The electronic structure of the 4d transition-metal oxide PdO is investigated by photoemission (UPS and XPS), inverse photoemission (BIS; ), and electron energy loss spectroscopy in reflection geometry (REELS; primary energy, ). The valence band spectra are compared to recent theoretical ab initio band-structure calculations. Good agreement between theory and experiment is found in the occupied part of the band structure down to 8 eV below as well as in the unoccupied part up to 6 eV above . This confirms the common view that the electronic structure of the 4d transition-metal oxides, e.g. PdO, can be explained in terms of a single-electron picture. Nevertheless correlation effects among the Pd 4d electrons are clearly visible in the spectra, as e.g. satellites of the Pd core level spectra. In order to explain the origin of these satellites we performed simple cluster model calculations and as a result we can explain one satellite in a screening picture by means of a charge transfer process. In addition radiation damage effects in PdO during the electron bombardment in the BIS experiments are reported. This is explained by the formation of the Pd -like states connected with oxygen loss due to the electron bombardment.

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The nitrogen-doped (N-doped ), type Ib, synthetic diamond (100) surface was investigated by means of X-ray photoelectron spectroscopy ( XPS) and ultraviolet photoelectron spectroscopy ( UPS ). Photoelectron emission data from the boron-doped (B-doped ) and the N-doped diamond (100) surfaces were compared and permitted the energy band diagrams for these differently terminated surfaces to be drawn. We observed emission from energy levels below the conduction band minimum up to the vacuum level and therefore succeed in evaluating the negative electron affinity (NEA) of the hydrogen-terminated diamond surfaces. Both the hydrogen-terminated N-and B-doped diamond (100) surfaces show NEA values of at least −0.2 and −1.0 eV, respectively, while the hydrogen-free surfaces show positive electron affinity. In contrast to the hydrogen-terminated B-doped (100) surface, UPS measurements on the hydrogen-terminated N-doped (100) surface do not reveal a high intensity NEA peak owing to the strong upward band bending. The high intensity NEA peak of B-doped diamond seems to be due to the downward band bending together with the reduced work function because of hydrogen termination. The work function increases for subsequent hydrogen desorption at higher annealing temperatures with associated loss of NEA. For the N-doped diamond (100) surface the work function behaves similarly but the observation of a NEA peak is absent because of the surface barrier formed by the upward band bending.

We investigate a number of isostructural, quasi-two dimensional transition metal dichalcogenides with respect to Fermi surface nesting. Using angle-resolved photoemission we find no clear evidence for Fermi surface nesting as a key scenario for charge density wave formation in these materials. However, interesting and unusual behavior has been discovered. For 1T-TaS in the charge density wave phase, instead of finding an intact Fermi surface along the rounded parts of its 2 elliptically shaped contours and gaps along the parallel regions, the Fermi surface is essentially completely pseudogapped. For 1T-TiSe a model based on an excitonic insulator phase as described by Kohn [Phys. Rev. Lett., 19 (1967)

The electronic and structural properties of a calcium-induced chain system on Si(111) have been studied. Low-energy electron diffraction measurements clearly reveal a (3 × 2) periodicity and the Ca coverage is determined to be 1/6 monolayer. Angle-resolved photoemission measurements have been performed with two different light polarizations in order to study the symmetries of the surface states. In both polarizations no band crossing the Fermi level EF is found. The three detected surface state bands are in good agreement with theoretical calculations in the honeycomb chain-channel (HCC) model for an insulating case.