J. Hermanson

New experimental band width for Ni

Abstract An occupied d -band width of about 4.3 eV is observed in angle-resolved photoemission which agrees well with band calculations and is much larger than earlier reported measurements. The emission azimuthal dependence suggests why the width is not observed in angle-integrated data.

Low-energy electron diffraction studies of Si(111)-(√3 × √3)R30°-Bi system: Observation and structural determination of two phases

Abstract The initial epitaxial growth of Bi on a Si(111)-7 × 7 surface has been studied as a function of overlayer coverage and deposition conditions using low-energy electron diffraction (LEED) and Auger electron spectroscopy (AES). Experiments show for the first time that two equilibrium phases are formed in the growth process, each displaying a (√3 × √3)R30° LEED symmetry: an α-phase occurring at 1 3 ML Bi coverage and substrate temperature of 360° C, and a β-phase at 1 ML and 300°C. Quantitative structural information for each phase was determined by multiple scattering analysis of I - V curves. The analysis is facilitated by comparing LEED intensity data measured for each phase with calculated values using appropriate structural models. The T 4 geometry for the α-phase and a trimer geometry for the β-phase are revealed to be the “best” models; detailed atomic coordinates have been determined for each phase.

Electronic structure and magnetism of a Pd monolayer on Fe(100)

Abstract Spin-polarized self-consistent localized-orbital (SCLO) calculations have been performed for a five-plane slab simulating Pd/Fe(100). Pd monolayers were placed in registry with both faces of a three-plane Fe(100) slab. We chose a PdFe bond length equal to the sum of metallic radii, 2.62 A, and an FeFe bond length equal to the bulk value, 2.49 A. The computed energy bands for the Pd/Fe 3 /Pd slab resemble those calculated for a five-plane Fe(100) slab, except for a positive work-function shift of 0.5 eV. The Pd monolayer has a magnetic moment of 0.37 μ B /atom. The magnetic moment of an adjacent iron atom is 2.74 μ B , slightly smaller than the value 2.89 μ B at the surface of Fe 5 , but still significantly larger than the central-plane value 2.37 μ B . The d bands of the two metals are strongly hybridized, but very little charge transfer takes place across the interface. Compared with the isolated Pd(100) monolayer, or the clean Fe(100) slab, the surface density of states of Pd/Fe(100) is rather weak near the Fermi level, suggesting a reduced chemical reactivity for this surface.

Study of W bulk bands with normal (001) photoemission using synchrotron radiation

Abstract Photoemission normal to the (001) face of W was measured using polarized synchrotron radiation at normal incidence for 10 eV ⩽hv⩽ 30 eV. All the major features observed agree very well with the predictions of three-dimensional, bulk band calculations for direct transitions along the line Δ, even for final energies well above EF. No surface resonances were observed with s-polarized radiation.

Surface density of state for directional photoemission spectroscopy of W(001)

Abstract A semi-infinite tight-binding model of the W(001) surface has been solved, using a resolvent method. The one-dimensional surface density of states contains a localized surface state in the spd hybridization gap, and continuum modifications very different from those put forth by Feuerbacher and Christensen in their interpretation of normal emission spectra.

Observation and LEED I–V analysis of the Ge(111)-1×1-Sb system

Abstract When antimony is adsorbed at submonolayer coverage on a cleaved Ge(111) surface, the clean (2 × 1) surface transforms to a (1 × 1) structure. A dynamical low energy electron diffraction (LEED) intensity anlysis was performed to study this system. The results suggest that Sb adatoms replace the outermost Ge atoms, resulting in a well-ordered bulk-like (1 × 1) surface. This system, like that of a Sb overlayer on Si(111) surfaces, demonstrates that adatoms can remove a surface reconstruction.

Study of III–V semiconductor band structure by synchrotron photoemission

Angle-resolved synchrotron photoemission studies of six III-V semiconductors have been carried out. For emission normal to the (110) plane of these materials, peaks in the experimental spectra were identified with the bands involved in the transitions, and the critical point energies X/sub 3/, X/sub 5/, and ..sigma../sub 1//sup min/, were determined. The data indicate that k perpendicular is conserved in the transitions. Comparison of the data with theoretical bands permits an evaluation of k perpendicular associated with the experimentally observed transition, and from this information the bands were plotted out.

Surface densities of states for normal photoemission from Mo(110) and W(111)

Abstract Tight-binding calculations of one-dimensional densities of states on Mo(110) and W(111) are presented. As reported earlier for W(001), hybridization gaps contain localized surface states or resonances, and band-edge singularities are modified near the surface. Prominent structures in directional photoemission spectra are discussed in the light of our results, and further experiments using polarized light are suggested to test our assignments.

Collective excitations of a quasi-one-dimensional electron gas: nonlocal response theory

Abstract Self-consistent calculations of the subband electronic structure of semiconductor quantum wires are reported. The sample parameters were chosen to match the GaAs/AlGaAs heterostructure recently fabricated by molecular-beam epitaxy and ion milling by Weiner et al. The Schrodinger and Poisson equations were solved simultaneously in a rectangular waveguide geometry, using Fermi statistics for electrons at finite temperature. Calculated energy levels, wave functions, charge density, and potential differ from the predictions of the simple square well and harmonic oscillator models because of the influence of accumulation and depletion regions. The subband energies depend on the free-carrier density and the temperature as well as the band bending. Based on the self-consistently determined subband structure, the dynamical structure factor was evaluated using a nonlocal description of dielectric response in the random-phase approximation at finite temperature. We obtain intersubband as well as intrasubband plasmons and discuss their dispersion relations, localization, and line shapes. The dynamical structure factor of our model quasi-one-dimensional electron gas displays unique line shapes and dispersion relations which are in sharp contrast with the results expected for higher-dimensional electron gases. Two well-defined spectral features, which are almost free of Landau damping, are found, The calculated shift of the intersubband resonance frequency, caused by the depolarization effect, agrees well with previous experiments.

Surface states on unrelaxed GaAs (110) in the bond-orbital model

Abstract We have used the bond-orbital model of Pantelides and Harrison to compute eigenstates for a twelve layer slab of GaAs (110). Dispersion for each of the states is presented as a function of surface wave vector. Also, probability distributions for electrons in each of the surface states are given. These results are in good agreement with those of Joannopoulos and Cohen who did not make the bond-orbital approximation, thus helping to establish the usefulness of this method for surface calculations.