ELS study on initial oxidation of Ni(100) surfaces

Electron energy loss spectra of clean and oxygen-covered Ni(100) surfaces were observed with concomitant measurements of LEED, work function change, and Auger peak height ratio O(KL_{2, 3}L_{2, 3})/Ni(L_{2, 3}VV). The observed electronic transitions are interpreted on the basis of primary election energy dependence, and of comparison with the loss spectrum for a UHV-cleaved NiO(100) surface and optical data of Ni. The observed loss peaks at 9.1, 14, and 19 eV in the clean surface spectrum are ascribed to the bulk plasmon of the 4s electrons, the surface plasmon, and the bulk plasmon of the coupled 3d + 4s electrons, respectively, and the weak but sharp peak at 33 eV is tentatively attributed to the localized many-body effect in the final state. Three oxygen-derived peaks at 6.0, 8.0, and 10.3 eV in the low oxygen exposure region (?4 L) are ascribed to the O 2p(e) → Ni 3d, O 2p(a₁) → Ni 3d, and O 2p → Ni 4s transitions, respectively. In the high oxygen exposure region (?50 L), the spectra become quite similar to that of the UHV-cleaved NiO(100) surface. The oxidation process consistent with LEED, Auger peak height ratio and work function change measurements is discussed.     

New interpretations of XPS spectra of nickel metal and oxides

A current interpretation of XPS spectra of Ni metal assumes that the main 6 eV satellite is due to a two hole c3d⁹4s² (c is a core hole) final state effect. We report REELS observation in AES at low voltages of losses (plasmons and inter-band transitions) corresponding to the satellite structures in Ni metal 2p spectra. The satellite near 6 eV is attributed to a predominant surface plasmon loss. A current interpretation of Ni 2p spectra of oxides and other compounds is based on charge transfer assignments of the main peak at 854.6 eV and the broad satellite centred at around 861 eV to the cd⁹L and the unscreened cd⁸ final-state configurations, respectively (L is a ligand hole). Multiplet splittings have been shown to be necessary for assignment of Fe 2p and Cr 2p spectral profiles and chemical states. The assignments of Ni 2p states are re-examined with intra-atomic multiplet envelopes applied to Ni(OH)₂, NiOOH and NiO spectra. It is shown that the free ion multiplet envelopes for Ni²⁺ and Ni³⁺ simulate the main line and satellite structures for Ni(OH)₂ and NiOOH. Fitting the NiO Ni 2p spectral profile is not as straightforward as the hydroxide and oxyhydroxide. It may involve contributions from inter-atomic, non-local electronic coupling and screening effects with multiplet structures significantly different from the free ions as found for MnO. A scheme for fitting these spectra using multiplet envelopes is proposed.     

High-resolution KLM Auger spectra of Ni metal excited by X-rays

KLM Auger spectra of Ni metal were measured with high energy resolution and high statistical accuracy using monochromatic synchrotron radiation. The spectra were corrected for the background from inelastically scattered electrons using partial intensity analysis where the electron trajectories were calculated by Monte Carlo simulation. Following background correction, the corrected spectra were fitted to model peaks taking into account intrinsic excitations. The measured transition energy of the most intense KL₂M₃ (¹D₂) Auger line is 7388.1 eV (0.4). The obtained relative intensities and energies of the Auger diagram lines are compared to published calculations as well as to experimental data for other 3d transition metals. In addition, the presence of Ni 3s, 3p photoelectron peaks in the spectra excited internally by Ni K X-rays is shown.     

STM investigations of CO coadsorption with O and with S on Ni(110)

The interaction between CO coadsorbed with oxygen and sulfur on Ni (110) has been studied with room temperature STM and LEED. In the case of CO/O/Ni(110)−(θ_o0.3 ML), it is found that due to a large local repulsion between the differing species, the coadsorbed species phase separate into large domains of O−(3 × 1) and CO−p2mg(2 × 1) structure. Similarly in the case of CO/S/Ni(110)−(θ_s0.4 ML), at low local coverages of coadsorbed CO, island segregation of CO and S-c(2 × 2) is observed. At locally saturated CO coverage, the S-c(2 × 2) structure transforms into long -S-S- chains running predominantly along the [ ] direction and separated by a local p2mg(2 × 1)-CO structure; this transformation is attributed to the large CO-CO repulsion in the condensed overlayer structure.     

Local probing of adsorbate electronic structure using soft X-ray emission; atomic nitrogen on Ni(100) and Cu(100)

The N 2p partial density of states of p4g-N/Ni(100) and c(2 × 2)-N/Cu(100) overlayers have been studied by soft X-ray emission spectroscopy (SXES) and comparisons with corresponding UV photoelectron spectra are made. Broad states (∼10 eV) are observed due to the hybridisation between the N 2p and the substrate 3d and 4sp bands. For both N/Cu and N/Ni the intensity stretches out to the Fermi level, where a prominent peak for N/Cu is observed. These states close to the Fermi level are interpreted as antibonding 2p-3d hybridised states. The higher occupancy of these states in N/Cu is expected due to the higher binding energy of the 3d band in Cu than in Ni. For a complete interpretation of the SXE spectra, especially for N/Cu where many features are observed, further theoretical studies are required.     

The reaction of oxygen with Ti,Cr, Fe and Ni studied by appearance potential spectroscopy

The interaction of oxygen with the surface of evaporated films of Ti, Cr, Fe and Ni has been studied with appearance potential spectroscopy (APS). Both oxygen Is and metal 2p spectra were recorded. Two adsorption regimes were clearly distinguishable: (i) a chemisorption regime characterized by a single peak in the oxygen 1s spectra and unchanged metal 2p spectra, (ii) an oxide regime with pronounced multipeaked structures in the oxygen 1s spectra and appreciable changes in the metal 2p spectra. The technique allows the determination of the exposure at which an oxide starts to grow on the surface.     

利用第一性原理研究Ni掺杂ZnO铁磁性起源

采用基于密度泛函理论和局域密度近似的第一性原理分析了Ni掺杂ZnO磁性质.文中计算了8个不同几何结构的铁磁(FM)和反铁磁耦合能量,结果表明FM耦合更稳定.态密度结果显示Ni 3d 与O 2p发生杂化,导致费米能级附近电子态自旋极化.文中也分析了O空位对Ni掺杂ZnO铁磁性质的影响,O空位通过诱导电子调节FM耦合,从而稳定Ni掺杂ZnO铁磁性质,其强度足以引发室温铁磁性.通过Ni 3d能级耦合具体分析了Ni 掺杂ZnO铁磁性起源.另外,也分析了晶格应变对Ni掺杂ZnO FM耦合的影响. 关键词： 第一性原理 半导体 铁磁性 缺陷     

低速Xe~(q+)(4≤q≤20)离子与Ni表面碰撞中的光辐射

实验中测量了0.38V_(Bohr)(460 keV)高电荷态Xe~(q+)(4≤q≤20)离子轰击高纯Ni表面发射的400-510 nm光谱.实验结果包括NiⅠ原子谱线,NiⅡ离子谱线,以及入射离子中性化发射的XeⅠ,XeⅡ和XeⅢ谱线.研究了谱线XeⅡ410.419,XeⅢ430.444,XeⅡ434.200,XeⅡ486.254,NiⅠ498.245,NiⅠ501.697,NiⅠ503.502,NiⅠ505.061和NiⅠ508.293 nm的光子产额随着入射离子电荷态的变化.结果表明,入射离子中性化和溅射Ni原子发射谱线的光子产额随着入射离子电荷态的增加而增加,其趋势与入射离子势能一致.     

Quantum confinement induced molecular correlated insulating state in La4Ni3O8

The recently synthesized layered nickelate La4Ni3O8, with its cupratelike NiO2 layers, seemingly requires a Ni1 (d(8))+2Ni2 (d(9)) charge order, together with strong correlation effects, to account for its insulating behavior. Using density functional methods including strong intra-atomic repulsion (Hubbard U), we obtain an insulating state via a new mechanism: without charge order, correlated (Mott) insulating behavior arises based on quantum-coupled, spin-aligned molecular Ni2-Ni1-Ni2 d(z)(2) trimer states across the trilayer (molecular rather than atomic states), with antiferromagnetic ordering within layers. The weak and frustrated magnetic coupling between cells may account for the small spin entropy that is removed at the Néel transition at 105 K and the lack of any diffraction peak at the Néel point.     

Ni2+:RbMgF3的电子顺磁共振谱的研究

含有过渡金属离子的晶体的光学吸收谱、零场分裂D值和g因子与晶体结构有密切关系,应用Ni^2 的参量化d轨道和三角晶场中d^8电子组态的强场能量矩阵,通过建立完全对角化方法,精确地计算了具有C3ν和D3d两种对称的Ni^2 ：RbMgF3的电子顺磁共振谱,分析了Ni^2 ：RbMgF3的零场分裂D值和g因子与晶体结构参量R和θ的依赖关系。理论值与实验值符合得很好。     

The YbNi interface studied with photoemission spectroscopy

The development of the ytterbium valence band region was followed with Synchrotron radiation induced Photoemission Spectroscopy (SPS) by interdiffusion of Yb into a Ni (110) single crystal in order to identify the valence conditions of Yb in the bulk and on the surface. During this process, also the width of the Ni L₃VV Auger transition was investigated with X-ray induced Photoemission Spectroscopy (XPS), reflecting the electron donation of Yb to the Ni valence band. By comparison between theory and experiment, strong multiplet splittings were found to take place in the 4d and 5p core level spectra of Yb due to the promotion of one 4f electron to the valence band by reaction with Ni. The 5p level is demonstrated to resonate strongly at hν=181 as a consequence of the 4d–4f giant resonance.     

X-ray photoelectron spectroscopy of Ni in Ni–Zn and Ni–Al alloys

X-ray photoelectron spectroscopy measurements on Ni in the alloys Ni, Ni₅₀Zn₅₀, Ni₂₀Zn₈₀ and Ni₅₀Al₅₀ have been made and confirm previous measurements of the band structure. The satellite lines on the Ni 2p and 3s lines are found to be present in the spectra even when the density of 3d states at the Fermi energy is low.     

Cs Ⅳ离子4d内壳层激发态衰变过程的相对论理论研究

在相对论多组态Dirac-Fock理论方法基础上,通过系统考 虑电子关联效应和由于内壳层电子激发而导致的电子自旋-轨道波函数的弛豫效应,详细研究了Cs Ⅳ离子的4d内壳层电子激发组态4d95s25p5、辐射末态4d105s25p4及Auger末态4d105s25p3和4d105s15p4的能级结构及各种可能的辐射和Auger衰变过程.获得了与已有的实验结果和相关的半经 验准相对论组态相互作用计算结果相符的辐射跃迁能、振子强度以及线宽,预言了4d95s25p5态的以Auger衰变为主的 Auger电子谱的特 关键词： 内壳层激发态 辐射衰变 Auger衰变     

Origin of XPS binding energy shifts in Ni clusters and atoms on rutile TiO2 surfaces

Cluster-size-dependent binding energy (BE) shifts of Ni 2p_3/2 spectra in Ni clusters with respect to bulk Ni metal have been studied as a function of Ni coverage on clean rutile TiO₂(0 0 1) and TiO₂(1 1 0) surfaces at room temperature. As a common method to distinguish initial and final state contributions to the core-level binding energy shifts in clusters, Auger parameter (AP) analysis of photoelectron spectra has been employed and reveals an obvious initial state contribution at the coverage of 0.5 monolayers (ML). From a comparison of results for TiO₂(0 0 1) and (1 1 0) surfaces, the initial state effect is demonstrated to be strongly affected by the substrate and is assigned to a combination of eigenvalue shift in surface core-level shift (SCLS) and charge transfer between the metal clusters and substrates. The Ni 2p_3/2 BE’s of atomic Ni on TiO₂(0 0 1) and (1 1 0) surfaces are deduced to be 853.69 and 853.55 eV, respectively, from an extrapolation of the experimental BE curves to zero Ni coverage. Compared with atomic Ni in gas phase, relaxation shifts of 7.34 and 7.48 eV are obtained on TiO₂(0 0 1) and (1 1 0) surfaces, respectively. These values are very close to the relaxation shift of 7.3 eV due to d electron screening, indicating d-like screening effects from the TiO₂ substrates after Ni 2p photoionization.     

Low temperature electron energy loss spectra of acetylene chemisorbed on metal single-crystal surfaces; Cu(111), Ni(110) and Pd(110)

Vibrational spectra of acetylene chemisorbed on Cu(111), Ni(110) and Pd(110) at 110–120 K were measured using electron energy loss spectroscopy. Loss peaks were assigned to vibrational modes of the non-dissociatively adsorbed molecules with the aid of the corresponding C₂D₂ spectra. The spectra show that the molecules undergo significant rehybridisation on adsorption. Comparisons are made with the spectra of acetylene adsorbed on a range of other transition metal surfaces at low temperature. Taking into account these and earlier literature results, two distinct patterns of spectra are observed (Type A and Type B) for specular spectra. The Cu(111) spectrum is classified as Type A while the Ni(110) and Pd(110) spectra are classified as Type B. Suggestions are made for the structures of the surface species corresponding to the two spectral types.     

溴的类镁离子跃迁谱线和能级扩展分析

用中国原子能科学研究院HI 13串列加速器提供的 90和 130MeV的Br离子和束箔技术 ,研究了波长在 13— 2 9nm范围内Br的类Mg离子的光谱 .识别出 2 4条属于BrXXIV的“3,3”跃迁 ,即 3s2 ,3s3p ,3p2 ,3s3d和 3p3d组态之间的跃迁谱线 ,其中 19条以前未见报道 .基于实验跃迁谱线 ,19个观测能级得以确立 ,其中有 14个能级此前未见报道 .相对论Hartree Fock(HFR)方法的计算结果对所观测的能级进行了解释.The spectrum of Mg-like Br, Br XXIV is investigated by means of beam-foil technique. Bromine ions of 90 and 130 MeV energy from the HI-13 tandem accelerator are used, and the wavelength region 13-29 nm is investigated. In the spectra, 24 Br XXIV transitions within the n=3 complex, i.e. between the 3s 2, 3s3p, 3p 2, 3s3d and 3p3d configurations are identifies, among them 19 have not been reported before. Based on these transition lines 19 energy levels have been determined and 14 energy level...     

Formation and electronic properties of oxide and sulphide films of Co,Ni and Mo studied by XPS

Dry O₂ oxidation up to 400°C, water immersion at room temperature or H₂S sulphidation at 400°C forms oxide or sulphide films on polycrystalline Co and Ni foils. X-ray photoelectron spectra (XPS) of the Co 2p and Ni 2p core levels and valence band (VB) structure changes allow the identification of the chemical state of such films and their electronic properties. They are compared with the films obtained on Mo in similar conditions. Ni appears less reactive than Co during O₂ or water oxidation and is considered as a more noble metal. Dry oxidation mainly induces CoO while water immersion induces formation of CoO(OH). For Ni, phases like Ni₂O₃, Ni(OH)₂ and/or NiO(OH) are the most probable products, respectively. H₂S sulphidation always produces a sulphur-rich Co or Ni phase. The VB response to sulphidation of the three studied metals shows that Co or Ni sulphides are potential electron-donors to MoS₂. Such results are relevant to the synergy observed in hydrotreating catalysis with these sulphides.     

Interplay of intra-atomic and interatomic effects: an investigation of the 2p core level spectra of atomic Fe and molecular FeCl2

The 2p photoabsorption and photoelectron spectra of atomic Fe and molecular FeCl2 were studied by photoion and photoelectron spectroscopy using monochromatized synchrotron radiation and atomic or molecular beam technique. The atomic spectra were analyzed with configuration interaction calculations yielding excellent agreement between experiment and theory. For the analysis of the molecular photoelectron spectrum which shows pronounced interatomic effects, a charge transfer model was used, introducing an additional 3d(7) configuration. The resulting good agreement between the experimental and theoretical spectrum and the remarkable similarity of the molecular with the corresponding spectrum in the solid phase opens a way to a better understanding of the interplay of the interatomic and intra-atomic interactions in the 2p core level spectra of the 3d metal compounds.     

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.     

Coexisting antiferromagnetism and ferromagnetism in mechanically alloyed Fe-rich Fe–Ni alloys: implications regarding the Fe–Ni phase diagram below 400°C

Fe–Ni alloys below the Invar region with compositions Fe_100−xNi_x (x=21, 24, and 27 at%) were prepared by high-energy ball milling technique (mechanical alloying). The as-milled samples, characterized by X-ray diffraction and Mössbauer spectroscopy, contain a mixture of (BCC) and γ (FCC) phases, whereas the samples annealed at 650°C for 0.5 h show a single γ (FCC) phase displaying a single line Mössbauer spectrum at room temperature (RT). At low temperature, the Mössbauer spectra of annealed Fe₇₆Ni₂₄ and Fe₇₃Ni₂₇ alloys show the existence of a magnetically split pattern together with a broad singlet, which are ascribed to a high-moment ferromagnetic Ni-rich phase and a low-moment Fe-rich phase, respectively. The Fe-rich phase in annealed Fe₇₆Ni₂₄ alloy, which is paramagnetic at RT, undergoes antiferromagnetic ordering at 40 K, estimated from the dramatic line broadening of its spectrum, giving rise to a small hyperfine field (e.g. 2 T at 6 K). The coexistence of these phases is attributed to phase segregation occurring in these alloys as a result of enhanced atomic diffusion. The stability of these alloys towards martensitic (FCC→BCC) transformation at low temperatures is discussed in connection with the Fe–Ni phase diagram below 400°C.