质子与乙烯分子碰撞的密度泛函理论研究(英文)

采用含时局域密度近似与分子动力学相结合的方法研究了不同入射速度的质子与乙烯分子碰撞的动力学。计算了质子的能量损失及碰撞后乙烯分子的电子和离子的运动状态, 研究了质子的入射方向及入射动能对整个系统的碰撞动力学的影响。计算结果表明, 当入射质子的动能较小（E_k0<250 eV）时, 在相同的入射速度下, 当质子垂直于分子平面入射时, 系统的电离最大, 质子俘获的电子多; 当质子的入射动能E_k0>250 eV时, 质子的能量损失与入射方向有密切的关系。In the framework of the time dependent local density approximation (TDLDA),which applied to valence electrons, coupled non adiabatically to molecular dynamics of ions, the microscopic mechanisms of collisions between energetic protons and ethylene are studied. Not only the amount of energy lost of the projectile, but also the electron and vibration excitations of the target are identified. In addition, the influences of the collision orientation on the energy loss of the proton and excitation dynamics of ethylene are discussed. It is found that the ionization is enhanced and more electrons are captured by the proton when the proton with the impact energy less than 250 eV moves perpendicularly to the molecular plane. A strong relation between the proton energy lost and the impact orientation is obtained when the impact energy is larger than 250 eV.     

Electronic stopping power calculation method for molecular dynamics simulations using local Firsov and free electron-gas models

Molecular dynamics simulations have proven to be accurate in predicting depth distributions of low-energy ions implanted in materials. Free parameters adjusted for every ion-target combination are conventionally used to obtain depth profiles in accordance with the experimental ones. We have previously developed a model for predicting depth profiles in crystalline Si without free parameters. The electronic stopping power was calculated using local total electron density. The model underestimated the stopping in the ?1 1 0? channeling direction. We have now taken a new approach to calculate the electronic stopping power. We use the local valence (3p²) electron density to account for the electronic energy loss between collisions and the Firsov model to account for the electronic energy loss during collision. The lowest electron densities are adjusted with a parametrization that is same for all ions in all implanting directions to correct the problems in the ?1 1 0? channeling direction.     

Giant Barkas effect observed for light ions channeling in Si

Measurements of the electronic energy loss are presented for (4)He and (7)Li ions channeling along the Si main axial directions at intermediate to high projectile energies. The Barkas effect, an energy-loss enhancement proportional to the third power of the projectile charge at high energies, is clearly separated from other processes. It reaches about 50% for Li ions channeling along the Si [110] direction. The observed Barkas contribution from the valence-electron gas is in fair agreement with the Lindhard model.     

4He+在Al和Si单晶晶面沟道中的半波长及阻止本领

采用高分辨探测系统,在不同的入射角θ_in和出射角θ_out的条件下,测量了1—2MeV⁴He⁺入射在Al(100)面和Si(110),(100)面中的背散射能谱。得到了背散射能谱振荡峰的间距ΔE与cosθ_in/cosθ_out的直线关系,从而获得了1—2MeV⁴He⁺在这三个晶面中的振荡半波长及阻止本领。实验得到的半波长与理论计算值在误差范围内一致,晶面沟道方向的阻止本领略大于随机方向的阻止本领。 关键词：     

Angular and energy dependences of the surface excitation parameter for electrons crossing a solid surface

When fast electrons cross a solid surface, surface plasmons may be generated. Surface plasmon excitations induced by electrons moving in the vacuum are generally characterized by the surface excitation parameter. This parameter was calculated for 200-1000 eV electrons crossing the surfaces of Au, Cu, Ag, Fe, Si, Ni, Pd, MgO and SiO₂ with various crossing angles. Such calculations were performed based on the dielectric response theory for both incident (from vacuum to solid) and escaping (from solid to vacuum) electrons. Calculated results showed that the surface excitation parameter increased with crossing angle but decreased with electron energy. This was due to the longer time for electron-surface interaction by glancing incident or escaping electrons and by slow moving electrons. The results were fitted very well to a simple formula, i.e. , where P_s is the surface excitation parameter, E is the electron energy, α is the angle between the electron trajectory and the surface normal, and a, b and c are material dependent constants.     

CCD电子辐照效应三维蒙特卡罗模拟研究

CCD易受空间环境中高能电子辐射的影响,造成性能下降和工作异常,针对此问题,选取某国产N沟道3相多晶硅交迭栅、帧转移结构CCD开展了电子辐照效应研究。采用三维蒙特卡罗软件FLUKA建立电子辐照CCD的组成材料Si和SiO₂模型,仿真模拟电子和材料相互作用的物理过程,计算不同能量电子在Si和SiO₂中的总质量阻止本领和射程,与文献理论计算结果对比验证了本文仿真方法的正确性。建立CCD像元阵列的三维模型,模拟计算不同能量电子在CCD中能量沉积过程的影响,以及像元间有无边界对电子在CCD像元中平均原子离位（DPA）的影响,分析了辐照损伤差异产生的机理。结果表明,靠近入射点的像元能量沉积最大处对应的入射电子能量较小;对于无边界像元,电子辐照产生的DPA随入射深度的增加先增加后减小,而在有边界像元中产生的DPA随入射深度的增加先减小后增加,并且随入射深度的增加无边界像元中产生的DPA与有边界像元中产生的DPA差值越来越小。     

The experimental determination of the impact parameter dependence of inelastic energy loss of channeled ions

Using the channeling technique, the impact parameter dependence of inelastic energy loss of fast He and N ions in Si has been measured.     

Electron inelastic mean free paths and energy losses in solids: I. Aluminum metal

Inelastic mean free paths and energy losses in aluminum metal are calculated for electrons with energies from a few eV to 10⁴ eV above the Fermi level. We have represented the contribution from excitations of the valence electrons by using an electron gas model. The effect of damping in the electron gas on the mean free path and energy loss is included within the context of the Mermin-Kliewer-Fuchs model of the electron gas dielectric function. The influence of core polarizability and local field corrections are discussed briefly. The contributions to the mean free path and energy loss of electrons from ionization of inner shells have been evaluated from atomic models. Comparisons are made with experimental data taken over a wide range of energies.     

Features of the formation of radiation spectra at (111) planar channeling of relativistic electrons in a Si crystal

The spectral intensity of (111) channeling radiation from electrons is numerically calculated at the energy varying from 100 to 900 MeV and different electron incidence angles relative to the (111) planes in thin Si crystals. The calculation results show that the channeling radiation’s spectra have a more complicated structure, and the total channeling radiation’s yield is several times larger than that at (100) or (110) channeling.     

电子束放射照相的特性与参数优化

短脉冲强激光产生的电子束具有源尺寸小、脉宽窄、准单能谱等特点, 在放射照相诊断中具有独特作用. 本文通过分析电子在材料中散射并采用蒙特卡罗方法数值模拟, 研究了100 keV到几百MeV能量电子束对有厚度起伏或存在界面的靶的透视, 并与质子、X射线束透视结果比较, 给出了电子束放射照相的特性与参数优化: 基于电子在材料中非弹性散射或能量损失, 选用能量使其射程与靶厚度接近的电子束来诊断靶厚度不均匀性; 基于电子在材料中的弹性散射, 选用射程超过靶厚度的电子束来诊断靶界面.     

He原子价壳层跃迁的电子碰撞研究

在入射电子能量 2 5 0 0eV下测量了He的 11S→ 2 1S ,2 1P ,31S和 31P的微分散射截面和广义振子强度 ,并与前人的实验和理论结果进行了比较 ,认为在此入射电子能量下一阶Born近似对此 4个跃迁成立. With electron impact energy of 2 500 eV and energy resolution of 85 meV, the differential cross sections and the generalized oscillator strengths of the excitations of 1 1S→2 1S, 2 1P, 3 1S and 3 1P of helium has been measured by electron energy loss spectroscopy . Comparing with previous experimental and theoretical results, it seems that the first Born approximation is valid for these excitations under such an electron impact energy.     

Structures near the L2,3 core edges of clean and: Oxygen covered Si(111) studied with low-energy electrons

The L_2,3 core excitation spectra of clean and oxygen covered surfaces of Si(111), measured in low-energy electron energy loss Spectroscopy reproduce previous results obtained with highenergy electrons or synchrotron radiation. It is inferred that among the different transition channels, the matrix elements for the dipole term dominate. Spectra on oxidized surfaces indicate that oxygen adsorption on Si(111) induces the formation of SiO₄ structural units.     

Fusion burning waves in degenerate plasmas

The outcome of fusion burning waves in non-degenerate plasmas is limited by the strength of ion–electron Coulomb collisions and subsequent energy loss mechanisms as electron heat conduction and radiation emission. In this Letter, an analysis is presented on the degeneracy effects in the stopping power of suprathermal charged particles and in the energy transmitted from ions to electrons by Coulomb collision. Main results of this analysis is that very powerful fusion burning waves can be launched into previously compressed degenerate plasmas. This can be specially suitable for proton–boron fusion, but it also applicable to any type of fusion reaction, where ignition can be triggered by an incoming ion beam or another external source of energy deposited in a small fraction of the compressed plasma (fast ignition).     

质子照相中基于能量损失的密度重建

提出了一种质子能量在中高能时利用能量损失进行密度重建的方法,并利用Bethe-Bolch公式给出了利用能量损失进行密度重建的方程及条件.针对1.6 GeV的质子能量,通过定量计算常见材料的阻止本领,得出质子能量在1.45–1.6 GeV范围内时,材料的阻止本领的变化率小于1%,可近似为常数.最后,通过理论计算和Geant 4模拟,得出质子能量在1.6 GeV时,可以对面密度为113 g/cm²的缩比法国实验客体进行密度重建.     

Stopping of heavy ions in plasmas at strong coupling

Standard approaches to the energy loss of ions in plasmas like the dielectric linear response or the binary collision model are strictly valid only in the regimes where the plasma is close to ideal and the coupling between projectile-ion and the plasma target is sufficiently weak. In this review we explore the stopping power in regimes where these conditions are not met. Actually relevant fields of application are heavy ion driven inertial fusion and the cooling of beams of charged particles by electrons. The conventional linear mean-field treatments are extended by many-body methods and particle simulations to account for strong correlations between the particles and for nonlinear coupling. We report the following important results in connection with the stopping at strong coupling: The energy loss of an ion scales with its charge approximately like Z^1.5, the effective screening length depends on Z and is larger than the Debye length. Slow highly charged ions are surrounded by a cloud of electrons trapped by many body collisions. Quantum effects like the wave nature of the electrons and Pauli-blocking reduce the stopping power by mollifying the effective interactions.     

On the Kinetics of the Active Zone of the Stationary SF6 Beam Discharge Plasma

The paper deals with the impact of intensive electron attachment on the kinetics of the electrons in the active zone of the stationary band-like beam discharge plasma in SF₆ which is an alternative useful plasma medium for “dry etching”. The energy distribution of the electrons in this plasma was obtained by numerically solving the Boltzmann equation which includes apart from elastic collisions, different exciting collision processes, attachment in electron collisions, direct ionization, the ambipolar loss of electrons, Coulomb interaction between electrons and of electrons with ions and the power input to the electrons by the turbulent electric field. In particular, due to the needed fulfilment of the consistent electron particle balance, for an extended region of the turbulence energy density in this plasma a large impact on the electron kinetics of the intensive electron attachment, which is the prevailing electron loss process, was found enforcing independent of the turbulence energy density always a large power input to the electrons, smooth and only slowly decreasing energy distributions even in the energy region of direct ionization.     

15eV的质子与羟基碰撞的动力学

采用含时密度泛函理论和分子动力学非绝热自洽耦合的方法,全微观研究沿垂直羟基分子轴向入射初动能为15 eV的质子与羟基碰撞过程的电子-离子关联动力学.计算质子和羟基动能、碰撞后羟基电子和离子的运动状态及系统电子密度的实时分布.结果表明:质子与羟基碰撞后俘获羟基的一部分电子被反弹并损失26.7%的初始动能而羟基动能增加.碰撞后丢失1%电子的羟基在保持碰撞前收缩振动的同时向计算边界平动并以93%的中性和7%的+1价的几率存在.     

质子辐照硼硅酸盐玻璃盖片的物理效应分析

作为航天器电源系统的重要组成部分,太阳电池需要更高的转换效率和可靠性以及更长的使用寿命。通过在太阳电池表面覆盖抗辐照玻璃盖片,可以增强太阳电池对粒子辐射的防护,延长太阳电池的服役寿命,使航天器获得可靠的能源供应。硼硅酸盐玻璃就是一种理想的太阳电池玻璃盖片材料。采用蒙特卡罗方法,结合SRIM软件模拟研究质子辐照硼硅酸盐玻璃的损伤物理机理。基于粒子与物质相互作用的理论以及基本公式,通过分析不同入射能量的质子在硼硅酸盐玻璃中的阻止本领、电离能损、位移能损、空位的产生情况,对辐照损伤的物理机制进行研究。结果表明：能量为30～120 keV的质子辐照损伤主要发生在硼硅酸盐玻璃表面;质子沉积、空位分布等均为Bragg峰型分布;电离能损是能量损失的主要部分,随入射能量的增加而增大,导致电子的电离和激发;位移能损在玻璃内部随能量降低而增大,导致硼、氧和硅等空位缺陷的产生;电离效应和缺陷的产生是硼硅酸盐玻璃色心形成的重要原因。     

Effect of surface excitations on the reflection electron energy loss spectrum in silicon

The results of investigating the relative contribution of surface excitations to the reflection electron energy loss spectrum in pure silicon are presented. The primary electron energy is in the range 60–1000eV. Good agreement is obtained between the experimental values of the surface parameter P _S and theoretical calculations. The relative contribution of surface excitations is also determined by decomposing the integral reflection electron energy loss spectra into Gaussian curves.