Surface atom core-level shifts of clean and oxygen-covered Re(1231)

The 4f photoemission spectra of atomically rough Re(12 (3) over bar1) have been measured using synchrotron radiation. A surface core level shift of 0.17 eV towards higher binding energy than the bulk is obtained, and is supported by measurements at different photon energies and emission angles. This surface shift is suppressed upon oxygen adsorption, whereupon new O-induced surface features emerge that are attributed to Re atoms directly coordinated to different numbers of O adatoms.