Determination of the negative hydrogen ion concentration in a cesium-hydrogen discharge

The concentration N _H ⁻ of negative hydrogen ions in a low-voltage cesium-hydrogen discharge plasma N _H ⁻ is determined from experiments with laser radiation absorption caused by the photodetachment of electrons from the H⁻ ions. The resolution of a setup measuring the relative absorption is ≥10⁻⁵ for a signal-to-noise ratio of ∼10⁻² or less. A heated-cathode diode is used to initiate the discharge at a voltage of U≤10 V and a current density of j≤5 A/cm² (hydrogen pressure p _{H 2} is equal to several torr, and the cesium concentration in the plasma N _Cs ⁽⁰⁾ ∼10¹⁴ cm⁻³). The absorption due to the photoionization of excited Cs atoms is shown to be negligible. The measured concentration N _H ⁻ of the H⁻ ions is 10¹²–10¹³ cm⁻³. Experimental results are consistent with the theory.     

Electron-stimulated desorption of negative O? ions from the oxidized O/Ru surface

This paper reports on a study of the electron-stimulated desorption of negative oxygen ions from the O/Ru surface, which represents an additional factor responsible for the destruction of the protective oxide layer of the mirrors used in ultraviolet lithography. The cross section of degradation of the O/Ru layer due to the electron-stimulated desorption of the O⁺ and O⁻ ions and the O atoms has been found to be 1.6 × 10⁻¹⁹ cm². A comparison of the dependences of the electron-stimulated desorption yield of O⁺ and O⁻ ions on the incident electron energy E with the ionization cross section of the adsorbate core level σ _O2s (E) has revealed that the ionization of the O 2s level is the main channel of the electron-stimulated desorption of O⁻ ions.     

CHCl3电子吸附速率常数的离子迁移谱

利用电晕放电离子迁移谱, 使用高纯氮气作为载气和迁移气体, 研究了电场强度在200～500 V/cm变化时CHCl₃的解离电子吸附速率常数, 得到样品所对应的电子吸附速率常数为1.26×10^-8～8.24×10^-9 cm³/(molecules s)．利用该装置测量了固定电场下,样品的电子吸附速率常数与样品浓度之间的关系．此外利用所获得的离子迁移谱图得到了不同电场强度下Cl^-与CHCl₃之间的离子分子反应速率常数.     

Generation of multiply charged refractory metals in an electron-cyclotron resonant discharge in a direct magnetic trap

The possibility of additional ionization of refractory metal ions in the vacuum arc plasma injected to a magnetic trap due to additional heating of electrons by microwave radiation under the conditions of electron-cyclotron resonance is demonstrated. High-power short-wave radiation of gyrotrons used in experiment makes it possible to work with a higher (on the order of 10¹³ cm⁻³) density of the plasma and to ensure the confinement parameter at a level of 3 × 10⁸ cm⁻³ s at an electron temperature sufficient for multiple ionization.     

Experimental study and computer simulations of the implantation of laser plasma ions in pulsed electric fields

Results are presented from experimental studies of pulsed plasma flows generated by nanosecond laser pulses with an intensity of 7 × 10⁸ W/cm² from a solid-state target in a strong electric field. The current pulses through the laser target and the depth distributions of the iron ions implanted in a silicon substrate to which a negative high-voltage pulse was applied are measured. The physical processes occurring in laser plasma with an initial iron ion density of 6 × 10¹⁰ cm⁻³ are simulated numerically by the particle-in-cell method for different delay times and different shapes of the accelerating high-voltage pulse. The model developed allows one to calculate the ion flows onto the processed substrate, the electron flows onto the target, and the energy spectra of the implanted ions. The results from computer simulations are found to be in good agreement the experimental data.     

Negative ion effects in CO2 convection laser discharges

Negative ions are computed to be formed on a time scale and in quantities such that they may be a cause of plasma instability observed in low pressure electrical discharge convection CO₂ lasers. In a typical CO₂−N₂−He−H₂O laser mixture the principal ions are CO ₃ ⁻ , CO ₄ ⁻ and H⁻ with the total negative ion densityn ₋ given by 0.1n _e <n ₋<n _e , wheren _e is the electron density: but if the gases are re-cycled or if there is an air leak NO ₂ ⁻ and NO ₃ ⁻ are formed in significant amounts andn ₋ can become greater thann _e in a time considerably less than the gas dwell time in the electrical excitation discharge. CO is effective in reducingn ₋ in a system without re-cycling, but is ineffective in a re-cycled system with the oxides of nitrogen present.     

Gas-filled electron diode based on a glow discharge

Stable ignition and sustention of a pulsed discharge with a current of up to 180 A and duration of 12 μs at a pressure of 10⁻¹–10⁻² Pa are achieved in a glow-discharge plasma cathode with the help of an auxiliary initiating discharge. An electron emission current density of up to 100 A/cm² and accelerating voltageof 15 kV are obtained in a gas-filled diode based on this type of a plasma cathode. An electron beam witha neutralized space charge can be transported almost without losses in a weak axial magnetic field alonga plasma channel formed due to the gas ionization by the accelerated electrons over a distance of up to 30 cm.     

Electrical conductivity of BaCe0.9Nd0.1O3−α in H2+H2O+Ar gas mixture

Electroconductivity of BaCe_0.9Nd_0.1O_3−α was studied as a function of the composition of the H₂+H₂O+Ar mixture and temperature in the interval from 873 to 1173 K. It was shown that the electroconductivity was independent of P_H2 (0.97 to 0.10 atm) and P_O2 (10⁻²¹ to 10⁻²⁶ atm), but depended on P_H2O (0.08 to 0.005 atm). A mathematical processing of the P_H2O dependencies of the electroconductivity, which was performed in terms of a classical model of defect formation in high-temperature proton-conducting solid electrolytes, yielded equilibrium constants of the reaction of water dissolution in BaCe_0.9Nd_0.1O_3−α and mobilities of protons and oxygen ions. The temperature dependencies of these quantities were used to determine the mobility activation energies of protons (E_a=34±7 kJ/mole) and oxygen ions (E_a=72±8 kJ/mole), and also the enthalpy (ΔH=−150±25 kJ/mole) and the entropy (ΔS=153±26 kJ/mole·K) of the reaction of water dissolution in BaCe_0.9Nd_0.1O_3−α.     

Repetitive low-pressure volume discharge induced by attachment instability in an Ar/Cl<Subscript>2</Subscript> mixture

Ignition conditions and the characteristics of a repetitive volume discharge with a spherical anode and plane cathode are investigated. The discharge was ignited in Ar/Cl₂ mixtures (P≤2.0 kPa) used in excimer halogen lamps operating on the ArCl (B-X) 175-nm, Cl₂(D′-A′) 257-nm, and Cl ₂ ^** 195-to 200-nm molecular bands. At an interelectrode distance of 3 cm and a dc anode voltage of U _ch ≤1 kV, a stable repetitive pulsed discharge with a repetition rate of 1–50 kHz was ignited in chlorine or (0.1–2.0)/(0.04–0.12)-kPa Ar/Cl₂ mixtures. The development of attachment instability in the discharge plasma, in which the processes of the formation, decay, and diffusion of the Cl ₂ ⁻ and Cl⁻ negative ions play an important role, leads to the formation of a solitary pearlike plasma domain with an average diameter of 0.2–3.5 cm.     

Photodetachment of negative ion in a gradient electric field near a metal surface

Based on closed-orbit theory, the photodetachment of H in a gradient electric field near a metal surface is studied. It is demonstrated that the gradient electric field has a significant influence on the photodetachment of negative ions near a metal surface. With the increase of the gradient of the electric field, the oscillation in the photodetachment cross section becomes strengthened. Besides, in contrast to the photodetachment of H near a metal surface in a uniform electric field, the oscillating amplitude and the oscillating region in the cross section of a gradient electric field also become enlarged. Therefore, we can use the gradient electric field to control the photodetachment of negative ions near a metal surface. We hope that our results will be useful for understanding the photodetachment of negative ions in the vicinity of surfaces, cavities, and ion traps.     

A comparative study of the ionic keV X-ray line emission from plasma produced by the femtosecond,picosecond and nanosecond duration laser pulses

We report here an experimental study of the ionic keV X-ray line emission from magnesium plasma produced by laser pulses of three widely different pulse durations (FWHM) of 45 fs, 25 ps and 3 ns, at a constant laser fluence of ∼1.5 × 10⁴ J cm^− 2. It is observed that the X-ray yield of the resonance lines from the higher ionization states such as H- and He-like ions decreases on decreasing the laser pulse duration, even though the peak laser intensities of 3.5 × 10¹⁷ W cm^− 2 for the 45 fs pulses and 6.2 × 10¹⁴ W cm^− 2 for the 25 ps pulses are much higher than 5 × 10¹² W cm^− 2 for the 3 ns laser pulse. The results were explained in terms of the ionization equilibrium time for different ionization states in the heated plasma. The study can be useful to make optimum choice of the laser pulse duration to produce short pulse intense X-ray line emission from the plasma and to get the knowledge of the degree of ionization in the plasma.     

Multiply charged titanium cluster anions: production and photodetachment

Titanium clusters are produced by laser vaporization of a metal wire in a helium gas pulse, stored in a Penning trap, size selected and transformed into multiply charged anions by electron attachment. Both doubly and triply charged titanium clusters are observed. For the first observation of photodetachment of electrons from metal cluster dianions, Ti ₅₅ ^2- clusters are selected and excited by a laser pulse, which leads to the emission of an excess electron: Ti ₅₅ ^2- → e⁻ + Ti ₅₅ ^- . This revised version was published online in August 2006 with corrections to the Cover Date.     

Coherent control of photodetachment of H− in an electric field near a metal surface

We show that the photodetachment of H^? in an electric field near a metal surface can be controlled by using a single or double laser pulse. The method of theoretical analysis used is semi-classical closed orbit theory. The results show that if the period of a certain closed orbit is longer than the pulse width of the single-pulse laser, the contribution of that closed orbit to the photodetachment cross-section will be greatly reduced. As for the double-pulse laser, the pulse width, phase difference and the time delay between the two pulses all play an important role in the photodetachment cross-section. With the decrease of the time delay, the oscillating amplitude of the cross-section increases while the oscillating frequency decreases. Therefore, laser pulses can be used to control the photodetachment process of negative ions or atoms in an external field near metal surfaces.     

Quantum beats in excitons in Cu2O

A theoretical study is carried out of quantum beats (QB) in the time-dependent intensities of absorption of a test pulse and of spontaneous luminescence in a Cu₂O crystal under conditions of double optical resonance. It is assumed that pumping is effected by a CO₂-laser pulse which dynamically couples the exciton levels 1s(Γ ₅ ⁺ ) and 2p(Γ ₄ ⁻ ,Γ ₅ ⁻ ,Γ ₃ ⁻ Γ ₂ ⁻ ) and splits them into two or three pairs of quasi-energy levels. The frequency of the test pulse is in resonance with the frequency Γ ₅ ⁺ of the exciton. The corresponding intensities for various directions of the electric vector of the pump field E _L, the polarization vector ξ, and the wave vector q of the test pulse are obtained. The frequency of the quantum beats is twice the Rabi frequency, which for different values of E _L, ξ and q contains different sets of matrix elements of the dipole transitions between the levels 1s(Γ ₅ ⁺ ) and 2p(Γ ₄ ⁻ ,Γ ₅ ⁻ ,Γ ₃ ⁻ Γ ₂ ⁻ ). Thus, by measuring the period of the quantum beats it is possible to determine the unknown matrix elements of the indicated transitions. Fiz. Tverd. Tela (St. Petersburg) 39, 844–847 (May 1997)     

Ionic composition of a humid air plasma under ionizing radiation

A kinetic model is proposed for ion–molecular processes involving charged particles of a humid air plasma produced by a fast electron beam. The model includes more than 600 processes involving electrons and 41 positive and 14 negative ions, including hydrated ions H₃O⁺ (H₂O) _n and O ₂ ^? (H₂O) _n with n = 1, 2, …, 12. The energy costs of production of electron–ion pairs and electronic and vibrational (for water molecules, also rotational) excitation of molecules are calculated in nitrogen, oxygen, water vapor, air, and humid air. A method is proposed for calculating the energy costs in mixtures by the calculation data in pure gases. The evolution of the plasma composition is studied by the numerical solution of a system of 56 time-dependent balance equations for the number of charged particles of plasma by the fourth-order Runge–Kutta method. The steady-state composition of plasma is determined by solving nonlinear steady-state balance equations for the ionization rates of humid air from 10 to 10¹⁶ cm^–3/s and the fraction of water molecules from 10^–3% to 1.5%. It is established that, for water vapor content (the ratio of the number density of water molecules to the total number density of air molecules) of 0.015–1.5% in air at atmospheric pressure and room temperature, the main ion species are two types of positive ions H₃O⁺ (H₂O) _n with the number of water molecules n = 5, 6 and three species of negative ions O ₂ ^? (H₂O) _n with n = 5, 8, 9.     

Zur mikrophysikalischen Beschreibung des schwachionisierten Säulenplasmas von Glimmentladungen in Stickstoff-Neon-Gemischen III. Bilanzierung des Säulenplasmas und Berechnung seiner inneren Parameter

For the plasma of the low current positive column in the N,-Ne-mixture the equations for the concentration of different kinds of ions and excited particles are set up. The axial electric field strength, the degree of ionization and the concentration of excited Ne-atoms and of the different kinds of ions are calculated by simultaneous solution of these balances together with the electron Boltzmann equation for this mixture and the balances for the electric current and quasineutrality of the column plasma. All these macroscopic properties of the discharge column are investigated for electric currents of 0.5 mA to 13,5 mA, for total pressures of 0,37 torr to 3,7 torr and for any mixture ratio. A comparision between measured and calculated electric field strengths shows a good agree-ment. The ionization of the N,-molecules by collisions with the metastable Ne-atoms (Penning-ionization) is of great significance for the generation of new charge carriers in such a mixture. In these investigations the collision rate zp of the Penning-ionization was obtained to 3 · 10^?11 cm³ s^?1 by the aid of a comparision between measured and calculated electric axialgradients of the column.     

Emission characteristics and electron kinetic coefficients of the plasma of a transverse volume discharge initiated in a mixture of heavy inert gases with chlorine molecules

The results of studying the radiation due to argon, krypton, and xenon monochloride bands, as well as to the bands of chlorine molecules, from the plasma of a transverse Ar-Kr-Xe-Cl₂ volume discharge are reported. The working mixture of a pulse radiation source is optimized with regard to its pressure and elemental composition and parameters of an excitation system. By numerically solving the Boltzmann kinetic equation for the electron energy distribution function, the transport characteristics of plasma electrons and discharge power specific losses are found for different values of the reduced electric field strength. The plasma parameters are simulated for the quaternary mixture, which is most appropriate for a multiwave UV-VUV source. Qualitative analysis is conducted for the most important electron processes in the multicomponent plasma that govern the joint formation of argon, krypton, and xenon monochlorides in the transverse discharge.     

Effect of a magnetic field on the rate of etching of silicon dioxide in a CF4 + O2 plasma

A near-electrode nonuniform magnetic field crossed with an electric field is found to strongly affect the rate of etching of silicon dioxide on glass substrates in a CF₄ + O₂ plasma when the Larmor frequency (≈10⁹ s⁻¹) is much higher than the frequency of collisions of an electron with surrounding plasma particles (≈10⁶ s⁻¹) and the frequency of the applied rf electric field (≈10⁷ s⁻¹). The confinement of electrons by the magnetic field in the immediate vicinity of the substrate surface to be treated increases the rate of generation of chemically active particles, which increases the etching rate of silicon dioxide.     

Decay of an electronic vortex of a collisionless shock wave as a possible mechanism of a “Coulomb explosion”

A new mechanism of a “Coulomb explosion,” where ions are accelerated by the electric field separating charges at the magnetic Debye radius r _B∼B/4πen _e, is proposed on the basis of a nonquasineutral model of electronic vortices in a magnetic field. It is shown by means of numerical calculations that in the process of acceleration of the ions a collisionless shock wave, whose front has an effective width of the order of δ∼r _B, determined by the breakdown of quasineutrality, is formed in a time of the order of ω _pi ⁻¹ , where ω_pi is the ion plasma frequency. The origin of such explosive dynamics is the formation of “holes” in the electron density at characteristic times of the order of ω _pe ⁻¹ (ω_pe is the electronic plasma frequency) as a result of the generation of electronic vorticity by the Weibel instability of an electromagnetic wave. Calculations for a laser pulse with intensity J∼6×10¹⁸ W/cm² show that the ions expand in the radial direction with velocities up to 3.5×10⁸ cm/s. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 10, 669–674 (25 November 1999)     

Synthesis of starfish-like Cu2O nanocrystals through ��-irradiation and their application in lithium-ion batteries

In this study, single-crystalline starfish-like cuprous oxide (Cu₂O) nanocrystals with the backbones lengths in the range of 660 nm~16 ??m are successfully prepared through ??-irradiation, the cetyltrimethylammonium bromide (CTAB) is used as a capping material or soft colloidal templates. Without the addition of CTAB in the reaction system, irregular Cu₂O nanoclusters were obtained and their diameter is about 200 nm~1 ??m. Controlling the concentration ratio of CTAB to the copper ions, starfish-like morphology of Cu₂O can be obtained in high yield. Their structures are characterized by X-ray diffraction, scanning electron microscopy, and high-resolution transmission electron microscopy. The possible growth mechanism of the starfish structure is discussed in the text. For potential application in lithium-ion batteries, an electrode made of the starfish-like Cu₂O shows excellent electrochemical cycling performance and high-rate capability. Compared with the Cu₂O nanoclusters, the starfish-like Cu₂O exhibits an improved electrochemical cycling stability. The capacity of the starfish-like Cu₂O can maintain 340 and 215 mAh g^?1 after 50 cycles at the rate of 0.1 C and 5 C, respectively. The reversible capacity holds 60% as the discharge?Ccharge rate even increases by 50 times.