Yu. A. Lebedev

Computer simulation of microwave and DC plasmas: comparative characterisation of plasmas

Self-consistent calculations of the parameters of self-sustained MIP and DCP in argon and in model gases in the diffusion-controlled regime have been carried out. The calculated parameters of argon microwave produced plasmas (MIP) and direct current plasmas (DCP) are in satisfactory agreement with experimental data. The use of the proposed invariant group of parameters, namely specific absorbed power Pd, plasma gas pressure p, discharge tube radius R and tube wall temperature TW, for the comparisons of different types of electrical discharges have been grounded. The results of calculations in argon using different models of discharge and the results of calculations in model gas plasmas are given.

Performance of radio frequency hollow cathodes at low gas pressures

Abstract Typical hollow cathodes (HC) have distances between opposite inner walls in a millimeter range and can operate at gas pressures of approximately 0.1–10 Torr (13.3–1333 Pa). This is because the pressure and the cathode geometry must fulfill the condition for the hollow cathode effect, based on electron exchange between opposite walls. In this paper, we report on the performance of the radio frequency powered cylindrical and linear HC, with the gas flowing through the cathode, at the mTorr (0.1 Pa) pressure range typical for magnetron sputters or arc evaporators. Operation of simple cylindrical HC with inner diameters exceeding 10 mm was possible at pressures down to 0.9 mTorr (0.12 Pa) in argon. The plasma ion density did not exceed magnitude of 10 9 cm −3 . However, a plasma density as high as 5×10 11 cm −3 was measured 15 cm below 16 cm long linear Magnets-in-Motion (M-M) HC in mTorr pressure range. The M-M cathodes can be used as an efficient sputtering/evaporation source for large area PVD of films or incorporated into different hybrid PVD and PE CVD plasma systems with conventional sources for production of new quality coatings.

Diamond deposition in a microwave electrode discharge at reduced pressures

Abstract Diamond deposition on heated Si-substrates was studied under microwave discharge generated by an electrode-antenna either in a “point-to-plane” arrangement or in a “parallel-plane” arrangement at gas pressures of 1–15 Torr in a mixture of hydrogen with methane and oxygen. Diamond growth of 1 μm h −1 was obtained on surfaces up to 2 cm in diameter at microwave power of 150–200 W. No metal impurities from the electrode were detected in the diamond films. Typical gas mixture was 4% methane and 0.5% oxygen in hydrogen at a total pressure of 15 Torr. The role of additional r.f. potential during the film deposition was studied in the case of “point-to-plane” electrode arrangement. Correlation of the power absorbed in the plasma and the optical emission of H atoms have been observed.

Microwave discharges: generation and diagnostics

Microwave discharges are widely used for generation of quasi-equilibrium and nonequilibrium plasma for different applications. Microwave plasma can be generated at pressures from 10 -5 Torr up to atmospheric pressure in the pulse and continuum wave regimes at incident powers ranged between several Watts and hundreds of kW. The plasma absorbed power can be high enough and runs up to 90% of the incident power. This paper reviews the methods of microwave plasma generation, general features of microwave plasma, and selected aspects of microwave plasma diagnostics.

Heats of combustion of nitromethane and dinitromethane; enthalpies of formation of nitromethyl radicals and energies of dissociation of bonds in nitro derivatives of methane

1. The heats of combustion of nitromethane and dinitromethane, 168.0±0.3 and 137.3±0.2 kcal /mole, respectively, were measured. 2. The energies (kcal/mole) of dissociation of the C-N bond in nitro derivatives of methane were estimated on the basis of the available data: 60.3 in nitromethane, 53.8 in dinitromethane, 45.7 in trinitromethane, and 39.3 in tetranitromethane. 3. The energies (kcal/mole) of formation of nitromethyl radicals\([^ \cdot CH_2 NO_2 31.6;^ \cdot CH(NO_2 )_2 37.5;\) and\(^ \cdot C(NO_2 )_3 49.8]\) were estimated, and lead to energies of dissociation of the C-H bond in nitro derivatives of methane ∼103 kcal/mole.

Positioning of 72 potentially full size LTRs of human endogenous retroviruses HERV-K on the human chromosome 19 map. Occurrences of the LTRs in human gene sites.

Seventy-two near full size long terminal repeats (LTRs) of human endogenous retrovirus of K-family (HERV-K) have been precisely located on the metric map of human chromosome 19. The LTR-related sequences were identified and assigned to cosmids by hybridization with two independent chromosome 19 specific cDNA clones corresponding to different parts of U3 region of LTR of HERV-K. The presence of full-size LTR sequences in a cosmid was further verified by PCR assay with a pair of primers complementary to the termini of the LTR. Coincidences of the LTR and the known genes positions are discussed.

Electrodynamics of microwaves in a coaxial non-regular waveguide partly filled with plasma

The electrodynamics of microwave fields (f = 2.45?GHz), propagating inside a coaxial non-regular system with a plasma-ball at the tip of a central electrode, have been simulated. For this purpose, the time-dependent Maxwells equations have been solved numerically in a two-dimensional grid. To outline the main properties of distribution of the microwave energy in such a system, various shapes and densities of quasi-neutral uniform plasma have been investigated. The simulations have been carried out for hydrogen in the range of pressures 0.5?8?Torr and densities 0.2?20nc. It was found that for under-dense plasma of any given configuration the absorbed power mostly concentrated near the tip of the internal electrode. For over-dense plasma, the microwave power is located both near the electrode and inside the surface layer of the plasma-ball. This distribution of absorbed microwave power is similar to the plasma light emission distribution observed in experiments. Transformation of the TEM wave into the surface wave has been demonstrated.

Thermochemistry of N-nitro- and N -nitrosoamines of the alicyclic series

1. The thermochemical characteristics of N,N-dinitropiperazine and N,N-dinitrosopiperazine were determined. The enthalpy of sublimation of hexahydro-l,3,5-trinitrosotriazine was determined. 2. The difference in the thermochemical principles of aliphatic and alicyclic N-nitro-N-nitrosoamines is due to the interaction of the functional groups in the ring. 3. The cleavage energies of the nitrogen-oxygen bond in N-nitropiperazine, N,N-dinitropiperazine, and hexahydro-l,3,5-trinitrotriazine were calculated.

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.