Anisotropic fast electron emission from a microwave irradiated plasma slab

Experimental measurements of the anisotropic electron emission from a microwave irradiated plasma slab are presented. The indicate that electron emission is due to the occurence of the oscillating two-stream instability.     

Qualitative difference between the angular anisotropy parameters in fast electron scattering and photoionization

It is demonstrated for the first time that in spite of well known big similarities between atomic ionization by photons and fast electrons, a qualitative difference exists in angular anisotropy parameters of electrons knocked out in these processes. The difference is disclosed here and attributed to distinction between normal (transverse) and virtual (longitudinal) photons. Formulas are derived for dipole and non-dipole angular anisotropy parameters in fast electron-atom scattering. The ratio of quadrupole-to-dipole matrix elements is determined by the parameter ωR/v < 1, where ω is the transferred in collision energy, R is the ionized shell radius, and v is the speed of projectile. This factor can be much larger than that in the case of photoionization, where one has the speed of light c that is much higher than v. We illustrate general formulas by concrete results for outer s subshells of noble gas atoms Ar and Xe. Even for very low momentum transfer q, in the so-called optical limit, the deviation from photoionization case is prominent and instructive.     

Investigation of electron localization in harmonic emission from asymmetric molecular ion

We theoretically investigate the electron localization around two nuclei in harmonic emission from asymmetric molecular ion. The results show that the ionization process of electron localized around one nucleus competes with its transfer process to the other nucleus. By increasing the initial vibrational level, more electrons localized around the nucleus D+tend to transfer to the nucleus He2+so that the ionizations of electrons localized around the nucleus He2+increase. In this case, the difference in harmonic efficiency between He H2+and He D2+decreases while the difference in harmonic spectral structure increases. The evident minimum can be observed in the harmonic spectrum of He H2+compared with that in the spectral structure of He D2+, which is due to the strong interference of multiple recombination channels originating from two nuclei. Time-dependent nuclear probability density, electron-nuclear probability density, double-well model, and time-frequency maps are presented to explain the underlying mechanisms.     

Interferences in photo-detached electron spectra from a non-collinear tri-atomic anion

The electron flux oscillations in photo-detachment of a non-collinear tri-atomic anion have been studied by taking each atom of the system as a coherent source of detached-electron wave. These electron waves traversing along three different trajectories result in a quantum interference. An analytical expression of detached-electron flux is evaluated for various detached-electron energies and for different geometrical shapes of the system. The results show that the electron flux distributions exhibit molecular shape-induced oscillatory structures. These oscillations are explained using the semi- classical closed-orbit theory; the outgoing electron waves produced from one center are propagated in the vicinity of the sources at other centers. It is also observed that in a particular case our non-collinear tri-atomic system reduces to the collinear tri-atomic system recently published.     

Nuclear excitation by electron capture followed by fast x-ray emission

The resonance strength of the two-step process of nuclear excitation by electron capture followed by γ decay of the nucleus can be significantly increased in highly charged ions if the resonant capture proceeds via an excited electronic state with subsequent fast x-ray emission. For fully ionized ²³⁸₉₂U and ²³²₉₀Th, the x-ray decay stabilizes the system against internal conversion of the captured electron, with an increase of both nuclear lifetimes and resonance strengths of up to two orders of magnitude compared with the case when occupied atomic orbitals prevent the x-ray de-excitation. Applications of this effect to the measurement of the not yet experimentally observed nuclear excitation by electron capture and to dense astrophysical plasmas are discussed.     

Interferences of ultrashort free electron wave packets

Interferences of free electron wave packets generated by a pair of identical, time-delayed, femtosecond laser pulses which ionize excited atomic potassium have been observed. Two different schemes are investigated: threshold electrons produced by one-photon ionization with parallel laser polarization and above threshold ionization electrons produced by a two-photon transition with crossed laser polarization. Our results show that the temporal coherence of light pulses is transferred to free electron wave packets, thus opening the door to a whole variety of exciting experiments.     

Energy-resolved analysis of ferroelectric electron emission from TGS using emission electron microscopy

Ferroelectric electron emission arises when the spontaneous polarization of a ferroelectric is switched due to the application of an electric field. In order to study the origin of emission and the related emission mechanism, space-resolved emission electron microscopy has been employed. The integral energy distribution of the emitted electrons from triglycine-sulfate surfaces has been investigated using a cylindrical sector analyzer and an imaging retarding field analyzer. Space-resolved emission photography and energy distribution measurements were obtained, revealing the effect of ferroelectric switching on the electric field distribution and hence on the emission process. Evidence of secondary electron emission from the metal electrodes has been found.     

Interferences of molecular X-rays in heavy ion collisions

The possibility of coherence effects in molecular orbital X-rays emitted during multiple heavy ion collisions in a crystal target is investigated. That X-ray energy region is found, where in spite of the thermal vibrations of the target atoms interferences have to be expected. The dynamical theory for the molecular orbital evolution is used. The 70 MeV Ni — Ni collisions are treated as an example. An experiment for checking the coherent photon emission in multiple molecular scattering processes is suggested, which in turn can eventually be used to measure the ratio of e.g. triple to binary collision.     

Visualization of field induced ferroelectric electron emission from TGS using emission electron microscopy

Field induced electron emission from triglycinesulfate (TGS) has been investigated using parallel imaging electron emission microscopy (EEM). The emission phenomenon has been induced by applying an ac electrical field up to 2 kV/mm to a single crystal of approximately 0.1 mm thickness. Emission patterns have been observed as a function of the applied field amplitude and of the crystal temperature. At voltages below the coercive field, no emission is visible. When approaching the Curie temperature, emission gradually disappears. This indicates an electron emission mechanism relying on the existence of a switchable ferroelectric phase. The information content of the images is discussed, an interpretation is given on the basis of existing theories. PACS 68.37.-d; 77; 77.80.Fm; 77.80.-e     

Stimulated emission from molecular sodium

Intense stimulated emission from the A¹Σ⁺_u-X¹Σ⁺_g transition of diatomic moleculair sodium has been observed when it is pumped by a dye-laser beam at around 600 nm. The spectral lines are localized near the infrared edge of the band, i.e., between 790 and 810 nm. The intensity of the emission as a function of the dye-laser power and the molecular density has clear thresholds.     

Strong electron correlation in photoionization of spin-orbit doublets

A new and explicitly many-body aspect of the "leveraging" of the spin-orbit interaction is demonstrated, spin-orbit activated interchannel coupling, which can significantly alter the photoionization cross section of a spin-orbit doublet. As an example, it is demonstrated via a modified version of the spin-polarized random phase approximation with exchange, that a recently observed unexplained structure in the Xe 3d(5/2) photoionization cross section [A. Kivim?ki et al., Phys. Rev. A 63, 012716 (2000)] is entirely due to this effect. Similar features are predicted for Cs 3d(5/2) and Ba 3d(5/2).     

Characteristics of the fast electron emission produced during the cleavage of crystals

The present paper reports the fast electron emission produced during the cleavage of alkali halide crystals and models the dynamics of the process. The mechano-emission arises as a result of the ionization of surface traps at the expense of the energy which is released in the annihilation of the defects which are formed during cleavage. The slow electrons which appear upon the ionization of surface traps are subsequently accelerated in the field of negatively charged segment of the freshly cleaved surface. Considering the basic mechanism of fast electron emission, expressions are derived which are able to explain satisfactorily the temporal, thermal, charge, surface, coloration, water adsorption and other characteristics of the fast electron emission produced during the cleavage of crystals. The decay time of the charges on the newly created surfaces, and the velocity of cracks can be determined from the measurements of fast electron emission produced during the cleavage of crystals. It is shown that two types of diffusing centres are responsible for the charge relaxation and thereby for the emission of fast electrons produced during the cleavage of alkali halide crystals.     

Auger electron emission from fixed-in-space CO

We have measured the angular distribution of carbon K-Auger electrons from fixed in space, core-ionized, CO molecules in coincidence with the kinetic energy release of the C+ and O+ fragments. We find a very narrow ejection of Auger electrons in the direction of the oxygen and an oscillatory diffraction pattern. Even for similar electron energies, the angular distribution strongly depends on the symmetry of the final state.     

Ion-induced electron emission from clean metals

We report recent experimental work on electron emission from clean polycrystalline metal surfaces under ion bombardment. We critically discuss existing theories and point out the presently unsolved problems.     

光电离过程中Fe靶和V靶特征辐射的角相关研究

在发射角120°—170°的范围内,应用硅漂移探测器以10°为间隔对中心能量为13.1 keV的韧致辐射诱发Fe靶和V靶发射的典型K系X射线光谱进行了测量.得到特征X射线Kα和Kβ的特征谱线,考虑探测器对特征X射线的探测效率、靶对入射光子和出射光子吸收的校准及大气对特征X射线的吸收后,结果显示不同探测角度下Kβ与Kα的强度比为一常数.将本次实验探测角度为150°时的Kβ/Kα强度比值的实验值、理论计算值和Ertuğral的实验结果进行对比,发现实验结果与预期相符.对比不同探测角度下的强度比变化趋势推断特征X射线的角度依赖关系,分析认为Kα和Kβ在探测范围内是各向同性发射的.     

Low-energy nondipole effects in molecular nitrogen valence-shell photoionization

Observations are reported for the first time of significant nondipole effects in the photoionization of the outer-valence orbitals of diatomic molecules. Measured nondipole angular-distribution parameters for the 3sigma(g), 1pi(u), and 2sigma(u) shells of N2 exhibit spectral variations with incident photon energies from thresholds to approximately 200 eV which are attributed via concomitant calculations to particular final-state symmetry waves arising from (E1)multiply sign in circle(M1,E2) radiation-matter interactions first-order in photon momentum. Comparisons with previously reported K-edge studies in N2 verify linear scaling with photon momentum, accounting in part for the significantly enhanced nondipole behavior observed in inner-shell ionization at correspondingly higher momentum values in this molecule.     

Fluctuating emission from molecular vibrational-rotational bands

Fluctuating molecular vibrational-rotational band emission from an unsteady temperature field is formulated in terms of the intensity of the temperature fluctuation and the temperature total sensitivity function of the spectral radiance of a thin, isobaric layer. By examining the contributions of layer-density dilation, Planck's function and molecular spectral absorptivity, it is shown that this total sensitivity function can be either positive or negative with respect to layer temperature depending upon mean temperature and spectral region. The 4.3-μm CO₂ band is examined to illustrate these results and a simple quantum mechanical model is presented to estimate these effects in the general case.     

Plasmonic secondary electron emission from alkali metals

One of the authors (Gornyi) has demonstrated earlier the possibility of plasmonic secondary electron emission (PSEE). Here electrons striking a solid substance excite in it plasmons, which then break up and in turn excite electrons. These electrons, upon being emitted into vacuum, form clusters of secondary electrons with definite energy levels. When energy-loss spectra of electrons are compared with energy spectra of secondary electrons and with work-function curves for secondary electrons, all of them plotted for lithium, sodium, and potassium, then the occurrence of the PSEE phenomenon in these metals can be established. The PSEE explains the peaks along the energy spectra and the work-function curves for secondary electrons. These peaks were not understood before.     

Field electron emission from bunchy flake-like nano-carbonfilms

This paper reports that bunchy flake-like nano-graphite crystallite films (BNGCFs) were deposited on Si substrates by using the microwave chemical vapour deposition technique. Furthermore the BNGCFs were characterized by x-ray diffraction spectra, scanning electron microscopy, Raman spectra and field emission (FE) I--V measurements, and a lowest turn-on field of 1.5V/μm, and a high average emission current density of 30mA/cm^*