Pulsed discharge in nitrogen and argon under an elevated pressure in a nonuniform electric field

The characteristics of a discharge and radiation in nitrogen and argon under pressures of 10–760 Torr and the discharge formation without pre-ionization of the gap from an auxiliary source are considered. A peak is detected on the pressure dependence of the radiation power of the second positive system of nitrogen for E ₀/p ～ 270 V/cm Torr and nitrogen pressure p ～ 70 Torr. In the pressure range 10–760 Torr and for a voltage pulse leading front duration of ～ 10 ns, an electron beam is formed behind the grid anode with various half-amplitude pulse durations. It is shown that, under the given conditions, the electron beam is formed at the voltage pulse front both in the case of a discharge gap breakdown and in the absence of a clearly manifested breakdown, as well as for a 10-ns delay of breakdown at the leading front of a discharge current pulse.     

Parametric study of radiofrequency helium discharge under atmospheric pressure

The parameters of radiofrequency helium discharge under atmospheric pressure were studied by electrical and optical measurements using high voltage probe, current probe and optical emission spectroscopy. Two discharge modes α and γ were observed within certain limits. During α to γ mode transition, a decrease in voltage (280–168 V), current (2.05–1.61 A) and phase angle (76^°–56^°) occurred. The discharge parameters such as resistance, reactance, sheath thickness, electron density, excitation temperature and gas temperature were assessed by electrical measurements using equivalent circuit model and optical emission spectroscopy. In α mode, the discharge current increased from 1.17 to 2.05 A, electron density increased from 0.19 × 10¹² to 0.47 × 10¹² cm^?3 while sheath thickness decreased from 0.40 to 0.25 mm. The excitation temperatures in the α and γ modes were 3266 and 4500 K respectively, evaluated by Boltzmann’s plot method. The estimated gas temperature increased from 335 K in the α mode to 485 K in the γ mode, suggesting that the radiofrequency atmospheric pressure helium discharge can be used for surface treatment applications.     

Emission und Schwingungsverteilung der 1. neg. Gruppe und der 2. pos. Gruppe in einem Stickstoffplasma

The intensity of the first negative system ofN ₂ ⁺ (B ² Σ _u ⁺ -X ² Σ _g ⁺ and of the second positive system ofN ₂(C ³ Π _u -B ³ Π _g ) was observed in the discharge and in the afterglow as function of discharge current. An a. c. discharge in pure nitrogen was used at pressures of about 5 torr. The intensity of the first negative system ofN ₂ ⁺ — in the discharge and in the afterglow — rises to a maximum and decreases with further increase of the discharge current. The afterglow intensity of the second positive system ofN ₂ shows a maximum too. In the discharge, however, the intensity of the second positive system ofN ₂ increases with increasing discharge current. The relative population of the vibrational levelsN _v′ =i/N _v′ =0 (i=1,2,3,4) of theB ² Σ _u ⁺ state ofN ₂ ⁺ , in the discharge and in the afterglow, increases with increasing discharge current, while the relative population of the vibrational levelsN _v′ =i/N _v′ =0 (i=1, 2, 3, 4) of theC ³ Π _u state ofN ₂ reaches a maximum in the discharge. There seems to be evidence that the first negative system ofN ₂ ⁺ is not excited by electron impact withN ₂ molecules in ground state under the discharge conditions in question.     

Reversibler Gleichfeld- und Mikrowellen-Durchschlag in n-Typ-Germanium bei 4,2 °K

The microwave induced breakdown characteristic inn-type germanium at 4.2 °K has been observed and compared with the d.c. induced breakdown characteristic obtained from the same sample. The effective microwave breakdown field intensity is nearly equal to the field intensity observed in d.c. induced breakdown. However, in the breakdown region with conductivities greater than 0.1 ohm^?1 cm^?1 a relaxation effect was found and interpreted qualitatively as momentun relaxation. In the initial breakdown the relaxation time τ _m is small,ω ²τ _m ² being ?1 whereω/2π=9·10⁹s^?1 is the microwave frequency. The relaxation time is determined by predominant neutral impurity scattering with at last 5·10¹⁴ impurities per cm³. This scattering mechanism becomes ineffective when the impurities are ionized by hot carriers. Ionized impurity scattering or acoustic phonon scattering will then be predominant with increased and energy dependent values of τ _m . The increased phase shift between carriers and field causes a decreased energy transfer from the field to the carriers, an accordingly smaller ionization rate, and finally results in a nearly constant a.c. conductivity. The observed anisotropy of the breakdown field intensity is in qualitative agreement with the assumption that only carriers in “hot” valleys of the conduction band initiate the breakdown by impact ionization. The unsufficient quantitative agreement may be due to an inhomogeneity of doping which is suggested by comparing the values of the ohmic low temperature conductivity of the samples.     

The universal dependence of the relative voltage of static breakdown in gases on a generalized variable

In terms of the Townsend model of a static electrical gas discharge, the ratio of breakdown voltage U _B to its minimal value U _min is expressed as a function of generalized variable Ξ _B ? f(Ξ _b ), such that the function depends on neither the gas type nor the cathode material.     

Radiative transitions to localized Eu states in Pb<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Eu<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Te solid solutions

Two types of radiative transitions were observed in the low-temperature photoluminescence spectra of Pb_1?x Eu _x Te (0 ≤ x ≤ 0.09) solid solutions: an intense line corresponding to the transitions from the conduction to the valence band and a series (up to 15) of narrow lines corresponding to the transitions from the hybridized conduction band to the split Eu³⁺ levels. The intensity of the discrete lines increases with x, and their energies (and intensities) weakly depend on the temperature. The absorption and emission of the discrete lines are caused by the 4f ⁷(⁸ S _7/2) ? 4f ⁶(⁷ F _J )[L ₆ ^? + 5dt _2g ] transitions.     

Das Kernquadrupolmoment des Mn55

With a recording photoelectric Fabry-Perot spectrometer and an atomic-beam light source the hyperfine structure of the Mn I-resonance linesλ=4031 Å,λ=4033 Å,λ=4034 Å (3d ⁵4s ² a ⁶ S _5/2?3d ⁵4s4p z ⁶ P _7/2,5/2,3/2 ⁰)and of the inter-combination linesλ=5395 Å andλ=5433 Å (3d ⁵4s ² a ⁶ S _5/2?3d ⁵4s4p z ⁸ P _7/2,5/2 ⁰) was measured. Furthermore the resonance lines have been measured with a pulsed atomic-beam in absorption. In this case the quotient (I ₀(ν)?I(ν))/I ₀(ν) was recorded, whereI(ν)=I ₀(ν) exp(?α(ν)d) is the observed intensity with absorption andI ₀(ν) the intensity of the light source. From the hyperfine structure splitting the value of the electric quadrupole moment of Mn⁵⁵ was derived to be:Q(Mn⁵⁵)=+(0.35±0.05)·10^?24 cm².     

Production of Heavy Helium <Superscript>5</Superscript>Hе in the Absorption of Stopped Pions by <Superscript>10,11</Superscript>B Nuclei

Helium ⁵Hе states are sought in missing-mass (MM) spectra from reactions of the absorption of stopped pions: ¹⁰В(π^?, dt)Х and ¹¹В(π^?, tt)Х. The experiment is conducted using the LANL accelerator equipped with a two-arm semiconductor charged-particle spectrometer. The parameters of the ground state agree with the literature data. The best fit for the first excited level is obtained at E_r = 1.8(5) MeV and Γ = 4.7(7) MeV. Neither of the two reactions produce statistically significant evidence for the presence of highly excited (E_x ≥ 20 MeV) states of ⁵Hе.     

Untersuchung über die gasionisierende Strahlung einer Entladung II

This paper gives a report on measurements of the coefficient of absorption and intensities of a gas-ionizing radiation, which is emitted by a gas discharge. Earlier measurements in oxygen with a discharge in a cylindrical electrical field had yielded components of radiation with values ofμ≈550,μ≈250, andμ= 38 cm^?1 according to 760 mm Hg. By new measurements using a spark discharge an additional component with a value ofμ=2,5 has been found, which already has been measured by other authors. Measurements with mixtures of oxygen and nitrogen are compared with results of measurements in air. From this it may be deduced that the gas-ionizing radiation effective in air is essentially emitted by nitrogen and ionizes oxygen, the coefficient of absorption being aboutμ≈5 cm^?1. The number of ionizing quantums emitted per ionizing collision of electrons in the discharge tube is about 10^?3 for oxygen, nitrogen, and air. In oxygen this figure proves to be essentially independent ofE/p. In air, however, this figure is reduced with increasing values ofE/p. The absorption of the ionizing radiation in air is increased by the addition of methane (μ=960 cm^?1 for 760 mm Hg of methane). In carbon dioxyde several components of ionizing radiation are found, with coefficients of absorption in the range 200<μ<800.     

Radiation resistance of 4<Emphasis Type="Italic">H</Emphasis>-SiC Schottky diodes under irradiation with 0.9-MeV electrons

Degradation of the parameters of 4H-SiC Schottky diodes after irradiation with 0.9-MeV electrons is studied. A charge-carrier removal rate of 0.07–0.09 cm^–1 is determined. The Schottky diodes under investigation are shown to retain rectifying current-voltage characteristics up to doses of ~10¹⁷ cm^–2. The radiation resistance of SiC Schottky diodes is found to be much greater than that of Si p–i–n-diodes with the same breakdown voltage.     

Multiphoton transitions and the resonant optical Stark effect in AgBr nanocrystals

Nonlinear absorption of 30-ps light pulses with λ = 560 nm in AgBr nanocrystals is experimentally studied in the range of intensities 10⁸–10¹⁰ W/cm². The results of a theoretical analysis show that the absorption is related to direct interband n-photon transitions. With increasing light intensity j, the number n increases and the region of the k-space changes for the transitions predominantly contributing to the absorption. It is shown that, due to specific features of the AgBr electronic band structure, the probabilities of two-photon transitions for the light at λ = 560 nm are anomalously low, while those of four-photon transitions are anomalously high. In addition, the increase in the two-photon transition rate with increasing intensity is blocked at j ? 10⁸ W/cm² due to the resonant optical Stark effect and due to a gap arising in the band spectrum, rearranged because of the interaction with light.     

DD reaction enhancement and X-ray generation in a high-current pulsed glow discharge in deuterium with titanium cathode at 0.8–2.45 kV

The DD reaction yield (3-MeV protons) and the soft X-ray emission from a titanium (Ti) cathode surface in a periodic pulsed glow discharge in deuterium were studied at a discharge voltage of 0.8–2.45 kV and a discharge current density of 300–600 mA/cm². The electron screening potential U_e = 610 ± 150 eV was estimated in the range of deuteron energies 0.8 keV < E_d < 2.45 keV from an analysis of the DD reaction yield as a function of the accelerating voltage. The obtained data show evidence for a significant enhancement of the DD reaction yield in Ti in comparison to both theoretical estimates (based on the extrapolation of the known DD reaction cross section for E_d ≥ 5 keV to low deuteron energies in the Bosch-Halle approximation) and the results of experiments using accelerators at the deuteron energies E_lab ≥ 2.5 keV and current densities 50–500 μ A/cm². Intense emission of soft X-ray quanta (10¹³–10¹⁴ s^?1 cm^?2) was observed at an average energy of 1.2–1.5 keV. The X-ray emission intensity and the DD reaction yield enhancement strongly depend on the rate of deuterium diffusion in a thin subsurface layer of Ti cathode.     

Coulomb Rydberg electron <Emphasis Type="Italic">L</Emphasis>-mixing in collisions with atomic ions

The cross sections of the Rydberg electron L-mixing in a hydrogen atom and a hydrogen-like ion are calculated for slow collisions with atomic ions H*(n, L) + A⁺ = H*(n, L′) + A⁺ without variation of the principal quantum number n. The probability of the L-mixing L → L′ is associated with the quantum interference of the wave functions of adiabatic states, i.e., with the mixing of the time phases of these functions exp(?i∫E _k (t)dt). The effective cross section of such L-mixing for the states with n = 28 are 4–5 orders of magnitude greater than the cross sections determined in previous investigations. The expansion coefficients of spherical Coulomb wave functions in terms of parabolic ones and vice versa, which are necessary for determining cross sections, are calculated on the basis of a comprehensive analysis of the spatial properties of these functions.     

The dielectric and piezoelectric behaviour of pyrolusite (polycrystalline ore of MnO2)

The variation of dielectric constant? of pyrolusite (sintered polycrystalline ore of MnO₂) with temperature, frequency and voltage has been studied within the frequency range 200 c/s to 10 kc/s. The samples studied show a very high value of dielectric constant ≈ 10⁵. The?-temperature curve indicates that? attains a maximum value at a certain temperature. The temperature at which? attains a maximum value appears to vary from sample to sample. At higher temperatures (i.e. higher than that at which? attains a maximum value),? decreases with temperature as?=c/(T?Θ). The dielectric constant is dependent on the frequency; it has a higher value at lower frequencies. The applied voltage across the specimen has a marked influence on the dielectric constant, which increases rapidly with voltage. A capacity with pyrolusite as dielectric shows a hysteresis loop (electrical). The dielectric loss factor tanδ is found to depend on temperature, frequency and voltage. Tanδ attains a maximum value at lower range of frequencies between 300 c/s to 700 c/s, for a given voltage, and temperature. This indicates the existence of dielectric relaxation for these specimens. Tanδ also varies exponentially with temperature. Samples of pyrolusite studied show a piezo electric effect as well. The electromechanical coupling coefficient is found to vary from 2·4×10^?5 to 8·8×10^?5 e.s.u/ dyne. Slabs cut from the samples of pyrolusite mineral were found to control the frequency of a Hartley oscillatory circuit. The resonant frequency range was found to increase as the thickness of the slab is reduced.     

Characteristics of a photovoltaic X-ray detector based on a GaAs epitaxial structure

The characteristics of a photovoltaic X-ray detector based on the GaAs p ⁺-n-n′-n ⁺ epitaxial structure grown using gas-phase epitaxy are studied. Typical current-voltage and capacitance-voltage characteristics of the epitaxial structures are analyzed together with the built-in electric field profile in the n-GaAs depleted region. The efficiency of charge accumulation in the photovoltaic detector is measured for zero bias and for a bias voltage of 17 V. It is shown that the GaAs-based photovoltaic X-ray detector can operate with zero bias voltage at room temperature. The sensitivity of the detector is measured as a function of the effective energy of X-rays and the angle of incidence of X-ray photons.     

Mechanism of charge transfer in <Emphasis Type="Italic">n</Emphasis>-CdS/<Emphasis Type="Italic">p</Emphasis>-CdTe heterojunctions

The capacitance-voltage and current-voltage characteristics of the n-CdS/p-CdTe heterosystem are investigated. Analysis of these characteristics demonstrates that the CdTe_1?x S _x solid solution formed at the n-CdS/p-CdTe heterointerface is inhomogeneous in both the conductivity and composition. The thickness of solid solutions is estimated from the capacitance-voltage characteristics. It is shown that, for the n-CdS/p-CdTe heterosystem, the current-voltage characteristic in the current density range 10^?8-10^?5 A cm^?2 is governed by the thermal electron emission, whereas the current in the heterostructure at current densities in the range 10^?4-10^?2 A cm^?2 is limited by recombination of charge carriers in the electroneutral region of the CdTe_1?x S _x solid solution. The lifetime and the diffusion length of minority charge carriers in the CdTe_1?x S _x solid solution and the surface recombination rate at the interface between the CdS layer and the CdTe_1?x S _x solid solution are determined. It is demonstrated that the n-CdS/p-CdTe heterostructure operates as a p-i-n structure in which CdTe is a p layer, CdTe_1?x S _x is an i layer, and CdS is an n layer.     

Effective excitation cross section and lifetime of Er<Superscript>3+</Superscript> ions in Si: Er light-emitting diodes fabricated by sublimation molecular-beam epitaxy

A series of Si: Er electroluminescent diode structures is fabricated by sublimation molecular-beam epitaxy. The diode structures efficiently emit at a wavelength of 1.5 μm under conditions of p-n junction breakdown at room temperature. The effective cross section of excitation of Er³⁺ ions with hot carriers heated by the electric field of a reverse-biased p-n junction and the lifetime of Er³⁺ ions in the first excited state ⁴I_13/2 are determined for structures that emit in a mixed breakdown mode and are characterized by the maximum intensity and excitation efficiency of the Er³⁺ electroluminescence.     

Conductance of a single-wall carbon nanotube in a one-parameter tight-binding model

The dependence of current-voltage characteristics of single-wall nanotubes on their radius and chirality is studied theoretically. It is shown that the conductance of a single-wall nanotube at low voltages can assume discrete values equal to zero for a dielectric tube and 4(e²/h) for a conducting tube (e is the electron charge, h is the Planck constant). The current-voltage characteristic of a nanotube exhibits kinks related to the discreteness of the electron spectrum. The behavior of the conductance of the nanotube at zero temperature is analyzed in a quantizing longitudinal magnetic field that changes the type of tube conduction. In a magnetic field, the conductance of a dielectric tube at low voltages can assume a value of 2(e²/h) in the region where the tube becomes conducting. In a weak magnetic field, a conducting tube becomes dielectric with an energy gap depending on the magnitude of the magnetic field. The conductance of a carbon nanotube is calculated as a function of the temperature and longitudinal magnetic field.