Antonín Tálský

On the oxygen addition into nitrogen post-discharges

It is well known that the dissociation degree of nitrogen can be substantially increased if a small amount of oxygen is added into an active discharge. In this work it is experimentally shown that a very similar phenomenon occurs also when oxygen is added into the nitrogen late post-discharge. A detailed kinetic model, valid for the oxygen addition into the active discharge, fails to interpret these new experimental observations, and, consequently, its completeness has to be questioned.

Simultaneous measurement of N and O densities in plasma afterglow by means of NO titration

In this work we describe a method based on NO titration that permits us to measure at the same time the absolute concentrations of N and O atoms in the gas phase. This method is suitable for low concentrations of oxygen atoms. We also discuss the validity of the titration method, especially the influence of the reaction time. It was used to study the influence of O2 admixture on the degree of dissociation of nitrogen in the afterglow. The results of the NO titration technique were compared with those obtained by means of electron paramagnetic resonance and with the relative values determined from emission of .

Electron density measurements in afterglow of high power pulsed microwave discharge

In the paper we study, be means of microwave interferometry, the evolution of electron density in afterglow of pulsed driven nitrogen discharge. Recombination coeffients are derived, too.

Plasma diagnostics using electron paramagnetic resonance

Methods giving absolute concentrations of various species in the plasma are of utmost importance to plasma research. Besides currently prevalent laser methods, a method based on microwave absorption—electron paramagnetic resonance—can be successfully used for plasma diagnostics. It is able to detect many atoms, molecules and radicals in the ground or excited states. In this paper we give an overview of the method and several practical examples. (Some figures in this article are in colour only in the electronic version)

Kinetics of O2 + TEOS gas-phase chemical reactions in a remote RF plasma reactor with electron spin resonance

Kinetics of the reaction O+TEOS (tetraethoxysilane) was studied by means of the ESR method. Molecular oxygen was partially atomized by a 13.56-MHz discharge in the quartz tube that passed inside an ESR cavity. TEOS vapors were injected between the discharge and ESR cavity. O-atom loss occurring due to the reaction of atomic oxygen with TEOS molecules was measured and the rate coefficient k, of the reaction of O atoms with TEOS molecules was determined. The obtained results could be used for deposition process simulations.

An experimental study of high power microwave pulsed discharge in nitrogen

We investigated a plasma excited by high power pulsed microwaves (MWs) (pulse duration 2.5 µs, repetition rate 400 Hz, peak power 105 W, frequency 9.4 GHz) in nitrogen at reduced pressure (pressure range 10–2000 Pa) with the aim of a better understanding of such types of discharge. The construction of the experimental device suppresses the plasma–wall interactions and therefore the volume processes are predominant. To obtain the temporal evolution of the electron density we used two MW interferometers at frequencies of 15 and 35 GHz with dielectric rod waveguides which gives them the capability of localized measurements. We estimated the effective collision frequency from the absorption of a measurement beam. Time resolved optical emission spectroscopy of the 1st negative system and the 2nd positive system was carried out, too. Due to a high power input the discharge dynamics was fast and the steady state was typically reached in 1 µs. We found that the effective collision frequency has the same temporal behaviour as the 2nd positive system of N2, including a characteristic maximum at the beginning of the pulse.

CN chemiluminescence in N2 + CH4 Flowing afterglow at low temperatures

The spectra of flowing microwave post-discharge excited in N2 and N2 + CH4(N2 + C2H2) gas mixtures have been studied at low temperature (77 K). The molecular spectra of CN emitted by the collision-induced N + C and N + CH chemiluminescent reactions in the low-temperature afterglow system have been thoroughly investigated. The intensity of different CN (B2Σ+-X2Σ+) vibrational bands is very sensitive to low hydrocarbon concentration in nitrogen used as the working gas. Detection of hydrocarbon species has been demonstrated from concentrations of CH4 and C2H2 in N2 greater than 1010 molecules · cm−3.

Influence of admixtures on production rate of atomic nitrogen

In this paper, we present the dependencies of atomic nitrogen concentration in the afterglow on the amount of oxygen admixture added to the main gas. It is observed that until a certain threshold, the concentration of atomic nitrogen rises rapidly with the amount of admixture. If even more of the admixture is added, the concentration of nitrogen atoms decreases again. We suggest the explanation of this phenomenon by two antagonistic processes acting together: (i) decrease of the surface recombination coefficient by blocking of active sites and (ii) chemical reaction between N and O2 in the volume.

Role of admixtures on dissociation of molecular gases

It is known that dissociation degree in the afterglow can be increased substantially if a small admixture is added to to the main gas prior to its passage through the discharge. In this experimental work we measured the influence of the admixture on dissociation degree, when it is added directly into the afterglow.

Kinetic Study of Atmospheric Pressure Nitrogen Plasma Afterglow Using Quantitative Electron Spin Resonance Spectroscopy

Quantitative electron spin resonance spectroscopy is used to measure nitrogen atom density in atmospheric pressure dielectric barrier discharge afterglow. The experiment shows that oxygen injection into early afterglow increases the nitrogen dissociation in certain parts of the afterglow while it is decreased in the rest of the afterglow. Numerical kinetic modelling supports and explains the experimental data while the best fit provides some a priori unknown parameters such as initial concentrations and rate constants.