Evidence,by metastable quenching spectroscopy,that CO adsorbs on K/Ni(111) near potassium and lies flat or tilts when heated

By using metastable quenching spectroscopy (MQS) we show that if a K/Ni(111) surface with low K coverage (θ_K = 0.1 and 0.12) is exposed to low doses of CO (0.3 L), the CO molecules are adsorbed near the potassium atoms. Heating from 118 to 298 K results in spectral changes that indicate that the CO molecules closest to the potassium atoms tilt strongly or lie flat on the surface.     

Prediction of the electron spin polarised photoemission spectrum for Ni(111)

A calculation is made of the spin polarisation of electrons photoemitted from the (111) face of ferromagnetic nickel which, given a potential is exact within the single particle framework. The polarisation is strongly dependent upon photon energy in a manner similar to that found for the (001) face, rising rapidly from negative (minority spin) to positive (majority spin) as the photon energy increases from threshold. The influence on the spectrum of a surface dead layer is examined.     

Formation of textured Ni(200) and Ni(111) films by magnetron sputtering

The effect of the working gas pressure (P ≈ 1.33–0.09 Pa) and the substrate temperature (T_s ≈ 77–550 K) on the texture and the microstructure of nickel films deposited by magnetron sputtering onto SiO₂/Si substrates is studied. Ni(200) films with a transition type of microstructure are shown to form at growth parameters P ≈ 0.13–0.09 Pa and T_s ≈ 300–550 K, which ensure a high migration ability of nickel adatoms on a substrate. This transition type is characterized by a change of the film structure from quasi-homogeneous to quasi-columnar when a film reaches a critical thickness. Ni(111) films with a columnar microstructure and high porosity form at a low migration ability, which takes place at P ≈ 1.33–0.3 Pa or upon cooling a substrate to T_s ≈ 77 K.     

石墨烯在Ni(111)表面生长机理的紧束缚计算研究

本文采用SCC-DFTB方法,研究了石墨烯在Ni金属(111)表面上的生长机理及在台阶面生长情况.结果分析表明,苯环在Ni表面吸附时以界面fcc构型总能最低,结构最为稳定.边缘生长时,附着在衬底表面上的石墨烯层中C原子活性从边缘向中间逐渐降低.在由(111)晶面和(1-11)晶面相交形成的台阶面上,石墨烯片层可连续生长,同时相对衬底表面发生一定偏转,在较大面积时将出现缺陷.改善石墨烯与衬底台阶处的界面不匹配情况将有利于其大面积高质量生长.     

石墨烯在Ni(111)表面生长机理的紧束缚计算研究

本文采用SCC-DFTB方法,研究了石墨烯在Ni金属(111)表面上的生长机理及在台阶面生长情况.结果分析表明,苯环在Ni表面吸附时以界面fcc构型总能最低,结构最为稳定.边缘生长时,附着在衬底表面上的石墨烯层中C原子活性从边缘向中间逐渐降低.在由(111)晶面和(111)晶面相交形成的台阶面上,石墨烯片层可连续生长,同时相对衬底表面发生一定偏转,在较大面积时将出现缺陷.改善石墨烯与衬底台阶处的界面不匹配情况将有利于其大面积高质量生长.     

Growth and ordering of Ni(II) diphenylporphyrin monolayers on Ag(111) and Ag/Si(111) studied by STM and LEED

The room temperature self-assembly and ordering of (5,15-diphenylporphyrinato)nickel(II) (NiDPP) on the Ag(111) and Ag/Si(111)-(√3 × √3)R30° surfaces have been investigated using scanning tunnelling microscopy and low-energy electron diffraction. The self-assembled structures and lattice parameters of the NiDPP monolayer are shown to be extremely dependent on the reactivity of the substrate, and probable molecular binding sites are proposed. The NiDPP overlayer on Ag(111) grows from the substrate step edges, which results in a single-domain structure. This close-packed structure has an oblique unit cell and consists of molecular rows. The molecules in adjacent rows are rotated by approximately 17° with respect to each other. In turn, the NiDPP molecules form three equivalent domains on the Ag/Si(111)-(√3 × √3)R30° surface, which follow the three-fold symmetry of the substrate. The molecules adopt one of three equivalent orientations on the surface, acting as nucleation sites for these domains, due to the stronger molecule-substrate interaction compared to the case of the Ag(111). The results are explained in terms of the substrate reactivity and the lattice mismatch between the substrate and the molecular overlayer.     

Vibration spectroscopy of benzene adsorbed on Pt(111) and Ni(111)

High resolution electron energy loss spectroscopy has been applied to study the adsorption of benzene (C₆H₆ and C₆D₆) on Pt(111) and Ni(111) single crystal surfaces between 140 and 320 K. The vibrational spectra provide evidence that benzene is chemisorbed with its ring parallel to the surface, predominantly π bonded to the platinum and nickel surface respectively. A significant frequency increase of the CH-out-of-plane bending mode, largest in the case of platinum, is observed compared to the free molecule. On both metals two phases of benzene exist simultaneously, characterized by a different frequency shift. The shifts are explained by electronic interaction between the metal d-orbitals and molecules adsorbed in on top and threefold hollow sites respectively. The vibrational spectra of the multilayer condensed phase of benzene exhibit the infrared active modes of the gasphase molecule as expected.     

Interaction of NO with a Ni (111) surface

The interaction of NO with a Ni (111) surface was studied by means of LEED, AES, UPS and flash desorption spectroscopy. NO adsorbs with a high sticking probability and may form two ordered structures (c4 × 2 and hexagonal) from (undissociated) NO_ad. The mean adsorption energy is about 25 $\text{kcal}\text{mole}$. Dissociation of adsorbed NO starts already at ?120°C, but the activation energy for this process increases with increasing coverage (and even by the presence of preadsorbed oxygen) up to the value for the activation energy of NO desorption. The recombination of adsorbed nitrogen atoms and desorption of N₂ occurs around 600 °C with an activation energy of about 52 $\text{kcal}\text{mole}$. A chemisorbed oxygen layer converts upon further increase of the oxygen concentration into epitaxial NiO. A mixed layer consisting of N_ad + O_ad (after thermal decomposition of NO) exhibits a complex LEED pattern and can be stripped of adsorbed oxygen by reduction with H₂. This yields an N_ad overlayer exhibiting a 6 × 2 LEED pattern. A series of new maxima at ≈ ?2, ?8.8 and ?14.6 eV is observed in the UV photoelectron spectra from adsorbed NO which are identified with surface states derived from molecular orbitals of free NO. N_ad as well as O_ad causes a peak at ?5.6 eV which is derived from the 2p electrons of the adsorbate. The photoelectron spectrum from NiO agrees closely with a recent theoretical evaluation.     

A theoretical study of CHx chemisorption on the Ni(100) and Ni(111) surfaces

Cluster model calculations have been performed for CH_x, x = 0−3, chemisorbed on Ni(100) and Ni(111). The predicted chemisorption energies, at the present level of theory, based on bond-prepared clusters for Ni(100) are for carbon 150 kcal/mol, for CH 136 kcal/mol, for CH₂ 91 kcal/mol and for CH₃ 46 kcal/mol. The corresponding energies for Ni(111) are for CH 120 kcal/mol, for CH₂ 88 cal/mol and for CH₃ 49 kcal/mol. These chemisorption energies lead to similar stabilities for all CH_x fragments on both Ni(100) and Ni(111). Large basis sets and multi-reference correlation treatments are found to be very important in particular for the multiply bonded species. The vibrational C-H stretching frequencies predicted for CH_x on Ni(111) are for CH 3054 cm⁻¹ (2980 cm⁻¹), for CH₂ 3204 cm⁻¹ and for CH₃ 2709 cm⁻¹ (2680 cm⁻¹), where the available experimental values are given in parent The predicted ionization spectra of adsorbed CH_x are also in general agreement with experimental findings.     

Adsorption and decomposition of formic acid (DCOOD) on NiO(111) and Ni(111) surfaces probed by SFG

Received: 20 September 1998 / Revised version: 3 November 1998     

K/Cu(111)表面功函数的变化

本工作用俄歇电子能谱(AES)测定K在Cu(111)表面上的覆盖度,用Kelvin探头测量表面功函数的变化,得出功函数依赖于K覆盖度的关系曲线,功函数最大变化值△φ_max=3.14eV,功函数最小时的覆盖度θ_min=0.18,初始偶极矩p(0)=7.0Debye,实验结果与武汝前等人的理论模型相一致。 关键词：     

Electronic structure of graphene on Ni(111) and Ni(100) surfaces

Physics of the Solid State - A comparative investigation of graphene prepared by cracking of propylene (C3H6) on nickel surfaces with different orientations, Ni(111) and Ni(100), has been carried...     

Electronic structure of the Au-intercalated graphene/Ni(111) surface

We report the electronic structure of the Au-intercalated graphene/Ni(111) surface using angle-resolved photoemission spectroscopy and low energy electron diffraction. The graphene/Ni(111) shows no Dirac cone near the Fermi level and a relatively broad C 1s core level spectrum probably due to the broken sublattice symmetry in the graphene on the Ni(111) substrate. When Au atoms are intercalated between them, the characteristic Dirac cone is completely recovered near the Fermi level and the C 1s spectrum becomes sharper with the appearance of a 10?×?10 superstructure. The fully Au-intercalated graphene/Ni(111) surface shows a p-type character with a hole pocket of ～0.034?Å^?1 diameter at the Fermi level. When the surface is doped with Na and K, a clear energy gap of ～0.4?eV is visible irrespective of alkali metal.     

Scattering of N2 from Ni(111)

A cold (T_rot<10 K) beam of N₂ with an initial translational energy of 0.40 eV strikes an Ni(111) surface at surface temperatures from 300 to 873 K at several incident angles from 15 to 60°. The rotational energy and angular distributions of the scattered molecules are probed using (2+1) resonance-enhanced multiphoton ionization. Molecules scattered in the specular direction have mean rotational energies that are independent of surface temperature, whereas those scattered at angles far from the specular show a dependence on surface temperature, caused likely by multiple collisions with the surface before escape. A rotational rainbow, seen in systems such as CO–Ni(111) and N₂–Ag(111), is not seen in this system. For molecules that scatter close to the specular direction, approximately 10% of the initial translational energy is converted into rotational energy of the scattered N₂. For surface temperatures above room temperature, the angular distributions indicate that molecules that scatter into low-J states also tend to exit in a broad peak (10–20° FWHM) near the specular, and this peak is broadened with increasing incident angle. The molecules that scatter into high-J states have a much broader distribution, indicating that they are trapped rotationally during the initial collision and suffer multiple collisions before leaving the surface.