Production and loss of N 2 + , Ne+ and Ne 2 + during the decay period of plasmas produced in neon-nitrogen mixtures

Studies of the time dependencies of the number density of N ₂ ⁺ , Ne⁺ and Ne ₂ ⁺ ions have been made during the decay period of plasmas produced in neon containing various concentrations of nitrogen molecules. Reaction rate constants were obtained for N ₂ ⁺ +N₂+Ne→N ₄ ⁺ +Ne((1.2±0.2)×10^?29 cm⁶ sec^?1) and Ne⁺+N₂→N ₂ ⁺ + Ne ((2.9±0.3) × 10^?12 cm³ sec^?1). The ambipolar diffusion coefficient of N ₂ ⁺ in neon was found to beD _a p _o =350±20 cm² sec^?1 Torr.     

Population of 2p 55s levels of neon in He-Ne plasma: I. The evolution of mechanisms in the discharge and the afterglow

The spectroscopic study of population processes of neon 2p ⁵5s states was carried out in helium afterglow with small admixture of neon at PHe = 38.1 torr, [He]/[Ne]=10^?5 with pulsed discharge afterglow in helium with small admixture of neon (pressure equal to 38.1 mm Hg; ). It is established that the main mechanism of population of 3s ₂ level (in Paschen’s notation) in the discharge and the initial after-glow is the excitation transfer from metastable atoms of He(2¹ S ₀). The other three levels—3s ₃, 3s ₄, and 3s ₅—corresponding to 2p ⁵5s configuration are populated in the afterglow as a result of the dissociative recombination HeNe⁺ of ions with electrons. The same process is also the main channel of population of 3s ₂ level in the late afterglow phase, when the concentration of He(2¹ S ₀) atoms is small. The hypothesis of recombination mechanism is confirmed by observation of the response of line intensities to pulsed electron heating. The partial coefficients of dissociative recombination into 2p ⁵5s states are estimated.     

Charge transfer reaction of multi-charged oxygen ions with O2

The rate of transfer of electrons from O₂ to O²⁺ and O³⁺ has been measured at energies ? 2 eV using a stored ion technique. The rate for O²⁺ is k = 1.0(0.3) × 10^?9 cm³/s and for O³⁺, k = 2.5(0.3) × 10^?9 cm³/s, compared to calculated Langevin rates of 1.8 × 10^?9 cm³/s and 2.7 × 10^?9 cm³/s respectively.     

Eine Modellvorstellung für das „Auroral Afterglow“ und das „Pink Afterglow“

Based on own measurements of the decay of light intensity and electron density, a simple model for the auroral afterglow and the pink afterglow is proposed. To a certain extent the model can account for the influence of pressure and tube diameter on the behaviour of the afterglow. The first decay of the electron density towards the first minimum seems not to be influenced by creation processes for electrons during 3 to 15 ms. Therefore, the first decay can be used to measure the neutralization processes of electrons and positive ions. At pressures lower than 3 torr the electrons are removed by ambipolar diffusion with a rate given byD _a ·p≈2100 torr·cm²·s^?1. From this value an electron temperature of about 7200 °K could be derived. Assuming that ambipolar diffusion will remain the dominant loss process the time dependence of the electron creation rate has been evaluated. At a pressure of 1,75 torr the maximum electron creation rate was 4·10¹² s^?1·cm^?3. At the same time the emission density rate of the first negative bands was found to be 2.7·10¹³ cm^?3 s^?1. During one decay process about five times more electrons are created than the initial number. To explain the proportionality found between the electron density and the emission of the first negative bands, it is assumed that the ions, presumable N ₂ ⁺ -ions, are repeatedly excited to theB ² Σ _u ⁺ -state by metastables.     

An investigation of the energy exchange mechanisms involving the 23S metastable level in an RF helium plasma

The energy exchange mechanisms present in a pure helium and a helium-neon plasma were investigated using spectroscopic diagnostic techniques. The plasma was spatially resolved and only the volume element at the plasma centerline was considered in the energy- exchange analysis. The experiment was conducted with a constant total pressure of 0·7 torr, a fixed oscillator frequency of 4 MHz, and a constant input power of 1·8 kW. Emission line spectroscopy was used to determine the population densities of 16 levels in the n³S, n³P, and n³D series. Spatially resolved, self-absorption measurements of the 2³P-2³S transition were used to determine the 2³S metastable level number density. The electron number density of 3·3 × 10¹³ cm^-3 was determined from the spatially resolved H_β blue wing profile, and a lower bound excitation temperature of 8800 °K was determined from a Boltzmann plot of the spatially resolved lower bound levels of the excited helium. The addition of 10% and 20% by volume of neon gas caused a measurable decrease in the population densities of the lower bound levels of helium, while the electron number density and lower bound excitation temperature remained unchanged. Three energy exchange models (local thermal equilibrium, corona, and collisional- radiative) were examined, and the collisional-radiative model was found to best describe the excitation processes for the 2³S level. This model was also appropriate for describing the helium-neon plasma at this level.     

Two-dimensional electron-hole system in a HgTe-based quantum well

A two-dimensional electron-hole system consisting of light high-mobility electrons with a density of N _s = (4–7) × 10¹⁰ cm^?2 and a mobility of μ _n = (4–6) × 10⁵ cm²/V s and heavier low-mobility holes with a density of P _s = (0.7–1.6) × 10¹¹ cm^?2 and a mobility of μ _p = (3–7) × 10⁴ cm²/V s has been discovered in a quantum well based on mercury telluride with the (013) surface orientation. The system exhibits a number of specific magnetotransport properties in both the classical magnetotransport (positive magnetoresistance and alternating Hall effect) and the quantum Hall effect regime. These properties are associated with the coexistence of two-dimensional electrons and holes.     

Evaporated a-Si films with low ESR defect density by hydrogenation under NH3 ambient

a-Si films were obtained by a reactive evaporation of Si atoms with an electron gun, under a NH₃ ambient of 5 × 10^?5 torr. The H introduced amount efficiently reduces the ESR dangling bond density from 4 × 10¹⁹ cm^?3 in pure samples to 2 × 10¹⁷ cm^?3. The hydrogen presence is evidence by both the Si-H infrared bands and the strong spin-density increase with annealing. This increase, beginning at a temperature of 350°C, is attributed to the H effusion. XPS measurements show also an incorporation of bonded nitrogen.     

Pressure broadening of the NO2 hyperfine multiplet at 93 GHz

Line shapes of the hyperfine NO₂ 26(1,25)←25(2,24) rotational transition have been measured at pressures below 3 torr with a bridge spectrometer originally designed for direct absolute absorption studies. The multiplet consists of six lines with δF=δJ=δN=1 in the vicinity of 93,445 MHz. The same line-broadening parameter of 3.7 MHz/torr and the same maximum absorption of 1.8×10^-5 cm^-1 have been found for all 6 lines. The maximum absorption of the strongly overlapped multiplet at a pressure of 10 torr was measured to be 1.06×10^-4 cm^-1, in good agreement with the theoretical value. The interference effect of the overlapping lines turns out to be below ?10%, so that a simple superposition of lorentzian shapes is a good approximation for this case. The remaining difference can be compensated for by the introduction of an overlap parameter for each line.     

Proton-induced F-centers in LiF and MgF2

The growth of F-centers in LiF irradiated at room temperature with 40- and 85-MeV protons and with ⁹⁰Sr electrons was found to be proportional to the square root of the absorbed energy over the range 0.5 to 2.3 Mrad which corresponds to an F-center density range of 1 × 10¹⁶ to 1.5 × 10¹⁷ per cm³. The production efficiency was 5 × 10³eV per F-center at an absorbed energy of 2.3 Mrad. The density of F-centers produced in MgF₂ by 40- and 85-MeV protons was measured over an absorbed energy range of 0.2 to 29 Mrad which corresponds to a maximum F-center density of 2 × 10¹⁶ per cm³. The production efficiency for MgF₂ was 4 × 10⁵eV per F-center at an absorbed energy of 16 Mrad.     

Observation of RF superconductivity in Y1Ba2Cu3O9−δ AT 3 GHz

Two samples of Y₁Ba₂Cu₃O_9−δ, one fabricated at Los Alamos National Laboratory and the other at the University of Wuppertal, were tested in the rf field of a niobium cavity at 3 GHz and in a temperature range from 4.2 to 300 K. The data show a sharp reduction of the Joule losses in the samples beginning at an onset temperature of 98 and 92 K, respectively. The residual losses of the sample were measured at 4.2 K where the host cavity was superconducting. The ratio of these losses to the ones observed slightly above T_c was less than 1.1 × 10⁻². This indicates that only a small fraction of the conduction electrons of the Y₁Ba₂Cu₃O_9-δ sample remain unpaired. The dependence of the rf losses on the rf magnetic field allows the determination of a maximum surface current density which is found to be about 5 × 10⁴ A/cm².     

Far-infrared laser oscillation in p-Ge

Time-resolved measurements, together with spectroscopic study with a grating monochromator, are made on far-infrared stimulated emission from p-Ge in crossed electric and magnetic fields. Gain saturation is confirmed, for the first time, to occur to establish laser oscillation. Small-signal gain per unit length deduced from the time constant of light amplification is 7.4 × 10^-3 cm^-1 and 2.7 × 10^-2 cm^-2, respectively, for samples with N_A − N_D ≅ 4.5 × 10¹³cm⁻³ and 1.7 × 10¹⁴ cm^-3. Output power detected at distance 28 cm from the sample is of order 1–10 W, but higher power over 100W is suggested for the total output from the sample.     

Calculation of the pressure shift of the positronium hyperfine interval

We calculate the fractional positronium hyperfine pressure shift Δ(T) using a quantum mechanical thermal averaging and obtain for Δ(293 K)(±30%) in He, Ne, Ar, Kr, Xe, N₂ and SF₆ respectively; (-0.15, -0.34, -0.96, -1.41, -1.85, -1.12, -1.1) × 10^-7/torr (0°C).     

Excitation of the 3p3Πu level of H2 by electron impact; pressure effects

The excitation cross-section of the 3p³Π_u level of H₂ has been measured for electrons from energy threshold to 100 eV. We compare the intensities of the emitted lines to the Balmer lines whose excitation cross-sections from H₂ are known. The effects of dissociation, cascade, polarisation and pressure are discussed. The maximum excitation cross-section is found to be 3·30 × 10^-18 cm² ± 50% at 22·5 eV.     

Self-density frequency shift measurements of Raman N2 Q-branch transitions

We report stimulated Raman investigations of N₂ Q-branch transitions in view to measure the self-density frequency shift. These measurements performed at 295 K over the density range 0.02-0.8 Amagat lead to a mean shift value equal to -5.5×10^-3 cm^-1/Amagat. Moreover, our data extrapolated at zero density allowed new refinements of the N₂ molecular constants: v₀=2329.91165 (17) cm^-1, B₁–B₀=-0.0173714 (22) cm^-1 and D₁–D₀=(7.6±5.0)×10^-9 cm^-1.     

A 1-kW/cm2 flash KrCl excimer lamp

The amplitude-time characteristics of the emission from a one-barrier flash KrCl excimer lamp and conditions for the maximum luminosity in the UV spectrum range are reported. The best result is achieved for a Ne: Kr: Cl₂=50: 1: 1 (torr) mixture. When the lamp is excited by the combined Fitch circuit, the pulse half-height duration 107 ns and the power density E(0,0)=1.1 kW/cm² are attained.     

Effect of residual atmospheric pressure on the development of electrostatic discharges at the surface of protective glasses of solar cells

Electrostatic discharges obtained upon the irradiation of K-208 glass with 40-keV electrons at a flux density φ of 10¹⁰ to 2 × 10¹¹ cm^–2 s^–1 are studied. The residual pressure p _v in the vacuum chamber is varied from 5 × 10^–5 to 5 × 10^–3 Pa. Structural changes in the sample surfaces are studied by atomic-force microscopy. Depending on the pressure level, two types of discharges are observed in experiments at 3 × 10¹⁰ ≤ φ ≤ 1.2 × 10¹¹ cm^–2 s^–1: a microprojection at the glass–ionized-residual-atmosphere surface and a discharge which develops along the irradiated surface. It is found that at 5 × 10^–5 ≤ p _v ≤ 3 × 10^–4 Pa and 8 × 10¹⁰ ≤ φ ≤ 10¹¹ cm^–2 s^–1, discharges of the first type appear at the beginning of exposure; that is, an increase in microprojections is observed. Further, surface discharges propagate through these microprojections. At 10^–3 ≤ p _v ≤ 5 × 10^–3 Pa and 10¹⁰ ≤ φ ≤ 5 × 10¹⁰ cm^–2 s^–1, on the contrary, discharges of the second type are realized at the beginning. These discharges result in the appearance of channels with inhomogeneities on the glass, at which subsequently discharges of the first type occur. It is determined by calculations that in the region adjacent to the exposed glass surface, secondary electrons accelerated in a field of charge accumulated in the glass make the main contribution to the ionization of gases.     

Helium emission spectra—II. Pressures to 0.91 torr

Electron impact excitation is employed to study the pressure variation of the steady state luminescence from 27 levels of helium. Apparent cross sections are determined for these levels over the pressure range 0.025–0.91 torr, a much broader pressure range for observing collisional excitation transfer processes than has been previously investigated. Model calculations are carried out in which the data is fit to a set of coupled steady state equations. Primary and secondary electron excitation, radiative transfer, and bimolecular and termolecular collisional processes are accounted for in the analysis. We find that n¹P→n¹D collisional excitation transfer is much more important as a populating mechanism for n¹D levels than has been previously believed. The cross section for 4¹P→4¹D collisional transfer is estimated to be (1.3±0.3)×10^?14 cm². A termolecular process, believed to involve formation of He₂⁺, becomes an important loss mechanism for the 3¹P and 4¹P levels at pressures above 0.5 torr. Rate constants for this process are estimated to be (6.6±1.0)×10^?27 cm⁶/sec and (1.9±0.4)×10^?26 cm⁶/sec for 3¹P and 4¹P, respectively. The magnitude of the 3³D and 4³D apparent cross sections require a large 4³F population, a result which leads us to conclude that the 4F level is singlet-triplet mixed. There is evidence that collision induced transitions between all sublevels do not occur with equal probability. The most internally consistent results are arrived at by assuming ΔJ=0 to be a favored collisional transfer process.     

Energy spectrum of (Sn0.65Pb0.35)0.95Ge0.05Te solid solutions

The paper reports the study on the resistivity ρ and thermoemf S of the (Sn_0.65Pb_0.35)_0.95Ge_0.05Te solid solution layers. The dependences of ρ and S on the hole concentrations in the range 3×10¹⁹–2×10²¹ cm^?3 exhibit jumps in the resistivity and thermoemf minima at close hole concentrations p ₁≈9×10¹⁹ cm^?3, p ₂≈2.5×10²⁰ cm^?3, and p ₃≈4.5×10²⁰ cm^?3. The observed jumps and minima suggest a complex structure of the valence band and the presence of critical points in the energy spectrum of holes. According to the data for SnTe, the critical points in the energy spectrum at the given hole concentrations are identified as the Σ-extremum, saddle point LΣ, and Δ-extremum, respectively.     

ZrO2 films deposited by photo-CVD at low temperatures

Zirconium oxide layers have been successfully deposited by photo-CVD at low temperatures. ZrO₂ growth was observed at temperatures as low as 100 °C. When deposited at 250 °C and above, these films exhibited a polycrystalline structure with a mixture of different crystal phases. Deposition at 300 °C was found to form moisture-free ZrO₂ films with a high refractive index of 2.1, a very low effective density of trapped electrons of ∼8.8×10⁸ cm^-2 and an interface trap density of 6.6×10⁹ cm^-2 eV^-1 being readily obtained. Received: 17 December 2001 / Accepted: 6 January 2002 / Published online: 3 June 2002     

Spectroscopic study of a brush cathode plasma in a magnetic field

The brush cathode helium discharge in the magnetic field has been operated stably at discharge currents larger than those without magnetic field. The diameter of the plasma column has been determined by the configuration of the magnetic field. The measurements of the spectral intensities of the recombination continuum followed by the 2³S-n³P series reveals that the electron density is 1·8 × 10¹³ cm^-3 and the electron temperature is 0·17 eV at a discharge current of 500 mA and a pressure of 0·9 torr for a magnetic flux density of 1·3 kG. The principal quantum number for line merging is 20.