acta physica slovaca

Abstract: We present two simple, effective and low-cost experimental methods to control chaos in \textbf{d}ouble \textbf{p}lasma (DP) machine plasma. By using a capacitor, we can substitute the low-frequency chaos (uncorrelated oscillations), which appears in the S-type negative differential resistance region of the static current-voltage ($I-V)$ characteristic, by a nonlinear oscillation, the frequency of which is controlled by the external capacitance. By using an inductance we can suppress all higher harmonics of the natural nonlinear oscillations occurring in the N-type negative differential resistance region of the $I-V$ characteristic, obtaining purely sinusoidal oscillations, the frequency of which is determined by the external inductance.

Abstract: Two Hofmann-propanethiol-type clathrates of the form M(1-propanethiol)_2Ni(CN)_4.G (M = Cd or Ni; G = benzene) have been prepared in the powder form. The 1-propanethiol (1-PT) molecules provide the cavities in which the guest benzene molecules in clathrate structure are accommodated. The infrared investigations of the obtained clathrates indicate that these compounds are similar in structure to the other Hofmann-type clathrates.

Abstract: In this work the radial distributions of the emission coefficient of some atomic and ionic argon lines in the thin helium plasma (~1 mm diameter) produced by the axial injection torch are presented as a function of the supplied microwave power and the argon concentration. Radial distributions were obtained using an Abel inversion method on laterally resolved measurements of the plasma flame. Different radial behaviour was found for ionic and atomic argon levels.

Abstract: We report the results of rotational temperature T_R measurements in high-pressure (400 Torr) microhollow cathode (MHC) discharges in Ne with a trace admixture of N_2 using the unresolved N_2 second positive band and the N_2^+ first negative band. Significantly different values for T_R were obtained for respectively N_2 and N_2^+. The rotational temperatures obtained from the analysis of the N_2 band system are slightly above room temperature, increase with increasing discharge current, and may be interpreted as the gas kinetic temperature in the MHC discharge plasma. By contrast, the analysis of the N_2^+ band system yielded rotational temperatures of more than 900 K, which are the result of collisional reaction processes leading to the formation of rotationally excited N_2^+ ions. The effective lifetime of these ions is comparable to the rotational relaxation time, so that the ions retain much of their rotational excitation prior to emission and are not in thermal equilibrium with the bulk gas. Thus, the T_R values obtained for N_2^+ cannot be equated with the gas kinetic temperature in the plasma. We also carried out a rotational analysis of the unresolved N_2 second positive system emitted by an atmospheric-pressure capillary plasma electrode (CPE) discharge in ambient air and measured a temperature of 545 K. This temperature may be close to the gas kinetic temperature as the rotational analysis utilized N_2 emissions from inside the capillary which is the region of highest plasma density and highest gas temperature in a CPE discharge.

Abstract: A helium microwave plasma torch was studied and optimised as a destruction system of volatile organic compounds. Attention was focused on trichloroethylene as a prototypical volatile organic compound, which is used technologically and which poses known health risks. The dependence of the destruction efficiency on the plasma conditions was obtained for different values of trichloroethylene concentrations. The results show a destruction and removal efficiency greater than 99.999%.

Abstract: High voltage pulse electrical discharges in water solutions have been studied using different geometries of electrodes. It was demonstrated that discharges in all electrode configurations used (needle-plate, coaxial composite anode-tubular cathode and coaxial pinhole anode-tubular cathode) produce plasmas with very similar parameters. Plasma electron density depends strongly on the solution conductivity. Discharges in water have no counterpart in gas phase ones. The main chemically active specie produced by corona-like discharges is hydrogen peroxide, other species as H, O and OH radicals play a minor role. Degradation of phenol and decolorizing of organic dye "reactive blue 137" by OH radicals have been demonstrated. Corona-like discharges may find some applications in solution of environmental problems. At very high solution conductivity (5-20 mS/cm) multi-channel discharge with the composite anode generates strong acoustic waves. Focusing of the cylindrical pressure wave by parabolic metallic reflector and generation of spherically convergent wave has been demonstrated. Strong shock waves that lead to cavitation are formed at the focus region. Interaction of focused shock waves with cellular scale structures have been demonstrated. We believe that the focused shock waves will find some applications in medicine.

Abstract: The paper deals with the formation of polycrystalline structure of deposited YSZ and Si films on Si and YSZ crystals, respectively, depending on the substrate surface orientation and with the evolution of the YSZ/Si interface properties at the initial stage of the plasma anodization. The X-ray measurements confirmed that YSZ film deposited on Si is amorphous or polycrystalline. A well developed face centered cubic (fcc) phase with lattice parameter of 0.509 nm is typical for the best YSZ layers, four intense 111, 200, 220 and 311 diffractions being usually detected. The polycrystalline structure of Si-on-YSZ layers was affected by the orientation of YSZ substrate surface, namely (100) or (111). The surface of crystalline silicon at the interface with deposited YSZ layer consisted of large polycrystalline blocks, their size being reduced by one order of magnitude after the plasma anodization. The YSZ/Si interface electrical properties were changed remarkably as found by DLTS which revealed a continuous spectrum of interface states originating due to the anodization. It is attributed to the formation of a very thin silicon oxide interlayer between the YSZ layer and Si crystal. The other electrical and optical properties were investigated by C-V, capacitance-frequency, deep level transient spectroscopy and reflectance spectroscopy.

Abstract: This contribution is intended to summarize in a practically useful form the basic information about the detection of the gas phase atoms and free radicals by electron spin resonance spectroscopy (ESR) in gas discharge afterglow and in remote plasma reactors. This paper shows how ESR could be effectively used for the monitoring of relative or absolute concentrations of gas phase H, O, N atoms during the volume plasma chemical and wall recombination processes.

Abstract: The preparation of MgB_2 superconducting films is often linked with difficulties to obtain the film stoichiometry due to the different melting points of deposited materials (magnesium and boron) and the escape of Mg during in-situ annealing. The interaction of the MgB_2 films with an incident ion beam of the analytical technique applied can also be a problem, because it can cause distortion of the composition of the prepared films. Superconducting MgB_2 thin films have been prepared on carbon substrates using sequential e-beam evaporation of boron and magnesium to create a multi-layer structure with a total thickness of 500 nm. After deposition, an in situ annealing was performed at 700 °C at various partial pressures of Ar. We studied the composition of the as-prepared and annealed films by ion beam analysis. The distribution of boron was measured by resonance nuclear reaction ^11B(p,g)^12C and the obtained results were confronted with Rutherford backscattering analysis and measurements of electrical properties. A possible influence of incident ion beam on the examined film is discussed. We showed that process of a sequential deposition of B and Mg followed by in-situ annealing is suitable for preparation of superconducting MgB_2 film.

Abstract: The magnitude of four independent amplitudes are obtained in neutral pion photoproduction in the energy range of 1300 to 2100 MeV incident photon. Differential cross section and three polarization parameters are required for such amplitudes reconstruction at different pion scattering angles. Results of the direct amplitudes reconstruction have been compared with the solution of partial wave analysis SM95 and SM00K at all energies. This analysis indicates that we have a fair agreement between the present work and the results of partial wave analysis at meny angles.

Abstract: The (n,2n) reaction cross-section calculations for some neighbor deformed target nuclei have been made in the region of rare-earth elements between 8 and 24 MeV incident energy. In the calculations, the geometry dependent hybrid model and the exciton model have been used including the effects of pre-equilibrium. Pre-equilibrium direct effects have been examined using full exciton model. The measured cross-sections are taken from literatures. The cross-sections were calculated using other semi-empirical formulas for the incoming energieswhich satisfy the condition U_R = E_n + Q_{n,2n} = 6+-1 MeV. The obtained results were discussed and compared with the available experimental data, and found to be well in agreement.