Angle-resolved photoemission study of Pd(111) and Co/Pd(111)

Electronic structure of epitaxial Co films on Pd(111) has been investigated as a function of the Co overlayer thickness, by using angle-resolved photoemission spectroscopy (ARPES). It is found that experimental band structures for Pd(111) and work functions for Co/Pd(111) agree reasonably well with the results of band structure calculations. Compared to Pd(111), valence band ARPES spectra of Co/Pd(111) support the existence of the induced magnetic polarization of Pd atoms near the interface, suggesting large hybridization between Co 3d and Pd 4d states near the interface.     

Experimental band structure of GaSe obtained by angular resolved photoemission

A very detailed experimental band structure of the layered compound GaSe has been obtained in all the symmetry directions of the Brillouin zone for photon energy varying between 21 and 45 eV. It is shown that in this energy range the dispersion curves E (K//) are independent of the final state and that it is also possible, assuming a free electron like conduction band, to have information along the normal to the layers.     

The valence band structure of HfN0.93 (100) studied by angle-resolved photoemission

The valence band structure of a HfN_0.93 (100) crystal has been investigated utilizing angle-resolved photoemission and HeI, NeI and ArI radiation. The experimental data are compared with calculated spectra and calculated direct transitions for stoichiometric HfN. The comparison shows that most of the structures in the recorded spectra can be identified as originating from bulk band transitions. The dispersions of the experimental peaks are predicted reasonably well theoretically, using final states approximated by free-electron bands. However, the experimental peaks are in general found somewhat deeper below the Fermi level than the calculated positions.     

Electronic excitations on clean and adsorbate covered Pd(111) by angle resolved electron energy loss spectroscopy

Electronic excitations on clean and adsorbate covered Pd(111) have been investigated by angle resolved electron energy loss spectroscopy. Primary energies in the range of 50–1000 eV were chosen for strong specular reflection to emphasize elastic diffraction-before-loss processes. The clean Pd spectra are compared with optical data, and good correspondence is found for the optical limit (q ? 0). The loss features are interpreted in terms of plasmon resonances and interband transitions within the framework of a recent band structure calculation. Virtually no dispersion is observed for the intrinsic Pd losses, but vertical interband transitions decay fast in the dispersive (q ≠ 0) spectra. Two adsorbate systems are investigated in this study: CO in a disordered adsorbate layer and bromine in a well-ordered $\text{(}\text{3×}\text{3 )R30°}$ structure. Adsorbate derived loss features are generally prominent in the nonspecular (q ≠ 0) spectra. While no dispersion is seen for the intramolecular 13.5 eV excitation of adsorbed CO, dispersion up to 1 eV is found for the Br 4p derived loss feature of the ordered overlayer. This is discussed in terms of a two-dimensional adsorbate band structure of bromine.     

Angular resolved photoemission and the band structure of solids

Current models used to described angular resolved photoemission data are discussed. Emphasis is placed on the energies of structure in the spectrum and its relationship to the bulk band structure. Taking the lead salts (PbS, PbSe, PbTe) as an example a detailed comparison between measured and calculated spectra is given using time reversed LEED functions to describe the final state. On the basis of this comparison criteria are discussed that allow the application of simpler models for the interpretation of angular resolved photoemission. Such models include the direct, k-conserving model and the model of complete neglect of k conservation as well as the use of free electron like final states.     

The characterization of surface acetylene and ethylene species on Pt(111) by angle resolved photoemission using synchrotron radiation

Angle resolved photoemission using synchrotron radiation was employed to elucidate the molecular structure of the species present in the low and high temperature phases of ethylene and acetylene on Pt(111). The plane polarized nature of synchrotron radiation allows the use of simple symmetry arguments to determine the orientation of an adsorbed species relative to the surface. In the low temperature phases of acetylene and ethylene the data are consistent with the carbon-carbon bond axis being parallel to the surface in agreement with earlier work. The high temperature phases of both molecules were found to consist of identical surface complexes where the carbon-carbon bond axis is normal or nearly normal to the surface. The orbital symmetries determined from this study favor the ethylidyne structure originally proposed by Kesmodel et al.     

Angle resolved photoemission and experimental band structure of Ag

Angle resolved energy distribution curves of photoelectrons emitted from (100), (110) and (111) faces of Ag using unpolarized noble gas resonance radiation have been measured. From off-normal-emission spectra the final-state dispersion relations were determined. They show deviations from the calculated bands and from the free-electron parabola. Using the direct-transition model the dispersion of the occupied valence bands along the major symmetry directrions ΓX, ΓKX and ΓL have been determined. Slight deviations up to .4eV with respect to Christenen's theoretical band structure were found.     

Band structure of platinum from angle resolved photoemission experiments

Angle-resolved and angle-dispersed ultraviolet photoelectron spectroscopy (ARUPS) has been used to determine the experimental band structure of platinum at various points along the ΓX, ΓKX and ΓL directions in the Brillouin zone. Various methods have been employed to obtain the E(k) points, among them absolute methods which determine the energy and the momentum independently without any assumption about the final state dispersion. The experimental points are compared with a self-consistent relativistic band structure calculation for energies below and above the Fermi energy. Good agreement between theory and experiment is found.     

Mn/PbTe(111)界面行为的光电子能谱研究

利用X光电子能谱(XPS)对Mn在PbTe(111)表面上沉积生长的界面性质进行了研究.研究表明Mn的沉积使衬底发生了原子尺度上的突变及金属/半导体界面的形成.从X光电子能谱的芯态能级峰来看,随着Mn膜的沉积Pb 4f峰的低结合能端出现了金属Pb的特征新峰,而Te 3d峰的高结合能端却出现了MnTe特征新峰.且随着Mn膜厚度的增加这些新峰变得越来越明显,当Mn膜厚度超过7 ML(monolayer)(即超过Pb,Te的探测深度)时,衬底信号峰完全消失,只剩下金属Pb和MnTe的芯态能级峰.Mn膜厚度继续增 关键词： PbTe半导体 界面形成 光电子能谱 偏析     

Adsorbate band formation: The chemisorption of CO on Pd (100)

In ordered overlayers of adsorbed gases on metal surfaces, high coverage situations can lead to overlap between orbitals on adjacent species and hence to adsorbate band formation. We conclusively demonstrate the existence of this effect in chemisorption by examining the dispersion of the 4α level in the u.v. photoelectron spectrum of the CO/Pd (100) system. The results agree well with a first principles extended tight binding calculation of the two-dimensional band structure.     

CO2 adsorption and reaction on Fe(111): An angle resolved photoemission (ARUPS) study

Molecular CO₂ adsorption is observed on an Fe(111) surface at 85 K. For the main fraction of molecules the relative binding energies of the valence ion states as determined by ARUPS are consistent with those in the gas as well as in the condensed phase, and indicate that the electronic structure of that fraction of adsorbed molecules is only slightly distorted upon adsorption. There is a fraction of adsorbed molecules at 85 K that can be identified as bent, anionic CO₂⁻ species. While the weakly adsorbed, linear CO₂ molecules desorb at low temperature, the CO₂⁻ species is stable up to 160–180 K. The latter is proposed to be a precursor to dissociation. Above this temperature adsorbed carbon monoxide and oxygen are observed on the surface, and at room temperature the CO₂⁻ signals have disappeared. Heating above room temperature dissociates the CO molecules into carbon and oxygen.     

Angle resolved photoemission study and calculation of the electronic structure of the Pt(111) surface

Angle resolved photoemission spectra of Pt(111) were measured along the direction of the surface Brillouin zone (SBZ). The electronic structure of a semi-infinite Pt(111) crystal was calculated applying the LMTO-TB approximation to aid interpretation of the spectra. The experimental spectra are well described by the calculated bulk band structure. Both the experiment and calculation reveal a surface state near the Fermi level in the neighborhood of the point of the SBZ.     

Adsorption of water and methanol on GaAs(110) surfaces studied by ultraviolet photoemission

UV photoemission spectroscopy (UPS) with He 1 radiation (hν = 21.2 eV) has been used to study the interaction of H₂O and CH₃OH with GaAs(110) surfaces prepared by cleavage in ultrahigh vacuum (UHV). For H₂O two molecularly adsorbed phases can be distinguished at 300 K: at low coverage H₂O is chemisorbed by its oxygen lone-pair orbital to the surface whereas for higher exposures a less perturbed species which resembles more a “physisorbed” or condensed H₂O layer is found. At 180 K only the less perturbed species can be identified. Also CH₃OH is chemisorbed molecularly at lower coverage with its oxygen end to the GaAs surface. For higher exposures two additional emission bands are observed which are interpreted as due to the methoxy radical CH₃O resulting from a partial decomposition of CH₃OH.     

Electronic structure of a superconducting Bi2212 crystal by angle resolved ultra violet photoemission

The electronic structure of a high quality superconducting Bi₂Sr₂CaCu₂O_8+δ (Bi2212) single crystal is studied by angle resolved ultra violet photoemission (ARUPS) using He I (21.2 eV). Our results appear to show two bands crossing the Fermi level in ΓX direction of the Brillouin zone as reported by Takahashiet al. The bands at higher binding energy do not show any appreciable dispersion. The nature of the states near the Fermi level is discussed and the observed band structure is compared with the band structure calculations.     

Selenium and sulfur bonding on Ni(111); angular resolved photoemission

The bonding mechanism of selenium and sulfur on Ni(111) has been investigated by observing the variation of the normal component of the photocurrent as the angle of incidence of the light is varied. The application of simple arguments leads to the assignment of symmetries to the orbitals observed in the photoemission spectra. An interpretation in terms of a Ni₃ cluster model is made and consequences of this model are discussed.