V. A. Shakhatov

Kinetics of excitation of N2(A3Σu+, vA), N2(C3Πu, vc), and N2(B3Πg, vB) in nitrogen discharge plasmas as studied by means of emission spectroscopy and computer simulation

Using the methods of emission spectroscopy and computer simulation, the kinetics of excitation of vibrational distribution functions (VDFs) for the A3Σu+ (vA = 0–13), B3Πg (vB = 0–17), and C3Πu (vC = 0–4) electronic states of the nitrogen molecule in nitrogen of dc glow-discharge and electrode or resonant-cavity MW discharge plasmas was studied. The VDFs in the states A3Σu+ (vA = 0–13), B3Πg (vB = 0–17), and C3Πu (vC = 0–4) of the nitrogen molecule differ from the Boltzmann distribution. The main processes that generate these distributions were determined. It was shown that the pattern of the calculated VDFs depends on experimental conditions, level rate coefficients and, what is of particular importance, on the cross sections of elementary processes used in the model.

Spectroscopy of microwave discharge in liquid C7–C16 hydrocarbons

Emission spectra of in-liquid microwave plasma in C7–C16 hydrocarbons were studied in the range of wavelengths from 200 to 800 nm. It was shown that spectra are similar for all studied hydrocarbons. Swan-bands only were observed in the plasma emission. Model of Swan-bands emission was designed for experimental spectra processing. Rotational and vibrational temperatures determined from sequences with v = −1, 0, +1 of C2-bands were 1600 ± 200 K and 7000 ± 2000 K correspondingly. Addition of Ar in the plasma decreased the rotational up to 700 K but did not change the vibrational temperature. It was shown that studied in-liquid microwave plasma is non-equilibrium. Results of electrodynamic modeling of microwave discharge apparatus and some information on the solid phase generated in hydrocarbon plasma processing were presented.

Study of positive column of glow discharge in nitrogen by optical emission spectroscopy and numerical simulation

Nitrogen dc discharges are investigated at a constant pressure of 3 Torr and a variable discharge current of 17–100 mA. Optical emission spectroscopy is employed to detect the excited species at four axial positions far from the cathode (25, 75, 125 and 175 mm) and to determine the rotational and translational temperatures and the vibrational distribution functions (VDFs) of the B 3Πg and C 3Πu states of the nitrogen molecule. A semiempirical level-to-level collisional–radiative model is used for the modeling of the collisional and radiative processes and the processing of data. It provides detailed information on the processes occurring in the dc discharge, calculates the nitrogen emission spectra, predicts the translational and rotational temperatures, the VDFs in the ground and electronic excited B 3Πg (vB = 0–17) and C 3Πu (vC = 0–4) states together with the corresponding vibrational temperatures TV, TB and TC. Theoretical emission spectra and VDFs of the B 3Πg and C 3Πu states are also in good agreement with the experimental ones. The main processes responsible for the VDFs are also established.

Collisional-radiative model of hydrogen low-temperature plasma: Processes and cross sections of electron-molecule collisions

The experimental and calculated cross sections of the interaction of electrons with hydrogen molecules are reviewed. A self-consistent set of cross sections that is reasonable for use in calculating the electron energy distribution function (EEDF) is determined. The processes affecting the EEDF and its moments are analyzed in a wide range of the reduced electric field.

Radiation spectroscopy in the study of the influence of a helium-nitrogen mixture composition on parameters of DC glow discharge and microwave discharge

Studies of plasma of different types of discharge in He-N2 mixtures by the radiation spectroscopy technique are reviewed, and the main mechanisms of formation of emissive conditions are analyzed. The results of comparative study of the influence of the plasma composition on the radiation spectrum, translational temperature, and functions of distribution over rotational and vibrational levels in excited states of nitrogen molecule ions and nitrogen molecules in positive DC glow and in the electrode sheath of an inhomogeneous MW discharge in a He-N2 mixture are described. An approach is developed which allows retrieving the nonequilibrium distribution of the atom and molecule population in excited states with accounting for the aliasing atomic lines and molecular bands of radiations. It is shown that simulation of radiation spectra N2(C3Πu → B3Πg), N2(B3Πg → A3Σu+), and N2+(B2Σu+ → X2Σg+) under assumption of the Boltzmann distribution of the nitrogen molecule and its ion over rotational levels satisfactorily describes the measured gas discharge radiation spectra. It is ascertain that the distribution of the nitrogen molecule population over the vibrational level in the C3Πu state weakly differs from that calculated by the Boltzmann formula in both discharges, and the function of nitrogen molecule distribution over the vibrational levels gvB = 3−12 in the B3Πg state noticeably deviates from the Boltzmann distribution.

Diagnostics of a nonequilibrium nitrogen plasma from the emission spectra of the second positive system of N2

A method is proposed for determining the electron density Ne and the electric field E in the non-equilibrium nitrogen plasma of a low-pressure discharge from the spectra of the second positive system of N2. The method is based on measuring the specific energy deposition in the plasma and the distribution of nitrogen molecules over the vibrational levels of the C3Πu state, as well as on modeling this distribution for a given energy deposition. The fitting parameters of the model are the values of Ne and E. A kinetic model of the processes governing the steady-state density of the C3Πu nitrogen molecules is developed. The testing of this method showed it to be quite reliable. The method is of particular interest for diagnosing electrodeless discharges and provides detailed information on the processes occurring in the discharge plasma. Preliminary data are obtained on the plasma parameters in a cavity microwave discharge and an electrode microwave discharge. In particular, it is found that the electric field in an electrode microwave discharge in nitrogen is lower than that in a hydrogen discharge. This effect is shown to be produced by stepwise and associative processes with the participation of excited particles in nitrogen.

Studies of the distribution functions of molecular nitrogen and its ion over the vibrational and rotational levels in the dc glow discharge and the microwave discharge in a nitrogen-hydrogen mixture by the emission spectroscopy technique

The positive column and the electrode zones of the DC glow discharge and the microwave discharge in nitrogen with the hydrogen additions are investigated. The spectral composition of the emission is determined, and the distribution functions over the vibrational-rotational levels of the electron-excited states of the nitrogen molecule and the nitrogen molecule ion are recovered.

Electrode microwave discharge: Areas of application and recent results of discharge physics

The first paper on the electrode microwave discharge (EMD) appeared in 1996. Presently many problems of EMD physics and applications have already been solved. Several examples of EMD application are discussed: diamond growth, deposition of CNx films and nanotubes, deposition of metal films (Cu, Al), deposition of TiN and TiO2 films, generation of O2(a1Δ), and EMD as a plasma cathode. Results of EMD experiments and modeling give rise to the assumption that an EMD consists of a self-sustained domain (near-electrode plasma region with overcritical plasma density) which is surrounded by a region of a non-self-sustained discharge (ball shaped region with undercritical plasma density). We assumed that the layer of charge separation and of induced electrostatic field originated at the outer EMD boundary was one of the reasons for the abrupt decrease of the plasma density which leads to the formation of a compact plasma structure. Recent modeling results of the strongly nonuniform electrode microwave plasma based on a quasi static, 1D spherically symmetric model showed that such a layer can be generated at the point where a sudden increase of the total ionization rate takes place.

Microwave electrode discharge in nitrogen: Structure and characteristics of the electrode region

The parameters of the electrode region of an electrode microwave discharge in nitrogen are studied by emission spectroscopy. The radial and axial distributions of the intensities of the bands of the second (N2(C3Πu → B3Πg)) and first (N2(B3Πg → A3Σu+)) positive systems of molecular nitrogen and the first negative system of nitrogen ions (N2+ (B2Σu+ → X2Σg+)), the radial profiles of the electric field E and the electron density Ne, and the absolute populations of the vibrational levels vC = 0–4 of the C3Πu excited state of N2 and the vibrational level vBi = 0 of the B2Σu+ excited state of a molecular nitrogen ion are determined. The population temperature of the first vibrational level TV of the ground electronic state X1Σg+ of N2 and the excitation temperature TC of the C3Πu state in the electrode region of the discharge are measured. The radius of the spherical region and the spatially integrated plasma emission spectra are studied as functions of the incident microwave power and gas pressure. A method for determining the electron density and the microwave field strength from the plasma emission characteristics is described in detail.

Excitation kinetics of electronic states of hydrogen molecules in nonequilibrium discharges: Electronic ground state

This review offers an analysis of the vibrational kinetics of hydrogen molecules in the singlet ground state X1∑g+ for various gas discharges. The measured quasi-stationary vibrational-level distribution functions of a hydrogen molecule in the electronic ground state at the corresponding vibrational temperatures of the first level and those calculated in the framework of a semiempirical level collisional–radiative model of low-temperature plasma in hydrogen, developed in this study, are compared. A database of the measured and calculated characteristics of kinetic processes involving vibrational-excited hydrogen molecules, as well as macro and microparameters of hydrogen low-temperature plasma, is created.