A. Goldmann

Temperature dependence of Shockley-type surface energy bands on Cu(111), Ag(111) and Au(111)

Abstract Using angle-resolved photoemission at very high resolution we have measured thermally induced energy shifts of the Shockley surface states observed around the center \ gG of the surface Brillouin zones on the noble metal (111) surfaces. Based on calculations using the one-dimensional multiple reflection model we demonstrate that the observed shifts can be quantitatively traced back to the temperature-dependent shift of the relevant bulk band gaps which support these surface states. We have addressed care to a precise investigation of the \ gG state on Ag(111), since conflicting results had been reported earlier. Its initial state energy at \ gG is given by E 0 ( T ) = −(75 ± 5) meV + (0.17 meV/K) T in the temperature range up to about 600 K.

Atomic Adsorption of Oxygen on Cu(111) and Cu(110)

We have studied angle-resolved inverse photoemission (ħω = 9.7 eV) after room temperature adsorption of oxygen on Cu(111) and Cu(110). On Cu(111) exposure to 500 L induces a band (3.0 eV aboveEFatΓ) which shows clear dispersion (1.0 eV) to higher energies for off normal incidence. Since no LEED superstructure is seen for that system, our results present strong evidence for the presence of short-range surface order. Two adsorbate bands are identified (2.8 eV and 6.3 eV atΓ) on Cu(110)p(2×1)-O. Our results are in good agreement with a long-bridge adsorption site.

Experimental widths of excited electron states in metals

Abstract From angle-resolved inverse photoemission spectra we have derived estimated for the lifetime-width Γe of s, p-like electron states in metals. Their compilation together with results obtained from photoemission spectra by other authors indicates a “universal” relationship Γe (E) = (0.13 ± 0.01)(E − Ef) for electron energies E ⩽ 50 eV above the Fermi energy EF.

Hole dynamics in noble metals.

Hole dynamics in noble metals (Cu and Au) is investigated by means of first-principles many-body calculations. While holes in a free-electron gas are known to live shorter than electrons with the same excitation energy, our results indicate that d holes in noble metals exhibit longer inelastic lifetimes than excited sp electrons, in agreement with experiment. The density of states available for d-hole decay is larger than that for the decay of excited electrons; however, the small overlap between d and sp states below the Fermi level increases the d-hole lifetime. The impact of d-hole dynamics on electron-hole correlation effects is also addressed.

Temperature-dependent photoemission spectra from Cu(100) and Cu(111) surfaces

Abstract We have studied high-resolution angle-resolved photoelectron energy distribution curves from Cu(100) and Cu(111) in the temperature interval 38 ⩽ T ⩽ 70.,,0 K . For several well defined peaks, originating from bulk direct transitions as well as from surface states, we determined separately the temperature dependence of emission amplitude, peak area and peak width, respectively. Our results clearly demonstrate that the description of thermal effects in angle-resolved photoemission spectra by the definition of a Debye-Waller factor with an adjustable Debye temperature is not adequate.

Inverse photoemission studies of oxygen on Ni(110) and Ni(100)

We have used k-resolved inverse photoemission at ω = 9.7 eV (isochromat mode) to investigate (2 × 1)- and (3 × l)-oxygen overlayers on Ni(110). Empty 0–2p derived orbitals could be identified at about 3.3 eV (2 × 1) and 2.2 eV (3 × 1) above EF. The (2 × 1)-O band disperses by 1.2 eV to higher energies when going from Γ(k∥ = 0) to k∥ = 0.64 A−1 along the ΓKLU bulk mirror plane. A light polarization analysis of new results from Ni(100)c(2 × 2)-O shows, that the O-2p derived orbital observed slightly above EF is Δ5(x, y)-like at \gG.

Unoccupied and occupied surface states on Ni(1 1 1)

Abstract The energy versus momentum dispersion of Shockley surface states on ferromagnetic Ni(1 1 1) has been calculated employing the one-step model of photoemission with a rectangular shaped surface potential barrier. Both occupied and unoccupied Shockley states in the minority spin system are in good quantitative agreement with UPS and UBIS experiments. In the majority spin system there occur serious disagreements with the experiment which can be traced back to the fact, that current Ni bulk potentials give the bulk states L 2′ ↑ and L 3 ↑ in the wrong order.

Lifetime of d holes at Cu surfaces: Theory and experiment

We acknowledge support from the University of the Basque Country, the Basque Hezkuntza, Unibertsitate eta Ikerketa Saila, the Spanish Ministerio de Educacion y Cultura, and the European Union Research Training Network program NANOPHASE. P.M.E. gratefully acknowledges support from the Max Planck Research Award funds. Our experimental work is continuously supported by the Deutsche Forschungsgemeinschaft (DFG).

High-resolution photoemission study of the surface states near \̄gG on Cu(111) and Ag(111)

We present high-resolution angle-resolved photoemission results concerning the already well-known surface states at the center of the surface Brillouin zone on Cu(111) and Ag(111). Attention is focused on the influence of energy- and angle-resolution, sample temperature, and the proximity of the Fermi edge on the photoelectron line shape. We also discuss, to which extent photohole-lifetimes for Cu and Ag may be inferred from photoemission line-widths.

Oxygen chemisorption on Cu(110): A combined study by second-harmonic spectroscopy and photoemission

We have studied the formation of the addedrow (2×1)O overlayer on Cu(110) using Second-Harmonic Generation (SHG). To characterize the electronic properties of the surface, simultaneous observations with LEED and angle-resolved photoemission were performed. We are able to interpret our results in terms of transitions between surface bands of Cu(110) and Cu(110)-(2×1)O, respectively.