稀有气体原子在纳米碳管中的周期性振荡

采用TLHT势和经典分子动力学方法研究了稀有气体原子进入单壁纳米碳管(SWCNT)的动力学过程，计算得出SWCNT能吸入稀有气体原子(He，Ne，Ar，Kr，Xe)的管径阈值r₀分别为6.3 ?，7.0 ?，8.6 ?，8.6 ?，8.6 ?，同时计算了对应的每种稀有气体原子能封装在不同管径的SWCNT中的最大初始动能E_k0.计算给出有趣的结果是封装在纳米碳管中的稀有气体原子在管中不停地作周期性振荡，振荡周期与原子进入管中的能量无关，振幅与原子进入管中的能量有关，即振幅随着入射能量的增加而增加.分析表明：给定合适类型的碳管，具有很小初始动能的稀有气体原子可在碳管中稳定的周期性振荡，其振荡频率可达GHz.     

分子动力学模拟尺寸对纳米Cu颗粒等温晶化过程的影响

采用分子动力学方法和镶嵌原子势, 模拟了4000个Cu原子和13500个Cu原子(简称Cu₄₀₀₀和Cu₁₃₅₀₀)组成的纳米颗粒以及块体Cu的等温晶化过程. 通过对这些颗粒在晶化过程中结构和动力学行为的分析研究, 发现低温时, 不同尺寸的纳米Cu颗粒均出现多步晶化, 且晶化时间的分布曲线远比高温时范围大; 除了温度, 颗粒尺寸对晶化行为也有重要的影响, 尺寸越大, 晶化时间越长, 最终的晶化程度越高; 但是晶化时间随尺寸增大而增加的趋势不会一直持续, 发现存在一个临界尺寸r_c, 小于r_c时, 晶化时间随颗粒尺寸增大而增加, 大于r_c时,晶化时间随尺寸增大而减小.     

X@C20F20(X=He,Ne,Ar,Kr)几何结构和 电子结构的理论研究

采用密度泛函理论中的广义梯度近似, 对X@C₂₀F₂₀(X=He, Ne, Ar, Kr)几何结构和电子结构进行了计算研究. 几何结构优化发现: 惰性气体原子X内掺到C₂₀F₂₀笼后, 均稳定于碳笼中心, 随着内掺X原子序数的增大, X原子对C₂₀F₂₀笼的影响越来越大. 能隙、内掺能和振动频率计算表明: 内掺X原子使得C₂₀F₂₀的稳定性得到了显著提升, X@C₂₀F₂₀(X=He, Ne, Ar, Kr)都具有良好的稳定性, 并且随着X原子序数的增大, 其稳定性也基本呈现逐渐增强的趋势. 电子结构研究发现: X原子对X@C₂₀F₂₀费米能级附近的占据轨道基本没有贡献, 而对其未占据轨道贡献较大. 计算还发现: 在X@C₂₀F₂₀中, He 和Kr分别从C₂₀F₂₀的C 笼上获得了0.126和0.271个电子, 而Ne和Ar却分别向C笼转移了0.060和0.012个电子. 由此可见: X原子与C原子之间都发生了电荷转移, C笼上的C原子与惰性气体原子X间形成了一定的离子键.     

TiO2/ZnO纳米薄膜界面热导率的分子动力学模拟

采用平衡分子动力学方法及Buckingham势研究了金红石型TiO₂薄膜与闪锌矿型ZnO薄膜构筑的纳米薄膜界面沿晶面[0001](z轴方向)的热导率.通过优化分子模拟初始条件中的截断半径r_c和时间步后,计算并分析了平衡温度、薄膜厚度、薄膜截面大小对热导率的影响.研究表明,薄膜热导率受薄膜温度和厚度的影响很大,当温度由300 K升高600 K时,薄膜的热导率逐渐减小;当薄膜厚度由1.8 nm增大到5 nm时,热导率会逐渐增大;并在此基础 关键词： 热导率 分子动力学 2/ZnO纳米薄膜界面')" href="#">TiO₂/ZnO纳米薄膜界面 数值模拟     

电荷剥离截面的计算

采用二体碰撞近似(BEA)和托马斯费密近似(TFA),计算了多电荷离子(3Li2+,6C5+,10Ne+,18Ar+,36Kr+,54Xe+)的势函数分布和电子动量分布,以及它与中性原子H和He碰撞的电荷剥离截面. 关键词：     

离子束辅助沉积对类金刚石膜结构影响的计算机模拟

采用分子动力学(MD)模拟研究了离子束辅助沉积(1BAD)生长类金刚石(DLC)膜的物理过程.分 别选C₂分子和Ar离子作为沉积源和辅助沉积粒子.改变Ar的入射能量和到达比(A r／C)，研 究了它对DLC膜结构的影响.重点讨论了Ar辅助沉积引起表面原子的瞬间活性变化对薄膜结构 产生的影响.分析表明，由于Ar离子的轰击引起的能量和动量的传递，大大地增强了C原子在 表面的反冲动能及迁移概率，增加了合成薄膜的SP³键含量.研究结果和实验 观察一致，并从合成机理上给出了一些定量解释. 关键词： 类金刚石膜 离子束辅助沉积 分子动力学模拟     

基于HIRFL-CSR的高速高电荷态重离子与原子碰撞X射线谱学实验设计与研究

依据非相对论偶极近似、相对论程函近似、ECPSSR理论及平面波玻恩近似方法,计算了30～500 MeV/u的Ar18+、Kr36+和Xe54+离子与Ar、Kr和Xe原子碰撞过程中辐射电子俘获、非辐射电子俘获及内壳电离截面.在此基础上,结合光子探测器的能量分辨以及炮弹离子跃迁谱线的多普勒效应等因素,针对HIRFL-CSR...     

单、双原子空位缺陷对扶手椅型单层碳纳米管屈曲性能的不同影响

采用分子动力学方法,对完善和含缺陷扶手椅型单层碳纳米管进行轴向压缩的数值模拟,对比研究三种不同的温度环境下单、双原子空位缺陷对碳纳米管轴压变形性能的特殊影响.研究结果表明管壁缺陷显著降低了纳米管低温时的承载能力,由于单原子空位缺陷造成的特殊应力集中效应会引发纳米管过早发生局部屈曲,单原子缺陷管的屈曲强度反而小于双原子管的屈曲强度. 关键词： 分子动力学 碳纳米管 屈曲 缺陷     

BaTiO3铁电体中辐射位移效应的分子动力学模拟

运用基于壳模型的分子动力学方法研究了BaTiO₃铁电体中的辐射位移效应.采用O原子作为初级击出原子,模拟了当初级击出原子能量为1 keV时体系内缺陷的产生和演化.模拟结果表明,当入射方向为[001]时,体系内产生的缺陷最多.在所有缺陷中,以O缺陷的含量为最高,达80%以上.同时,这些缺陷的产生并不显著改变体系的自发极化强度,对体系的极化翻转过程也基本没有影响.在外电场作用下,观察到了显著的缺陷迁移. 关键词： 分子动力学 3铁电体')" href="#">BaTiO₃铁电体 辐射位移效应     

氦原子注入缺陷性纳米碳管的机理

采用经典分子动力学方法和TLHT势模型,研究了He注入不同管壁缺陷的单壁纳米碳管（SWNCT）的动力学过程,发现对应不同入射能量,He有4种典型的运动模式。管壁缺陷的尺寸对He在SWNCT中的吸附存储行为有很大影响。 Based on the classical molecular processes of He atom into SWCNT with wall dynamics method and TLHT potential model, the injection defects of different radius are studied. The calculated results indicate that there are four typical moving patterns of He atom with different injective energy and the size of wall defects make a great difference to the absorption and storage behavior of He into SWNT.     

The dynamics simulation of Ne atom injected into single-wall carbon nanotube

The dynamical processes of Ne atom injected into single-wall carbon nanotube (SWCNT) are modeled with molecular dynamics simulations. The threshold energies to encapsulate rare-gas atoms in SWCNT are presented. The range of tube radius for stable oscillation is revealed, which is independent of the type of carbon nanotubes. And the oscillatory frequency is sensitive to the change in the diameter, the length and chirality of the tube.     

Elastic properties of compressed rare-gas crystals in a model of deformable atoms

Physics of the Solid State - The elastic properties of compressed Ne, Ar, Kr, and Xe rare-gas crystals were studied in a model of deformable and polarizable atoms. The second-order Fuchs elasticity...     

Elastic properties of heavy rare-gas crystals under pressure in the model of deformable atoms

The quantum-mechanical model of deformable and polarizable atoms has been developed for the purpose of investigating the elastic properties of crystals of rare gases Kr and Xe over a wide range of pressures. The inclusion of the deformable electron shells in the analysis is particularly important for the shear moduli of heavy rare-gas crystals. It has been shown that the observed deviation from the Cauchy relation δ(p) for Kr and Xe cannot be adequately reproduced when considering only the many-body interaction. The individual dependence δ(p) for each of the rare-gas crystals is the result of two competitive interactions, namely, the many-body and electron-phonon interactions, which manifests itself in a quadrupole deformation of the electron shells of the atoms due to displacements of the nuclei. The contributions of these interactions in Kr and Xe are compensated with good accuracy, which provides a weakly pressure-dependent value for the parameter δ. The ab initio calculated dependences δ(p) for the entire series Ne-Xe are in good agreement with the experiment.     

Formation and migration properties of the rare gases He,Ne, Ar,Kr, and Xe in nickel

The energies of formation and migration of various rare gas-point defect complexes in an f.c.c. nickel lattice have been calculated for He, Ne, Ar, Kr, and Xe. Formation energies of rare gas atoms at interstitial sites are compared with those in substitutional sites. Binding energies are presented for self-interstitials and vacancies trapped to the various rare gas substitutionals. We also present migration energies and migration paths for various rare gas interstitials and substitutionals with and without trapped vacancies and self-interstitials. The migration energies are compared with the breakup energies for the corresponding complexes. We find that divacancy-rare gas complexes are rather stable and will migrate at relatively low energies compared to other substitutional rare gas migration processes.     

Electronic and geometric structure of doped rare-gas clusters: surface, site and size effects studied with luminescence spectroscopy

The electronic and geometric structure of rare gas clusters doped with rare-gas atoms Rg = Xe, Kr or Ar is investigated with fluorescence excitation spectroscopy in the VUV spectral range. Several absorption bands are observed in the region of the first electronic excitations of the impurity atoms, which are related to the lowest spin-orbit split atomic ³P₁ and ¹P₁ states. Due to influence of surrounding atoms of the cluster, the atomic lines are shifted to the blue and broadened (“electronical cage effect”). From the known interaction potentials and the measured spectral shifts the coordination of the impurity atom in Ar_N, Kr_N, Ne_N and He_N could be studied in great detail. In the interior of Kr_N and Ar_N the Xe atoms are located in substitutional sites with 12 nearest neighbours and internuclear distances comparable to that of the host matrix. In Ne_N and He_N the cluster atoms (18 and 22, respectively) arrange themselves around the Xe impurity with a bondlength comparable to that of the heteronuclear dimer. The results confirm that He clusters are liquid while Ne clusters are solid for N≥ 300. Smaller Ne clusters exhibit a liquid like behaviour. When doping is strong, small Rg_m-clusters (Rg = Xe, Kr, Ar, m≤10 ²) are formed in the interior sites of the host cluster made of Ne or He. Specific electronically excited states, assigned to interface excitons are observed. Their absorption bands appear and shift towards lower energy when the cluster size m increases, according to the Frenkel exciton model. The characteristic bulk excitons appear in the spectra, only when the cluster radius exceeds the penetration depth of the interface exciton, which can be considerably larger than that in free Rg_m clusters. This effect is sensitive to electron affinities of the guest and the host cluster.     

Die Anregung des Tochterions Rb+ durch die plötzliche Kernladungsänderung von85Kr,eingebaut in feste Edelgase

By the sudden change of nuclear charge the daughter-ion is excited with a propability of some percent (monopole-excitation). When⁸⁵Kr is trapped in various solids of rare gases, the daughter-ion Rb⁺ acts as a probe: The spectra of emitted photons contain information about the influence of the surrounding solid on the levels of the excited Rb⁺. These spectra have been observed in delayed coincidence with the nuclear process (β-decay); direct excitation by charged particles is excluded. The results are closely connected to the behaviour of the decaying atom in free state and solid krypton: There are narrow bands (the daughter-ion occupies a regular lattice site) and blue-shifted (Δ v) broad bands (emission from daughter-ion displaced to interstitial sites by recoil).Δ v is different in the various solids of rare gases and increases from Ar to Xe; this is due to the various polarizabilities and lattice constants. A theoretical estimate fits well the experimental values. Besides, the experimental results show that the excitation-probability for⁸⁵Kr in Kr is greater than for⁸⁵Kr in Ar or Xe, which also agrees with theoretical estimates. Furthermore, information about the displacement energies of the Rb⁺ in the various solids of rare gases are gained from the ratio of intensities of the narrow bands to that of the broad bands, which are compared to displacement energies gained from rare-gas pair potentials.     

Plasma line emission during single-bubble cavitation

Emission lines from transitions between high-energy states of noble-gas atoms (Ne, Ar, Kr, and Xe) and ions (Ar(+), Kr(+), and Xe(+)) formed and excited during single-bubble cavitation in sulfuric acid are reported. The excited states responsible for these emission lines range 8.3 eV (for Xe) to 37.1 eV (for Ar(+)) above the respective ground states. Observation of emission lines allows for identification of intracavity species responsible for light emission; the populated energy levels indicate the plasma generated during cavitation is comprised of highly energetic particles.     

Periodic structures in the Franck-Hertz experiment with neon: Boltzmann equation and Monte-Carlo analysis

A new experimental technique for the measurements of the total cross section for electron scattering from atoms and molecules at very low energy is described. Momentum transfer cross sections for scattering from Ar, Kr and Xe at very low energies were carefully derived using the modified effective range theory from the recently measured total cross sections, which were obtained with a new experimental technique utilizing the threshold photoelectron source. A significant discrepancy between the momentum cross sections derived from the present analysis and those determined in the previous electron swarm studies was found at energies below 100 meV. The findings emphasize the need of further high precision experiments in the very low energy region as well as re-analysis of the previous swarm data.