Photoemission Study of the Initial Growth of Co on Ru(0001)

The growth process of cobalt on Ru(0001) was characterized by photoelectron spectroscopy excited by X-ray and synchrotron radiation. The binding energy position and intensity of the Co 2p$\text{}_{3}\text{}_{/}\text{}_{2}$ and Ru 3d$\text{}_{5}\text{}_{/}\text{}_{2}$ core levels as well as the shape and structure of the valence band spectra corresponding to the different stages of the deposition were investigated. An observed small positive binding energy shift is a consequence of an increase in the cobalt adatoms coordination number. The core-level shift between bulk and surface Ru atoms is determined as -360 meV. Upon adsorption of cobalt, the interface peak appears with a shift of -(70÷80) meV relative to the bulk one. On the basis of unchanged energy positions and widths of the Ru-derived features of the valence band spectra, a weak interaction between cobalt and substrate is suggested. The measured valence band could be reproduced by superimposing the spectra of the pure elements.