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[en] The structure of the Pd(110)(2x1)-CO ordered adsorption phase has been determined by scanned-energy mode photoelectron diffraction. The CO molecules are adsorbed close to short-bridge sites with alternating tilts along the close-packed <110> surface rows. This local geometry is consistent with that found in previous theoretical total energy calculations and an earlier X-ray photoelectron diffraction study, but is in direct contradiction to the results of an earlier quantitative low energy electron diffraction investigation. While the best-fit model structure involves some twist of the CO molecules out of the <100> mirror planes of the surface creating a surface phase of p1g1 symmetry, the more symmetric p2mg falls within the estimated limits of precision of the analysis

[en] Synchrotron radiation from the Advanced Light Source has been used to investigate the electronic structure of α-Pu and (delta)-Pu. Measurements include core level and valence band photoelectron spectroscopy, Resonant Photoelectron Spectroscopy (REPES), and X-ray Absorption Spectroscopy (XAS)

[en] Quantum well states (QWS's) in Cu thin films grown on Co/Cu(001) were studied using angle-resolved photoemission spectroscopy. For the normal photoemission, QWS's from both lower and higher energy bands relative to the vacuum level were measured, and explained by phase accumulation method. QWS's from the lower band were studied in detail as a function of the in-plane momentum k. We found that the QWS dispersion depends on the Cu film thickness. From the experimental data, we deduced the quantized perpendicular momentum k(perpendicular) and the energy as a function of k(parallel). Our results show that the in-plane effective mass cannot be obtained by a simple parabolic fitting of the E vs k(parallel) due to the dependence of k-perp on k(parallel)

[en] Valence-band spectra of Cr and Fe metal were measured with photon energies around their respective 2p energies. An Auger signal is found to be superimposed on the valence-band photoemission signal for photon energies at and above the 2p absorption energy, but also for excitation energies down to approx. 4 eV below the 2p absorption energy. This is the radiationless resonance Raman (resonant Raman Auger) regime and gives rise to a signal that is equivalent, in terms of the final state, to the 6 eV satellite in Ni with energies at 3.5 eV below EF in Cr and 3.2 eV below EF in Fe

[en] Two-dimensional Fermi contours of clean and hydrogen-induced surface electronic states have been systematically measured vs coverage of H on W(110) using angle-resolved photoemission. We observe a new pair of spin-orbit-interaction-split surface states, whose splitting grows systematically with hydrogen coverage and whose Fermi contours are strongly nested due to their opposing curvatures. Momentum-dependent electronic transitions between these states drive two previously observed anomalous behaviors: The phonon anomalies along ΓH and ΓS observed with inelastic helium scattering and electron energy loss spectroscopy, and the shifted-upper-layer reconstruction observed by low-energy electron diffraction for coverages greater than 0.5 monolayer. copyright 1998 The American Physical Society

No abstract available

[en] Investigation of the initial oxidation and interface formation of cubic silicon carbide for the silicon rich β-SiC(100) 3?2 surface reconstruction by high resolution synchrotron radiation-based soft x-ray photoemission spectroscopy is described. The surface is exposed to low doses of molecular oxygen ranging from 1 up to 10 000 L, at surface temperatures from 25 to 500 deg C. Significant formation of SiO₂ is found for the surface at room temperature, with the rate of oxidation increasing with temperature. Valence band data and Si 2p core level spectra show that even at low exposures, significant oxidation is taking place, with a surface reactivity to oxygen much larger than for silicon surfaces. The oxidation products, which are grown at very low temperatures (≤ 500 ^oC) include SiO₂ as a dominant feature but also substoichiometric oxides Si⁺¹, Si⁺², Si⁺³, and significant amounts of mixed oxide products involving C atoms (Si-O-C)

[en] The apparent contradiction of one-dimensional adsorbate chains on Si(111) having a 3x2 unit cell and yet a 3x1 diffraction pattern is resolved for the example of Ba/Si(111)-(3x2). Random registry shifts between adsorbate chains are observed in tunneling microscopy, with very short interchain correlation lengths. Fourier analysis provides a natural explanation for a pseudo-(3x1) diffraction pattern. Within density-functional theory such registry shifts can occur with essentially negligible energy cost, leading to entropy-driven, virtually perfect disorder. Substrate states of high symmetry and one-dimensional character are inferred to promote this phenomenon

No abstract available