Spin-resolved photoemission of surface states of W(110)-(1 x 1)H

The surface electronic states of W(110)-(1 x 1)H have been measured using spin- and angle-resolved photoemission. We directly demonstrate that the surface bands are both split and spin-polarized by the spin-orbit interaction in association with the loss of inversion symmetry near a surface. We observe 100% spin polarization of the surface states, with the spins aligned in the plane of the surface and oriented in a circular fashion relative to the Smacr; symmetry point. In contrast, no measurable polarization of nearby bulk states is observed.     

Surface states calculation for the (100), (110) and (111) faces of Si

Using essentially the Heine and Jones model of the band structure for diamond-type semiconductors and a 3-dimensional surface state secular equation, we have calculated the bands of surface states for the (100), (110) and (111) orientations of the surface plane of ideal Si. Our bands for the (110) surface are very similar to those obtained by Jones. Based on these bands of surface states, we can explain reasonably both optical and electrical measurements on the (111) surface.     

High-resolution photoemission from Ag(100), Ag(110), and Ag(111)

Energy distribution curves of photoelectrons emitted normal to (100), (110), and (111) faces of silver have been obtained at photon energies of 21.22, 16.85, and 11.83 eV. The results are compared with Christensen's relativistic band structure calculation of bulk silver yielding a close correspondence between experiment and theory. A surface state in the L gap immediately below the Fermi level is identified.     

Surface states at the clean surfaces of cleaved Si(111) and GaAs(110)

A combination of ellipsometric data on the electronic transitions from occupied to unoccupied surface states and published photoemission data on the energy distribution of the occupied surface states has been used to construct models of the surface states densities at the cleaved Si (111) and GaAs (110) surfaces.     

Thickness dependence of the spin- and angle-resolved photoemission of ultrathin,epitaxial Ni(111)/W(110) layers

The thickness dependence of the magnetic band structure of ultrathin, epitaxial Ni(111)/W(110) layers has been studied by spin and angle-resolved photoemission spectroscopy. The changes of the spin-resolved photoemission intensities upon reducing the layer thickness depend strongly on the wavevector along the -L line of the Brillouin zone. The measured exchange splitting atk 1/3(-L) andk 1/2(-L) is found to be independent of the layer thickness for layers consisting of 3 or more atomic layers, while decreases rapidly with the layer thickness atk2/3(-L). This behavior is very similar to the temperature dependence of the spin-resolved photoemission spectra of bulk Ni(111) at the samek-points.     

Surface states on GaAs(110)

The electronic structure of the (110) surface of GaAs is recalculated using the relaxation geometry recently obtained from analyzing elastic low-energy electron diffraction intensity data and a self-consistent ab initio pseudopotential approach. Better agreement is found for the occupied surface states compared with photoemission data, giving support for the new structural model. The influence of convergence of the plane-wave expansion and relativistic effects on the surface states is also examined.     

Surface resonant states and the adsorption of 4d atoms on Mo (110) and (100)

The adsorptive properties of Mo (110) and Mo (100) relative to 4d transition adatoms are investigated and compared using a tight-binding model. The surface resonant states existing on the (100) free surface are shown to have a drastic influence. On Mo (110) a Mo adatom retains a strong atomic character while on Mo (100) one approaches a surface molecule limit which is due to a strong interaction between the adsorbate atomic state and the free surface resonance. Consequently a large anisotropy of binding energy is found. The case of different 4d adatoms is also discussed.     

Directional UV photoemission from clean and sulphur saturated (100), (110) and (111) nickel surfaces

Angle resolved photoemission energy distribution curves (EDC's) were obtained on clean and sulphur saturated (100), (110) and (111) nickel surfaces for excitation energies equal to 10.2, 13.5, 16.8 and 21.2 eV. The EDC's of clean surfaces are weakly structured at θ = 0° and become more rich in features for oblique angles. In the explored energy range, adsorption of sulphur produces two extra-structures at initial energies depending on surface orientation. One of which situated at about ?4.5 eV below the Fermi level is in good agreement with Hagstrum ion neutralization spectroscopy results, the other at around ?1.8 cV has never been observed before. A remarkable similarity of adsorption effects on the three surfaces is found. These results are compared with experimental data obtained previously on equivalent sulphur saturated surfaces by INS and discussed in relation to recent theoretical calculations on chalcogen adsorption on nickel.     

The shape of the total energy distribution from W(110) in sub-threshold photoemission

Measurements of the final state energy distribution of electrons photoemitted from W(110) at energies less than the vacuum level are presented. A 127° velocity selector analyzer was used to energy resolve the photoemitted current. A significant improvement in both energy resolution and signal-to-noise ratio over previous studies resulted. The energy distributions obtained from W(110) are compared the theoretical predictions based on a recent model of photofield emission. The sensitivity of this theoretical model to various parameters of interest are investigated. The reasonable agreement between theory and experiment indicates that the final states probed in these measurements are free electron-like and not strongly representative of the final bulk density of states of the emitting material.     

Monte Carlo simulations of hydrogen adsorption on the W(110) and Mo(110) surfaces

Kinetics of low-temperature hydrogen and deuterium adsorption on W(110) and Mo(110) surfaces have been studied by the real-time Monte Carlo simulations. Recently reported qualitative dependence of the adsorption characteristics on variation of the H₂ flux is described in terms of the dynamical equilibrium between incident and desorption fluxes and improved conditions for accommodation for the hydrogen molecules at high incident fluxes. The role of the intrinsic precursor state in hydrogen dissociative adsorption is analyzed.Received: 16 February 2004, Published online: 28 May 2004PACS: 82.65. + r Surface and interface chemistry; heterogeneous catalysis at surfaces - 02.50.Ng Distribution theory and Monte Carlo studies - 82.20.Wt Computational modeling; simulation     

Density of states of the clean Mo (110) surface

The electronic structure of the (110) surface of Mo is calculated using transfer matrix method. The Hamiltonian is of tight-binding type with a basis of nine orbitals per atom. Spectral densities of states for special points of the 2-D Brillouin zone are presented on the surface and in the three consecutive layers. The band structure in the σ direction and the local density of states are also calculated. The results are compared with the few experimental data available in the literature.     

Surface magnetism of iron on W(110)

Ultrathin bcc iron films grown epitaxially on W(110) have been investigated by means of angle and spin resolving photoelectron spectroscopy. The electron spin polarization, spin resolved intensities and corresponding band structure have been experimentally investigated in dependence of the film thickness, exciting photon energy and variation of the photoelectron detection angle. Additionally, photoemission calculations for bulk iron have been performed in the framework of a relativistic one-step formalism. The comparison between measured and calculated spectra turns out to be in very good agreement for different excitation energies as well as for different angles of emission.     

Surface crystallography of W(110) and W(110) p (2×1)-O: The position of W atoms

The position of W atoms in the surface layers of clean W (110) and W (110) p (2 × 1)-O is studied using Constant-Momentum-Transfer Averaging of LEED intensities. It is shown that the clean surface is not relaxed to an uncertainty of < 0.06 Å. Analysis of superstructure beam intensity averages from W(110) p (2 × 1)-O indicates that oxygen does not reconstruct W(110) at these coverages and below 1000 ° K. An upper limit of 0.05 Å can be put on the out-of-plane displacement of W atoms by the oxygen. Substrate beam averages from W (110) p (2 × 1)-O verify the non-reconstruction. The use of CMTA for adsorbed-layer crystallography in general is briefly discussed.     

Electron states and atomic positions at the {001}, {110} and {111} faces of W and Mo

The results of ab initio calculations on the {001}, {110} and {111} surfaces of W and Mo and on the (√2 × √2)R45° reconstructed W {001} surface are presented. A distribution of surface states in reasonable agreement with experiment is found. A simple parametrisation of the short range repulsive force between transition metal atoms is used to predict, for all these surfaces, relaxations which are comparable with those observed. This same parametrisation indicates that the W and Mo {001} surfaces are stable to proposed reconstructive displacements.