We present a spectrometer for inverse photoemission in the VUV range with variable energy resolution between 400 and 165 meV FWHM (full width at half maximum). The energy distribution of the electron beam used for excitation can be adjusted between 300 and 125 meV by the use of a toroidal 90 o electrostatic deflector combined with a slit aperture. The emitted photons are detected by Geiger-Müller counters filled with either acetone or iodine as counting gas. The optical bandpasses of the detectors can be tuned between 100 and 330 meV by varying the temperature of their entrance windows. The overall resolution of the spectrometer is determined by measuring the Fermi-level onset in inverse-photoemission data of polycrystalline gold. Furthermore, the resolution enhancement is demonstrated by spectra of image-potential-induced surface states at Cu(001).

We present a combined experimental setup for spin- and angle-resolved direct and inverse photoemission in the vacuum ultraviolet energy range for measurements of the electronic structure below and above the Fermi level. Both techniques are installed in one ultrahigh-vacuum chamber and, as a consequence, allow quasisimultaneous measurements on one and the same sample preparation. The photoemission experiment consists of a gas discharge lamp and an electron energy analyzer equipped with a spin polarization detector based on spin-polarized low-energy electron diffraction. Our homemade inverse-photoemission spectrometer comprises a GaAs photocathode as spin-polarized electron source and Geiger-Muller counters for photon detection at a fixed energy of 9.9 eV. The total energy resolution of the experiment is better than 50 meV for photoemission and better than 200 meV for inverse photoemission. The performance of our combined direct and inverse-photoemission experiment with respect to angular and energy resolutions is exemplified by the Fermi-level crossing of the Cu(111) L-gap surface state. Spin-resolved measurements of Co films on Cu(001) are used to characterize the Sherman function of the spin polarization detector as well as the spin polarization of our electron source.

We have performed a combined scanning tunneling spectroscopy, photoemission, and inverse photoemission study of the surface electronic structure of Cr͑001͒. Our results show three surface-related features, one below, one above, and one right at the Fermi level E F . While the surface-sensitive features below and above the Fermi level show characteristics of d xz,yz orbital symmetry, the feature right at E F exhibits predominantly d z 2-like orbital symmetry. Upon exposure to oxygen, its spectral weight continuously shifts into the unoccupied electronic states. These results are in conflict with the interpretation of this peak as orbital Kondo resonance but point toward a Shockley-type surface state.

The surface electronic structure of face-centred-cubic cobalt films on Cu(0 0 1) was studied by spin-resolved one- and two-photon photoemission. A minority surface state in a Δ1-symmetry gap of the minority band-structure was identified at about 0.45 eV below the Fermi energy. This state causes a resonance-like enhancement in the population of the minority image-potential surface state in the two-photon-photoemission experiment excited by p-polarized light. Additionally, it appears as a surface-sensitive spectral feature in normal photoemission (PE) and its existence is confirmed by calculations within the one-step model of PE. The majority counterpart of the surface state is theoretically expected at a binding energy of about 1.95 eV. Due to lifetime broadening and bulk transitions in this energy range, the majority state does not appear as a pronounced feature in the spectra. Bulk-derived states close to the Fermi level exhibit shifts to higher binding energy with increasing film thickness, while the minority surface state does not change its energy as a function of Co coverage. These results provide a basis for the interpretation of time-resolved measurements concerning ultrafast magnetization dynamics, which rely on a detailed knowledge of the surface electronic structure of ultrathin films.

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