering or result from initial nucleation processes.

Characterization of low-pressure microwave and radio frequency discharges in oxygen applying optical emission spectroscopy and multipole resonance probe

Optical emission spectroscopy (OES) and multipole resonance probe (MRP) are adopted to characterize low-pressure microwave (MW) and radio frequency (RF) discharges in oxygen. In this context, both discharges are usually applied for the deposition of permeation barrier SiOx films on plastic foils or the inner surface of plastic bottles. For technological reasons the MW excitation is modulated and a continuous wave (cw) RF bias is used. The RF voltage produces a stationary low-density plasma, whereas the high-density MW discharge is pulsed. For the optimization of deposition process and the quality of the deposited barrier films, plasma conditions are characterized using OES and MRP. To simplify the comparison of applied diagnostics, both MW and RF discharges are studied separately in cw mode. The OES and MRP diagnostic methods complement each other and provide reliable information about electron density and electron temperature. In the MW case, electron density amounts to ne = (1.25 ± 0.26) × 1017 m−3, and kTe to 1.93 ± 0.20 eV, in the RF case ne = (6.8 ± 1.8)×1015 m−3 and kTe = 2.6 ± 0.35 eV. The corresponding gas temperatures are 760±40 K and 440±20 K.

Impedance spectroscopy study of relaxor ferroelectric PLZT thin films obtained by PLD and RF-PLD

Ac conductivity of (Pb0.67La0.22)(Zr0.2Ti0.8)O3 thin films has been investigated by impedance spectroscopy. Thin films have been grown by pulsed laser deposition (PLD) and by PLD assisted by radiofrequency discharge in oxygen. A cubic perovskite structure similar to that of the target has been found by XRD analysis. The ac conductivity of the films has been studied as a function of the frequency, ac driving field and dc bias field amplitudes. We found a power law dependence on frequency at short time scale (high frequencies) and/or low field amplitude, while at low frequencies and/or high field amplitude the dc conductivity contribution was dominant. Measurements at high dc field (up to 150 kV/cm) indicate that films grown by RF-PLD have the ac conductivity decreased by one order of magnitude with respect to PLD-grown films.

OLED substrate conditioning by low power density RF plasmas

Capacitively coupled radio-frequency discharges in oxygen and tetrafluoromethane were used for surface conditioning of indium tin oxide (anode) and ZPN1168-30 (bank material) thin films, respectively, prior to the inkjet printing during organic display device fabrication. The actual power density delivered to the plasmas was calculated by cancelling the stray impedance of the cell and taking into account the transmission function of the system. This calculation allowed the systematic study of the influence of the main process parameters to the wetting properties of the films. Hydrophilic indium tin oxide (min contact angle 12 deg) and hydrophobic ZPN1168-30 resist (max contact angle 112 deg) were obtained, while the power density was maintained lower than 15 mW/cm 2 in both discharges. Positive-ion flux measurements were carried out, using an RF-biased single-sided planar probe, and values up to 10 14 cm -2 s -1 were found at this low power density. Optical emission spectroscopy showed that oxygen plasma was rich in O 2 + ions and tetrafluoromethane plasma in CF 2 +. Thus, the ion contribution to the treatment mechanism was discussed and the complementary role of other plasma particles, like excited neutrals and photons, in the treatment process remained a question in debate.

Particle in Cell Simulation of Low Temperature Laboratory Plasmas

AbstractSeveral applications of PIC simulations for understanding basic physics phenomena in low‐temperature plasmas are presented: capacitive radiofrequency discharges in Oxygen, dusty plasmas and negative ion sources for heating of fusion plasmas. The analysis of these systems based on their microscopic properties as accessible with PIC gives improved insight into their complex behavior. These studies are results of joint efforts over about one decade of research groups from Greifswald University, Germany; Bari University, Italy; Keio University, Japan and Innsbruck University, Austria. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Spectral researches on interaction of laser radiation with targets from titanium oxides

Spectral characteristics and kinetic processes of the laser-induced plasma used for the growth of films from titanium oxides were investigated. The experiments were carried out in vacuum, oxygen, and an oxygen radiofrequency discharge plasma and its afterglow. A collision-radiative model describing the state-to-state kinetics of titanium atoms and ions at various stages of flight of laser-induced plasma was proposed. It was shown that the conditions of local thermodynamic equilibrium are disturbed because of a fast gas-dynamic expansion of plasma. Nonetheless, the distribution functions of titanium atoms and ions over excited states are described by the Boltzmann formulas with different temperatures.

Radio-frequency discharges in oxygen: I. Particle-based modelling

In this series of three papers we present results from a combined experimental and theoretical, particle-based study to quantitatively describe capacitively coupled radio-frequency discharges in oxygen. The particle-in-cell Monte Carlo model on which the theoretical description is based is described in this paper. It treats space charge fields and transport processes on an equal footing with the most important plasma–chemical reactions. For given external voltage and pressure, the model determines the electric potential within the discharge and the distribution functions for electrons, negatively charged atomic oxygen and positively charged molecular oxygen. Previously used scattering and reaction cross section data are critically assessed and in some cases modified. To validate our model, we compare the densities in the bulk of the discharge with experimental data and find good agreement, indicating that essential aspects of an oxygen discharge are captured.

Dissipated power in a radio-frequency discharge inoxygen

Radio-frequency discharges in oxygen are widely used in plasmaprocesses like etching and covering technologies. The manner and location inwhich power is dissipated in the discharge determines the character of the etchor deposition. Discrepancies between experimental values of power dissipationwith theoretically predicted values as reported in the literature are themotivation for the present paper. The basic idea is to identify varioussources of power dissipation in the bulk and the sheath, and use scalingrelationships available from existing models to compute their contributions.It was seen that a two-temperature distribution better approximates theelectron energy distribution function as opposed to a single-temperatureMaxwellian. Also, at given ranges of power and pressure, ohmic heating inthe pre-sheath region and not stochastic heating in the sheath region maybe the predominant mechanism.

Patterning of immobilized antibody layers via photolithography and oxygen plasma exposure

A novel technique for patterning immobilized antibody layers based upon photolithography and oxygen plasma exposure has been developed. Mouse monoclonal antibodies specific for thiabendazole (a post-harvest fungicide and veterinary anthelmintic) were covalently linked through free amine groups to aminosilanized silicon dioxide films using glutaraldehyde. Immobilized antibody layers were stabilized with sucrose, dehydrated, and stored refrigerated with desiccant. Photolithographic patterning was performed with a positive photoresist with modified bake temperatures and times, selective UV exposure with a contact mask, and aqueous alkaline solubilization of exposed resist. Exposded regions of immobilized antibody were then removed by exposure to a low power, radio frequency oxygen discharge. Residual resist was stripped with acetone. Successful patterning was demonstrated by challenging surfaces with goat anti-mouse antibody conjugated to tetramethylrhodamine isothiocyanate Sucrose stabilization was necessary for antibody to undergo photoresist processing without loss of binding activity. Challenge with enzyme linked antigen of oxygen plasma exposed antibody layers demonstrated that plasma treatment completely neutralized antibody capture ability. Ellipsometry measurements of oxygen plasma exposed antibody layers indicated complete removal of immobilized antibodies. Fluorescent imaging demonstrated smallest line widths of 2–3 μm.

Negative ion-containing plasma in parallel-plate radio-frequency discharge in oxygen

The properties of a plasma in a parallel-plate radio frequency (rf) symmetric discharge of 13.56 MHz in oxygen have been investigated. The plasma contains negative ions. The temperature and density of the negative ions have been determined from the slope and height of the semilog-plotted second derivative of the probe characteristics. The laser photodetachment technique is applied, and data indicating the existence of negative ions are obtained. The negative ion densities deduced by both methods are comparable. The negative ion temperature is found to be from 0.1 to 0.6 eV, depending on the pressure and rf power density. The electron energy distribution f(E) deviates from Maxwellian and has a depletion of low-energy parts, which may be due to the loss of low-energy electrons in attachments. A shifted annular-shaped distribution is fitted to the measured f(E), and the data analysis is made according to this form of f(E).

Decrease in the etch rate of polymers in the oxygen afterglow with increasing gas flow rate

AbstractIn this paper we report the variation of the etch rate of polymers in the afterglow of a radio frequency discharge in oxygen as a function of total flow rate in the range 2–10 cm3 (STP)/min. The measurements were made at ambient temperature with the O(3P) concentration held essentially constant. We report results on three polymers: cis‐polybutadiene, a polybutadiene with 33% 1,2 double bonds, and a polybutadiene with 40% 1,2 double bonds. We have observed that the etch rate of these polymers decreases significantly with increasing flow rate, strongly suggesting that the vapor‐phase products of polymer degradation contribute to the degradation process.