M. Oehlers et al., HREELS STUDY OF SUBSURFACE OXYGEN ON THE NI(100) SURFACE, Journal of electron spectroscopy and related phenomena, 64-5, 1993, pp. 269-278
New high frequency vibrational loss features have been measured on O/N
i(100) for low oxygen coverages, using high-resolution electron-energy
-loss spectroscopy (HREELS). These high frequency losses only appear a
fter thermal annealing. Oxygen atoms are migrating underneath the surf
ace with increasing temperature, giving rise to the high frequency mod
es. The modes are shown to result from subsurface oxygen atoms, squeez
ed in interstitial sites. We have detected five different high frequen
cy loss signals, while five different interstitial sites are precisely
available below the Ni(100) surface. Model calculations have been per
formed in order to relate frequencies to interstitial sites. The match
ing technique approach has been applied to analyze the case of periodi
c structures, whereas a cluster approach has been used to obtain the l
ocalized vibrational states associated with interstitial oxygen atoms.