Energy spectrum of ejected electrons in ionization of hydrogen atoms by electrons

Energy spectrum of ejected electrons in ionization of hydrogen atoms has been calculated following a multiple scattering theory of Das and Seal [15]. The results show peaks around two to three Rydbergs of energies of the ejected electrons, for incident electron energy of 250 eV and 500 eV, considered here, and for different combinations of the angular variables of the scattered and the ejected electrons, for scattering in a plane. The peaks are very similar to those observed in relativistic K-shell ionization of Ag atoms by electrons at 500 KeV energy [6]. The physical origin of these peaks may be traced to the second order scatterings, scattering first by the atomic nucleus (or the atomic electron) and then a second time by the atomic electron. These peaks are, however, absent in the first Born results. Experimental verification of the present results and theoretical calculation by some other well-known methods will be interesting.     

(e,2e) and (e,3-1e) coincidence experiments for studying the PCI effect of low energy ionizing electrons in the Auger process of Ar

Our (e,3-1e) measurements for studying the post-collision interaction (PCI) after electron impact inner shell ionization of argon were continued and completed at different energy conditions. Emitted LMM Auger electrons are detected in coincidence with the ionizing scattered electrons and the energy of the slow PCI inducer ejected electron was calculated from energy conservation. Particularly the effect of the very low energy (i.e. 0–5 eV) ejected electrons (strongly asymmetric energy sharing) is studied at 500 and 460 eV primary electron energies. In the latter case, the background caused by outer-shell electrons was measured by itself and then removed from the coincident spectrum. Nevertheless, the evaluation of PCI distorted Auger lines is still considerably disturbed by the resonant Auger electrons from the high Rydberg states, their (e,2e) contribution was estimated in the paper.     

Ejected electron spectrum of sodium autoionizing levels obtained by electron impact excitation 'at 500 eV incident energy

The ejected electron spectrum of sodium vapour has been observed at 90° to the direction af an incident electron beam with kinetic energy 500 eV. Comparisons are made with the ultraviolet absorption data.     

Xe(4d~(10))(e,2e)反应三重微分截面的理论研究

采用修正后的扭曲波玻恩近似理论,计算了共面不对称几何条件下Xe(4d~(10))(e,2e)反应的三重微分截面.散射电子能量为1000 eV,敲出电子能量为20 eV,散射电子角度分别固定在2°,4°和7.5°.理论计算与Avaldi等人的实验结果和扭曲波玻恩近似理论计算进行了比较,发现出射电子之间的后碰撞相互作用较弱,极化效应在反应过程中起着重要作用.     

Electron emission from surfaces of alkali halides under the impact of metastable helium and neon atoms

Energy distributions of the electrons ejected from the evaporated film surfaces of LiF, LiCl, LiBr, NaF and NaCl by the impact of metastable He and Ne atoms have been measured. The observed distribution curves have two distinct structures: one peak is identified as the valence band structure caused by Penning ionization, while the other peak is ascribed to scattered electrons. The positions of the valence band peaks are shifted to lower ionization energy from the corresponding photoelectron peaks (by 0.1–1.5 eV depending on the substance). In contrast to the photoelectron spectra, the structure attributable to conduction bands appears only very weakly. The relative intensity of the peak caused by scattered electrons is either strong or weak depending on the combination of the metastable atom and the sample. The interpretation of this observation is that the scattered electron peak is enhanced when the energy of the metastable atom exceeds twice the band gap energy, i.e. when the electron—electron scattering of Penning electrons in the solid is feasible.     

Electron emission spectra in low energy positron-atom collisions

Energy spectra of electrons ejected from an Ar target, in the forward direction, by a low energy positron beam have been measured and compared with theory. Structures are present in these spectra at energies compatible with electron capture to continuum states of the scattered positron (ECC) and with binary collisions.     

“Photoelectron” spectroscopy by electron impact coincidence measurements of scattered and ejected electrons in CO

The relative intensities for ionization to the lowest three electronic states of CO⁺ have been obtained by detecting forward scattered 3.5 keV electrons in coincidence with electrons ejected at 90°. Data are reported for energy losses of the projectile electron in the range of 18–50 eV. A simple relation is derived between our data, photoelectron intensities and the angular anisotropy parameter β. This relation appears to be fulfilled satisfactorily for a (photon) energy of 21.2 eV, for which photoelectron intensities and β are available.     

ELECTRON MOMENTUM SPECTRA OF EXCITED He(2~1S) AND He(2~3S)

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Energy distributions of ions produced by electron-stimulated desorption

We have measured the initial kinetic energy distributions of ions produced by electron bombardment of various oxides and halides. The instrument used allows ions directly ejected from the sample surface to be distinguished from ions formed by electron impact in the gas phase. Singly and multiply charged positive ions of species present in the matrix as anions and cations were desorbed by high energy ( 11 keV) electron impact. Directly desorbed positive halogen ions show a narrow, low energy peak, consistent with conventional models of electron stimulated desorption (ESD). In addition, some of the cation species exhibited similar narrow energy spectra. Charge states up to +6 were observed for the halides; with the exception of F²⁺ and Cl²⁺, multiple charge states were due to electron impact ionization of desorbed neutrals. Charge states up to +4 were seen for silicon from electron-bombarded SiO₂; energy distributions of Si⁺, Si²⁺ and Si³⁺ showed that these species were desorbed directly from the surface. The energy distributions of O⁺ and O²⁺ ions ejected from SiO₂ are relatively wide, compared to the energy distribution of Si⁺ ions. In contrast, O⁺ ions ejected from TiO₂ have a much narrower energy distribution, like those observed for the halogen ions.     

Measurement of the energy dependences of the photoelectron angular distribution parameters for Ar 3p and Kr 4p electrons using an electron-electron coincidence experiment

The energy dependence of the photoelectron angular distribution parameter (β) has been measured for Ar 3p and Kr 4p electrons in the energy ranges 4–54 eV and 4–40 eV above threshold respectively, using 3.5 keV electron impact with coincidence detection of the scattered and ejected electrons. This energy range is considerably greater than that covered in previous experiments. The data over the whole energy range are compared with the Hartree-Fock calculations of Kennedy and Manson and with those of Amusia et al., using the random phase approximation with exchange method. For Ar the calculations of Amusia et al., which take into account many-electron correlations, are shown to agree more closely with the present data. The data are also shown to be in very good agreement with earlier experimental data obtained over a more limited energy range using electron synchrotron radiation.     

脉冲激光烧蚀碲镉汞材料的等离子体发射谱

脉冲激光辐照处于不同背景气压下的Hg0.8Cd0.2Te材料表面,用时间和空间分辨诊断技术探测了激光照射后产生的等离子体发射谱,根据所获得的飞行时间谱测量了等离子体中粒子的出射速度,结果表明粒子速度随着出射距离的增加迅速减小,且背景气压对出射速度有很大的影响,而激光能量对粒子速度的影响不大。另外根据谱线的展宽计算了等离子体中的电子密度,结果表明,电子密度在激光辐照样品后的短时间内迅速减小,且电子密度最大的位置不是出现在靶的表面而是在距表面一定距离处。     

The threshold electron impact spectrum of H2O

The threshold electron spectrum of H2 O was obtained using a high resolution electron impact spectrometer combined with the penetrating field method for scattered electrons with energies close to zero eV. The valence, triplet Rydberg states, as well as the resonances were identified and are discussed in the energy region 5.2–14.3 eV. The threshold spectrum confirms the influence of resonances on the enhancement of the intensity of some Rydberg states above 10 eV. The vibrational spacing of the observed transitions of the Rydberg states indicates that the water molecule is excited in the symmetric stretching mode.     

Differential cross sections for ionization of laser-aligned atoms by electron impact

The first experimental data are given for (e,2e) ionization from laser-aligned atoms. A linearly polarized laser excited Mg atoms to the 31P? state prior to ionization by low energy electrons. The scattered and ejected electrons were detected in coincidence and the differential cross section determined for a range of alignment angles. An asymmetric coplanar geometry was used, with one electron fixed and the other detected at different angles. The data are compared to that from the spherically symmetric 31S? state. Significant differences are found, in both magnitude and angular distribution.     

Absolute double differential ionization cross-section for electron impact: He

Summary A complete set of absolute double differential cross-section (DDCS) for electron impact ionization of helium has been measured at an incident energyE ₀=500 eV. The angular distributions of the ejected and scattered electrons between 40 and 435.5 eV have been measured over the angular range of (10÷145)^o. This work supplements the mapping of DDCS for ejected electron energies close to (E ₀−IP)/2 (IP is the He 1s ionization energy), a region where the experimental data are fragmentary. The possibility of representing the full Bethe surface with a simple functional form is investigated. To speed up publication, the authors of this paper have agreed to not receive the proofs for correction.     

Carbon K-shell excitation in acetone by 2.5 keV electron impact

The energy loss spectrum of 2.5 keV electrons, scattered by gaseous acetone through small angles, has been obtained in the region of the carbon K-edges. Discrete structure observed below the ionization threshold is interpreted as arising from the promotion of a carbon K-shell electron to Rydberg orbitals. Broad peaks observed above the K-edges are associated with the simultaneous transitions of a carbon K-shell and valence shell electrons (shake-up and shake-off processes).     

Quasi-binary incident electron—centre of mass collision in (e, 3e) process on He and He-like ions

We present in this communication the results of our first Born calculation in the three-Coulomb (3C) wave approach for the (e, 3e) process on He and He-like ions at an incident electron energy 5599 eV in the coplanar constant θ12 as well as out-of-plane constant φ12 modes. These two geometrical modes are such that the quasi-binary collision between the incident electron and centre of mass of the ejected electrons is in the scattering plane. The theoretical formalism has been developed using plane waves, Le Sech wave function and approximated BBK-type wave function respectively for the incident and scattered, bound and ejected electrons to calculate five-fold differential crosssection (FDCS) of the (e, 3e) process. We emphasize on the similarities and dissimilarities (asymmetries) in the angular profile of the FDCS in two modes as well as the effects of post-collision interaction (between the ejected electrons) and nuclear chargeZ on the angular profile of the FDCS. We observe that with the increment of nuclear charge the two quasi-binary collisions approach towards identical behaviour at larger mutual angles and thus bringing less asymmetry in FDCS for higherZ target.     

低能He~(2+)与He原子碰撞转移电离出射电子能谱研究

利用反应显微成像谱仪对70和100keV He2+与He原子碰撞转移电离(TI)过程中不同出射角度的电子能谱进行了测量,观测到出射电子能谱具有如下分布特征:出射电子速度分布介于0和入射离子速度vp之间;在不同出射角度电子能谱分布均有一极大值存在,随着出射角度的增大,能谱分布极大值逐渐减小;当电子出射角度等于45°时,多数电子集中在0eV附近。上述特征可由低能离子-原子碰撞"准分子"模型进行定性解释。在100keV He2+-He转移电离出射电子能谱中有靶电子被俘获至散射离子连续态(electron capture to continuum,简称ECC)电子的贡献,这可看做是动力学两步过程的作用。     

Calculation by plane wave Born approximations of electron-impact ionization of silver and copper

The plane wave Born approximation is used to calculate total electron impact ionization cross section of silver and copper. Wavefunctions of the target and residual ions were modeled by non orthogonal Hartree-Fock and Dirac-Fock orbitals. The wave functions of the atom and residual ion are calculated with allowance for relaxation effects. The one-electron wavefunction of the continuous spectrum for the ejected electron is obtained using single-configuration Hartree-Fock and Dirac-Fock method. The orthogonalization of the ejected electron wave functions to all occupied orbitals of the target atom is performed. Results of calculations are compared to available experimental measurements and theoretical calculations performed by non relativistic one-electron PWBA, where the ejected electrons is modeled by the hydrogenic Coulomb wave function.     

低能电子入射电离He原子二重微分截面的理论研究

研究了低能电子入射单电离He原子的二重微分截面(DDCS)，通过对散射电子三重微分截面在全空间的角度积分得到敲出电子的DDCS.分别用DS3C模型和BBK模型计算了入射能为26.3，28.3，30.3，32.5，34.3，36.5和40.7eV时，低能电子入射电离He原子的DDCS；研究表明：DS3C的计算结果，除在低入射能(比如26.3eV)和小敲出角之外，均能与绝对测量的实验结果较好地符合.此外，对直接和交换效应也进行了研究，给出了交换效应对截面的贡献.     

Application of a scanning electron microscope in simulating a beta-emission-induced current

The current induced by emission from a thin ⁶³Ni layer is simulated with allowance for the real spectrum of ejected electrons and their angular distribution in Si and GaN. The calculated results are compared with simulation data obtained for a monoenergetic electron beam perpendicular to the semiconductor detector. For both Si and GaN, the ratio between the currents induced by the SEM beam and β emission from ⁶³Ni is demonstrated to be almost completely independent of the diffusion length, if the electron-beam energy of a scanning electron microscope (SEM) is appropriately selected.