R.G. Jordan

An experimental and theoretical study of the photoemission from Ni(110)

The authors have investigated the electronic structure of the d bands in Ni along the Gamma ( Sigma )K(S)X direction using a combination of angle-resolved UV photoemission measurements and photocurrent calculations including correlation effects. In the calculations they used a potential for the excited state that included self-energy corrections based on the model of Treglia et al. (1982). The calculations reproduce all of the main features in the experimental spectra. In particular, there is good agreement with the observed dispersion of the quasiparticle states of Sigma 3(S3) and Sigma 4(S4) symmetry. The calculations indicate that the correlations produce a marked energy dependence of the exchange splitting, in contrast to the essentially rigid shift obtained in standard one-electron calculations, and the results for the Sigma 4 states are in very good agreement with photoemission measurements along KX.

EXPERIMENTAL AND THEORETICAL SPECTRA FROM THE 4P CORE LEVELS OF YTTRIUM

Abstract We have carried out an investigation of the surface core level shift and the photoemission from the 4p core level at the (0001) surface of yttrium. We calculated the electronic structure surface at the surface/vacuum interface using the self-consistent field, linearized muffin-tin orbital method in a supercell geometry. We find that the 4p eigenvalues for atoms in the first and second layers are shifted by +0.56 eV and -0.18 eV, respectively, from the bulk value. We used the layer-dependent potential functions in first-principles calculations of the photocurrent and the theoretical spectra are in excellent agreement with the experimental observations.

Surface states at the M-point on Cu(100)

Abstract We have calculated the electronic structure of Cu in the vicinity of the (100) surface. We used the relativistic SCF-LMTO-ASA method, within a slab geometry and including the surface dipole terms. We find two surface states at the M -point; the first lies about 0.2 eV above the d-band continuum and the second lies within a spin-orbit gap near the top of the d-band continuum. Both states have been observed experimentally and our calculated dispersion relations are in reasonably good agreement with the measurements. We have also carried out first-principles photocurrent calculations using the layer-by-layer potential functions and the spectra are in excellent agreement with previous photoemission measurements.

Surface structure of rare earth metals

Abstract We have performed LEED, angle-resolved UV photoemission (ARUPS) and inverse photoemission (IPE) measurements on a representative set of hcp rare earth surfaces in order to obtain basic structural information. LEED patterns from the (0001) surfaces show six-fold symmetry due to the two equally probable bulk terminations. ARUPS data show a large non-dispersing peak at ~ 10 eV binding energy, with intensity extremely sensitive to surface order, which is not reproduced in one-electron calculations. Suggestions that this many-body feature is due to an unoccupied surface state are supported by our IPE data, which appear to show such a state just above the Fermi level. LEED patterns from the (1120) surfaces of Y. Ho and Er also show six-fold symmetry, with no visible substrate spots, implying that these relatively open surfaces have collapsed to a (7 × 1) close-packed structure many layers deep. ARUPS data from the reconstructed (1120) surface of Ho are virtually indistinguishable from those obtained from Ho(0001). This suggests that the two structures are identical within the probing depth of this technique.

Local Fe moments in α- and γ-phase Fe-rich FeNi alloys

Abstract We have used photoemission measurements of the Fe-3s core level to investigate the Fe local moments in two Fe-Ni alloys containing 70% and 72.5% Fe in both the γ- and α-phases. Previous magnetization measurements indicate that in this composition range the average total moments of alloys in the γ-phase are considerably lower than in the α-phase. However, our photoemission measurements suggest that the local moment on the Fe site is approximately the same in both phases. Furthermore, a determination of the spin-splitting suggests that at room temperature the Fe local moments in the alloys are smaller than in pure Fe.

Surface states on the (001) and (100) surfaces of equi-atomic CuAu I

Abstract We have observed for the first time two Tamm-type surface states on the (001) and (100) surfaces of equi-atomic CuAu I, at binding energies of about 1.5 eV and 6.2 eV. By measuring their dispersions in k | - space we have located symmetry points in the surface Brillouin zones, which has enabled us to deduce the lattice spacings in the surface layer. We find that these values are very similar to those of the bulk.

Correspondence between the Fe 3s photoemission line-shape and the Fe local moment in Fe-V alloys

Abstract We have examined the relationship between the line-shape of the Fe 3s photoemission spectrum and the Fe local moment in a series of Fe-V alloys. We find that the shoulder on the higher binding energy side of the spectrum becomes less apparent with increasing V concentration, i.e., as the local moment decreases. A recent spin-resolved measurement of the Fe 3s photoemission spectrum indicated that the conventional method of fitting ‘standard’ line-shapes may not be justified. As a result we are unable to deduce at this stage whether the changes are a consequence of a reduction in spin-splitting or a decrease in intensity of the higher binding energy component. We calculated also the local moments in α-FeV (CsCl-structure) using the SCF-LMTO-ASA method. The result for the average moment per unit cell is in good agreement with previous magnetization measurements.

Core level shifts and density of states at the (100) surface of Cu3Au

We have calculated the layer-by-layer core level eigenvalues and densities of states of Cu3Au in the vicinity of the (100) surface, assuming a 50:50 Cu:Au termination. We used the relativistic SCF-LMTO-ASA method in a slab geometry and we included the surface dipole terms. We obtain very good agreement with the available experimental photoemission data.

Some properties of Cu-Au alloy surfaces

The purpose of this article is to review some recent studies of the electronic structure in the vicinity of the low-index surfaces of Cu-Au ordered alloys. The work described in this article involved a combination of first-principles calculations, using the self-consistent-field linear muffin-tin orbital method within the atomic sphere approximation (SCF-LMTO-ASA) and a supercell geometry in which the vacuum space above the surface is treated as “empty” spheres, and angle-resolved photoemission measurements. A range of surface-related phenomena were investigated; however, the author limits this article to studies of the (100) surfaces of Cu and Cu3Au and the (100) and (001) surfaces of equiatomic CuAuI. The focus is particularly on the occurrence and properties of surface states and surface core level shifts and their dependence on termination. The author shows that photoemission measurements provide a very sensitive probe of such subtle behavior.

The long-period superlattice in CuAu II

We report the results of a series of calculations of the electronic structure of ordered, equi-atomic CuAu. We have investigated the effects of the creation of superzone boundaries on the Fermi surface of CuAu I when the long-period superlattice, the CuAu II phase, is formed. The new boundaries destroy appreciable regions of Fermi surface, thus favouring the formation of the latter phase. The positions of the boundaries are related directly to the period of the long-period superlattice and we have investigated their dependence on the electron/atom ratio and pressure. We find that the results are in very good agreement with previous experimental measurements of the average domain size in CuAu II. Thus, we provide strong evidence that Fermi surface topology plays an important role in determining the period of the long-period superlattice in CuAu II.