HREELS study of subsurface oxygen on the Ni(100) surface

Abstract

New high frequency vibrational loss features have been measured on O/Ni(100) for low oxygen coverages, using high-resolution electron-energy-loss spectroscopy (HREELS). These high frequency losses only appear after thermal annealing. Oxygen atoms are migrating underneath the surface with increasing temperature, giving rise to the high frequency modes. The modes are shown to result from subsurface oxygen atoms, squeezed in interstitial sites. We have detected five different high frequency loss signals, while five different interstitial sites are precisely available below the Ni(100) surface. Model calculations have been performed in order to relate frequencies to interstitial sites. The matching technique approach has been applied to analyze the case of periodic structures, whereas a cluster approach has been used to obtain the localized vibrational states associated with interstitial oxygen atoms.