Electronic Structure of NiO(100) with Adsorbed Na

Adsorption of Na on single crystals of NiO(1 0 0) at room temperature has been investigated via angle-resolved photoemission spectroscopy and measurements of work-function changes. The drastic changes in the valence band spectra upon Na deposition are assigned to a chemical reaction between Na and O where metallic Ni is left as by-product. At short deposition times, Na mainly acts as an inert electron donor, and at these coverages no dispersion is observed in the angle-resolved photoemission spectra which indicates that the electronic states are localized. The measurements were performed both for a polished and an in-situ cleaved NiO crystal

Angle resolved photoemission on NiO: on the nature of the valence band

Angle resolved photoelectron spectroscopy has been performed on the valence band of NiO at the National Swedish Laboratory for Synchrotron Radiation. Normal emission spectra have been recorded for photon energies between 17 and 140 eV in order to study the electronic structure of the valence band. The experimentally determined band structure has been compared with a local density augmented plane wave band structure calculation. Signs of the influence of antiferromagnetic ordering are found and the general agreement between experimental and theoretical oxygen derived bands indicates strong hybridization between Ni 3d and O 2p orbitals

Photoemission and x-ray absorption study of superconducting and semiconducting Ba1-xKxBiO3 single crystals

Semiconducting Ba0.9K0.1BiO3 and superconducting Ba0.6K0.4BiO3 single crystals cleaved in situ have been studied by core level and valence band photoelectron spectroscopy and O K edge x-ray absorption spectroscopy. It was found that the general shape of the valence band spectrum agrees with the shape predicted by band structure calculations, but the intensity near the Fermi level was lower in the experimental spectrum as compared to the calculated. The O K edge spectra showed that the metallic phase is not related to the presence of doping inducted O 2p holes. This property of Ba1-xKxBiO3 shows that the semiconductor-metal transition of this system is of a different nature than that of the hole doped cuprate high-Tc superconductors. The core level photoemission spectra of the cations showed a small asymmetry for Ba0.9K0.1BiO3. Corresponding spectra for Ba0.6K0.4BiO3 showed a larger asymmetry resulting in a resolved high binding energy shoulder in the Bi 4f spectrum. The origin of this feature is discussed