Theoretical study of the migration of the hydrogen atom adsorbed on aluminum nanowire

We study the behavior of a hydrogen atom adsorbed on aluminum nanowire based on density functional theory. In this study, we focus on the electronic structure, potential energy surface (PES), and quantum mechanical effects on hydrogen and deuterium atoms. The activation energy of the diffusion of a hydrogen atom to the axis direction is derived as 0.19 eV from PES calculations. The probability density, which is calculated by including quantum effects, is localized on an aluminum top site in both cases of hydrogen and deuterium atoms of the ground state. In addition, some excited states are distributed between aluminum atoms on the surface of the nanowire. The energy difference between the ground state and these excited states are below 0.1 eV, which is much smaller than the activation energy of PES calculations. Thus using these excited states, hydrogen and deuterium atoms may move to the axial direction easily. We also discuss the electronic structure of the nanowire surface using quantum energy density defined by one of the authors.     

Non-statistical excitation of the magnetic substates of the 1P1 level of group II metal atoms in collision with 800 eV helium atoms

A large polarization has been observed for the emission lines of strontium and calcium excited by a beam of neutral helium atoms with 800 eV lab energy. The measured value of 15% indicates a preferential population of the magnetic substates of the correlated atom states of the target species. Depolarization of the emission in a magnetic field has been observed demonstrating the feasibility of Hanle-type lifetime measurements.     

Electron-impact excitation cross sections of gallium atom

Excitation of gallium atom in collisions with slow electrons is studied using the method of extended crossing beams with recording of the optical signal of excited atoms. At an electron energy of 30 eV, 66 excitation cross sections are measured. In the electron energy range of 0–200 eV, 24 excitation optical functions are recorded. The dependence of the cross sections on the principal quantum number of an upper level is obtained for eight spectral series of Ga I. The results obtained are compared with the data of the previous experiment.     

Untersuchungen über die Erzeugung und den Nachweis von Alkaliatomstrahlen im Energiebereich zwischen 6 und 4000 eV

An alkali metal atomic beam source for the 6–4000 eV energy range is described. The fast atomic beam is obtained by the neutralization of an alkali ion beam and is detected by surface ionization on an unheated filament. The processes involved in collisions of fast alkali atoms with a tungsten surface are investigated and the behaviour of the atoms is compared with the behaviour of the corresponding ions.     

Dissociative excitation of doublet and octet levels of the manganese atom in collisions of electrons with manganese diiodide molecules

The dissociative excitation of doublet and octet levels of the manganese atom in collisions of slow electrons with manganese diiodide molecules is studied. At the exciting electron energy of 100 eV, the excitation cross sections for 28 and 12 transitions, respectively, from doublet and octet states of manganese atom are measured. In the exciting electron energy range of 0–100 eV, six optical excitation functions are recorded. The possible channels of the formation of excited manganese atoms at low electron energies are discussed.     

Energieverluste monochromatisierter 30 keV-Lithiumionen an Argon und Äthylen

The energy loss spectra of 30-keV Li₇ ⁺ ions after interaction with argon and ethylene have been studied. Wien filters were used as monochromator and energy analyzer, an energy resolution of 0.2 eV was achieved. The ion energy loss spectra obtained differ from those taken with electrons at the same primary energy mainly in two points: In the ion spectra energy losses are found with strong intensities corresponding to optically forbidden transitions which are not excited by fast electrons. Furthermore in the energy range beyond the first ionization limit energy losses appear which are due to charge transfer into excited states of the lithium atom and re-ionization.     

Electron-impact excitation of the 3 P o and 3 D o levels of a nickel atom

The excitation cross sections of transitions from the ³ P ^o and ³ D ^o levels of a nickel atom in electron-atom collisions at an exciting-electron energy of 50 eV have been analyzed by the method of extended crossing beams with detection of the optical signal from excited atoms. Eleven optical excitation functions have been recorded in the electron-energy range of 0?C200 eV. The direct excitation cross sections of the energy levels and the contribution of the cascade transitions were calculated using the data obtained.     

高通量中性原子氧束流的发生与控制

 采用微波同轴耦合氧气放电产生高密度氧等离子体, 经磁场约束后与一施加负偏压的金属板碰撞复合并反射, 得到通量在10¹³~10¹⁶atom/cm²×s范围可控, 动能约为6-10eV的中性氧原子束流。用双探针技术对生成的氧等离子体进行了诊断测量。根据聚酰亚胺在原子氧作用下的剥蚀率对原子氧束流进行了标定测量。     

Electronic and magnetic properties of copper-family-element atom adsorbed graphene nanoribbons with zigzag edges

We have investigated the electronic and magnetic properties of copper-family-element (CFE) atom adsorbed graphene nanoribbons (GNRs) with zigzag edges using first-principles calculations based on density functional theory. We found that CFE atoms energetically prefer to be adsorbed at the edges of nanoribbons. Charges are transferred between the CFE atom and carbon atoms at the edge, which reduce the local magnetic moment of carbon atoms in the vicinity of adsorption site and change the electronic structure of GNRs. As a result, Cu adsorbed zigzag GNR is a semiconductor with energy band gap of 0.88 eV in beta-spin and energy gap of 0.22 eV in alpha-spin, while Ag adsorbed zigzag GNR and Au adsorbed zigzag GNR are both half-metallic with the energy gaps of 0.68 eV and 0.63 eV in beta-spin, respectively. These results show that CFE atom adsorbed zigzag GNRs can be applied in nanoelectronics and spintronics.     

Excitation of undecuplet levels of the gadolinium atom belonging to the 4f 75d 26p configuration

The electron-impact excitation cross sections for 104 transitions from undecuplet levels of the gadolinium atom are measured by the method of extended crossing beams with the exciting electron energy of 30 eV and recording an optical signal of excited atoms from the crossing region. In the electron energy range of 0-200 eV, 16 excitation optical functions are recorded.     

两原子相干共振能量传递的单次与N次能量提取

两原子间隔一定距离且两原子跃迁频率接近时,两原子之间可发生能量传递.理论研究了供能原子和受能原子两共振原子的能量传递.求解薛定谔方程得出两原子共振能量传递效率.结果表明,供能原子在真空场中的激发态寿命在能量传递效率中起到十分重要的作用.能量传递效率与两原子间距离的负三次幂的正弦值的平方成正比,在一阶近似条件下,与两原子间距离的6次方成反比.以供能原子处于激发态时为初始时刻,能量从初始时刻随时间由供能原子向受能原子传递,对受能原子的单次能量提取的最大值大约在供能原子寿命的2/3时刻;对受能原子的连续N次能量提取的最大值,每次提取时间大约在供能原子寿命的1/2时刻.     

Work function dependence of the Li(2p) formation in slow collisions of Li atoms with partially cesiated tungsten surfaces

The reflection of Li atoms from partially cesiated polycrystalline tungsten is studied at impact energies between 100 and 1000 eV at near-grazing incidence angles. The work function dependence of the yield for Li(2p) formation is studied between φ = 1.27 and 4.8 eV together with the probability for Li⁺ formation. While Li⁺ formation is only important for φ > 3.5 eV, the probability for Li(2p) excitation has its maximum of several percents near (at φ = 1.7±0.1 eV), but not exactly at the minimum of the work function. The dependence of the absolute photon yield is given as a function of the impact energy. The polarization properties of the Li(2p → 2s) photons are also studied. The angular distribution of the excited Li(2p) atoms for various φ values is obtained by applying photon-scattered atom coincidence techniques. An effort is made to understand the Li(2p) formation on cesiated metal surfaces on the basis of the nonadiabatic coupling between different Li states induced by the motion of the Li atom relative to the surface.     

Electron spectroscopy of autoionizing states of oxygen,chlorine and bromine atoms

The autoionizing atomic states are obtained in dissociation Of O₂, Cl₂ and Br₂ molecules excited by either fast neutral He atoms (O₂) or by photons with 21.217 eV energy (Cl₂, and Br₂). Tentative assignment of the autoionizing levels is given for Cl* and for Br* atoms, and a more detailed one for O* atoms.     

Inversion of low-energy electron diffraction data with no pre-knowledge factor beyond optical holography

In this review, I describe how low-energy (typically below 500eV) electron diffraction spectra can be inverted to produce three-dimensional coordinates of atoms neighbouring a reference atom with no prior knowledge of what type or types of atom are present. The reference atom may be one of many equivalent near-surface atoms from which a core-level photoelectron is excited or, in the case of diffuse low-energy electron diffraction, one of many equivalent adsorbate atoms (lacking in long-range order) on the surface of a crystalline substrate. Other variants apply to low-energy electron diffraction, Kikuchi electron diffraction and time-reversed versions in which the wavenumber (energy) and direction of the incident beam are varied. I show that, for such low-energy electron diffraction spectra, the relative phases between the reference wave and scattered waves have a known geometric form if the spectra are taken from within a small angular cone in the near-back-scattering directions. By using the back-scattering small cone at each direction of interest, a simple algorithm is developed to invert the spectra and extract object atomic positions with no input of calculated dynamical factors. The article also reviews key ideas and works which led to the current understanding of this field.     

Casimir-Polder interaction of excited media

The potential of long-range interaction between two dissimilar atoms, one of which is excited, drops as 1/R ₂ with the distance for the Casimir-Polder limit of large distances in comparison with the wave-length of atom transitions (E.A. Power and T. Thirunamachandran, Phys. Rev. A 51, 3660 (1995)). It is shown that such a dependence, obtained with the help of perturbation technique, results in a divergence for the interaction potential between an excited atom and a medium of dilute gas. We develop a nonperturbative method based upon quantum Green’s functions (Yu. Sherkunov, Phys. Rev. A 72, 052703 (2005)) to calculate the interaction potential for an excited atom and a ground-state atom embedded in a dielectric medium, taking into account the absorption of photons in the dielectric medium. The exponential suppression of the interaction between the atoms is demonstrated. The force acting on an excited atom near the interface of dilute gas medium is calculated. The result is no more divergent. The force between gas media in Casimir-Polder regime is calculated as well. The text was submitted by the author in English.     

An experimental approach for investigating many-body phenomena in Rydberg-interacting quantum systems

Recent developments in the study of ultracold Rydberg gases demand an adwanced level of experimental sophistication, in which high atomic and optical densities must be combined with excellent control of external fields and sensitive Rydberg atom detection. We describe a tailored experimental system used to produce and study Rydberg-interacting atoms excited from dense ultracold atomic gases. The experiment has been optimized for fast duty cycles using a high flux cold atom source and a three beam optical dipole trap. The latter enables tuning of the atomic density and temperature over several orders of magnitude, all the way to the Bose--Einstein condensation transition. An elec- trode structure surrounding the atoms allows for precise control over electric fields and single-particle sensitive field ionization detection of Rydberg atoms. We review two experiments which highlight the influence of strong Rydberg---Rydberg interactions on different many-body systems. First, the Rydberg blockade effect is used to pre-structure an atomic gas prior to its spontaneous evolution into an ultracold plasma. Second, hybrid states of photons and atoms called dark-state polaritons are studied. By looking at the statistical distribution of Rydberg excited atoms we reveal correlations between dark-state polaritons. These experiments will ultimately provide a deeper understanding of many-body phenomena in strongly-interacting regimes, including the study of strongly-coupled plasmas and interfaces between atoms and light at the quantum level.     

CH3�벻ͬ�����¶ȵľ۱�������໥����

采用分子动力学方法模拟200eV的CH3粒子轰击到不同基底温度的钨样品上,分析了C、H原子在钨表面的沉积、散射及溅射情况,结果表明C、H原子的沉降量均随入射剂量的增加而增加。在基底温度为100K时,相同入射剂量下沉积的C原子最多,而当基底温度为1200K,在入射剂量大于1.5X1016cm-2时,C原子的沉降量小于其它基底温度下的C的沉降量。CH3在轰击样品时发生了分解,各种分解情况随基底温度变化较小,其中不同基底温度下一级分解率在40%上下波动,二级分解在23%左右,而完全分解的CH3在9%左右。C、H原子的散射角主要分布在5°~85°间,散射C原子分布的最大值分布在40%~50°或50°~60°间,散射C原子分布的最小值分布在0°~10°或80°~90°间;而不同基底温度下散射H原子分布的最大值均在40°~50°间,最小值均在0°~10°间。散射C原子的能量在0~140eV之间,散射能量为0~120eV的C原子占散射总量的98%以上,散射C原子平均能量随基底温度的增加而增加,其变化从65.5eV增加到68.5eV;散射H原子的能量也在0~140eV之间,但大约70%的散射H原子能量在40eV以内,散射平均能量随基底温度的增加而减小,其变化从13.92eV减小到13.05eV。     

Elektronenstoßanregung und Polarisation der He II-Fowler-α-Linie

The hydrogen-like He II-Fowler-α-(λ=4686 Å)-line has been excited by single electron impact collisions with ground-state helium atoms. The excitation-ionization function was measured from the threshold (76 eV) to 300 eV in a pressure-independent range. A broad maximum of the excitation-ionization function was observed at 200 eV. The line excited by a parallel electron beam has been proved polarized in the energy range quoted above. The degree of polarization increased monotonously from 6% at 300 eV to 13% near the excitation threshold. Comparison was made with previous experimental work. No polarization of the Fowler-α-Line was reported in other investigations. The shape of the excitation-ionization function agrees with that ofJohn andLin. Comparison with theoretical calculations is not as yet possible because only results of Born approximations are available.     

CH基团与金刚石(111)面的碰撞反应及其对碳膜生长的影响

等离子体增强化学气相沉积技术中的碳膜选择性自组装机理是高性能碳膜制备过程中的挑战性基础课题.采用经典分子动力学方法,模拟了不同能量(1.625-65 eV)的CH基团在清洁金刚石和吸氢金刚石(111)面上的轰击行为,获得了吸附、反弹、反应等各类事件的发生概率,并据此探讨了含氢碳膜制备过程中CH基团的贡献.结果表明,随着入射能量的增加,CH基团对薄膜生长的贡献由单纯的吸附、反弹机理向反应、吸附混合机理转变,其中最主要的反应过程是释放一个或两个氢原子的反应,而释放氢分子的反应则很少发生.这些反应不仅使薄膜生长过程更均匀、薄膜表面更平整,还降低了薄膜的氢含量.生长机理的转变导致低能量条件下所成薄膜中的多数碳原子都包含一个氢原子作为配位原子,而高能量条件下的薄膜中的碳原子则很少有氢原子作为配位原子.另外,通过分析sp~3-C和sp~2-C数目的变化,研究了CH基团对金刚石基底的破坏作用.     

Electron ejection by helium metastable atoms incident on the clean and chalcogen covered Ni(100) surface

An intense, essentially photon free, helium metastable beam has been used to cause electron ejection from the clean, oxygen and sulphur covered Ni(100) surface, in a system equiped with an AES facility to monitor surface cleanness. The ejected electron energy distribution obtained for the clean Ni(100) surface is narrow and peaked at ～2 eV, unlike the distribution obtained from INS studies, and consequently indicates different de-excitation mechanisms for incident ions and excited atoms. The ejected electron distribution from the adsorbate covered surface is also narrow, but peaked at ～1 eV with structure which is essentially independent of the nature of the adsorbate. The yield of ejected electrons is found to increase linearly with coverage of both oxygen and sulphur, in contrast to the results obtained from INS. These data indicate that Auger neutralization does not occur at the surface; the possibility of Auger de-excitation is considered.