钠原子在银(001)表面吸附的理论研究

用密度泛函理论(DFT)的广义梯度近似(GGA)方法对钠原子在银(001)面吸附的性质进行了理论研究. 计算表明, 钠原子吸附在银(001)面空位最稳定, 桥位次之, 而顶位吸附能量最高;优化得到的吸附结构几何参数与实验测定结果吻合. 对3种吸附结构的电子结构和局域态密度分析表明, 钠原子吸附到银表面后, 其电子将部分转移到金属表面, 导致银的费米能级上升, 化学活性增强. 通过比较氢气分子在洁净银表面和吸附了钠的银表面进行的裂解反应活性证实, 金属钠吸附在银表面表现出明显的助催化作用.     

钠原子在银(001)表面吸附的理论研究

用密度泛函理论（DFT）的广义梯度近似（GGA）方法对钠原子在银（001）面吸附的性质进行了理论研究．计算表明,钠原子吸附在银（001）面空位最稳定,桥位次之,而顶位吸附能量最高;优化得到的吸附结构几何参数与实验测定结果吻合．对3种吸附结构的电子结构和局域态密度分析表明,钠原子吸附到银表面后,其电子将部分转移到金属表面,导致银的费米能级上升,化学活性增强．通过比较氢气分子在洁净银表面和吸附了钠的银表面进行的裂解反应活性证实,金属钠吸附在银表面表现出明显的助催化作用．     

O在Rh(100)表面吸附的密度泛函理论研究

采用第一性原理的密度泛函理论计算了O原子在Rh(100)表面的吸附,得到了电子特性及各种结构参数,并给出了不同覆盖度下O原子在Rh(100)表面上3个位置吸附后的能量.结果表明,O原子在Rh(100)表面可以发生稳定的吸附,最高吸附能为2.53 eV.同时,通过对O原子的态密度进行分析,得到如下结论:O原子在Rh(100)面上的吸附主要是由于O的2p轨道与基底金属的4d轨道相互作用的结果.     

O在Rh(100)表面吸附的密度泛函理论研究

采用第一性原理的密度泛函理论计算了O原子在Rh（100）表面的吸附,得到了电子特性及各种结构参数,并给出了不同覆盖度下O原子在Rh（100）表面上3个位置吸附后的能量,结果表明,O原子在Rh（100）表面可以发生稳定的吸附,最高吸附能为2．53eV。同时,通过对O原子的态密度进行分析,得到如下结论：O原子在Rh（100）面上的吸附主要是由于O的2p轨道与基底金属的4d轨道相互作用的结果。     

Si(001)-(2×2×1):H表面弛豫研究

目的 研究Si(001)-(2×2×1):H表面的几何结构和电子特性.方法 在周期边界条件下,采用基于密度泛函理论的广义梯度近似平面波超软赝势法,对Si(001)-(2×2×1):H表面结构进行了弛豫计算并对该表面进行电子结构分析.结果 结果表明弛豫作用使得部分电子从第一层硅原子转移到了第二层硅原子上,从而导致表层硅呈现正电性.结论 这样的电子结构特性将有助于负电性强的氧气分子在硅氢表面的吸附. 弛豫后的Si(001)-(2×2×1):H表面的能带结构具有半导体材料的特征.     

甲醇在碳负载PtNi合金表面吸附的理论研究

采用密度泛函理论和周期平板模型相结合的方法, 对CH3OH分子在Pt-Ni(111)/C表面top,fcc,hcp和bridge位的吸附模型进行了构型优化、能量计算, 结果表明bridge位是较有利的吸附位. 考虑抗中毒性发现: CO在Pt(111)/C面上的吸附能比甲醇吸附能要高, CO在Pt-Ni(111)/C的吸附能比甲醇的吸附能要低, 可说明CO在Pt(111)/C面上有中毒效应, 而Pt-Ni(111)/C的抗CO中毒化能力增强, 是催化氧化甲醇良好的催化剂.     

石墨烯基碱金属原子有效电荷变化规律

应用S.Yu.Davydov提出的石墨烯态密度模型,求出吸附在石墨烯上的碱金属原子的有效电荷数,研究了吸附原子的电子能级、能级移动量、有效电荷数随金属原子元素的变化以及有效电荷数随电子能量的变化规律.结果表明:(1)被吸附的碱金属原子的电子能级和能级移动量随原子序数的变化为非线性,在Li,Na,K,Rb,Se,Fr这6种碱金属原子中,以Na原子的值为最小,其原因在于碱金属原子的电离能以及石墨烯与吸附原子的相互作用能均随原子序数的增大而减小;(2)石墨烯能带电子和吸附原子的局域态电子对有效电荷的贡献以及总有效电荷数,均随原子序数的增加而非线性地减小.其中,能带电子对有效电荷的贡献与电子能量无关,而吸附原子局域态电子的贡献与总有效电荷数和电子能量都有关,且随电子能量的变化有明显的局域特点,最可几电子能量随原子序数的增大而增大.     

镍小团簇中金属键的E L F和L O L函数研究

用非限制性密度泛函方法UBP86泛函结合def2-TZVP基组获得了Ni2～6团簇的几何结构并用ELF(ElectronLocalized Function)和LOL(Localized Orbital Locator)函数对小镍团簇的电子结构进行拓扑分析.研究结果表明,除Ni2团簇外,团簇中Ni—Ni键的成键临界点不在键轴上,为弯曲键.镍团簇中Ni—Ni间的金属键为部分共价键,其价层Basin的布局数均小于1e,并且团簇中存在多个多中心价层Basin.团簇中各个化学键均强烈离域化.团簇中的单电子主要位于内层轨道,并没有参与成键.     

Mg2Ni-Cu体系相结构稳定性的密度泛函理论研究

采用基于密度泛函理论的第一原理赝势平面波方法,计算了Mg2Ni相Cu合金化前后体系的能量与电子结构,结果发现:2个Cu原子最易占据 Ni(Ⅱ)的(0,0.5,0.166 7)与(0.5,0,0.5)位置,而在Cu合金化Mg2Ni的相结构中,Mg2Ni(Ⅱ)″1-xCux(x=1/3)的结构稳定性最高.电子态密度(DOS)的进一步分析结果表明:Mg2Ni(Ⅱ)″1-xCux(x=1/3)相结构的稳定性主要取决于体系在费米能级处成键电子数N(EF)的多少.     

室温稀磁半导体Zn_(0.9)Ni_(0.1)O纳米棒的制备与表征

利用溶胶-凝胶方法制备了Zn0.9Ni0.1O纳米棒.运用X射线衍射分析表明样品中不存在镍及镍的氧化物,镍进入晶格中取代了部分Zn原子的位置.SEM显示煅烧温度是影响其形貌的主要因素.随着温度的升高,样品形貌逐渐从棒状变为颗粒状.样品的磁学性能由振动样品磁强计测量,发现在室温下存在明显的铁磁性,并且通过M-T曲线得到Zn0.9Ni0.1O居里温度为575 K左右,表明其磁性来源于稀磁半导体.     

Improved oxygen reduction activity on Pt3Ni(111) via increased surface site availability

The slow rate of the oxygen reduction reaction (ORR) in the polymer electrolyte membrane fuel cell (PEMFC) is the main limitation for automotive applications. We demonstrated that the Pt3Ni(111) surface is 10-fold more active for the ORR than the corresponding Pt(111) surface and 90-fold more active than the current state-of-the-art Pt/C catalysts for PEMFC. The Pt3Ni(111) surface has an unusual electronic structure (d-band center position) and arrangement of surface atoms in the near-surface region. Under operating conditions relevant to fuel cells, its near-surface layer exhibits a highly structured compositional oscillation in the outermost and third layers, which are Pt-rich, and in the second atomic layer, which is Ni-rich. The weak interaction between the Pt surface atoms and nonreactive oxygenated species increases the number of active sites for O2 adsorption.     

The Chemistry of Bulk Hydrogen: Reaction of Hydrogen Embedded in Nickel with Adsorbed CH3

Studies in heterogeneous catalysis have long speculated on or have provided indirect evidence for the role of hydrogen embedded in the catalyst bulk as a primary reactant. This report describes experiments carried out under single-collision conditions that document the distinctive reactivity of hydrogen embedded in the bulk of the metal catalyst. Specifically, the bulk H atom is shown to be the reactive species in the hydrogenation of CH(3) adsorbed on Ni(111) to form CH(4), while the H atoms bound to the surface were unreactive. These results unambiguously demonstrate the importance of bulk species to heterogeneous catalytic chemistry.     

(111)晶面暴露的NiO纳米催化剂的制备及其CO催化氧化性能

采用溶剂热法,以Ni(NO_3)_3·6H_2O、均苯三甲酸以及N,N-二甲基甲酰胺(DMF)为原料快速合成金属有机骨架材料Ni_3(BTC)_2·12H_2O晶体。以Ni_3(BTC)_2·12H_2O为前体,通过焙烧得到具有(111)面的NiO颗粒用于CO催化氧化反应,并与由硝酸镍热解得到的NiO(R)催化剂进行对比。通过X射线衍射(XRD)、N_2物理吸附-脱附、透射电子显微镜(TEM)以及X射线光电子能谱(XPS)等方法对具有(111)面的NiO颗粒的组成、结构和形貌进行表征。CO催化氧化结果表明,具有(111)面的NiO颗粒的催化活性优于普通NiO催化剂的催化活性。     

Controlling the Kondo effect of an adsorbed magnetic ion through its chemical bonding

We report that the Kondo effect exerted by a magnetic ion depends on its chemical environment. A cobalt phthalocyanine molecule adsorbed on an Au111 surface exhibited no Kondo effect. Cutting away eight hydrogen atoms from the molecule with voltage pulses from a scanning tunneling microscope tip allowed the four orbitals of this molecule to chemically bond to the gold substrate. The localized spin was recovered in this artificial molecular structure, and a clear Kondo resonance was observed near the Fermi surface. We attribute the high Kondo temperature (more than 200 kelvin) to the small on-site Coulomb repulsion and the large half-width of the hybridized d-level.     

Single-atom spin-flip spectroscopy

We demonstrate the ability to measure the energy required to flip the spin of single adsorbed atoms. A low-temperature, high-magnetic field scanning tunneling microscope was used to measure the spin excitation spectra of individual manganese atoms adsorbed on Al2O3 islands on a NiAl surface. We find pronounced variations of the spin-flip spectra for manganese atoms in different local environments.     

Atomic resolution imaging of adsorbates on metal surfaces in air: iodine adsorption on pt(111)

The adsorption of iodine on platinum single crystals was studied with the scanning tunneling microscope (STM) to define the limits of resolution that can be obtained while imaging in air and to set a target resolution for STM imaging of metal surfaces immersed in an electrochemical cell. Two iodine adlattice unit cells of slightly different iodine packing density were clearly imaged: ( radical7 x radical7) R19.1 degrees -I, surface coverage ?(I) = 3/7; and (3 x 3)-I, ?(I) = 4/9. The three iodine atoms in the ( radical7 x radical7) unit cell form a regular hexagonal lattice interatomic distance d(I) = 0.424 nanometer, with two atoms adsorbed in threefold hollow sites and one atom adsorbed at an atop site. The (3 x 3) unit cell showed two different packing arrangements of the four iodine atoms exit. In one of the (3 x 3) structures, the iodine atoms pack to form a hexagonal lattice, d(I) = 0.417 nanometer, with three of the iodine atoms at twofold adsorption sites and one atom at an atop site. Another packing arrangement of iodine into the (3 x 3) unit cell was imaged in which the iodine atoms are not arranged symmetrically.     

Dissociation of individual molecules with electrons from the tip of a scanning tunneling microscope

The scanning tunneling microscope (STM) can be used to select a particular adsorbed molecule, probe its electronic structure, dissociate the molecule by using electrons from the STM tip, and then examine the dissociation products. These capabilities are demonstrated for decaborane(14) (B(10)H(14)) molecules adsorbed on a silicon(111)-(7 x 7) surface. In addition to basic studies, such selective dissociation processes can be used in a variety of applications to control surface chemistry on the molecular scale.     

Re对Ni和Ni3Al 结构稳定性影响的分子动力学模拟研究

应用分子动力学方法模拟研究了Re在Ni和Ni3Al中的分布及其对材料微结构的影响.研究发现,Re的添加量影响Ni和Ni3Al晶体中空位的产生,但Re在Ni中对体系结构的破坏程度小于其在Ni3Al中占据Ni位时的程度.在Ni中,Re添加量较少且增大空位比时,其结构依然能保持稳定;随着Re数目的增多,空位比的增大,其影响逐渐变得明显.Re在Ni3Al中占据Ni,Re含量或空位比较小时,结构皆会出现局部不稳定.随着Re添加量的增多,结构的破坏程度加剧.然而Re占据Ni3Al中的Al位时其结构并未发生明显的变化,直至Re的添加量大至1%和空位比增至1%~1.5 % 时体系中才出现局部不稳定.相比而言,Re置换Al比置换Ni时对体系结构的影响较弱,在Ni3Al中Re占据Al位比占据Ni位更稳定.     

Observation of metastable structural excitations and concerted atomic motions on a crystal surface

The addition of a small number of lead atoms to a germanium(111) surface reduces the energy barrier for activated processes, and with a tunneling microscope it is possible to observe concerted atomic motions and metastable structures on this surface near room temperature. The formation and annihilation of these metastable structural surface excitations is associated with the shift in position of large numbers of germanium surface atoms along a specific row direction like beads on an abacus. The effect provides a mechanism for understanding the transport of atoms on a semiconductor surface.