A solution of the core-exciton issue for silicon and germanium

The large discrepancies among the Si L_2,3 core-excitonic shifts measured by different techniques can be explained by the recently discovered surface shifts of the Si 2p level. New, accurate photoemission measurements of both the L_2,3 edge and of the 2p binding energy with equal surface sensitivity have been performed. Our present results and those of previous experiments are consistent with a single value 0.3^-00_+0.15 eV for the Si L_2,3 core excitonic shift. Preliminary results for the 3d core exciton in Ge give a shift of 0.35 ± 0.25 eV.     

Observation of opposite 4f-surface core level binding energy shifts for W(111) and Ta(111)

Surface 4f core level binding energy shifts have been measured in photoemission from W(111) and Ta(111). The surface shift was found to change sign across the row of 5d-metals: for the topmost layer of Ta(111) a +0.40 eV shift toward higher binding energy is found, whereas for W(111) the shift is -0.43 eV toward lower binding energy. The shifts are shown to be dependent on surface crystallography. Chemical shifts are determined for saturation coverage of hydrogen.     

Electronic properties of gold on Mo(110): d → s,p charge redistribution and valence band shifts

The interaction between Au atoms and Mo(110) has been investigated using photoelectron spectroscopy and ab initio self-consistent field calculations. The formation of AuMo bonds induces shifts toward higher binding energy (0.3–0.7 eV) in the core levels and valence d band of gold. This is accompanied by an important redistribution of charge, in which Au loses 5d electrons and gains (6s,6p) electrons. The positive binding-energy shifts in the Au 4f levels and 5d band reflect the effects of a Mo-induced reduction in the Au 5d electron population.     

Hydrogen chemisorption on metal surfaces

The adsorption of H atoms on metal (jellium) surfaces has been investigated using linear response theory within the density functional formalism. The adsorbate is represented initially by a 1S orbital on the H atom, which perturbs the jellium surface and indirectly the adsorbate itself. The interaction energy curves, atomic binding energies, induced dipole moments, chemical shifts associated with the adsorbate, and vibrational excitation energies at the equilibrium internuclear separation have been calculated for a single H atom chemisorbed on metal surfaces. The sum of the atomic binding energy and the ionization potential of the H 1S level may be regarded as the initial state energy in the case of photoemission from the chemisorbed H. The rather satisfactory overall agreement between the theory and the experimental results for binding energies, vibrational excitation energies, and dipole moments suggests that this simple formalism could also have useful applications in more complicated chemisorbed systems.     

Angle-resolved resonant photoemission of Ni(100) and Ni(110) single crystals

We have studied the valence band photoemission spectra of Ni(100) and Ni(110) single crystals near the excitation threshold for 3p core electrons. The resonant behavior of the 6 eV satellite does not depend on both the surface orientation and the polarization of the electric vector of an incident light for excitation. These results indicate that the 6 eV satellite should be under little influence of spatial symmetry of the valence band. In the angle-resolved photoemission spectra of Ni(100), we have observed another broad feature near the 6 eV satellite. It shows the large energy dispersion and is interpreted as due to the interband transition. In Ni(110), we have observed the weak valence band satellites at binding energies of about 9.3 eV and 13.4 eV. They do not show well-defined resonance around the 3p threshold.     

The influence of dipoles in intermediate layers on the electronic levels of physisorbed species studied by UPS

Angle-resolved UV photoelectron spectra were measured at 20 K on Xe/ N₂/X/Ni (110) multilayers in which X were chemisorbed H₂O, N₂ and CO molecules. The chemisorbed molecules change the work function by different amounts. The binding energy of Xe referred to the Fermi edge of the substrate is shifted according to these work-function changes, but it stays constant with respect to the vacuum level. This experiment proves that there is no measurable interaction between the photon created hole and the dipole of the chemisorbed molecule, in the final state of the photoemission process.     

Ge在Ru(0001)表面上生长及其性质研究

报道Ge在Ru(0001)表面上生长以及相互作用行为的扫描隧道显微镜（STM）和x射线光电子能谱（XPS）研究. STM的实验结果表明Ge在Ru(0001)表面的生长呈典型的Stranski_Krastanov生长模式，Ge的覆盖度小于单原子层时呈层状生长，而从第二层开始呈岛状生长. XPS测量显示衬底Ru(0001)与Ge的相互作用很弱. Ru(0001)表面的Ru 3d5/2和Ru 3d3/2芯态结合能分别处于2798和2840 eV. 随着Ge的生长，到Ge层的厚度为20个单原子层，衬底Ru 3d芯态结合能减小了约02 eV，而Ge 3d芯态结合能从Ge低覆盖度时的289 eV增加到了290 eV，其相对位移约为01 eV. 关键词： Ge Ru表面 生长 相互作用     

Cadmium oxidation in different environments: an XPS study

The behaviour of polycrystalline cadmium in different oxidative atmospheres was investigated. The interactions between cadmium and O₂, CO₂, water, and mixtures of these were studied. The cadmium sample was only reactive towards oxygen. A progressive growth of the O1s signal as a function of O₂ exposure was observed, together with a shift in the Cd3d and Cd MNN peaks towards the positions reported for CdO. The O1s spectra show the presence of several components in the range of exposures analysed and the best fit of the experimental signals is obtained for the components at 529.3 eV and 531.3 eV. The signal at lower binding energy is characteristic of O²⁻ in the oxide state, while the component at higher binding energy could be due to either chemisorbed oxygen or oxygen in a non-equivalent site in the oxide structure.     

苯并咪唑苝与金属Ag的界面电子结构研究

利用同步辐射光电子能谱实验技术考察了苯并咪唑苝(BZP)和Ag的界面形成过程与电子结构.单层覆盖度以下时，BZP分子与Ag有弱相互作用，在有机分子禁带中出现明显界面反应态，结合能位于0.9eV.单层铺满后，BZP分子呈现三维岛式生长，且与Ag的相互作用逐渐减弱，同时最高占据分子轨道由于终态效应逐渐向高结合能方向位移至体相结合能位置(2.3eV). Ag衬底上BZP分子的生长导致样品表面功函数减小，表明形成了表面偶极势(Δ=0.3eV)，且电子从有机分子向金属Ag偏移.最后，考察了BZP/Ag 关键词： 有机-金属界面 电子结构 光电子能谱 同步辐射     

Valence band and core level studies of InSb via photoemission measurements in the 20–70 eV range

We report photoemission measurements of valence band critical points, core level binding energies and spin-orbit splittings, and Auger processes using synchrotron radiation in the 20–70 eV range for InSb. Based on our studies of InSb and other semiconductors, several precautions when interpreting photoemission data in this energy range (e.g. Auger processes, matrix elements) are discussed.     

NiSi2化合物的电子结构

采用自洽LMTO方法,计算了NiSi₂化合物的电子结构。所得结果与ARUPS光电子谱结果以及LAPW等计算结果符合得相当好。在NiSi₂化合物中Ni3p芯能级移动是与镍原子的电子组态变化有关;镍的3d电子减少导致对镍的3p电子屏蔽作用减弱。计算结果表明离子性对化学键贡献很小。 关键词：     

Theory of resonant photoemission in black phosphorus

Resonant photoemission in black phosphorus is studied theoretically with a model of simplified energy bands. It is shown that a core exciton state plays an essentially important role both in the resonant enhancement of the photoemission peak at the binding energy 10.8eV and the Fano type interference at 2.7eV, which have recently been observed experimentally.     

UV photoemission from physisorbed atoms and molecules: Electronic binding energies of valence levels in mono- and multilayers

Angle-resolved UV photoemission spectra were measured for Ar, Kr, Xe, CO, O₂ and N₂ adsorbed on a Ni(110) surface at 20 K. The different gases were adsorbed also on the Ni(110) surface which had been precovered by mono- and multilayers of the same gases. Upon physisorbing one of these species onto the bare and precovered Ni surface, binding energy shifts up to 3 eV were found. These shifts will be explained by work function changes of the substrate onto which the gas is physisorbed. It will be shown that for the investigated gases the binding energy referred to the vacuum level is an atomic or molecular property which is independent of the substrate, to a first approximation. By physisorption of a known gas the work function of any substrate can be evaluated by UPS. The density of valence states for bulk Ar, Kr and Xe will be discussed. There is evidence that the conduction band can be seen in the secondary electron background of the UP spectra.     

A LEED/UPS study on the interaction of oxygen with a Ni(111) surface

Exposure of a Ni(111) surface to oxygen leads at first to the formation of a chemisorbed overlayer which is characterized by a 2 × 2-superstructure and a maximum in the photoemission spectrum (hv = 40.8 eV) centered at 5.6 eV below the Fermi level E_F. The emission from the Ni d-states is nearly unaffected at this stage of interaction. After high oxygen exposures the epitaxial growth of NiO can be identified from the LEED pattern. The corresponding photoelectron spectrum is strongly altered and exhibits close agreement with the transition energies as calculated by Messmer et al. for a NiO₆^10- -cluster.     

Multielectron effects in the XPS spectra of nickel

Extra structure in the XPS spectra of Ni metal is interpreted as arising from a localized d-hole accompanying the hole state created by the photoemission process. This d-hole state has a binding energy of approximately 6 eV.     

UV-photoemission study of barium,europium and ytterbium

Measurements are reported of the photoemission spectra and absolute yield of thin films of Eu, Ba and Yb for the photon energy range 2 to 21 eV. Transitions from the occupied 4f-states in Eu and Yb have been observed and the binding energies deduced. The excitation probability of the 4f electrons is found to be very low and an explanation based on their atomic-like nature is given. Transitions involving valence band states are compared with predictions based on published energy band schemes and the density of states for the unoccupied 5d band in Yb is deduced. The effect of chemisorbed oxygen on Ba and Eu surfaces is reported.     

Unusual superexchange pathways in an NiS2 triangular lattice with negative charge-transfer energy

We have studied the electronic structure of the Ni triangular lattice in NiGa(2)S(4) using photoemission spectroscopy and subsequent model calculations. The cluster-model analysis of the Ni 2p core-level spectrum shows that the S 3p to Ni 3d charge-transfer energy is approximately -1 eV and the ground state is dominated by the d(9)L configuration (L is a S 3p hole). Cell perturbation analysis for the NiS(2) triangular lattice indicates that the strong S 3p hole character of the ground state provides the enhanced superexchange interaction between the third-nearest-neighbor sites.     

Chemisorption and reaction of NH3 on Ni(111)

The chemisorption of ammonia on Ni(111) has been investigated using LEED, thermal desorption, and angle-resolved photoemission. For exposures at 200 K, thermal desorption shows a coverage-dependent binding energy associated with dipole-dipole interactions. A (2 × 2) LEED pattern occurs at 2–4 L exposure. Time dependence of the LEED pattern and changes in the thermal desorption induced by the LEED beam indicate that the (2 × 2) pattern is due to a stable intermediate decomposition species. Using synchrotron radiation photoemission all three valence orbitals of ammonia have been observed for the first time. The energies of the ammonia-induced features in the photoemission (?22.0, ?11.0 and ?6.7 eV below the Fermi energy) and the observed symmatries positively identify the absorbed species as molecular ammonia. Additional structure observed in the photoemission spectra after electron bombardment is associated with the stable adsorbed intermediate.