Photoemission and Optical Investigation of the Electronic Structure of Ruthenium

Photoemission and optical studies on vapor-deposited films and bulk samples of ruthenium are reported for the spectral range below 12.0 eV. The photoemission data locate structure in the $d$-like states at 0.5, 1.3, and 3.6, eV below the Fermi energy, and they show no structure due to states above the vacuum level. The data were found to be consistent with the nondirect model, with the possible exception of a small decrease in the amplitude of the structure at $E-E_F=-0.\mathrm{}5$ eV for $h\nu >10\mathrm{}$ eV. A combined analysis of the optical and photoemission data locates a strong peak in the $d$-like density of states about 1.5 eV above the Fermi energy. The studies are discussed with respect to band calculations, data for related metals, and the absence of an isotopic-mass dependence of the superconducting transition temperature. Photoemission data from a material tentatively identified as ruthenium oxide are presented.