High-resolution electron energy-loss spectroscopy at EuO surfaces

We investigated EuO(1 0 0) single-crystal surfaces by high-resolution electron energy-loss spectroscopy (HREELS). Not only surface phonons but also dipole-forbidden f-f excitations within the spin-orbit and crystal-field split 7FJ ground state of Eu3+ ions, which are not observable with optical absorption spectroscopy, could be measured. The measurements show that disorder, valence of Eu ions and oxygen content of the near-surface layers are strongly correlated and can vary from sample to sample. The observation of vibrational modes of adsorbed hydroxyl groups and hydrocarbons show that EuO surfaces act in a similar manner onto water and hydrocarbon molecules as transition-metal oxide surfaces do