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First principles calculation of the interface state in fcc-Fe/Cu(111)

The interfacial properties of fcc-Fe/Cu(lll) superlattices are investigated by the first principles all-electron Linearized augmented plane wave method in the local spin-density functional approximation. For the paramagnetic phase an interface state located at 2.61 eV below the Fermi level at the (K) over bar point of the two-dimensional Brillouin zone is obtained and it develops extending along the (K) over bar - direction. This is consistent with the experimental observation

Angle-resolved photoemission study of the Ag band structure along the ΓΛL line

Angle-resolved photoemission experiments have been carried out on Ag(111) in the photon energy range from 13 to 65 eV with both s- and sp-polarised synchrotron radiation. The valence band structure of Ag has been determined along the high-symmetry Lambda line by normal emission measurements. For photon energies smaller than 24 eV, the photoemission peaks could be interpreted as results of direct transitions between initial and final energy bands in the relativistic band structure calculated by Christensen (1972), and by Eckardt et al. (1984). For photon energies larger than 24 eV, the final band was obtained by fitting a free-electron-like final band (m*e=1.10, V0=-5.0 eV) to experimentally verified calculated symmetry points. The experimental valence bands deviate by about -0.3 eV from theory. Measured critical-point energies (in eV, band indices in parentheses) are: E( Gamma 8+(2,3))=-6.15+or-0.10, E( Gamma 7+(4))=-5.70+or-0.10, E( Gamma 8+(5,6))=-4.95+or-0.10, E(L6+(1))=-7.10+or-0.10, E(L4,5+(2))=-6.25+or-0.10, E(L6+(3))=-5.80+or-0.10, E(L6+(4))=-4.55+or-0.10 and E(L4,5+(5))=-4.30+or-0.10. A surface resonance was detected 4.2 eV below the Fermi level at the centre of the surface Brillouin zone Gamma , which has an origin similar to that of the surface resonances that have been observed on Cu(001) and Ag (001). A possible surface state is also reported at about 7.4 eV below the Fermi level at the Gamma point. The nature of this impurity-sensitive structure is not understood.

Oxidation of ethylene on the ordered alloy surface Pd{001}c(2 × 2)-Mn

Abstract Ethylene adsorption and coadsorption with oxygen on the ordered alloy surface Pd{001}c(2 × 2)-Mn were studied with high resolution electron energy loss spectroscopy (EELS). The vibrational spectrum for C 2 H 4 adsorbed on Pd{001}c(2 × 2)-Mn at 140 K is similar to that for C 2 H 4 adsorbed on Pd{001} at 80 K, which has been ascribed to di-σ-bonded C 2 H 4 . In contrary to the observation on Pd{001}, where oxygen preadsorption inhibits C 2 H 4 by limiting the formation of di-σ-bonded C 2 H 4 , on Pd{001}c(2 × 2)-Mn, the vibrational spectrum of C 2 H 4 adsorbed at 140 K is not affected by the preadsorbed oxygen. At 230 K, the coadsorbed C 2 H 4 and O 2 react with each other and form CO and H 2 O on the surface.

Coadsorption of carbon monoxide and oxygen on Pd{001}c(2×2)-Mn : an oxidation pathway for CO2 formation

CO adsorption and coadsorption with O2 on a Pd{001}c(2 x 2)-Mn ordered alloy surface were studied with low energy electron diffraction (LEED) and high-resolution electron energy loss spectroscopy (HREELS), At room temperature, the energy loss at 253 meV in the EEL spectra of CO on Pd{001}c(2 x 2)-Mn, is attributed to the C-O stretching vibration of CO molecules at on-top sites of first layer Pd atoms. This peak diminished as the surface was exposed to oxygen. At 140 K, a new feature located at 285 meV has been observed in the EEL spectra of the coadsorption of CO and O2. The peak position is near the asymmetric stretch mode of the CO2 gas phase (293 meV). As the oxygen precoverage was increased under constant CO exposure, the intensity of this peak was increased. This peak disappeared upon annealing to 300 K for 1 min. Analyses indicate that the 285 meV peak is caused by CO2 chemisorbed on Pd{001}c(2 x 2)-Mn with the molecular axis perpendicular to the surface. The reaction that produced CO2 could be explained by the microscopic process of the interaction between the oxygen atoms, which are dissociatively adsorbed at the hollow sites between two Mn and two Pd atoms, and CO molecules, at on-top sites of neighboring Pd atoms.

Effect of the convergence of Cu cap on the structure of Co/Cu(111) film

Annealing Cu(111) covered with more than 10 ML Co film results in substrate Cu atoms diffusing through the Co film, and forming a Cu overlayer capping the Co him. Through AES and LEED experiments and QKLEED calculation, we found that the coverage of the Cu cap has an important effect on the top layers of the Co film. When the coverage of the Cu cap is less than 0.7 ML, the stacking sequence of the top layers is hcp, the same as that of Co film. When the coverage of the Cu cap is more than 1 ML, the top layers become fee and present twinned fee because of stacking on hcp Co him. This tends to explain the results of Co/Cu(111) superlattice studies in which Co show a fee stacking sequence

CORE SHELL ELECTRON BINDING ENERGY BEHAVIOR OF C60F42 MOLECULE ON THE C60 PRECOVERED GAAS(100) SURFACE

X-ray photoemission and synchrotron radiation photoemission were used to investigate both the C 1s, F 1s core levels and valence bands features of C60F42 thin films on the C60 precovered surface. The C 1s core - level upshift toward the Fermi level EF in the C60 and downshift in the C60F42 molecules imply an evident final state relaxation screening effect through extra - adsorbate interactions. The F 1s and valence bands provide complementary proof to the above consideration.

Oxidation of carbon monoxide and ethylene on Pd(001)-C(2×2)Mn☆

Abstract Oxidation of carbon monoxide and ethylene on an in situ prepared ordered Pd(001)-C(2×2)Mn alloy surface was investigated by LEED and HREELS. At 140 K, coadsorption of carbon monoxide and oxygen gives a new HREELS feature at 2300 cm −1 which is tentatively assigned to the formation of adsorbed carbon dioxide with the molecular axis nearly perpendicular to the alloy surface. Meanwhile, ethylene reacts with oxygen on the ordered alloy surface at temperatures higher than 230 K to produce surface hydroxyl species and adsorbed CO. Bimetallic composition and the buckled structure of the alloy surface are responsible for the high reactivity and the stabilization of reaction intermediates in the two oxidation processes.