R. Paniago

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.

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.

Quantization of electron states in ultrathin xenon layers

Abstract Physisorbed Xe was grown at temperatures T ⩽ 55 K in a layer-by-layer mode on Ag(111) and Cu(100). High-resolution normal-emission photoelectron spectra from the Xe 5p valence levels show clear evidence for a quantization of the electron states, depending on the layer thickness. Their energies and their numbers can be explained within a very simple potential well model. We have also determined values for the electron mean free path in solid xenon from the attenuation of core level photoemission intensities.

Localization of d-like Surface Resonances on Reconstructed Au(111)

We have investigated d-like surface resonances observed already earlier on the reconstructed Au(111)(22 × √3) surface at initial-state energies Ei = -5.65 and -4.25 eV relative to EF. At sample temperatures below T = 100 K a non-reconstructed Au(111) surface can be prepared by gentle bombardment with Ne+ at 200 eV. It exhibits sufficient order to show a clear (1 × 1) pattern. However, the above-mentioned surface resonances are missing in angle-resolved normal-emission photoelectron spectra from the (1 × 1) face. This observation proves that the surface resonance states are spatially localized within the outermost corrugated atomic layer of the reconstructed surface.

Upper limits for d-hole inverse lifetimes in copper

Abstract From high-resolution angle-resolved photoemission spectra we have derived upper limits for the d -hole lifetime-width Г h in copper. For bulk band direct transitions with initial state energies E i between -3.6eV and the Fermi energy E F , we find Г h -3 eV -1 ( E i - E F ) 2 . We discuss implications of this result for the extraction of quasi-particle lifetimes for photoemission spectra.

Temperature dependence of d-like surface states on Cu(100) and Cu3Au(100)-an angle-resolved photoemission study

We report on the temperature dependence of high-resolution angle-resolved photoemission spectra from d-like (Tamm) surface states on Cu3Au(100) and Cu(100). The temperature was varied between T=39 and 600 K, the surface states were investigated in the vicinity of the M point of the corresponding surface Brillouin zones. On both samples, the temperature influences the Tamm states in a very similar way. We propose that d-like surface states may be used as sensitive probes to monitor the T-dependent potential changes in the outermost layer.

Giant temperature effects in normal-emission photoelectron spectra from Ag(111) and Au(111)

Abstract The experimental determination of electronic energy bands E ( k ) from the kinematical analysis of angle-resolved photoelectron spectra is now nearly routine. In contrast only very few attempts have been made to quantitatively interpret peak intensities (going beyond the application of polarization selection rules). In this context we did investigate the influence of temperature T on peak intensities and linewidths. During that work we detected that at particular k -space points bulk direct transition intensities exhibit a “giant” T dependence, with temperature coefficients larger by an order of magnitude as compared to other k -space points nearby. We present such data and compare them to calculations performed within the one-step theory of photoemission. An interpretation is given by multiple scattering effects and a constructive final state interference

Electron diffraction in angle-resolved UV-photoemission spectra from Au(111)

We present experimental and calculated evidence that pronounced bulk emission intensity variations found within rather narrow angular intervals may be explained by photoelectron diffraction. We propose that such interference effects within the bulk lattice may be identified experimentally by their characteristic and pronounced dependence on sample temperature.

Giant temperature-dependence in angle-resolved ultraviolet-photoemission from Au(100)

Abstract Angle-resolved photoelectron spectra from both the (1 × 1) and (5 × 20) surfaces of Au(100) exhibit peak intensity variations by an order of magnitude with changing polar angle of emission. We present experimental evidence that the observed intensity modulation is caused by photoelectron diffraction and may be identified by an unusually strong dependence on sample temperature.

Temperature-dependent surface Fermi contours: Origin of unusual surface geometries on Ag(1 1 1)?

Abstract The well-known Shockley-type surface state observed in normal photoemission from Ag(1 1 1) shifts linearly with temperature T and is located above the Fermi energy at T > 450 K. In consequence it gets partially empty at increasing T. We raise the question whether this is the reason for a surface reconstruction observed under particular electrochemical conditions [Y. Tang et al., Phys. Rev. Lett.67, 2814 (1991)] and for an unusual surface relaxation reported recently [P. Statiris et al., Phys. Rev. Lett.72, 3574 (1994)].