Optical characteristics of the plasma of a nanosecond atmospheric-pressure volume discharge in a nonuniform electric field

Optical characteristics of the plasma of nanosecond volume discharges in air, nitrogen, krypton, argon, neon, and Ar/N₂ and Ar/Xe mixtures at elevated pressures are investigated. The discharges are excited in a gap with a cathode of small curvature radius. The waveforms and spectra of plasma emission from discharges in different gases in the 230-to 600-nm spectral range are measured. Optical generation in an Ar/Xe mixture is achieved at an active length of 1.5 cm. A comparison is performed of the spectral characteristics of the emission from nitrogen, krypton, argon, and neon excited by a volume discharge in a nonuniform electric field, by a nanosecond electron beam, and by a pulsed volume discharge in a uniform electric field at a high initial voltage.     

Temporal extension of stable glow discharges in fluorine-based excimer laser gas mixtures by the addition of xenon

The effect of addition of xenon on the long term homogeneity of discharges in F₂and ArF excimer laser gas mixtures was investigated in a small-volume discharge chamber. The gas mixture in the discharge chamber was preionized by X-rays. A special electrical excitation circuit containing a pulse forming line provided a long, square-shaped current pumping pulse of a predetermined duration to the discharge electrodes. The initiation and the development of the discharge was monitored via its fluorescence signal with an intensified CCD camera. We found that adding Xe up to partial pressures of 0.53 mbar extended the homogeneous phase of the discharge from 80 ns to approximately 200 ns in He/F₂as well as in He/Ar/F₂and Ne/Ar/F₂excimer laser gas mixtures. Monitoring of the ArF and XeF spontaneous emission signals showed that the formation of ArF excimers remained unaffected by the addition of xenon (up to 1.3 mbar) to the laser gas mixture.     

Ion beam induced modifications of TiN and Ti films on Al-3% Mg substrates

Thin titanium nitride films (50–110 nm) deposited via magnetron sputtering on Al+3 wt.% Mg substrates were irradiated with Ar, Kr, and Xe ion beams at room temperature and with energies between 0.1–0.9 MeV. Sputtering yields and interface mixing rates were determined using Rutherford backscattering (RBS) as depth profiling method. The obtained TiN sputtering yields for Ar and Xe irradiation are found to be in good agreement with predictions of the Sigmund approach. A systematic study with Ar and Xe beams revealed a correlation of the mixing rate with the parameter d/R _p, where d denotes the layer thickness and R _p the mean projected ion range. The mixing data and Monte-Carlo calculations of the collision cascades elucidate the importance of focused recoil transport, especially in the case of Xe irradiations. The results from ion mixing experiments of titanium films (70–140 nm) on Al-3% Mg with 0.1–1.0 MeV Xe beams and 0.05–0.2 MeV Ar beams support these conclusions.     

Magneto-resistance above 300 K in nano-crystalline Co–Ag metastable solid solutions

A series of nano-crystalline Co_xAg_100−x solid solutions have been prepared by NaBH₄ reduction of the corresponding metal salts at room temperature in Ar gas flow. Alloys heat-treated at 600 °C in Ar/H₂ (5%) show the evolution of metastable fcc Co precipitates in Ag. Magnetic studies indicate that all the compositions are ferromagnetic with Curie temperatures >400 K. For a nominal composition of Co₆₀Ag₄₀, heat-treated at 600 °C, an effective negative magneto-resistance (MR) ratio of the order of ∼21% at 350 K, at 2 T is observed. This could arise from the influence of magnetic field on the electron–phonon scattering effects near to T_c and to the spin-mixing scattering by magnons.     

Spectral anomalies of the light-induced drift of rubidium atoms caused by the velocity dependence of transport collision frequencies

The spectral features of the light-induced drift (LID) velocity for rubidium atoms (⁸⁵Rb and ⁸⁷Rb) in an argon buffer medium and in binary buffer mixtures of noble gases (Ne + Ar, Ne + Kr, Ne + Xe, He + Ar, He + Kr, and He + Xe) have been investigated theoretically. A strong temperature dependence of the spectral shape of the LID signal for Rb atoms in an Ar atmosphere is predicted in the temperature range 450 K < T < 800 K. It is shown that the anomalous LID of Rb atoms in binary buffer mixtures of noble gases can be observed at almost any temperature (including the room one) depending on the fractions of neon or helium in these mixtures. The results obtained enable a highly accurate testing of the interatomic interaction potentials used to calculate the drift velocity for anomalous LID in LID experiments.     

Sputtering of condensed noble gases by keV ions

Layers of Kr and Xe condensed at ～ 15 K and 35 K have been bombarded by 3-6 keV Ar+, Kr+ and Xe+ ions.

The sputtered neutrals were detected after a 1.43 m flight path by means of a mass spectrometer. Among the sputtered particles are considerable numbers of Van der Waals molecules, like Kr₂, Kr₃, Xe₂ XeKr and XeKr₂. The energy distribution of the sputtered particles give clues to the sputtering mechanisms involved.     

Ar+ and Xe+ velocities near the presheath-sheath boundary in an Ar/Xe discharge

The velocities of Ar+ and Xe+ ions near the presheath-sheath boundary in an Ar/Xe discharge are studied by particle-in-cell Monte Carlo simulation. For a pure argon discharge the argon ion has almost the same velocity profile as it does in the mixture of argon and xenon. Similarly, for a xenon discharge the xenon ion has almost the same velocity profile as it does in the mixture of argon and xenon. The ion speed at the sheath-presheath boundary is the same for an ion in a pure argon or xenon discharge and for the same ion in a mixture of argon and xenon. We conclude that, in our simulation, each ion reaches its own Bohm speed at the presheath-sheath interface.     

High‐pressure Brillouin study of the elastic properties of rare‐gas solid xenon at pressures up to 45 GPa

The pressure dependences of three adiabatic elastic constants, adiabatic bulk modulus, refractive index, and elastic anisotropy, as well as Cauchy deviation of fcc solid Xe have been determined up to 10 GPa at 296 K by high‐pressure Brillouin scattering spectroscopy. The characteristics of elastic properties at high pressure of rare‐gas solid Xe are investigated by comparison with the previous studies on Ne, Ar, and Kr. Above 10 GPa, the occurrence of splitting in the Brillouin signals and the direction dependence of acoustic velocities for solid Xe clearly show partial phase transformation to the hcp structure reported by the previous X‐ray diffraction and Raman scattering studies. The shear elastic modulus in the hcp phase of solid Xe has also been estimated at pressures up to 45 GPa by using the pressure dependence of the Raman wavenumber shift for the E_2g mode. Copyright © 2008 John Wiley & Sons, Ltd.     

Refractive index and mass density of quench condensed argon-xenon films

The refractive index and mass density of Ar _x –Xe_100–x films, which are condensed on a silicon substrate held at liquid helium temperature, are determined by ellipsometric measurements in combination, with a quartz microbalance. The mass density is typically about 10% less than the corresponding bulk density. This is consistent with the existence of a porous film structure. No annealing effect, except for pure Xe, can be observed until the Ar evaporates from the layer. Films condensed with a high initial Ar concentration remain in a highly porous sponge structure after the Ar atoms have left the film with a mass density of less than 50% of the Xe bulk density.     

Pressure-induced ultraviolet absorption in rare gases: Absorption coefficients for mixtures of Xe and Ar at pressures up to 40 atm in the vicinity of 147 nm

Absorption coefficient κ_υ for mixtures of Xe (0.2–20 kg/cm²) and Ar (5–40 kg/cm²) has been measured in the range 0.1 cm^-1 < κ_υ < 40 cm^-1. Exponential and power dependencies of κ_υ on wavenumber were observed and are discussed. The κ_υ-dependencies on the pressure of mixture components are explained by photon absorption at multiparticle collisions of Xe and Ar atoms.     

Control of composition and crystallinity in hydroxyapatite films deposited by electron cyclotron resonance plasma sputtering

Hydroxyapatite (HAp) films were deposited by electron cyclotron resonance plasma sputtering under a simultaneous flow of H₂O vapor gas. Crystallization during sputter-deposition at elevated temperatures and solid-phase crystallization of amorphous films were compared in terms of film properties. When HAp films were deposited with Ar sputtering gas at temperatures above 460 °C, CaO byproducts precipitated with HAp crystallites. Using Xe instead of Ar resolved the compositional problem, yielding a single HAp phase. Preferentially c-axis-oriented HAp films were obtained at substrate temperatures between 460 and 500 °C and H₂O pressures higher than 1×10⁻² Pa. The absorption signal of the asymmetric stretching mode of the PO₄³⁻ unit (ν₃) in the Fourier-transform infrared absorption (FT-IR) spectra was the narrowest for films as-crystallized during deposition with Xe, but widest for solid-phase crystallized films. While the symmetric stretching mode of PO₄³⁻ (ν₁) is theoretically IR-inactive, this signal emerged in the FT-IR spectra of solid-phase crystallized films, but was absent for as-crystallized films, indicating superior crystallinity for the latter. The Raman scattering signal corresponding to ν₁ PO₄³⁻ sensitively reflected this crystallinity. The surface hardness of as-crystallized films evaluated by a pencil hardness test was higher than that of solid-phase crystallized films.     

Resonance Raman and fluorescence spectra of chlorine dioxide in argon,krypton, xenon,and nitrogen matrices at 16 K

Laser excitation studies of matrix-isolated ClO₂ at 16 K using the 4579, 4765, 4880, and 5145 Å argon ion lines and argon, krypton, xenon, and nitrogen matrices were conducted. Quenching of fluorescence by the matrix was evidenced by the observation of displaced bands in the Ar, Kr, and N₂ work and increased background in the Xe studies. An intense progression in ν₁ of ClO₂ with regularly decreasing intensities out to 6ν₁ observed in solid Ar with 4579 Å excitation was attributed to the resonance Raman effect. Shorter resonance Raman progressions were observed in Xe and N₂ matrices.     

Comparison of VO<Subscript>2</Subscript> thin films prepared by inorganic sol-gel and IBED methods

VO₂ thin films with semiconductor-to-metal phase-transition properties were prepared by inorganic sol-gel and IBED (ion-beam-enhanced deposition) methods on SiO₂/Si substrate. The crystalline phase and the shape and width of the hysteresis curves of these VO₂ films were significantly different. For sol-gel VO₂ films, the transition started at close to 62 °C upon heating. The temperature interval needed to complete the phase transition was 8 °C, the ratio of resistance (R_{20 °C}/R_{80 °C}) reached three orders and the hysteresis width was 6 °C. However, the IBED film post-annealed in Ar at 700 °C underwent a phase transition from 45 °C to 80 °C, the ratio of resistance was more than two orders and the hysteresis width was 2 °C. In addition, the TCR (temperature coefficient of resistance) at 22 °C of the IBED film was 3.5%/K, much larger than the 0.7%/K TCR of the sol-gel film. PACS 73.50.F; 73.66.E; 81.20; 81.05.Z; 81.15     

Angular distribution of photoelectrons at 584 Å using polarized radiation

Photoelectron angular distributions for Ar, Xe, N₂, O₂, CO, CO₂, and NH₃ have been obtained at 584 Å by observing the photoelectrons at a fixed angle and simply rotating the plane of polarization of a highly polarized photon source. The radiation from a helium DC glow discharge source was polarized (84%) using a reflection type polarizer.     

Electrical and optical characteristics of inert-gas plasmas in spatially nonuniform electrode systems

The characteristics of unipolar and bipolar corona discharges in mixtures He/Ar/Kr, He/Ar/Xe, and He/Kr/Xe at atmosphere pressures in electrode systems of the point-plane and point-grid type distributed along the length. It is shown that bipolar corona discharges can be used in the preionization systems of high-pressure inert-gas-atom lasers. The spectral characteristics of the plasma are investigated, and the dependence of the relative intensity of the radiation in the lines Ar(4s-4p), Kr(5s-5p), and Xe(6s-6p) on the composition and pressure of the working mixtures and on the value of the corona discharge current are determined. Zh. Tekh. Fiz. 67, 15–18 (November 1997)     

CO2 laser-induced plasma CVD synthesis of diamond

2 laser maintenance of a stationary optical discharge in a gas stream, exhausting over a substrate into the air (laser plasmatron). Nano- and polycrystalline-diamond films were deposited on tungsten substrates from atmospheric-pressure Xe(Ar):H₂:CH₄ gas mixtures at flow rates of 2 ?/min. A 2.5-kW CO₂ laser focused beam produced plasma. The deposition area was about 1 cm² and growth rates were up to 30–50 μm/h. Peculiarities and advantages of laser plasmatrons are discussed. Received: 15 January 1998/Accepted: 16 January 1998     

High-Jc GdBa2Cu3O7−δ films fabricated by the metal–organic deposition process

We report a successful fabrication of high-J_c GdBa₂Cu₃O_7−δ (GdBCO) films by the metal–organic deposition process on the LaAlO₃ (LAO) (0 0 1) substrates. The coating solution was prepared by mixing Gd, Cu fluorine-free sources with Ba trifluoroacetate. Samples were dip-coated, pyrolized within 3 h at the temperature up to 400 °C in a humid oxygen atmosphere, and finally fired at various high temperatures in 100 ppm Ar/O₂ atmosphere. The GdBCO films fired at 775 and 800 °C exhibited J_c values of ∼2.1 MA/cm² at 77 K in a self-field, which are attributable to both high T_c,zero values of ∼89 K and high in-plane textures of 1.3–1.4°. Above 800 °C, however, the superconducting properties of GdBCO films are degraded due to the thermal decomposition of GdBCO film in 100 ppm Ar/O₂ atmosphere.     

Population processes in high-pressure inert-gas-mixture lasers

Working-level-population processes are analyzed on the basis of detailed investigations of the amplitude-time structure of the laser and spontaneous emission following a pulsed electric discharge in the mixtures He + R (R = Ar, Kr, Xe), Ar + Xe. Account is taken in the analysis of excitation by electrons (direct and stepwise) and of population as a result of relaxation processes (collisions of second kind with electrons; radiative cascades, recombination processes; collisions with the atoms of the working and buffer gases; excitation transfer from helium molecules). It is concluded that under optimum efficiency conditions inversion is produced in the lasers considered as a result of direct electron collision with the working atoms (Ar, Kr, Xe), which are in the ground state.Translated from Lazernye Sistemy, pp. 15–34, 1982.     

Wetting and evaporation behaviors of molten Mg on partially oxidized SiC substrates

The wetting and evaporation behaviors of molten Mg drops on pressureless-sintered SiC surfaces were studied in a flowing Ar atmosphere at 973-1173 K by an improved sessile drop method. The initial contact angles are between 83° and 76°, only mildly depending on temperature. The formation of a ridge at the triple junction as a result of reaction between molten Mg and the SiO₂ film on the SiC surface pins the triple line and leads to a constant contact diameter mode during the entire evaporation process. Moreover, the diffusion coefficients of the Mg vapor at different temperatures were evaluated based on a simple model.     

The empirical Kestin model and the second order transport properties of binary mixtures of Ne,Ar, Kr and Xe

It is showed from the experimental α_T data for the dilute binary mixtures of Ne, Ar, Kr and Xe at 340 K that the law of corresponding states proposed by Kestin, Ro and Wakeham is able to predict the mentioned second order kinetic property altogether with the first order transport and thermodynamic properties of the examined mixtures.