泰克频谱仪IQT文件的后台处理及在电子冷却实验中的应用

泰克实时频谱仪存储的IQT格式数据文件的特殊结构给后期实验数据处理带来不便。分析了IQT文件的存储结构,说明了泰克实时频谱仪的IQT格式数据文件的后台处理过程,通过数学方法提高了文件中频变弱信号的强度;通过对频谱仪实验数据进行数学处理,得到了兰州重离子加速器冷却储存环36Ar18+离子束的纵向电子冷却力大小随离子-电子相对速度的变化曲线。该处理方法弥补了频谱仪离线分析软件的局限性。     

Imaging and spectroscopy of defects in semiconductors using aberration-corrected STEM

The distribution of single dopant or impurity atoms can dramatically alter the properties of semiconductor materials. The sensitivity to detect and localize such single atoms has been greatly improved by the development of aberration correctors for scanning transmission electron microscopes. Today, electron probes with diameters well below 1 Å are available thanks to the improved electron optics. Simultaneous acquisition of image signals and electron energy-loss spectroscopy data provides means of characterization of defect structures in semiconductors with unprecedented detail. In addition to an improvement of the lateral spatial resolution, depth sensitivity is greatly enhanced because of the availability of larger probe forming angles. We report the characterization of an alternate gate dielectric interface structure. Isolated Hf atoms are directly imaged within a SiO₂ thin film formed between an HfO₂ layer and the silicon substrate. Electron energy-loss spectroscopy shows significant changes of the silicon valence state across the interface structure.     

钎锌矿相GaN电子高场输运特性的Monte Carlo 模拟研究

应用全带多粒子Monte Carlo模拟方法,研究了钎锌矿相GaN 材料电子的高场输运特性. 模拟中利用了基于第一性原理总能量赝势方法计算得到的纤锌矿GaN的能带结构数据. 用Cartier的方法,计算碰撞电离散射率. 计算得到了电子平均漂移速度和电子平均能量与电场的关系曲线. 电离系数的分析表明当电场强度大于1 MV/cm时,才会有明显的碰撞电离发生,量子产额的分析表明当电子的能量大于7 eV时,量子产额随能量增加迅速增大. 研究了在0—4 MV/cm电场强度范围内电子在各导带的分布,低场下电子全部位于 关键词： 碰撞电离 高场输运 能带结构 Monte Carlo模拟     

Electron density and electron redistribution in alloys—I: Electron density in elemental metals

The changes in electronic structure around each metal atom in an alloy are more accurately described in terms of electron redistribution than electron transfer. The important elements in a model for such electron redistribution are the electron configuration and radius of the positive ion cores and the conduction electron density and its variation in the interstitial regions. Positive ion core radii for metals are derived from an empirical relation between ion core radii and intermetallic distance with electronic configurations of the core from positron annihilation data. These derived ion core radii are in good agreement with those calculated for metal electron densities by Welch and Lynn from Hartree-Fock wave functions. Average conduction electron densities can be directly calculated from these radii and the experimental atomic volume; the variation of conduction electron density in the interstitial region is calculated by assigning electrons to octahedral and tetrahedral interstices according to the Interstitial Electron Model. The calculated electron densities and the interstitial variation agree very well with the experimental electron densities of Be as determined from X-ray diffraction data as well as with calculated electron densities for Na, Mg and Al. Ion core configurations are compared with those derived from band theory and also those of the Engle-Brewer Correlation and the Samsonov-Pryadkov-Pryadkov Configurational Model.     

The influence of ion irradiation on the structure and properties of amorphous carbon films

Presented in this work are the results of investigation of the structure and electrophysical properties of amorphous carbon films. The films were produced by sputtering of graphite by ion beam and usin ion irradiation (E=0–200 eV) during condensation process. The structure of i-C films has been studied by means of transmission electron microscope. The electron diffraction data have been interpretated by employing the calculated interference function of carbon clusters. The structure of V-band was obtained from AES by deconvolution method. Experimental data shows that under ion irradiation the transformation of short range order and electron bonds is an oscillating function of ion energy E. This paper presents a theoretical calculation of tunneling neutralization cross-section of Ar⁺ ions on carbon surface. The process also has an oscillating dependence on ion energy. A significant importance of inelastic processes in carbon phase transformation has been revealed.     

Methods of calculating the band structure and low-energy secondary electron spectroscopy of iridium

A theoretical interpretation is put forward for the fine structure of the secondary electron emission spectra of Ir normal to the (111) surface and the total current spectrum of an Ir polycrystal. The calculations took into account the energy dependence of the broadening of the energy band levels, the electron-electron and electron-plasmon contributions to the nonequilibrium electron distribution function, and the isotropic component of the current from the electrons scattered at the surface. It is shown that the fine structure of the secondary electron emission spectrum and the total current spectrum is mainly attributable to the electron structure of the final states into which the electrons enter or from which they are emitted so that the characteristics of the band configuration in the energy band structure can be reconstructed directly from the experimental data. This method can be used to separate bulk effects from surface effects in the secondary electron emission and total current spectra. It is confirmed that the fine structure of the secondary electron emission and total current spectra depends on the geometric structure and the degree of ordering of the crystals. A reduction in the intensity of the fine structure serves as a measure of the defect structure in the surface region of the sample which can be successfully used to monitor the surface state during treatment. Zh. Tekh. Fiz. 69, 94–96 (June 1999)     

Theory of secondary electron emission

The fine structure in angle-resolved secondary electron spectra is shown to be related to the total reflectivity in low-energy electron diffraction (LEED). Theoretical results for tungsten are compared with experimental data. For non-normal emission, spin-orbit coupling is predicted to produce spin polarization of the emitted electrons.     

Study on differential algebraic method for electron optical properties of wide electron beams in immersion electrostatic-magnetic lenses

Differential algebraic method for calculation of electron optical properties is extended to wide electron beams in combined immersion electrostatic-magnetic lenses, based on Taylor series expansion of the differential algebraic data structure of wide electron beam focusing systems. Higher order aberrations referred to off-axis central trajectories are calculated and this makes the evaluation of wide electron beam focusing properties much simplified with high-enough precision. A program was written, and a specific combined immersion electrostatic-magnetic lens is calculated as an example. Computed results show that the second aperture aberrations referred to off-axis central trajectories of the system of the primary one, whereas the third- and over third-order ones only play a secondary role.     

New data on RC radiation centers obtained from a photoluminescence study of cubic boron nitride irradiated with electrons of near-threshold energies

New data on radiation centers of the RC series are obtained by studying the photoluminescence of boron nitride cubic crystals irradiated with electrons of energies of 150 to 300 eV and annealed in vacuum at temperatures of 400 to 800°C. Changes in the fine structure of no-phonon lines from these centers were observed as the electron energy reached the “threshold” value or after annealing. These changes are likely to be associated with the response of a vacancy (which is a structural element of RC defects) to differently directed uniaxial stresses. The fine structure of the no-phonon line from the RC3 center is less sensitive to threshold effects and relaxes more easily during annealing in comparison with those from the RC1 and RC2 centers. New data are obtained on the fine structure of phonon replicas of no-phonon lines from RC centers; this structure is due to interaction of the corresponding electron transitions with lattice phonons of energies of 0.1 to 0.125 eV.     

Electronic structure of bivalent copper off-center complexes in SrF<Subscript>2</Subscript> crystals from data of EPR and ENDOR spectroscopy

The electronic structure of bivalent copper off-center complexes in SrF₂ crystals is calculated from experimental data obtained earlier by electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) spectroscopy. The electronic structure parameters characterizing the unpaired-electron density in the vicinity of the nucleus of a copper impurity ion are determined, and the parameters of covalent bonds between an impurity copper ion and three groups of the fluorine ions nearest to this impurity are calculated. It is demonstrated that states of the ground electron configuration of the bivalent copper impurity complex involve an admixture of excited electron configurations due to electron transfer from the ligand to 4s and 4p unfilled shells of the copper ion.     

What do electron and neutrino experiments tell us about nuclear effects in the deuteron?

We have performed an analysis of data from electron, neutrino and antineutrino scattering experiments on hydrogen and deuterium within the framework of the quark-parton model. The data indicate that the distortion of the structure functions of the neutrons and protons in the deuteron are small. This is in contrast with the observed distortion of the structure functions of nucleons bound in a heavy nucleus such as iron. These results support the hypothesis that the “EMC Effect” is related to the density of nucleons in a nucleus.     

Analysis of continuous generation of electron beams in medium-pressure gases

Stationary and stable open discharges are obtained in air, helium, and helium with an admixture of a few percent of air. The structure of the generator of an electron beam with a wide set of cathode and insulator materials is described. The experiments are performed under an air pressure of hundreds of pascals and under a helium pressure of thousands of pascals. The current-voltage characteristics of the discharge are measured and the results on the maximal current density attained are compared with the available data.     

Formation of plasma dust structures at atmospheric pressure

The formation of strongly coupled stable dust structures in the plasma produced by an electron beam at atmospheric pressure was detected experimentally. Analytical expressions were derived for the ionization rate of a gas by an electron beam in an axially symmetric geometry by comparing experimental data with Monte Carlo calculations. Self-consistent one-dimensional simulations of the beam plasma were performed in the diffusion drift approximation of charged plasma particle transport with electron diffusion to determine the dust particle levitation conditions. Since almost all of the applied voltage drops on the cathode layer in the Thomson glow regime of a non-self-sustained gas discharge, a distribution of the electric field that grows toward the cathode is produced in it; this field together with the gravity produces a potential well in which the dust particles levitate to form a stable disk-shaped structure. The nonideality parameters of the dust component in the formation region of a highly ordered quasi-crystalline structure calculated using computational data for the dust particle charging problem were found to be higher than the critical value after exceeding which an ensemble of particles with a Yukawa interaction should pass to the crystalline state.     

Resonant tunneling through electronic trapping states in thin MgO magnetic junctions

We report an inelastic electron tunneling spectroscopy study on MgO magnetic junctions with thin barriers (0.85-1.35 nm). Inelastic electron tunneling spectroscopy reveals resonant electronic trapping within the barrier for voltages V>0.15 V. These trapping features are associated with defects in the barrier crystalline structure, as confirmed by high-resolution transmission electron microscopy. Such defects are responsible for resonant tunneling due to energy levels that are formed in the barrier. A model was applied to determine the average location and energy level of the traps, indicating that they are mostly located in the middle of the MgO barrier, in accordance with the high-resolution transmission electron microscopy data and trap-assisted tunneling conductance theory. Evidence of the influence of trapping on the voltage dependence of tunnel magnetoresistance is shown.     

Raman scattering by electron and phonon excitations in FeSi

The temperature evolution of Raman scattering by electron and phonon excitations in FeSi is studied within the range of 10–500 K. At low temperatures, the frequency dependence for the spectra of light scattered by electrons exhibits vanishing intensity in the range up to 500–600 cm^–1, which suggests the existence of an energy gap of about 70 meV. The calculations of the electronic excitation spectra based on the band structure determined using the LDA+DMFT technique (local electron density + dynamic mean field approximation) are in good agreement with the low-temperature experimental data and confirm that FeSi is a material with intermediate electron correlations. The changes in the shape of the electronic excitation spectrum and in the self-energy of optical phonons indicate a transition to the metallic state above 100 K. The analysis of experimental data demonstrates an appreciable decrease in the electron lifetime with the growth of temperature determining the (insulator–poor metal) transition.     

S波段6 MeV边耦合电子直线加速器的设计研究（英文）北大核心CSCD

近年来,对紧凑、稳定及可靠型电子直线加速器的需求越来越多,其能量主要分布在几百keV到十几个MeV的范围内,其中需求最多的则是能量在MeV量级的微波电子直线加速器。在这种形势下,中国科学院高能物理研究所正在研制一台S波段6 MeV的边耦合电子直线加速器,本文对基于该加速器的模拟计算研究进行了介绍。EGUN和HFSS分别用来设计电子枪和边耦合加速结构。通过将EGUN计算得到的电子束流参数和HFSS计算得到的三维电磁场分布数据引入到PARMELA中,完成了对该加速器的多粒子动力学研究。模拟结果显示,所设计的加速器完全能够满足设计指标的要求。最终,在考虑束流负载效应的因素后,完成了边耦合加速结构的微波结构设计。     

含重金属硅化物SiM(M=Au,Ag,Cu)的从头算理论研究

在不同电子相关水平上基于相对论和非相对论赝势,对含重金属硅化物SiM(M=Au,Ag,Cu)的基态几何结构和光谱特性进行了研究,并讨论了电子相关效应和相对论效应的影响.结果表明:重金属硅化物SiM(M=Au,Ag,Cu)的基态电子状态是2Π.电子相关效应缩短了金属硅化物的键长,提高了分离能,谐振频率也增加,使SiM(M=Au,Ag,Cu)的结构变得更加紧凑,基态更加稳定.相对论效应加强了它的强度,使三种硅化物更加稳定.相对论作用的顺序为AuSi>AgSi>CuSi.     

Theoretical study of divalent samarium defects in lanthanum fluoride crystals

The results from a theoretical study of the electron structure of an impurity rare-earth Sm²⁺ defect in a LaF₃ crystal are presented. The electron energy levels of the rare-earth impurity defect and the transitions between them are studied using the multiconfigurational CASSCF/CASPT2 method. The absorption spectrum obtained during the calculations is consistent with the experimental data. Based on our model, we can state definitively that a vacancy on an anion sublattice serves as a charge compensator for a divalent ion.     

150 eV电子入射电离He原子三重微分截面的动量转移依赖

用BBK模型和DS3C模型在入射能150 eV对氦原子截面依赖动量转移几何条件下的三重微分散射截面(TDCS)进行了理论计算, 把计算结果与实验测量结果进行了比较, 对截面的结构进行了分析, 并对该几何条件下的交换效应进行了系统的研究.